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.

中文翻译：

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植物群落的最终产量是否稳定？


在一定密度范围内生长并在生长一段时间后收获的植物单一栽培物的总生物量产量随密度单调增加，然后在较高密度下趋于平稳。这种模式称为恒定最终产量（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，它将成为理解和预测许多群落层面现象的关键。我们通过实验测试了两个主要假设：（1）几个物种的混合物显示出 CFY。 (2) 如果是这样，则混合物中各组分物种的生物量生产比例在达到 CFY 的密度以上时不会发生变化。我们使用“群落密度系列”进行了一系列温室实验，历时三年，其中五个物种的总体密度发生变化，但其比例保持不变。在第一个实验中，我们在中生态系统中混合种植一年生和多年生草本物种，所有物种也以相应的密度进行单一栽培。在第二年和第三年进行了类似的实验，但仅限于一年生植物。第三次仅使用混合物的实验在盆中进行了两年多。在所有情况下，地上生物量均被收获、按物种分离、干燥并称重。具有地下储存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，其中两个物种在单一栽培中以第二高密度产生了最大生物量，而所有五个物种的混合物都表现出经典的 CFY 行为，并且该物种对混合物的贡献在产生 CFY 的最低密度之上几乎没有变化。第三次实验的结果也与假设一致。 总之，在一年生物种群落中观察到了地上生物量生产的CFY，并且单个物种的贡献对于达到CFY以上的密度增加相对不敏感，即物种的竞争表现随着密度的变化而变化，直到达到CFY 。混合栽培中 CFY 的证据比单一栽培中的证据更强。如果密度低于 CFY，共存理论必须包括密度和频率依赖性。