Effects of synthetic fertilizer and farm compost on soil nematode community in long-term crop rotation plots

Soil biodiversity plays a key regulation role in the ecosystem services that underpin regenerative sustainable agriculture. It can be impacted by agricultural management techniques, both positively (through measures such as compost application) and negatively (through, for example, application of synthetic nitrogen). As one of the most numerous members of the soil biota, nematodes are well established as indicators for the soil food web. However, compost application also includes the addition of nematodes present in compost and their subsequent survival in soil is unknown. Nematode communities within the compost applied to soil, and nematode communities in the soil of a multi-year rotational cropping field trial in Melle (Belgium) were studied using morphological and metabarcoding techniques. Compost (C) and nitrogen fertilizer (NF) treated plots were compared. Three replicate plots were investigated for each of the following treatments: C application only; C and NF application; NF only; no C and no NF (control). Plots were sampled six times between 2015-2017, before and after C or NF were added each spring and after crop harvest (except for 2017). NF treatment resulted in a significant decrease of fungal feeding and predatory nematodes, while herbivorous nematodes were positively affected. Remarkably, we did not find compost addition to exert any noticeable effects on the soil nematode community. The morphological and metabarcoding data resulted in different results of the nematode community composition. However, trends and patterns in the two data sets were congruent when observed with NMDS plots and using the nematode maturity index. Metabarcoding of individual compost nematode taxa demonstrated that nematodes originating from compost did not persist in soil.

土壤生物多样性（soil biodiversity）在支撑再生可持续农业的生态系统服务中发挥关键调控作用。农业管理措施可对其产生双向影响：正向措施如堆肥施用，负向措施如合成氮肥施加。线虫（nematodes）作为土壤生物群中数量最为丰富的类群之一，已被广泛确立为土壤食物网的指示生物。然而，堆肥施用过程中也会带入堆肥本身携带的线虫，此类线虫在土壤中的后续存活情况尚未明确。本研究针对比利时梅勒（Melle）市一处多年轮作大田试验样地，采用形态学鉴定与元条形码（metabarcoding）技术，分别对施入土壤的堆肥内线虫群落，以及试验田土壤中的线虫群落进行了研究。研究设置了堆肥施用（C）、氮肥施用（NF）两类处理，并针对以下四种处理设置三次重复样地：仅堆肥施用组；堆肥与氮肥配施组；仅氮肥施用组；无堆肥无氮肥的对照组。2015年至2017年间，研究人员分别于每年春季施入堆肥或氮肥前后，以及作物收获后（2017年除外）共完成6次采样。结果显示：氮肥施用会显著降低食真菌线虫与捕食性线虫的种群丰度，却对植食性线虫产生正向影响。值得注意的是，本研究未发现堆肥添加对土壤线虫群落产生任何可观测的显著影响。形态学数据与元条形码测序数据得到的线虫群落组成结果存在差异，但通过非度量多维尺度（NMDS）排序图分析与线虫成熟度指数（nematode maturity index）评估时，两类数据集的变化趋势与分布模式保持一致。针对堆肥内线虫类群的元条形码分析表明，源自堆肥的线虫并未在土壤中持续存活。