Responses of leaf water potential and gas exchange to the precipitation manipulation in two shrubs on the Chinese Loess Plateau

Abstract

Regulation of leaf gas exchange plays an important role in the survival of trees and shrubs under future climate change. However, the responses of leaf water potential and gas exchange of shrubs in semi-arid areas to the precipitation alteration are not clear. Here, we conducted a manipulated experiment with three levels of precipitation, i.e., a control with ambient precipitation, 50% above ambient precipitation (irrigation treatment), and 50% below ambient precipitation (drought treatment), with two common shrubs, Salix psammophila C. Wang & C. Y. Yang (isohydric plant, maintaining a constant leaf water potential by stomatal regulation) and Caragana korshinskii Kom. (anisohydric plant, having more variable leaf water potential), on the Chinese Loess Plateau in 2014 and 2015. We measured the seasonal variations of predawn and midday leaf water potential (Ψ pd and Ψ md ), two parameters of gas exchange, i.e., light-saturated assimilation (A n ) and stomatal conductance (g s ), and other foliar and canopy traits. The isohydric S. psammophila had a similar A n and a higher g s than the anisohydric C. korshinskii under drought treatment in 2015, inconsistent with the view that photosynthetic capacity of anisohydric plants is higher than isohydric plants under severe drought. The two shrubs differently responded to precipitation manipulation. Ψ pd , A n and g s were higher under irrigation treatment than control for S. psammophila, and these three variables and Ψ md were significantly higher under irrigation treatment and lower under drought treatment than control for C. korshinskii. Leaf water potential and gas exchange responded to manipulated precipitation more strongly for C. korshinskii than for S. psammophila. However, precipitation manipulation did not alter the sensitivity of leaf gas exchange to vapor-pressure deficit and soil moisture in these two shrubs. Acclimation to long-term changes in soil moisture in these two shrubs was primarily attributed to the changes in leaf or canopy structure rather than leaf gas exchange. These findings will be useful for modeling canopy water-carbon exchange and elucidating the adaptive strategies of these two shrubs to future changes in precipitation.

Hydraulic trade-off and coordination strategies mediated by leaf functional traits of desert shrubs

“…Additionally, desert shrub species are more resistant to embolism (more negative P 50 ) owing to their ability to tolerate very negative water potentials ( Lopez et al., 2005 ). Thus, they have higher xylem hydraulic safety margins that can avoid mortality triggered by short-term drought ( Xu et al., 2011 ; Li et al., 2020 ). Unquestionably, the variation in morphological and physiological characteristics of desert plants results from life history strategies shaped in long-term adaptation to drought conditions and are the main reason for their survival in harsh desert habitats.…”