以NH4NO3作为氮源，对广州东北郊木荷（Schima superba）人工幼林地进行模拟氮沉降处理，共设置3个氮沉降水平，分别为N0（N：0 g·m-2·a-1）、N5（N：5 g·m-2·a-1）以及N10（N：10 g·m-2·a-1），每月进行喷施。在连续施氮22个月（当月当次施氮5天后）对土壤氮素（硝氮、氨氮、总氮）、碳素（总碳）以及微生物量（脂磷）在0~60 cm土层中的垂直分布进行研究。结果显示：在3个氮沉降水平下，随着土层加深，pH呈现出下降的趋势，氮沉降存在加剧土壤酸化的风险；在N0、N5、N10水平下，土壤全氮和总碳的垂直分布趋势大体一致，随着土层加深，其含量下降，但在深层土壤（40~60 cm）中，施氮与对照比较，总碳呈现一定的增加趋势；除40~50 cm土层，N5、N10水平下的硝态氮含量在各个深度土壤中都表现为比对照组要高，氮沉降导致土壤一定程度上硝态氮的积累；在浅层土壤（0~20 cm）中，铵态氮水平较低并且其含量明显低于对照组，而在较深的土层中铵态氮有较多的积累，说明存在污染地下水的风险；N5和N10水平下，无机氮比例（无机氮含量与总氮含量之比）在各个深度土壤中总体高于N0水平；用脂磷含量表征土壤微生物含量，结果表明外加氮源对微生物含量有显著性影响，在N5、N10水平下，微生物含量在30~40 cm土层中出现峰值。%A field experiment in young Schima superb plantation was conducted in Zengcheng, Guangzhou to study the response of the vertical distribution of soil nitrogen, soil carbon and soil microbial biomass to 3 levels of simulated nitrogen deposition (N0 treatment: N 0 g·m-2·a-1. N5 treatment: N 5 g·m-2·a-1. And N10 treatment: N 10 g·m-2·a-1). Soil samples were collected from the depth of 0~10, 10~20, 20~30, 30~40, 40~50 cm and 50~60 cm after successive 22 months’ simulation. Indexes including soil nitrogen (nitrate, ammonia, and total nitrogen), carbon (total carbon) and microbial biomass (lipid-P) were measured. The results show that: pH showed a downward trend in three levels with the increase of soil depth, which means a risk of soil acidification; total nitrogen and total carbon in all levels show a similar trend in vertical distribution: decreases with depth; but in the depth of 40~60 cm, total carbon in N5 and N10 shows an increase compared with N0; the concentration of nitrate in N5 and N10 is higher than N0 except for that at 40~50 cm, which suggests nitrogen deposition lead to a certain degree of nitrate accumulation; in the depth of 0~20 cm, am-monium is at a low level and significantly lower than the control group (N0), while in the deeper layers, ammonium shows a higher content, which poses a threat to groundwater; in all layers, the proportion of inorganic nitrogen to total nitrogen in N5 and N10 level is higher than that in N0; microbial biomass differs significantly at different nitrogen deposition levels, and there are peak values in the depth of 30~40 cm at both levels of N5 and N10.
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