Beckman Noelle G, Dybzinski Ray, Tilman David
Department of Biology and Ecology Center, Utah State University, Logan, Utah, USA.
School of Environmental Sustainability, Loyola University Chicago, Chicago, Illinois, USA.
Ecology. 2023 Feb;104(2):e3883. doi: 10.1002/ecy.3883. Epub 2022 Dec 11.
Mounting evidence suggests that plant-soil feedbacks (PSF) may determine plant community structure. However, we still have a poor understanding of how predictions from short-term PSF experiments compare with outcomes of long-term field experiments involving competing plants. We conducted a reciprocal greenhouse experiment to examine how the growth of prairie grass species depended on the soil communities cultured by conspecific or heterospecific plant species in the field. The source soil came from monocultures in a long-term competition experiment (LTCE; Cedar Creek Ecosystem Science Reserve, MN, USA). Within the LTCE, six species of perennial prairie grasses were grown in monocultures or in eight pairwise competition plots for 12 years under conditions of low or high soil nitrogen availability. In six cases, one species clearly excluded the other; in two cases, the pair appeared to coexist. In year 15, we gathered soil from all 12 soil types (monocultures of six species by two nitrogen levels) and grew seedlings of all six species in each soil type for 7 weeks. Using biomass estimates from this greenhouse experiment, we predicted coexistence or competitive exclusion using pairwise PSFs, as derived by Bever and colleagues, and compared model predictions to observed outcomes within the LTCE. Pairwise PSFs among the species pairs ranged from negative, which is predicted to promote coexistence, to positive, which is predicted to promote competitive exclusion. However, these short-term PSF predictions bore no systematic resemblance to the actual outcomes of competition observed in the LTCE. Other forces may have more strongly influenced the competitive interactions or critical assumptions that underlie the PSF predictions may not have been met. Importantly, the pairwise PSF score derived by Bever et al. is only valid when the two species exhibit an internal equilibrium, corresponding to the Lotka-Volterra competition outcomes of stable coexistence and founder control. Predicting the other two scenarios, competitive exclusion by either species irrespective of initial conditions, requires measuring biomass in uncultured soil, which is methodologically challenging. Subject to several caveats that we discuss, our results call into question whether long-term competitive outcomes in the field can be predicted from the results of short-term PSF experiments.
越来越多的证据表明，植物 - 土壤反馈（PSF）可能决定植物群落结构。然而，我们对短期PSF实验的预测与涉及竞争植物的长期田间实验结果如何比较仍知之甚少。我们进行了一项相互温室实验，以研究草原草种的生长如何依赖于田间同种或异种植物物种培养的土壤群落。源土壤来自长期竞争实验（LTCE；美国明尼苏达州雪松溪生态系统科学保护区）中的单一栽培。在LTCE中，六种多年生草原草在低氮或高氮有效性条件下，以单一栽培或八个成对竞争小区种植12年。在六种情况下，一个物种明显排除了另一个物种；在两种情况下，这一对物种似乎共存。在第15年，我们从所有12种土壤类型（六种物种的单一栽培，两种氮水平）中收集土壤，并在每种土壤类型中种植所有六种物种的幼苗7周。利用这个温室实验中的生物量估计，我们使用Bever及其同事推导的成对PSF预测共存或竞争排斥，并将模型预测与LTCE内观察到的结果进行比较。物种对之间的成对PSF范围从负（预计促进共存）到正（预计促进竞争排斥）。然而，这些短期PSF预测与LTCE中观察到的实际竞争结果没有系统的相似性。其他力量可能对竞争相互作用有更强的影响，或者PSF预测所基于的关键假设可能未得到满足。重要的是，Bever等人推导的成对PSF分数仅在两个物种表现出内部平衡时有效，这对应于稳定共存和奠基者控制的Lotka - Volterra竞争结果。预测其他两种情况，即无论初始条件如何，任一物种的竞争排斥，需要测量未培养土壤中的生物量，这在方法上具有挑战性。尽管存在我们讨论的几个注意事项，但我们的结果质疑了是否可以从短期PSF实验的结果预测田间的长期竞争结果。
