Drying and rewetting (D/W) of soil have significant impacts on soil organic matter (SOM) turnover. We hypothesised that frequent D/W cycles would release the labile organic matter locked away in soil aggregates, increasing the priming effect (PE) (acceleration or retardation of SOM turnover after fresh substrate addition) due to preferential utilisation by microbes. 13C-labelled lignocellulose was added to the soil, and the effects of 0, 1, or 4 cycles of D/W were evaluated at 5 °C and 25 °C after a 27-day incubation of undisturbed soil cores from a temperate forest (Araucaria araucana). Following the incubation, macroaggregates (> 250 μm), microaggregates (250–53 μm), and silt + clay materials (< 53 μm) were separated. For each aggregate size class, three organic matter (OM) fractions (light (fPOM < 1.6 g cm−3), occluded (oPOM 1.6–2.0 g cm−3), and heavy (Hf > 2.0 g cm−3) were determined. D/W cycles caused macroaggregates to increase and a decrease in microaggregates (> 15%) at warm temperatures, and preferential use of the novel particulate organic matter (13C labelled), formerly protected fPOM. CO2 efflux was three times higher at 25 °C than at 5 °C. The D/W cycles at 25 °C had a strong negative impact on cumulative CO2 efflux, which decreased by approximately − 30%, induced by a negative PE of −50 mg C kg−1 soil with 1 D/W cycle and − 100 mg C kg−1 soil with 4 D/W cycles, relative to soil under constant soil moisture receiving 13C-labelled lignocellulose, but no cycles. Increasing the temperature and the number of D/W cycles caused a decrease in substrate use efficiency of particulate lignocellulose. In conclusion, D/W cycles at warm temperatures accelerated OM turnover due to preferential use from fPOM, increasing macroaggregates at the expense of microaggregates. A novel pathway of OM release and PE due to the D/W cycles is discussed.

中文翻译：

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干燥/再润湿对土壤团聚体动力学的影响和对有机物质周转的影响

土壤的干燥和再润湿 (D/W) 对土壤有机质 (SOM) 周转有显着影响。我们假设频繁的 D/W 循环会释放锁定在土壤团聚体中的不稳定有机物质，由于微生物的优先利用，增加了启动效应 (PE)（添加新鲜底物后 SOM 周转的加速或延迟）。将 13C 标记的木质纤维素添加到土壤中，并在来自温带森林的未受干扰的土壤核心培养 27 天后，在 5°C 和 25°C 下评估了 0、1 或 4 个 D/W 循环的影响（南洋杉）。培养后，大团聚体（> 250 μm）、微团聚体（250-53 μm）和淤泥+粘土材料（< 53 μm）被分离。对于每个骨料尺寸等级，三个有机物 (OM) 部分（轻（fPOM < 1.6 g cm−3）、被遮挡的（oPOM 1.6–2. 0 g cm-3) 和重 (Hf > 2.0 g cm-3) 被确定。D/W 循环在温暖的温度下导致大团聚体增加和微团聚体减少（> 15%），并优先使用新型颗粒有机物（标记为 13C），以前受保护的 fPOM。25 °C 时的 CO2 流出量是 5 °C 时的三倍。25 °C 下的 D/W 循环对累积 CO2 流出有强烈的负面影响，减少了大约 - 30%，这是由负 PE 引起的 -50 mg C kg-1 土壤和 1 D/W 循环和 - 100具有 4 个 D/W 循环的 mg C kg-1 土壤，相对于接受 13C 标记的木质纤维素但没有循环的恒定土壤湿度下的土壤。增加温度和 D/W 循环次数会导致颗粒木质纤维素的底物使用效率降低。综上所述，由于优先使用 fPOM，在温暖温度下的 D/W 循环加速了 OM 周转，以牺牲微团聚体为代价增加了大团聚体。讨论了由于 D/W 循环导致 OM 释放和 PE 的新途径。