Inter-seasonal nitrogen loss with drought depends on fertilizer management in a semi-natural Australian grassland

Drought can increase nitrogen (N) loss due to enhanced asynchronicity between N release through mineralization and plant N uptake. Organic amendments of N could potentially mitigate this loss where the N is more slowly released and made available at times when plants need it. Drought (ambient vs. reduced precipitation implemented with rainout shelters) and fertilizer addition (compost vs. mineral fertilizer) were used to examine the changes in mineralization, plant uptake and loss of N during dry and wet periods in a grassland of Australia. Both gross N mineralization (GNM) and plant N uptake were high in wet summers and low in dry summers, while in the winter the relatively high GNM was not matched with similarly high plant N uptake. Drought conditions combined with mineral fertilizer addition resulted in the highest plant δ15N values, reflecting a more open N cycle (high N loss). In contrast, under drought conditions, compost released N more slowly and showed greater synchronicity with plant N demand. Because drought has become increasingly more intense and frequent, compost addition to grasslands could be a beneficial management strategy to improve soil health and increase plant productivity, and most importantly, to reduce N loss compared to mineral fertilizers.

干旱可通过强化氮（N）矿化释放与植物氮吸收之间的异步性，加剧氮素损失。施加氮素有机改良剂可通过延缓氮素释放速率，使其匹配植物需氮时段，从而潜在缓解该类氮素损失。本研究以澳大利亚某天然草原为研究对象，采用防雨棚设置降水处理（自然降水组 vs. 减雨组）与施肥处理（堆肥组 vs. 矿质肥料组），探究干湿周期内氮矿化、植物氮吸收与氮素损失的变化规律。湿润夏季的总氮矿化（gross N mineralization, GNM）与植物氮吸收水平均处于高位，干旱夏季则双双走低；而冬季的总氮矿化水平虽相对偏高，却未伴随同等强度的植物氮吸收。干旱结合矿质肥料施用处理下，植物的δ¹⁵N值达到最高，这反映出氮循环更为开放（氮素损失量更高）。与之相反，在干旱条件下，堆肥的氮素释放速率更为平缓，且与植物需氮时段的同步性更强。鉴于干旱事件的强度与发生频率日益提升，相较于矿质肥料，在草原中施加堆肥可作为一项有益的管理策略，能够改善土壤健康状况、提升植物生产力，且最为关键的是可降低氮素损失。