Effects Of Simulated Nitrogen And Sulfur Deposition On Litter Decomposition In Evergreen Broad-leaved Forest In Rainy Area Of Western China

In recent years,with the large consumption of fossil fuels and the increasing number of motor vehicles,the increasing release of nitrogen oxides and sulfur oxides into the atmosphere has led to the expansion of the amount and area of atmospheric acid deposition and acid deposition.Acid deposition has become the global common concern of the major ecological and environmental problems.The effects of acid deposition on leaf litter decomposition and nutrient release are closely related to the carbon balance and nutrient cycling of forest ecosystems.Based on this,we performed the following experiment in an evergreen broad-leaved forest in Rainy Area of West China from April 2013 to April 2015.Responses of leaf litter decomposition and nutrient release to the deposition of Nitrogen(N),Sulphur(S)and their combination were studied based on an experimental design of leaf litter decomposition per se.Two factors,nitrogen deposition and sulfur deposition,were set up in nine treatments:comparison(CK),low nitrogen 5 g N·m-2·a-1(LN)?high nitrogen 15 g N·m-2·a-1(HN)?low sulfur 20 g S·m-2·a-1(LS)?high sulfur 40 g ·m-2·a-1(HS)?low nitrogen 5 g N ·m-2·a-1 and low sulfur 20 g S·m-2·a-1(LNLS)?high nitrogen 15 g N·m-2·a-1 and low sulfur 20 g S·m-2·a-1(HVLS)?low nitrogen 5 g N·m-2·a-1 and high sulfur 40 g S·m-2·a-1(LNHS)?high nitrogen 15 g N·m-2·a-1 and high sulfur 40 g S·m-2·a-1(HNHS).The main results were shown as follows:(1)After two year deposition of N and S combination,the residual rates of litter leaves treated by LN and HN were 2.29%and 4.41%higher than CK,respectively,which indicated that nitrogen deposition inhibited the decomposition of litter.The residual rate of litter leaves treated with LS was lower than CK by 2.54%while HS was 8.74%higher than that of CK,which indicated that low sulfur treatment promoted the decomposition of litter,while high sulfur treatment inhibited the decomposition of litter.The results showed that the residual residue of LNLS and HNLS was 2.87%and 1.08%lower than that of CK,while HNHS and LNHS were 7.74%and 9.37%higher than CK respectively.This indicated that low nitrogen and low sulfur and high nitrogen and low sulfur composite sedimentation produced antagonistic effect,promoted the decomposition of litter leaves;low nitrogen and high sulfur and high nitrogen and high sulfur composite sedimentation produced a synergistic effect,inhibiting the decomposition of litter.(2)Nitrogen deposition inhibited the degradation of lignin and cellulose in leaf litter.Low sulfur deposition promotes the degradation of litter lignin and cellulose,while high sulfur deposition inhibits the degradation of lignin and cellulose.The interaction between the combined deposition of N and S was significant.HNLS and LNLS combined treatment significantly reduced the lignin residual rate of litter fall,showing antagonistic effect;The combined treatment of LNHS and HNHS significantly increased the residual lignin and cellulose residues,and showed synergistic effect.The residual cellulose treatment rate of LNLS and HNLS was not significantly different from that of CK.(3)The release of C,N and P elements in litter leaves was inhibited by the treatment of nitrogen deposition.Low sulfur treatment promoted the release of C,N and P elements in litter,while high sulfur treatment inhibited the release of C,N and P elements.Nitrogen and sulfur composite sedimentation interacted significantly.Treatment LNHS and HNHS significantly inhibited the release of C,N and P elements,showing a synergistic effect.Treatment HNLS significantly promoted the release of C element,showing antagonistic effect,while LNLS had no significant effect on the release of leaf litter C element.Treatment LNLS and HNLS inhibited the release of N,which showed an antagonistic effection.Treatment LNLS promoted the release of P element,which showed antagonistic effect,and the treatment HNLS had no obvious effect on the release of P element.(4)Nitrogen deposition decreased C/N,with a 3.10%and 1.26%decrease in treatment LN and HN,respectively.Nitrogen deposition increased C/P by 49.98%and 16.15%in treatment LN and HN,respectively.Sulfur deposition reduced the leaf litter C/N,with a 8.57%and 5.76%reduction in LS and HS,respectively.LS treatment reduced leaf litter C/P by 4.68%,while high sulfur treatment increased leaf litter C/P by 16.92%.The interaction between nitrogen and sulfur deposition was obvious.Treatment combined deposition of nitrogen and sulfur decreased the leaf C/N,but increased the leaf litter C/P.(5)The correlation between mass residual rate and lignin residual rate was decreased under overall Nitrogen deposition and treatments of LNHS and HNHS.However,the relationship between mass residual rate and lignin residual rate was increased for treatment HNLS.No significant correlation between the rate of mass residual and C/N was found.The decomposition of leaf litter under Nitrogen and Sulphur decposition can be best illustrated by C residual rate,N residual rate,P residual rate,cellulose residual rate and C/P.