| Nitrogen(N) deposition is one of the major environmental issue that affects global climate change. It’s a hot spot about how N deposition impact on forest ecosystems. Atmospheric N deposition and soil phosphorus(P) limits is distributed mainly over a red soil hilly land of subtropical China. It is worthy of attention about how N deposition affects forest ecosystems in subtropical China. However N deposition effects on N P transformations and plant nutrient conent remain unclear. In the present study, a coniferous tree(Cunninghamia lanceolata) and a broadleaf tree(Liquidambar formosana) each 15 years of age were selected to evaluate in suit N deposition. Trees were treated with 10 g N m-2 a-1 and compared to the controi, in 2014, rhizosphere and bulk soils, fresh branches and leaves, roots for both tree species during growing season. During non-growing season, fresh and litter branches and leaves, roots for both tree species have been collected again. In 2015, rhizosphere and bulk soils, plant boby for 4 kinds of understorey vegetation during growing season. Soil available nutrients content, soil respiration, major enzyme activities and non-structural carbohydrates content were analyzed using the chemical extraction and biochemical methods. Try to reveal different species, ecological process underground and different plant organ response to N deposition. Main results are as follows:(1) N deposition significantly decreased soil p H and C. lanceolata rhizosphere soil available P(P<0.05); N deposition significantly decreased both the rhizosphere effects of NO3--N and the early OC mineralization rate in L. formosana, N deposition significantly increased OC mineralization rates in C. lanceolata rhizosphere and bulk soil by 71.2% and 41.2%, respectively; but decreased OC mineralization rates in L. formosana rhizosphere and bulk soil by 10.6% and 44.1%, respectively. N deposition significantly decreased both the rhizosphere effects of NO3--N and the early OC mineralization rate in L. formosana, but increased its late OC mineralization rate; whereas the rhizosphere effects of all measured variables in C. lanceolata showed no significant differences between control(CK) and N treatments.(2) N deposition generally increased total N nutrient content of both trees and total P nutrient content of C. lanceolata’s one-year-old leaves during growing season. According to N/P of leaves, N/P of CK and N treatments was 16.2 and 18.9 in C. lanceolata’s one-year-old leaves, 15.4 and 17.0 in C. lanceolata’s two-year-old leaves. While the L. formosana’s leaves N/P was 19.1 and 24.6, respectively. N deposition significantly decreased nutrient recycling efficiency in C. lanceolata branches and leaves N, P nutrient. In addition, N deposition significantly decreased soluble sugar consumption rate in C. lanceolata branches and leaves.(3) N deposition significantly increased NH4+-N and NO3--N content in Dicranopteris. dichotoma, Lophatherum gracile and Melastoma dodecandrum rhizosphere and bulk soil. For Woodwardia japonica, N deposition significantly decreased NO3--N and available P contents of soil by 29.9% and 30.0%, respectively. Compared with the control, the N treatment significantly increased β-1,4-glucosidase activities while did not cause significant changes in(leucine aminopeptidase and acid phosphatase activities.(4) For understorey vegetation stem leaf and root nutrient contents, N deposition significantly increased total N contents in D. dichotoma, L. gracile and M. dodecandrum. Compared with the control, the treatments of N deposition significantly decreased W. japonica stem leaf and root avaviable P content by 7.6% and 11.5%, respectively. N deposition significantly increased available P contents in L. gracile and M. dodecandrum stem leaf and root by 23.5% and 98.7%, respectively.The response of various species and understory plants to N deposition were different, N deposition significantly changed the trees and undergrowth of soil nutrient absorption. Different plants had different N/P, which determined the nutrient limiting or not. N deposition promoted the C. lanceolata of P nutrient absorption, which for L. formosana inhibited the absorption of P nutrient. N deposition also had a promoting effect on W. japonica, L. gracile and M. dodecandrum, Especially for W. japonica.Our study reveals N depositon influence on the different kinds of plants. And linked ground and underground ecological processes. For under the background of global change in subtropical forests provide a scientific basis for management. |
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