Effects Of Nitrogen And Water Addition On Soil And Plant Nutrients Of Artemisia Ordosica Community

Global climate forecasts suggest that future global atmospheric nitrogen deposition will continue to increase,meanwhile,rainfall in arid and semi-arid areas of northern China may also increase by 10～20%.This situation may affect plant nutrients use strategy,which in turn affect the structure and function of these ecosystems.However,in the case of increased nitrogen deposition and precipitation,it is not clear what response Artemisia Ordosica community will have,which is the largest and most typical plant community in the distribution area of the Mu Us Sandy land.In this study,the dominate vegetation A.ordosica community in the southwest margin of Mu Us sand land was studied,and we conducted a field experiment simulating three nitrogen addition levels(NO:0 kg N ha-1 yr-1,;N10:10 kg N ha-1 yr-1;N60:60 kg N ha-1 yr-1)and three water addition levels(WO:natural precipitation;W20:increase 20%precipitation;W40:increase 40%precipitation)from 2015 to 2017.The effects of nitrogen and water addition on soil environment and nutrient status of the two dominant plant leaves in A.ordosica community were analyzed.Moreover,the potential response mechanism of nutrient strategy of A.ordosica community to nitrogen and water addition was also investigated.The main research results and conclusions are as follows:(1)Nitrogen and water addition significantly improved the soil moisture and available nitrogen of A.ordosica community,but the effects on soil pH,organic matter,total nitrogen and total phosphorus were very limited.In addition,nitrogen addition had limited influences on soil base cations and trace elements(Fe,Mn),while water addition reduced the content of soil Ca2+,but had no impact on other trace elements(K,Fe,Mn).(2)Nitrogen and water addition had no significant effect on leaf C concentration,nitrogen addition significantly increased the N concentration and N:P of plant leaves,besides reduced the P concentration of Leymus secalinus and C:N of the two dominate plants.Water addition increased the leaf N concentration of A.ordosica and reduced the C:N,but the effect on L.secalinus was very limited.Nitrogen addition reduced the leaf Fe,Mn concentration of A.ordosica,while water addition reduced the leaf Fe concentration of A.ordosica,and the leaf trace elements of L.secalinus had no obvious response to nitrogen and water addition.(3)Soil Ca2+ can inhibit the absorption of phosphorus by plants,and there was a significant negative correlation between soil Ca2+and plant leaf P content,and a significant positive correlation with leaf N:P.Nitrogen addition directly affected the N:P of plant leaves,resulting in the change of the two dominant plants in A.ordosica community from N to P limit,and the increase of water indirectly reduced the N:P of plant leaves by affecting soil Ca2+content,which in turn,would mediate the phosphorus limit to a certain degree,and then promote the growth of plants.There was no significant correlation between leaf nutrient and soil nutrients,and the relationship between soil and plant leaf nutrients may be decoupled under the background of future climate change.The results show that the increase of nitrogen will lead to the change of the dominant plants of A.ordosica community from N to P limit,and the response of herbaceous grass,L.secalinus,to nitrogen addition will be stronger;And the increase of water will reduce the content of soil Ca2+,thus relieve the phosphorus limit to a certain extent,and promote the growth of plants.Our results imply that future environmental changes under the scenarios of increased precipitation and nitrogen deposition,nitrogen and phosphorus cycling and plant growth in A.ordosica community will be promoted,which in turn drive changes in the structure and function of ecosystems,thus having a profound impact on regional desertification.