Research On Standing Litter Decomposition In The Coastal Wetlands Of Yellow River Delta,China

Litter decomposition is an important component of the carbon cycle in the wetland ecosystem,and the standing litter is an important phrase of litter decomposition.Until now,most studies concentrate on the decomposition of leaf litter on the surface of soil or water.However,decomposition of standing litter is still less known,especially the decomposition of non-leaf organs（e.g.,sheath and culm）.In this study,the litter of Phragmites australis and Suaeda sala was collected in the coastal wetlands of the Yellow River Delta,China.The characteristics of litter decomposition in the air and on the ground were investigated including the mass loss,nutrient dynamics,dissolved organic carbon（DOC）and CO₂ flux,and enzyme activities.The results showed that:（1）After 360 days of decomposition,the mass loss rate of standing litter is equivalent to55.25%to 98.7%of the same type of litter on the surface of soil.The mass loss rate of the culm and sheath litter of Phragmites australis and the aboveground litter of Suaeda sala were respectively equivalent to 57.48%to 68.55%,72.87%to 101.41%,and 66.43%to 85.28%of those in leaf litter of Phragmites australis.The mass loss rate of litter positively correlated with the enzyme activities（phosphatase and urease activity）,air temperature and relative air humidity,and negatively correlated with the C/N ratio of litter（P<0.05）.（2）After 360 days of decomposition,the residual rate of total nitrogen in standing litter was similar to that on the surface of soil.The residual rate of total nitrogen in the culm and sheath litter of Phragmites australis and the aboveground litter of Suaeda sala were respectively equivalent to 133.51%to 137.29%,108.68%to 122.71%,and 93.52%to 97.62%of those in leaf litter of Phragmites australis.The residual rate of total phosphorus in standing litter of the leaf and sheath of Phragmites australis were respectively equivalent to 51.22%%and 46.11%of the same type of litter on the surface of soil,the residual rate of total phosphorus in standing litter of the culm of Phragmites australis and the aboveground litter of Suaeda sala were similar to that the same type of litter on the surface of soil.The residual rate of total phosphorus in the culm and sheath litter of Phragmites australis and the aboveground litter of Suaeda sala were respectively equivalent to 100.13%to 198.58%,123.69%to 137.38%,and63.39%to 118.79%of those in leaf litter of Phragmites australis.（3）After one year of decomposition,the cumulative CO₂ emission of standing litter was equivalent to 56.76%to 79.04%of the same type of litter on the surface of soil.The cumulative CO₂ emission in non-leaf litter of Phragmites australis and aboveground litter of Suaeda sala were greater than or equal to those in leaf litter of Phragmites australis.There was a significantly positive relationship between the cumulative CO₂ emission and the decomposition rate of labile organic carbon in the litter（P<0.05）.The litter on the soil surface had larger value of temperature sensitivity(Q₁₀)of CO₂ emission than standing litter,and the Q₁₀ value positively related to the percentage of recalcitrant organic carbon（P<0.05）.（4）The concentration of DOC in standing litter was greater than or equal to that on the surface of soil,and the highest DOC concentration of standing litter was 1.74 times that on the surface of soil.The DOC concentration in the culm and sheath litter of Phragmites australis and the aboveground litter of Suaeda sala were respectively equivalent to 40.14%to 96.14%,63.67%to 118.48%,and 36.06%to 84.04%of those in leaf litter of Phragmites australis.E₂/E₃ratios of DOC in standing litter were higher than those on the surface of soil,indicating a higher quality of DOC in standing litter.E₂/E₃ ratios of DOC in leaf litter of Phragmites australis and aboveground litter of Suaeda sala were lower than those in non-leaf litter of Phragmites australis,indicating a higher quality of DOC in non-leaf litter of Phragmites australis.In conclusion,the traditional research always concentrated on the litter decomposition on the surface of soil and ignored the decomposition of standing litter,overestimating the mass loss rate and CO₂ emission and underestimating nutrient（e.g.,total phosphorus）and DOC release in the early stage of litter decomposition in the coastal wetlands of Yellow River Delta,China.Moreover,the negligence of non-leaf litter decomposition will underestimate the whole processes of litter decomposition.