Construction Of An Alpine Meadow Root Water Uptake Model And Its Application On The Qinghai-Tibetan Plateau

Alpine meadows are a unique vegetation type on the Qinghai-Tibet Plateau and play a vital role in maintaining the stability of the ecological environment and ecosystem services in alpine regions.Under the influence of climate change and human activities,alpine meadows on the Qinghai-Tibet Plateau show a certain degree of degradation.The key to plant growth lies in the utilization of water,and an accurate grasp of the water absorption capacity of plants will help to protect and restore the alpine meadow ecosystem in a reasonable way.At the same time,climate change has also caused changes in the water cycle processes of ecosystems.Quantifying the water use capacity of the root in the profile is essential for understanding the water balance of the Qinghai-Tibet Plateau ecosystem under climate warming conditions and for sound water management policies.In this paper,the Nagqu watershed was used as the basis of research and field monitoring sites were established.Five main experiments were carried out at each site,including soil sample collection,aboveground biomass measurement in alpine meadows,root growth dynamics monitoring,continuous observation of soil temperature,humidity and water potential,and determination of soil hydraulic conductivity and saturated hydraulic conductivity.We collected and compiled a large amount of data on meteorology,soil physical and chemical properties,root distribution,aboveground biomass,and soil saturation hydraulic conductivity,and used them to construct a root water uptake model suitable for alpine meadows and to analyze the mechanism of plant and soil effects on root water uptake.The main results are as follows:（1）The optimal root water uptake model for alpine meadows was evaluated.The performance of the model was judged by RMSE and moisture variation,and it was found that the model performance of the Selim-Iskandar model was stronger than that of the improved Feddes model and Molz-Remson model,and its simulation performance was improved by40.55%and 6.83%compared to the other two model distributions.Therefore,the Selim-Iskandar model is more consistent with the actual soil moisture variation while taking into account soil and root factors.（2）The key water uptake root indexes were identified.The root tip density function more accurately reflected the water uptake pattern of the root,and the simulated performance of the root water uptake model established with root density as an effective water uptake root index was improved by 24.64%on average compared to root length density.Therefore,the model is more consistent with the actual situation of soil water change trend while considering the actual physiological situation of plant water uptake.Accordingly,the root water uptake pattern of alpine meadows in the Nagqu watershed was obtained,and the root water uptake rate increased by 30.24%on average during the regreening stage compared with the wilting stage,while the top 67%of the rhizosphere took up 86.76%of the total root water uptake on average.（3）The distribution of aboveground biomass and root water uptake rate in alpine meadows on the Tibetan Plateau was simulated.The aboveground biomass was below 100 g.m^-2 in most areas during the regreening and wilting stages,and the annual growth rate was concentrated at±5 g.m^-2.a^-1.The variation from regreening stage to wilting stage was mainly concentrated at±40 g.m^-2,accounting for 99.10%of the total variation range.The distribution characteristics of root water uptake rate in alpine meadows on the Qinghai-Tibet Plateau during the two key phenological stages showed that the area where the regreening stage was larger than the wilting stage occupied 78.06%of the Qinghai-Tibet Plateau on average,while the root water uptake rate at different depths increased by 35.38%on average during the regreening stage compared to the wilting stage.This study will address the methodological vacancy of quantitative calculation of root water uptake rate in alpine meadows,contribute to the development of root water uptake model,clarify the distribution characteristics of root water uptake rate in soil profile,and understand the influencing factors and influence mechanism of root water consumption in alpine meadows.The results of the study can provide theoretical references for the sustainable development of the Tibetan Plateau and suggest feasible suggestions for the local ecological restoration.