No abstract

Summary Plants are able to detect the presence of their neighbours below‐ground. 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 propose 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 set‐ups is still lacking. We grew split‐root pea plants in the presence or absence of a below‐ground 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 below‐ground neighbour generally reduced plant root mass by 21% and total mass by 9%. A doubling of rooting volume generally increased plant root mass by 22% and total mass by 11%. Pod mass was only directly and positively correlated with vegetative mass. The presence of a below‐ground 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 below‐ground neighbour. The obtained results can help to reconcile the various responses to below‐ground neighbours as they are published in the literature.

The phenomenon that organisms can distinguish genetically related individuals from strangers (i.e., kin recognition) and exhibit more cooperative behaviours towards their relatives (i.e., positive kin discrimination) has been documented in a wide variety of organisms. However, its occurrence in plants has been considered only recently. Despite the concerns about some methodologies used to document kin recognition, there is sufficient evidence to state that it exists in plants. Effects of kin recognition go well beyond reducing resource competition between related plants and involve interactions with symbionts (e.g., mycorrhizal networks). Kin recognition thus likely has important implications for evolution of plant traits, diversity of plant populations, ecological networks and community structures. Moreover, as kin selection may result in less competitive traits and thus greater population performance, it holds potential promise for crop breeding. Exploration of these evo‐ecological and agricultural implications requires adequate control and measurements of relatedness, sufficient replication at genotypic level and comprehensive measurements of performance/fitness effects of kin discrimination. The primary questions that need to be answered are: when, where and by how much positive kin discrimination improves population performance.

Forested ecosystems represent an important part of the global carbon cycle, with accurate estimates of gross primary productivity (GPP) crucial for understanding ecosystem response to environmental controls and improving global carbon models. This research investigated the relationships between leaf area index (LAI) and leaf chlorophyll content (Chl Leaf ) with forest carbon uptake. Ground measurements of LAI and Chl Leaf were taken approximately every 9 days across the 2013 growing season from day of year (DOY) 130 to 290 at Borden Forest, Ontario. These biophysical measurements were supported by on-site eddy covariance flux measurements. Differences in the temporal development of LAI and Chl Leaf were considerable, with LAI reaching maximum values within approximately 10 days of bud burst at DOY 141. In contrast, Chl Leaf accumulation only reached maximum values at DOY 182. This divergence has important implications for GPP models which use LAI to represent the fraction of light absorbed by a canopy (fraction of absorbed photosynthetic active radiation (fAPAR)). Daily GPP values showed the strongest relationship with canopy chlorophyll content (Chl Canopy ; R 2 = 0.69, p < 0.001), with the LAI and GPP relationship displaying nonlinearity at the start and end of the growing season (R 2 = 0.55, p < 0.001). Modeled GPP derived from LAI × PAR and Chl Canopy × PAR was tested against measured GPP, giving R 2 = 0.63, p < 0.001 and R 2 = 0.82, p < 0.001, respectively. This work demonstrates the importance of considering canopy pigment status in deciduous forests, with models that use fAPAR LAI rather than fAPAR Chl neglecting to account for the importance of leaf photosynthetic potential.