Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544;
Santa Fe Institute, Santa Fe, NM 87501.
Proc Natl Acad Sci U S A. 2022 Mar 1;119(9). doi: 10.1073/pnas.2117514119.
Recent findings point to plant root traits as potentially important for shaping the boundaries of biomes and for maintaining the plant communities within. We examined two hypotheses: 1) Thin-rooted plant strategies might be favored in biomes with low soil resources; and 2) these strategies may act, along with fire, to maintain the sharp boundary between the Fynbos and Afrotemperate Forest biomes in South Africa. These biomes differ in biodiversity, plant traits, and physiognomy, yet exist as alternative stable states on the same geological substrate and in the same climate conditions. We conducted a 4-y field experiment to examine the ability of Forest species to invade the Fynbos as a function of growth-limiting nutrients and belowground plant-plant competition. Our results support both hypotheses: First, we found marked biome differences in root traits, with Fynbos species exhibiting the thinnest roots reported from any biome worldwide. Second, our field manipulation demonstrated that intense belowground competition inhibits the ability of Forest species to invade Fynbos. Nitrogen was unexpectedly the resource that determined competitive outcome, despite the long-standing expectation that Fynbos is severely phosphorus constrained. These findings identify a trait-by-resource feedback mechanism, in which most species possess adaptive traits that modify soil resources in favor of their own survival while deterring invading species. Our findings challenge the long-held notion that biome boundaries depend primarily on external abiotic constraints and, instead, identify an internal biotic mechanism-a selective feedback among traits, plant-plant competition, and ecosystem conditions-that, along with contrasting fire regime, can act to maintain biome boundaries.
最近的研究结果表明，植物根系特征可能对塑造生物群落的边界以及维持生物群落内部的稳定性具有重要意义。我们检验了两个假说：1）在土壤资源匮乏的生物群落中，可能会更倾向于选择根系较细的植物策略；2）这些策略可能与火一起，维持南非菲英布和非洲温带森林生物群落之间的鲜明边界。这两个生物群落在生物多样性、植物特征和外貌上存在差异，但在相同的地质基底和气候条件下，它们以替代稳定状态存在。我们进行了为期 4 年的野外实验，以研究森林物种作为功能生长限制养分和地下植物-植物竞争的因素，入侵菲英布的能力。我们的研究结果支持了这两个假说：首先，我们发现根系特征在生物群区之间存在显著差异，菲英布物种的根系是全球所有生物群区中报道的最细的根系。其次，我们的野外操作表明，地下竞争的激烈程度抑制了森林物种入侵菲英布的能力。尽管长期以来人们一直认为菲英布受到严重的磷限制，但出人意料的是，氮是决定竞争结果的资源，而不是磷。这些发现确定了一种由特征决定资源的反馈机制，其中大多数物种具有适应性特征，这些特征改变土壤资源以有利于自身生存，同时阻止入侵物种。我们的研究结果挑战了长期以来的观点，即生物群区边界主要取决于外部非生物限制因素，而是确定了一种内部生物机制——特征、植物-植物竞争和生态系统条件之间的选择性反馈机制，以及与对比火的生态系统模式，共同维持生物群区的边界。
