UFZ - Helmholtz Centre for Environmental Research, Department of Conservation Biology, Leipzig, Germany.
PLoS One. 2013 Sep 30;8(9):e75599. doi: 10.1371/journal.pone.0075599. eCollection 2013.
Numerous studies have reported positive effects of species richness on plant community productivity. Such biodiversity effects are usually quantified by comparing the performance of plant mixtures with reference monocultures. However, several mechanisms, such as the lack of resource complementarity and facilitation or the accumulation of detrimental agents, suggest that monocultures are more likely than mixtures to deteriorate over time. Increasing biodiversity effects over time could therefore result from declining monocultures instead of reflecting increases in the functioning of mixtures. Commonly, the latter is assumed when positive trends in biodiversity effects occur. Here, we analysed the performance of 60 grassland species growing in monocultures and mixtures over 9 years in a biodiversity experiment to clarify whether their temporal biomass dynamics differed and whether a potential decline of monocultures contributed significantly to the positive net biodiversity effect observed. Surprisingly, individual species' populations produced, on average, significantly more biomass per unit area when growing in monoculture than when growing in mixture. Over time, productivity of species decreased at a rate that was, on average, slightly more negative in monocultures than in mixtures. The mean net biodiversity effect across all mixtures was continuously positive and ranged between 64-217 g per m(2). Short-term increases in the mean net biodiversity effect were only partly due to deteriorating monocultures and were strongly affected by particular species gaining dominance in mixtures in the respective years. We conclude that our species performed, on average, comparably in monocultures and mixtures; monoculture populations being slightly more productive than mixture populations but this trend decreased over time. This suggested that negative feedbacks had not yet affected monocultures strongly but could potentially become more evident in the future. Positive biodiversity effects on aboveground productivity were heavily driven by a small, but changing, set of species that behaved differently from the average species.
大量研究报告表明，物种丰富度对植物群落生产力有积极影响。这种生物多样性效应通常通过比较植物混合物与参考单一种群的表现来量化。然而，有几个机制，如资源互补性和促进作用的缺乏或有害物的积累，表明单一种群比混合物更有可能随着时间的推移而恶化。因此，随着时间的推移，生物多样性效应的增加可能是由于单一种群的减少，而不是反映混合物功能的增加。通常，当生物多样性效应出现积极趋势时，会假设后者。在这里，我们分析了 60 种草原物种在生物多样性实验中单种和混种生长 9 年的表现，以澄清它们的时间生物量动态是否不同，以及单种群的潜在减少是否对观察到的正净生物多样性效应有重要贡献。令人惊讶的是，与混种相比，个体物种在单种群中生长时，单位面积的生物量平均显著增加。随着时间的推移，物种的生产力以平均而言，单种群的下降速度略快于混种群。所有混种的平均净生物多样性效应持续为正，范围在 64-217 克/平方米之间。短期平均净生物多样性效应的增加部分归因于单种群的恶化，并且受到特定物种在当年混合物中获得优势的强烈影响。我们的结论是，我们的物种在单种和混种中表现平均；单种群的生产力略高于混种群，但这种趋势随着时间的推移而下降。这表明负反馈尚未对单种群产生强烈影响，但未来可能会更加明显。地上生产力的正生物多样性效应主要由一小部分但不断变化的物种驱动，这些物种的行为与平均物种不同。
