| 1. |
- Lin, Yan-Shih, et al.
(author)
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Optimal stomatal behaviour around the world
- 2015
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In: Nature Climate Change. - 1758-6798 .- 1758-678X. ; 5:5, s. 459-464
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Journal article (peer-reviewed)abstract
- Stomatal conductance (g(s)) is a key land-surface attribute as it links transpiration, the dominant component of global land evapotranspiration, and photosynthesis, the driving force of the global carbon cycle. Despite the pivotal role of g(s) in predictions of global water and carbon cycle changes, a global-scale database and an associated globally applicable model of g(s) that allow predictions of stomatal behaviour are lacking. Here, we present a database of globally distributed g(s) obtained in the field for a wide range of plant functional types (PFTs) and biomes. We find that stomatal behaviour differs among PFTs according to their marginal carbon cost of water use, as predicted by the theory underpinning the optimal stomatal model(1) and the leaf and wood economics spectrum(2,3). We also demonstrate a global relationship with climate. These findin g(s) provide a robust theoretical framework for understanding and predicting the behaviour of g(s) across biomes and across PFTs that can be applied to regional, continental and global-scale modelling of ecosystem productivity, energy balance and ecohydrological processes in a future changing climate.
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| 2. |
- Medlyn, Belinda E, et al.
(author)
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How do leaf and ecosystem measures of water-use efficiency compare?
- 2017
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In: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 216:3, s. 758-770
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Journal article (peer-reviewed)abstract
- The terrestrial carbon and water cycles are intimately linked: the carbon cycle is driven by photosynthesis, while the water balance is dominated by transpiration, and both fluxes are controlled by plant stomatal conductance. The ratio between these fluxes, the plant water-use efficiency (WUE), is a useful indicator of vegetation function. WUE can be estimated using several techniques, including leaf gas exchange, stable isotope discrimination, and eddy covariance. Here we compare global compilations of data for each of these three techniques. We show that patterns of variation in WUE across plant functional types (PFTs) are not consistent among the three datasets. Key discrepancies include the following: leaf-scale data indicate differences between needleleaf and broadleaf forests, but ecosystem-scale data do not; leaf-scale data indicate differences between C3 and C4 species, whereas at ecosystem scale there is a difference between C3 and C4 crops but not grasslands; and isotope-based estimates of WUE are higher than estimates based on gas exchange for most PFTs. Our study quantifies the uncertainty associated with different methods of measuring WUE, indicates potential for bias when using WUE measures to parameterize or validate models, and indicates key research directions needed to reconcile alternative measures of WUE.
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| 3. |
- Wieloch, Thomas, 1979-
(author)
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Intramolecular isotope analysis reveals plant ecophysiological signals covering multiple timescales
- 2019
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Doctoral thesis (other academic/artistic)abstract
- Our societies' wellbeing relies on stable and healthy environments. However, our current lifestyles, growth-oriented economic policies and the population explosion are leading to potentially catastrophic degradation of ecosystems and progressive disruption of food chains. Hopefully, more clarity about what the future holds in store will trigger stronger efforts to find, and adopt, problem-focused coping strategies and encourage environmentally friendly lifestyles.Forecasting environmental change/destruction is complicated (inter alia) by lack of complete understanding of plant-environment interactions, particularly those involved in slow processes such as plant acclimatisation and adaptation. This stems from deficiencies in tools to analyse such slow processes. The present work aims at developing tools that can provide retrospective ecophysiological information covering timescales from days to millennia.Natural archives, such as tree-rings, preserve plant metabolites over long timescales. Analyses of intramolecular isotope abundances in plant metabolites have the potential to provide retrospective information about metabolic processes and underlying environmental controls. Thus, my colleagues and I (hereafter we) analysed intramolecular isotope patterns in tree rings to develop analytical tools that can convey information about clearly-defined plant metabolic processes over multiple timescales. Such tools might help (inter alia) to constrain plants' capacities to sequester excess amounts of anthropogenic CO2; the so-called CO2 fertilisation effect. This, in turn, might shed light on plants' sink strength for the greenhouse gas CO2, and future plant performance and growth under climate change.In the first of three studies, reported in appended papers, we analysed intramolecular 13C/12C ratios in tree-ring glucose. In six angiosperm and six gymnosperm species we found pronounced intramolecular 13C/12C differences, exceeding 10‰. These differences are transmitted into major global C pools, such as soil organic matter. Taking intramolecular 13C/12C differences into account might improve isotopic characterisation of soil metabolic processes and soil CO2 effluxes. In addition, we analysed intramolecular 13C/12C ratios in a Pinus nigra tree-ring archive spanning the period 1961 to 1995. These data revealed new ecophysiological 13C/12C signals, which can facilitate climate reconstructions and assessments of plant-environment interactions at higher resolution; thus providing higher quality information. We proposed that 13C/12C signals at glucose C-1 to C-2 derive from carbon injection into the Calvin-Benson cycle via the oxidative pentose phosphate pathway. We concluded that intramolecular 13C/12C measurements provide valuable new information about long-term metabolic dynamics for application in biogeochemistry, plant physiology, plant breeding, and paleoclimatology.In the second study, we developed a comprehensive theory on the metabolic and ecophysiological origins of 13C/12C signals at tree-ring glucose C-5 and C-6. According to this theory and theoretical implications of the first study on signals at C-1 to C-3, analysis of such intramolecular signals can provide information about several metabolic processes. At C-3, a well-known signal reflecting CO2 uptake is preserved. The glucose-6-phosphate shunt around the Calvin-Benson cycle affects 13C/12C compositions at C-1 and C-2, while the 13C/12C signals at C-5 and C-6 reflect carbon fluxes into downstream metabolism. This theoretical framework enables further experimental studies to be conducted in a hypothesis-driven manner. In conclusion, the intramolecular approach provides information about carbon allocation in plant leaves. Thus, it gives access to long-term information on key ecophysiological processes, which could not be acquired by previous approaches.The abundance of the hydrogen isotope deuterium, δD, is important for linking the water cycle with plant ecophysiology. The main factors affecting δD in plant organic matter are commonly assumed to be the δD in source water and leaf-level evaporative enrichment. Current δD models incorporate biochemical D fractionations as constants. In the third study we showed that biochemical D fractionations respond strongly to low ambient CO2 levels and low light intensity. Thus, models of δD values in plant organic matter should incorporate biochemical fractionations as variables. In addition, we found pronounced leaf-level δD differences between α-cellulose and wax n-alkanes. We explained this by metabolite-specific contributions of distinct hydrogen sources during biosynthesis.Overall, this work advances our understanding of isotope distributions and isotope fractionations in plants. It reveals the immense potential of intramolecular isotope analyses for retrospective assessment of plant metabolism and associated environmental controls.
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