Abstract
A better understanding of plant drought responses is essential to improve plant water use efficiency, productivity, and resilience to ever-changing climatic conditions. Here, we investigated the growth, morpho-anatomical, physiological, and biochemical responses of Quercus acutissima Carruth., Quercus serrata Murray, and Betula schmidtii Regel to progressive water-stress. Seedlings were subjected to well-watered (WW) and water-stressed (WS) conditions while regularly monitoring the soil volumetric water content, stem diameter (SD), height, biomass, stomatal conductance (gs), intercellular CO2 concentration (Ci), and leaf relative water content (RWC). We also investigated the variation in stomatal pore (SP) area, specific leaf area (SLA), root xylem vessel diameter (VD), and total soluble sugar (TSS) concentration between treatments. After 2 months, WS significantly suppressed SD growth of Q. acutissima and B. schmidtii but had no impact on Q. serrata. Total biomass significantly declined at WS-treated seedlings in all species. WS resulted in a smaller SLA than WW in all species. The SP of WS-treated seedlings of Q. acutissima and B. schmidtii significantly decreased, whereas it increased significantly with time in Q. serrata. Larger vessels (i.e., >100 to ≤ 130) were more frequent at WS for Q. acutissima and B. schmidtii, whereas smaller vessels (i.e., >40 to ≤ 90) were more frequent at WS than at WW for Q. serrata after 8 weeks. Tylosis was more frequent at WS than WW for Q. serrata and B. schmidtii at eighth week. WS seedlings showed lower gs, Ci, and RWC compared with WW-treated ones in Q. acutissima and B. schmidtii. TSS concentration was also higher at WS-treated seedlings in two Quercus species. Overall, principal component analysis (PCA) showed that SLA and SP are associated with WS seedlings of Q. serrata and B. schmidtii and the tylosis frequency, TSS, and VD are associated with WS seedlings of Q. acutissima. Therefore, water-stressed plants from all species responded positively to water stress with increasing experimental duration and stress intensity, and that is largely explained by morpho-anatomical traits and soluble sugar concentration. The present study should enhance our understanding of drought-induced tree growth and short-term tree-seedling responses to drought.
Highlights
Droughts are expected to occur more often at larger spatio-temporal scales due to increasing global warming and unprecedented impacts of climate change (Han and Singh, 2020)
tylosis frequency (TYF), total soluble sugars (TSS), and VD were strongly associated with water-stressed seedlings of Q. acutissima, suggesting that water stress resistance strategies of the species were mainly controlled by anatomical and biochemical traits
Because most of the physiological traits declined in Q. acutissima at the end of experiment, the species may have increased the frequency of larger xylem vessels in fine root to structurally adapt to large changes in pressure and survive amid progressive water stress
Summary
Droughts are expected to occur more often at larger spatio-temporal scales due to increasing global warming and unprecedented impacts of climate change (Han and Singh, 2020). Plant responses to water stress can be first seen in the alterations in cell growth and structure caused by turgor loss and a decrease in stomatal conductance, chlorophyll content, and photosynthesis (Sanchez et al, 1982; Tanaka et al, 2013). These physiological effects occurred primarily due to closing of stomata, decreasing leaf water content and/or water potential, malfunctioning of enzymes, and cellular damage (Kumawat and Sharma, 2018; Sharma et al, 2020). The presence or accumulation of soluble sugars has long been considered a mechanism for tolerating water stress in some studies (Wang et al, 1995; Yakushiji et al, 1996; Ogawa and Yamauchi, 2006; Masouleh et al, 2019)
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