Gas exchange recovery following natural drought is rapid unless limited by loss of leaf hydraulic conductance: evidence from an evergreen woodland

Stomatal response to environmental conditions forms the backbone of all ecosystem and carbon cycle models, but is largely based on empirical relationships. Evolutionary theories of stomatal behaviour are critical for guarding against prediction errors of empirical models under future climates. Longstanding theory holds that stomata maximise fitness by acting to maintain constant marginal water use efficiency over a given time horizon, but a recent evolutionary theory proposes that stomata instead maximise carbon gain minus carbon costs/risk of hydraulic damage. Using data from 34 species that span global forest biomes, we find that the recent carbon-maximisation optimisation theory is widely supported, revealing that the evolution of stomatal regulation has not been primarily driven by attainment of constant marginal water use efficiency. Optimal control of stomata to manage hydraulic risk is likely to have significant consequences for ecosystem fluxes during drought, which is critical given projected intensification of the global hydrological cycle.

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“…; Skelton et al . ), opportunity costs of lost photosynthesis and risk of mortality (Anderegg et al . ).…”

Section: Discussionmentioning

confidence: 99%

Woody plants optimise stomatal behaviour relative to hydraulic risk

et al. 2018

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“…The ability to account for losses of rehydration capacity as a function of dehydration would thus improve the ability to estimate RWC from LT as it varies over the courses of minutes and hours and during seasonal cycles of dehydration and rehydration. Notably, further studies are equally needed of long‐scale responses of leaves on droughted plants, weeks or months after recovery from water deficits (Anderegg et al, ; Brodribb et al, ), to determine whether leaves not shed can recover further rehydration capacity and function, or whether they remain only partially intact but dysfunctional, for species of a range of leaf habits that vary in other parameters (e.g., Skelton, Brodribb, McAdam, & Mitchell, ).…”

Section: Discussionmentioning

confidence: 99%

Leaf rehydration capacity: Associations with other indices of drought tolerance and environment

John

Henry

Sack

2018

Plant Cell & Environment

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Clarifying the mechanisms of leaf and whole plant drought responses is critical to predict the impacts of ongoing climate change. The loss of rehydration capacity has been used for decades as a metric of leaf dehydration tolerance but has not been compared with other aspects of drought tolerance. We refined methods for quantifying the percent loss of rehydration capacity (PLRC), and for 18 Southern California woody species, we determined the relative water content and leaf water potential at PLRC of 10%, 25%, and 50%, and, additionally, the PLRC at important stages of dehydration including stomatal closure and turgor loss. On average, PLRC of 10% occurred below turgor loss point and at similar water status to 80% decline of stomatal conductance. As hypothesized, the sensitivity to loss of leaf rehydration capacity varied across species, leaf habits, and ecosystems and correlated with other drought tolerance traits, including the turgor loss point and structural traits including leaf mass per area. A new database of PLRC for 89 species from the global literature indicated greater leaf rehydration capacity in ecosystems with lower growing season moisture availability, indicating an adaptive role of leaf cell dehydration tolerance within the complex of drought tolerance traits.

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“…, Skelton et al. ). Concomitantly, respiration also continuously decreases carbohydrate levels during drought and, whereas carbon starvation is rare in adult plants, lack of reserves has been documented in seedlings (Pratt et al.…”

Section: Resilience To Fire At Population Levelmentioning

confidence: 99%

Fire‐induced deforestation in drought‐prone Mediterranean forests: drivers and unknowns from leaves to communities

Karavani

Boer

Baudena

et al. 2018

Ecological Monographs

113

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Over the past 15 years, 3 million hectares of forests have been converted into shrublands or grasslands in the Mediterranean countries of the European Union. Fire and drought are the main drivers underlying this deforestation. Here we present a conceptual framework for the process of fire‐induced deforestation based on the interactive effects of fire and drought across three hierarchical scales: resistance in individuals, resilience in populations, and transitions to a new state. At the individual plant level, we review the traits that confer structural and physiological resistance, as well as allow for resprouting capacity: deforestation can be initiated when established individuals succumb to fire. After individuals perish, the second step toward deforestation requires a limited resilience from the population, that is, a reduced ability of that species to regenerate after fire. If individuals die after fire and the population fails to recover, then a transition to a new state will occur. We document trade‐offs between drought survival and fire survival, as embolism resistance is negatively correlated with fire tolerance in conifers and leaf shedding or drought deciduousness, a process that decreases water consumption at the peak of the dry season, temporally increases crown flammability. Propagule availability and establishment control resilience after mortality, but different hypotheses make contrasting predictions on the drivers of post‐fire establishment. Mycorrhizae play an additional role in modulating the response by favoring recovery through amelioration of the nutritional and water status of resprouts and new germinants. So far, resprouter species such as oaks have provided a buffer against deforestation in forests dominated by obligate seeder trees, when present in high enough density in the understory. While diversifying stands with resprouters is often reported as advantageous for building resilience, important knowledge gaps exist on how floristic composition interacts with stand flammability and on the “resprouter exhaustion syndrome,” a condition where pre‐fire drought stress, or short fire return intervals, seriously restrict post‐fire resprouting. Additional attention should be paid to the onset of novel fire environments in previously fire‐free environments, such as high altitude forests, and management actions need to accommodate this complexity to sustain Mediterranean forests under a changing climate.

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Gas exchange recovery following natural drought is rapid unless limited by loss of leaf hydraulic conductance: evidence from an evergreen woodland

Cited by 131 publications

References 64 publications

Woody plants optimise stomatal behaviour relative to hydraulic risk

Woody plants optimise stomatal behaviour relative to hydraulic risk

Leaf rehydration capacity: Associations with other indices of drought tolerance and environment

Fire‐induced deforestation in drought‐prone Mediterranean forests: drivers and unknowns from leaves to communities

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