ABSTRACT

To examine the hypothesis that the soil microbial community in a nitrogen (N) limited forest responds to moderately elevated N deposition (< 10 kg ha⁻¹ yr⁻¹), correlations between N deposition and soil microbial properties were analyzed in a cool temperate forest surrounded by normally fertilized pasture grasslands in northern Japan. Three experimental plots were established in forest edges adjacent to the grasslands, and the other three plots were in forest interiors at least 700 m away from the grasslands. N deposition in each plot was measured from May to November 2018. In August 2018, we collected litter and surface soil samples from all plots to measure net N mineralization and nitrification rates as indicators of microbial activity, and microbial biomass and various gene abundances (i.e., bacterial 16S rRNA gene, fungal ITS region, and bacterial and archaeal amoA genes) as indicators of microbial abundance. N deposition in forest edges was 1.4-fold greater than that in forest interiors, whereas maximum N deposition was 3.7 kg ha⁻¹. N deposition was significantly correlated with net N mineralization and nitrification rates and 16S rRNA and bacterial amoA gene abundances. Microbial community structures analyzed for bacterial 16S rRNA gene and fungal ITS region amplicons were different between litter and soil samples but were similar between the forest edge and interior, although this analysis was made only for single pair of the two plots in the forest edge and interior. N deposition was also correlated with the soil C/N ratio and nitrate and ammonium contents. Thus, it was suggested that some soil microbial activities and abundances in an N limited forest likely responded to moderately elevated N deposition. These findings provide primary information on soil microbial response to moderately elevated N deposition.

摘要

为了检验氮 (N) 限制森林中的土壤微生物群落对适度升高的氮沉积（< 10 kg ha ^-1 yr ^-1)，在日本北部正常施肥的牧场草原环绕的凉爽温带森林中分析了氮沉积与土壤微生物特性之间的相关性。3个试验样地设在靠近草原的林缘，另外3个样地在距草原至少700 m的森林内部。2018 年 5 月至 11 月测量了每个地块的氮沉积。 2018 年 8 月，我们从所有地块收集枯枝落叶和表层土壤样本，以测量净氮矿化和硝化速率作为微生物活动的指标，以及微生物生物量和各种基因丰度（即、细菌 16S rRNA 基因、真菌 ITS 区域以及细菌和古菌amoA基因）作为微生物丰度的指标。森林边缘的氮沉积量是森林内部的 1.4 倍，而最大的氮沉积量为 3.7 kg ha ^-1。N 沉积与净 N 矿化和硝化速率以及 16S rRNA 和细菌amoA显着相关基因丰度。分析细菌 16S rRNA 基因和真菌 ITS 区域扩增子的微生物群落结构在凋落物和土壤样品之间不同，但在森林边缘和内部之间相似，尽管该分析仅针对森林边缘和内部的两个地块的单对进行. 氮沉降还与土壤 C/N 比和硝酸盐和铵含量相关。因此，有人认为，氮限制森林中的一些土壤微生物活动和丰度可能对适度升高的氮沉积做出反应。这些发现提供了土壤微生物对适度升高的氮沉积反应的主要信息。