In - Situ Decomposition Of Litter Organic Carbon In Spartina Alterniflora

The decomposition of organic carbon of wetland plant litter is an important part of wetland ecosystem carbon cycle. So it is necessary to pay attention to the effects of Spartina alterniflora litter on Yancheng salt marsh where has been invaded by S. alterniflora. In order to characterize the decomposition process of total organic carbon (TOC), recalcitrant organic carbon (RC) and liable organic carbon (LC), the chemical composition changes and stable carbon isotope variation(δ13C) of S. alterniflora litter, we buried decomposition bags at developing S. alterniflora salt marsh of 3-year (SAF2011),5-year (SAF2009),11-year (SAF2003),25-year (SAF1989) and 25-year S. alterniflora-Suaeda salsa saltrnarsh (SAF-SS) along the Xinyanggang coastal wetland in Yancheng, where the largest area of S. alterniflora saltmarsh in China has developed. The results revealed the following.(1) The development period of saltmarsh affects the S. alterniflora litter organic carbon decomposition process. During the one-year decomposition, the litter TOC remaining percentage, RC remaining percentage and LC remaining percentage decreased by month. The litter RC remaining percentage was higher than the LC remaining percentage, and the remaining percentage of TOC, RC and LC increased in the saltmarsh with longer development period; it indicated that more litter RC deposited than litter LC did, and more litter organic carbon deposited in the saltmarshes with longer development period. After litter decomposition, RC to TOC ratio increased, showing a lower decomposition ratio of RC than LC. The annual litter TOC loss were found to be 0.3167、0.2632、0.2608、0.2583 and 0.2380 g·g-1 in SAF1989, SAF2003, SAF2009, SAF2011 and SAF-SS, respectively, and the highest value was observed in the 3-year saltmarsh (SAF2011).(2) The litter organic carbon decomposition rates differed with seasonal rhythm. The higher decomposition rates of litter TOC, RC and LC occurred in August, January and June, respectively, whereas the lower decomposition rates of litter TOC and LC occurred in October and February, and the lower decomposition rates of litter RC were observed in December and February. The LC decomposition rates were higher than that of RC, while the TOC and LC decomposition rates decreased with the increase of S. alterniflora development period. The RC decomposition rates were higher in SAF2011 than that in the other saltmarshes where RC decomposed at similar rates.(3) The structure of the S. alterniflora litter organic carbon in the decomposition process changed. The S. alterniflora litter organic carbon was mainly composed of alcoxyl carbon rather than other carbon fractions and its proportion of litter organic carbon is 78.86%. There was little difference between aromatic carbon proportion (9.75%) and alkyl carbon proportion (8.13%). The carboxyl carbon proportion was for a minimum of 3.26%. During litter decomposition, alcoxyl carbon ratio in general was first decreased and then increased, contrary to aromatic carbon change. The alkyl carbon and carboxyl carbon proportion changes little and trends similarly between different sampling sites. The alkyl carbon and carboxyl carbon proportion change in the opposite in the same sampling site.(4) There are different changes in salt marsh development time of litter organic carbon fractions in the decomposition process. In the litter decomposition in 1-10 months, changes of alkoxyl carbon ratio of different developmental stages in different salt marsh, salt marsh development time shortest kind alkoxy carbon proportion is low; in the litter decomposition in 5-8 months, aromatic carbon ratio have different changes, S. alterniflora and S. salsa ecotone kind of aromatic carbon ratio the lowest; different developmental time of salt marsh changes within the carboxyl carbon and aromatic carbon ratio difference.(5) After the decomposition of organic carbon changes in the nature of the litter of S. alterniflora, the litter decomposition of organic carbon in structural complexity increases, more conducive to the accumulation of organic carbon, the band structure of complexity increase at least S. alterniflora and S. salsa staggered; along with the increase of salt marsh development time, reduce the degree of salt marsh litter decomposition, the development time is short, the distance from the sea close to the kind of litter decomposition of organic carbon in litter the highest degree; in the process of decomposition of organic matter humification degree increased first and then decreased and finally tends to be stable, and ultimately higher than the initial value, indicating the litter organic carbon accumulation; kinds of aromatic carbon/ carbon ratio increased alkyl alkoxy carbon/alkoxy carbon, alkyl carbon in litter decomposition of S. alterniflora more easily than aromatic carbon.(6) Salt marsh development time changes in the decomposition of organic carbon isotope and inert organic carbon l3C process has little effect on the litter, the litter organic carbon and inert organic carbon accumulation in both 13C decomposition. The decomposition of organic carbon in 13C process fluctuant in 0-10 months of S. alterniflora litter, increased in October, salt marsh development time shortest kind of δ13C,δ13C and other plots had little difference; leaf litter decomposition in an inert organic carbon 13C at the early stage of the decomposition in the decomposition of late has little change the difference between plots increased significantly; the decomposition process of S. alterniflora is inert organic carbon and labile organic carbon and carbon co decomposition and accumulation effect, carbon transfer between inert organic carbon and labile organic carbon.