外源氮持续输入对相应氮梯度下碱蓬残体分解及硫养分释放的影响

以黄河口北部滨岸高潮滩的碱蓬残体为研究对象,将第一年度野外原位氮输入试验(N0:无额外氮处理;N1:低氮处理;N2:中氮处理;N3:高氮处理)获得的不同基质质量残体(NL0,NL1,NL2和NL3),原位投放至来源样区,并通过第二年度的持续输氮,探讨外源氮持续输入条件下残体基质质量改变对其分解速率和硫养分释放的影响。结果表明,随着氮输入量的增加,不同基质质量残体的分解速率整体表现为NL1NL3NL2NL0,说明外源氮持续输入条件下基质质量改变促进了残体的分解,且该促进作用在低氮处理下表现的最为明显,原因主要与其在残体分解过程中C/N比的改变程度最为明显有关。不同基质质量残体中的TS含量均呈不同程度波动变化特征,且其与相应的C/S比均呈相反规律变化,说明C/S比是调控不同氮持续输入条件下残体分解过程中硫含量变化的主控因素。不同基质质量残体的硫养分在分解期间均发生不同程度的净释放,且释放强度整体表现为NL3NL1NL2NL0,说明外源氮持续输入条件下残体基质质量改变促进了其硫养分释放,且该促进作用在高氮处理下表现的最为明显。研究发现,未来黄河口氮养分负荷增加的情况下,碱蓬残体的基质质量(C/N和C/S)将发生改变,而持续增强的氮负荷又会促进不同基质质量残体的硫养分归还,从而加速硫的生物循环速率。

Effect of continuous import of exogenous nitrogen on decomposition and sulfur release of Suaeda salsa litters in the corresponding nitrogen gradient

The Suaeda salsa marsh in the high tidal flat of the northern Yellow River estuary was selected as the study object. In the first year, in situ experiment of different nitrogen (N) loadings (N0, no N import treatment; N1, low N import treatment; N2, middle N import treatment; and N3, high N import treatment) was conducted. At the end of the growing season, litters with different substrate qualities (NL0, NL1, NL2, and NL3) were sampled from different N import plots. In the second year, these litters were placed in the corresponding N import plots, and N loadings were continuously conducted as the same with the first year. The objective of this study was to investigate the effect of exogenous nitrogen enrichment on decomposition and sulfur (S) release of S. salsa litters. The results showed that the decomposition rates of S. salsa litters generally followed the order of NL1 > NL3 > NL2 > NL0, indicating that, as N was continuously imported, the alteration of substrate quality promoted litter decomposition and the promotion was particularly obvious in the low N treatment (N1), which was mainly related to alterations in C/N ratios during decomposition. The total sulfur (TS) contents in litters of different N loadings showed different fluctuations, which were opposite to the corresponding C/S ratios, indicating that the C/S ratio was the main factor controlling the variations in TS contents of different litters during decomposition. For litters with different substrate qualities, the net release of S was observed throughout the decomposition process and the release amounts were generally in the order of NL3 > NL1 > NL2 > NL0, indicating that, as N was continuously imported, alterations in litter quality stimulated the release of S and the stimulation was predominant in the high N treatment (N3). This study showed that increasing N loading in the intertidal zone of the Yellow River estuary would alter the substrate quality of S. salsa litters and continuous N loading would promote S returning from the litters. As a result, the S biological cycling rate in S. salsa marsh would be accelerated.