Biophysical regulations of transpiration and water use strategy in a mature Chinese pine (Pinus tabulaeformis) forest in a semiarid urban environment

Abstract

Urban trees and forests provide multiple ecosystem services for urban dwellers. However, forest water use for these benefits has become one of the critical concerns in dryland regions where water is limited. Negative forest water use impacts could be reduced by selecting tree species with low rates of transpiration. However, the possible changes of urban tree transpiration and its biophysical controls are still unclear. This study monitored the sap flow of a 58‐year‐old Chinese pine (Pinus tabulaeformis) plantation in a semiarid urban environment of northern China. Soil moisture played an important role in stand transpiration (Ec). Ec had a strong positive relationship with vapour pressure deficit (VPD) and solar radiation (Rs) when soil water was sufficient. In addition, the sensitivity of leaf stomata to VPD was not related to leaf and branch water potential. Under soil water stress, Ec was significantly reduced by 63.1% (p < 0.001) and was weakly related to VPD and Rs. Canopy conductance (gc) was reduced (p < 0.001) by 74.3% due to leaf stomatal closure, and the sensitivity of leaf stomata to VPD was significantly increased (p < 0.05) with increasing leaf and branch water potential. Wind speed had no significant effects on Ec. P. tabulaeformis tended to be isohydric with a relatively constant midday leaf water potential (i.e. −2.46 to −2.92 MPa) and strong stomatal regulation as a function of soil water stress. However, slopes (0.53–0.56) of the linear relationship between m (dgc/dlnVPD) and reference canopy conductance were significantly lower than the widely recognized 0.6 (p < 0.001). Therefore, urban tree transpiration drivers and forest impacts need to be clarified to better understand the proper tradeoff between water consumption and ecological services for urban areas.

The Seasonal Variability and Environmental Factors Influencing the Transpiration of Western Juniper (Juniperus occidentalis) Saplings

“…Many environmental variables, including soil moisture, soil temperature, air temperature, solar radiation, relative humidity, vapor pressure deficit, and precipitation, help explain the process of plant transpiration [8]. Different studies have indicated that soil moisture plays an important role in transpiration [9][10][11]. Other studies [8,12] have reported that tree transpiration was closely related to changes in solar radiation and vapor pressure Hydrology 2023, 10, 232 2 of 14 deficit.…”

Increased uptake of deep soil water promotes drought resistance in mixed forests

“…Besides, drought conditions change the water potential at the leaf surface and the atmospheric interface, disrupting water Plant Cell Environ. 2023;46:3218-3228. wileyonlinelibrary.com/journal/pce penetration between the soils and foliar, thus, blocking water transportation from the root to the leaves (Anderegg et al, 2019;Chen, Chen, Xu, et al, 2022). Zhang et al (2022) showed that shallow roots absorb less water when SWC is low, reducing the sap flow (SF).…”

“…Drought stress modifies hydraulic characteristics and causes xylem embolism under negative pressure, forming cavitation and duct blockage. Besides, drought conditions change the water potential at the leaf surface and the atmospheric interface, disrupting water penetration between the soils and foliar, thus, blocking water transportation from the root to the leaves (Anderegg et al, 2019; Chen, Chen, & Kong, 2022; Chen, Chen, Xu, et al, 2022). Zhang et al (2022) showed that shallow roots absorb less water when SWC is low, reducing the sap flow (SF).…”

“…Chen, Helliker, et al (2020) and Chen, Wang, et al (2020) stated that Quercus ilex implements strict stomatal control on transpiration, but its hydraulic conductivity is low in the absence of rain. Notably, stomatal control of transpiration can optimize plant water use and reduce the damage caused by drought (Chen, Chen, & Kong, 2022; Chen, Chen, Xu, et al, 2022). Thus, this mechanism maintains a constant and optimal transpiration rate, maintaining the water potential of plants above the critical level (González‐Rebeles et al, 2021).…”