Abstract As global population increases and industrialization expands, carbon dioxide CO 2 and toxic air pollutants can be expected to be injected into the atmosphere at increasing rates. This analysis reviews a wide range of direct plant responses to rising CO 2 , increasing levels of gaseous pollutants, and climate change, and to potential interactions among the factors.
Although several environmental interactions on stomata and foliage temperatures are reviewed briefly, a comprehensive review of effects of potential climatic change on plants is not a major objective of this analysis. Research shows that elevated CO 2 increases photosynthetic rates, leaf area, biomass, and yield. Elevated CO 2 also reduces transpiration rate per unit leaf area, but not in proportion to reduction of stomatal conductance, because foliage temperature tends to rise.
With increasing leaf area and foliage temperature, water use per unit land area is scarcely reduced by elevated CO 2. Increases in photosynthetic water-use efficiency are caused primarily by increased photosynthesis rather than reduced transpiration. However, information on the interaction of CO 2 and air pollutants is scanty. More research is needed on these interactions, because regional changes in air pollutants are occurring concurrently with global changes in CO 2.
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Skip to main content. Email Address. Increasing R Light with measurement temperature also led to the lowest CUE at the highest temperatures. Mid-summer estimates of CUE were greater than early season, a pattern also observed in field grown Quercus ilex under drought and control conditions Sperlich et al.
While our study did not explicitly examine the impact of warmed growth conditions to assess acclimation, there is evidence of intra-seasonal adjustments to longer-term thermal conditions: both R Dark and R Light of a common reference temperature declined with increasing day average growth temperature. This decline in respiration with intra-season changes in growth temperature recalls similar trends observed in evergreen and deciduous species Ow et al.
The flexibility in leaf respiratory fluxes in the light and dark due to short-term, within-season acclimation can have a pronounced impact on terrestrial C exchange Lombardozzi et al. Canopy position mediates the light environment of a leaf, and the resulting intra-canopy resource allocation and function Mooney et al. We found significant influence of canopy position through the growing season in Q.
Respiration in the light has only previously been reported at multiple canopy heights in a tropical forest in Northern Queensland on evergreen broadleaf trees, in which top-canopy leaves released more carbon than lower-canopy leaves Weerasinghe et al. A main objective of our study was to quantify the degree of light inhibition of R across the growing season and at different measurement temperatures and canopy heights. Across all sampling and measurement conditions, we found significant inhibition by light and a seasonally mediated change in the degree of the inhibitory effect. The late-season relaxation of inhibition that we observe at the leaf level in Harvard Forest was also reported at the ecosystem scale through isotopic flux partitioning methods: Wehr et al.
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The lack of significant variation in degree of light inhibition with canopy height agrees was also found in tropical trees Weerasinghe et al. The positive relationship between inhibition and the day prior mean temperature suggests a potential longer-term thermal influence on this phenomenon, and assessing different temporal scales of environmental variables on inhibition may contribute to a greater understanding of its control. Recent gas exchange and isotopic labeling studies suggest a bottleneck of unrecycled amino acids and the resulting photorespiratory demand for glutamate enhance nitrogen metabolism and stimulate not only rates of R Light , but also CO 2 assimilation under normal i.
Pursuing the convergence of daytime C release, nitrogen assimilation and root-to-leaf transport of non-leaf-originated CO 2 , and how these processes co-vary with phenology and environmental change may prove to be a valuable research direction for understanding leaf-to-canopy daytime C cycling. Bridging observed nuances of leaf-level processes to whole forest ecosystem fluxes, and doing so across growing seasons-shaped environmental and biological influences, poses challenges when creating models of C exchange.
In our study, we confront this challenge by isolating a handful of the controlling environmental temperature, light and biological canopy position, phenology factors. In modeling daytime R across the growing season at the leaf and ecosystem scales, we applied two approaches to examine the influence of light inhibition on C efflux.
The application of a fixed value of inhibition resulted in a higher reduction of leaf respiration overall Scaling the impact of light inhibition to ecosystem fluxes requires the quantitative dissembling and modeling of eddy covariance data. The degree of overestimation in canopy respiration is lower than a modeled value Ecosystem-scale studies have also identified a reduction in daytime total respiration fluxes using a range of eddy covariance-based methods Wohlfahrt et al.
The variability in the effect of inhibition on total R Eco across the season is likely related to the relative contribution of leaves to total R Eco ; as leaves comprise a greater proportion of the total flux, the impact of inhibition may be more significant.
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However, values of leaf contribution to total ecosystem fluxes in forest systems are often reported to be much lower, can vary widely, and are sure to be influenced by environment and phenology Tang et al. Based on our leaf-level measurements of a dominant canopy tree, Q. We also present two approaches and the resulting models of seasonal autotrophic respiration that apply the light inhibition of respiration to the leaf and canopy scale. Collectively, the data show a seasonally influenced light inhibition of leaf respiration that impacts many metrics of leaf and forest carbon cycling: a decrease in leaf CUE, decreased seasonal cumulative leaf respiration using leaf-based and eddy covariance-derived data, and decreased ecosystem respiration.
Our field study focuses primarily on course categories of controls on physiology—canopy height as a proxy for light, temperature, and wind microenvironment, and seasonal time points that capture phenology of forest environmental and leaf development. There remains a need to better understand the metabolic intricacies and biochemical networks that control leaf metabolism in the light, especially in leaves across developmental stages that are exposed to the stochastic setting of a forest canopy, and not a controlled setting.
Our study adds to the growing body of literature on metabolic underpinnings and environmental controls of the light inhibition of leaf R , which collectively urge for incorporation in studies of ecosystem C exchange. We suggest integrating seasonally variable daytime fluxes when calculating R Eco and gross photosynthetic assimilation of forest canopies and believe the integration of these variables may lead to more robust estimates of canopy carbon uptake when applying methods such as solar-induced fluorescence and carbonyl sulfide.
Small, environmentally sensitive leaf fluxes such as R Light do not fit easily into the eddy covariance-driven narrative of ecosystem C exchange and longer-term C storage in forests. However, integrating these small fluxes, and importantly, their response to long- and short-term environmental change, are likely to reduce uncertainty in current and future projections of terrestrial C cycling. We also thank Elizabeth de la Reguera for her support in the lab and field.
Heskel and The Ecosystems Center.
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Advanced Search. Article Navigation. Close mobile search navigation Article Navigation. Volume Article Contents. Materials and methods. Conflict of interest. Environmental controls on light inhibition of respiration and leaf and canopy daytime carbon exchange in a temperate deciduous forest Mary A Heskel. Corresponding author mheskel macalester. Oxford Academic.
Google Scholar. Jianwu Tang. Cite Citation. Permissions Icon Permissions. Abstract Uncertainty in the estimation of daytime ecosystem carbon cycling due to the light inhibition of leaf respiration and photorespiration, and how these small fluxes vary through the growing season in the field, remains a confounding element in calculations of gross primary productivity and ecosystem respiration. Figure 1. Open in new tab Download slide. Respiration in the light for replicate leaves at each measurement temperature were estimated using the Kok method Kok , to ensure the greatest number of replicates in field conditions across the growing season.
For a current comparison of the different methods for estimating light inhibition, see Tcherkez et al. The y -intercept of this regression is the estimated apparent rate of respiration in the light R Light. To retrieve more accurate estimates of the rate of R Light , we needed to account for changes in intercellular [CO 2 ] c i that occur with decreasing PAR. To do this, we adjusted values of R Light obtained via the fitting of the regression described above to a constant c i value, using calculations described by Kirschbaum and Farquhar Kirschbaum and Farquhar An additional goal of this study was to relate photosynthetic parameters to the degree of inhibition by light in leaves, and how this may vary across the growing season and with canopy height.
For these reasons, fluxes of R Dark and R Light were modeled as a log-linear response of T Leaf for each replicate leaf. These temporal divisions were determined by inflection points, where the slope of average net ecosystem exchange NEE changed from baseline pre-leaf-out to greatly positive, and in autumn, where the slope became sharply negative during senescence across the growing season. Early season was marked by an increasing slope of NEE, mid-season was marked by a non-increasing or -decreasing mean slope of NEE, and late season was marked by a sharp decline of NEE that parallels leaf senescence.
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Rennenberg, H. (Heinz)
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