Consequences of climate change on tree phenology are readily observable, but little is known abou... more Consequences of climate change on tree phenology are readily observable, but little is known about the variations in phenological sensitivity to drought between populations within a species. In this study, we compare the phenological sensitivity to temperature and water availability in Abies pinsapo Boiss., a drought-sensitive Mediterranean fir, across its altitudinal distribution gradient. Twig growth and needle fall were related to temperature, precipitation and plant water status on a daily scale. Stands located at the top edge of the distributional range showed the most favourable water balance, maximum growth rates and little summer defoliation. Towards higher elevations, the observed delay in budburst date due to lower spring temperatures was overcome by a stronger delay in growth cessation date due to the later onset of strong water-deficit conditions in the summer. This explains an extended growing season and the greatest mean growth at the highest elevation. Conversely, lower predawn xylem water potentials and early partial stomatal closure and growth cessation were found in low-elevation A. pinsapo trees. An earlier and higher summer peak of A. pinsapo litterfall was also observed at these water-limited sites. Our results illustrate the ecophysiological background of the ongoing altitudinal shifts reported for this relict tree species under current climatic conditions.
ÐMost models predict that high atmospheric CO 2 concentrations will lead to an increase in the C-... more ÐMost models predict that high atmospheric CO 2 concentrations will lead to an increase in the C-toN ratio of litter production in terrestrial ecosystems. The eect of an increase in the soil C-toN ratio on the nitrogen dynamics in a Mediterranean shrubland was simulated by mixing with the litter layer wood shavings with a high C-toN ratio. Samples of mineral soil, taken subsequently eight times during 404 d, were analyzed for total C, total N, total soil carbohydrates, potential net N mineralization, potential net nitri®cation and microbial biomass-N. We found signi®cant increases in the concentration of total carbohydrates, C-toN ratio and microbial biomass N in amended soils during the experiment, while potential net N mineralization rate and net nitri®cation rate signi®cantly decreased; amounts of available nitrogen (NH 4 + ±N + NO 3 ±N) were unaected by the amendment treatment. However, by the end of the experiment, no signi®cant dierences between amended and control soil samples were found. The total carbohydrates-to-K 2 SO 4-extractable total-N ratio was the best predictor of both net mineralization rate and microbial biomass N, showing that the available C-to-available-N ratio is a better indicator of N dynamics than the total C to total N ratio. Our results support the hypothesis that increasing C availability in soils leads to a decrease in N availability for plants through the immobilization of N in microbial biomass and to an increase in the temporal heterogeneity of soil properties in a Mediterranean shrubland.
Climate variability and land-use modifications are among the main components of global change, bu... more Climate variability and land-use modifications are among the main components of global change, but their combined effects on forests have rarely been addressed. Relict tree species from the Mediterranean Basin are appropriate experimental models to investigate these effects since they grow in climatically-stressed areas, which have undergone intensive land-use changes. We hypothesize that intense logging and overgrazing could be related to forests decline, but also the abandonment of traditional land-use practices and subsequent enhancement of density-dependent factors acted as a predisposing stressor that modified the response of several tree species from the Mediterranean Basin to recent climate change. We summarize results from current forest structure and mortality patterns, as well as relationships between tree radial-growth and regional climatic trends in four tree species from western Mediterranean Mountains: Silver fir (Abies alba) from the North of Spain, Pinsapo fir (Abies...
The geographic distribution of deciduous versus evergreen woody species has been intensively inve... more The geographic distribution of deciduous versus evergreen woody species has been intensively investigated, but the ecological significance of both leaf habits is still far from being fully understood. The purpose of this chapter is to review the factors that are related with the carbon gain of deciduous and evergreen oak species under Mediterranean environmental conditions. We will focus on the morphological, anatomical and chemical adaptations of evergreens necessary to guarantee leaf survival during the unfavorable part of the year. We will review the information available about the construction and maintenance costs associated with the leaf traits of deciduous and evergreen oak species. Moreover, we will compare these traits with those of non-Mediterranean oaks and species belonging to other families. One central leaf trait is the leaf mass per area (LMA), which depends on the leaf anatomy and chemical composition. Differences in LMA are related to photosynthesis and the costs of...
The terminal part of the mitochondrial electron pathway, consists of two terminal oxidases: the c... more The terminal part of the mitochondrial electron pathway, consists of two terminal oxidases: the cytochrome oxidase (sensitive to cyanide) and the alternative oxidase (both resistant to cyanide and sensitive to salicylhidroxamic acid). This study assesses the presence and importance of these two respiratory branches in the roots of seven Mediterranean Quercus species (4 evergreens and 3 deciduous) typical of the South Spain landscapes. The experiments were carried out with seedlings growing under controlled conditions. Determinations were performed using specific inhibitors of both respiration systems (potassium cyanide and salicylhydroxamic acid). The results showed that, under the experimental growth conditions, root respiration of all species was sensitive to salicylhydroxamic acid, indicating that the alternative oxidase was engaged. Under the experimental growth conditions, the seven woody species studied have a range of cyanide-resistant respiration (37.7 % - 60.9 %) which is i...
Background and aimsDetermining the increase in maintenance respiration in response to stress is c... more Background and aimsDetermining the increase in maintenance respiration in response to stress is critical for understanding the cost of adaptation, in terms of expenditure of assimilated carbon. Here, we ask how maintenance costs vary for populations native to contrasting habitats and whether maintenance cost remains constitutive or induced in response to stress.MethodsTwo populations of Quercus ilex were selected in southern Iberian Peninsula, one growing close to the altitudinal limit and the other growing at mean elevations for the species. Maintenance respiration, growth, and structural variables were measured in leaves and fine roots. We modelled the results found here and those published for populations native to stressed (both soil and latitudinal) habitats.ResultsThe maintenance respiration measured at 20 °C was higher in expanding (90 %) and in mature (35 %) leaves and in roots (78 %) of individuals growing at higher elevations. Furthermore, our meta-analysis supports that the cost of organ maintenance is higher in stressed habitats, irrespective of the stress factor.ConclusionsAs regards the whole plant metabolic design, Q. ilex seems to combine high phenotypic plasticity according to current growth conditions, and high adaptive capacity for local differentiation in response to average stress conditions in the provenance habitat.
Abstract. We studied the influence of litter quality on the decomposition rate of leaves from nin... more Abstract. We studied the influence of litter quality on the decomposition rate of leaves from nine Mediterranean shrubs and trees using litter bag methods for a 2-yr period at two ecosystems in southwest Spain. Linear and nonlinear regressions were calculated be-tween mass ...
Abstract. We studied the influence of litter quality on the decomposition rate of leaves from nin... more Abstract. We studied the influence of litter quality on the decomposition rate of leaves from nine Mediterranean shrubs and trees using litter bag methods for a 2-yr period at two ecosystems in southwest Spain. Linear and nonlinear regressions were calculated be-tween mass ...
Environmental pollution (Barking, Essex : 1987), Jan 28, 2017
Mediterranean Basin ecosystems, their unique biodiversity, and the key services they provide are ... more Mediterranean Basin ecosystems, their unique biodiversity, and the key services they provide are currently at risk due to air pollution and climate change, yet only a limited number of isolated and geographically-restricted studies have addressed this topic, often with contrasting results. Particularities of air pollution in this region include high O3 levels due to high air temperatures and solar radiation, the stability of air masses, and dominance of dry over wet nitrogen deposition. Moreover, the unique abiotic and biotic factors (e.g., climate, vegetation type, relevance of Saharan dust inputs) modulating the response of Mediterranean ecosystems at various spatiotemporal scales make it difficult to understand, and thus predict, the consequences of human activities that cause air pollution in the Mediterranean Basin. Therefore, there is an urgent need to implement coordinated research and experimental platforms along with wider environmental monitoring networks in the region. In...
The current scenario of global warming has resulted in considerable uncertainty regarding the cap... more The current scenario of global warming has resulted in considerable uncertainty regarding the capacity of forest trees to adapt to increasing drought. Detailed ecophysiological knowledge would provide a basis to forecast expected species dynamics in response to climate change. Here, we compare the water balance (stomatal conductance, xylem water potential, needle osmotic adjustment) of Abies pinsapo, a relict drought-sensitive Mediterranean fir, along an altitudinal gradient. We related these variables to soil water and nutrient availability, air temperature, atmospheric water potential, and vapour pressure deficit during two consecutive years. Our results indicate that A. pinsapo closed stomata rapidly over a very narrow range of soil water availability and atmospheric dryness. This isohydric response during water stress suggests that this relict conifer relied on the plant hormone abscisic acid to maintain closed stomata during sustained drought, instead of needle desiccation to passively drive stomatal closure, needle osmotic adjustment
Aims This work tests the hypothesis that growth and maintenance costs of plant organs are higher ... more Aims This work tests the hypothesis that growth and maintenance costs of plant organs are higher in more stressful soils. Methods Two populations of Quercus ilex L were selected in the southern Iberian Peninsula, these growing in similar climates but different soil types, namely a brown well-developed soil on slate rock, and a stressful lithosol on gypsum rock. In both localities, growth and maintenance respiration were measured in undetached young and mature leaves (trees under natural conditions) and fine roots (hydroponically grown seedling). Results Young leaves of the two populations displayed an almost identical growth cost (1.53 g glucose g-1). The maintenance cost was higher in the young (40.2 vs. 25.3 mg glucose g-1 day-1 ; P<0.05) and in the mature (7.64 vs. 4.33 mg glucose g-1 day-1 ; P<0.001) leaves of individuals growing in gypsum soils. The growth cost of fine roots was the same in both populations (1.18 g glucose g-1) while the maintenance cost was higher in the Gypsum population (8.95 vs. 7.39 mg glucose g-1 day-1 ; P<0.01). 34 Conclusions The results show for first time that the 35 cost of organ maintenance may be related to the degree 36 of soil stress in their native habitats.
Chronic atmospheric N deposition has modified relative N availability, altering the biogeochemica... more Chronic atmospheric N deposition has modified relative N availability, altering the biogeochemical cycles of forests and the stoichiometry of nutrients in trees, inducing P limitation, and modifying the N:P ratios of plant biomass. This study examines how the variation in the foliar stoichiometry of Abies pinsapo across an N deposition gradient affects foliar traits and photosynthetic rate. We measured the maximum net assimilation rates (Amax) and the foliar nitrogen (N) and phosphorus (P) concentrations in A. pinsapo needles of five age classes. The leaf mass per area and photosynthetic N and P use efficiencies (PNUE and PPUE, respectively) were also estimated. The results from the N-saturated stand (Sierra Bermeja, B) differed from the comparable N-limited stands under investigation (Yunquera, Y, and Sierra Real, SR). The trees from Y and SR exhibited a reduction in the N content in older needles, whereas the foliar N concentration at the B site increased with needle age. N and P were positively correlated at Y and SR, but not at B, suggesting that the overload of N in the trees at site B has exceeded the homeostatic regulation capacity of the N-saturated stand in terms of foliar stoichiometry. A max and PNUE were correlated positively with P and negatively with the N/P ratio at the three study sites. The foliar N concentration was positively correlated with A max at Y and SR. However, this relationship was negative for the B site. These findings suggest that the nutritional imbalance caused by increased chronic deposition of N and an insufficient supply of P counteracts the potential increase in net photosynthesis induced by the accumulation of foliar N.
The gas-exchange and radial growth responses of conifer forests to climatic warming and increasin... more The gas-exchange and radial growth responses of conifer forests to climatic warming and increasing atmospheric CO 2 have been widely studied. However, the modulating effects of variables related to stand structure (e.g., tree-to-tree competition) on those responses are poorly explored. The basal-area increment (BAI) and C isotope discrimination (C stable isotope ratio; d 13 C) in the Mediterranean fir Abies pinsapo were investigated to elucidate the influences of stand competition, atmospheric CO 2 concentrations and climate on intrinsic water-use efficiency (WUEi). We assessed the variation in d 13 C of tree-rings from dominant or co-dominant trees subjected to different degrees of competition. A high-(H) and a lowelevation (L) population with contrasting climatic constraints were studied in southern Spain. Both populations showed an increase in long-term WUEi. However, this increase occurred more slowly at the L site, where a decline of BAI was also observed. Local warming and severe droughts have occurred in the study area over the past 30 years, which have reduced water availability more at lower elevations. Contrastingly, trees from the H site were able to maintain high BAI values at a lower cost in terms of water consumption. In each population, trees subjected to a higher degree of competition by neighboring trees showed lower BAI and WUEi than those subjected to less competition, although the slopes of the temporal trends in WUEi were independent of the competitive microenvironment experienced by the trees. The results are consistent with an increasing drought-induced limitation of BAI and a decreasing rate of WUEi improvement in lowelevation A. pinsapo forests. This relict species might not be able to mitigate the negative effects of a decrease in water availability through a reduction in stomatal conductance, thus leading to a growth decline in the more xeric sites. An intense and poorly asymmetric competitive environment at the stand level may also act as an important constraint on the adaptive capacity of these drought-sensitive forests to climatic warming. Keywords Carbon isotope discrimination Á Global change Á Stand structure Á Drought Á Abies pinsapo Communicated by Juan-Carlos Linares.
Dark respiration in light as well as in dark was estimated for attached leaves of an evergreen (H... more Dark respiration in light as well as in dark was estimated for attached leaves of an evergreen (Heteromeles arbufifolia Ait.) and a deciduous (Lepechinia fragans Creene) shrub species using an open gas-exchange system. Dark respiration in light was estimated by the Laisk method. Respiration rates in the dark were always higher than in the light, indicating that light inhibited respiration in both species. The rates of respiration in the dark were higher in the leaves of the deciduous species than in the evergreen species. However, there were no significant differences in respiration rates i n light between the species. Thus, the degree of inhibition of respiration by light was greater in the deciduous species (62%) than in the evergreen species (51 %). Respiration in both the light and darkness decreased with increasing leaf age. However, because respiration in the light decreased faster with leaf age than respiration in darkness, the degree of inhibition of respiration by light increased with leaf age (from 36% in the youngest leaves to 81 Yo in the mature leaves). This suggests that the rate of dark respiration in the light i s related to the rate of biosynthetic processes. Dark respiration i n the light decreased with increasing light intensity. Respiration both in the light and i n the dark was dependent on leaf temperature. We concluded that respiration i n light and respiration in darkness are tightly coupled, with variation i n respiration in darkness accounting for more than 60% of the variation in respiration in light. Care must be taken when the relation between respiration in light and respiration in darkness is studied, because the relation varies with species, leaf age, and light intensity. Previous studies of the relationship between carbon balance and respiration have focused on R,, assuming that it equals R,. However, investigations using crop species suggest that respiration is partly inhibited in the light (Sharp et al., 1984; Brooks and Farquhar, 1985). There is considerable debate about the leve1 of respiration in photosynthetic tissue that occurs in the light (Graham, 1980; Turpin and Weger, 1990). The contrasting estimates of R, may, in part, be due simply to the different Supported by Comisidn Interministerial de Ciencia y Tecnología, Spain (project PB 87/0935 and PB 90/0894), and Junta de Andalucía, Spain (grupo No. 4056).
... Bio-mass, productivity, and successional changes of the area are described by Merino &amp... more ... Bio-mass, productivity, and successional changes of the area are described by Merino &amp;amp; Martin Vicente (198 1). Average annual ... is formed mainly by Teline monspessulana, Calicotome villosa, Crataegus monogyna, Smilax aspera and Rubus ulmifolius (Gallardo &amp;amp; Pino 1988). ...
... Bio-mass, productivity, and successional changes of the area are described by Merino &amp... more ... Bio-mass, productivity, and successional changes of the area are described by Merino &amp;amp; Martin Vicente (198 1). Average annual ... is formed mainly by Teline monspessulana, Calicotome villosa, Crataegus monogyna, Smilax aspera and Rubus ulmifolius (Gallardo &amp;amp; Pino 1988). ...
We tested whether growth and maintenance costs of plant organs vary with environmental stress. Qu... more We tested whether growth and maintenance costs of plant organs vary with environmental stress. Quercus ilex L. seedlings from acorns collected from natural populations in the northern Iberian Peninsula and in a lower elevation and putatively less stressful habitat in the southern Iberian Peninsula were grown in pots under the same conditions. Growth and maintenance respiration were measured by CO 2 exchange. Young leaves from 5-month-old seedlings of both populations had similar mean specific leaf areas, nitrogen and carbon concentrations and specific growth rates, and almost identical growth costs (1.26 g glucose g-1). Leaf maintenance cost was higher in northern than in the southern population (27.3 versus 22.4 mg glucose g-1 day-1 , P < 0.01). In both populations, leaf maintenance cost decreased by 90% as leaves aged, but even in mature leaves, the maintenance cost was higher in the northern population than in the southern population (3.38 versus 2.53 mg glucose g-1 day-1 , P < 0.01). The growth costs of fine roots < 1 mm in diameter were similar in the two populations (1.20 g glucose g-1), whereas fine root maintenance cost was higher in the northern population than in the southern population (9.86 versus 7.45 mg glucose g-1 day-1 ; P < 0.05). The results suggest that the cost of organ maintenance is related to the severity of environmental stress in the native habitat. Because the observed differences in both leaves and roots were constitutive, the two populations may be considered ecotypes.
Consequences of climate change on tree phenology are readily observable, but little is known abou... more Consequences of climate change on tree phenology are readily observable, but little is known about the variations in phenological sensitivity to drought between populations within a species. In this study, we compare the phenological sensitivity to temperature and water availability in Abies pinsapo Boiss., a drought-sensitive Mediterranean fir, across its altitudinal distribution gradient. Twig growth and needle fall were related to temperature, precipitation and plant water status on a daily scale. Stands located at the top edge of the distributional range showed the most favourable water balance, maximum growth rates and little summer defoliation. Towards higher elevations, the observed delay in budburst date due to lower spring temperatures was overcome by a stronger delay in growth cessation date due to the later onset of strong water-deficit conditions in the summer. This explains an extended growing season and the greatest mean growth at the highest elevation. Conversely, lower predawn xylem water potentials and early partial stomatal closure and growth cessation were found in low-elevation A. pinsapo trees. An earlier and higher summer peak of A. pinsapo litterfall was also observed at these water-limited sites. Our results illustrate the ecophysiological background of the ongoing altitudinal shifts reported for this relict tree species under current climatic conditions.
ÐMost models predict that high atmospheric CO 2 concentrations will lead to an increase in the C-... more ÐMost models predict that high atmospheric CO 2 concentrations will lead to an increase in the C-toN ratio of litter production in terrestrial ecosystems. The eect of an increase in the soil C-toN ratio on the nitrogen dynamics in a Mediterranean shrubland was simulated by mixing with the litter layer wood shavings with a high C-toN ratio. Samples of mineral soil, taken subsequently eight times during 404 d, were analyzed for total C, total N, total soil carbohydrates, potential net N mineralization, potential net nitri®cation and microbial biomass-N. We found signi®cant increases in the concentration of total carbohydrates, C-toN ratio and microbial biomass N in amended soils during the experiment, while potential net N mineralization rate and net nitri®cation rate signi®cantly decreased; amounts of available nitrogen (NH 4 + ±N + NO 3 ±N) were unaected by the amendment treatment. However, by the end of the experiment, no signi®cant dierences between amended and control soil samples were found. The total carbohydrates-to-K 2 SO 4-extractable total-N ratio was the best predictor of both net mineralization rate and microbial biomass N, showing that the available C-to-available-N ratio is a better indicator of N dynamics than the total C to total N ratio. Our results support the hypothesis that increasing C availability in soils leads to a decrease in N availability for plants through the immobilization of N in microbial biomass and to an increase in the temporal heterogeneity of soil properties in a Mediterranean shrubland.
Climate variability and land-use modifications are among the main components of global change, bu... more Climate variability and land-use modifications are among the main components of global change, but their combined effects on forests have rarely been addressed. Relict tree species from the Mediterranean Basin are appropriate experimental models to investigate these effects since they grow in climatically-stressed areas, which have undergone intensive land-use changes. We hypothesize that intense logging and overgrazing could be related to forests decline, but also the abandonment of traditional land-use practices and subsequent enhancement of density-dependent factors acted as a predisposing stressor that modified the response of several tree species from the Mediterranean Basin to recent climate change. We summarize results from current forest structure and mortality patterns, as well as relationships between tree radial-growth and regional climatic trends in four tree species from western Mediterranean Mountains: Silver fir (Abies alba) from the North of Spain, Pinsapo fir (Abies...
The geographic distribution of deciduous versus evergreen woody species has been intensively inve... more The geographic distribution of deciduous versus evergreen woody species has been intensively investigated, but the ecological significance of both leaf habits is still far from being fully understood. The purpose of this chapter is to review the factors that are related with the carbon gain of deciduous and evergreen oak species under Mediterranean environmental conditions. We will focus on the morphological, anatomical and chemical adaptations of evergreens necessary to guarantee leaf survival during the unfavorable part of the year. We will review the information available about the construction and maintenance costs associated with the leaf traits of deciduous and evergreen oak species. Moreover, we will compare these traits with those of non-Mediterranean oaks and species belonging to other families. One central leaf trait is the leaf mass per area (LMA), which depends on the leaf anatomy and chemical composition. Differences in LMA are related to photosynthesis and the costs of...
The terminal part of the mitochondrial electron pathway, consists of two terminal oxidases: the c... more The terminal part of the mitochondrial electron pathway, consists of two terminal oxidases: the cytochrome oxidase (sensitive to cyanide) and the alternative oxidase (both resistant to cyanide and sensitive to salicylhidroxamic acid). This study assesses the presence and importance of these two respiratory branches in the roots of seven Mediterranean Quercus species (4 evergreens and 3 deciduous) typical of the South Spain landscapes. The experiments were carried out with seedlings growing under controlled conditions. Determinations were performed using specific inhibitors of both respiration systems (potassium cyanide and salicylhydroxamic acid). The results showed that, under the experimental growth conditions, root respiration of all species was sensitive to salicylhydroxamic acid, indicating that the alternative oxidase was engaged. Under the experimental growth conditions, the seven woody species studied have a range of cyanide-resistant respiration (37.7 % - 60.9 %) which is i...
Background and aimsDetermining the increase in maintenance respiration in response to stress is c... more Background and aimsDetermining the increase in maintenance respiration in response to stress is critical for understanding the cost of adaptation, in terms of expenditure of assimilated carbon. Here, we ask how maintenance costs vary for populations native to contrasting habitats and whether maintenance cost remains constitutive or induced in response to stress.MethodsTwo populations of Quercus ilex were selected in southern Iberian Peninsula, one growing close to the altitudinal limit and the other growing at mean elevations for the species. Maintenance respiration, growth, and structural variables were measured in leaves and fine roots. We modelled the results found here and those published for populations native to stressed (both soil and latitudinal) habitats.ResultsThe maintenance respiration measured at 20 °C was higher in expanding (90 %) and in mature (35 %) leaves and in roots (78 %) of individuals growing at higher elevations. Furthermore, our meta-analysis supports that the cost of organ maintenance is higher in stressed habitats, irrespective of the stress factor.ConclusionsAs regards the whole plant metabolic design, Q. ilex seems to combine high phenotypic plasticity according to current growth conditions, and high adaptive capacity for local differentiation in response to average stress conditions in the provenance habitat.
Abstract. We studied the influence of litter quality on the decomposition rate of leaves from nin... more Abstract. We studied the influence of litter quality on the decomposition rate of leaves from nine Mediterranean shrubs and trees using litter bag methods for a 2-yr period at two ecosystems in southwest Spain. Linear and nonlinear regressions were calculated be-tween mass ...
Abstract. We studied the influence of litter quality on the decomposition rate of leaves from nin... more Abstract. We studied the influence of litter quality on the decomposition rate of leaves from nine Mediterranean shrubs and trees using litter bag methods for a 2-yr period at two ecosystems in southwest Spain. Linear and nonlinear regressions were calculated be-tween mass ...
Environmental pollution (Barking, Essex : 1987), Jan 28, 2017
Mediterranean Basin ecosystems, their unique biodiversity, and the key services they provide are ... more Mediterranean Basin ecosystems, their unique biodiversity, and the key services they provide are currently at risk due to air pollution and climate change, yet only a limited number of isolated and geographically-restricted studies have addressed this topic, often with contrasting results. Particularities of air pollution in this region include high O3 levels due to high air temperatures and solar radiation, the stability of air masses, and dominance of dry over wet nitrogen deposition. Moreover, the unique abiotic and biotic factors (e.g., climate, vegetation type, relevance of Saharan dust inputs) modulating the response of Mediterranean ecosystems at various spatiotemporal scales make it difficult to understand, and thus predict, the consequences of human activities that cause air pollution in the Mediterranean Basin. Therefore, there is an urgent need to implement coordinated research and experimental platforms along with wider environmental monitoring networks in the region. In...
The current scenario of global warming has resulted in considerable uncertainty regarding the cap... more The current scenario of global warming has resulted in considerable uncertainty regarding the capacity of forest trees to adapt to increasing drought. Detailed ecophysiological knowledge would provide a basis to forecast expected species dynamics in response to climate change. Here, we compare the water balance (stomatal conductance, xylem water potential, needle osmotic adjustment) of Abies pinsapo, a relict drought-sensitive Mediterranean fir, along an altitudinal gradient. We related these variables to soil water and nutrient availability, air temperature, atmospheric water potential, and vapour pressure deficit during two consecutive years. Our results indicate that A. pinsapo closed stomata rapidly over a very narrow range of soil water availability and atmospheric dryness. This isohydric response during water stress suggests that this relict conifer relied on the plant hormone abscisic acid to maintain closed stomata during sustained drought, instead of needle desiccation to passively drive stomatal closure, needle osmotic adjustment
Aims This work tests the hypothesis that growth and maintenance costs of plant organs are higher ... more Aims This work tests the hypothesis that growth and maintenance costs of plant organs are higher in more stressful soils. Methods Two populations of Quercus ilex L were selected in the southern Iberian Peninsula, these growing in similar climates but different soil types, namely a brown well-developed soil on slate rock, and a stressful lithosol on gypsum rock. In both localities, growth and maintenance respiration were measured in undetached young and mature leaves (trees under natural conditions) and fine roots (hydroponically grown seedling). Results Young leaves of the two populations displayed an almost identical growth cost (1.53 g glucose g-1). The maintenance cost was higher in the young (40.2 vs. 25.3 mg glucose g-1 day-1 ; P<0.05) and in the mature (7.64 vs. 4.33 mg glucose g-1 day-1 ; P<0.001) leaves of individuals growing in gypsum soils. The growth cost of fine roots was the same in both populations (1.18 g glucose g-1) while the maintenance cost was higher in the Gypsum population (8.95 vs. 7.39 mg glucose g-1 day-1 ; P<0.01). 34 Conclusions The results show for first time that the 35 cost of organ maintenance may be related to the degree 36 of soil stress in their native habitats.
Chronic atmospheric N deposition has modified relative N availability, altering the biogeochemica... more Chronic atmospheric N deposition has modified relative N availability, altering the biogeochemical cycles of forests and the stoichiometry of nutrients in trees, inducing P limitation, and modifying the N:P ratios of plant biomass. This study examines how the variation in the foliar stoichiometry of Abies pinsapo across an N deposition gradient affects foliar traits and photosynthetic rate. We measured the maximum net assimilation rates (Amax) and the foliar nitrogen (N) and phosphorus (P) concentrations in A. pinsapo needles of five age classes. The leaf mass per area and photosynthetic N and P use efficiencies (PNUE and PPUE, respectively) were also estimated. The results from the N-saturated stand (Sierra Bermeja, B) differed from the comparable N-limited stands under investigation (Yunquera, Y, and Sierra Real, SR). The trees from Y and SR exhibited a reduction in the N content in older needles, whereas the foliar N concentration at the B site increased with needle age. N and P were positively correlated at Y and SR, but not at B, suggesting that the overload of N in the trees at site B has exceeded the homeostatic regulation capacity of the N-saturated stand in terms of foliar stoichiometry. A max and PNUE were correlated positively with P and negatively with the N/P ratio at the three study sites. The foliar N concentration was positively correlated with A max at Y and SR. However, this relationship was negative for the B site. These findings suggest that the nutritional imbalance caused by increased chronic deposition of N and an insufficient supply of P counteracts the potential increase in net photosynthesis induced by the accumulation of foliar N.
The gas-exchange and radial growth responses of conifer forests to climatic warming and increasin... more The gas-exchange and radial growth responses of conifer forests to climatic warming and increasing atmospheric CO 2 have been widely studied. However, the modulating effects of variables related to stand structure (e.g., tree-to-tree competition) on those responses are poorly explored. The basal-area increment (BAI) and C isotope discrimination (C stable isotope ratio; d 13 C) in the Mediterranean fir Abies pinsapo were investigated to elucidate the influences of stand competition, atmospheric CO 2 concentrations and climate on intrinsic water-use efficiency (WUEi). We assessed the variation in d 13 C of tree-rings from dominant or co-dominant trees subjected to different degrees of competition. A high-(H) and a lowelevation (L) population with contrasting climatic constraints were studied in southern Spain. Both populations showed an increase in long-term WUEi. However, this increase occurred more slowly at the L site, where a decline of BAI was also observed. Local warming and severe droughts have occurred in the study area over the past 30 years, which have reduced water availability more at lower elevations. Contrastingly, trees from the H site were able to maintain high BAI values at a lower cost in terms of water consumption. In each population, trees subjected to a higher degree of competition by neighboring trees showed lower BAI and WUEi than those subjected to less competition, although the slopes of the temporal trends in WUEi were independent of the competitive microenvironment experienced by the trees. The results are consistent with an increasing drought-induced limitation of BAI and a decreasing rate of WUEi improvement in lowelevation A. pinsapo forests. This relict species might not be able to mitigate the negative effects of a decrease in water availability through a reduction in stomatal conductance, thus leading to a growth decline in the more xeric sites. An intense and poorly asymmetric competitive environment at the stand level may also act as an important constraint on the adaptive capacity of these drought-sensitive forests to climatic warming. Keywords Carbon isotope discrimination Á Global change Á Stand structure Á Drought Á Abies pinsapo Communicated by Juan-Carlos Linares.
Dark respiration in light as well as in dark was estimated for attached leaves of an evergreen (H... more Dark respiration in light as well as in dark was estimated for attached leaves of an evergreen (Heteromeles arbufifolia Ait.) and a deciduous (Lepechinia fragans Creene) shrub species using an open gas-exchange system. Dark respiration in light was estimated by the Laisk method. Respiration rates in the dark were always higher than in the light, indicating that light inhibited respiration in both species. The rates of respiration in the dark were higher in the leaves of the deciduous species than in the evergreen species. However, there were no significant differences in respiration rates i n light between the species. Thus, the degree of inhibition of respiration by light was greater in the deciduous species (62%) than in the evergreen species (51 %). Respiration in both the light and darkness decreased with increasing leaf age. However, because respiration in the light decreased faster with leaf age than respiration in darkness, the degree of inhibition of respiration by light increased with leaf age (from 36% in the youngest leaves to 81 Yo in the mature leaves). This suggests that the rate of dark respiration in the light i s related to the rate of biosynthetic processes. Dark respiration i n the light decreased with increasing light intensity. Respiration both in the light and i n the dark was dependent on leaf temperature. We concluded that respiration i n light and respiration in darkness are tightly coupled, with variation i n respiration in darkness accounting for more than 60% of the variation in respiration in light. Care must be taken when the relation between respiration in light and respiration in darkness is studied, because the relation varies with species, leaf age, and light intensity. Previous studies of the relationship between carbon balance and respiration have focused on R,, assuming that it equals R,. However, investigations using crop species suggest that respiration is partly inhibited in the light (Sharp et al., 1984; Brooks and Farquhar, 1985). There is considerable debate about the leve1 of respiration in photosynthetic tissue that occurs in the light (Graham, 1980; Turpin and Weger, 1990). The contrasting estimates of R, may, in part, be due simply to the different Supported by Comisidn Interministerial de Ciencia y Tecnología, Spain (project PB 87/0935 and PB 90/0894), and Junta de Andalucía, Spain (grupo No. 4056).
... Bio-mass, productivity, and successional changes of the area are described by Merino &amp... more ... Bio-mass, productivity, and successional changes of the area are described by Merino &amp;amp; Martin Vicente (198 1). Average annual ... is formed mainly by Teline monspessulana, Calicotome villosa, Crataegus monogyna, Smilax aspera and Rubus ulmifolius (Gallardo &amp;amp; Pino 1988). ...
... Bio-mass, productivity, and successional changes of the area are described by Merino &amp... more ... Bio-mass, productivity, and successional changes of the area are described by Merino &amp;amp; Martin Vicente (198 1). Average annual ... is formed mainly by Teline monspessulana, Calicotome villosa, Crataegus monogyna, Smilax aspera and Rubus ulmifolius (Gallardo &amp;amp; Pino 1988). ...
We tested whether growth and maintenance costs of plant organs vary with environmental stress. Qu... more We tested whether growth and maintenance costs of plant organs vary with environmental stress. Quercus ilex L. seedlings from acorns collected from natural populations in the northern Iberian Peninsula and in a lower elevation and putatively less stressful habitat in the southern Iberian Peninsula were grown in pots under the same conditions. Growth and maintenance respiration were measured by CO 2 exchange. Young leaves from 5-month-old seedlings of both populations had similar mean specific leaf areas, nitrogen and carbon concentrations and specific growth rates, and almost identical growth costs (1.26 g glucose g-1). Leaf maintenance cost was higher in northern than in the southern population (27.3 versus 22.4 mg glucose g-1 day-1 , P < 0.01). In both populations, leaf maintenance cost decreased by 90% as leaves aged, but even in mature leaves, the maintenance cost was higher in the northern population than in the southern population (3.38 versus 2.53 mg glucose g-1 day-1 , P < 0.01). The growth costs of fine roots < 1 mm in diameter were similar in the two populations (1.20 g glucose g-1), whereas fine root maintenance cost was higher in the northern population than in the southern population (9.86 versus 7.45 mg glucose g-1 day-1 ; P < 0.05). The results suggest that the cost of organ maintenance is related to the severity of environmental stress in the native habitat. Because the observed differences in both leaves and roots were constitutive, the two populations may be considered ecotypes.
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