Transpiration characteristics and biophysical response of Pinus tabuliformis plantations on the Loess Plateau of northern China under different precipitation gradients

Objective The Loess Plateau is characterized by uneven precipitation distribution, with frequent seasonal droughts. This study aims to explore the characteristics of transpiration and the biophysical regulation mechanisms in response to drought of Pinus tabuliformis plantations by setting up different precipitation gradients. The findings were expected to provide practical insights for the management of P. tabuliformis plantations and the rational allocation of water resources in this region.

Method Taking the P. tabuliformis plantations on the Loess Plateau as the research object, the thermal dissipation probe (TDP) technique was employed to monitor the transpiration process of P. tabuliformis under different precipitation gradients. Meanwhile, meteorological factors and soil water content were synchronously measured to analyze the biophysical regulation mechanisms of P. tabuliformis in response to drought.

Result (1) Rainfall reduction treatment significantly decreased soil water content. At the hourly scale, the transpiration rate of P. tabuliformis showed a single-peak pattern, consistent with the diurnal rhythm of transpiration-driving factors; at the seasonal scale, the transpiration rate of P. tabuliformis exhibited a relatively large variation amplitude under high moisture conditions. At both scales, rainfall reduction led to a decline in transpiration rate. (2) Under different precipitation conditions, the daily transpiration of P. tabuliformis was comprehensively regulated by meteorological factors, among which solar radiation and vapor pressure deficit were the main environmental driving factors. (3) Rainfall reduction treatment not only decreased the canopy conductance of P. tabuliformis but also weakened the sensitivity of canopy conductance to vapor pressure deficit. However, under different precipitation conditions, P. tabuliformis in the sample plots still maintains a strong stomatal regulation capacity.

Conclusion Rainfall reduction significantly reduces the transpiration rate of P. tabuliformis. In addition to the main environmental factors (solar radiation and vapor pressure deficit), P. tabuliformis relies on strong stomatal regulation to control transpiration, thereby enhancing its adaptability to drought conditions. The conclusions of this study are conducive to deepening the understanding of variation law of transpiration water consumption process of P. tabuliformis plantations under drought conditions.