Effect Of Nitrogen Fertilization And Litter Addition And Exclusion On Soil Respiration In Two Forests Of Central South China

With rapid development of global economics and population growth, more and more attentions have been paid to the problems of global greenhouse effect and high nitrogen deposition such as a serious threat to human life and the sustainable development of society. These problems affect the forest ecosystems, which can alter the rates of carbon. As a huge carbon stock, soil is the carbon source and sink of the atmospheric. The changes of soil carbon flux will seriously affect the atmospheric CO2concentration. Nitrogen can affect soil respiration by changed the chemical composition of the litter and soil physical and chemical properties and microbial biomass. Therefore, study on the variation of soil respiration of forest ecosystem is very important. In this paper, soil respiration was investigated in two typical forest (Cinnamomum camphora and pinus elliottii) stands at Botanical Garden of Changsha city. In order to better understand the effect of nitrogen addition and litter decomposition on soil respiration of Cinnamomum camphora and pinus elliottii forest, and whether nitrogen fertilization and litter decomposition alters the temperature sensitivity of soil respiration. We used LI-8100to investigate the response of soil respiration of Cinnamomum camphora and pinus elliottii for nitrogen fertilization, litter addition and exclusion, a field experiment with litter removal and exclusion and litter addition in4nitrogen levels (0,5,15,30g N·m-2·a-1)for one year, the soil temperature at5cm and soil moisture at5cm were recorded at the same time,. The main conclusions are as follow:(1) Soil respiration rate had an obvious daily variation of camphora forest, In CK and LN and MN plot, the maximum value appears at night, the minimum value appears at noon. In HN plot, the maximum value appears at noon. But the daily variation is not significant in pinus elliottii forest. Soil respiration rate had an obvious seasonal change of the two forests, with the maximum from June to August and the minimum from January to February. On average, the average rate of soil respiration of Cinnamomum camphora was LN (2.03±0.25μmol·m-2·s-1), MN(2.24±0.18μmol·m-2·s-1and HN(2.01±0.23μmol·m-2·s-1), reduced by33.4%and26.6%and34.1%Respectively compared with control level(3.05±0.36 μmol·m-2·s-1)in natural litter material conditions(CT). The ranking of soil respiration rate was CK>MN>LN>HN. The average rate of soil respiration of pinus elliottii was LN(1.21±0.16μmol·m-2·s-1), MN(1.29±0.14μmol·m-2·s-1)and HN(1.17±0.11μmol·m-2·s-1), reduced by27.5%and22.8%and29.9%respectively compared with control level(1.67±0.22μmol·m-2·s-1)in natural litter material conditions(CT). The ranking of soil respiration rate was CK>MN>LN>HN. The soil respiration rate of camphora forest is higher than pinus elliottii forest. The relationship between soil respiration and soil temperature is significant.(2)In the control plot (CK), the soil respiration in litter addition treatment (L+) and litter removal treatment (L-) and natural litter material conditions (CT) of the two forests followed a similar seasonal trend, results show that:Litter addition treatment increased soil respiration rate, litter removal treatment reduced soil respiration rate. The average rate of camphora forest was increased10.8%by (L+), reduced31.8%by (L-). The average rate of pinus elliottii forest was increased12.0%by (L+), reduced14.4%by (L-).(3)In the LN and MN and HN plot, results show that:Litter addition treatment increased soil respiration rate, but litter removal treatment could increase soil respiration rate and was also able to reduce soil respiration rate. In the camphora forest, the average rate was increased53.5%by (L+), increased12.9%by (L-) in LN plot; the average rate was increased49.4%by (L+), reduced2.6%by (L-) in MN plot; in the HN plot it was increased55.8%by (L+), increased21.53%by (L-). In the pinus elliottii forest, the average rate was increased33.2%by (L+), increased4.8%by (L-) in LN plot; the average rate was increased22.2%by (L+), reduced0.6%by (L-) in MN plot; in the HN plot it was increased40.27%by (L+), increased24.59%by(L-)..(4) The relationship between soil respiration and soil temperature at5cm of Cinnamomum camphora and pinus elliottii forest was significant(P<0.01), But The relationship between soil moisture and soil temperature at5cm was not significant(P>0.05). Soil temperature and moisture together could explain changes in soil respiration ranged from "68.8%to93.4%" and "57.1%to95.8%" in the two types of forests. Q10valued at different treatments ranged from1.92to2.29and1.27to1.97 of Cinnamomum camphora and pinus elliottii forest.The results indicated that nitrogen and litter are important factors in affecting soil CO2efflux.