Effects Of Soil Water Stress On Carbon-water Coupling In Ecosystems

As the main source of direct water supply in the ecosystem,Soil in terrestrial system plays an important role in the utilization of carbon reservoir.In addition,the warming and the rise of carbon dioxide concentration cause global climate change,the land-atomosphere feedback process intensifies,and the coupling process of the global carbon and water flux cycle changes.The quantification study of water stress and carbon and water flux coupling directly involves the development state of large carbon cycle and water cycle,but there is little research data on this aspect.In this study,based on the characteristics of obvious savanna dry and wet season differences in long-term monsoon precipitation formation,Using soil moisture data,meteorological factor data and energy flux data at six fluxtower sites in the Australian-New Zealand Flux Research Observation Network(ozflux)and the Australian Superstation network.Using combining the Montieth GPP model,LUE-EF model and Penman-Montieth model to simulate the carbon and water flux flux and carbon and water flux coupling state(water utilization efficiency)under ideal water conditions,to understand the effect of water restriction on carbon and water flux coupling,Combined with the soil moisture data,So as to explore the way of carbon and water flux coupling under soil water stress;The fitting slope parameter(WUE ε)of carbon and water flux coupling and carbon and water flux flux are used to understand the long-term utilization of carbon and water flux coupling under the soil water stress condition;Finally,through path analysis and Pearson correlation analysis,we can understand the difference of water and carbon flux coupling with water limitation caused by soil water stress and the relative differences of related influencing factors.The main findings of this study are as follows:During the soil.water stress period,the soil water is in a low and stable dynamic balance due to the low annual precipitation supply.The low stability dynamic soil water balance will further promote the role of soil water in stomatal limitation,and under the annual precipitation of higher soil water ecosystem more reflects the role of VPD in stoma limitation,and VPD and soil water during water stress show higher negative correlation,to some extent indirectly weaken the role of soil moisture in stomatal conductivity control.Soil moisture stress increases the control of soil water on evapotranspiration restriction,especially in arid sites(AU-ASM site and AU-Sturt site)showing high sensitivity to soil moisture.Compared with evapotranspiration restriction,soil water stress has a more obvious effect on the primary productivity of GPP ecosystems,especially in arid savanna sites(AU-ASM and AU-Sturt sites),where the actual photosynthetic yield coefficient is relatively low.(3)Long-term soil moisture dynamics in ecosystems affect the relative utilization forms of carbon-water coupling(partial water use water use efficiency and partial water dissipation water use efficiency),and the wet sites Au-Dap,AU-Das and AU-How with higher soil moisture dynamics all have higher WUE ε(partial water use water use efficiency),while the overall lower soil moisture dynamics show lower WUE ε(partial water dissipation water use efficiency).In addition,WUE ε has seasonal characteristics at each site,with soil moisture and precipitation likely to be the main influencing factors.(4)Soil water stress increases the degree of control of water use efficiency by GPP changes at sites with relatively high primary productivity in ecosystems.In addition,at sites where the dynamic change of soil moisture as a whole is lower,GPP tends to have a higher control effect on water use efficiency than the evapotranspiration limit.The overall coupling of carbon and water flux fluxes decreased based on the increased effects of soil moisture stress.(5)The influence factor of water restriction(VPD and soil moisture)has a high negative correlation on the daily scale,and this directly leads to the presence of two restrictions during soil moisture stress.There are differences in the effects of the two water restrictions on the carbon flux,with the VPD controlling the water use efficiency mainly by evapotranspiration,while the soil water control efficiency by the primary productivity of the ecosystem(GPP).VPD(atmospheric moisture deficit limiting)has a greater impact than soil moisture restriction during periods of soil moisture stress.At sites where soil moisture is relatively low,water use efficiency is mainly affected by the leaf area index,temperature,and finally the water limiting factor effect.Based on the influence of water limitation(VPD limitation and soil water limitation)and related influence factors(leaf area index and temperature),the variation of the carbon and water flux coupling,and understand the water utilization difference and the water utilization efficiency limitation,so as to provide reference for the interpretation of carbon and water flux cycle dynamics and their coupling strength differences under drought mechanism.The results are helpful to understand the carbon and water flux cycle mechanism of typical terrestrial ecosystems under global climate change,and they are of great significance in dealing with arid malignant climate change,increasing the availability of carbon and water,improving ecological performance,formulating effective sustainable development strategies and measures,and improving and protecting ecological resources.