Grazer effects on soil carbon storage vary by herbivore assemblage in a semi‐arid grassland

Abstract

Accounting for 10%–30% of global soil organic carbon, grassland soils potentially present a large reservoir for storing atmospheric CO2. Livestock grazing management can substantially affect grassland soil carbon (C) storage, but few controlled experiments have explored how herbivore assemblages (different herbivore species and combinations) affect soil C storage. We examined effects of moderate grazing by different herbivore assemblages (no grazing; sheep grazing; cattle grazing; mixed grazing by sheep and cattle) on soil organic carbon storage in two types of grassland communities (high forbs/high diversity and low forbs/low diversity), within a semi‐arid grassland with a 5‐year grazing history. We found that herbivore assemblage generated varying effects on soil C storage and the effects were subject to grassland community types. In the low diversity community, none of three herbivore assemblages studied had obvious effects on soil C storage. In the high diversity community, however, sheep grazing significantly decreased soil C storage due to high selectivity for high quality forbs, and cattle grazing had no effects on soil C storage, while mixed grazing by sheep and cattle significantly increased soil C storage. Overall, soil C storage was highest in mixed‐grazed grassland sites with high diversity. Synthesis and applications. Our study suggests that explicitly incorporating grazer species and the combination of grazing livestock into grassland grazing management may help mitigate greenhouse gas emissions. Caution should be exercised when using grazer species with high food selectivity in grazing management aimed at climate mitigation, especially in grasslands with abundant high quality forbs and high plant diversity, as sheep grazing may reduce soil carbon (C) storage. Moreover, mixed grazing, including multiple herbivore species, may contribute to a reduction in foraging selectivity for a plant community by means of complementary foraging. It could therefore be considered as an optimal grazing management strategy to maintain and improve soil C storage.

Interactive effects of nitrogen addition and litter on soil nematodes in grassland

“…The study was carried out at the Songnen Grassland Ecological Research Station of Northeast Normal University, Jilin Province, PR China (44°35′ N, 123°30′ E). The study site has a semiarid, continental climate with a frost‐free period of about 140 days, annual mean temperature ranging from 4.6 to 6.4°C, and annual precipitation from 280 to 400 mm (Chang et al, ; Huang et al, ; Li et al, ; J. Liu et al, ; Zhong et al, ). The main soil types in the study area include a light Chernozem soil, saline meadow soil, alkaline meadow soil, alkaline saline soil and a Chernozem type sandy soil (pH 8.5–10.0).…”

Interactions between biogeochemical and management factors explain soil organic carbon in Pyrenean grasslands

“…4B, Table 3). This result emphasises that mixed livestock assemblages deserve particular attention as they can affect plant composition distinctly from single grazing species regimes or alter traveling and trampling behaviours of grazing animals (Chang et al, 2018;Liu et al, 2015).…”

“…4B). Chang et al (2018) found that in a N poor semiarid grassland, sheep decreased SOC content in comparison to cattle due to vegetation changes caused by their feeding preference for highly palatable forbs, promoting less palatable grasses which supported less root biomass. A shift towards higher grass biomass with sheep grazing was also found in the Pyrenees (Sebastia et al, 2008).…”

“…Under such conditions, palatable plants could produce higher SOC inputs, since plant productivity is more reliant on the ability of fixing atmospheric N of legumes (Van Der Heijden et al, 2008) and the exceptional capacity of forbs to allocate C in roots is especially stimulated (Ågren and Franklin, 2003;Warembourg et al, 2003). However, these processes could be different under different soil N conditions, although the concrete mechanisms are hard to suggest, since livestock type may affect SOC content not only through changes in plant composition, but other differences in certain features of livestock assemblages, like trampling, faeces deposition patterns or effects on plant regrowth, which could promote differences in soil respiration and/or plant productivity (Aldezabal et al, 2019;Chang et al, 2018;Liu et al, 2018), resulting in different SOC levels under different grazers. Grasslands with mixed grazed regimes stored even more SOC than sheep grazed ones under high soil N conditions (Fig.…”

“…It is known that herbivores can affect SOC through different paths, such as regulating the quantity and quality of organic matter returned to soil (Bardgett and Wardle, 2003), or affecting soil respiration and nutrients by animal trampling or soil microbiota alteration (Lu et al, 2017). However, most of the studies investigating grazing effects on SOC focus on grazing intensity, in spite of evidence pointing to a greater role of grazer species in determining vegetation and SOC (Chang et al, 2018;Sebastia et al, 2008). Moreover, several studies describing interactions of grazing with other SOC predictors at diverse scales have been published (Abdalla et al, 2018;Eze et al, 2018;Lu et al, 2015Lu et al, , 2017Zhou et al, 2017).…”