Plant Nutrient And Litter Decomposition In Short-term Response To Simulated N Deposition In Subtropical Chinese Fir Artificial Forest

Atmospheric deposition of nitrogen—specifically oxides of nitrogen mainly from fossil fuele missions and also ammonium from production and use of fertilizers remain elevated in industrial regions of the world and are accelerating in many developing regions. Concern about the ecological effects of elevated N deposition on the functioning of forest ecosystem is increasing. Chronically elevated atmospheric N deposition to forests can affect nutrition state of plant and litter decomposition, critical processes affecting soil fertility and primary productivity of ecosystems. An assessment of the effects of increased atmospheric N deposition on nutrient state of plant and litter decomposition is critical to understanding its effects on forest structure and function. The emission of nitrogenous compounds from industry and agriculture is likely to increase rapidly in China. However, little information about the impacts of nitrogen deposition on forest ecosystems in China is available. Chinese fir artificial forest is representative forest type in subtropical China. To partially fill this information gap, nutrient state of plant and its responses, litter decomposition and its responses to simulated N deposition for the Chinese fir artificial forest in subtropical China were studied.The background level of Chinese fir artificial forest was investigated at the end of 2003. Nitrogen addition experiments were initiated in Janual 2004. Four N addition treatments in three replicates (three plots) were established in middle-age forest: N0 (Control), N1 (60 kg N hm^-2.a^-1), N2 (120 kg N hm^-2.a^-1) and N3 (240 kg N hm^-2.a^-1). For this purpose 12 plots (20m×20m) were set up. All plots and treatments were laid out randomly. CO(NH₂)₂ solution was sprayed monthly by hand onto the floor of these plots beginning in Janual 2004.Fresh needles were hand plucked from the same mean sampletrees of each plot at the end of year after the start of study. Litter decomposition was determined by using closed, mesh litter bags in the plots. A total of 480 bags were prepared from mesh (1mm) polyvinyl screen of approximately 25cm×25cm in dimension (40 bags for each plot). Each bag was filled about 17g～20g, air-dried mass, of needle litter. In Janual 2005 these litter bags were evenly distributed among plots randomly. Three litter bags were collected from each plot every two months after the start of the study.The major results are as follows: 1 Plant nutrientThe simulated N deposition experiments carried out two years, the concentration of P in needle with all nitrogen addition treatments increased 16.09% (N1 treatment), 36.68% (N2 treatment), 8.13% (N3 treatment) respectively. The increment proportion of N2, N3 treatments were more than NO treatment (12.34%). In first year N2, N3 treatments stimulated...