Effect Of Nitrogen Addition On Growth And Soil Nutrient Of Cunninghanmia Lanceolata Plantation

Chinese fir(Cunninghamia lanceolata)is a unique tree species in southern China and is widely used for fast-growing timber plantation.Nitrogen is one of the most important macro-elements necessary for plants.Usually,more nitrogen was absorbed during plant growth than other mineral elements,and thus become major elements limiting plant growth.In order to reveal the effects of N addition on stand growth and soil nutrient,an experiment was conducted in a 12-year-old Chinese fir plantation.The main results obtained are as follows.The increments of mean DBH,2013-2014 N(1.25 cm)> CK(0.90 cm);2014-2015 N(0.76 cm)> CK(0.41 cm)DBH growth rate of 2014-2015 high and 2013-2014.The difference was significant.This result indicate that the response of Chinese fir growth to N addition was rapidly.In 0-10 cm soil layer,DOC concentration N(124.0 mg/kg)> CK(107.1 mg/kg);DON content N(10.7 mg/kg)> CK(8.6 mg/kg).In 10-30 cm layer,DOC content N(114.8 mg/kg)> CK(104.4 mg/kg);DON content N(9.3 mg/kg)> CK(6.4 mg/kg)and in 30-50 cm soil layer,DOC content N(65.58 mg/kg)> CK(61.39 mg/kg);DON content(9.0 mg/kg)> CK(6.2 mg/kg).Soil DOC and DON had a clearly seasonal trends in both N addition and the control,with the highest DOC content in spring.The DON contents were significantly different between the treatments and soil layers.The DON and DOC content was significantly positively correlated with.increments of mean DBH?The average contents of MBC and MBN were higher in the stands with N addition than in the controls for the whole soil profile.In 0-10 cm soil layer,MBC N content(129.3 mg/kg)> CK(120.6 mg/kg),MBN content N(7.3 mg/kg)> CK(6.8 mg/kg);in the 10-30 cm soil,MBC N content(127.2 mg/kg)> CK(114.3 mg/kg),MBN content N(6.8 mg/kg)> CK(5.4 mg/kg);in 30-50 cm soil layer,MBC N content(120.9 mg/kg)> CK(102.8 mg/kg),MBN content N(6.7 mg/kg)> CK(4.9 mg/kg).The MBN content was significantly positively correlated with.increments of mean DBH?The N addition had an obvious impact on soil nutrient status.Soil total nitrogen,total P content decreased with soil depth;total K and total Ca contents did not change significantly with soil depth.However,Mg content showed a growing trend with soil depth.N addition increased total phosphorus content(11.7%)in surface soil(0-10 cm)layer.N addition could improve storage of N,P,K,Ca and Mg in foliage,twig and fine-root of Chinese fir compared with the control,in which the most significant in fine-roots.The fine-root biomass of Chinese fir forest were positively correlated to soil nitrogen and soil moisture.The regression analysis showed that the DBH growth was significantly correlated with fine root-biomass.