Water and Heat Flux Characteristics of Alpine Wetland and Alpine Steppe under Grazing Enclosure on the Northern Xizang

Grazing enclosure has been extensively employed as a direct and effective management measure for grassland restoration on the Qinghai-Xizang Plateau.Enclosures significantly increased vegetation coverage and affected the water and heat exchange between the land surface and the atmosphere.However， there is still a lack of quantitative research on how enclosures regulates water and heat fluxes in typical alpine ecosystems.Based on continuous data observed from eddy covariance system from July 2019 to June 2021 at alpine steppe and alpine wetland of the Northern Xizang， the changes of surface energy flux after enclosure was analyzed by using the eddy covariance method.The results show that： The water and heat fluxes in alpine steppe and alpine wetland shows significant unimodal diurnal variations.The exchange of land-atmosphere in alpine steppe is mainly dominated by sensible heat （Bowen ratio： 1.60） except in Summer， while wetland mainly transfers energy to the atmosphere by latent heat （Bowen ratio： 0.31） whole year.Grazing enclosure decreased the surface fluxes in alpine steppe， the sensible heat flux reduced by 5.99 W·m-2 and the latent heat flux increased by 4.84 W·m-2.Grazing enclosures increased the surface fluxes in alpine wetland， the sensible and latent heat raised by 3.04 W·m-2 and 30.95 W·m-2， respectively.The daily and average sensible and latent heat fluxes decreased in alpine steppe but increased in alpine wetland.The effect of enclosure on surface energy fluxes was stronger during the day and weaker at night.The collected literature data demonstrated that fencing decreased soil temperature and increased soil water holding capacity.Given the data of soil temperature， soil moisture， latent heat flux， and sensible heat flux， our study shows the cooling potential of enclosure on alpine steppe and alpine wetland.