Centro de Investigación en Ecosistemas de la Patagonia (CIEP), Coyhaique, Chile.
Ann Bot. 2019 Nov 27;124(6):1121-1131. doi: 10.1093/aob/mcz128.
Cluster roots (CRs) constitute a special root adaptation that enables plants to take up nutrients, especially phosphorus (P), from soils with low nutrient availability, including recent volcanic deposits. It is unclear, however, how CR species interact with non-cluster root-bearing (NCR) species, and how substrates' fertility modulates potential interactions.
We experimentally assessed the net interaction between CR and NCR species using two substrates of contrasting fertility: nutrient-rich nursery mix and tephra (low P availability). We planted seedlings of two southern South American (SSA) Proteaceae, CR species and two NCR Nothofagus species in pairs (conspecifics and heterospecifics) and as singles. We analysed the effect of seedling neighbours on survival, growth performance (e.g. total biomass and leaf area) and leaf and substrate nutrient concentrations (including manganese, a proxy for P-acquisition efficiency through CR activity) using the relative interaction index.
After three growing seasons, we found that (1) Proteaceae species had fewer CRs and lower CR biomass and grew less in the tephra than in the nursery substrate; (2) Nothofagus species did not improve their survival and growth in the presence of Proteaceae species in any substrate; (3) contrary to Nothofagus, Proteaceae species improved their growth more when planted with any neighbour (including conspecifics) than when planted alone, which was accompanied by a significant accretion of leaf P; and (4) the presence of a neighbour increased the final nitrogen and P concentrations in the nursery substrate, regardless of species identity.
CRs provide Proteaceae a competitive advantage over NCR species at the seedling stage, which may have important consequences for species coexistence and community structuring. The investigated SSA Proteaceae, which have not evolved in nutrient-impoverished soils, as have their relatives in south-western Australia and South Africa, improve their growth when cultivated in pairs, especially in nutrient-rich substrates.
丛根（CRs）是一种特殊的根系适应，使植物能够从养分供应较低的土壤中吸收养分，特别是磷（P），包括最近的火山沉积物。然而，CR 物种与非丛根（NCR）物种如何相互作用，以及基质的肥力如何调节潜在的相互作用尚不清楚。
我们使用两种肥力不同的基质——养分丰富的苗圃混合物和凝灰岩（低 P 供应），实验性地评估了 CR 和 NCR 物种之间的净相互作用。我们将两种南美的南部（SSA）植物科的幼苗，CR 物种和两种 NCR 的山毛榉物种成对（同种和异种种间）和单种种植。我们使用相对相互作用指数分析了幼苗邻居对存活、生长性能（例如总生物量和叶面积）以及叶片和基质养分浓度（包括锰，作为通过 CR 活性获取 P 效率的代理）的影响。
经过三个生长季节，我们发现：（1）与苗圃基质相比，Proteaceae 物种的 CR 较少，CR 生物量较低，在凝灰岩中的生长较少；（2）在任何基质中，Nothofagus 物种都没有因有 Proteaceae 物种的存在而提高其存活率和生长；（3）与 Nothofagus 相反，当与任何邻居（包括同种）一起种植时，Proteaceae 物种的生长改善得更多，而单独种植时则没有，这伴随着叶片 P 的显著增加；（4）无论物种身份如何，邻居的存在都会增加苗圃基质中的最终氮和 P 浓度。
在幼苗阶段，CR 为 Proteaceae 提供了相对于 NCR 物种的竞争优势，这可能对物种共存和群落结构具有重要意义。本研究中所研究的 SSA Proteaceae 没有在贫瘠的土壤中进化，就像它们在澳大利亚西南部和南非的亲缘关系一样，当在成对种植时，尤其是在养分丰富的基质中，它们的生长会得到改善。
