Department of Plant and Environmental Sciences, University of Copenhagen, Frederiksberg, Denmark.
Institute of Landscape and Plant Ecology, University of Hohenheim, Stuttgart, Germany.
Ecology. 2022 Nov;103(11):e3802. doi: 10.1002/ecy.3802. Epub 2022 Aug 18.
Total biomass production of plant monocultures growing over a range of densities and harvested after a period of growth increases monotonically with density and then levels out at higher densities. This pattern is called constant final yield (CFY) and is considered one of the most general phenomena in plant ecology. If CFY applies to plant communities, it would be a key to understanding and predicting many community-level phenomena. We tested two primary hypotheses experimentally: (1) Mixtures of several species show CFY. (2) If so, the proportion of biomass production by the component species in a mixture does not change at densities above the density that reaches CFY. We performed a series of glasshouse experiments over 3 years using a "community density series," in which the overall density of five species was varied while their proportions remained unchanged. In the first experiment, we grew a mixture of annual and perennial herbaceous species in mesocosms, and all species were also grown in monocultures at the corresponding densities. A similar experiment was performed in the second and third years, but only with annuals. A third experiment with mixtures only was performed in pots over 2 years. In all cases, aboveground biomass was harvested, separated by species, dried, and weighed. Perennials with underground storage organs produced maximum aboveground biomass at low or intermediate densities. In the second experiment, two of the species produced maximum biomass at the second-highest density in monoculture, while mixtures of all five species showed classical CFY behavior, and the contribution of the species to the mixture changed very little above the lowest density producing CFY. The results of the third experiment were also consistent with the hypotheses. In conclusion, CFY in aboveground biomass production was observed in communities of annual species, and the contribution of the individual species was relatively insensitive to an increase in density above that reaching CFY, i.e., competitive performance of the species changed with density until CFY was reached. Evidence for CFY was stronger in mixture than in monoculture. Coexistence theory must include density as well as frequency dependence if densities are below CFY.
植物单种群在一系列密度下生长并在一段时间后收获，其总生物量产量随着密度的增加单调增加，然后在更高的密度下趋于平稳。这种模式被称为恒最终产量（CFY），被认为是植物生态学中最普遍的现象之一。如果 CFY 适用于植物群落，那么它将是理解和预测许多群落水平现象的关键。我们通过实验检验了两个主要假设：（1）几种物种的混合物表现出 CFY。（2）如果是这样，混合物中各物种生物量产量的比例在达到 CFY 的密度以上的密度下不会改变。我们在 3 年内通过一系列温室实验使用“群落密度系列”进行了测试，其中五种物种的总密度变化，而它们的比例保持不变。在第一个实验中，我们在中观模型中种植了一年生和多年生草本物种的混合物，所有物种也在相应密度的单种群中生长。第二年和第三年进行了类似的实验，但仅使用一年生植物。在两年内的第三个实验中，仅在花盆中进行了混合物实验。在所有情况下，收获地上生物量，按物种分离，干燥并称重。具有地下贮藏器官的多年生植物在低或中等密度下产生最大的地上生物量。在第二个实验中，两种物种在单培养中最高密度下产生最大生物量，而所有五种物种的混合物表现出经典的 CFY 行为，并且在达到 CFY 的最低密度以上，物种对混合物的贡献变化很小。第三个实验的结果也与假设一致。总之，在一年生物种的群落中观察到地上生物量生产的 CFY，并且单个物种的贡献相对不敏感于达到 CFY 以上的密度增加，即，物种的竞争表现随着密度的变化而变化，直到达到 CFY。在混合物中，而不是在单培养中，CFY 的证据更强。如果密度低于 CFY，共存理论必须包括密度和频率依赖性。
