Abstract:

Objective: Plant water regulation strategy, defined as the response of plants under environmental water deficit, plays a crucial role in plant adaptation to stressed environment. Accurately evaluating plant water regulation strategies is instrumental to elaborate the water use characteristics of plants and comprehensively understand the water relations of plants, thereby revealing the adaptive strategies of plants to drought. However, current methods for accurately quantifying and evaluating plant water regulation strategies remains controversial. The objective of this study is to explore and assess the methods for accurately evaluating plant water regulation strategies, so as to provide theoretical basis for a deeper understanding of the physiological mechanisms of fast-growing tree species growing under water deficit sites. Method: Populus tomentosa (B301) was used as the experimental material. Trees were subjected to two different soil water gradients (full irrigation and no irrigation) in different seasons (dry season and wet season), and suitability of different methods quantifying plant water regulation strategy was contrasted and analyzed. Result: 1) The evaluation results of the plant water regulation strategy of P. tomentosa with hydroscape area (HSA) and daily maximum difference between predawn and midday leaf water potential under well-watered conditions (ΔΨ) were the same across different soil moisture conditions and different seasons. The results of both methods showed that the water regulation strategy of non-irrigated treatment was more isohydric than that of the irrigation treatment, and the water regulation strategy of dry season was more isohydric than that of the wet season. The results were in line with the evaluation principles of "consistency" and "homogeneity" water regulation strategies proposed in this study. 2) When the slope method of the relationship between leaf noon water potential and water vapor pressure deficit (K_ΨMD-VPD) was used to evaluate plant water regulation strategies, the results of water regulation strategies obtained from different seasons and irrigation treatments were inconsistent. The results were the same as those produced by HSA and ΔΨ in different seasons, but opposite to those of HSA and ΔΨ under different irrigation treatments. 3) When the slope method for the relationship between pre-dawn and noon leaf water potential (K_ΨPD-ΨMD) was applied, the ranking across season under full irrigation was consistent with that generated by other methods, but the ranking of inter-season evaluation under no irrigation was contrary to that generated by other methods. Conclusion: The evaluation results on the water regulation strategy of P. tomentosa with HSA and ΔΨ are relatively accurate, and the evaluation results conform to the principles of “consistency” and “homogeneity”. Therefore, the HSA and ΔΨ are ideal evaluation indexes for the water regulation strategy of P. tomentosa. However, K_ΨPD-ΨMD and K_ΨMD-VPD are not suitable for evaluating the water regulation strategies of P. tomentosa. The generality of this conclusion will need to be tested in more species in the future. The results of this study can provide methodological reference for the evaluation of plant water regulation strategies.

Key words: water regulation relationship, hydroscape area, iso-/anisohydric behavior, irrigation, poplar