Effects Of Leaf And Root Litter Decay On Mangrove Soil Organic Carbon Accumulation And Their Mechanisms

As an important type of blue carbon ecosystems,mangrove forest plays a vital role in global carbon budget and climate change mitigation due to its high carbon storage and carbon sequestration potential.Mangrove soils,which store large amounts of carbon,play an important role in capturing carbon.Derived from allochthonous and autochthonous sediments,mangrove soil organic carbon(SOC)mainly benefits from the production and decomposition of aboveground litter and belowground root.On the other hand,mangrove soils release carbon dioxide(CO2)and methane(CH4)into the atmosphere through soil respiration due to the metabolism of soil microorganisms,thereby offsetting soil organic carbon accumulation to some extent.The balance between carbon input and carbon output can reflect whether mangrove wetland is a carbon sink or a carbon source.Therefore,it is helpful for understanding ecosystem carbon cycle to explore the effects of litter input on mangrove soil organic carbon accumulation,release and their regulating mechanisms.In this study,laboratory incubation experiments were conducted to study the effects of coastal plant leaf and root litter decomposition on soil organic carbon concentration,carbon fraction content and soil respiration,aiming to explore soil carbon balance mechanism in mangrove ecosystems.The results and conclusions of the present study are as follows:(1)Leaf litter of four species of coastal plants,Kandelia obovata,Aegiceras corniculatum,Sonneratia apetala and Spartina alterniflora were selected and added to soil sampled from mangrove wetland.During 45 days of decomposition experiment,Kandelia and Spartina leaf litter decomposed faster and had higher litter carbon loss than other two species.The addition of plant leaf litter increased carbon gases emissions from mangrove soil,and priming effect size varied with species.Compared with Aegiceras and Sonneratia leaf litter,Kandelia and Spartina leaf litter input had a stronger priming effect on soil respiration.According to the ratio between litter carbon and soil carbon in the microcosm,we speculated that CO2 and CH4 emissions were mostly from litter rather than soil.In addition,SOC concentration increased due to plant leaf litter input,but values varied with species.It was most obvious that increment of SOC concentration responded to Kandelia leaf litter input.Similarly,plant leaf litter input increased permanganate oxidizable carbon(POX-C)and dissolved organic carbon(DOC)concentration,which made SOC more unstable.The soil carbon balance mechanisms caused by four species of coastal plant leaf litter decomposition were obtained according to litter carbon loss,soil carbon increment and carbon gases emissions.The efficiencies of SOC formation from leaf litter were 26.7%,8.65%,16.5%and 11.5%for Kandelia,Aegiceras,Sonneratia and Spartina,respectively.We concluded that Kandelia leaf litter had the greatest contribution to SOC formation among four species of plant.(2)Randomized design was adopted to conduct a decomposition experiment of Kandelia and Spartina leaf litter,which were added to soil sampled from local field and away field.After 27 days of decomposition experiment,mass loss of Spartina leaf litter showed a positive home field advantage.Plant leaf litter input promoted soil carbon gases emissions.There was not significant difference for soil CO2 and CH4 emissions between local field and away field due to Kandelia leaf litter input.However,Spartina leaf litter decay stimulated more CO2 and CH4 emissions from local field soil than away field soil.In terms of litter carbon transformation patterns,Kandelia leaf litter decay caused higher SOC increment and efficiency of SOC formation in local field than in the away field,while there was not significant difference for SOC increment and efficiency of SOC formation between local field and away field due to Spartina leaf litter input.Soil source had a differential impact on litter carbon transformation patterns of both plants and efficiency of SOC formation from Kandelia leaf litter was higher,especially in local field.(3)Root litter of two species of coastal plants,Kandelia and Spartina were selected and added to soil sampled from mangrove wetland.During 160 days of decomposition experiment,root litter decomposition rate of both plants was comparable.Soil carbon gases emissions increased due to the addition of plant root litter,but there was not significant difference in priming effect size between both plants.According to the ratio between litter carbon and soil carbon in the microcosm,we speculated that root litter and soil made an equal contribution to CO2 emission.It was comparable for SOC increment caused by both plant root litter input.Similarly,plant root litter input increased soil POX-C and DOC concentration,which made SOC more unstable.Considering the soil carbon balance mechanisms caused by root litter decay,the efficiencies of SOC formation from root litter were 19.1%and 13.2%for Kandelia and Spartina.In summary,the input of coastal plant leaf and root litter enhanced soil carbon gases emissions and SOC concentration.Litter type and soil source affected litter decomposition rate,which in turn regulated efficiency of SOC formation.The findings from this study enhance our understanding of soil carbon cycle and regulating mechanisms under the influence of leaf and root litter decay in mangrove ecosystem,which can provide scientific guidance for mangrove wetland management.