Interpreting the water use strategies of plantation tree species by canopy stomatal conductance and its sensitivity to vapor pressure deficit in South China

Abstract

Stomatal regulation controls tree transpiration rate and is central to plant function. However, most previous studies that investigated the stomatal regulation of forest trees mainly focused on arid and semi-arid zones, uncertainty remains about how trees adjust their stomatal response to the changing environment in subtropical moist areas. In this study, we investigated the tree transpiration (El), canopy stomatal conductance (Gs), and Gs sensitivity to vapor pressure deficit (VPD) of four typical plantation tree species (Schima wallichii, Acacia mangium, Eucalyptus urophylla, and Cunninghamia lanceolata) in hilly lands of South China. Datasets including the continuously measured sap flow and meteorological parameters, as well as the physiological traits of the four species, were collected during the year of 2018. Our results showed that the coniferous C. lanceolata had significantly lower El, Gs, and weak sensitivity to VPD than the other three broadleaved species. We attributed the different water use and stomatal behavior to the various species-specific traits. The three broadleaved species generally possessed higher leaf area, specific leaf area (SLA), the ratio of sapwood area (As) to leaf area (Al), and deeper root depth, facilitating their transpiration and gas exchange. During the experimental period, a super typhoon “Mangkhut” hit the research site and caused substantial decline in leaf area, while the whole tree transpiration experienced slighter decrease, indicating the rapid compensatory effect of stomatal regulation. Moreover, the increased Gs sensitivity to VPD (m values) and reference Gs for the introduced A. mangium and E. urophylla in the dry season highlighted their ability to function well even under the much drier condition with no strict stomatal control. Our analyses on the response of Gs to the changing environment for typical species in the subtropical moist forests will provide important insights for forest management and ecosystem stability under future climate changes.