Ex situ decomposition and phosphorus release characteristics of Spartina alterniflora litter in Minjiang estuary
Aims The ex situ decomposition of litter caused by tidal fluctuations is the most common decomposition approach in estuarine marshes.Exploring the effects of environmental variation on litter decomposition and nutrient release is of great significance for understanding nutrient cycling in estuaries.Methods From March to December 2021,the natural environmental gradient in Spartina alterniflora distribution area in the Minjiang estuary was applied to simulate changes in decomposition environment.Three decomposition sub-zones including S.alterniflora marsh(M7,litter was denoted by L7)after seaward invasion for seven years,S.alterniflora marsh(Ml,litter was denoted by L1)after seaward invasion for one year,and bare flat(BF)before invasion were laid in a seaward direction;and the potential effects of simulated environmental variation on the decomposition and phosphorus(P)release of S.alterniflora litter(L7 and L1)with different invasion years were investigated by using the litter bag method.Important findings The change in environment could significantly affect the decomposition rate of S.alterniflora litter.The L7 in the M1 and BF environments decomposed faster than that in its original environment(M7),while the L1 in the M7 and BF environments decomposed slower than that in its original environment(M1).The variation in decomposition rate of L7 or L1 with the changing decomposition environments not only depended on the variations in the key environmental factors(temperature and pH)but also rested on the great alterations in litter quality(carbon/nitrogen and nitrogen/phosphorus ratios).Compared to the original decomposition environment,changes in the decomposition environment increased the concentration of total phosphorus(TP)in L7 generally increased while those in L1 decreased as a whole.It should be noted that the TP concentrations in L7 and L1 reached the highest values in the M1.The remaining dry mass was the common factor affecting the variations of TP in litter under different decomposition environments,while the alterations of the key environmental factor(electrical conductivity)and litter quality associated with decomposition environment changes were the primary drivers in inducing the differences of TP concentrations in different decomposition sub-zones.Stocks of P in decaying litter in different sub-zones generally showed the transfer from litter to the surroundings.This study found that both the decomposition rate and the amounts of P released from L7 and L1 were much higher in the Ml,indicating that the P return rate in the Ml might be faster and this was favorable for elevating the P availability for the newly invaded S.alterniflora.
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