Livestock grazing promotes ecosystem multifunctionality of a coastal saltmarsh

The effects of livestock grazing on grasslands have garnered much attention; however, little is known about how grazing affects ecosystems’ ability to simultaneously support multiple ecosystem functions (i.e., ecosystem multifunctionality, hereafter EMF) in coastal saltmarshes.

To comprehensively evaluate the ecological effects of livestock grazing and tidal flooding on saltmarshes, we conducted a grazing-exclusion experiment in the high and middle marsh zones of the Yangtze River Estuary, China.

Livestock grazing generally enhanced EMF in the salt marshes, with a stronger impact in the middle marshes than in the high ones. Although plant biomass, aboveground N of plants, soil organic C, and sediment deposition rate decreased under grazing, activities of soil microbes and nematodes, soil N pool, N mineralization, decomposition and soil respiration increased.

Synthesis and applications. We suggest that tidal flooding and associated replenishment of sediments may mitigate the negative effects of grazing on plants and sedimentation and strengthen positive grazing impacts on nutrient cycling, consequently reinforcing the beneficial effects of livestock grazing on the saltmarsh ecosystem multifunctionality. Our results provide a holistic framework of ecosystem-level responses to livestock grazing in saltmarshes and highlight the regulatory role of external environmental factors such as tidal flooding. Although livestock grazing enhanced the overall EMF of saltmarshes in our study, it was not necessarily desirable for ecosystem services.  Integration of ecosystem function-multifunctionality and ecosystem service-multifunctionality of saltmarshes need to be recommended in future multifunctionality studies.

牲畜放牧对草地的影响已受到学界广泛关注，但目前对放牧如何影响滨海盐沼生态系统同时支撑多种生态系统功能（即生态系统多功能性，ecosystem multifunctionality，下文简称EMF）的能力仍知之甚少。

为全面评估牲畜放牧与潮汐淹水对盐沼的生态影响，我们在中国长江河口的中高潮盐沼带开展了放牧排除实验。

总体而言，牲畜放牧提升了盐沼的生态系统多功能性，且中潮盐沼的响应效应强于高潮盐沼。尽管放牧会降低植物生物量、植物地上氮含量、土壤有机碳以及沉积物沉积速率，但土壤微生物与线虫活性、土壤氮库、氮矿化作用、分解过程以及土壤呼吸均有所增强。

综合与应用。我们认为，潮汐淹水及其伴随的沉积物补给可缓解放牧对植物与沉积过程的负面影响，并强化放牧对养分循环的积极作用，进而增强牲畜放牧对盐沼生态系统多功能性的有益效应。本研究结果为盐沼生态系统对牲畜放牧的响应提供了一套整体性的生态系统尺度分析框架，并强调了潮汐淹水等外部环境因子的调控作用。尽管本研究中牲畜放牧提升了盐沼的整体生态系统多功能性，但这并不意味着其对生态系统服务而言必然是有利的。未来的多功能性研究中，建议整合盐沼的生态系统功能-多功能性与生态系统服务-多功能性维度。