Effects Of Grazing On Nitrogen Availability In Grasslands With Different Plant Diversity In Context Of Nitrogen Deposition

Nitrogen(N)is an essential nutrient for plants and animals,and N may be a critical limiting factor of productivity in many grasslands.The nitrogen which terrestrial plants take up is mainly from soil organic mineralization.Large herbivores are key drivers of N mineralization in ecosystems worldwide.It has been widely studied that effects of herbivore grazing on grassland nitrogen cycling of grasslands.However,currently increasing global changes including atmospheric nitrogen deposition and declining plant diversity and so on,might exert a strong effect on nitrogen cycling in grassland.Therefore,the effects of herbivore grazing on the mineralization of nitrogen in context of global changes will be confronted a new challenge.It’s of important significance to maintain function of grassland ecosystem and manage the grassland on studying the interaction effect of herbivores grazing,plant diversity and nitrogen deposition on soil nitrogen availability.The major pathways through which large herbivores affect the soil nitrogen mineralization rates are foraging,trampling and faeces/urine deposition.Herbivore foraging behavior is the most complex and un-deterministic factors that affecting soil nitrogen mineralization.In the long term,diet selection by herbivores can shape the plant community structure and composition,which may either enhance or reduce overall plant litter quality and decomposability.Herbivores also can effect on soil N availability through altering the quantity of resources that are transferred to soil due to changes in root exudation patterns in the short term.Here we studied the short-term effect of sheep grazing on grassland soil nitrogen availability in different plant diversity and simulated nitrogen deposition background.The study revealed the principle of soil nitrogen mineralization rate in response to livestock foraging within 14 ds.We also analyzed the regulatory mechanism by the altered plant diversity and simulated nitrogen deposition affecting livestock foraging effects on soil N availability.We acquired the main findings as follows:1)The influence of grazing on soil nitrogen availability depends on the different levels of grassland plant diversity and nitrogen addition.At low plant diversity,the effect of sheep grazing had no significant effect on soil nitrogen availability.While the soil nitrogen availability was significantly reduced by sheep grazing when simulated nitrogen deposition was present.However,at high plant diversity,sheep grazing had no influence on soil nitrogen availability,even though in the presence of simulated nitrogen deposition.2)Simulation nitrogen deposition can strongly impact the effects of livestock grazing on soil nitrogen availability,while plant diversity had no effect.However,the interaction between plant diversity and nitrogen deposition changed the effect of grazing on soil nitrogen availability.Under the background of plant diversity losses and atmospheric nitrogen deposition,the short-term effect of livestock grazing on soil nitrogen mineralization rate,mainly occurred in 0-7 d.3)The interacting effects between livestock grazing and nitrogen deposition on soil nitrogen availability were regulated by the plant diversity.At low plant diversity,the interaction effect between grazing and nitrogen deposition to soil nitrogen availability was significantly,but not at high plant diversity.Based on the above analysis we can conclude that,foraging behavior of sheep did not affect soil nitrogen mineralization rate in short-term in the grassland where L.chinensis is dominant plants,Whereas,the atmospheric N deposition can urge livestock foraging to exert a short-term negative effect on soil nitrogen availability.But high plant diversity can offset the negative effect.This study indicated that protecting plant diversity is very important to maintain ecosystem stability and improve the resistance of grassland ecosystem.