Long-term impact of domestic ungulates versus the local controls of the litter decomposition process in arid steppes

Abstract

Aims
Soil processes in arid ecosystems are strongly controlled by resource scarcity. Grazing intensification can induce changes in ecosystem processes through multiple pathways, adding new constraints to those of local conditions. We focus on grazing-induced changes in litter traits and soil environment that may affect litter decomposition and N dynamics in temperate grass-shrub steppes.

Methods
We performed three litterbag decomposition experiments to evaluate: i) the effect of litter traits in a common garden (ex situ), ii) the effect of soil environment using a foreign common litter substrate (in situ), and iii) the interactive effects of litter traits and soil environment (grazed vs.vs. exclosure communities, reciprocal transplants in situ). Field experiments were replicated in three blocks with paired plots under a long-term exclosure (> 25 years) and under year-round sheep grazing. Local litter included mixtures of species of grasses and shrubs, separately.

Results
Grazing exclusion did not alter litter decomposition rates, either through changes in litter traits or in soil environment. Nevertheless, N released during grass litter decomposition was 286% higher in exclosures than in grazing communities. The difference was associated to changes in litter C:N ratio. The effects were maintained when results were integrated to the entire litter community.

Conclusion
Our study suggests that litter decomposition rates in arid steppes are strongly controlled by local drivers. Ungulate grazing does not have an important influence on litter mass loss, but it can exert a strong control on N flux during decomposition, by changing grass litter traits.

Published in:
Piazza, MV., Oñatibia, G.R., Aguiar, M.R., Chaneton E.J. Long-term impact of domestic ungulates versus the local controls of the litter decomposition process in arid steppes. Plant Soil (2021). https://doi.org/10.1007/s11104-021-05088-4

摘要

研究目的
在干旱生态系统，土壤过程受到资源稀缺性的强烈制约。放牧强度的增加可以通过多种途径引起生态系统过程的变化，从而对局部条件施加新的限制。本研究聚焦于放牧引起的凋落物特性变化及土壤环境的变化，这些变化可能影响温带草原-灌木草原的凋落物分解和氮循环。

研究方法
本研究进行了三项凋落物分解实验，以评估：i) 在公共花园（离体）中凋落物特性的影响；ii) 使用外来公共凋落物基质对土壤环境的影响（原位）；以及iii) 凋落物特性和土壤环境的交互作用（放牧与围栏群落，原位互移）。现场实验在三个区块中重复进行，在长期围栏（> 25 年）和全年放牧的条件下进行。本地凋落物包括草和灌木种类的混合。

结果
放牧排除并未通过改变凋落物特性或土壤环境来改变凋落物分解速率。然而，在围栏中，草凋落物分解过程中释放的氮含量比放牧群落高出 286%。这种差异与凋落物碳氮比的变化有关。当将这些结果整合到整个凋落物群落中时，这些影响仍然存在。

结论
本研究表明，干旱草原的凋落物分解速率受到当地驱动力的强烈控制。食草动物的放牧对凋落物质量损失的影响并不显著，但它可以通过改变草凋落物的特性，对分解过程中的氮通量施加强烈控制。

发表在：Piazza, MV., Oñatibia, G.R., Aguiar, M.R., Chaneton E.J. 长期影响家畜放牧与干旱草原凋落物分解过程局部控制。植物土壤 (2021)。https://doi.org/10.1007/s11104-021-05088-4