Effects Of Soil PH Decrease On Decomposition And Chemical Component Changes In Litter Decomposition In A Tibetan Alpine Meadow

The Qinghai-Tibet Plateau,with an average altitude of more than 4000 m,harbors unique ecosystems and high biodiversity,and is very sensitive to climate and environmental changes.Due to low temperatures and slow litter decomposition,there is a large stock of soil organic carbon in the soil of the Qinghai-Tibet Plateau,which is an important organic carbon pool in China's terrestrial ecosystems.With global change and anthropogenic disturbance,ecosystems in the Qinghai-Tibet Plateau are increasingly threatened.In recent decades,due to excessive industrial activities and agricultural fertilization,atmospheric acid deposition has been increasing,resulting in soil acidification,particularly in most parts of Asia.In the Qinghai-Tibet Plateau,soil pH also shows a significant trend of decrease.Soil pH is a key driver of belowground ecological processes,including litter decomposition,and plays important roles in biogeochemical cycles.But we still know little about the effect of soil acidification on litter decomposition in alpine ecosystems.On the one hand,soil pH can influence decomposition through changing soil microbial abundance and activity;on the other hand,changes in soil pH can alter litter quality and thus change its decomposition.In addition,root biomass accounts for more than two thirds of total plant biomass in the Qinghai-Tibet Plateau,and the root systems can have large effects on litter decomposition through rhizosphere priming effect.Therefore,how environmental(soil pH)and biological(litter quality,live roots)factors can affect litter decomposition in the QinghaiTibet Plateau still needs to be studied,which can benefit our understanding of responses in ecosystem functioning decreasing soil pH conditions.Based on the Alpine Meadow and Wetland Ecosystem Research Station of Lanzhou University,field soil pH was manipulated through acid addition,and its effects on mass loss,nutrient release and lignin decay in the above-and below-ground litter decomposition were investigated with litter bags in this study.For aboveground litter decomposition,two factors were included,namely soil pH and litter source,to examine the effects of soil acidification and related changes in litter quality on leaf litter decomposition.For belowground litter decomposition,an additional factor(the presence or absence of live roots)was included to examine the effect of plant root growth on belowground decomposition.The main results of this study were as follows:(1)Decreased soil pH significantly inhibited the the decomposition of aboveground and belowground litter due to reduced microbial abundance and activity;(2)With slowed litter decomposition,contents of various elements of the litter also changed,particularly that the release of N was reduced;(3)Soil acidification altered chemical properties of plant litter,for example,the decrease in soil pH increased the nitrogen content of the aboveground litter,decreased the calcium and magnesium content of the aboveground litter,but increased the nitrogen content of the belowground litter,and increased the phosphorus,Calcium and magnesium content,there by reduced its decomposability,and thereby further inhibited litter decomposition;(4)The presence of living roots promoted the decomposition of plant litter,and to a certain extent alleviated the inhibiting effect of soil acidification on decomposition;at the same time,the plant root system will promote the decomposition of manganese and nitrogen in the plant litter,which will affect the litter nutrient composition of alpine meadow.In summary,soil acidification and pH-induced changes in litter properties jointly affected litter decomposition;moreover,plant roots played an important role in regulating litter decomposition in the Qinghai-Tibet Plateau.Reduced decomposition rates caused by soil acidification will reduce nutrient cycling,thereby limiting the primary productivity of the ecosystem.More attention should be paid to the effects of soil acidification on decomposition and soil fertility in future grassland management in the Qinghai-Tibet Plateau.