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经典理论预测,草食动物通过选择性植物啃食和富含氮的排泄物的沉积影响草本植物组成和土壤氮循环,其影响取决于生态系统氮的有效性.据预测,草食动物在氮有效性高时可加速氮循环,而在氮有效性低时减慢其循环.然而,在自然系统中对这些理论的实验验证比较有限,并且有些结果相互矛盾.美国加利福尼亚州广泛分布的灌木林地为验证这些理论提供了一个可行的系统.它们易于发生周期性的林冠火,这会暂时移除活的灌木覆盖物,使土壤中的矿质氮沉积,并利于各种草本植物组合在3-5年内形成主导景观.灌丛也越来越容易受到草本植物的入侵;哺乳动物的食草性可能会限制灌丛下层非本地草本植物的建立.我们设置一项为期两年的植食动物-围封实验,评估火灾后早期灌丛演替期间哺乳动物食草性对草本植物组合和土壤氮和碳循环的影响.我们预测,在火灾后高氮条件下,哺乳类食草动物不会更倾向于取食固氮草本植物,会加速氮循环并减少非本地草本植物的丰富度.研究结果表明,排除哺乳类食草动物后,尽管草本植物的现存生物量增加了54％,但固氮与非固氮草本植物的相对丰富度没有改变,也没有改变氮和碳循环的指标.在两年的实验期间内,草食动物对养分循环的影响可能并不显著,草食动物活动的物理影响可能抵消了植物凋落物和动物粪/尿输入的影响.哺乳类食草动物主要以典型的非本地草本植物为食,略微降低了它们的相对丰度;然而,在火灾后的前两年,哺乳动物的食草性并不能有效地阻止侵入性草本植物对灌丛的入侵,也不能改变植物的碳和氮循环.“,”Aims Classical theory predicts that herbivores impact herb assemblages and soil nitrogen(N)cycling through selective plant consumption and the deposition of N-rich waste,with effects dependent upon ecosystem N availability.Herbivores are predicted to accelerate N cycling when N availability is high and decelerate cycling when availability is low.However,experimental tests of these theories in natural systems are limited and have yielded contradictory results.California's widespread chaparral shrublands provide a tractable system in which to test these theories.They are prone to periodic crown fire,which temporarily removes living shrub cover,deposits mineral N on soils and allows diverse herbaceous assemblages to dominate the landscape for 3-5 years.Chaparral is also increasingly vulnerable to herbaceous invasion;mammalian herbivory may limit the establishment of non-native herbs in the shrub understory.Methods We implemented a 2-year herbivore-exclosure experiment(Hopland,CA)to assess the impact of mammalian herbivory during early post-fire chaparral succession,both on herbaceous plant assemblages and soil N and C cycling.We predicted that,in high-N post-fire conditions,mammalian herbivory would not demonstrate a strong preference for N-fixing herbs,would accelerate N cycling and would reduce the abundance of non-native herbs.Important Findings Excluding mammalian herbivores increased herb standing biomass by 54％,but changed neither the relative abundance of N-fixing vs.non-N-fixing herbs nor any measure of N or C cycling.Herbivore impacts on nutrient cycling may not be significant over the 2-year time scale of the experiment and physical effects of herbivore activity could have counteracted the influence of plant litter and animal dung/urine inputs.Mammalian herbivores concentrated their feeding on typical non-native herbs,slightly decreasing their relative abundance;however,mammalian herbivory was not sufficient to stem the invasion of chaparral by invasive herbs or alter C and N cycling over the first 2 years after fire.