Data from: Intraspecific variation in litter palatability to macroarthropods in response to grazing and soil fertility

1. Clarifying the functional consequences of intraspecific trait variability in response to interacting trophic levels would provide a significant improvement in our understanding of aboveground-belowground linkages. In particular, the effects of grazing on plant traits may translate into altered litter quality, with potentially important consequences for litter-feeding decomposers. Plant and litter variability in response to grazing is expected to depend on soil fertility levels, with tolerance and defensive strategies more commonly expressed on fertile and poorer soils, respectively. However, how grazing and fertility interactively alter litter quality and palatability to detritivores has not been explored yet. 2. We conducted a cafeteria experiment with three common millipede (Diplopoda) species feeding on leaf litter from two plant species, the grass Bromopsis erecta and the forb Potentilla verna. Each millipede was offered a binary choice between litter types produced by the same plant species, but sampled in plots with distinct herbivory and fertilization status: litter originating from grazed areas or from one-year sheep exclosures, both in native areas and in adjacent paddocks that received chemical N and P fertilization, as well as litter from a 25-year sheep exclusion in the native area. 3. We found that fertilization and herbivore exclusion interactively affected Bromopsis litter quality and palatability, whereas Potentilla was much less affected. Bromopsis litter palatability was not affected by grazing when litter was collected in native plots, except for the long-term exclosure which led to a very low palatability. In contrast, and in line with our expectations, herbivory was associated with much higher palatability in fertilized plots. The changes in palatability were associated with important alterations of litter quality. 4. Overall, our study demonstrates that intraspecific variation in litter can have profound consequences for soil functioning. It emphasizes the role of grazing as a key, but plant species-specific factor controlling litter intraspecific variability, and its complex interaction with soil fertility level. Moreover, our results advocate for a better understanding of the response of the different organisms involved in the decomposition process, in particular litter-feeding macro-detritivores. We encourage future studies aiming at disentangling the various and complex relationships between aboveground processes such as herbivory and soil functioning.

1. 阐明响应营养级互作的种内性状变异的功能效应，将极大推动我们对地上-地下联系的认知。具体而言，放牧对植物性状的影响可转化为凋落物质量的改变，进而对食凋落物分解者产生潜在的重要效应。植物与凋落物对放牧的响应变异通常依赖于土壤肥力水平：耐受策略更多见于高肥力土壤，而防御策略则更多出现在贫瘠土壤中。然而，放牧与肥力如何通过交互作用改变凋落物质量及其对腐食者的适口性，目前尚未有相关研究探索。
2. 本研究采用cafeteria实验（cafeteria experiment）方法，选取3种常见马陆（倍足纲 Diplopoda）作为实验生物，供试凋落物来自2种植物：草本植物硬雀麦（Bromopsis erecta）与杂类草委陵菜（Potentilla verna）。每头马陆均可在同一植物物种产生的两类凋落物间进行二元选择：两类凋落物分别采自具有不同植食与施肥处理的样地——包括原生境中的放牧区、1年绵羊排除区，以及相邻的施加化学氮（N）、磷（P）肥的牧场样地的凋落物，同时还包含原生境中25年绵羊排除区的凋落物。
3. 研究发现，施肥与植食者排除处理对硬雀麦凋落物的质量与适口性存在交互影响，而委陵菜凋落物受其影响则显著更小。在原生境样地中，放牧并未显著改变硬雀麦凋落物的适口性，唯有长期排除植食者的样地所产凋落物的适口性极低。与之相反，且与本研究预期一致，在施肥样地中，植食作用与更高的凋落物适口性显著相关。适口性的变化与凋落物质量的显著改变密切相关。
4. 综上，本研究表明，凋落物种内变异可对土壤生态系统功能产生深远影响。本研究强调了放牧作为调控凋落物种内变异的关键因子——但其效应具有植物物种特异性，以及放牧与土壤肥力水平间的复杂交互作用。此外，本研究结果呼吁学界更深入地理解分解过程中不同生物类群的响应规律，尤其是食凋落物大型腐食者。我们期待未来研究能够厘清植食作用等地上过程与土壤功能之间多样且复杂的关联机制。