Many alternative hypotheses have been proposed about the mechanisms governing plant community structure and how plant species compete for resources. Seeking general conclusions requires identifying those hypotheses, describing them and comparing the results of the studies that tested them in a diversity of scenarios. However, comprehensive reviews and comparative studies on the hypotheses that have been actually tested rather than theoretically proposed are lacking. In this study, we focused on the relationships between four variables of interest to plant community and resource competition research: biodiversity, productivity, light and nutrients.

We performed a novel type of systematic literature search in which we selected studies that had intended to quantify all four variables. From the shortlisted papers (88 out of 1557 initial), we identified causal interactions (effects) by doing a “backwards inference” from the statistical analyses, and assembled them as causal networks. We refer to each particular network as a tested hypothesis. The tested hypotheses that showed the same directionality of effects between the four variables of interest were simplified and grouped as compatible.

We identified 43 hypotheses that could be classified into groups based on compatibility, with varying degrees of complexity in the number and directionality of relationships tested between variables. Only seven of these hypotheses had been tested in more than one study. The most tested hypothesis (47 times) has been one considering changes in nutrient amount (fertilization) as a sole effect variable driving changes in species richness, biomass and light penetration through canopy. Arguably, this is the simplest hypothesis and associated experimental design that one could think of for this system. Although more complex hypotheses that include indirect effect such as those of light penetration on biomass, would presumably better represent the higher complexity of the natural system, they have been tested only a handful of times each (2–21 times).

Our results depict the landscape of hypotheses that have been tested for this system, a comparative description of their degrees of complexity, and information on available evidence. This information would be relevant to evaluate whether it is possible to proceed with more rigorous generalizations about mechanisms driving plant community structure. Moreover, our method facilitates the identification of knowledge gaps and mismatches between hypotheses, study designs and statistical tests being performed.

关于控制植物群落结构的机制以及植物物种如何竞争资源的许多替代假设已被提出。寻求一般性结论需要确定这些假设，对其进行描述，并比较在各种情况下对其进行测试的研究结果。但是，缺乏对已经经过实际检验而不是理论上提出的假设的全面审查和比较研究。在这项研究中，我们着重研究了植物群落和资源竞争研究感兴趣的四个变量之间的关系：生物多样性，生产力，光照和养分。

我们进行了一种新型的系统文献检索，其中我们选择了旨在量化所有四个变量的研究。从入围的论文（1557份中的88份）中，我们通过对统计分析进行“向后推断”来确定因果相互作用（效应），并将它们组合为因果网络。我们将每个特定网络称为经过检验的假设。检验的假设表明了所关注的四个变量之间的效应具有相同的方向性，这些假设被简化并分组为兼容的。

我们确定了43个假设，这些假设可以根据兼容性分为不同的组，变量之间关系的数量和方向性的复杂程度各不相同。在一项以上的研究中，仅对其中的七个假设进行了检验。经受最多考验的假设（47次）是一种将营养素含量（施肥）变化视为唯一因素的变量，该变量驱动物种丰富度，生物量和通过树冠的光穿透性变化。可以说，这是该系统可能想到的最简单的假设和相关的实验设计。尽管更复杂的假设包括间接影响，例如光对生物质的渗透，可能会更好地代表自然系统的更高复杂性，但每个假设仅进行了几次测试（2至21次）。

我们的结果描述了已针对该系统进行过测试的假设的概况，对它们的复杂程度的比较描述以及有关可用证据的信息。此信息将与评估是否有可能对驱动植物群落结构的机制进行更严格的概括有关。此外，我们的方法有助于识别假设，研究设计和进行的统计检验之间的知识差距和错配。