Division of Marine Science and Conservation, Nicholas School of the Environment, Duke University, Beaufort, North Carolina, United States of America.
Instituto de Investigaciones Marinas y Costeras (IIMyC), CONICET - UNMDP, Mar del Plata, Argentina.
PLoS One. 2023 May 25;18(5):e0286327. doi: 10.1371/journal.pone.0286327. eCollection 2023.
While the effects of top-down and bottom-up forces on aboveground plant growth have been extensively examined, less is known about the relative impacts of these factors on other aspects of plant life history. In a fully-factorial, field experiment in a salt marsh in Virginia, USA, we manipulated grazing intensity (top-down) and nutrient availability (bottom-up) and measured the response in a suite of traits for smooth cordgrass (Spartina alterniflora). The data presented within this manuscript are unpublished, original data that were collected from the same experiment presented in Silliman and Zieman 2001. Three categories of traits and characteristics were measured: belowground characteristics, litter production, and reproduction, encompassing nine total responses. Of the nine response variables measured, eight were affected by treatments. Six response variables showed main effects of grazing and/ or fertilization, while three showed interactive effects. In general, fertilization led to increased cordgrass belowground biomass and reproduction, the former of which conflicts with predictions based on resource competition theory. Higher grazing intensity had negative impacts on both belowground biomass and reproduction. This result contrasts with past studies in this system that concluded grazer impacts are likely relegated to aboveground plant growth. In addition, grazers and fertilization interacted to alter litter production so that litter production disproportionately increased with fertilization when grazers were present. Our results revealed both predicted and unexpected effects of grazing and nutrient availability on understudied traits in a foundational plant and that these results were not fully predictable from understanding the impacts on aboveground biomass alone. Since these diverse traits link to diverse ecosystem functions, such as carbon burial, nutrient cycling, and ecosystem expansion, developing future studies to explore multiple trait responses and synthesizing the ecological knowledge on top-down and bottom-up forces with trait-based methodologies may provide a promising path forward in predicting variability in ecosystem function.
虽然已经广泛研究了自上而下和自下而上的力量对地上植物生长的影响，但对于这些因素对植物生活史其他方面的相对影响知之甚少。在美国弗吉尼亚州的一个盐沼中，我们进行了一个完全因子的野外实验，操纵了放牧强度（自上而下）和养分供应（自下而上），并测量了光滑大米草（Spartina alterniflora）的一系列特征的响应。本文呈现的数据是未发表的原始数据，是从 Silliman 和 Zieman 2001 年提出的相同实验中收集的。测量了三个类别的特征和特性：地下特征、凋落物生产和繁殖，共涵盖了九个总响应。在所测量的九个响应变量中，有八个受到处理的影响。六个响应变量显示了放牧和/或施肥的主要影响，而三个则显示了相互作用的影响。一般来说，施肥导致大米草地下生物量和繁殖增加，这与基于资源竞争理论的预测相矛盾。较高的放牧强度对地下生物量和繁殖都有负面影响。这一结果与该系统过去的研究结果形成对比，过去的研究结论认为食草动物的影响可能仅限于地上植物的生长。此外，食草动物和施肥相互作用改变了凋落物的产生，使得在有食草动物存在的情况下，随着施肥的增加，凋落物的产生不成比例地增加。我们的研究结果揭示了放牧和养分供应对基础植物中未被充分研究的特征的预期和意外影响，而且这些结果并不能仅从理解对地上生物量的影响来完全预测。由于这些不同的特征与不同的生态系统功能相关，如碳埋藏、养分循环和生态系统扩张，因此开展未来的研究来探索多种特征响应，并利用基于特征的方法将自上而下和自下而上的力量的生态知识综合起来，可能是预测生态系统功能变异性的一个有前途的途径。
