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 (Maryland) of these sites, 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 the 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.

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微生物活动对简单和复杂轮作农业土壤水分胁迫的响应

干旱和洪水等日益增加的气候压力对全球农业系统及其管理提出了挑战。农业土壤对土壤水分极端情况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土壤在不同作物轮作复杂性下对干旱或洪水压力的响应。分别关注这些不同的压力源，我们研究了沿降水梯度（科罗拉多州，MAP 421 毫米；南达科他州，MAP 580 毫米；密歇根州，MAP 893 毫米；马里兰州，马里兰州，地图 1192 毫米）；每个地点有两个作物轮作复杂性处理。在这些地点中最干燥（科罗拉多州）和最潮湿（马里兰州）的地方，₂在单个和重复的应力循环期间和之后产生 O。总的来说，我们发现对土壤水分极端情况的特定地点响应，与作物轮作复杂性和降水历史无关。与洪水相比，干旱通常会导致呼吸速率和潜在酶活性发生更严重的变化。一旦土壤在干旱或洪水胁迫后恢复到控制水位，所有土壤就大多数测量参数恢复到控制水平，这表明所研究的土壤对施加的压力具有高度弹性。去除压力源后缺乏持续响应可能是因为它们完全处于调查地点的自然原位土壤水波动范围内。在我们的实验中不包括植物的情况下，我们发现无论作物轮作的复杂性如何，