Food webs obscure the strength of plant diversity effects on primary productivity

Plant diversity experiments generally find that increased diversity causes increased productivity; however, primary productivity is typically measured in the presence of a diverse food web, including pathogens, mutualists and herbivores. If food web impacts on productivity vary with plant diversity, as predicted by both theoretical and empirical studies, estimates of the effect of plant diversity on productivity may be biased. We experimentally removed arthropods, foliar fungi and soil fungi from the longest-running plant diversity experiment. We found that fungi and arthropods removed a constant, large proportion of biomass leading to a greater reduction of total biomass in high diversity plots. As a result, the effect of diversity on measured plant productivity was much higher in the absence of fungi and arthropods. Thus, diversity increases productivity more than reported in previous studies that did not control for the effects of heterotrophic consumption.

植物多样性实验普遍表明，物种多样性提升可促进生产力提升；然而，初级生产力（primary productivity）的测定通常是在包含病原菌、互惠共生生物与植食动物的复杂食物网背景下开展的。正如理论与实证研究的预测，若食物网对生产力的影响随植物多样性发生变化，则植物多样性对生产力的效应评估可能存在偏差。本研究在持续时间最长的植物多样性控制实验样地中，通过实验手段移除了节肢动物（arthropods）、叶面真菌（foliar fungi）与土壤真菌（soil fungi）。研究发现，真菌与节肢动物会持续移除大量生物量，进而导致高多样性样地的总生物量降幅更为显著。因此，在去除真菌与节肢动物的样地中，多样性对实测植物生产力的提升效应显著更高。综上，相较于未控制异养消费（heterotrophic consumption）效应的既往研究，植物多样性对生产力的实际提升幅度大于既往报道结果。