Effects Of Simulated Rainfall Reduction On Litter Decomposition In A Robinia Pseudoacacia Plantation In Sub-humid Loess Region

Litter is an important component of ecosystem productivity.Litter decomposition is a key process in the material cycle of ecosystems.This process is affected by soil moisture.Soil moisture in the Loess Plateau is strongly dependent on rainfall recharge.Under the background of global change,there is a trend of further reduction in rainfall in the Loess Plateau.It is of theoretical and practical significance to explore the response of litter decomposition to rainfall reduction in the Loess Plateau.This study took Robinia pseudoacacia plantation in the semi humid region of the Loess Plateau as the research object.A 30% isolated rainfall treatment sample plot and a non reduced rainfall control sample plot were set up in the forest to continuously monitor soil moisture and temperature in various plots.In the fourth year of rain reduction treatment,two treatment zones,namely,the non root zone and the fine root zone,were set up in each sample plot to shield the roots.A one-year litter decomposition experiment was conducted using the decomposition bag method.By regularly measuring the residual mass of litter,the activities of five enzymes in the litter layer,and the content of soil organic carbon(SOC),total nitrogen(TN),and total phosphorus(TP).The effects of soil water content and fine roots on litter decomposition rate were studied.The variation characteristics of soil enzyme activity,soil nutrient content,and C/N/P ecological stoichiometry during litter decomposition were analyzed.The relationship between litter decomposition rate,soil enzyme activity,and soil nutrients was revealed.The main conclusions are as follows:(1)There was no significant difference in soil temperature at 10 cm between the treated and control plots.The decrease of rainfall decreased the soil water content of each soil layer.During the growing season,the soil water content at 10 cm of the treated sample plot was significantly lower than that of the control sample plot(P<0.05).Under the condition of removing litter,there was no significant difference in the soil SOC,TN,and TP contents between the treated and control plots.The soil SOC,TN contents decreased significantly at first and then increased significantly during the growth season.There was no significant difference in TP content.(2)In the area with fine roots,the mass loss rates of litter in the treatment and control plots were 39.29% and 43.63%,respectively.The litter decomposition coefficient(0.71)in the control plot was significantly higher than that in the treatment plot(0.61)(P<0.05).In the control plot,the mass loss of litter in the area with and without fine roots was 43.63% and42.46%,respectively,and the difference in litter decomposition coefficient was not significant(0.71 and 0.69).Rainfall reduction significantly inhibited the decomposition of litter in the Robinia pseudoacacia plantation,while short-term sheltering of fine roots had no significant impact on litter decomposition.(3)Reduced rainfall significantly reduced the activities of sucrase and catalase during the decomposition process of litter,increased the activity of polyphenol oxidase(P<0.05),and had no significant effect on alkaline phosphatase activity.The treatment without fine roots significantly reduced the activities of sucrase,alkaline phosphatase,and catalase during the decomposition process of litter,and significantly increased the activity of polyphenol oxidase(P<0.05).The changes in rainfall and the presence or absence of fine roots have significant effects on urease activity at different stages of litter decomposition,but there is no clear pattern.(4)There were no significant differences in SOC,TN,TP,C/N,N/P,and C/P.There were no significant differences in SOC,TN,TP,C/N,N/P,and C/P between the treated and control plots,indicating that soil moisture had a small impact on soil nutrients in this study;In the same field,the SOC,TN,N/P,and C/P in the zone with fine roots were significantly higher than those in the zone without fine roots(P<0.05),indicating that fine roots were the main factor affecting soil nutrient content.(5)Plant fine roots can affect the correlation between litter decomposition rate and alkaline phosphatase activity,and there is a significant negative correlation between litter decomposition rate and catalase activity.The correlation between soil nutrient content and soil enzyme activity is regulated by soil moisture and plant fine roots.Overall,the relationship between litter decomposition rate,soil enzyme activity,and soil nutrient content varies with changes in soil moisture and fine roots,and the effects of other forest environmental factors are not excluded.