Antecedent Drought Condition Affects Responses of Plant Physiology and Growth to Drought and Post-drought Recovery

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.

Detecting Agricultural and Meteorological Drought With Gross Primary Production Recovery Including Spatiotemporal Statistical Analysis in East Africa's Lake Victoria Basin

Drought imposes severe, long-term effects on global environments and ecosystems. A better understanding of how long it takes a region to recover to pre-drought conditions after drought is essential for addressing future ecology risks. In this study, drought-related variables were obtained using remote sensing and reanalysis products for 2003 to 2016. The meteorological drought index (standardized precipitation evapotranspiration index [SPEI]) and agricultural drought index (vegetation condition index [VCI]) were employed to estimate drought duration time (DDT) and drought recovery time (DRT). To the basin’s west, decreasing rainfall and increasing potential evapotranspiration led to decreasing SPEI. On the east side, decreasing soil moisture from each depth effects vegetation condition, which results in a decreasing gross primary productivity and VCI. Extreme meteorological drought events are likely to occur in the basin’s northeastern and middle western areas, while the southern basin is more likely to suffer from extreme agricultural drought events. The mean SPEI-based DDT (2.45 months) was smaller than the VCI-based DDT (2.97 months); the average SPEI-based DRT (2.02 months) was larger than the VCI-based DRT (1.63 months). Most of the area needs 1 or 2 months to recover from drought except for the basin’s northwestern area, where the DRT is more than 8 months. DDT is the most important parameter in determining DRT. These results provide useful information about regional drought recovery that will help local governments looking to mitigate potential environmental risks and formulate appropriate agricultural policies in Lake Victoria Basin.