Comparisons Of Effects Of Sea Level Rise On Main Processes Of Organic Carbon Between Kandelia Obovata And Avicennia Marina Mangrove Ecosystems

In this study,two mangrove plants named Kandelia obovata and Avicennia marina forests with different intertidal elevations,regarded as Sea Level Rise?SLR?of 80?SLR80 cm?,40?SLR 40 cm?respectively,along the coastline of Zengying,Xiamen were studied toinvestigate the effects of SLR on some parts of processes of organic carbon in mangrove ecosystems.With the rise of sea level,the soil water content increased in both the K.obvata plots and A.marina plots.Among them,the soil water content was lower than others significantly in A.marina SLR 40 cm plot,because of the sandy soil and poor water retention capacity.In the vertical direction,the dry density increased with the increase of soil depth but the water content decreased.The pH of the sample plots was between6.5⁷.2,showing faintly acid and weakly alkaline,and no uniform rule was obtained.The physical and chemical parameters of soil were different under the two plants.The contents of TOC and TN in the soil increased with the rise of the sea level in the A.marina plots.The TOC content in all soil layers decreased except the layer of 30⁴0cm in the K.obvata plots.The contents of TOC and TN decreased with the increase of the soil depth in all theplots.The C/N ratio of the soil covered by two plants showed different variation patterns.In the A.marina plots,the ratio of the SLR 80 cm plot was higher than SLR 40 cm plot.While in the K.obovata plots,it was on contrary.In the K.obovata plots,the plants in the SLR 80 cm plot were short and sparse,and the growth indexes were highly lower than those in the SLR 80 cm plot.When comparing the biomass of each of the plants,it was found that the stem>root>branch>leaf.The biomass ratio of aboveground and underground parts of plants in SLR 80 cm plot was significantly higher than the SLR 40 cm plot.There was no significant difference in plants' growth between the two different plants,and the biomass of each organic in two plots was branch>stem>root>leaf.Comparing the plots with two different plants,the changes of organic carbon accumulation and annual increment were consistent with those of biomass.In this decomposition of one year,the decomposition rate of leaf litters in various field was shown as summer>autumn>spring>winter.The decomposition rate reached the maximum in the first two weeks,and the slowed down.In the K.obovata plots,the decomposition rate of leaf litters was generally higher than SLR 80 cm plot.While in the A.marina plots,it was on contrary.When studying the dynamic changes of each nutrient element in the decomposition process,it was found that TOC remained a relatively stable state during the process.TN content in leaf litters tends to increase in the early period of decomposition and slightly decreases with the decrease of decomposition rate in the later stage.As a whole,the TN content after decomposition is higher than the initial content.In the field of SLR 40 cm of A.marina plots,the TN content was higher than the SLR 80 cm plot.It was on opposite in the K.obovata plots.In general,the C/N ratio means the decomposition rate of leaf litters,the larger the value is,the slower thedecomposition will be.When studying the influence of the sea level rise on the C/N ratio of SLR 40 cm in the K.obvata plots was lower than SLR 80 cm plot.The SLR 40 cm of A.marina plots was higher than the SLR 80 cm plot,which contacted with the dry weight loss rate.In the hot and rainy months,the leaf consumption by crabs was apparently higher than others.the K.obvataplots,the consumption rate by crabs in the SLR 80 cm plot was lower than SLR 40 cm plot,while was on the contrary in the A.marina plots related to the serious desertification in SLR 40 cm plot.The standing stock of forest land in various fields was higher in summer and autumn than in the winter and spring.According to the result,the total standing stock of leaves in the K.obovata plots much more than in the A.marina plots.Beyond that,in the K.obvata plots,the SLR 40 cm plot's standing stock was more than the SLR 40 cm plot,which was on opposite in the A.marina plots.The improvement of the temperature leads to the increase emissions of N₂O,CH₄and CO₂.In general,the CO₂ emission of SLR 40 cm plot was higher than that of SLR80 cm.In face of the different sea level heights,the two kind of plots have different N₂O emission rules.The N₂O emission of SLR 80 cm plot was higher than SLR 40 cm in the K.obvata plots all the seasons.While in the A.marina plots,the N₂O emissionof SLR 80 cm plot was generally lower than SLR 40 cm.Sea level rise also has a certain impact on CH₄ emissions.In the A.marina plots,the CH₄ emission load in the SLR 80 cm plot was higher than that in the SLR 40 cm in spring,summer and autumn.In the K.obovata plots,as the sea level rise,the TOC content and C/N ratio of surfacesoil generally decreased,but the TN increased.In the A.marina plots,the TOC content andCON ratio increased but TN decreased.The N₂O emission was positively correlated with soil water,TN and NH₄-N content,negatively correlated with NO₃-N content in theK.obovata plots.There was a significant positive correlation between CO₂ emission and TOC,TN content in these two plots.In the A.marina plots,the emission of CO₂ and N2 O was significant positively with the soil water content and soil temperature.The amount of CO₂ and CH₄ was significant negatively correlated with redox potential.