Data from: Feces nitrogen release induced by different large herbivores in a dry grassland

Large herbivores have pronounced effects on nutrient cycling in grasslands. These organisms are known to alter the quality and quantity of plant production as well as the amounts and quality of plant litter and animal wastes. The generalization that the relative quality of detritus inputs is enhanced by herbivores is well known, but how this process is affected by diet selection processing and feces production of different large herbivores remains largely unstudied. Here, we measured how these differences for cattle and sheep on a dry grassland might influence nitrogen (N) mineralization from feces. We found that cattle of larger body size tended to select low quality grass Stipa grandis as the major food source. In contrast, the subdominant grass Leymus chinensis with relatively high N content was a majority in the diet of smaller sheep, when palatable forbs were insufficient in the field. This diverse diet quality resulted in a C/N ratio of cattle feces that was higher than that of sheep feces. Relatively higher labile C availability in the cattle feces, namely relatively higher cellulose/hemicellulose contents, promoted microbial growth and in turn accelerated cattle feces decomposition. A surprise finding was that the feces from cattle mineralized about twice as much N as feces from sheep, despite the latter having slightly higher N content. From a grassland productivity perspective, increasing the proportion of large body-sized species in grazing herbivore assemblages perhaps is beneficial to forage productivity and nutrient recycling by the rapid degradation of feces.

大型草食动物对草原养分循环具有显著影响。这类生物会改变植物生产力的质量与规模，同时也会影响植物凋落物与动物排泄物的总量与品质。学界已普遍认可草食动物可提升枯落物输入的相对品质，但不同大型草食动物的采食选择过程与粪便产生如何影响这一过程，目前仍鲜有研究。本研究针对干旱草原上的牛与羊，探究这类差异如何影响粪便中的氮（N）矿化过程。研究发现，体型较大的牛倾向于以低品质牧草大针茅（Stipa grandis）为主要食物来源；与此相对，当田间适口性优良的杂类草匮乏时，体型更小的羊的日粮中占比最高的为氮含量相对较高的亚优势种牧草羊草（Leymus chinensis）。这种日粮品质的差异使得牛粪便的碳氮比（C/N）高于羊粪便。牛粪便中相对更高的易变碳有效性，即相对更高的纤维素/半纤维素含量，促进了微生物生长，进而加速了牛粪便的分解。一项意外发现是，尽管羊粪便的氮含量略高，但牛粪便的氮矿化量约为羊粪便的两倍。从草原生产力的角度来看，提升放牧草食动物群落中体型较大物种的占比，或许可通过粪便的快速降解，有益于牧草生产力与养分循环。