Litter Decomposition, Soil Respiration And Their Response To Simulated Atmosphere Nitrogen Deposition In Bambusa Pervariabilis×Dendrocalamopsis Daii Forest, Rainy Area Of West China

With the global rapid economic development and human population growth, fossil fuel consumption, atmospheric nitrogen deposition increased proportionally. Now, China has become one of the most serious regions under nitrogen, deposition followed by Europe and America. The nitrogen deposition's increase induced a series significant environment problems, which includes threating the human survival and development directly. So it has become to the global ecological and environmental problems which attract the attentions of many countries'governments and scientists. Bambusa pervariabilis×Dendrocalamopsis daii, which is deemed as one of the most important species of bamboo in the project of returning land from farming to forestry, have positive effects on ecological reconstruction and economic development along the upper and middle reaches of Yangtze River. Therefore, under the background of nitrogen deposition increased remarkably in this region, studies on litter decomposition, soil respiration and their response to simulated atmosphere nitrogen deposition in Bambusa pervariabilis×Dendrocalamopsis daii forest in Rainy Area of West China played important roles in management and supervision of subtropical bamboo ecosystem. The further study on the mechanisms of the bamboo ecosystem response to nitrogen deposition could provide comprehensions in influence of nitrogen deposition and references in protection of plantation in similar areas and basic data for the degraded bamboo's regeneration and renewal.From Jan. 2008 to Feb. 2009, the study was conducted in Bambusa pervariabilis x Dendrocalamopsis daii in Rainy Area of West China. Four treatments (three repeats) were established, i.e., control (ck, Og N m-2·a-1), low nitrogen deposition (In,5 g N m-2·a-1), medium nitrogen deposition (mn,15 g N m-2·a-1) and high nitrogen deposition (hn,30 g N m-2-a-1). All plots (3m×3m) and treatments were laid out randomly, Ammonium nitrate (NH4NO3) solution was sprayed on floor of these plots during decomposition process twice a month.Litter decomposition was determined by using closed litter bags in the plots. These bags were polyvinyl screen (lmm in the top and bottom) of approximately 20cmx20cm in dimension. In one condition, each bag was filled with lOg air-dried leaves, while the filled material were 15g sheathes in another condition. In Jan. 2008, these bags were evenly distributed among three plots selected randomly. Three leaf litter bags were collected from each plot at about decomposing 2,4,6,7,10,12 months after the start of the experiment, while the sheath bags were fetched at about decomposing 3,6,10,13 months.From Jan. 2008 to Feb.2009, in the end of each month, soil respiration was measured by infrared gas analyzers.The results showed as follows.(1) The leaf had a higher decomposition rate than the sheath during the first 10 months, and the difference were significant (p<0.05), while the difference were not significant 10 month later. After decomposing for 12 months, the remained litter mass in leaf and sheath were 33.29% and 33.59%. It would take 2.53 years to decompose 95% of leaf litter mass, which were 0.28 years shorter than sheath. 12 month later of leaf decomposition, the decomposition rates of In, mn, and hn were lower than ck, and the difference were significant (p<0.05) while sheath decomposition rates of In, mn, and hn were lower than ck, and the difference were also significant(p<0.05) 13 month later. At each stages, the lignin and cellulose of leaf and sheath were lowest in ck. So, the effects of N deposition on decomposition rates of the two component litter were negative.The mineralizations of nutrient elements were inhibited by N deposition in all treatments.(2) Soil respiration exhibited a clear seasonal pattern, with the highest rate observed in July in every treatment. Soil respiration correlated strongly with 0～10cm soil temperature(p<0.001)but there was no linear relationship between soil respiration and soil water content. The soil respiration were promoted in In and mn while inhibited in hn since Jun.2008.Daily variation of soil respiration from Jun.2008 to Sep.2008 also revealed the same response to increasing level of N addition. Soil respiration correlated strongly with the microbial biomass carbon。The pH of soil was negatively related to the quantity of N deposition. The pH was below 4.0 in soil of hn which might be the cause of the soil respiration inhibition. Temperature sensitivity of soil respiration in In and mn increased while it decreased in hn. It indicate that the temperature sensitivity of soil respiration might correlate with the quantity of N deposition.