Abstract
Antecedent environmental conditions may have a substantial impact on plant response to drought and recovery dynamics. Saplings of Eucalyptus camaldulensis were exposed to a range of long-term water deficit pre-treatments (antecedent conditions) designed to reduce carbon assimilation to approximately 50 (A50) and 10% (A10) of maximum photosynthesis of well-watered plants (A100). Thereafter, water was withheld from all plants to generate three different levels of water stress before re-watering. Our objective was to assess the role of antecedent water limitations in plant physiology and growth recovery from mild to severe drought stress. Antecedent water limitations led to increased soluble sugar content and depletion of starch in leaves of A50 and A10 trees, but there was no significant change in total non-structural carbohydrate concentration (NSC; soluble sugar and starch), relative to A100 plants. Following re-watering, A50 and A10 trees exhibited faster recovery of physiological processes (e.g., photosynthesis and stomatal conductance) than A100 plants. Nonetheless, trees exposed to the greatest water stress (−5.0 MPa) were slowest to fully recover photosynthesis (Amax) and stomatal conductance (gs). Moreover, post-drought recovery of photosynthesis was primarily limited by gs, but was facilitated by biochemistry (Vcmax and Jmax). During recovery, slow regrowth rates in A50 and A10 trees may result from insufficient carbon reserves as well as impaired hydraulic transport induced by the antecedent water limitations, which was dependent on the intensity of drought stress. Therefore, our findings suggest that antecedent water stress conditions, as well as drought severity, are important determinants of physiological recovery following drought release.
Highlights
Understanding the impacts of drought stress on plant physiology and growth is essential for predicting the structure and function of plant communities (O’Brien et al, 2017a; Choat et al, 2018; Brodribb et al, 2020), especially within the context of global climate change in which drought episodes are projected to be more common in the future (Dai, 2013)
Growth nearly ceased while leaf photosynthesis continued during the phase of antecedent drought treatment, yet total non-structural carbohydrate concentration (NSC) content remained stable across treatment groups (Figure 1), similar to the findings reported by Klein et al (2014) in branches of Pinus halepensis subjected to drought
Our findings demonstrate that antecedent drought conditions may modify leaf biochemistry and physiology, which can be translated into different responses upon subsequent drought stress and recovery dynamics, following the alleviation of water limitation
Summary
Understanding the impacts of drought stress on plant physiology and growth is essential for predicting the structure and function of plant communities (O’Brien et al, 2017a; Choat et al, 2018; Brodribb et al, 2020), especially within the context of global climate change in which drought episodes are projected to be more common in the future (Dai, 2013). Adjustments in plant morphology and/or physiology triggered by antecedent, non-lethal water deficit can often result in divergent responses during subsequent drought stress, with potential impacts on plant performance during recovery (Kannenberg et al, 2020). This is evident in field-grown trees, for which the growth response to recurring drought differs over time (Xu et al, 2010; O’Brien et al, 2017b; Wu et al, 2018; Anderegg et al, 2020). Variation in NSCs induced by antecedent drought conditions can have important implications for the fate of plants during subsequent drought and recovery cycles
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