Data from: Nutrient presses and pulses differentially impact plants, herbivores, detritivores and their natural enemies

Anthropogenic nutrient inputs into native ecosystems cause fluctuations in resources that normally limit plant growth, which has important consequences for associated food webs. Such inputs from agricultural and urban habitats into nearby natural systems are increasing globally and can be highly variable, spanning the range from sporadic to continuous. Despite the global increase in anthropogenically-derived nutrient inputs into native ecosystems, the consequences of variation in subsidy duration on native plants and their associated food webs are poorly known. Specifically, while some studies have examined the effects of nutrient subsidies on native ecosystems for a single year (a nutrient pulse), repeated introductions of nutrients across multiple years (a nutrient press) better reflect the persistent nature of anthropogenic nutrient enrichment. We therefore contrasted the effects of a one-year nutrient pulse with a four-year nutrient press on arthropod consumers in two salt marshes. Salt marshes represent an ideal system to address the differential impacts of nutrient pulses and presses on ecosystem and community dynamics because human development and other anthropogenic activities lead to recurrent introductions of nutrients into these natural systems. We found that plant biomass and %N as well as arthropod density fell after the nutrient pulse ended but remained elevated throughout the nutrient press. Notably, higher trophic levels responded more strongly than lower trophic levels to fertilization, and the predator/prey ratio increased each year of the nutrient press, demonstrating that food web responses to anthropogenic nutrient enrichment can take years to fully manifest themselves. Vegetation at the two marshes also exhibited an apparent tradeoff between increasing %N and biomass in response to fertilization. Our research emphasizes the need for long-term, spatially diverse studies of nutrient enrichment in order to understand how variation in the duration of anthropogenic nutrient subsidies affects native ecosystems.

人为养分输入至本地生态系统，会打破原本限制植物生长的资源的动态平衡，进而对关联食物网产生重要影响。这类源自农业与城市生境、输入至周边自然系统的养分输入，在全球范围内呈上升趋势，且具有高度变异性，输入模式涵盖从偶发至持续的全谱系。
尽管全球范围内输入本地生态系统的人为来源养分不断增加，但关于补给时长的差异对本地植物及其关联食物网所产生的影响，目前仍知之甚少。具体而言，尽管已有部分研究探讨了单次年度养分补给，即养分脉冲 (nutrient pulse) 对本地生态系统的影响，但跨多年度的持续性养分输入，即养分持续输入 (nutrient press) 更能反映人为养分富集的长期本质。
为此，本研究在两处盐沼中，对比了为期1年的养分脉冲与为期4年的养分持续输入对节肢动物消费者的影响。盐沼是研究养分脉冲与持续输入对生态系统及群落动态产生差异化影响的理想系统，因为人类开发与其他人为活动会持续向这类自然系统输入养分。
研究发现，养分脉冲结束后，植物生物量、%N以及节肢动物密度均出现下降；而在养分持续输入期间，上述指标则始终维持在较高水平。值得注意的是，相较于低营养级生物，高营养级生物对施肥处理的响应更为强烈；且在养分持续输入的每一年中，捕食者与猎物的比例均有所上升，这表明食物网对人为养分富集的响应可能需要数年时间才能完全显现。
两处盐沼的植被在响应施肥时，%N提升与生物量增加之间呈现出显著的权衡关系。
本研究强调，为阐明人为养分补给时长的差异如何影响本地生态系统，亟需开展长期、多空间尺度的养分富集相关研究。