Effect Of Litter Addition And Exclusion On Soil Respiration In Different Aged Chinese Fir Plantation

Forest soil respiration is an important part of the soil respiration in terrestrial ecosystems,the variation of which will bring far-researching influence on the balance of global carbon.In this paper,the amount of composition and dynamic change for litter,soil respiration,soil temperature and soil humidity have been observed in different aged Chinese fir plantations from March 2014 to February 2015.The objective is to provide data for revealing the carbon flux and its driving mechanism in subtropical forest ecosystems.The results show that:The total quantity of litter of four aged Chinese fir plantations was order by 27-year-old(3886.93kg·hm-2·a-1),18-year-old(3886.93kg·hm-2·a-1),23-year-old(3238.50 kg·hm-2·a-1),12-year-old(2708.77 kg·hm-2·a-1).The branches were the most in various components of the litter.Among them,the 27-year-old of Chinese fir was the most(58.74%)and 12-year-old was at least(45.58%).The monthly dynamic changes were three-peak type of curve on 27-year-old and 18-year-old,and others were the anomalous types.The three types of forests have the obviously seasonal rule and the most amount of litter was in July that was significantly higher than other seasons,expect 18-year-old of Chinese fir.Specific changes for rule of seasonal were:summer>autumn>spring>winter in all different age Chinese fir.The annual variation of soil respiration in different aged Chinese fir plantations was a single peak similarly,with the minimum value appearing in February.The annual average soil respiration values are 12-year-old Chinese fir(1.62 umolCO2·m-2·s-1)<18-year-oldChinesefir(1.95 umolCO2·m-2·s-1)<23-year-old Chinese fir(2.18 umol CO2·m-2·s-1)<27-year-old Chinese fir(2.53 umol CO2·m-2·s-1)Significant relationships were found between litter-fall and soil respiration in four-aged types of Chinese fir.The soil reparation rates in four age types presented downward trend with litter removal and the annual average soil reparation rates in 12-year-old Chinese fir,18-year-old Chinese fir,23-year-old Chinese fir,27-year-old Chinese fir are 1.34,1.63,1.89 and 2.17 umol CO2·m-2·s-1 relatively.Soil respiration was significantly decreased about 36.16%,28.18%,66.18%and 30.12%relatively to controls.The soil respiration rates in four-aged types presented increasing trend with litter addition and the annual average soil respiration rates in 12-year-old Chinese fir,18-year-old Chinese fir,23-year-old Chinese fir,27-year-old Chinese fir are 2.12,2.26,2.56 and 2.97 umol CO2·m-2·s-1 relatively.Soil respiration was significantly increased about 30.65%,15.73%,17.42%and 28.16%relatively to controls,respectively.There were significant differences(p<0.05)between litter removal,litter addition and controls.The relationship between soil respiration rate and soil temperature in 5 cm soil with different litter treatments was significant(P<0.001)and the regression residues equation are R=aebt and Rs=a+bTs with the range of fitting coefficient R2 are form52.02%to 77.11%and form 56.12%to 78.87%;soil moistures at 5 cm and soil reparation couldn't achieve significant(P>0.05).Soil temperature and soil moistures in four forest types explain the change of soil respiration rate is 60.5%-85%and the double-factor module analysis relative coefficient is higher than the single-factor module analysis.The result shows that soil temperature and soil moistures together can affect soil respiration.The Q10 Value of soil respiration in 12-year-old Chinese fir,18-year-old Chinese fir,23-year-old Chinese fir and 27-year-old Chinese fir are 1.51,1.58,1.67 and 1.73 relatively,the Q10 value of soil respiration with litter removal are 2.04,2.08,1.87 and 1.98 relatively;The Q10 value of soil respiration with litter addition are1.60?1.63?1.65 and 1.80 relatively;The Q10 in all ages of Chinese fir presented:litter addition>controls>litter removal.The annual average soil respiration rates in gap and understory are 2.47 and 2.13 umol CO2 m-2·s-1;Soil respiration was significantly increased about 22.89%and 25.89%relatively to controls.There were extremely significant exponential correlations between soil respiration,soil temperature and soil moisture in understory and gap.The double-factor module analysis relative coefficient is higher than the single-factor module analysis.The result shows that soil moistures and soil temperature together can have better effects on soil respiration.The Q10 value of soil respiration in understory and gap with litter removal are 1.39 and 1.37.There have couldn't achieve significant differences(P=0.634)between gap and understory with litter remover.The Q10 value of soil respiration in understory and gap with litter addition are 1.40 and 1.55.There were significant differences(p=0.01)between gap and understory with control.