We analysed Ball's empirical model of stomatal conductance (Ball, Woodrow and Berry, 1987). The o... more We analysed Ball's empirical model of stomatal conductance (Ball, Woodrow and Berry, 1987). The original interpretation was found to be flawed, and a new one is proposed which views the model as a description of the relationship between CO2 flux rate and stomatal conductance, rather than as a model of stomatal conductance alone. It is shown that this model is useful for describing changes in intercellular CO2 concentration. The model was tested against data from experiments in which the responses of stomatal conductance and CO2 flux density to humidity and temperature were measured in leaves of Hedera helix. It was found that the responses to temperature and humidity are not treated in a satisfactory way in the model whereas the response of the model to other variables is realistic. An alternative to Ball's model is described and tested. It is concluded that Ball's model is a useful starting point for development of simulation models to be used as submodels in canopy and regional models. However, as any empirical model, it is of no use for defining causal relationships.
The experiments and simulations reported in this paper show that, for stomata sensitive to both C... more The experiments and simulations reported in this paper show that, for stomata sensitive to both CO2 and water vapour concentrations, responses of stomatal conductance (gws) to boundary layer thickness have two components, one resulting from changes in intercellular CO2 concentration (χci) and another from changes in leaf surface water vapour saturation deficit (Dws). The experiments and simulations also show that the boundary layer conductance (gwb) can significantly alter the apparent response of gws to ambient air CO2 mole fraction (χca) and water vapour mole fraction (χwa). Because of the feedback loop involved the responses of gws for χca and χwa each include responses to both χci and Dws. The boundary layer alters the state of the variables sensed by the guard cells—i.e. χci and Dws—and so it is a source of feedback. Thus, when scaling up from responses of stomata to the response of gws for a whole leaf, the effect of the boundary layer must be considered. The results indicate that, for given responses of gws to χci and Dws, the apparent responses of gws to Dwa and χca depend on the size of the leaf and wind speed, showing that this effect of the boundary layer should be considered when comparing data measured under different conditions, or with different methods.
Abstract. The objective of the work reported was to answer the following questions: (1) Do stomat... more Abstract. The objective of the work reported was to answer the following questions: (1) Do stomata respond to both humidity and temperature? (2) Do these responses interact in such a way that relative humidity at the leaf surface is a more appropriate variable than water vapour saturation deficit at the leaf surface and yields a simpler description of the compound response? To answer these questions, we measured the response of leaf conductance to humidity under constant leaf temperature, and the response to increasing leaf temperature under constant relative humidity and under constant water vapour saturation deficit. We found that, in Hedera helix subsp. canariensis (Willd.) Coutinho, there was a reversible response to humidity under constant temperature, and that there was also a response to temperature under constant relative humidity. The relationship between leaf conductance and relative humidity was different when measured at the same temperature rather than at different temperatures. An inversely proportional response was consistently obtained when stomatal conductance was expressed in relation to water vapour saturation deficit. The interaction between the effects of leaf temperature and water vapour saturation deficit was not compatible with a mechanism of response to humidity and temperature based solely on relative humidity. From these data, we conclude that water vapour saturation deficit is a more appropriate variable for describing stomatal responses to humidity.
Tulevaisuuden ilmastossa eri kasvutekijät eivät välttämättä korreloi toistensa kanssa samalla tav... more Tulevaisuuden ilmastossa eri kasvutekijät eivät välttämättä korreloi toistensa kanssa samalla tavalla kuin tällä hetkellä, ja kokeellisella tutkimuksella voidaan selvittää puiden menestymistä uusissa olosuhteissa. Joensuun dasotronit ovat erikoisvalmisteisia kasvukammioita, joissa ilman ja maan lämpötilaa voidaan säädellä erikseen, samoin kuin valotasoa, päivänpituutta ja ilman kosteutta.
Abstract In contrast to earlier beliefs, it is now known that boron (B) can be retranslocated com... more Abstract In contrast to earlier beliefs, it is now known that boron (B) can be retranslocated complexed with sugar alcohols in some plant species. Conifers had been thought not to translocate sugar alcohols in the phloem. However, 1 d after applying 10 B enriched boric acid to shoots of Scots pine and Norway spruce seedlings, we found increases in both the amount and proportion of 10 B in the root systems in both species.
Abstract Soil temperature is a main factor limiting root growth in the boreal forest. To simulate... more Abstract Soil temperature is a main factor limiting root growth in the boreal forest. To simulate the possible soil-warming effect of future climate change, 5-year-old Norway spruce (Picea abies (L.) Karst.) seedlings were subjected to three simulated growing seasons in controlled environment rooms. The seedlings were acclimated to a soil temperature of 16 C during the first (GS I) and third growing seasons (GS III), but were assigned to random soil-temperature treatments of 9, 13, 18 and 21 C during the second growing season (GS II).
Abstract We analysed Ball's empirical model of stomatal conductance (Ball, Woodrow and Berry, 198... more Abstract We analysed Ball's empirical model of stomatal conductance (Ball, Woodrow and Berry, 1987). The original interpretation was found to be flawed, and a new one is proposed which views the model as a description of the relationship between CO 2 flux rate and stomatal conductance, rather than as a model of stomatal conductance alone. It is shown that this model is useful for describing changes in intercellular CO 2 concentration.
Abstract Photomorphogenic responses triggered by low fluence rates of ultraviolet B radiation (UV... more Abstract Photomorphogenic responses triggered by low fluence rates of ultraviolet B radiation (UV-B; 280–315 nm) are mediated by the UV-B photoreceptor UV RESISTANCE LOCUS8 (UVR8). Beyond our understanding of the molecular mechanisms of UV-B perception by UVR8, there is still limited information on how the UVR8 pathway functions under natural sunlight.
Abstract We studied the effects of light quality and nutrient supply on growth and nitrogen accum... more Abstract We studied the effects of light quality and nutrient supply on growth and nitrogen accumulation in silver birch (Betula pendula Roth) seedlings to test three hypotheses:(1) growth of birch seedlings is sensitive to changes in light quality;(2) the response of birch seedling growth to light quality depends on nutrient supply; and (3) assimilation and allocation of nitrogen by birch seedlings are affected by light quality.
Abstract Five-year-old Norway spruce (Picea abies (L.) Karst.) seedlings were subjected to three ... more Abstract Five-year-old Norway spruce (Picea abies (L.) Karst.) seedlings were subjected to three simulated growing seasons in controlled environment chambers. Plants were acclimated to a soil temperature of 16 C during the first and third growing seasons, but were allocated at random to soil temperature treatments of 9, 13, 18 and 21 C during the second growing season.
Recent molecular and physiological studies have demonstrated that ultraviolet-B radiation (UV-B) ... more Recent molecular and physiological studies have demonstrated that ultraviolet-B radiation (UV-B) can affect some of the processes involved in leaf growth, but the phases of leaf growth affected have not been clearly delimited. We used functional growth analysis to assess the effects of UV-B radiation on the time course of leaf growth in seedlings of two birch species (Betula pendula and Betula pubescens). Our aim was to identify the phase(s) of leaf development affected by UV-B radiation. In a greenhouse study, 1-year-old birch seedlings were subjected to three daily doses of supplemental UV-B radiation treatments (UV-B + ) and no UV-B radiation controls (UV-B − ). Leaf growth measurements every 2 days were complemented by assessment of other functional traits over a 4-week period at the start of the growing season. Using fitted curves, we were able to determine that the rate of leaf expansion was slowed by the UV-B + treatment in leaves of B. pendula because of a slower maximum leaf growth rate compared with plants under the UV-B − controls, but that compensation toward the end of the period of expansion negated this difference when leaves reached their final size. UV-B + had little effect on the rate of B. pubescens leaf growth despite a larger reduction in leaf final size due to UV-B + than occurred in B. pendula leaves. In conclusion, effective regulation ameliorated the effects of UV-B radiation on leaf and seedling growth in B. pendula, whereas in B. pubescens, reductions in leaf final size under UV-B + were consistent with a slightly reduced rate of height growth.
Lolium perenne (cv. AberDart) was grown at 14 locations along a latitudinal gradient across Europ... more Lolium perenne (cv. AberDart) was grown at 14 locations along a latitudinal gradient across Europe (37-68 • N) to study the impact of ultraviolet radiation (UV) and climate on aboveground growth and foliar UV-B absorbing compounds. At each location, plants were grown outdoors for 5 weeks in a replicated UV-B filtration experiment consisting of open, UV-B transparent (cellulose diacetate) and UV-B opaque (polyester) environments. Fourier transform-infrared spectroscopy was used to compare plant metabolite profiles in relation to treatment and location. UV radiation and climatic parameters were determined for each location from online sources and the data were assessed using a combination of ANOVA and multiple regression analyses. Most of the variation in growth between the locations was attributable to the combination of climatic parameters, with minimum temperature identified as an important growth constraint. However, no single environmental parameter could consistently account for the variability in plant growth. Concentrations of foliar UV-B absorbing compounds showed a positive trend with solar UV across the latitudinal gradient; however, this relationship was not consistent in all treatments. The most striking experimental outcome from this study was the effect of presence or absence of filtration frames on UV-absorbing compounds. Overall, the study demonstrates the value of an European approach in studying the impacts of natural UV across a large latitudinal gradient. We have shown the feasibility of coordinated UV filtration at multiple sites but have also highlighted the need for open controls and careful interpretation of plant responses.
gives an accurate but very accessible account of the physiology of plants, including the historic... more gives an accurate but very accessible account of the physiology of plants, including the historical background of how and when different phenomena were described and explained.
Seasonal variation in leaf phenolic composition may be important for acclimation of plants to sea... more Seasonal variation in leaf phenolic composition may be important for acclimation of plants to seasonal changes in their biotic and abiotic environment. For a realistic assessment of how plants respond to solar UV-B (280-315 nm) and UV-A (315-400 nm) radiation, seasonal variation in both environment and plant responses needs to be taken into account. This also has implications for studies concerning stratospheric ozone depletion and resulting increased UV-B radiation, as other environmental variables and/or plant phenology could interact with UV radiation. To elucidate this, we established a field experiment using plastic films attenuating different parts of the solar UV spectrum. The concentration of individual phenolic compounds was measured during one growing season in leaves of grey alder (Alnus incana) and white birch (Betula pubescens) trees. Our results showed changes in concentration of, e.g. hydrolyzable tannins in birch that suggest an effect of UV-A alone and e.g. chlorogenic acids in alder indicate a quadratic effect of UV-B irradiance and both linear and quadratic effect for UV-A in second-degree polynomial fits. Further, there was interaction between treatment and sampling time for some individual metabolites; hence, the UV response varied during the season. In addition to the UV effects, three temporal patterns emerged in the concentrations of particular groups of phenolics. Possible implications for both sampling methods and timing are discussed. Moreover, our results highlight differences in responses of the two tree species, which are taken to indicate differences in their ecological niche differentiation.
Go to AGRIS search. Silva Fennica (2002). Leaf life span and the mobility of "non-mo... more Go to AGRIS search. Silva Fennica (2002). Leaf life span and the mobility of "non-mobile" mineral nutrients : the case of boron in conifers. ...
Plants from high altitudes and/or low latitudes will, typically, be exposed to relatively high do... more Plants from high altitudes and/or low latitudes will, typically, be exposed to relatively high doses of UV-B, therefore it might be hypothesised that these plants are particularly well protected from potentially harmful effects of such radiation. Analysis of the UVsusceptibility of 224 Arabidopsis thaliana accessions from across the northern hemisphere (15 and 67°N; and − 6 and 300 m altitude) revealed a continuum of UV-protection levels. However, the relationship between the geographic origin of accessions and UVtolerance is complex, and appears to be limited to altered acclimation induction thresholds, rather than UV-tolerance per sé. Thus, our data emphasise the importance of (regulation of) inducible UV-B protection responses. Detailed molecular-physiological analysis of the UV-B acclimation response in A. thaliana shows parallel changes in gene-expression and plant architecture. Chronic UV-B treatment causes a re-distribution rather than a cessation of growth, and this comprises decreases in rosette diameter, decreases in inflorescence height but increases in the number of flowering stems. Gene expression profiling indicated that UV-induced morphogenesis is associated with subtle changes in phytohormone homeostasis, and this link is confirmed using physiological experiments.
The physiological mechanisms controlling plant responses to dynamic changes in ambient solar ultr... more The physiological mechanisms controlling plant responses to dynamic changes in ambient solar ultraviolet (UV) radiation are not fully understood: this information is important to further comprehend plant adaptation to their natural habitats. We used the fluorimeter Dualex to estimate in vivo the epidermal flavonoid contents by measuring epidermal UV absorbance (A 375 ) in Betula pendula Roth (silver birch) leaves of different ages under altered UV. Seedlings were grown in a greenhouse for 15 days without UV and transferred outdoors under three UV treatments (UV-0, UV-A and UV-A+B) created by three types of plastic film. After 7 and 13 days, Dualex measurements were taken at adaxial and abaxial epidermis of the first three leaves (L1, L2 and L3) of the seedlings. After 14 days, some of the seedlings were reciprocally swapped amongst the treatments to study the accumulation of epidermal flavonoids in the youngest unfolded leaves (L3) during leaf expansion under changing solar UV environments. A 375 of the leaves responded differently to the UV treatment depending on their position. UV-B increased the A 375 in the leaves independently of leaf position. L3 quickly adjusted A 375 in their epidermis according to the UV they received and these adjustments were affected by previous UV exposure. The initial absence of UV-A+B or UV-A, followed by exposure to UV-A+B, particularly enhanced leaf A 375 . Silver birch leaves modulate their protective pigments in response to changes in the UV environment during their expansion, and their previous UV exposure history affects the epidermal-absorbance achieved during later UV exposure.
We examined the quality and decomposition of naturally abscised leaves of silver birch (Betula pe... more We examined the quality and decomposition of naturally abscised leaves of silver birch (Betula pendula) seedlings subjected to three different levels of fertilization under ambient and elevated levels of temperature and CO2. At the end of the second growing season, the chemical composition of the litter collected from the seedlings was analyzed. Whole-leaf samples from pooled litter from each of
We analysed Ball's empirical model of stomatal conductance (Ball, Woodrow and Berry, 1987). The o... more We analysed Ball's empirical model of stomatal conductance (Ball, Woodrow and Berry, 1987). The original interpretation was found to be flawed, and a new one is proposed which views the model as a description of the relationship between CO2 flux rate and stomatal conductance, rather than as a model of stomatal conductance alone. It is shown that this model is useful for describing changes in intercellular CO2 concentration. The model was tested against data from experiments in which the responses of stomatal conductance and CO2 flux density to humidity and temperature were measured in leaves of Hedera helix. It was found that the responses to temperature and humidity are not treated in a satisfactory way in the model whereas the response of the model to other variables is realistic. An alternative to Ball's model is described and tested. It is concluded that Ball's model is a useful starting point for development of simulation models to be used as submodels in canopy and regional models. However, as any empirical model, it is of no use for defining causal relationships.
The experiments and simulations reported in this paper show that, for stomata sensitive to both C... more The experiments and simulations reported in this paper show that, for stomata sensitive to both CO2 and water vapour concentrations, responses of stomatal conductance (gws) to boundary layer thickness have two components, one resulting from changes in intercellular CO2 concentration (χci) and another from changes in leaf surface water vapour saturation deficit (Dws). The experiments and simulations also show that the boundary layer conductance (gwb) can significantly alter the apparent response of gws to ambient air CO2 mole fraction (χca) and water vapour mole fraction (χwa). Because of the feedback loop involved the responses of gws for χca and χwa each include responses to both χci and Dws. The boundary layer alters the state of the variables sensed by the guard cells—i.e. χci and Dws—and so it is a source of feedback. Thus, when scaling up from responses of stomata to the response of gws for a whole leaf, the effect of the boundary layer must be considered. The results indicate that, for given responses of gws to χci and Dws, the apparent responses of gws to Dwa and χca depend on the size of the leaf and wind speed, showing that this effect of the boundary layer should be considered when comparing data measured under different conditions, or with different methods.
Abstract. The objective of the work reported was to answer the following questions: (1) Do stomat... more Abstract. The objective of the work reported was to answer the following questions: (1) Do stomata respond to both humidity and temperature? (2) Do these responses interact in such a way that relative humidity at the leaf surface is a more appropriate variable than water vapour saturation deficit at the leaf surface and yields a simpler description of the compound response? To answer these questions, we measured the response of leaf conductance to humidity under constant leaf temperature, and the response to increasing leaf temperature under constant relative humidity and under constant water vapour saturation deficit. We found that, in Hedera helix subsp. canariensis (Willd.) Coutinho, there was a reversible response to humidity under constant temperature, and that there was also a response to temperature under constant relative humidity. The relationship between leaf conductance and relative humidity was different when measured at the same temperature rather than at different temperatures. An inversely proportional response was consistently obtained when stomatal conductance was expressed in relation to water vapour saturation deficit. The interaction between the effects of leaf temperature and water vapour saturation deficit was not compatible with a mechanism of response to humidity and temperature based solely on relative humidity. From these data, we conclude that water vapour saturation deficit is a more appropriate variable for describing stomatal responses to humidity.
Tulevaisuuden ilmastossa eri kasvutekijät eivät välttämättä korreloi toistensa kanssa samalla tav... more Tulevaisuuden ilmastossa eri kasvutekijät eivät välttämättä korreloi toistensa kanssa samalla tavalla kuin tällä hetkellä, ja kokeellisella tutkimuksella voidaan selvittää puiden menestymistä uusissa olosuhteissa. Joensuun dasotronit ovat erikoisvalmisteisia kasvukammioita, joissa ilman ja maan lämpötilaa voidaan säädellä erikseen, samoin kuin valotasoa, päivänpituutta ja ilman kosteutta.
Abstract In contrast to earlier beliefs, it is now known that boron (B) can be retranslocated com... more Abstract In contrast to earlier beliefs, it is now known that boron (B) can be retranslocated complexed with sugar alcohols in some plant species. Conifers had been thought not to translocate sugar alcohols in the phloem. However, 1 d after applying 10 B enriched boric acid to shoots of Scots pine and Norway spruce seedlings, we found increases in both the amount and proportion of 10 B in the root systems in both species.
Abstract Soil temperature is a main factor limiting root growth in the boreal forest. To simulate... more Abstract Soil temperature is a main factor limiting root growth in the boreal forest. To simulate the possible soil-warming effect of future climate change, 5-year-old Norway spruce (Picea abies (L.) Karst.) seedlings were subjected to three simulated growing seasons in controlled environment rooms. The seedlings were acclimated to a soil temperature of 16 C during the first (GS I) and third growing seasons (GS III), but were assigned to random soil-temperature treatments of 9, 13, 18 and 21 C during the second growing season (GS II).
Abstract We analysed Ball's empirical model of stomatal conductance (Ball, Woodrow and Berry, 198... more Abstract We analysed Ball's empirical model of stomatal conductance (Ball, Woodrow and Berry, 1987). The original interpretation was found to be flawed, and a new one is proposed which views the model as a description of the relationship between CO 2 flux rate and stomatal conductance, rather than as a model of stomatal conductance alone. It is shown that this model is useful for describing changes in intercellular CO 2 concentration.
Abstract Photomorphogenic responses triggered by low fluence rates of ultraviolet B radiation (UV... more Abstract Photomorphogenic responses triggered by low fluence rates of ultraviolet B radiation (UV-B; 280–315 nm) are mediated by the UV-B photoreceptor UV RESISTANCE LOCUS8 (UVR8). Beyond our understanding of the molecular mechanisms of UV-B perception by UVR8, there is still limited information on how the UVR8 pathway functions under natural sunlight.
Abstract We studied the effects of light quality and nutrient supply on growth and nitrogen accum... more Abstract We studied the effects of light quality and nutrient supply on growth and nitrogen accumulation in silver birch (Betula pendula Roth) seedlings to test three hypotheses:(1) growth of birch seedlings is sensitive to changes in light quality;(2) the response of birch seedling growth to light quality depends on nutrient supply; and (3) assimilation and allocation of nitrogen by birch seedlings are affected by light quality.
Abstract Five-year-old Norway spruce (Picea abies (L.) Karst.) seedlings were subjected to three ... more Abstract Five-year-old Norway spruce (Picea abies (L.) Karst.) seedlings were subjected to three simulated growing seasons in controlled environment chambers. Plants were acclimated to a soil temperature of 16 C during the first and third growing seasons, but were allocated at random to soil temperature treatments of 9, 13, 18 and 21 C during the second growing season.
Recent molecular and physiological studies have demonstrated that ultraviolet-B radiation (UV-B) ... more Recent molecular and physiological studies have demonstrated that ultraviolet-B radiation (UV-B) can affect some of the processes involved in leaf growth, but the phases of leaf growth affected have not been clearly delimited. We used functional growth analysis to assess the effects of UV-B radiation on the time course of leaf growth in seedlings of two birch species (Betula pendula and Betula pubescens). Our aim was to identify the phase(s) of leaf development affected by UV-B radiation. In a greenhouse study, 1-year-old birch seedlings were subjected to three daily doses of supplemental UV-B radiation treatments (UV-B + ) and no UV-B radiation controls (UV-B − ). Leaf growth measurements every 2 days were complemented by assessment of other functional traits over a 4-week period at the start of the growing season. Using fitted curves, we were able to determine that the rate of leaf expansion was slowed by the UV-B + treatment in leaves of B. pendula because of a slower maximum leaf growth rate compared with plants under the UV-B − controls, but that compensation toward the end of the period of expansion negated this difference when leaves reached their final size. UV-B + had little effect on the rate of B. pubescens leaf growth despite a larger reduction in leaf final size due to UV-B + than occurred in B. pendula leaves. In conclusion, effective regulation ameliorated the effects of UV-B radiation on leaf and seedling growth in B. pendula, whereas in B. pubescens, reductions in leaf final size under UV-B + were consistent with a slightly reduced rate of height growth.
Lolium perenne (cv. AberDart) was grown at 14 locations along a latitudinal gradient across Europ... more Lolium perenne (cv. AberDart) was grown at 14 locations along a latitudinal gradient across Europe (37-68 • N) to study the impact of ultraviolet radiation (UV) and climate on aboveground growth and foliar UV-B absorbing compounds. At each location, plants were grown outdoors for 5 weeks in a replicated UV-B filtration experiment consisting of open, UV-B transparent (cellulose diacetate) and UV-B opaque (polyester) environments. Fourier transform-infrared spectroscopy was used to compare plant metabolite profiles in relation to treatment and location. UV radiation and climatic parameters were determined for each location from online sources and the data were assessed using a combination of ANOVA and multiple regression analyses. Most of the variation in growth between the locations was attributable to the combination of climatic parameters, with minimum temperature identified as an important growth constraint. However, no single environmental parameter could consistently account for the variability in plant growth. Concentrations of foliar UV-B absorbing compounds showed a positive trend with solar UV across the latitudinal gradient; however, this relationship was not consistent in all treatments. The most striking experimental outcome from this study was the effect of presence or absence of filtration frames on UV-absorbing compounds. Overall, the study demonstrates the value of an European approach in studying the impacts of natural UV across a large latitudinal gradient. We have shown the feasibility of coordinated UV filtration at multiple sites but have also highlighted the need for open controls and careful interpretation of plant responses.
gives an accurate but very accessible account of the physiology of plants, including the historic... more gives an accurate but very accessible account of the physiology of plants, including the historical background of how and when different phenomena were described and explained.
Seasonal variation in leaf phenolic composition may be important for acclimation of plants to sea... more Seasonal variation in leaf phenolic composition may be important for acclimation of plants to seasonal changes in their biotic and abiotic environment. For a realistic assessment of how plants respond to solar UV-B (280-315 nm) and UV-A (315-400 nm) radiation, seasonal variation in both environment and plant responses needs to be taken into account. This also has implications for studies concerning stratospheric ozone depletion and resulting increased UV-B radiation, as other environmental variables and/or plant phenology could interact with UV radiation. To elucidate this, we established a field experiment using plastic films attenuating different parts of the solar UV spectrum. The concentration of individual phenolic compounds was measured during one growing season in leaves of grey alder (Alnus incana) and white birch (Betula pubescens) trees. Our results showed changes in concentration of, e.g. hydrolyzable tannins in birch that suggest an effect of UV-A alone and e.g. chlorogenic acids in alder indicate a quadratic effect of UV-B irradiance and both linear and quadratic effect for UV-A in second-degree polynomial fits. Further, there was interaction between treatment and sampling time for some individual metabolites; hence, the UV response varied during the season. In addition to the UV effects, three temporal patterns emerged in the concentrations of particular groups of phenolics. Possible implications for both sampling methods and timing are discussed. Moreover, our results highlight differences in responses of the two tree species, which are taken to indicate differences in their ecological niche differentiation.
Go to AGRIS search. Silva Fennica (2002). Leaf life span and the mobility of "non-mo... more Go to AGRIS search. Silva Fennica (2002). Leaf life span and the mobility of "non-mobile" mineral nutrients : the case of boron in conifers. ...
Plants from high altitudes and/or low latitudes will, typically, be exposed to relatively high do... more Plants from high altitudes and/or low latitudes will, typically, be exposed to relatively high doses of UV-B, therefore it might be hypothesised that these plants are particularly well protected from potentially harmful effects of such radiation. Analysis of the UVsusceptibility of 224 Arabidopsis thaliana accessions from across the northern hemisphere (15 and 67°N; and − 6 and 300 m altitude) revealed a continuum of UV-protection levels. However, the relationship between the geographic origin of accessions and UVtolerance is complex, and appears to be limited to altered acclimation induction thresholds, rather than UV-tolerance per sé. Thus, our data emphasise the importance of (regulation of) inducible UV-B protection responses. Detailed molecular-physiological analysis of the UV-B acclimation response in A. thaliana shows parallel changes in gene-expression and plant architecture. Chronic UV-B treatment causes a re-distribution rather than a cessation of growth, and this comprises decreases in rosette diameter, decreases in inflorescence height but increases in the number of flowering stems. Gene expression profiling indicated that UV-induced morphogenesis is associated with subtle changes in phytohormone homeostasis, and this link is confirmed using physiological experiments.
The physiological mechanisms controlling plant responses to dynamic changes in ambient solar ultr... more The physiological mechanisms controlling plant responses to dynamic changes in ambient solar ultraviolet (UV) radiation are not fully understood: this information is important to further comprehend plant adaptation to their natural habitats. We used the fluorimeter Dualex to estimate in vivo the epidermal flavonoid contents by measuring epidermal UV absorbance (A 375 ) in Betula pendula Roth (silver birch) leaves of different ages under altered UV. Seedlings were grown in a greenhouse for 15 days without UV and transferred outdoors under three UV treatments (UV-0, UV-A and UV-A+B) created by three types of plastic film. After 7 and 13 days, Dualex measurements were taken at adaxial and abaxial epidermis of the first three leaves (L1, L2 and L3) of the seedlings. After 14 days, some of the seedlings were reciprocally swapped amongst the treatments to study the accumulation of epidermal flavonoids in the youngest unfolded leaves (L3) during leaf expansion under changing solar UV environments. A 375 of the leaves responded differently to the UV treatment depending on their position. UV-B increased the A 375 in the leaves independently of leaf position. L3 quickly adjusted A 375 in their epidermis according to the UV they received and these adjustments were affected by previous UV exposure. The initial absence of UV-A+B or UV-A, followed by exposure to UV-A+B, particularly enhanced leaf A 375 . Silver birch leaves modulate their protective pigments in response to changes in the UV environment during their expansion, and their previous UV exposure history affects the epidermal-absorbance achieved during later UV exposure.
We examined the quality and decomposition of naturally abscised leaves of silver birch (Betula pe... more We examined the quality and decomposition of naturally abscised leaves of silver birch (Betula pendula) seedlings subjected to three different levels of fertilization under ambient and elevated levels of temperature and CO2. At the end of the second growing season, the chemical composition of the litter collected from the seedlings was analyzed. Whole-leaf samples from pooled litter from each of
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