Soil organic carbon (SOC) is both a source and sink of atmospheric carbon dioxide (CO2), with important implications for global climate change. Irrigation of grazed pastures has reportedly increased, reduced or made no difference to SOC stocks relative to dryland management. This study examined, over an annual plant growth cycle, the persistence of photosynthate-derived carbon (C) previously allocated to the plant–soil system during summer, under irrigated or dryland conditions. A continuous 13CO2 pulse labelling method was used to label ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) mesocosms under simulated dryland or irrigated conditions. Plant and soil 13C was traced over 349 days using destructive sampling on days 1, 12, 125, 237 and 349 (T1–T5 respectively). After the cessation of labelling and summer irrigation, the mesocosms were maintained under the same seasonal soil moisture conditions. The persistence of 13C in the aboveground plant C pools was lower than in the root C pool. Approximately 50% of the initial mass of 13C recovered in roots at T1 remained by T5. There was no difference between the summer irrigated and dryland treatments in terms of the 13C recovered from the soil over the subsequent annual growing season. There was also no significant change in the 13C recovered in the soil between T1 and T5. However, summer irrigation did affect the spatial and temporal distribution of the photosynthate-derived C within the soil size fractions relative to summer dryland conditions. Summer irrigation promoted the transfer and storage of 13C in the fine particulate organic matter and clay size fractions.

中文翻译：

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夏季牧场灌溉增强了土壤有机碳在颗粒和矿物相关有机质部分中的转移和短期储存

土壤有机碳 (SOC) 是大气二氧化碳 (CO2) 的来源和汇，对全球气候变化具有重要意义。据报道，相对于旱地管理，放牧牧场的灌溉对 SOC 储量增加、减少或没有影响。这项研究检查了在一年的植物生长周期中，先前在夏季、灌溉或旱地条件下分配给植物 - 土壤系统的光合产物碳 (C) 的持久性。使用连续 13CO2 脉冲标记方法在模拟旱地或灌溉条件下标记黑麦草 (Lolium perenne L.) 和白三叶草 (Trifolium repens L.) 中胚层。植物和土壤 13C 在第 1、12、125、237 和 349 天（分别为 T1-T5）使用破坏性采样追踪了 349 天。在停止贴标和夏季灌溉后，中世界保持在相同的季节性土壤湿度条件下。13C在地上植物碳库中的持久性低于根系碳库。在 T1 时在根中回收的 13C 初始质量的大约 50% 在 T5 时仍然存在。在随后的年度生长季节从土壤中回收的 13C 方面，夏季灌溉和旱地处理之间没有差异。在 T1 和 T5 之间，土壤中回收的 13C 也没有显着变化。然而，相对于夏季旱地条件，夏季灌溉确实影响了土壤大小部分内光合产物碳的时空分布。夏季灌溉促进了 13C 在细颗粒有机物和粘土粒度级分中的转移和储存。