Effects of nitrogen deposition on nutrient elements and coupling coordination in urban forest litter
At present,the increase of nitrogen deposition presents a global trend,affecting the biogeochemical cycle of forest ecosystem,and has become one of the hot topics in the international ecological and environmental research.To explore the effects of increased nitrogen deposition on the nutrient content of urban forest litter and fur-ther understand the nutrient cycling process in urban forests,so as to provide a scientific basis for the ecological risk assessment of regional urbanization processes,the litter of Shushan National Forest Park in Hefei,Anhui Province,China were selected to study after conducting a simulated nitrogen deposition experiment for three consecutive years(with three nitrogen addition levels:control group:0 kg·hm-2·a-1,CK;low nitrogen:50 kg·hm-2·a-1,LN;high nitro-gen:100 kg·hm-2·a-1,HN),for the purpose of examining the effects of nitrogen deposition on the nutrient element content and coupling of the urban forest litter(branches,leaves and fruits).The results showed that:(1)Under differ-ent nitrogen application levels,there were significant differences(P<0.05)in the carbon(C)content between CK and HN in the fruit litter,as well as in the nitrogen(N)content between CK and LN,and LN and HN in the leaf and fragment litter.(2)Among different litter components,nitrogen deposition significantly influenced the calcium(Ca)content(P<0.05),but it had no significant effect on the carbon content.There were significant differences(P<0.05)in the potassium(K)content among branch litter components,and significant differences(P<0.05)in N content between leaf litter and other groups,as well as significant differences(P<0.05)in phosphorus(P)content between the fruit litter and other groups.There was a significant difference in magnesium(Mg)content between the leaf litter and fruit litter.(3)Nitrogen deposition had no significant effect on ecological stoichiometric ratios such as C/N,C/P and N/P among different litter components,however,it significantly inhibited the C/N ratio in leaf and fruit litter(P<0.05).(4)Nitro-gen deposition significantly influenced the correlations between C and N,as well as Ca and Mg,showing that LN sig-nificantly enhanced the correlations,while HN significantly inhibited them.Nitrogen deposition significantly en-hanced the correlations between P and K,while it significantly reduced the correlations between K,Ca and Mg.(5)Nitrogen deposition had a significant impact on the coupling of C/N with N/P,and C/P with N/P,with LN significantly enhancing the coupling of ecological stoichiometric ratios,and HN significantly reducing the coupling.The results provide a theoretical basis for the response of nutrient cycling process of urban forest litter to nitrogen deposition.
nitrogen depositionurban forestlitternutrient elementcontent of carbon and nitrogen
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