Rebollar Eria A, Sandoval-Castellanos Edson, Roessler Kyria, Gaut Brandon S, Alcaraz Luis D, Benítez Mariana, Escalante Ana E
Departamento de Ecología Evolutiva, Instituto de Ecología, Universidad Nacional Autónoma de México, Mexico City, Mexico.
Centro de Ciencias de la Complejidad, Universidad Nacional Autónoma de México, Mexico City, Mexico.
Front Microbiol. 2017 Dec 18;8:2478. doi: 10.3389/fmicb.2017.02478. eCollection 2017.
The milpa is a traditional maize-based polyculture in Mexico that is typically practiced as rainfed agriculture. Because milpa cultivation has been practiced over a vast range of environmental and cultural conditions, this agroecosystem is recognized as an important repository of biological and cultural diversity. As for any agroecosystem, the relationship between plant development and the biogeochemical processes of the soil is critical. Although the milpa has been studied from different perspectives, the diversity and structure of microbial communities within milpa soils remain largely unexplored. In this study, we surveyed a milpa system in Central Mexico across cropping season: before planting (dry season; ), during the early growth of plants (onset of the rainy season; ), and before harvest (end of the rainy season; ). In order to examine changes in community structure through time, we characterized bacterial diversity through high-throughput sequencing of 16S rRNA gene amplicons and recorded the nutrient status of multiple (5-10) soil samples from our milpa plots. We estimated microbial diversity from a total of 90 samples and constructed co-occurrence networks. Although we did not find significant changes in diversity or composition of bacterial communities across time, we identified significant rearrangements in their co-occurrence network structure. We found particularly drastic changes between the first and second time points. Co-occurrence analyses showed that the bacterial community changed from a less structured network at () into modules with a non-random composition of taxonomic groups at (). We conclude that changes in bacterial communities undetected by standard diversity analyses can become evident when performing co-occurrence network analyses. We also postulate possible functional associations among keystone groups suggested by biogeochemical processes. This study represents the first contribution on soil microbial diversity of a maize-based polyculture and shows its dynamic nature in short-term scales.
米尔帕是墨西哥一种传统的以玉米为基础的多元种植模式，通常作为雨养农业来实施。由于米尔帕种植在广泛的环境和文化条件下进行，这种农业生态系统被认为是生物和文化多样性的重要宝库。对于任何农业生态系统而言，植物发育与土壤生物地球化学过程之间的关系至关重要。尽管已经从不同角度对米尔帕进行了研究，但米尔帕土壤中微生物群落的多样性和结构在很大程度上仍未得到探索。在本研究中，我们在墨西哥中部的一个米尔帕系统中进行了整个种植季节的调查：种植前（旱季）、植物生长早期（雨季开始时）和收获前（雨季结束时）。为了研究群落结构随时间的变化，我们通过对16S rRNA基因扩增子进行高通量测序来表征细菌多样性，并记录了我们米尔帕地块中多个（5 - 10个）土壤样本的养分状况。我们从总共90个样本中估计微生物多样性并构建了共现网络。尽管我们没有发现细菌群落的多样性或组成随时间有显著变化，但我们确定了它们共现网络结构的显著重排。我们发现第一次和第二次采样时间点之间的变化尤为剧烈。共现分析表明，细菌群落从（第一个时间点）时结构较少的网络转变为（第二个时间点）时具有分类群非随机组成的模块。我们得出结论，在进行共现网络分析时，标准多样性分析未检测到的细菌群落变化可能会变得明显。我们还推测了生物地球化学过程所暗示的关键菌群之间可能的功能关联。本研究是对基于玉米的多元种植土壤微生物多样性的首次贡献，并展示了其在短期尺度上的动态性质。
