Regulation Of Leaf Gas Exchange Research Articles

Contrasting regulation of leaf gas exchange of semi-arid tree species under repeated drought

Abstract Predicting how plants respond to drought requires an understanding of how physiological mechanisms and drought response strategies occur, as these strategies underlie rates of gas exchange and productivity. We assessed the response of eleven plant traits to repeated experimental droughts in four co-occurring species of central Australia. The main goals of this study were to i) compare the response to drought between species; ii) evaluate whether plants acclimated to repeated drought; and iii) examine the degree of recovery in leaf gas exchange after cessation of drought. Our four species of study were two tree species and two shrub species, which field studies have shown to occupy different ecohydrological niches. The two tree species (Eucalyptus camaldulensis and Corymbia opaca) had large reductions in stomatal conductance (gs) values, declining by 90% in the second drought. By contrast, the shrub species (A. aptaneura and H. macrocarpa) had smaller reductions gs in the second drought of 52 and 65% respectively. Only, A. aptaneura showed a physiological acclimatation to drought due to small declines in gs vs ᴪpd (0.08 slope) during repeated droughts, meaning they maintained higher rates of gs compared with plants that only experienced one final drought (0.19 slope). All species in all treatments rapidly recovered leaf gas exchange and leaf mass per area following drought, displaying physiological plasticity to drought exposure. This research refines our understanding of plant physiological responses to recurrent water stress, which has implications for modelling of vegetation, carbon assimilation and water-use in semi-arid environments under drought.

Responses of leaf water potential and gas exchange to the precipitation manipulation in two shrubs on the Chinese Loess Plateau

Regulation of leaf gas exchange plays an important role in the survival of trees and shrubs under future climate change. However, the responses of leaf water potential and gas exchange of shrubs in semi-arid areas to the precipitation alteration are not clear. Here, we conducted a manipulated experiment with three levels of precipitation, i.e., a control with ambient precipitation, 50% above ambient precipitation (irrigation treatment), and 50% below ambient precipitation (drought treatment), with two common shrubs, Salix psammophila C. Wang & C. Y. Yang (isohydric plant, maintaining a constant leaf water potential by stomatal regulation) and Caragana korshinskii Kom. (anisohydric plant, having more variable leaf water potential), on the Chinese Loess Plateau in 2014 and 2015. We measured the seasonal variations of predawn and midday leaf water potential (Ωpd and Ωmd), two parameters of gas exchange, i.e., light-saturated assimilation (An) and stomatal conductance (gs), and other foliar and canopy traits. The isohydric S. psammophila had a similar An and a higher gs than the anisohydric C. korshinskii under drought treatment in 2015, inconsistent with the view that photosynthetic capacity of anisohydric plants is higher than isohydric plants under severe drought. The two shrubs differently responded to precipitation manipulation. Ωpd, An and gs were higher under irrigation treatment than control for S. psammophila, and these three variables and Ωmd were significantly higher under irrigation treatment and lower under drought treatment than control for C. korshinskii. Leaf water potential and gas exchange responded to manipulated precipitation more strongly for C. korshinskii than for S. psammophila. However, precipitation manipulation did not alter the sensitivity of leaf gas exchange to vapor-pressure deficit and soil moisture in these two shrubs. Acclimation to long-term changes in soil moisture in these two shrubs was primarily attributed to the changes in leaf or canopy structure rather than leaf gas exchange. These findings will be useful for modeling canopy water-carbon exchange and elucidating the adaptive strategies of these two shrubs to future changes in precipitation.

Element content and expression of genes of interest in guard cells are connected to spatiotemporal variations in stomatal conductance.

Element content and expression of genes of interest on single cell types, such as stomata, provide valuable insights into their specific physiology, improving our understanding of leaf gas exchange regulation. We investigated how far differences in stomatal conductance (gs ) can be ascribed to changes in guard cells functioning in amphistomateous leaves. gs was measured during the day on both leaf sides, on well-watered and drought-stressed trees (two Populus euramericana Moench and two Populus nigra L. genotypes). In parallel, guard cells were dissected for element content and gene expressions analyses. Both were strongly arranged according to genotype, and drought had the lowest impact overall. Normalizing the data by genotype highlighted a structure on the basis of leaf sides and time of day both for element content and gene expression. Guard cells magnesium, phosphorus, and chlorine were the most abundant on the abaxial side in the morning, where gs was at the highest. In contrast, genes encoding H+ -ATPase and aquaporins were usually more abundant in the afternoon, whereas genes encoding Ca2+ -vacuolar antiporters, K+ channels, and ABA-related genes were in general more abundant on the adaxial side. Our work highlights the unique physiology of each leaf side and their analogous rhythmicity through the day.

Controlling stomatal aperture in semi-arid regions—The dilemma of saving water or being cool?

Stomatal regulation of leaf gas exchange with the atmosphere is a key process in plant adaptation to the environment, particularly in semi-arid regions with high atmospheric evaporative demand. Development of stomata, integrating internal signaling and environmental cues sets the limit for maximum diffusive capacity of stomata, through size and density and is under a complex genetic control, thus providing multiple levels of regulation. Operational stomatal conductance to water vapor and CO2 results from feed-back and/or feed-forward mechanisms and is the end-result of a plethora of signals originated in leaves and/or in roots at each moment. CO2 assimilation versus water vapor loss, proposed to be the subject of optimal regulation, is species dependent and defines the water use efficiency (WUE). WUE has been a topic of intense research involving areas from genetics to physiology. In crop plants, especially in semi-arid regions, the question that arises is how the compromise of reducing transpiration to save water will impact on plant performance through leaf temperature. Indeed, plant transpiration by providing evaporative cooling, is a major component of the leaf energy balance. In this paper we discuss the dilemma of ‘saving water or being cool’ bringing about recent findings from molecular genetics, to development and physiology of stomata. The question of ‘how relevant is screening for high/low WUE in crops for semi-arid regions, where drought and heat co-occur’ is discussed.

A dynamic leaf gas-exchange strategy is conserved in woody plants under changing ambient CO2 : evidence from carbon isotope discrimination in paleo and CO2 enrichment studies.

Rising atmospheric [CO2 ], ca , is expected to affect stomatal regulation of leaf gas-exchange of woody plants, thus influencing energy fluxes as well as carbon (C), water, and nutrient cycling of forests. Researchers have proposed various strategies for stomatal regulation of leaf gas-exchange that include maintaining a constant leaf internal [CO2 ], ci , a constant drawdown in CO2 (ca -ci ), and a constant ci /ca . These strategies can result in drastically different consequences for leaf gas-exchange. The accuracy of Earth systems models depends in part on assumptions about generalizable patterns in leaf gas-exchange responses to varying ca . The concept of optimal stomatal behavior, exemplified by woody plants shifting along a continuum of these strategies, provides a unifying framework for understanding leaf gas-exchange responses to ca . To assess leaf gas-exchange regulation strategies, we analyzed patterns in ci inferred from studies reporting C stable isotope ratios (δ(13) C) or photosynthetic discrimination (∆) in woody angiosperms and gymnosperms that grew across a range of ca spanning at least 100ppm. Our results suggest that much of the ca -induced changes in ci /ca occurred across ca spanning 200 to 400ppm. These patterns imply that ca -ci will eventually approach a constant level at high ca because assimilation rates will reach a maximum and stomatal conductance of each species should be constrained to some minimum level. These analyses are not consistent with canalization toward any single strategy, particularly maintaining a constant ci . Rather, the results are consistent with the existence of a broadly conserved pattern of stomatal optimization in woody angiosperms and gymnosperms. This results in trees being profligate water users at low ca , when additional water loss is small for each unit of C gain, and increasingly water-conservative at high ca , when photosystems are saturated and water loss is large for each unit C gain.

Plant and soil δ13C and δ15N are linked to community biomass, litter production, and litter turnover rate in mature subtropical forests

The natural abundance of 13C and 15N can integrate information on the dynamics of C and N, respectively. This study tested whether and how δ13C and δ15N of the plant and soil samples (including leaf, forest floor litters, fine roots, and 0–15 cm mineral soil) can detect local variations in community biomass, litter production, and litter turnover rate were explored in eight mature subtropical forests in southern China. Community biomass, litter production, and litter turnover rate were significantly positively correlated with each other and revealed similar correlations with other plant and soil parameters. Leaf δ13C was significantly negatively correlated with litter production, suggesting the stomatal regulation of leaf gas exchange. Similar correlations were also observed for δ13C of the mineral soil and other plant materials. Leaf and forest floor litters δ15N were positively correlated with community biomass, litter production, and litter turnover rate. Such correlations were significantly positively mediated by soil availability of P rather than N, as demonstrated by the multiple regression analysis. In contrast, fine roots δ15N was not related significantly to community biomass, litter production, or litter turnover rate. Significant differences in δ13C and δ15N among forests were related to the species composition, topography conditions, and land use history. Our results suggest that δ13C and δ15N of most plant and soil samples can indicate local variations in community biomass, litter production, and litter turnover rate in mature subtropical forests. Better understanding of these linkages could significantly improve our knowledge of C and N dynamics in forest ecosystems.

Regulation and acclimation of leaf gas exchange in a piñon–juniper woodland exposed to three different precipitation regimes

Leaf gas-exchange regulation plays a central role in the ability of trees to survive drought, but forecasting the future response of gas exchange to prolonged drought is hampered by our lack of knowledge regarding potential acclimation. To investigate whether leaf gas-exchange rates and sensitivity to drought acclimate to precipitation regimes, we measured the seasonal variations of leaf gas exchange in a mature piñon-juniper Pinus edulis-Juniperus monosperma woodland after 3 years of precipitation manipulation. We compared trees receiving ambient precipitation with those in an irrigated treatment (+30% of ambient precipitation) and a partial rainfall exclusion (-45%). Treatments significantly affected leaf water potential, stomatal conductance and photosynthesis for both isohydric piñon and anisohydric juniper. Leaf gas exchange acclimated to the precipitation regimes in both species. Maximum gas-exchange rates under well-watered conditions, leaf-specific hydraulic conductance and leaf water potential at zero photosynthetic assimilation all decreased with decreasing precipitation. Despite their distinct drought resistance and stomatal regulation strategies, both species experienced hydraulic limitation on leaf gas exchange when precipitation decreased, leading to an intraspecific trade-off between maximum photosynthetic assimilation and resistance of photosynthesis to drought. This response will be most detrimental to the carbon balance of piñon under predicted increases in aridity in the southwestern USA.

Leaf Abscisic Acid Accumulation in Response To Substrate Water Content: Linking Leaf Gas Exchange Regulation with Leaf Abscisic Acid Concentration

Quantitative differences in leaf abscisic acid (ABAL) among four cultivars of red maple (Acer rubrum L.) and one freeman maple (Acer ×freemanii E. Murray) cultivar were investigated. This study tested the hypothesis that ABAL concentration can be used to compare the effects of water stress on the gas exchange response of five different maple genotypes, including four red maple cultivars [`Summer Red', `October Glory', `Autumn Flame', and `Franksred' ('Red Sunset')] and one hybridized freeman maple cultivar ['Jeffersred' ('Autumn Blaze')]. Two-year-old cloned genotypes of red maple and freeman maple were subjected to two treatments: irrigated daily to container capacity or irrigation withheld for one drought and recovery cycle. Leaf abscisic acid concentration, gas exchange, and wholetree sap flow measurements were conducted under well-watered and drought stress conditions. Over the course of the drought stress and recovery phase, net photosynthesis (Anet), stomatal conductance (gs), and transpiration (E) declined as ABAL and instantaneous water use efficiency (A/gs) increased. Until severe water stress conditions were prominent, water use was higher in `Summer Red' as compared to `October Glory'. This study found that ABAL tracked gs and that stomatal responsiveness to substrate moisture deficit is likely mediated by ABA accumulation in leaf tissue. This research demonstrates a leaf level physiological response to substrate volumetric water content that appears to depend on ABAL concentration. In addition, the evidence in this study indicates that ABAL may be used as a potential surrogate for the gs response to substrate water stress and could become part of a cultivar drought tolerance selection strategy for red maple and freeman maple.

Interannual and seasonal variation in fluxes of water and carbon dioxide from a riparian woodland ecosystem

Fluxes of water, energy and carbon dioxide (CO 2) were measured using the eddy covariance technique over a mesquite ( Prosopis velutina) woodland along the San Pedro River in southeastern Arizona for the entire growing seasons of 2001 and 2002, between the last freeze event of spring and the first of fall. Although the general pattern of ecosystem response to climate forcing was similar in both years, latent heat and CO 2 fluxes showed significant variations between and within the growing seasons. The main differences between the two years were a consequence of an extended drought that lasted from October 2001 to July 2002. Most of the within season variability was attributable to the timing and magnitude of mid-summer precipitation associated with the North American Monsoon. Following new tree leaf production and prior to the monsoon onset, there was little precipitation; daytime air temperatures were high and relative humidity low. Evapotranspiration and water level data indicated that the mesquite trees always had ready access to groundwater, though they were likely supplementing this with vadose zone soil water when abundant. Nonetheless, decreases in afternoon transpiration and CO 2 uptake suggest stomatal regulation of leaf gas exchange, possibly in response to the high vapor pressure deficit. Because near-surface soil moisture was limited prior to the summer rains, ecosystem respiration was low and there was little evapotranspiration from understory plants and soil. With the arrival of the monsoon rains, understory vegetation activity and, consequently, total ecosystem evapotranspiration increased. Total ecosystem photosynthesis also increased, but the net uptake of carbon decreased, due to enhanced respiration from the abundant carbon sources, stimulated by the precipitation and warm temperatures. The nighttime measurements of CO 2 fluxes, although of questionable accuracy, imply the ecosystem was a net sink of CO 2 for most of the two growing seasons.

Leaf conductance and CO(2) assimilation of Larix gmelinii growing in an eastern Siberian boreal forest.

In July 1993, we measured leaf conductance, carbon dioxide (CO(2)) assimilation, and transpiration in a Larix gmelinii (Rupr.) Rupr. ex Kuzen forest in eastern Siberia. At the CO(2) concentration of ambient air, maximum values (mean of 10 highest measured values) for CO(2) assimilation, transpiration and leaf conductance for water vapor were 10.1 micro mol m(-2) s(-1), 3.9 mmol m(-2) s(-1) and 365 mmol m(-2) s(-1), respectively. The corresponding mean values, which were much lower than the maximum values, were 2.7 micro mol m(-2) s(-1), 1.0 mmol m(-2) s(-1) and 56 mmol m(-2) s(-1). The mean values were similar to those of Vaccinium species in the herb layer. The large differences between maximum and actual performance were the result of structural and physiological variations within the tree crowns and between trees that reduced maximum assimilation and leaf conductance by about 40 and 60%, respectively. Thus, maximum assimilation and conductance values averaged over the canopy were 6.1 micro mol m(-2) s(-1) and 146 mmol m(-2) s(-1), respectively. Dry air caused stomatal closure, which reduced assimilation by an additional 26%. Low irradiances in the morning and evening had a minor effect (-6%). Daily canopy transpiration was estimated to be 1.45 mm day(-1), which is higher than the value of 0.94 mm day(-1) measured by eddy covariance, but similar to the value of 1.45 mm day(-1) calculated from the energy balance and soil evaporation, and less than the value of 2.1 mm day(-1) measured by xylem flux. Daytime canopy carbon assimilation, expressed on a ground area basis, was 0.217 mol m(-2) day(-1), which is higher than the value measured by eddy flux (0.162 mol m(-2) day(-1) including soil respiration). We discuss the regulation of leaf gas exchange in Larix under the extreme climatic conditions of eastern Siberia (temperature > 35 degrees C and vapor pressure deficit > 5.0 kPa).

Interactive effects of elevated CO(2) and soil drought on growth and transpiration efficiency and its determinants in two European forest tree species.

The responses of growth and transpiration efficiency (W = biomass accumulation/water consumption) to ambient and elevated atmospheric CO(2) concentrations (350 and 700 micro mol mol(-1), respectively) were investigated under optimal nutrient supply in well-watered and in drought conditions in two temperate-forest tree species: Quercus petraea Liebl. and Pinus pinaster Ait. Under well-watered conditions, doubling the CO(2) concentration for one growing season increased biomass growth by 138% in Q. petraea and by 63% in P. pinaster. In contrast, under drought conditions, elevated CO(2) increased biomass growth by only 47% in Q. petraea and had no significant effect on biomass growth in P. pinaster. Transpiration efficiency was higher in Q. petraea than in P. pinaster in all treatments. This difference was linked (i) to lower carbon isotope discrimination (Delta), and thus lower values of the intercellular/ambient CO(2) concentration (c(i)/c(a)) ratio, in Q. petraea, (ii) to lower values of leaf mass ratio (LMR, leaf mass/whole plant mass), which we suggest was positively related to the proportion of daytime carbon fixation lost by respiration (Phi), in Q. petraea, and (iii) to slightly lower C concentrations in Q. petraea than in P. pinaster. The CO(2)-promoted increase in W was higher in Q. petraea (+80%) than in P. pinaster (+50%), and the difference was associated with a more pronounced decrease in Phi in response to elevated CO(2) in Q. petraea than in P. pinaster, which could be linked with the N dilution effect observed in Q. petraea. Because Phi also directly affects growth, the CO(2)-induced enhancement of Phi in Q. petraea is a crucial determinant of the growth stimulation observed in this species. Leaf gas exchange regulation was not the only factor involved in the responses of growth and W to elevated CO(2) and drought, other physiological processes that have crucial roles include carbon and N allocation and respiration.

Pioneer and late stage tropical rainforest tree species (French Guiana) growing under common conditions differ in leaf gas exchange regulation, carbon isotope discrimination and leaf water potential.

Leaf gas exchange rates, predawn Ψwp and daily minimum Ψwm leaf water potentials were measured during a wet-to-dry season transition in pioneer (Jacaranda copaia, Goupia glabra andCarapa guianensis) and late stage rainforest tree species (Dicorynia guianensis andEperua falcata) growing in common conditions in artificial stands in French Guiana. Carbon isotope discrimination (Δ) was assessed by measuring the stable carbon isotope composition of the cellulose fraction of wood cores. The Δ values were 2.7‰ higher in the pioneer species than in the late stage species. The calculated time integratedC i values derived from the Δ values averaged 281 μmol mol-1 in the pioneers and 240 μmol mol-1 in the late stage species. The corresponding time-integrated values of intrinsinc water-use efficiency [ratio CO2 assimilation rate (A)/leaf conductance (g)] ranged from 37 to 47 mmol mol-1 in the pioneers and the values were 64 and 74 mmol mol-1 for the two late stage species. The high Δ values were associated-at least inJ. copaia-with high maximumg values and with high plant intrinsinc specific hydraulic conductance [C≔g/(Ψwm-Ψwp], which could reflect a high competitive ability for water and nutrient uptake in the absence of soil drought in the pioneers. A further clear discriminating trait of the pioneer species was the very sensitive stomatal response to drought in the soil, which might be associated with a high vulnerability to cavitation in these species. From a methodological point of view, the results show the relevance of Δ for distinguishing ecophysiological functional types among rainforest trees.

Influence of Root-zone Temperature on Growth of Ailanthus altissima (Mill.) Swingle

Abstract Growth of tree-of-heaven (Ailanthus altissima (Mill.) Swingle) seedlings was evaluated during a 28-day exposure to constant root-zone temperatures of 18°, 24°, 30°, and 36°C (64°,75°, 86°, and 97°F). Leaf area, stem length, root-to-shoot ratio, and shoot and root dry weights were greatest among plants with 24°C (75°F) root zones. Diminished growth among plants at high root-zone temperatures was associated with reduced leaf conductance. After 14 days of treatment, leaf diffusive resistance of plants in the 36°C (97°F) regime was eight times greater than that of plants with 24°C (75°F) root zones. Regulation of leaf gas exchange among plants with 36°C (97°F) root zones probably contributed to the maintenance of moderate leaf water potentials but limited the fixation of carbon necessary to sustain growth.