外源氮输入对闽江河口芦苇湿地土壤磷形态赋存特征的影响

河口湿地是响应全球气候变化和人类活动最为敏感的生态系统之一,是外源氮的一个重要"汇",其对于生源元素循环过程可产生深刻的影响。在当前闽江河口区氮负荷增强背景下,探讨外源氮输入对湿地土壤磷形态赋存及其关键转化过程具有重要意义。为此,选择闽江河口鳝鱼滩的芦苇湿地为研究对象,基于野外原位氮输入模拟试验,研究了不同氮输入水平（N_Nt,对照处理;N_Lt,低氮处理;N_Mt,中氮处理;N_Ht,高氮处理）对湿地土壤磷形态赋存特征的影响。结果表明,外源氮输入不但增加了湿地土壤的TP含量,而且改变了其土层分布特征。除N_Mt与N_Nt处理下的TP含量相当外,N_Lt和N_Ht处理下的全磷（TP）含量相比N_Nt处理分别增加了3.5%和4.4%。氮输入整体上增加了湿地土壤的活性磷和闭蓄态磷含量,但降低了中等活性磷含量。相比N_Nt处理,N_Mt和N_Ht处理下的活性磷含量分别增加了6.5%和12.6%,而N_Lt、N_Mt和N_Ht处理下的闭蓄态磷含量分别增加了3.3%、3.9%和7.0%。中等活性磷在N_Mt处理下的降幅尤为明显,其值相比N_Nt处理降低了6.7%。不同氮处理下湿地土壤以闭蓄态磷占比最高（51.8%-54.1%）,中等活性磷次之（38.1%-41.2%）,活性磷最低（7.0%-7.9%）。不同氮处理下的各形态磷占比以HCl-P_i、Residual-P、NaOH-P_o和NaOH-P_i较高,Sonic-P_o和NaHCO₃-P_i次之,而NaHCO₃-P_o、Resin-P和Sonic-P_i较低。研究发现,氮输入主要通过改变土壤养分及酸碱状况来进一步影响土壤中各形态磷的赋存。其中,N_Mt和N_Ht处理下活性磷含量的增加主要与Resin-P和NaHCO₃-P_o有关,N_Lt、N_Mt和N_Ht处理下闭蓄态磷含量的增加主要与Residual-P有关,而N_Mt处理下中等活性磷的显著降低主要与NaOH-P_i和Sonic-P_o有关。

Effects of exogenous nitrogen enrichment on distribution of phosphorus fractions in soils of Phragmites australis marsh in the Min River estuary, China

Estuarine marsh is one of the most sensitive ecosystems that respond to global change and human activities. The estuarine marsh generally acts as a sink of exogenous nitrogen (N), which might produce significantly influences on the processes of biogenic elements. In the background of enhanced exogenous N import in the Min River estuary, it is significance to explore the effects of N import on the distributions and key transformation processes of phosphorus (P) fractions in marsh soils. In this paper, the effects of exogenous N import levels (N_Nt, control treatment; N_Lt, low N treatment; N_Mt, medium N treatment; N_Ht, high N treatment) on P fractions in soils of Phragmites australis marsh in Shanyutan of the Min River estuary were investigated by in situ N enrichment experiment. Result showed that the exogenous N enrichment not only increased the total phosphorus (TP) contents in soils, but also altered its distributions in soil layers. The TP contents in soils of the N_Mt and N_Nt were approximated, but the values in soils of the N_Lt and N_Ht, compared with N_Nt, increased by 3.5% and 4.4%, respectively. The enrichment of N generally increased the contents of available and non-available P in soils, but reduced the values of moderately available P. Compared with N_Nt, the contents of available P in the N_Mt and N_Ht increased by 6.5% and 12.6%, while the values of non-available P in the N_Lt, N_Mt and N_Ht increased by 3.3%, 3.9% and 7.0%, respectively. It should be noting that the decline of moderately available P contents in the N_Mt was particularly evident and the deceasing amplitude reached 6.7%.The proportions of non-available P in TP in soils of different treatments were the highest (51.8%-54.1%), followed by moderately available P with 38.1%-41.2% and available P with 7.0%-7.9%. Moreover, the proportions of HCl-P_i, Residual-P, NaOH-P_o and NaOH-P_i in TP in soils of different enrichments were much higher, followed by Sonic-P_o and NaHCO₃-P_i, while those for NaHCO₃-P_o, Resin-P and Sonic-P_i were generally lower. This study found that the exogenous N enrichment altered the nutrient and acid-base conditions of soils greatly, which further influenced the distribution and availability of P fractions in soils. The increase of available P contents in the N_Mt and N_Ht, was mainly associated with Resin-P and NaHCO₃-P_o, while those of non-available P contents in the N_Lt, N_Mt and N_Ht was primarily related to Residual-P. By comparison, the significant increase of moderately available P contents in the N_Mt was mainly dependent on NaOH-P_i and Sonic-P_o.