Data from: Corrections for rooting volume and plant size reveal negative effects of neighbour presence on root allocation in pea

Plants are able to detect the presence of their neighbours belowground. The associated root responses may affect plant performance, plant-plant interactions and community dynamics, but the extent and direction of these responses is heavily debated. Some studies suggest that plants will over-proliferate roots in response to neighbours at the expense of reproduction, which was framed as a “tragedy of the commons”. Others proposed an “ideal free distribution” hypothesis, stating that plants produce roots simply as a function of the amount of available nutrients. However, experimental evidence for either hypothesis that is unbiased by confounding effects of rooting volume and plant size in their experimental setups is still lacking. We grew split-root pea plants in the presence or absence of a belowground neighbour at a range of rooting volumes, while providing equal amounts of nutrients per plant. Path analyses were used to disentangle the direct effects of neighbour presence on allocation patterns from the confounding effects of rooting volume and plant size. Within the chosen range of rooting volumes, the presence of a belowground neighbour generally reduced plant root mass by 21% and total mass by 9%. A doubling of rooting volume generally increased plant root mass by 18% and total mass by 11%. Pod mass was only directly and positively correlated with vegetative mass. The presence of a belowground neighbour induced less root allocation but more pod allocation, whereas increased rooting volume caused a reduction in reproductive allocation. A large part of these effects, however, was indirectly mediated through the influence on plant total mass. Synthesis: Not considering the effects of rooting volume and plant size may lead to misinterpretations of plant growth strategies in response to neighbours. Accounting for these factors, we found pea allocating less mass to roots in the presence of a belowground neighbour. The obtained results can help to reconcile the various responses to belowground neighbours as they are published in the literature.植物能够感知地下邻株的存在。由此引发的根系响应可影响植物生长表现、种间互作与群落动态，但此类响应的程度与方向迄今仍存在广泛争议。部分研究指出，植物会在邻株存在时过度增殖根系，却以牺牲繁殖能力为代价，该现象被称为‘公地悲剧（tragedy of the commons）’。另有研究提出‘理想自由分布（ideal free distribution）’假说，认为植物根系的生成仅与有效养分含量直接相关。然而，目前尚未有研究能在实验设计中排除根系容积与植株体量的混淆效应，为任一假说提供无偏的实验证据。本研究设置了不同根系容积梯度，在有、无地下邻株的条件下种植分根豌豆植株（split-root pea plants），并为每株植株提供等量养分。本研究采用路径分析（path analysis），将邻株存在对生物量分配模式的直接影响，与根系容积、植株体量的混淆效应拆解区分。在本研究选定的根系容积范围内，地下邻株的存在通常会使植株根系生物量降低21%、总生物量降低9%；根系容积翻倍则通常会使植株根系生物量提升18%、总生物量提升11%。豆荚生物量仅与营养体生物量呈显著正相关。地下邻株的存在会降低根系分配比例，但提升豆荚分配比例；而根系容积增大则会降低繁殖分配比例。不过，上述效应的很大一部分是通过影响植株总生物量间接介导的。综合分析：若未考虑根系容积与植株体量的影响，可能会对植物响应邻株的生长策略产生误判。纳入上述因素后，本研究发现，当存在地下邻株时，豌豆会将更少的生物量分配至根系。本研究结果有助于调和已发表文献中关于植物响应地下邻株的各类分歧结论。