The Decomposition Of Livestock Dung And Dominant Plant Litter In A Typical Steppe Of Inner Mongolia

The synthesis and decomposition of organic matter is a pair of basic processes of the material cycle in ecosystems.Decomposition process includes the fragmentation of dead organic matter,the release of carbon into the atmosphere,and the release of nutrients into soil for plants and microbial production.The decomposition of plant litter and animal dung is the key process of nutrient cycling in grassland ecosystem.It is vitally important to understand and quantify these processes and their responses to environmental and management changes for predicting grassland dynamics under climate and land use changes and helping to develop better management.Many studies exists on the decomposition of grass plant litter and animal feces,but most of them are separately done for either plant litter or animal feces.In natural grassland ecosystems,plant litter and animal feces are mixed as the soil surface organic matter.There is still a lack of knowledge on whether the decomposition process of animal feces and plant litter interacts.There has been a long history of livestock grazing in the typical steppe grassland of Inner Mongolia,but no studies so far have been done on the interactive effects of livestock dung and plant litter in their decomposition.Except for herbivorous(cow,sheep and horse)dung addition,how did the different addition amount of dung affect litter decomposition,addition amount and litter species and its interaction affect litter and dung decomposition and nutrients release?We designed an in-situ decomposition experiment and used litterbags to measure the decomposition processes of plant litter of two dominant steppe species and the dung of three livestock species,putting them separately or in combination in the grassland.That is,the experiment included 2 plant treatments(Leymus chinensis and Stipa grandis),3 dung treatments(cow,horse and sheep),and each dung treatment had two levels of dung amount;each treatment is replicated 5 times.The experiment started in June 2018,we determined the mass loss and chemical composition of litter and dung at the time of decomposition for 2 months,4 months,12 months,and 15 months.Our aims were to test the effects of litter quality,dung types,and different addition amounts of dung on the litter and dung decomposition and nutrient release,and their interactions.The main findings were as follows:(1)The litter N content was positively correlated with litter decomposition rates and nutrient release(P<0.001).Both C/N and lignin/N were negatively correlated with litter decomposition rates and nutrient release,respectively(P<0.01).The decomposition rate and nutrient release of Leymus chinensis was greater than Stipa grandis.(2)Dung addition promoted the mass loss and nutrient release of plant litter.The promotion effect of cow dung was the strongest,and that of sheep dung was the weakest,and that of horse dung was in between.The dung effect decreased with time.(3)The N contents in dung was positively correlated(P<0.001),whereas the hemicellulose,cellulose and lignin contents,as well as C/N and lignin/N were negatively correlated(P<0.05),with the decomposition rate.The decomposition rate and nutrient release of horse dung were the fastest,followed by cow dung and sheep dung.Plant litter had no significant effect on the decomposition rate of dung(P>0.05).(4)No significant effects of the litter,dung or their combination on the enzyme activities and total carbon and total nitrogen content of the soils underneath them during the decomposition time(P>0.05).This study has deepened our understanding of the decomposition processes in grazed grassland ecosystems,and provided fundamental information for quantifying nutrient cycling rate and improving nutrient management of grassland ecosystems.