Ladd Brenton, Facelli José M
School of Biological Earth and Environmental Sciences, University of New South Wales, Sydney 2052, Australia.
Oecologia. 2008 Oct;157(4):687-96. doi: 10.1007/s00442-008-1110-2. Epub 2008 Jul 25.
Litter may indirectly affect competitive interactions. It is not clear whether these changes are additive or non-additive indirect effects. Non-additivity could result from: (1) changes in biomass allocation patterns by competitors towards organs not directly involved in resource acquisition (e.g., longer hypocotyls); (2) changes in the proportion of different functional groups (e.g., grasses and forbs) that possess different competitive abilities; or (3) through priority effects caused by subtle changes in timing of emergence. We used a combination of field and glasshouse experiments in which Eucalyptus obliqua seedlings were grown either with or without leaf litter (grass litter/eucalypt litter), and with or without competitors. Eucalypt species growing in the field and in pots attained more biomass with litter than without when competitors were absent. Competition substantially decreased the biomass of eucalypt seedlings. Competitive intensity was heavily influenced by litter type and was most intense in the presence of grass litter. Litter produced a small change in patterns of biomass allocation in the competing herbaceous vegetation, and there was a slight (marginally non-significant) indication of a change in the proportion of grasses relative to forbs when litter was present. However, when the integral of competitor biomass over time was used to calculate competitive intensity, the combined effects of the experimental factors (litter and competition) became additive, suggesting that the effect of leaf litter on the timing of germination and establishment in the grasses and forbs, relative to that of Eucalyptus seedlings, was the principal mechanism by which leaf litter altered the interaction strength of the species studied.
凋落物可能会间接影响竞争相互作用。目前尚不清楚这些变化是累加性间接效应还是非累加性间接效应。非累加性可能源于：（1）竞争者的生物量分配模式向不直接参与资源获取的器官（如更长的下胚轴）转变；（2）具有不同竞争能力的不同功能组（如禾本科植物和杂类草）比例的变化；或（3）由于出苗时间的细微变化导致的优先效应。我们结合了田间和温室实验，在实验中斜叶桉幼苗在有或没有落叶（禾本科落叶/桉树叶落叶）以及有或没有竞争者的情况下生长。当没有竞争者时，生长在田间和花盆中的桉树种在有落叶的情况下比没有落叶时获得了更多生物量。竞争显著降低了桉树苗的生物量。竞争强度受落叶类型的影响很大，在有禾本科落叶的情况下最为强烈。落叶使竞争草本植被的生物量分配模式发生了微小变化，并且当有落叶时，禾本科植物相对于杂类草的比例有轻微（边缘不显著）的变化迹象。然而，当用竞争者生物量随时间的积分来计算竞争强度时，实验因素（落叶和竞争）的综合效应变得具有累加性，这表明相对于桉树苗而言，落叶对禾本科植物和杂类草发芽和定植时间的影响是落叶改变所研究物种相互作用强度的主要机制。
