The James Hutton Institute, Craigiebuckler AB15 8QH Aberdeen, UK.
Tree Physiol. 2013 Apr;33(4):438-45. doi: 10.1093/treephys/tpt023. Epub 2013 Apr 10.
Herbivore effects on leaf litter can have a strong impact on ecosystem nutrient cycling. Although such effects are well described for insect herbivory, research on the impacts of browsing by mammalian herbivores on leaf litter dynamics and nutrient cycling has been more limited, particularly at the level of the individual plant. Clipping treatments (66% shoot removal twice, plus unclipped) were applied to analyse the effect of browsing on the phenology (start date and pattern of leaf shedding) and leaf litter quality (nitrogen (N), soluble sugars, starch and total non-structural carbohydrate concentrations, plus C : N ratios) of Betula pubescens Ehrh. and Quercus petraea [Matt.] Liebl. saplings. Clipping decreased leaf litter biomass and delayed leaf senescence and shedding, but did not change the phenological timing of litterfall between senescence and shedding. The quality of leaf litter of both species was increased by simulated browsing, through an increase in N and carbohydrate concentrations (mainly soluble sugars) and a decreased C : N ratio. This is the first evidence we are aware of that browsing may cause changes in leaf shedding phenology, delaying the process without altering its pattern. Our results also indicate that simulated browsing increases the quality of leaf litter. However, the potential positive effect of browsing on N cycling through litter quality may be offset by its negative impact on the amount of N shed per tree.
食草动物对凋落物的影响可能对生态系统养分循环产生强烈影响。尽管昆虫食草动物的这种影响已得到很好的描述，但对哺乳动物食草动物对凋落物动态和养分循环的影响的研究则更为有限，特别是在单个植物的层面上。我们采用修剪处理（两次去除 66%的枝条，外加未修剪的枝条）来分析食草对欧洲白桦和栓皮栎幼树的物候（开始日期和落叶模式）和凋落物质量（氮（N）、可溶性糖、淀粉和总非结构性碳水化合物浓度，以及 C：N 比）的影响。修剪减少了凋落物生物量并延迟了叶片衰老和脱落，但并未改变从衰老到脱落之间凋落物的物候时间。模拟食草增加了两种物种的凋落物质量，通过增加 N 和碳水化合物浓度（主要是可溶性糖）和降低 C：N 比来实现。这是我们首次发现食草可能会改变落叶物候，延迟但不改变其模式。我们的研究结果还表明，模拟食草增加了凋落物的质量。然而，食草对每棵树脱落的 N 量的负面影响可能会抵消其通过凋落物质量对 N 循环的潜在积极影响。
