Abstract. Increasing climatic pressures such as drought and flooding challenge agricultural systems and their management globally. How agricultural soils respond to soil water extremes will influence biogeochemical cycles of carbon and nitrogen in these systems. We investigated the response of soils from long term agricultural field sites under varying crop rotational complexity to either drought or flooding stress. Focusing on these contrasting stressors separately, we investigated soil heterotrophic respiration during single and repeated stress cycles in soils from four different sites along a precipitation gradient (Colorado, MAP 421 mm; South Dakota, MAP 580 mm; Michigan, MAP 893 mm; Maryland, MAP 1192 mm); each site had two crop rotational complexity treatments. At the driest (Colorado) and wettest of these sites (Maryland) we also analyzed microbial biomass, six potential enzyme activities and N₂O production, during and after individual and repeated stress cycles. In general, we found site specific responses to soil water extremes, irrespective of crop rotational complexity and precipitation history. Drought usually caused more severe changes in respiration rates and potential enzyme activities than flooding. All soils returned to control levels for most measured parameters as soon as soils returned to control water levels following drought or flood stress, suggesting that the investigated soils were highly resilient to the applied stresses. The lack of sustained responses following the removal of the stressors may be because they are well in the range of natural in situ soil water fluctuations at the investigated sites. Without inclusion of plants in our experiment, we found that irrespective of crop rotation complexity, soil and microbial properties in the investigated agricultural soils were more resistant to flooding but highly resilient to drought and flooding, during single or repeated stress pulses.

中文翻译：

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简单和复杂的作物轮作对农业土壤中水分胁迫的微生物活性响应

摘要。气候压力不断增加，例如干旱和洪水，对全球的农业系统及其管理提出了挑战。农业土壤对极端土壤水分的反应将影响这些系统中碳和氮的生物地球化学循环。我们调查了长期农田下土壤在不同轮作复杂性下对干旱或洪水胁迫的响应。我们分别针对这些相反的压力源，研究了沿着降水梯度（科罗拉多州MAP 421毫米;南达科他州MAP 580毫米;南达科他州MAP 580毫米;密歇根州MAP 893毫米）在四个不同地点的土壤中的单次和重复应力循环过程中的土壤异养呼吸。 MAP 1192毫米）；每个站点都进行了两种作物轮作复杂性处理。_2个在单个和重复的应力循环期间和之后产生O。总的来说，我们发现了针对土壤极端水的站点特定响应，而与作物轮作复杂性和降水历史无关。与洪水相比，干旱通常引起呼吸频率和潜在酶活性的更严重变化。干旱或洪水胁迫后，所有土壤只要恢复到控制水位，所有土壤就恢复到控制水平，这表明所研究的土壤对施加的应力具有高度的适应性。去除压力源后缺乏持续的响应可能是因为它们在调查地点的自然原位土壤水分波动范围内很好。在我们的实验中，在不包括植物的情况下，我们发现无论轮作复杂程度如何，