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The physiological acclimation of Taxodium hybrid ‘zhongshanshan 118’ (T.118) plants to a progressive drought stress and drought-stressed to recovery treatment (DS-R) was investigated in this study. Plants of control (C) treatment were watered daily throughout the experiment. Results indicated that water deficit reduced stomatal conductance (g S) to improve water use efficiency (WUE) and, as a consequence, net photosynthetic rate (P n), transpiration rate (T r), and intercellular CO2 concentration (C i) were also decreased in DS-R T.118 plants compared with C plants. These reductions became more significant with decreasing soil water availability. Correlation analysis showed g S was positively correlated (P < 0.01) with the soil water content as well as leaf relative water content (RWC). There was a tendency to accumulate proline, malondialdehyde (MDA), antioxidases, and membrane electrolyte leakage as stress intensity increased. Moreover, drought stress induced significant (P < 0.05) decline in total chlorophyll contents (Chlt) and increase of nonphotochemical quenching (NPQ) on day 8 as a photo-protective mechanism. Cluster analysis distinguished the adaption of T.118 plants to water deficit in two ways. First, photosynthesis was related to thermal dissipation, and second antioxidation was related to morphology and osmosis. Furthermore, tested parameters showed a reversed tendency and restored equivalently to C levels after 9 days of rewatering. These findings suggest that T.118 plants demonstrated considerable tolerance to short-term drought stress and recovery due to a high degree of plasticity in physiological acclimation.
Roots are vital organs for resource uptake. However, the knowledge regarding the extent by which responses in roots influence plant resistance is still poorly known. In this study, we examined the morphological and physiological responses of lateral roots of Taxodium hybrid ‘Zhongshanshan 406’ (Taxodium mucronatum♀ and Taxodium distichum♂, T. 406) to 8 (DS-8) and 12 days (DS-12) drought. Control plants (CK-8 and CK-12) were well-watered throughout the experiment. Results indicated that drought resulted in significantly decreased root length, surface area, volume, and biomass and a relatively high death rate of roots (>2 mm). Specific root length (SRL) and specific root surface area (SRA) of drought-stressed T. 406 plants were reduced to enhance resource uptake. Meanwhile, root relative water content (RWC) of T. 406 plants in CK-12 treatment was 5.81 times of those in DS-12 treatment. Under drought stress and root superoxide dismutase and ascorbic acid (ASA) activities, proline and hydrogen peroxide (H2O2) contents consistently increased to benefit the elimination of O2 −. At the ultrastructural level, the organelle structure of T. 406 plant root tip was visibly damaged because of dehydration. The nucleus swelled and then exhibited uncommon features of disorganization and disruption. In short, our results provided substantial information about lateral root traits of T. 406 plants in response to drought stress, which is crucial to improve the drought resistance of Taxodium hybrid in the future breeding.