Limited mesophyll diffusion conductance to CO 2 (g m) can significantly constrain plant photosynt... more Limited mesophyll diffusion conductance to CO 2 (g m) can significantly constrain plant photosynthesis, but the extent of g m-limitation is still imperfectly known. As g m scales positively with foliage photosynthetic capacity (A), the CO 2 drawdown from substomatal cavities (C i) to chloroplasts (C C , C i-C C ¼A/g m) rather than g m alone characterizes the mesophyll diffusion limitations of photosynthesis. The dependencies of g m on A, foliage structure (leaf dry mass per unit area, M A), and the resulting drawdowns across a dataset of 81 species of contrasting foliage structure and photosynthetic potentials measured under non-stressed conditions were analysed to describe the structure-driven potential photosynthetic limitations due to g m. Further the effects of key environmental stress factors and leaf and plant developmental alterations on g m and CO 2 drawdown were evaluated and the implications of varying g m on foliage photosynthesis in the field were simulated. The meta-analysis demonstrated that g m of non-stressed leaves was negatively correlated with M A , and despite the positive relationship between g m and A, the CO 2 drawdown was larger in leaves with more robust structure. The correlations were stronger with mass-based g m and A, probably reflecting the circumstance that mesophyll diffusion is a complex three-dimensional process that scales better with mesophyll volume-weighted than with leaf area-weighted traits. The analysis of key environmental stress effects on g m and CO 2 drawdowns demonstrated that the effect of individual stresses on CO 2 drawdowns varies depending on the stress effects on foliage structure and assimilation rates. Leaf diffusion limitations are larger in nonsenescent older leaves and also in senescent leaves, again reflecting more robust leaf structure and/or nonco-ordinated alterations in leaf photosynthesis and g m. According to simulation analyses, in plants with a larger part of the overall diffusion conductance from the ambient atmosphere to the chloroplasts in the mesophyll, photosynthesis is less sensitive to changes in stomatal conductance. Accordingly, in harsher environments that support vegetation with tougher long-living stress-tolerant leaves with lower g m , reductions in stomatal conductance that are common during stress periods are expected to alter photosynthesis less than in species where a larger part of the total diffusion limitation is determined by stomata. While structural robustness improves plant performance under environmental stress, low g m and inherently large CO 2 drawdown in robust leaves limits the photosynthesis of these plants more severely under favourable conditions when stomatal conductance is high. The differences in overall responsiveness to environmental modifications of plants with varying g m need consideration in current large-scale ecosystem productivity models.
Volatile (VOC) flux from leaves may be expressed as G S ÁP, where G S is stomatal conductance to ... more Volatile (VOC) flux from leaves may be expressed as G S ÁP, where G S is stomatal conductance to specific compound and ÁP partial pressure gradient between the atmosphere and substomatal cavities. It has been suggested that decreases in G S are balanced by increases in ÁP such that stomata cannot control VOC emission. Yet, responses of emission rates of various volatiles to experimental manipulations of stomatal aperture are contrasting. To explain these controversies, a dynamic emission model was developed considering VOC distribution between gas and liquid phases using Henry's law constant (H, Pa m 3 mol À1). Our analysis demonstrates that highly volatile compounds such as isoprene and monoterpenes with H values on the order of 10 3 have gas and liquid pool half-times of a few seconds, and thus cannot be controlled by stomata. More soluble compounds such as alcohols and carboxylic acids with H values of 10 À2-10 1 are controlled by stomata with the degree of stomatal sensitivity varying with H. Inability of compounds with high solubility to support a high partial pressure, and thus to balance ÁP in response to a decrease in G S is the primary explanation for different stomatal sensitivities. For compounds with low H, the analysis predicts bursts of emission after stomatal opening that accord with experimental observations, but that cannot be currently explained. Large within-leaf VOC pool sizes in compounds with low H also increase the system inertia to environmental fluctuations. In conclusion, dynamic models are necessary to simulate diurnal variability of the emissions of compounds that preferably partition to aqueous phase.
Heterogeneity is one of the key components of sustainable development of every living system. It ... more Heterogeneity is one of the key components of sustainable development of every living system. It provides the source for restocking of ecosystem living components, irregular distribution of nutrients and habitats. Main components of forest horizontal heterogeneity are related with horizontal distribution of dominant species, soil properties, topography and as natural as human disturbances. Soil as the main source for nutrients supply plays essential role in functioning terrestrial ecosystems. The understanding of spatial distribution principles of such soil properties as soil acidity, nutrients available for living organisms, soil moisture and temperature, soil density and the role of tree dominant and co-dominant species can give deeper knowledge about ecosystem functioning. Models based on this knowledge can be more precise and give possibilities to predict more exactly the behavior of ecosystem in terms of global climate changing. The aim of the project is to assess spatial distr...
Fungal infections result in decreases in photosynthesis, induction of stress and signaling volati... more Fungal infections result in decreases in photosynthesis, induction of stress and signaling volatile emissions and reductions in constitutive volatile emissions, but the way different physiological processes scale with the severity of infection is poorly known. We studied the effects of infection by the obligate biotrophic fungal pathogen Melampsora larici-populina Kleb., the causal agent of poplar leaf rust disease, on photosynthetic characteristics, and constitutive isoprene and induced volatile emissions in leaves of Populus balsamifera var. suaveolens (Fisch.) Loudon. exhibiting different degrees of damage. The degree of fungal damage, quantified by the total area of chlorotic and necrotic leaf areas, varied between 0 (noninfected control) and ∼60%. The rates of all physiological processes scaled quantitatively with the degree of visual damage, but the scaling with damage severity was weaker for photosynthetic characteristics than for constitutive and induced volatile release. Over the whole range of damage severity, the net assimilation rate per area (A A) decreased 1.5-fold, dry mass per unit area 2.4-fold and constitutive isoprene emissions 5-fold, while stomatal conductance increased 1.9-fold and dark respiration rate 1.6-fold. The emissions of key stress and signaling volatiles (methanol, green leaf volatiles, monoterpenes, sesquiterpenes and methyl salicylate) were in most cases nondetectable in noninfested leaves, and increased strongly with increasing the spread of infection. The moderate reduction in A A resulted from the loss of photosynthetically active biomass, but the reduction in constitutive isoprene emissions and the increase in induced volatile emissions primarily reflected changes in the activities of corresponding biochemical pathways. Although all physiological alterations in fungal-infected leaves occurred in a stress severity-dependent manner, modifications in primary and secondary metabolic pathways scaled differently due to contrasting operational mechanisms.
Needle dimensions, needle surface area, needle dry weight per area (LWA) and needle density (ND, ... more Needle dimensions, needle surface area, needle dry weight per area (LWA) and needle density (ND, needle weight per volume) were measured in terminal current-year shoots in a natural canopy of variably sized Picea abies (L.) Karst. trees growing along a light gradient. Needle shape was described as a rhomboid. Needle width (D 2 ) increased with increasing diffuse site factor, a d (relative amount of penetrating diffuse solar radiation), whereas needle thickness (D 1 ) remained nearly constant, resulting in an inverse relationship between D 1 /D 2 and a d and an increase in the ratio of total (TLA) to projected needle surface area (PLA) with increasing a d . Because of the variations in needle morphology with respect to light availability, the shoot parameters used in present canopy models are also expected to be light-sensitive, and studies involving shoot morphology should also consider the variability in needle geometry. Needle dimensions and total tree height were not correlated. However, LWA increased with both increasing a d and total tree height. When LWA was expressed as the product of ND and needle height (NH, height of the rhomboidal transverse section of a needle), LWA appeared to increase with irradiance, because of changing NH, and with total tree height, because of changing needle density.
Leaf hydraulic conductance (K leaf ) and several characteristics of hydraulic architecture and ph... more Leaf hydraulic conductance (K leaf ) and several characteristics of hydraulic architecture and physiology were measured during the first 10 weeks of leaf ontogeny in Populus tremula L. saplings growing under control, mild water deficit or elevated temperature conditions. During the initial 3 weeks of leaf ontogeny, most measured characteristics rapidly increased. Thereafter, a gradual decrease in K leaf was correlated with a decrease in leaf osmotic potential under all conditions, and with increases in leaf dry mass per area and bulk modulus of elasticity under mild water deficit and control conditions. From about Week 3 onward, K leaf was 33% lower in trees subjected to mild water deficit and 33% higher in trees held at an elevated temperature relative to control trees. Mild water deficit and elevated temperature treatment had significant and opposite effects on most of the other characteristics measured. The ontogenetic maximum in K leaf was correlated positively with the width of xylem conduits in the midrib, but negatively with the overall width of the midrib xylem, number of lateral ribs, leaf dry mass per area and bulk modulus of elasticity. The ontogenetic maximum in K leaf was also correlated positively with the proportion of intercellular spaces and leaf osmotic potential, but negatively with leaf thickness, volume of mesophyll cells and epidermis and number of cells per total mesophyll cell volume, the closest relationships being between leaf osmotic potential and number of cells per total mesophyll cell volume. It was concluded that differences in protoplast traits are more important than differences in xylem or parenchymal cell wall traits in determining the variability in K leaf among leaves growing under different environmental conditions.
Plant defence can be induced by exposing plants to the plant hormone jasmonic acid (JA) or its vo... more Plant defence can be induced by exposing plants to the plant hormone jasmonic acid (JA) or its volatile ester, methyl jasmonate (MeJA). Carrageenans (Carr) -sulphated d-galactans extracted from red algae -can also induce plant defences. In this study, the effects of exogenous MeJA and Carr application (concentration 300 and 12.7 lmol, respectively) on volatile emissions from two widespread evergreen woody species, Pinus sylvestris (nine Turkish and one Finnish provenance) and Quercus ilex (Italian provenance) were investigated. We collected headspace samples from seedlings and analysed the quality and quantity of volatile compounds emitted by treated and control plants. In total, 19 monoterpenes, 10 sesquiterpenes, 10 green leaf volatiles (GLVs) and two aromatic compounds were emitted by P. sylvestris from all the provenances studied. Foliar MeJA application clearly affected the volatile profiles of trees from all the provenances. Effects of Carr were genotype specific. In Q. ilex, emissions of sesquiterpenes, GLVs and the homoterpene (E)-DMNT were all induced by MeJA application. However, emissions of most constitutively emitted monoterpenes were significantly reduced. Carr application also led to a significant reduction in monoterpene emissions, but without corresponding increases in other emissions. Our results indicate that exogenously applied MeJA and Carr can both significantly modify the volatile profiles of P. sylvestris and Q. ilex, but also that there are important provenance-and species-specific differences in the overall degree of elicitation and compositions of elicited compounds.
Limited mesophyll diffusion conductance to CO 2 (g m) can significantly constrain plant photosynt... more Limited mesophyll diffusion conductance to CO 2 (g m) can significantly constrain plant photosynthesis, but the extent of g m-limitation is still imperfectly known. As g m scales positively with foliage photosynthetic capacity (A), the CO 2 drawdown from substomatal cavities (C i) to chloroplasts (C C , C i-C C ¼A/g m) rather than g m alone characterizes the mesophyll diffusion limitations of photosynthesis. The dependencies of g m on A, foliage structure (leaf dry mass per unit area, M A), and the resulting drawdowns across a dataset of 81 species of contrasting foliage structure and photosynthetic potentials measured under non-stressed conditions were analysed to describe the structure-driven potential photosynthetic limitations due to g m. Further the effects of key environmental stress factors and leaf and plant developmental alterations on g m and CO 2 drawdown were evaluated and the implications of varying g m on foliage photosynthesis in the field were simulated. The meta-analysis demonstrated that g m of non-stressed leaves was negatively correlated with M A , and despite the positive relationship between g m and A, the CO 2 drawdown was larger in leaves with more robust structure. The correlations were stronger with mass-based g m and A, probably reflecting the circumstance that mesophyll diffusion is a complex three-dimensional process that scales better with mesophyll volume-weighted than with leaf area-weighted traits. The analysis of key environmental stress effects on g m and CO 2 drawdowns demonstrated that the effect of individual stresses on CO 2 drawdowns varies depending on the stress effects on foliage structure and assimilation rates. Leaf diffusion limitations are larger in nonsenescent older leaves and also in senescent leaves, again reflecting more robust leaf structure and/or nonco-ordinated alterations in leaf photosynthesis and g m. According to simulation analyses, in plants with a larger part of the overall diffusion conductance from the ambient atmosphere to the chloroplasts in the mesophyll, photosynthesis is less sensitive to changes in stomatal conductance. Accordingly, in harsher environments that support vegetation with tougher long-living stress-tolerant leaves with lower g m , reductions in stomatal conductance that are common during stress periods are expected to alter photosynthesis less than in species where a larger part of the total diffusion limitation is determined by stomata. While structural robustness improves plant performance under environmental stress, low g m and inherently large CO 2 drawdown in robust leaves limits the photosynthesis of these plants more severely under favourable conditions when stomatal conductance is high. The differences in overall responsiveness to environmental modifications of plants with varying g m need consideration in current large-scale ecosystem productivity models.
Volatile (VOC) flux from leaves may be expressed as G S ÁP, where G S is stomatal conductance to ... more Volatile (VOC) flux from leaves may be expressed as G S ÁP, where G S is stomatal conductance to specific compound and ÁP partial pressure gradient between the atmosphere and substomatal cavities. It has been suggested that decreases in G S are balanced by increases in ÁP such that stomata cannot control VOC emission. Yet, responses of emission rates of various volatiles to experimental manipulations of stomatal aperture are contrasting. To explain these controversies, a dynamic emission model was developed considering VOC distribution between gas and liquid phases using Henry's law constant (H, Pa m 3 mol À1). Our analysis demonstrates that highly volatile compounds such as isoprene and monoterpenes with H values on the order of 10 3 have gas and liquid pool half-times of a few seconds, and thus cannot be controlled by stomata. More soluble compounds such as alcohols and carboxylic acids with H values of 10 À2-10 1 are controlled by stomata with the degree of stomatal sensitivity varying with H. Inability of compounds with high solubility to support a high partial pressure, and thus to balance ÁP in response to a decrease in G S is the primary explanation for different stomatal sensitivities. For compounds with low H, the analysis predicts bursts of emission after stomatal opening that accord with experimental observations, but that cannot be currently explained. Large within-leaf VOC pool sizes in compounds with low H also increase the system inertia to environmental fluctuations. In conclusion, dynamic models are necessary to simulate diurnal variability of the emissions of compounds that preferably partition to aqueous phase.
Heterogeneity is one of the key components of sustainable development of every living system. It ... more Heterogeneity is one of the key components of sustainable development of every living system. It provides the source for restocking of ecosystem living components, irregular distribution of nutrients and habitats. Main components of forest horizontal heterogeneity are related with horizontal distribution of dominant species, soil properties, topography and as natural as human disturbances. Soil as the main source for nutrients supply plays essential role in functioning terrestrial ecosystems. The understanding of spatial distribution principles of such soil properties as soil acidity, nutrients available for living organisms, soil moisture and temperature, soil density and the role of tree dominant and co-dominant species can give deeper knowledge about ecosystem functioning. Models based on this knowledge can be more precise and give possibilities to predict more exactly the behavior of ecosystem in terms of global climate changing. The aim of the project is to assess spatial distr...
Fungal infections result in decreases in photosynthesis, induction of stress and signaling volati... more Fungal infections result in decreases in photosynthesis, induction of stress and signaling volatile emissions and reductions in constitutive volatile emissions, but the way different physiological processes scale with the severity of infection is poorly known. We studied the effects of infection by the obligate biotrophic fungal pathogen Melampsora larici-populina Kleb., the causal agent of poplar leaf rust disease, on photosynthetic characteristics, and constitutive isoprene and induced volatile emissions in leaves of Populus balsamifera var. suaveolens (Fisch.) Loudon. exhibiting different degrees of damage. The degree of fungal damage, quantified by the total area of chlorotic and necrotic leaf areas, varied between 0 (noninfected control) and ∼60%. The rates of all physiological processes scaled quantitatively with the degree of visual damage, but the scaling with damage severity was weaker for photosynthetic characteristics than for constitutive and induced volatile release. Over the whole range of damage severity, the net assimilation rate per area (A A) decreased 1.5-fold, dry mass per unit area 2.4-fold and constitutive isoprene emissions 5-fold, while stomatal conductance increased 1.9-fold and dark respiration rate 1.6-fold. The emissions of key stress and signaling volatiles (methanol, green leaf volatiles, monoterpenes, sesquiterpenes and methyl salicylate) were in most cases nondetectable in noninfested leaves, and increased strongly with increasing the spread of infection. The moderate reduction in A A resulted from the loss of photosynthetically active biomass, but the reduction in constitutive isoprene emissions and the increase in induced volatile emissions primarily reflected changes in the activities of corresponding biochemical pathways. Although all physiological alterations in fungal-infected leaves occurred in a stress severity-dependent manner, modifications in primary and secondary metabolic pathways scaled differently due to contrasting operational mechanisms.
Needle dimensions, needle surface area, needle dry weight per area (LWA) and needle density (ND, ... more Needle dimensions, needle surface area, needle dry weight per area (LWA) and needle density (ND, needle weight per volume) were measured in terminal current-year shoots in a natural canopy of variably sized Picea abies (L.) Karst. trees growing along a light gradient. Needle shape was described as a rhomboid. Needle width (D 2 ) increased with increasing diffuse site factor, a d (relative amount of penetrating diffuse solar radiation), whereas needle thickness (D 1 ) remained nearly constant, resulting in an inverse relationship between D 1 /D 2 and a d and an increase in the ratio of total (TLA) to projected needle surface area (PLA) with increasing a d . Because of the variations in needle morphology with respect to light availability, the shoot parameters used in present canopy models are also expected to be light-sensitive, and studies involving shoot morphology should also consider the variability in needle geometry. Needle dimensions and total tree height were not correlated. However, LWA increased with both increasing a d and total tree height. When LWA was expressed as the product of ND and needle height (NH, height of the rhomboidal transverse section of a needle), LWA appeared to increase with irradiance, because of changing NH, and with total tree height, because of changing needle density.
Leaf hydraulic conductance (K leaf ) and several characteristics of hydraulic architecture and ph... more Leaf hydraulic conductance (K leaf ) and several characteristics of hydraulic architecture and physiology were measured during the first 10 weeks of leaf ontogeny in Populus tremula L. saplings growing under control, mild water deficit or elevated temperature conditions. During the initial 3 weeks of leaf ontogeny, most measured characteristics rapidly increased. Thereafter, a gradual decrease in K leaf was correlated with a decrease in leaf osmotic potential under all conditions, and with increases in leaf dry mass per area and bulk modulus of elasticity under mild water deficit and control conditions. From about Week 3 onward, K leaf was 33% lower in trees subjected to mild water deficit and 33% higher in trees held at an elevated temperature relative to control trees. Mild water deficit and elevated temperature treatment had significant and opposite effects on most of the other characteristics measured. The ontogenetic maximum in K leaf was correlated positively with the width of xylem conduits in the midrib, but negatively with the overall width of the midrib xylem, number of lateral ribs, leaf dry mass per area and bulk modulus of elasticity. The ontogenetic maximum in K leaf was also correlated positively with the proportion of intercellular spaces and leaf osmotic potential, but negatively with leaf thickness, volume of mesophyll cells and epidermis and number of cells per total mesophyll cell volume, the closest relationships being between leaf osmotic potential and number of cells per total mesophyll cell volume. It was concluded that differences in protoplast traits are more important than differences in xylem or parenchymal cell wall traits in determining the variability in K leaf among leaves growing under different environmental conditions.
Plant defence can be induced by exposing plants to the plant hormone jasmonic acid (JA) or its vo... more Plant defence can be induced by exposing plants to the plant hormone jasmonic acid (JA) or its volatile ester, methyl jasmonate (MeJA). Carrageenans (Carr) -sulphated d-galactans extracted from red algae -can also induce plant defences. In this study, the effects of exogenous MeJA and Carr application (concentration 300 and 12.7 lmol, respectively) on volatile emissions from two widespread evergreen woody species, Pinus sylvestris (nine Turkish and one Finnish provenance) and Quercus ilex (Italian provenance) were investigated. We collected headspace samples from seedlings and analysed the quality and quantity of volatile compounds emitted by treated and control plants. In total, 19 monoterpenes, 10 sesquiterpenes, 10 green leaf volatiles (GLVs) and two aromatic compounds were emitted by P. sylvestris from all the provenances studied. Foliar MeJA application clearly affected the volatile profiles of trees from all the provenances. Effects of Carr were genotype specific. In Q. ilex, emissions of sesquiterpenes, GLVs and the homoterpene (E)-DMNT were all induced by MeJA application. However, emissions of most constitutively emitted monoterpenes were significantly reduced. Carr application also led to a significant reduction in monoterpene emissions, but without corresponding increases in other emissions. Our results indicate that exogenously applied MeJA and Carr can both significantly modify the volatile profiles of P. sylvestris and Q. ilex, but also that there are important provenance-and species-specific differences in the overall degree of elicitation and compositions of elicited compounds.
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