Individual and interactive responses of woody plants' biomass and leaf traits to drought and shade.

Aim: While drought and shade are critical factors that determine seedling survival and growth, whether the responses of woody seedlings to drought are facilitated, aggravated or unaffected by shade remains uncertain. Location: Global. Time period: 1993 to 2021. Major taxa studied: Woody plants. Methods: We compiled 58 studies (including 75 woody species from 33 families) in which water and light availability were simultaneously manipulated, and conducted a meta‐analysis on the acclimation and adaptive responses of biomass production and allocation and leaf traits to drought and/or shade. Results: Shade alleviated the adverse impact of drought on photosynthesis (A) by decreasing stomatal limitation and photoinhibition, and increasing leaf relative water content, and thus facilitated biomass production, but shade aggravated the effect of drought on osmotic adjustment as evidenced by the lack of responses of osmotic potential at the full turgor and modulus elasticity at the maximum turgor to drought under shade. The effects of drought and shade on biomass allocation and specific leaf area were orthogonal. Biomass responses to drought and its interaction with shade were least responsive for drought‐tolerators, but the individual and interactive effects of shade and drought on most traits showed little dependence on shade tolerance. Drought–shade interaction increased root biomass and root mass fraction more for deciduous angiosperms than for evergreen angiosperms. Main conclusions Both shade and drought had negative impacts on biomass production and photosynthesis, but their interaction had positive effects that were less significant for drought‐tolerators and evergreen angiosperms. In contrast to shade, drought increased biomass allocation to roots, but shade and drought had orthogonal effects on biomass allocation and leaf morphology. These acclimation and adaptive responses of woody seedlings to drought and shade individually and interactively have important implications for predicting woody plant growth and distribution under global climate changes. [ABSTRACT FROM AUTHOR]