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.

植物能够检测到地下邻株的存在。由此引发的根系响应会影响植物生长表现、种间互作及群落动态，但这类响应的程度与方向仍存在广泛争议。部分研究指出，植物会在感知到邻株时过度增殖根系，却以牺牲繁殖能力为代价，这一现象被定义为“公地悲剧（tragedy of the commons）”。另有学者提出“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，目前仍缺乏能够在实验设计中排除根系容积与植株大小混杂效应的无偏证据，以验证上述任一假说。本研究以分根豌豆植株（split-root pea plants）为材料，设置了地下邻株存在与不存在两组处理，并设置了一系列梯度的根系容积，同时为所有植株提供等量养分。我们采用路径分析（path analyses）分离出邻株存在对生物量分配模式的直接效应，以及根系容积与植株大小带来的混杂效应。在本次实验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%；将根系容积翻倍则通常使根系生物量提升18%，总生物量提升11%。豆荚生物量仅与营养体生物量呈直接正相关。地下邻株的存在会诱导植株减少根系生物量分配、增加豆荚生物量分配，而根系容积增大则会降低繁殖生物量分配。但上述多数效应是通过影响植株总生物量间接介导的。综合分析表明，若未考虑根系容积与植株大小的影响，可能会误判植物对邻株的生长响应策略。纳入上述因素后，我们发现当存在地下邻株时，豌豆会将更少生物量分配至根系。本研究结果有助于调和现有文献中关于地下邻株响应的各类分歧。