Biophysical factors affecting transpiration of typical afforestation species under environmental change in the Loess Plateau, China

Abstract

Transpiration in artificial forests has a vital role in the ecohydrological cycle and evolution of afforestation in semi-arid regions. However, further research is required to understand the impacts of biotic and abiotic factors on transpiration and water regulation strategies in tree species under climate change. We used the sap flow method to quantify transpiration in three adjacent plantations (Pinus tabuliformis, Populus simonii, and Ulmus pumila) spaced 40 m apart, and concurrently monitored soil moisture and meteorological variables. Significant differences in average transpiration were observed in the following order: P. simonii (1.31 ± 0.49 mm d^–1) > U. pumila (1.04 ± 0.45 mm d^–1) > P. tabuliformis (0.75 ± 0.31 mm d^–1), due to differences in the canopy conductance, which followed the order of P. simonii (2.02 ± 0.18 mm s⁻¹) > U. pumila (1.70 ± 0.15 mm s⁻¹) > P. tabuliformis (1.26 ± 0.11 mm s⁻¹) (P < 0.05). Under severe soil water stress, high vapor pressure deficit, and high solar radiation, transpiration was reduced in all species during the drought period in 2022 because of reduced canopy conductance (P < 0.05). Our findings demonstrate that a fast growth rate, deep root systems, and close relationships between the leaf water potential and stomatal regulation are vital strategies for trees responding to drought. Consequently, we recommend P. simonii for shelter forests and P. tabuliformis for ecological landscape forests to improve the stability of afforestation in semi-arid regions.