Water Stress

In photosynthetic tissues superoxide dismutase (SOD) plays an important role by scavenging the superoxide radical whose production is an usual reaction in chloroplast thylakoids. To test the differential response of SOD, two Andean potato species differing in frost resistance, Solanum curtilobum (frost resistant) and Solanum tuberosum (frost sensitive), were subjected to methyl viologen-mediated oxidative stress and polyethylene glycol (PEG)-induced water stress. A significant increment (approximately two-fold) in total SOD and FeSOD activity, which occupied about 50% of the total activity, was found when leaves of S. curtilobum were exposed to water stress. In contrast, the SOD activity in leaves of S. tuberosum remained unchanged. The exposure of leaves of S. curtilobum to oxidative stress increased total SOD and FeSOD activity by 350%. High correlation between SOD activity and the F v /F m ratio under both PEG induced water stress and MV-mediated oxidative stress was observed. This suggests that SOD can protect PSII from superoxide generated by oxidative and water stress. The higher SOD activity could be an important mechanism to explain why some natives Andean potato like S. curtilobum are more resistant to abiotic stresses than S. tuberosum.

African smallholder farmers face perennial food shortages due to low crop yields. The major cause of poor crop yields is soil fertility decline. The diversity of sites and soils between African farming systems is<span class=GramE>great,</span>therefore strategies to solve soil fertility problems should suit the opportunities and problems encountered in the different climatic regions. This thesis characterizes the semi-arid regions of south-western Zimbabwe and explores some of the strategies that can be used to provide farmers with more options for soil fertility improvement.<o:p></o:p></span>Resource flow maps were used to study the characteristics of the semi-arid farming system of Tsholotsho (Mkhubazi)in south-western<st1:place w:st="on"><st1:country-region w:st="on">Zimbabwe. The results revealed that farmers in the region face perennial cereal grain shortages, but the poorly-resourced farmers are the most affected. N...

This paper describes two case studies of demand-side water management in the Okanagan region of southern British Columbia, Canada. The case studies reveal important lessons about how local context shapes the process of adaptation; in these cases, adaptation to rising and changing water demand under a regime of increasingly limited supply in a semi-arid region. Both case studies represent examples of water meter implementation, specifically volume-based pricing in a residential area and as a compliance tool in a mainly farming district. While the initiative was successful in the residential setting, agricultural metering met with stiff resistance. These cases suggest many factors shape the character of the adaptation process, including: interpretation of the signal relative to context, newness of the approach, consumer values, and local and provincial political agendas. Although context has been explored in resource management circles, thus far climate change adaptation research has not adequately discussed the embeddedness of adaptation. In other words, how context matters and what aspects of context, unrelated to climate change, could encourage or thwart the act of adapting. This study is a simple illustration of the potential drivers, barriers and enabling factors that have influenced the adaptation process of water management decisions in the Okanagan.

Abiotic and biotic host-plant stress, such as desiccation and herbivory, may strongly affect sap-sucking insects such as aphids via changes in plant chemicals of insect nutritional or plant defensive value. Here, we examined (i) water deprivation and (ii) defoliation by the beetle Leptinotarsa decemlineata as stresses indirectly affecting the aphid Macrosiphum euphorbiae via its host plant Solanum tuberosum. For plant-induced stress, aphids were reared on healthy vs. continuously stressed potato for 14 days (no watering; defoliation maintained at $40%). Aphid performance under stress was correlated with metabolic responses monitored by profiling of the aphid proteome. M. euphorbiae was strongly affected by water stress, as adult survival, total aphid number and biomass were reduced by 67%, 64%, and 79%, respectively. Aphids performed normally on defoliated potato, indicating that they were unaffected or able to compensate any stress induced by plant defoliation. Stressed aphid proteomes revealed 419-453 protein spots, including 27 that were modulated specifically or jointly under each kind of host-plant stress. Reduced aphid fitness on water-stressed plants mostly correlated with modulation of proteins involved in energy metabolism, apparently to conserve energy in order to prioritize survival. Despite normal performance, several aphid proteins that are known to be implicated in cell communication were modulated on defoliated plants, possibly suggesting modified aphid behaviour. The GroEL protein (or symbionin) of the endosymbiont Buchnera aphidicola was predominant under all conditions in M. euphorbiae. Its expression level was not significantly affected by aphid host-plant stresses, which is consistent with the high priority of symbiosis in stressed aphids. r

By 2025, it is estimated that around 5 billion people, out of a total population of around 8 billion, will be living in countries experiencing water stress (using more than 20% of their available resources). Climate change has the potential to impose additional pressures in some regions. This paper describes an assessment of the implications of climate change for global hydrological regimes and water resources. It uses climate change scenarios developed from Hadley Centre climate simulations (HadCM2 and HadCM3), and simulates global river #ows at a spatial resolution of 0.5;0.53 using a macro-scale hydrological model. Changes in national water resources are calculated, including both internally generated runo! and upstream imports, and compared with national water use estimates developed for the United Nations Comprehensive Assessment of the Freshwater Resources of the World. Although there is variation between scenarios, the results suggest that average annual runo! will increase in high latitudes, in equatorial Africa and Asia, and southeast Asia, and will decrease in mid-latitudes and most subtropical regions. The HadCM3 scenario produces changes in runo! which are often similar to those from the HadCM2 scenarios * but there are important regional di!erences. The rise in temperature associated with climate change leads to a general reduction in the proportion of precipitation falling as snow, and a consequent reduction in many areas in the duration of snow cover. This has implications for the timing of stream#ow in such regions, with a shift from spring snow melt to winter runo!. Under the HadCM2 ensemble mean scenario, the number of people living in countries with water stress would increase by 53 million by 2025 (relative to those who would be a!ected in the absence of climate change). Under the HadCM3 scenario, the number of people living in countries with water stress would rise by 113 million. However, by 2050 there would be a net reduction in populations in stressed countries under HadCM2 (of around 69 million), but an increase of 56 million under HadCM3. The study also showed that di!erent indications of the impact of climate change on water resource stresses could be obtained using di!erent projections of future water use. The paper emphasises the large range between estimates of`impacta, and also discusses the problems associated with the scale of analysis and the de"nition of indices of water resource impact.

Potted plants of two cultivars of almond (Amygdalus communis L.), Ramillete and Garrigues, growing under field conditions were subjected to drought by withholding irrigation for 28 days. Stressed plants were reirrigated and the recovery was studied for 8 days. Control plants were drip irrigated daily maintaining the soil matric potential at about -30 kPa. Predawn leaf water potential declined progressively due to water stress effect, reaching -0.80 MPa in Garrigues and -0.98 MPa in Ramillete at the end of the stress period. The reduction in midday leaf conductance in plants under water stress could be related to the reduction in midday leaf water potential. The reductions in leaf conductance values were about 62% and 79% for Garrigues and Ramillete, respectively. Garrigues exhibited osmotic adjustment during the greater part of the stress period and this was sufficient to maintain the leaf turgor. The relationship between leaf conductance and turgor pressure at midday appeared to be nearly linear over the range of turgor pressure observed. Ramillete presented lower leaf water potential at turgor loss point than did Garrigues. Roth cultivars presented high relative apoplastic water contents. The increase in these parameter values by water stress effect observed in Ramillete could indicate changes in cell wall structure. After rewatering, most of the parameters studied recovered quickly, although leaf conductance was delayed.

This paper describes an attempt to model soil moisture over the Australian continent with an integrated system of dynamic models and a Geographic Information System (GIS) data base. A land surface scheme with improved treatment of soil hydrological processes is described. The non-linear relationships between soil hydraulic conductivity, matric potential and soil moisture are derived from the Broadbridge and White soil model. For a single location, the prediction of the scheme is in good agreement with the measurements of the Hydrological and Atmospheric Pilot Experiment (HAPEX). High resolution atmospheric and geographic data are used in soil moisture prediction over the Australian continent. The importance of reliable land surface parameters is emphasized and details are given for deriving the parameters from a GIS. Predicted soil moisture patterns over the Australian continent in summer, with a 50 km spatial resolution, are found to be closely related to the distribution of soil types, apart from isolated areas and times under the influence of precipitation. This is consistent with the notion that the Australian continent in summer is generally under water stress. In contrast, predicted soil temperatures are more closely related to radiation patterns and changes in atmospheric circulation. The simulation can provide details of soil moisture evolution both in space and time, that are very useful for studies of land use sustainability, such as plant growth modelling and soil erosion prediction.

Most atmospheric scientists agree that climate changes are going to increase the mean temperature in Europe with increased frequency of climatic extremes, such as drought, floods, and storms. Under such conditions, there is high probability that forests will be subject to increased frequency and intensity of stress due to climatic extremes. Therefore, impacts of climate change on forest health should be carefully evaluated. Given these assumptions, several fungal diseases on trees may become more devastating because of the following factors: (i) abiotic stresses, such as drought and flooding, are known to predispose trees to several pathogens; (ii) temperature and moisture affect pathogen sporulation and dispersal, and changes in climatic conditions are likely to favour certain pathogens; (iii) migration of pathogens triggered by climatic change may increase disease incidence or geographical range, when pathogens encounter new hosts and (or) new potential vectors; and (iv) new threats may appear either because of a change in tree species composition or because of invasive species. If infection success is dependent on temperature, higher mean temperatures may lead to more attacks. Pathogens that have been of importance in southern Europe may spread northward and also upward to mountains. Pathogens with evolutionary potential for greater damage should be identified to estimate the magnitude of the threat and to prepare for the changing conditions. A review of the above-mentioned cases is presented. Some priorities to improve the ability to predict impacts of climate change on tree diseases are discussed.

Nitrogen (N) is the largest agricultural input in many Australian cropping systems and applying the right amount of N in the right place at the right physiological stage is a significant challenge for wheat growers. Optimizing N uptake could reduce input costs and minimize potential off-site movement. Since N uptake is dependent on soil and plant water status, ideally, N should be applied only to areas within paddocks with sufficient plant available water. To quantify N and water stress, spectral and thermal crop stress detection methods were explored using hyperspectral, multispectral and thermal remote sensing data collected at a research field site in Victoria, Australia. Wheat was grown over two seasons with two levels of water inputs (rainfall/irrigation) and either four levels (in 2004; 0, 17, 39 and 163 kg/ha) or two levels (in 2005; 0 and 39 kg/ha N) of nitrogen. The Canopy Chlorophyll Content Index (CCCI) and modified Spectral Ratio planar index (mSRpi), two indices designed to measure canopy-level N, were calculated from canopy-level hyperspectral data in 2005. They accounted for 76% and 74% of the variability of crop N status, respectively, just prior to stem elongation (Zadoks 24). The Normalised Difference Red Edge (NDRE) index and CCCI, calculated from airborne multispectral imagery, accounted for 41% and 37% of variability in crop N status, respectively. Greater scatter in the airborne data was attributable to the difference in scale of the ground and aerial measurements (i.e., small area plant samples against whole-plot means from imagery). Nevertheless, the analysis demonstrated that canopy-level theory can be transferred to airborne data, which could ultimately be of more use to growers. Thermal imagery showed that mean plot temperatures of rainfed treatments were 2.7 8C warmer than irrigated treatments (P < 0.001) at full cover. For partially vegetated fields, the two-Dimensional Crop Water Stress Index (2D CWSI) was calculated using the Vegetation Index-Temperature (VIT) trapezoid method to reduce the contribution of soil background to image temperature. Results showed rainfed plots were consistently more stressed than irrigated plots. Future work is needed to improve the ability of the CCCI and VIT methods to detect N and water stress and apply both indices simultaneously at the paddock scale to test whether N can be targeted based on water status. Use of these technologies has significant potential for maximising the spatial and temporal efficiency of N applications for wheat growers.

O ur ohjective is to descrihe a multi-layer model of C.r canopy processes that effectively simulates houri)' C02 :uul latent ener gy (U~) lluxcs in a mixed deciduous Quercus-Acer (oak-maple) st'.111d in c~ntral l\ l~1ssac~1u selts, US/\. The key hy pothesis J!OVe rnmg the b1oloA1cal component of the model is Urnt stomata! conductance (g,.) is var ied s o that d ail y carbon uptake per unit of foliar nit r oj:!en is maximized wit hin the limitations of ca1101>Y water avr1ilability. T he h ydraulic system is modelled as :m a nalo~ue to simple electr ical circuits in parallel. includinJ! a separate soil hydraulic resistance. plant resistance and plant capacitance for each c:m op y layer. Stomata! openin(! is initially controlled to conserve plant water stores and delay the o nset or water stress. Stomata! clos ure at :i threshold minimum l~1f water potential prevents xyle m cavitation and contr ols the maximum r:itc of wate r llux through the h ydraulic system. We show a strong correlat ion between predicted hourly C0 2 exchange rate (r2 = 0•86) and LE (r 2 = 0•87) with independent whole-forest measurements made by the eddy correlation method during the s ummer of 1992. Our theoretical derivation s hows that observed relationships between C0 2 assimilation a nd LE nux can he explained on the basis of s tomata! behaviour 01>timizing c:irhon gain, and provides mt exi>licit link hetwecn canopy structure, soil pro1>erties. atmos pheric conditions and stomatal conductance.

It is well known that rivers connect upstream and downstream ecosystems within watersheds. Here we describe the concept of precipitationsheds to show how upwind terrestrial evaporation source areas contribute moisture for precipitation to downwind sink regions. We illustrate the importance of upwind land cover in precipitationsheds to sustain precipitation in critically water stressed downwind areas, specifically dryland agricultural areas. We first identify seven regions where rainfed agriculture is particularly vulnerable to reductions in precipitation, and then map their precipitationsheds. We then develop a framework for qualitatively assessing the vulnerability of precipitation for these seven agricultural regions. We illustrate that the sink regions have varying degrees of vulnerability to changes in upwind evaporation rates depending on the extent of the precipitationshed, source region land use intensity and expected land cover changes in the source region.

Photosynthesis, respiration, and other processes produce reactive oxygen species (ROS) that can cause oxidative modifications to proteins, lipids, and DNA. The production of ROS increases under stress conditions, causing oxidative damage and impairment of normal metabolism. In this work, oxidative damage to various subcellular compartments (i.e. chloroplasts, mitochondria, and peroxisomes) was studied in two cultivars of wheat differing in ascorbic acid content, and growing under good irrigation or drought. In well-watered plants, mitochondria contained 9-28-fold higher concentrations of oxidatively modified proteins than chloroplasts or peroxisomes. In general, oxidative damage to proteins was more intense in the cultivar with the lower content of ascorbic acid, particularly in the chloroplast stroma. Water stress caused a marked increase in oxidative damage to proteins, particularly in mitochondria and peroxisomes. These results indicate that mitochondria are the main target for oxidative damage to proteins under well-irrigated and drought conditions.

The impact of water stress was analysed in the xero-halophyte Mediterranean shrub Atriplex halimus using two Tunisian populations originating from a subhumid coastal site (Monastir) or from a semi-arid area (Kairouan). Seedlings were exposed for 10 days to nutrient solution containing either 0 or 15% polyethylene glycol. Water potential (W w), osmotic potential (W s), osmotic potential at full turgor [W s (100)], relative water content (RWC), shoot dry weight (DW) and changes in solute concentrations were quantified every 2 days throughout the stress period and inorganic solutes contents were determined at the end of the treatment. The water deficit induced a decrease in W w , W s and RWC in both populations, recorded changes being higher in plants of Monastir than those of Kairouan while the shoot dry weight was reduced in a similar extent in stressed plants from both populations. Water deficit induced an increase in proline, glycinebetaine and sugar concentrations. Proline accumulated as early as after the 24-h stress treatment while, glycinebetaine required more than 6 days of stress to accumulate. At the end of the stress period, the plants of Kairouan population accumulated higher amounts of proline than those of Monastir, while an opposite trend was reported for glycinebetaine. Both populations specifically accumulated Na ? in response to drought stress, suggesting that this element could play a physiological role in the stress response of this xero-halophyte species. Presented results suggest that the non-recyclable osmotic solute glycinebetaine does not necessarily preferentially accumulates in population facing permanent water stress and that other strategy than osmotic adjustment might be involved in drought tolerance of A. halimus.

The plant hormone abscisic acid (ABA) is necessary for the regulation of several aspects during seed development and for the response to environmental stresses such as desiccation, salt and cold. An important part of the physiological response to ABA is achieved through gene expression. Although different signal molecules have been identified, the signal transduction pathway from ABA perception to the induction of specific genes is not very well established yet. In particular, phosphorylation and dephosphorylation events have been identified as important in ABA signalling. A great effort has been focused on analysing the promoters of ABA-responsive genes in order to identify cis-and transacting elements that mediate transcriptional regulation. Many different proteins accumulate in response to water deficit, some of them with a clear function in protecting the cells against dehydration. Other proteins, whose function is not completely understood, include LEA proteins that accumulate during late embryogenesis and in response to ABA.

In plant factory, optimal control, expert systems, and robotics applications for obtaining higher yield and better quality of plant is essential. Sunagoke moss is one of the plant products which are produced by plant factory. The objectives of this research are developing an intelligent irrigation system, line tracer robot transporter, and precision artificial lighting system in a cultured moss mat production factory. In the intelligent irrigation system, machine vision device is used as non-destructive sensing to detect water stress in cultured moss mat. A miniature of line tracer robot transporter has been developed to simulate the transport process of moss mat in plant factory. A combination of machine vision and scanning type laser diodes lighting system is used to control the light condition. The intelligent irrigation system using artificial neural network is able to predict the deficit water content of moss accurately and fulfil the water needs in moss mat precisely. The line tracer robot transporter has been tested successfully to describe the relationship between the load variations and the transport speed and energy. The precision artificial lighting system can recognize the moss mat area which lack of light and provide accurate light in each moss mat area according to their needs. Overall, the proposed control systems in this study are acceptable to develop automated precision plant factory.

Survivorship and growth of seedlings of four dipterocarp species (Dipterocarpus actangulus, D. globosus, Dryobalanops aromatica, Dryobalanops lanceolata) were studied for 2.5 years in a mixed dipterocarp forest in Sarawak, East Malaysia. Predispersal seed predation rates were larger for D. globosus (75%) than D. lanceolata (27-34%) and D. aromatica (18-26%). Less than 20% of the two Dryobalanops seeds were damaged by vertebrates after seed dispersal. During the period from seed dispersal to the time when the seedlings had shed cotyledons, more dispersed seeds died in the two Dipterocarpus (ca 90%) than the two Dryobalanops (ca 60-70%). The major mortality factors during this period were uprooted and seed/seedling predation by insects or vertebrates. After the seedlings shed cotyledons, all species showed constant mortality rates of 34, 15-16, 17 and 6%/year for D. actangulus, D. lanceolata, D. aroma tica and D. globosus, respectively, in the forest understorey. Mortality was lower in less shaded conditions than in more shaded ones for D. aromatica and D. actangulus, but not significantly different for D. lanceolata and D. globosus. A majority of dead seedlings were killed by fallen branches or were found standing with wilted leaves, probably due to water stress. No significant correlation was found between seed/seedling mortality and distance from mother trees or the initial density of seeds/seedings for all species. The mean leaf production was positively correlated with the estimated diffuse light factor of their habitats for each species.

The article details the development and uses of the water poverty index (WPI). The index was developed as a holistic tool to measure water stress at the household and community levels, designed to aid national decision makers, at community and central government level, as ...

One of the major environmental factors limiting plant productivity is lack of water. This is especially true for the major cereals maize, rice, and wheat, which demonstrate a range of susceptibility to moisture deficit. Although conventional breeding and marker-assisted selection are being used to develop varieties more tolerant to water stress, these methods are time and resource consuming and germplasm dependent. Genetic engineering is attractive because of its potential to improve abiotic stress tolerance more rapidly. Transcription factors have been shown to produce multiple phenotypic alterations, many of which are involved in stress responses. DREB1A, a transcription factor that recognizes dehydration response elements, has been shown in Arabidopsis thaliana to play a crucial role in promoting the expression of drought-tolerance genes. In our efforts to enhance drought tolerance in wheat, the A. thaliana DREB1A gene was placed under control of a stress-inducible promoter from the rd29A gene and transferred via biolistic transformation into bread wheat. Plants expressing the DREB1A gene demonstrated substantial resistance to water stress in comparison with checks under experimental greenhouse conditions, manifested by a 10-day delay in wilting when water was withheld.

Contrasting temperate climates the vegetation in semi-arid and arid areas generally is insufficiently supplied with water from precipitation. Because of this water supplied to an ecosystem, excluding that from precipitation, such as dew deposition, water vapor absorption (

A field experiment was carried out during the autumn season in 2013 in a farm located in Alhashimiya (20 km south east of Hilla), to study the effect of salicylic acid and phosphorus spraying on yield of maize under conditions of deficit irrigation. Split-split plot arrangement in randomized complete block design (RCBD) with three replications was used, operated irrigation treatments (A0 full irrigation, A1 deficit irrigation) in panels major plots , while concentrations of phosphorus (0, 1000 and 2000 mg.L-1) panels the sub plot and concentrations of salicylic acid (0, 0.5 and 1 mM) panels the sub-sub plots. Maize grain (cv. Research 106) was seeded in 20-July/2013. The results showed that deficit irrigation led to reduce most of yield components (rows number, grain number, length and diameter of ear) significantly. Salicylic acid and phosphorous spraying led to remove or reduce this negative effect of water stress, in which P at 1000 mg.L-1 was superior in giving the highest rate of most yield components (ear length, rows number and weight of 500 grain). Salicylic acid 1 mM was superior in ear length and grain number.ear-1. The interaction between the factors had a significant effect in most of traits studied.

Photosynthetic carbohydrate content in Setaria sphacelata var. splendida under rapidly and slowly induced water deficit and its contribution to osmotic adjustment were studied. In short-term stress experiments, a decrease in the total content of sucrose (Su) and starch (St) was observed in leaf discs submitted to stress. An increase in the ratio between free hexoses and sucrose was found in stressed leaves, but no significant differences were found in the amount of free hexoses nor in the ratio between soluble and insoluble sugars. In long-term stress experiments, a higher amount of soluble sugars and a lower amount of starch were found in stressed leaves, when compared to the control. The ratios of free hexoses to sucrose and of soluble to insoluble sugars were also higher in stressed leaves. The contribution of the accumulation of soluble sugars to osmotic adjustment was absent in rapidly stressed leaves and was of minor importance in slowly stressed leaves.

Cassava or manioc (Manihot esculenta Crantz), a perennial shrub of the New World, currently is the sixth world food crop for more than 500 million people in tropical and sub-tropical Africa, Asia and Latin America. It is cultivated mainly by resource-limited small farmers for its starchy roots, which are used as human food either fresh when low in cyanogens or in many processed forms and products, mostly starch, flour, and for animal feed. Because of its inherent tolerance to stressful environments, where other food crops would fail, it is often considered a food-security source against famine, requiring minimal care. Under optimal environmental conditions, it compares favorably in production of energy with most other major staple food crops due to its high yield potential. Recent research at the Centro Internacional de Agricultura Tropical (CIAT) in Colombia has demonstrated the ability of cassava to assimilate carbon at very high rates under high levels of humidity, temperature and solar radiation, which correlates with productivity across all environments whether dry or humid. When grown on very poor soils under prolonged drought for more than 6 months, the crop reduce both its leaf canopy and transpiration water loss, but its attached leaves remain photosynthetically active, though at greatly reduced rates. The main physiological mechanism underlying such a remarkable tolerance to drought was rapid stomatal closure under both atmospheric and edaphic water stress, protecting the leaf against dehydration while the plant depletes available soil water slowly during long dry periods. This drought tolerance mechanism leads to high crop water use efficiency values. Although the cassava fine root system is sparse, compared to other crops, it can penetrate below 2 m soil, thus enabling the crop to exploit deep water if available. Leaves of cassava and wild Manihot possess elevated activities of the C4 enzyme PEP carboxylase but lack the leaf Kranz anatomy typical of C4 species, pointing to the need for further research on cultivated and wild Manihot to further improve its photosynthetic potential and yield, particularly under stressful environments. Moreover, a wide range in values of K m (CO2) for the C3 photosynthetic enzyme Rubisco was found among cassava cultivars indicating the possibility of selection for higher affinity to CO2, and consequently higher leaf photosynthesis. Several plant traits that may be of value in crop breeding and improvement have been identified, such as an extensive fine root system, long leaf life, strong root sink and high leaf photosynthesis. Selection of parental materials for tolerance to drought and infertile soils under representative field conditions have resulted in developing improved cultivars that have high yields in favorable environments while producing reasonable and stable yields under stress.

Saplings of Pinus sylvestris were subjected to drought stress periods and inoculated with Sphaempsis sapinea in a greenhouse experiment. Six wk after inoculation, saplings that had low needle water potentials for 14 to 21 days after inoculation exhibited more dieback and developed significantly (P < 0.05) longer cankers than saplings that had equivalent water stress for 3 to 4 days after inoculation or unstressed saplings. The results indicate that drought stress increases susceptibility of Scots pine to Sphaeropsis canker and that canker growth can be suppressed by watering drought-stressed trees.

This study combines existing hydraulic principles with recently developed methods for probing leaf hydraulic function to determine whether xylem physiology can explain the dynamic response of gas exchange both during drought and in the recovery phase after rewatering. Four conifer species from wet and dry forests were exposed to a range of water stresses by withholding water and then rewatering to observe the recovery process. During both phases midday transpiration and leaf water potential (C leaf) were monitored. Stomatal responses to C leaf were established for each species and these relationships used to evaluate whether the recovery of gas exchange after drought was limited by postembolism hydraulic repair in leaves. Furthermore, the timing of gas-exchange recovery was used to determine the maximum survivable water stress for each species and this index compared with data for both leaf and stem vulnerability to water-stress-induced dysfunction measured for each species. Recovery of gas exchange after water stress took between 1 and .100 d and during this period all species showed strong 1:1 conformity to a combined hydraulic-stomatal limitation model (r 2 = 0.70 across all plants). Gas-exchange recovery time showed two distinct phases, a rapid overnight recovery in plants stressed to ,50% loss of leaf hydraulic conductance (K leaf) and a highly C leaf-dependent phase in plants stressed to .50% loss of K leaf. Maximum recoverable water stress (C min) corresponded to a 95% loss of K leaf. Thus, we conclude that xylem hydraulics represents a direct limit to the drought tolerance of these conifer species.

The effects of pre-anthesis water deficit and cycle length were examined in Papaver somniferum L., cultivated for alkaloid production, in two locations in southern Spain. The vegetative period was shortened by extending the photoperiod through supplemental lighting in the field, while water deficit in pre-anthesis was induced by avoiding irrigations and installing rain shelters. The treatments were: IN (irrigated-normal photoperiod), IL (irrigated-hastened flowering), DN (water deficit in pre-anthesisnormal photoperiod) and DL (water deficit in pre-anthesis and hastened flowering). The artificial photoperiod hastened the flowering by 15 and 21 days, for irrigated and deficit treatments respectively. Seasonal evapotranspiration (ET) ranged from 398 (DN) to 505 mm (IN). There was evidence of root water uptake deeper than 1.5 m. Stomatal conductance was reduced (16%) during water stress, and did not recover in post-anthesis after resuming irrigation. Head yields (capsule + seeds + 7 cm stem) ranged between 3.8 and 4.3 t ha −1 ; water deficit and short vegetative period both reduced the biomass accumulated, although the effect on yields in these treatments was counterbalanced by a higher harvest index. Early flowering had a detrimental effect on alkaloid concentration in the capsule. Alkaloids yield ranged between 27 and 37 kg ha −1 . Water use efficiency (WUE) ranged between 0.78 and 0.96 kg m −3 ET for yield and between 63.4 and 73.7 g m −3 ET for alkaloids. Water stress increased slightly the Water Use Efficiency. A shorter vegetative phase had no effect on WUE for biomass or yield, but decreased the WUE for alkaloids production.

North American coastal sandplain heathlands are unique in species composition and vegetation, but the extent to which edaphic factors influence the structure of these communities is currently debated. It was hypothesized that salt spray and edaphic factors maintain the dwarf stature and community composition of heathlands by limiting plant growth and excluding competitively dominant woody species close to the ocean. Field surveys were carried out to investigate the spatial patterns of salt spray accumulation, soil salt and soil moisture. High salt spray correlated significantly with increased leaf necrosis and water stress in Myrica pensylvanica and with decreased plant height. Plant community composition changed across a salt spray and soil gradient, as well. Distinctive sub-communities were identified that separated according to soil salt and soil moisture but salt spray was the main factor affecting sites occupied only by heathland vegetation. Results from this study suggest that salt spray suppresses the growth of heathland plants in close proximity to the ocean, and therefore maintains the low stature in these dwarf shrublands. This research also demonstrates that the physical environment influences the community structure in heathlands, particularly by limiting tree species from growing in high salt spray, low water availability sites.

Progress in assessing the feasibility for imaging fluorescence using the O 2 -A band with 1 nm full-width halfmaximum (FWHM) bands centered at 757.5 and 760.5 nm is reported in this paper. Multispectral airborne data was acquired at 150 m above ground level in the thermal, visible and near infrared regions yielding imagery at 15 cm spatial resolution. Simultaneous field experiments conducted in olive, peach, and orange orchards (water stress trials), and an olive orchard (variety trial) enabled the detected variability in fluorescence emission to be examined as function of stress status. In a parallel modelling activity the coupled leaf-canopy reflectance-fluorescence model, FluorMOD, was used to assess fluorescence retrieval capability by the in-filling method, as well as by fluorescence indices from the published literature. Fluorescence retrievals using the in-filling method, the derivative index D702/D680 and reflectance indices R690/R630, R761-R757, and R761/R757 yielded the best results in the simulation study, while demonstrating insensitivity to leaf area index (LAI) variation. The fluorescence in-filling method, derivative index D702/ D680, and R761-R757 were the indices least affected by chlorophyll a + b (Cab) variation. On the other hand, other published indices for fluorescence detection at leaf and canopy levels exhibited high sensitivity to variations in Cab and LAI, and therefore were considered less suitable for in-field fluorescence detection. The fluorescence signal extraction from airborne imagery using the in-filling method was validated through comparisons with field-measured steady-state fluorescence (Fs) using the PAM-2100 and GFS-3000 instruments, confirming simulation predictions. The water stress experiments conducted on olive and peach orchards demonstrated the feasibility of chlorophyll fluorescence (F) extraction at the tree level from the airborne imagery, yielding determination coefficients r 2 = 0.57 (olive), and r 2 = 0.54 (peach). Consistent results were obtained between airborne F and ground truth assimilation (A) measured in the olive variety field experiment under no water stress levels, yielding r 2 = 0.71.

In normal rye caryopses, five phenolic acids were detected: ferulic, sinapic, vanillic, caffeic and p-coumaric, three of which were found in the free phenolic fraction (p-coumaric, ferulic and sinapic). Total phenolic compound and phenolic acid contents were the highest at the initial stage of development and the lowest at the final stage of maturation of rye grains. After the dehydration treatment, total phenolic content decreased relatively slightly in all examined samples of rye caryopses of various ripeness. The phenolic acid fraction (consisting of both bound and free forms) decreased more during dehydration, especially at the initial stage of caryopses development. Cells of unripe rye grains reacted to water stress by lowering the level of total phenolic compounds, and especially the content of phenolic acids. During the development and ripening of rye caryopses, a gradual increase in precocious germination ability of the grain was observed. The enforced dehydration stimulated processes of precocious germination of unripe caryopses. The highest stimulation of germination was observed at the initial stage of development of caryopses (22 and 29 DAF). One of the reasons for inducing faster germination of unripe rye caryopses may be the lowering of the level of phenolic acids (considered as inhibitors of germination) in caryopses after the dehydration treatment. © 2000 Éditions scientifiques et médicales Elsevier SAS cereal grains / development / enforced dehydration / phenolic acids / precocious germination / Secale cereale ABA, abscisic acid / DAF, days after flowering / DW, dry weight / GA, gibberellic acid / HPLC, high performance liquid chromatography / PAL, phenylalanine ammonia-lyase

Background: Constraints on tree regeneration have been described from several temperate treeline sites, however data from tropical mountains are few. Aim: We test the hypothesis that high altitude treelines are caused by constraints on tree regeneration. We report the results of recent studies on climatic variables and on the reproduction of Erica spp. in east Africa, and compare those with similar studies on treeline stands of Polylepis spp. in Ecuador and Bolivia. Methods: We established altitudinal and horizontal transects comprising sampling plots from forests to surrounding grasslands. Data on microclimate, vegetation structure and reproductive activity were collected in the field, and supplemented by tests on germination requirements in the field in permanent exclosures and in the laboratory. Results: Our measurements demonstrated that the number and severity of frost events and potential water stress were higher near the soil surface (0.5 m) than in free air (2.0 m). Seeds of Erica trimera did not germinate, as the necessary climatic requirements (high diurnal temperature range, but no frost) were rarely fulfilled in the field. Most studied species were capable of clonal growth, and the relative importance of vegetative persistence tended to increase with altitude. These effects were independent of the intensity of land use. Conclusions: The harsh microclimate near the soil surface at tropical treelines may be one reason why recruitment from seed is limited for treeline-forming species. This is important for restoration or conservation schemes as well as predictions of treeline dynamics under global change.

Experiments were carried out to study which soil physical factors, if any, would restrict germination and emergence of sorghum (Sorghum bicolor (L.) Moench.) and cowpea (Vigna unguiculata (L.) Walp.), under field conditions in Tanzania. The study also aimed to consider the usefulness of mulching as a strategy to overcome such problems, and to contribute to the development of a strategy for modelling seedling emergence in seedbeds in the field.

A methodology for the assessment of fruit quality in crops subjected to different irrigation regimes is presented. High spatial resolution multispectral and thermal airborne imagery were used to monitor crown temperature and the Photochemical Reflectance Index (PRI) over three commercial orchards comprising peach, nectarine and orange fruit trees during 2008. Irrigation regimes included sustained and regulated deficit irrigation strategies, leading to high variability of fruit quality at harvest. Stem water potential was used to monitor individual tree water status on each study site. Leaf samples were collected for destructive sampling of xanthophyll pigments to assess the relationship between the xanthophyll epoxidation state (EPS) and PRI at leaf and airborne-canopy level. At harvest, fruit size, Total Soluble Solids (TSS) and Tritatable Acidity (TA) were measured to characterize fruit quality. A statistically significant relationship between EPS and PRI was found at the leaf (r 2 = 0.81) and canopy level (r 2 = 0.41). Airborne-derived crown PRI calculated from the imagery acquired during the fruit growth was related to the ratio of the total soluble solids normalized by the tritatable acidity (TSS/TA), an indicator of fruit quality measured on the same trees, yielding a coefficient of determination of r 2 = 0.50. The relationship between the integral of PRI time-series and TSS/TA yielded a coefficient of determination of r 2 =0.72 (peach) and r 2 = 0.61 (nectarines). On the contrary, the relation between TSS/TA and the time-series of crown thermal imagery was very weak (r 2 = 0.21 and 0.25 respectively). These results suggest that a physiological remote sensing indicator related to photosynthesis, such as PRI, is more appropriate for fruit quality assessment than crown temperature, the established method of water stress detection, which is more related to crown transpiration. A radiative transfer modelling study was conducted to assess the potential validity of this methodology for fruit quality assessment when using medium spatial resolution imagery. The analysis shows important effects of soil and shadows on the PRI vs EPS relationship used for fruit quality assessment if non-pure crown reflectance was extracted from the imagery.

ABSTRACT Maize grain yields have increased dramatically over the past fifty years, and concurrently end-uses have proliferated requiring special quality characteristics. Plant breeders have developed many specialty types of maize, all of which are influenced by the agronomic practices used to produce the crop. Grain yield increases have resulted in lower protein concentration except when the yield increase resulted from nitrogen fertilizer application. Irrigation improves the biological value of protein, while higher nitrogen application rates alter the amino acid balance thereby reducing the nutritional value. Kernel breakage susceptibility and kernel density increase with higher nitrogen fertilizer application rates, and are reduced by irrigation. Extractable starch and oil concentration are largely influenced by hybrid choice, but small production practice effects have been documented. Essential mineral nutrient levels are often influenced by soil or foliar fertilizer application. The production of aflatoxin can be reduced by irrigation or other strategies to avoid water stress during grain fill. Although genetics usually exerts the largest effect on maize grain quality, agronomic practices are also important.

Broadbeans were grown on clay in tanks and irrigated with water of three different levels of salinity. During the experiment, soil salinity, determined from the salt balance and soil water samples, showed a gradual increase. The water stress of the broadbeans was determined by measuring the predawn leaf water potential, the stomatal conductance and the differences in radiation temperature between the treatments. Growth was measured as leaf area and dry-matter production and, finally, the yield and its components were determined. The three water stress parameters and the two growth parameters showed good coherence, with all parameters indicating systematic differences between the saline treatments and the control. At increasing salinity water potential of the leaf and the stomatal conductance decreased, the difference in radiation temperature increased, and the leaf area, dry matter production and yield were reduced.

There is an algorithm presented that uses multispectral images as a result of the processing of images and the MATLAB software. These multispectral images could be applied on cacao and coffee crops which not only are the most representative type of the region of Santander, but also the ones with most economic growth on the last two decades. The strategy of deploying these images, also help to demarcate the dried lands from the better hydrated ones, which is crucial to develop Precision Farming since it makes it more productive, with less losses and with better benefits. The graphical user interface (GUI) was developed in order to facilitate the interaction between the software and the user. On this graphical interface, it’s possible to identify the varied applications that could be run and recognized. It is worth mentioning that this process has several stages. it begins from the analysis of a satellite images data base, which stablish the characteristics and condition of the crops; from it, it’s possible to obtain a more accurate and detailed radiogram that illustrates the reality of each crops.

Intra-specific variability can be used as
an important tool to contrast and mitigate the negative
impacts of climate change. In particular, under
Mediterranean climate conditions drought stress is
becoming a crucial issue for growers. Vine performance,
taking into account vine yield and grape composition,
is dependent on the vine capability of assimilating
CO2 and fix it into carbohydrates throughout the
growing season. Under water stress, stomatal regulation,
that allow plants to prevent excessive water loss
and t issue drying, l imi ts leaf gas exchanges.
Understanding the mechanisms regulating stomatal
closure is crucial to determine the behaviour of genotypes
under water stress. Two main mechanisms are
accredited for controlling stomatal conductance under
water stress: active mechanisms, based on the
biosynthesis of hormonal signals, mainly abscisic acid
(ABA), and passive mechanisms, mainly based on
the variation of leaf turgor pressure as the plant water
potent ial decreases dur ing water stress. New
research evidences pointed out that the capability of
genotypes to close stomata at a given stem water
potential threshold was correlated with its xylem vulnerability
to cavitation. ABA accumulation in the leaf
appears to be subsequent to stomata closure suggesting
that, in vivo, stomatal conductance mainly rely
to passive mechanism rather than to active ones.
Hydraulic properties of each genotype appear to control
their stomatal behavior under water stress consistently
with the rising opinion that intraspecific variability
of stomatal behavior cannot be discriminated into
two different categories (isohydric and anisohydric)
but should be represented as a continuum of genotypes
with different levels of anisohydry. These results
underline the need to learn more about the phenotype
of grape cultivars. Growers will be able to use such
information by planting more tolerant genotypes
depending on vineyard conditions and to use different
water potential thresholds for irrigation scheduling.