沉积强度及氮养分改变对闽江河口短叶茳芏残体短期分解与养分释放的影响

互花米草入侵过程中较强的促淤作用可导致湿地沉积环境和养分状况发生明显变化。2017年4月,选择闽江河口鳝鱼滩西北部受互花米草入侵影响的短叶茳芏湿地为研究对象,基于野外原位沉积及养分改变模拟试验,设置无沉积强度（S₀,0 cm·a^-1）、当前沉积强度（S₅,5 cm·a^-1,氮养分水平为沉积物自然氮背景值）以及当前沉积强度+氮养分倍增（S_5N,5 cm·a^-1,氮养分水平为沉积物氮背景值的两倍）三种处理,探讨沉积强度及氮养分改变对短叶茳芏残体短期分解（30 d）与养分释放的影响。结果表明,不同处理下残体的分解速率表现为S₀（0.017207 d^-1）> S_5N（0.012166 d^-1）>S₅（0.011478 d^-1）。与S₀相比,S₅和S_5N的分解速率分别降低了33.29%和29.30%,说明沉积作用抑制了残体分解,但氮养分倍增又使得抑制程度得到一定缓解。沉积增强导致残体的TC含量增加,而TN、TP和TS含量降低;相同沉积强度下,氮养分倍增对TN、TS含量变化的影响最为明显。不同处理下残体的C、N、P和S在分解初期均表现为不同程度地净释放,沉积作用降低了残体的C释放,但增加了N、P养分释放;相同沉积强度下,氮养分倍增对残体C释放的影响不大,但降低了N、P养分释放。尽管残体质量损失均是影响不同处理下残体分解初期养分变化的共性因素,但沉积及氮养分变化对残体基质质量的改变是导致残体中养分含量及释放强度存在差异的重要原因。研究发现,互花米草促淤导致的沉积增强使得短叶茳芏残体在分解初期释放的较多N、P养分在很大程度上可能被互花米草所利用,进而在一定程度上可增强其入侵能力;但在氮养分增加条件下,互花米草可能优先利用分解环境中的氮养分来增强其入侵优势。

Effects of sedimentation and nitrogen variations on short-term decomposition and nutrient release of Cyperus malaccensis litters in the Minjiang River estuary

The strong sedimentation by Spartina alterniflora invasion can lead to significant changes in marsh sedimentary environment and nutrient status. In April 2017, the Cyperus malaccensis marsh affected by the invasion of S. alterniflora in Northwest Shanyutan of the Minjiang River estuary was selected as the study site. The effects of sedimentation and nitrogen (N) changes on short-term decomposition (30 days) and nutrients release of C. malaccensis litters were determined by in situ decomposition experiment, which included three one-off deposition treatments no sedimentation treatment (0 cm·a ^-1, S₀), current sedimentation treatment (5 cm·a^-1, S₅), the N level was the natural background value in sediments), and current sedimentation treatment + nitrogen treatment (5 cm·a^-1, S_5N, the N level was twice the natural background value in sediments)]. Results showed that the decomposition rates of C. malaccensis litters generally followed the sequence of S₀ (0.017207 d^-1) > S_5N (0.012166 d ^-1) > S₅ (0.011478 d ^-1). Compared with S₀ treatment, the decomposition rates in S₅ and S_5N treatments decreased by 33.29% and 29.30%, respectively, indicating that the sedimentation inhibited the decomposition of litters, but the doubled N, to some extent, relieved the inhibition. With increasing deposition, the contents of TC in litters increased while those of TN, TP and TS decreased. At the same deposition intensity, the effects of N doubling on variations of TN and TS contents in decomposing litters were particularly evident. At the initial stage of decomposition, stocks of C, N, P, and S in litters of different deposition treatments generally evidenced the export from litter to environment. The sedimentation reduced the release of C but increased the release of N and P. At the same deposition intensity, the double N showed no significant influence on the release of C but decreased the release of N and P. Although the mass loss was the common factor which affected the nutrient variations in decomposing litters at different treatments, the alterations of substrate quality caused by the changes of sedimentation and N nutrient were the main reason in inducing the differences of nutrient contents and release intensity. This study found that, at the early stage of decomposition, the elevated sedimentation caused by S. alterniflora resulted in releasing more N and P from C. malaccensis litters, which might be used by S. alterniflora and its invasion ability enhanced. However, with increasing N nutrient, the invasion advantage of S. alterniflora was very likely to enhance by utilizing the N nutrient in decomposition environment.