Effects Of Soil Warming And Nitrogen Addition On Fine Root Nutrient Foraging Behavior Of Chinese Fir (Cunninghamia Lanceolata) Seedlings

Global climate change has a significant impact on terrestrial ecosystems forest carbon and nitrogen cycles,fine roots are very sensitive to environmental changes.In order to reveal the response of global warning and atmospheric nitrogen deposition to the nutrient foraging behavior of Chinese fir seedlings,a mesocosm experiment with a factorial design of soil warming and nitrogen addition(ambient,ambient + 40 kg·hm-2·a-1),was carried out in the Chenda State-owned Forest Farm in Sanming City,Fujian Province,China.Including four treatments:the control treatment(CT),the soil warming treatment(W,ambient+4?),the nitrogen addition treatment(N,ambient + 40 kg·hm-2·a-1)and the soil warming + nitrogen addition treatment(WN).We measured changes in root morphology,biomass,element stoichiometry property,fine,root respiration,non-structural carbon(NSC),mycorrhizal colonization rate,nutrient(N)absorption rate and fine root enzyme activity in Spring,Summer,Autumn.The results showed:(1)Soil warming has negative effect on fine root biomass in spring and autumn,but the RTD was increased.Plants increasing root SRL to increase nutrient,water forging in summer.Nitrogen addition reduces consumption of forge nutrients,decreased 0-1 mm fine root SRL in spring.In summer,nitrogen addition significantly increased biomass of fine root 0-1 mm to obtain more water and nutrients.The soil warming + nitrogen addition reduced the fine root biomass in spring;biomass was significantly higher than soil warming in autumn,indicate that the soil warming + nitrogen addition showed different morphological adaptation in different seasons with soil warming.(2)Soil warming,nitrogen addition and their interaction promoted the rate of fine root ammonium nitrogen absorption,increased the maximum value of fine root absorption of ammonium nitrogen,and there were seasonal differences.In summer,soil warming declined the affinity of fine root nitrogen absorption;In spring and Autumn,nitrogen addition declined the affinity of fine root nitrogen absorption,this may be related to the change of soil nutrient.The fine root absorption of nitrate showed biphasic absorption kinetics.The rate of absorption was much lower than ammonium nitrogen.In summer,the effect of soil warming and nitrogen addition on nitrate uptake was small.The absorption of nitrate was lower than the control in spring,which also indicated that plants had selectivity in absorbing and utilizing nitrogen,which would give priority to the utilization of ammonia nitrogen.(3)Soil warming increased the fine root N concentration in spring significantly,decreased fine roots C:N ratio;it had no significant effect on fine roots C,N concentration in summer and autumn.Nitrogen addition promoted fine roots absorption of N in spring,but had little effect in summer and autumn,it may be related to the season of seedling growing.Soil warming and nitrogen addition did not change the P concentration of soil and fine roots.The fine root N:P Ratio of all these treatments were smaller than the national average level,indicating that the fast-growing Chinese fir young trees may be more restricted by N.Soil warming significantly decreased the concentration of fine root starch and NSC in spring,fine root specific root respiration increased significantly,which indicated that the maintenance cost of fine root was higher,while nitrogen addition increased the storage of fine root starch and NSC in spring.A large amount of starch changed into soluble sugar in nitrogen addition in summer,and it is similar in soil warming.(4)Soil warming had no significant effect on the colonization of fine root,which may be due to the shorter time of warming or the smaller seedlings.There was no significant difference in community composition of AMF.Nitrogen addition significantly reduced fine root colonization in summer and autumn.Soil warming,nitrogen addition significantly increased AP activity in spring,but had no significant effect on NAG enzyme activity,it shows that the fine root has a strong demand for p element.These appeared opposite trend in autumn,It shows that fine root adjusts the absorption of N,P after soil warming and nitrogen addition.(5)The fine root NAG enzyme was correlated with the colonization rate of mycorrhiza,which may reflect the ability of fine root to obtain organic N in soil.The SRL is highly correlated with the AP enzyme,which may indicate the ability of fine root to obtain P.The fine roots biomass may be independent of other nutrient acquisition strategies.Vmax reflects that the absorption of N in the soil may also be independent of other nutrient acquisition strategies.There may be several independent and different strategies for the acquisition of nutrients of Chinese fir.This may also mean that there is no economic spectrum similar to leaves in fine roots.