Functions Of Feeding Leaf Litter By Crabs On Pools Of Organic Carbon In Mangrove Soils And The Impacts Of Environmental Changes

In the context of global changes and increasingly fierce human activities,"blue carbon" protection has gradually become a hot topic of the times.As one of the three"blue carbon" ecosystems,mangroves are an important carbon pool with both economic and ecological value in the world,and most of the carbon is stored in sediments or soils.As an important consumer,crabs play the role of "ecological engineer" in mangroves.A series of biological disturbances such as feeding,excretion and burrowing make the relationship between litter and soil closer,to a certain extent speed up the process of material-circulation and energy-flow within the ecosystem.Studying the role of crab feeding in the carbon cycle of mangrove ecosystems,especially the influence and contribution to the ecological process of soil organic carbon,can provide basic parameters for the establishment of a more complete coastal wetland carbon cycle prediction model in the future;combining global changes and human activities interfere with the study of crab feeding,which will also help to understand the ecological relationship between the organisms and the environment in the mangrove ecosystem more comprehensively,and provide a theoretical basis for better formulation and implementation of "blue carbon" protection policies.In this study,Sesarma plicata was used as the research object,and the method of establishing a microcosm laboratory system(microcosm)was used to explore the influence and contribution of different individual size crabs feeding Kandelia obovata leaf litter on mangrove soil organic carbon.By comparing the feeding of Spartina alterniflora and Kandelia obovata leaf litters on the soil organic carbon accumulation,and by setting up different shrimp pond sewage treatments and different flooding intensity treatments,respectively,to explore the impact of crab feeding on the soil organic carbon pool and the response mechanism under the disturbance of global changes and human activities.The preliminary research results are as follows:(1)The feeding rate of Kandelia obovata leaf litters by Sesarma plicata of different individual sizes showed that large crabs and medium crabs were significantly higher than small crabs,while the leaf loss rate was opposite.For small crabs,crab droppings can significantly promote the removal of total organic carbon from leaf litters.Reflecting the accumulation of total organic carbon in the soil,the expression is:large crab>medium crab>small crab,feces and leaf litters have a certain driving and regulating effect on this difference.Under natural conditions,the disturbance of large crabs and small crabs can promote the accumulation of soil organic carbon.The total organic carbon in litter enters the soil mainly through crab feeding,self-decomposition and microbial decomposition.Crab feeding account for the largest proportion,and most of the carbon ingested by crabs will re-enter the soil through feces.(2)The feeding rate of Kandelia obovata leaves was significantly higher than Spartina alterniflora,and the feces inhibited the removal of total organic carbon in Spartina alterniflora by crabs.Spartina alterniflora played a role of replacing feces with nitrogen supplementation in crab feeding activities.Crab feeding can narrow the gap between Kandelia obovata and Spartina alterniflora in the contribution of soil total organic carbon,play an ecological compensation role to a certain extent,and can alleviate the negative impact of Spartina alterniflora invasion on the carbon sink function of mangroves.(3)Using natural soil and shrimp pond clearing sludge to form a series of ratios,conduct indoor cultivation experiments to simulate sewage discharge sites of different intensities.There are significant differences in the feeding rate of the crabs under different sewage treatments,and moderate sewage can promote the growth and development of individuals.The leaf loss rate is not regulated by pollutant discharge,but low-level pollutant discharge can promote the removal of total organic carbon from the leaf litters,and this promotion will gradually decrease or even disappear as the pollutant discharge increases.Cumulative total carbon emissions are controlled by both pollutant discharge and crab feeding,and the main contribution comes from CO2 emissions.With the increase of sewage intensity,the promotion effect of crabs on the accumulation of soil total organic carbon gradually weakened and then stabilized.(4)The intensity of flooding is controlled by flooding time and depth,so as to realize a simple simulation of the tide process in the field,and studying the changes in mangrove soil organic carbon pool caused by crab feeding by sea level rise.Flooding will significantly reduce the crab feeding rate and leaf loss rate,but has no significant effect on the total organic carbon removal from leaf litters.The total organic carbon accumulation in the overlying water under high intensity flooding is significantly higher than that under low intensity flooding.Under flooding conditions,the control of total carbon emissions is mainly achieved by CH4,and flooding has a significant inhibitory effect on the accumulation of soil total organic carbon.However,the interference of crab feeding can increase the accumulation of soil total organic carbon and it plays a certain role of compensation at the same time.