Physiological responses of a black locust plantation to drought stress based on a throughfall exclusion experiment in semi-arid northwestern China

Abstract Drought poses a significant threat on the ecosystem stability of extensive areas of black locust (Robinia pseudoacacia L.) plantations in northwestern China. However, limited understanding of the physiological responses of black locust to drought has impeded the development of proactive measures to alleviate potential adverse effects of drought. This study investigated the physiological impacts of varying drought intensities, manipulated by a throughfall exclusion experiment, on a 20-year-old black locust plantation in northwestern China. The experiment involved 40% throughfall exclusion for moderate drought, 80% exclusion for extreme drought, and no exclusion for control. One year after the implementation of the experiment, both predawn (Ψpd) and midday (Ψmd) leaf water potentials were significantly lower under drought treatments compared to those in control (P < .01). Stomatal conductance (gs) exhibited a strong reduction, leading to decreased leaf transpiration and photosynthesis under drought. However, the reduction in gs did not effectively prevent the decrease in Ψmd. Instead, both Ψpd and Ψmd became more negative with increasing drought stress, but their difference remaining relatively constant (being ~1.1 MPa) across treatments. These results suggest that black locust adopts a balanced water regulatory strategy between isohydry and anisohydry to cope with drought stress. These results contribute to an enhanced understanding of the crucial physiological responses of black locust under drought stress, offering valuable insights for future management strategies aimed at sustaining the ecosystem stability of black locust plantations in an increasingly arid climate.