氮负荷增强对闽江河口芦苇残体分解及其养分释放的影响

选择闽江河口鳝鱼滩西北部的纯芦苇湿地为研究对象,基于野外氮负荷增强分解试验,探讨了氮负荷增强对芦苇残体分解及其养分释放的影响。试验设置了4个氮负荷水平,即NL0（无氮负荷处理,0 g N m^-2 a^-1）、NL1（低氮负荷处理,12.5 g N m^-2 a^-1）、NL2（中氮负荷处理,25.0 g N m^-2 a^-1）和NL3（高氮负荷处理,75.0 g N m^-2 a^-1）。结果表明,不同氮负荷处理下残体的分解速率整体表现为NL2（0.00284 d^-1）>NL1（0.00263 d^-1）>NL0（0.00257 d^-1）>NL3（0.00250 d^-1）,低氮和中氮负荷总体促进了残体分解,而高氮负荷抑制了残体分解,原因主要与不同处理下残体分解过程中基质质量及pH的明显改变有关。不同氮负荷处理下,残体中的全碳（TC）含量在分解期间均呈不同波动变化特征;全氮（TN）和全磷（TP）含量均在分解初期（0-30 d）骤然降低,之后则呈不同波动变化,其中TN含量呈波动上升变化,而TP含量呈小幅波动变化。残留率是影响不同氮负荷处理下残体分解期间碳（C）、氮（N）和磷（P）净释放的共性因素,而氮负荷增强导致的残体基质质量（C/N、C/P、N/P）和主要环境因子（pH、电导率（EC））改变影响了其释放强度。研究发现,在氮负荷增强背景下残体养分的累积与释放发生了明显改变,闽江河口氮负荷水平的增加整体将抑制芦苇残体中C、N养分的释放,但其在分解中后期（90-240 d）可能对P养分释放具有较为明显的促进作用。

Effects of enhanced nitrogen load on decomposition and nutrient release of Phragmites australis detritus in the Min River estuary

The pure Phragmites australis marsh in northwest Shanyutan of the Min River estuary was selected as the study object. The effects of enhanced nitrogen (N) load on decomposition and nutrient release of P. australis litters were determined by field N load decomposition experiment which included four N load levels:NL0 (no N load treatment, 0 g N m^-2 a^-1); NL1 (low N load treatment, 12.5 g N m^-2 a^-1); NL2 (medium N load treatment, 25.0 g N m^-2 a^-1) and NL3 (high N load treatment, 75.0 g N m^-2 a^-1). Results showed that the decomposition rates of P. australis litters generally followed the sequence of NL2 (0.00284 d^-1) > NL1 (0.00263 d^-1) > NL0 (0.00257 d^-1) > NL3 (0.00250 d^-1), indicating that the low load level and medium load level generally promoted the decomposition of detritus while the high load level inhibited its decomposition, which was primarily related to the great alterations in substrate quality and pH during decomposition in different N load treatments. The total carbon (TC) contents in decomposing litters of different N load treatments showed distinct fluctuations during decomposition. By comparison, the total nitrogen (TN) or total phosphorus (TP) contents in detritus in the four treatments decreased abruptly at the early stage (0-30 days), after which the values showed different fluctuations. Thereinto, the total nitrogen (TN) contents in detritus generally showed an increasing trend, while the total phosphorus (TP) contents in decomposing litters showed slight fluctuations. Stocks of C, N, and P in decomposing litters in different N load treatments generally evidenced the export from detritus to the environment. Litter mass remaining was a common factor influencing the net release of C, N and P from decomposing litters in different N load treatments. However, the release amounts of C, N and P from detritus primarily rested with the alterations of substrate quality (e.g., C/N, C/P, N/P) and key environmental variables (e.g., pH, EC) which were caused by different N load levels. The study found that the accumulation and release of detritus nutrients have changed significantly under the background of effects of N load enhancement. In the Min River estuary, elevation of N load levels would inhibit the release of C and N from P. australis litters as a whole, but it might show obvious stimulation on P release during the middle and late stages (90-240 days) of decomposition.