Seasonal Dynamics Of Aerial Litter Decomposition Of Spartina Alterniflora: A Comparison Of In Situ And Litterbag Methods

In order to compare the differences of in situ experiment and litterbag methods for examining aerial litter decomposition, we used Spartina altemiflora as materials to investigate the seasonal dynamics of aerial litter decomposition and other related parameters from Jan, 2008 to Dec, 2008 at Chongming Dongtan, the Yangtze River Estuary, China. The initial litter mass for in situ decomposition experiment was 1389g m^-2. The aerial litter decomposition rate by in situ experiment was significantly higher than that by litterbag method (F_1.65=17.603,P<0.05) . The average aerial decomposition rates of stem, leaf and sheath litters in in situ experiment were 0.662, 0.754 and 0.476 respectively, while those with litterbag method were 0.602, 0.668 and 0.429, repectively. The aerial decomposition rates of stem, leaf and sheath litters had significant difference between in situ experiment and litterbag methods on the aerial litter decomposition (stem: F_{1, 129}= 12.326, P<0.05; leaf: F_1.129= 113.224,P<0.05; sheath: F_1.129= 166.173, P<0.05).In in situ decomposition, carbon concentration dynamics was variable. The carbon concentration of stem litter was significantly variable during decomposition (F_{1, 65}= 3.378, P<0.05), and those of leaf and sheath litters were invariant during decomposition (P>0.05). The absolute amount of carbon in different parts of aerial litter significantly decreased during decomposition (leaf:F_1.65= 1.518, P>0.05;sheath;F_1.65=0.295, P>0.05). Nitrogen concentration was also variable during decomposition. The nitrogen concentration in different parts of aerial litter significantly increased during decomposition (stem:F_1.65= 9.371, P<0.05; leaf:F_1.65=11.002, P<0.05; sheath;F_1.65= 6.961, P<0.05), and the absolute amount of nitrogen in different parts of aerial litter significantly decreased during decomposition (stem:F_1.65= 7.703, P<0.05; leaf:F_1.65= 9.772, P<0.05; sheath;F_1.65= 5.076, P<0.05).Druing decomposition in litterbags, carbon concentrations of leaf and stem litters significantly differed among the sampling times (leaf:F_1.65= 3.884, P<0.05; stem:F_1.65= 4.473, P<0.05) ), and that of sheath litter was invariant (P>0.05). The absolute amount of carbon in different parts of aerial litter significantly decreased during decomposition (stem:F_{1. 65}=77.595 , P<0.05; leaf:F_{1. 65}= 10.955 , P<0.05; sheath:F_{1. 65}= 9.050, P<0.05). The nitrogen concentration in different parts of aerial litter significantly increased with time (stem:F_{1. 65}=5.504, P<0.05; leaf:F_{1. 65}= 6.523, P<0.05; sheath:F_{1. 65}= 1-960 , P<0.05). The absolute amount of nitrogen of leaf and stem significantly decreased with time (leaf:F_{1. 65}= 3.457, P<0.05; stem:F_{1. 65}=2.308, P<0.05), and that of sheath litter had was invariant over time (P>0.05).Carbon and lignin concentration in different parts of aerial litter had no significant difference between in situ experiment and litterbag methods (in situ:F_1.10=0..154, P>0.05; litterbag: F_{1. 10}=1.238, P>0.05). The absolute amount of carbon in stem, leaf and sheath liter had significant difference between the two methods (stenv.F_{1. 10}=16.154, P<0.05; leaf:F_{1. 10}=34.966, P<0.05; sheath:F_{1. 10}=83.24, P<0.05). The nitrogen concentration of stem, leaf and sheath litters had significant difference between the two methods (stem:F_{1. 10}=38.585, P<0.05; leaf:F_{1. 10}=8.74, P<0.05; sheath:F_{1. 10}=13.977, P<0.05). The absolute amount of nitrogen in stem, leaf and sheath litters had significant difference between the two methods (stem:F_{1. 10}=29.234,P<0.05; leaf:F_{1. 10}=51.894,P<0.05; sheath F_{1. 10}=33.381, P<0.05).In conclusion, this study shows that the aerial litter decomposition of Spartina alterniflora differed in rate between in situ experiment and litterbag methods. Due to the limitation of in situ decomposition, this method is not suitable for studing the aerial litter decomposition dynamics. However, this method can be used to study the nutrient dynamics of the aerial litter and biodiversity of microorganisms that is associated with litter decomposition. Although the data obtained from the litterbag method was slightly different from the actual situation, the litterbag method can quantify the aerial litter decomposition dynamics, and can be used widely. Therefore, the two methods can be combined to study litter decomposition dynamics, as well as the status of microorganisms that are associated with litter decomposition.