Characteristics of Canopy Conductance and Environmental Driving Mechanism in Three Monsoon Climate Regions of China

Abstract

Canopy conductance was an important index to measure the process of water exchange between canopy and atmosphere interface of forest ecosystem, as well as to judge the status of water use or the degree of drought stress. Therefore, the accurate estimation of forest canopy conductance was of great significance for the research of water-use efficiency. In the past, canopy conductance was measured on vegetation types in a single-point region, but there were few studies on systematic comparison in different climate zones. Based on the data sets of EC flux and conventional meteorological elements from the eddy covariance (EC) flux observation station during 2003–2010 in three typical climate zones (temperate continental monsoon climate zone, south subtropical monsoon climate zone, and mid-subtropical monsoon climate zone), Penman-Monteith model was used to calculate forest canopy conductance in different climate regions and analyze the dynamic changes of canopy conductance in different time scales. At the same time, combined with environmental factors including temperature, net radiation, soil water content, and vapor pressure deficit to explore their driving ability on the canopy conductivity of forest ecosystem in different climate regions, we finally explored the mechanism driving the canopy conductivity of forest ecosystem under different climates. The results showed that: 1) the driving ability of environmental factors in different climate regions to the canopy conductance was different, and the contribution rate of soil water content to the canopy conductance in subtropical monsoon climate zone was the largest. It was 36.01%, and the contribution rate of vapor pressure deficit to the canopy conductance in mid-subtropical monsoon climate region was the largest. It was 29.4% and the contribution rate of temperature to the canopy conductance in temperate monsoon climate region was the largest; it was 28.14%. 2). Temperature was an important factor limiting and driving canopy conductance, and there was a synergistic effect between water and temperature, which jointly drove the change in canopy conductance. 3) Environmental factors in different climate regions had threshold for the synergistic driving effect of canopy conductance. When the factors were within the appropriate threshold, the factors had a strong promoting effect on canopy conductance.

Predicting the canopy conductance to water vapor of grapevines using a biophysical model in a hot and arid climate

“…A subsequent analysis of g c obs , also showed a strong and significant correlation with the biophysical variables used in the proposed model (see Table 4). Similar results were referred by Monteith (1995); Wang and Leuning (1998); Irmak et al (2008); Lhomme et al (2012); Ding et al (2014) or Wu et al (2022). As indicated in Table 4, when considering all the variables used to calculate g c obs , it is worth noting that only measured wind speed, U, exhibited a weak correlation with the observed changes in canopy conductance (g c obs ).…”

“…significant impact of stomata on gas exchange, affecting both leaflevel transpiration (Chaves et al, 2016) and canopy-level transpiration (Irmak et al, 2008;Ding et al, 2014;Wehr et al, 2017;Wehr and Saleska, 2021;Wu et al, 2022).…”

“…The value of g c lies in its ability to elucidate the division of R n between latent heat and sensible heat fluxes (Monteith, 1995), thereby influencing plant transpiration. As the canopy acts to stabilize the considerable variability in g sw across individual leaves, g c offers a suitable spatio-temporal measure of stomatal response to soil water and atmospheric conditions within the boundary layer (Avissar, 1993;Damour et al, 2010;Fuentes et al, 2012;Wu et al, 2022). Consequently, it allows the identification of temporal and spatial patterns of water stress in the vineyard (Zhai et al, 2020).…”

Variation in canopy conductance of Cunninghamia lanceolata forest and its response to environmental factors after an extreme rainfall event

“…This variation pattern was consistent with previous studies' results on the daytime variation of g c , such as temperate Japanese cypress forest after wetness ended (Jiao et al, 2021), Eucalyptus crebra and Callitris glaucophylla forests (Whitley et al, 2009) and Eucalyptus globulus trees (Quentin et al, 2011) in arid Australia, experimental farm under drought and wet conditions in Japan (Nakano et al, 2015). When the temperature increased, the increase of the vapour pressure in the lower stomatal cavity was greater than that of the air vapour pressure, thus the increase of the VPD made the water escape in the leaves of plants and strengthened the transpiration rate (Wu et al, 2022). Trees regulated their sizes of stomata to control canopy transpiration in order to avoid excess water loss and maintain physiological homeostasis.…”

“…On the longer timescales such as daily and monthly scales, SWC and VPD were found as the critical variables to regulate g c (Ouyang et al, 2022; Zhang et al, 2017). Wu et al (2022) found that in subtropical monsoon climate regions, SWC contributed largely, while in mid‐subtropical monsoon climate regions, VPD dominated the variation in g c . Additionally, it was found that the increase in T a does not directly cause the decrease in g c , this may be due to the increase in T a leading to an increase in VPD (Tacarindua et al, 2013).…”