Soil microbial communities maintain many ecosystem functions including decomposition and symbiotic nutrient uptake. Prior field studies have focused on either geospatial or relatively large-time scale trends in these communities. Whereas, their small-time scale (e.g., weekly) dynamics in agricultural fields have largely been overlooked. Our objective was to determine the effects and characteristics of short-time scales on five phospholipid fatty acid (PLFA) microbial groups throughout the whole growing season, while under two soil disturbance levels. The microbial community groups included total microbial abundance (TMA), arbuscular mycorrhizal fungi (AMF), total fungi, actinomycetes, and total bacteria. The fungal to bacterial ratio (F:B) was also determined. Soils were sampled twice per week from planting to harvest during two consecutive growing seasons (N = 62) and analyzed for microbial abundances and chemical and physical properties. The study was conducted at an on-farm site with a corn [Zea mays] – soybean [Glycine max] – wheat [Triticum aestivum] rotation and two soil disturbance levels [high (chisel plow) and low (shallow vertical till)] using a randomized complete block design. Data analysis included 1) spatial and temporal coefficients of variations, 2) a mixed linear model to test for time and disturbance level effects, and 3) a Fourier analysis to detect and characterize cyclical patterns via autocorrelation spectral densities. The Fourier analysis also included cross spectral densities and phase lags with a large suite of soil chemical, soil physical, and weather states. Temporal variations of microbial communities were one to threefold greater than their spatial variations. Significant time effects were observed for TMA, AMF, and bacteria, where these communities behaved as sine and consine functions over time. However, strong cyclical patterns were above white noise levels at the experimental plots level for all microbial groups during each growing season. Cross spectral densities indicated that bacteria and actinomycetes tended to cycle at short and long periods (biweekly to whole season) associated with soil physical and weather states, whereas TMA, AMF, fungi, and F:B cycles at long periods (bimonthly to whole season) associated with soil chemical states. These microbial communities in a field setting clearly undergo cyclical patterns over small periods with some modulations from soil disturbance levels, fertilization, and microtopography. Further research on these cyclical and cross-correlated dynamics is warranted to determine the magnitude of influence on ecosystem services and crop productivity.

土壤微生物群落维持许多生态系统功能，包括分解和共生养分吸收。先前的野外研究集中于这些社区的地理空间趋势或相对较大的时间尺度趋势。然而，它们在农业领域的小规模规模（例如每周）动态却被大大忽略了。我们的目标是确定在两个土壤扰动水平下，在整个生长季节中短期比例对五个磷脂脂肪酸（PLFA）微生物群的影响和特征。微生物群落组包括总微生物丰度（TMA），丛枝菌根真菌（AMF），总真菌，放线菌和总细菌。还确定了真菌与细菌的比率（F：B）。从种植到收获的两个连续生长季节（N = 62），每周两次对土壤取样，并分析其微生物丰度以及化学和物理特性。该研究是在农场现场用玉米[玉米（Zea mays）–大豆[ Glycine max] –小麦[ Triticum aestivum旋转和两个土壤扰动水平（高（凿犁）和低（垂直耕作浅）），采用随机完整块设计。数据分析包括1）空间和时间变化系数，2）混合线性模型以测试时间和干扰水平的影响，3）傅立叶分析以通过自相关光谱密度检测和表征周期性模式。傅立叶分析还包括交叉光谱密度和相位滞后以及大量的土壤化学，土壤物理和天气状况。微生物群落的时间变化比其空间变化大一到三倍。对于TMA，AMF和细菌，观察到了显着的时间效应，这些群落随时间的变化表现为正弦和余弦功能。然而，在每个生长季节中，所有微生物组的实验地块水平上，强烈的周期性模式均高于白噪声水平。交叉光谱密度表明细菌和放线菌倾向于在短期和长期（每两周到整个季节）循环，与土壤物理和天气状况相关，而TMA，AMF，真菌和F：B则在长时期（每两个月到整个季节）循环）与土壤化学状态有关。在田间环境中，这些微生物群落在短时期内显然经历了周期性变化，并受到土壤扰动水平，施肥和微观地形的一些调节。有必要对这些周期性和相互关联的动力学进行进一步研究，以确定对生态系统服务和作物生产力的影响程度。