Effects Of Simulated Warming And Nitrogen Addition On Soil And Plant Nutrient In Subtropical Chinese Fir Plantation

Soil nutrient plays an important role in plants growth and development,affecting plant community composition and vitality,as well as the structure,function and productivity of ecosystem.Availability of soil nutrient is closely related to soil parent materials,management mode and climate type.Climate change alters biogeochemical cycle process of nutrients by influencing soil moisture,aeration,temperature and fertilizer,which certainly would make a difference to soil nutrients availability and plant nutrient uptake.Therefore,it is of great significance to study the effect of climate change on nutrient cycling in forest ecosystems.As two important aspects of global change,warming and nitrogen deposition bring a lot of uncertain effects to nutrients cycle in terrestrial ecosystem.Current research usually focused on soil macronutrients like carbon(C),nitrogen(N),phosphorus(P),which is of great demand for higher plants.However,there is relatively few studies pay attention to micronutrients that necessary for higher plants,as well as a indicator of soil and plant health.In addition,the effect of warming on soil nutrient availability and plant nutrient uptake in tropical and subtropical forests has not been reported;neither do warming and nitrogen deposition interaction.Therefore,based on Forest Ecosystem and Global Change Research Station in Chenda Town,Sanming City in Fujian Province,we set up experiment to study the effects of warming,nitrogen deposition and their interactions on nutrients of soil and plants in subtropical Chinese fir plantation by measuring the nutrient availability,and the total nutrient concentration of soil and plant.The response of regional limiting nutrient--phosphorus to warming and nitrogen deposition was emphasized,and the corresponding mechanism was discussed in our study,in order to provide the theoretical basis for forest soil nutrient management under the condition of future climate change.The main results of our study were as follows:(1)Warming treatment affecting soil microbial activity and phosphorus uptake of Chinese fir by changing soil temperature and moisture,thus altering the soil P composition.In warming treatment,soil available Pi and labile Pi had significantly increased 81%and 24%,but soil microbial phosphorus(MBP),soil acid phosphatase,fine root P and leaf P concentration had significantly decreased 24%,51%,29%and 19%,respectively.The result suggested that short-term warming may increase soil phosphorus availability by reducing P immobilization of soil microbe and P uptake of Chinese fir,but the significant warming-induced decrease of MBP which is potentially available for plants is likely to exacerbate the regional P limitation.(2)There are no significant effects of nitrogen addition on soil P fractions,but the downtrend of soil MBP,the significant decrease of leaf P concentration and the uptrend of leaf biomass P indicated that Chinese fir may be limited by nitrogen,and nitrogen addition had promoted its growth,which is conductive to the absorption of P.(3)Labile Pi and Slow Pi under warming x nitrogen addition treatment had significantly increased 33%and 20%,meanwhile,total extractable inorganic P and soil total P also presented the same trend.Warming x nitrogen addition treatment had no effects on fine root P and leaf P concentration,while leaf biomass P had showed a downward trend.The results showed that the warming effect was the main effect of warming x nitrogen addition treatment,P uptake and the plant growth was inhibited by treatment.(4)Warming significantly increased fine root Ca concentration and soil available K;decreased fine root Na concentration;had no effect on leaf base nutrient concentration.Nitrogen addition had decrease leaf K concentration,while availability of soil base nutrient was not significantly affected.Warming x nitrogen addition treatment had decreased leaf K,fine root Na,soil available Ca and available Mg concentration;whereas soil available K and Ca concentration of leaf and fine root was increased by treatment.These results indicated that the responses of each base nutrient to warming and nitrogen addition were different.Besides,warming and nitrogen addition changed the soil K,Ca,Na,Mg availability through affecting their uptake by plants and the nutrient return of litter.(5)Warming treatment significantly decreased fine root Cu and Mo concentration,but had no significant effect on leaf micronutrients concentration and availability of soil micronutrients.Leaf Zn and Ni concentration under nitrogen addition treatment increased significantly,while leaf Fe concentration had decreased.Availability of soil micronutrients was no affected by nitrogen addition treatment.Similarly,soil micronutrients availability had no significant change under warming x nitrogen addition treatment,but Cu,Zn,Ni Mn concentration of leaf increased significantly,while fine root Cu,Mo,Mn and leafFe concentration had opposite trend.These results demonstrated that different micronutrients were affected by treatments in different ways.Among the micronutrients,Fe may be more sensitive to warming and nitrogen addition since leaf Fe had showed downward trend in other three treatments compare with control treatment.Fe has the possibility of becoming a limiting nutrient in the context of future climate change.