Abstract
Understanding species-specific water use patterns across contrasting sites and how sensitivity of responses to environmental variables changes for different species is critical for evaluating potential forest dynamics and land use changes under global change. To quantify water use patterns and the sensitivity of tree transpiration to environmental drivers among sites and species, sap flow and meteorological data sets from three contrasting climatic zones were combined and compared in this analysis. Agathis australis from NZHP site, Schima wallichii Choisy (native) and Acacia mangium Willd (exotic) from CHS site, Liquidamber formosana Hance, Quercus variabilis Blume and Quercus acutissima Carruth from CJGS site were the dominant trees chosen as our study species. Biological traits were collected to explain the underlying physiological mechanisms for water use variation. Results showed that the strongest environmental drivers of sap flow were photosynthetically active radiation (PAR), vapor pressure deficit (VPD) and temperature across sites, indicating that the response of water use to abiotic drivers converged across sites. Water use magnitude was site specific, which was controlled by site characteristics, species composition and local weather conditions. The species with higher sap flow density (Fd) generally had greater stomatal conductance. Native deciduous broadleaved species had a higher Fd and faster response to stomatal regulation than that of native evergreen broadleaved species (S. wallichii) and conifer species A. australis. The analysis also showed that exotic species (A. mangium) consumed more water than native species (S. wallichii). Trees with diffuse porous and lower wood density had relatively higher Fd for angiosperms, suggesting that water use was regulated by physiological differences. Water use characteristics across sites are controlled by both external factors such as site-specific characteristics (local environmental conditions and species composition) and internal factors such as biological traits (xylem anatomy, root biomass and leaf area), which highlights the complexity of quantifying land water budgets for areas covered by different species.
Highlights
At landscape and regional scales, forest transpiration depends on a number of site-specific characteristics that are related to the physical properties of geology, soil type, vegetation and ambient meteorological conditions because of their influence on water and energy availability [5,6]
Rainfall was mostly concentrated from April to September, accounting for about 63%–73%, 77%–87%, and 85%–86% of total annual precipitation for New Zealand-Huapai temperate conifer forest (NZHP), China-Heshan subtropical evergreen broadleaved forest (CHS) and China-Jigongshan temperate mixed deciduous forest (CJGS)
Our study showed that water use responses to environmental factors were similar across sites, with vapor pressure deficit (VPD) and photosynthetically active radiation (PAR) playing the strongest role in driving transpiration
Summary
Transpiration, the process of water movement through a plant and release from the canopy is the most important component of evapotranspiration [1], integrating physical and biological processes within the energy, water and carbon cycles of ecosystems [2,3]. There are two main categories of factors that influence transpiration: environmental drivers conditions of the Creative Commons. At landscape and regional scales, forest transpiration depends on a number of site-specific characteristics that are related to the physical properties of geology, soil type, vegetation and ambient meteorological conditions because of their influence on water and energy availability [5,6]. The primary environmental drivers for forest evapotranspiration are solar radiation, vapor pressure deficit and soil moisture [6,7]. Rising atmospheric concentration of CO2 enhances photosynthesis, but elevated CO2 causes rising temperatures, and other climatic changes such as significant drought, causing worldwide forests mortality with atmospheric shifts continuing in the future [10]
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