黄河口盐沼湿地盐地碱蓬和互花米草凋落物的分解特征

凋落物分解在湿地生态系统中扮演重要的角色。为探索潮汐梯度下凋落物分解过程中质量和营养元素变化情况,采用分解袋的方法,选择盐地碱蓬（Suaeda salsa）和互花米草（Spartina alterniflora）凋落物作为研究对象,沿着潮汐梯度开展凋落物分解的野外实验。结果表明：凋落物分解速率与凋落物类型、土壤盐度、含水率以及潮汐干扰强弱有关;潮汐干扰强的区域互花米草分解快于盐地碱蓬,潮汐干扰弱的区域盐地碱蓬分解快于互花米草,两种凋落物分解速率在0.00134~0.00234 d^-1之间。分解末期,凋落物都呈现C和N的净释放,盐地碱蓬凋落物平均释放了36.9%的C和55.8%的N,互花米草凋落物平均释放了53.1%的C和47.1%的N。本研究强调关注潮汐梯度下的凋落物分解,其在调节生物地球化学循环以及碳累积上具有重要意义。

Decomposition characteristics of vegetation litter of Suaeda salsa and Spartina alterniflora in saltmarsh of the Yellow River Estuary,China

Litter decomposition plays a vital role in governing ecological processes of wetland ecosystems. To investigate the variations of litter quality and nutrients during decomposition varying with tidal regime, we conducted manipulative experiments with different species of Suaeda salsa and Spartina alterniflora, at four sites along a tidal gradient, to test the decomposition rates, by putting the litter of each plant into the decomposition bags. Our results showed that losses of litter mass were related to litter species, soil salinity, soil water content and tidal disturbance, revealing that the tidal disturbance can be an important force to influence the retention and decomposition. We found that S. alterniflora litter decomposed faster than S. salsa litter at the sites with strong tidal disturbance, but for the sites with weak tidal disturbance, a converse trend was found that S. salsa decomposed faster than the S. alterniflora. The decomposition rates of them ranged from 0.00134 d^-1 to 0.00234 d^-1. We also found that the decomposition varies with time. After 270 days of ending experiments, the mass losses of S. alterniflora and S. salsa litter exceeded 30%, showing that the losses at the sites with stronger tidal disturbance were larger than those at sites with weak tidal disturbance. The variations of N and C/N of S. salsa and S. alterniflora litter differed significantly among sites (N: F₇₁=3.280, P<0.05; C/N: F₇₁=3.571, P<0.05), expect for C content (F₇₁=0.856, P>0.05). The average contents of C, N and C/N of S. salsa litter were 40.81±1.15%, 0.51±0.08% and 82.22±13.18, respectively, while the average contents of C, N and C/N of S. alterniflora litter were 31.72±2.37%, 0.39±0.05% and 82.59±14.91, respectively. Both litters showed a net release of carbon and nitrogen. The average releasing amounts of C and N were 36.9% and 55.8%, respectively in S. salsa litter and the average release amount of C and N were 53.1% and 47.1%, respectively in S. alterniflora litter. The net releasing amount of carbon at sites with strong tidal disturbance was larger than that of sites with weak tidal disturbance. Our result suggests that decomposition of coastal vegetation litter provided nutrient element (e.g. C and N) for coastal wetland ecosystems, in the Yellow River Delta. Therefore, our study highlights that tidal regime should be regarded as an important environmental factor in regulating biogeochemical cycles and carbon accumulation, consequently altering the ecosystem functioning.