Background and aims: One goal of revegetating riparian zones is to mitigate nutrient movement into waterways, however release of dissolved nutrients and organic compounds from decaying leaf litter during rainfall may partially offset these benefits. We aim to understand how litter-derived nutrients and organics affect nutrient leaching from riparian soil, and how tree species affect these processes. Methods: In the laboratory we simulated large rainfall events through the leaf litter of two riparian woody tree species, Eucalyptus tereticornis and Casuarina cunninghamiana, with and without subsequent leaching through soil, as well as soil alone. We compared the forms and loads of nitrogen and phosphorus in leachate. Results: Litter of both tree species stimulated additional nitrate release from soil (~100–200%) compared to bare soil. More ammonium and dissolved organic nitrogen also leached from soil with E. tereticornis litter, whereas less leached with C. cunninghamiana litter. More phosphate leached from soil with either species litter compared to bare soil. Increased nitrogen releases from soil with litter were greater than inputs from litter, suggesting they are driven by positive priming of soil microbial processes, whereas litter inputs increased phosphorus leaching. Conclusions: This information could be combined with rates of other riparian nutrient processes (e.g. plant uptake and denitrification) to quantify the net impact of trees on nutrient retention in riparian zones.

中文翻译：

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在大降雨事件期间，两种河岸树种的落叶对从土壤中浸出的养分有不同的影响

背景和目标：重新植被河岸带的一个目标是减少营养物质进入水道，但是降雨期间腐烂的枯枝落叶中溶解的营养物质和有机化合物的释放可能会部分抵消这些好处。我们的目标是了解凋落物衍生的养分和有机物如何影响河岸土壤中的养分浸出，以及树种如何影响这些过程。方法：在实验室中，我们通过两种河岸木本树种 Eucalyptus tereticornis 和 Casuarina cunninghamiana 的落叶模拟了大降雨事件，有和没有随后通过土壤浸出，以及单独的土壤。我们比较了渗滤液中氮和磷的形态和负荷。结果：与裸土相比，两种树种的凋落物都刺激了土壤中额外的硝酸盐释放 (~100–200%)。使用 E. tereticornis 凋落物从土壤中浸出更多的铵和溶解的有机氮，而使用 C. cunninghamiana 凋落物浸出的较少。与裸土相比，使用任一物种凋落物从土壤中浸出的磷酸盐更多。有凋落物的土壤释放的氮增加大于来自凋落物的输入，表明它们是由土壤微生物过程的积极启动驱动的，而凋落物输入增加了磷的浸出。结论：该信息可以与其他河岸养分过程（例如植物吸收和反硝化）的速率相结合，以量化树木对河岸带养分保留的净影响。与裸土相比，使用任一物种凋落物从土壤中浸出的磷酸盐更多。有凋落物的土壤释放的氮增加大于来自凋落物的输入，表明它们是由土壤微生物过程的积极启动驱动的，而凋落物输入增加了磷的浸出。结论：该信息可以与其他河岸养分过程（例如植物吸收和反硝化）的速率相结合，以量化树木对河岸带养分保留的净影响。与裸土相比，使用任一物种凋落物从土壤中浸出的磷酸盐更多。有凋落物的土壤释放的氮增加大于来自凋落物的输入，表明它们是由土壤微生物过程的积极启动驱动的，而凋落物输入增加了磷的浸出。结论：该信息可以与其他河岸养分过程（例如植物吸收和反硝化）的速率相结合，以量化树木对河岸带养分保留的净影响。