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近植株的存在。由此引发的根系响应可能会影响植物的生长表现、种间互作以及群落动态，但这类响应的程度与方向仍存在广泛争议。部分研究指出，植物会在邻近植株存在时过度增殖根系，却以牺牲生殖生长为代价，这一现象被概括为“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，认为植物根系的产生仅与有效养分含量直接相关。然而，目前仍缺乏能在实验设计中排除生根容积与植株大小混杂效应干扰的、针对任一假说的无偏实验证据。

我们设置了不同生根容积梯度，在有、无地下邻近植株的条件下培养分根豌豆植株（split-root pea plants），并为每株植物提供等量养分。我们采用路径分析（path analyses）来拆解邻株存在对生物量分配模式的直接效应，同时排除生根容积与植株大小的混杂影响。在本次实验选定的生根容积范围内，地下邻株的存在通常会使植物根系生物量降低21%，总生物量降低9%；而生根容积每增加一倍，植物根系生物量通常提升18%，总生物量提升11%。荚果质量仅与营养体质量呈直接正相关。地下邻株的存在会诱导植物减少根系分配、增加荚果分配，而生根容积增大则会降低生殖分配比例。不过，上述效应中有很大一部分是通过影响植物总生物量间接介导的。

综合分析表明：若未考虑生根容积与植株大小的影响，可能会对植物响应邻株的生长策略产生误判。纳入这些影响因素后，我们发现豌豆在感知到地下邻株存在时，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地下邻株响应的各类分歧结论。