华西雨屏区天然常绿阔叶林土壤可培养微生物数量对模拟氮沉降的响应

为了解氮沉降对华西雨屏区天然常绿阔叶林土壤微生物数量的影响,从2013年11月至2014年12月,通过野外模拟N(NH_4NO_3)沉降,氮沉降水平分别为对照(CK 0 kg N hm~(-2)a~(-1))、低氮沉降(L 50 kg N hm~(-2)a~(-1))、中氮沉降(M 150 kg N hm~(-2)a~(-1))和高氮沉降(H 300 kg N hm~(-2)a~(-1)),研究了氮沉降对天然常绿阔叶林0—10cm和10—20cm土层土壤可培养微生物数量的影响。结果表明:华西雨屏区天然常绿阔叶林0—10cm土层的细菌、真菌和放线菌数量均显著大于10—20cm土层,氮沉降未改变原有垂直分布格局。L处理对0—10cm和10—20 cm土层土壤微生物总量无显著影响,M和H处理则显著降低了土壤微生物总量。氮沉降降低了0—10cm和10—20cm土层的细菌数量,且抑制作用随氮沉降量的增加而增强。氮沉降降低了0—10cm土层的真菌数量,但下降幅度与氮沉降量之间无明显规律;在10—20cm土层,M和H处理在夏季显著增加了真菌数量,表明适量氮沉降能有效缓解夏季土壤真菌的氮限制状态。氮沉降对0—10cm土层放线菌数量的影响表现为先促进再抑制,L和M处理增加了放线菌数量,H处理降低了放线菌数量;氮沉降增加了10—20cm土层的放线菌数量,其中M处理的促进作用最大。氮沉降对土壤微生物数量的影响随土壤深度的增加而减弱。

Response of culturable soil microorganisms to simulated nitrogen deposition in a natural evergreen broadleaf forest in the Rainy Area of Western China

Forest soil microbial activity is an important aspect of soil properties, and the number of the three kinds of microorganisms (bacteria, fungi, and actinomycetes) is an important indicator of the level of soil microbial activity. To understand the effects of increasing nitrogen deposition on soil microorganisms, an in situ experiment was conducted in a natural evergreen broadleaf forest in Ya''an City, Sichuan Province. We conducted the field experiment between November 2013 and December 2014. Four levels of nitrogen deposition were set:control (CK 0 kg N hm^-2 a^-1), low nitrogen (L 50 kg N hm^-2 a^-1), medium nitrogen (M 150 kg N hm^-2 a^-1), and high nitrogen (H 300 kg N hm^-2 a^-1). The results indicated that the number of bacteria, fungi, and actinomycetes in the 0-10 cm soil layer was significantly greater than that in the 10-20 cm layer. Nitrogen deposition did not change the original vertical distribution pattern of bacteria, fungi, and actinomycetes in the natural evergreen broadleaf forest in the Rainy Area of Western China. The L treatment did not have a significant effect on total soil microbial number, whereas the M and H treatments significantly reduced the total soil microbial number in both the 0-10 cm and 10-20 cm soil layers. Nitrogen deposition inhibited the number of bacteria in the 0-10 cm and 10-20 cm soil layers, and as nitrogen deposition increased, the inhibition effect was enhanced. Compared with the control, the M and H treatments significantly increased the number of fungi in the 10-20 cm soil layer during summer, indicating that a suitable amount of nitrogen deposition could effectively alleviate the nitrogen limitation of soil fungi in that season. Nitrogen deposition decreased the amount of fungi in the 0-10 cm soil layer, but there was no obvious relationship between the decrease and nitrogen deposition rate, whereas nitrogen deposition increased the number of actinomycetes in the 10-20 cm soil layer, and the increase was greatest in the M treatment. Nitrogen deposition first increased and then inhibited the number of actinomycetes in the 0-10 cm soil layer. The L and M treatments increased the number of actinomycetes, whereas the H treatment reduced the number of actinomycetes. The effects of nitrogen deposition on the quantity of soil microbial organisms decreased with increasing soil depth.