Characteristics of litter decomposition and nutrient release of several dominant annual herbaceous species in the riparian zone of the Three Gorges Reservoir Area

The effects of flooding on the ground litter decomposition and nutrient release of three dominant annual herbaceous plants (Bidens tripartita, Echinochloa crus-galli, and Polygonum hydropiper) from a water-level fluctuation zone were investigated using the litter-bag method. The control group (CK) and water flooding group (F) were designed according to the characteristics of flooding in the Three Gorges Reservoir Area (TGRA) during summer. The results revealed the following: 1) The initial contents and ratios of elements in the three herbaceous litters were different (P < 0.05). The initial nitrogen (N), phosphorus (P), and potassium (K) contents and ratios of the litters were positively correlated with the dry mass loss rates and element release rates, and negatively correlated with the initial carbon (C) and lignin contents and lignin/N and C/N ratios. 2) Flooding accelerated the dry mass loss rates and element release rates of the three herbaceous litters, having the greatest influence on the rates of N, P, and K release. 3) Except for the rate of P release by the CK group and of K release by the F group, the dry mass loss rates and element release rates of B. tripartita and E. crus-galli were higher than those of P. hydropiper (P < 0.05). This indicates that B. tripartita and E. crus-galli may have great influence on the nutritional status of the water and sediments in the TGRA, and the rapid decomposition of their litter may lead to increases in the N and P contents, whereas P. hydropiper has little effect in this regard. Therefore, it is suggested that priority should be given to the timely recovery and mowing of B. tripartita and E. crus-galli before the summer flood season in order to reduce the release of nutrients to the water and sediments.