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Despite widespread evidence that biological invasion influences both the biotic and abiotic soil environments, the extent to which these two pathways underpin the effects of invasion on plant traits and performance remains unknown. Leveraging a long-term (14-year) field experiment, we show that an allelochemical-producing invader affects plants through biotic mechanisms, altering the soil fungal community composition, with no apparent shifts in soil nutrient availability. Changes in belowground fungal communities resulted in high costs of nutrient uptake for native perennials and a shift in plant traits linked to their water and nutrient use efficiencies. Some plants in the invaded community compensate for the disruption of nutritional symbionts and reduced nutrient provisioning by sanctioning more nitrogen to photosynthesis and expending more water, which demonstrates a trade-off in trait investment. For the first time, we show that the disruption of belowground nutritional symbionts can drive plants towards alternative regions of their trait space in order to maintain water and nutrient economics.

Premise We developed a novel low-cost method to visually phenotype belowground structures in the plant rhizosphere. We devised the method introduced here to address the difficulties encountered growing plants in seed germination pouches for long-term experiments and the high cost of other mini-rhizotron alternatives. Methods and results The method described here took inspiration from homemade ant farms commonly used as an educational tool in elementary schools. Using compact disc (CD) cases, we developed mini-rhizotrons for use in the field and laboratory using the burclover Medicago lupulina. Conclusions Our method combines the benefits of pots and germination pouches. In CD mini-rhizotrons, plants grew significantly larger than in germination pouches, and unlike pots, it is possible to measure roots without destructive sampling. Our protocol is a cheaper, widely available alternative to more destructive methods, which could facilitate the study of belowground phenotypes and processes by scientists with fewer resources.

Strategies of herbaceous species in deciduous forests are often characterized by the timing of life history phases (e.g. emergence, flowering, leaf senescence) relative to overstory tree canopy closure. Although springtime photosynthesis is assumed to account for the majority of their annual carbon budgets, the 12-month photosynthetic trajectories of forest herbs have not been quantified. We measured the temporal dynamics of carbon assimilation for seven native herbaceous perennials and the biennial Alliaria petiolata, a widespread invader in eastern North American forests. We assessed the relative importance of spring, summer, and autumn to species-level annual carbon budgets. Spring-emerging species showed significant variation in carbon assimilation patterns. High spring irradiance before canopy closure accounted for 39-100% of species-level annual carbon assimilation, but summer and autumn accounted for large proportions of some species' carbon budgets (up to 58% and 19%, respectively). Alliaria was phenologically unique, taking advantage both autumn and spring irradiance. Although spring-emerging understory species are often expected to rely on early-season irradiance, our results highlight interspecific differences and the importance of mid-late season carbon gain. Phenological strategies of forest herbs are a continuum rather than discrete categories, and invasive species may follow strategies that are underrepresented in the native flora.

Evolutionary ecologists often seek to identify the mechanisms maintaining intraspecific variation. In social animals, whole groups can exhibit between-group differences in their collective traits. We examined whether negative frequency-dependent selection (that is, a rare-type advantage) could help to maintain between-group variation. We engineered neighbourhoods of social spider colonies bearing bold or shy foraging phenotypes and monitored their fecundity in situ. We found that bold colonies enjoyed a rare-type advantage that is lost as the frequency of bold colonies in a neighbourhood increases. The success of shy colonies was not frequency dependent. These dynamics seem to be driven by a foraging advantage of bold colonies that is lost in bold neighbourhoods because prey become scarce, and shy colonies perform better than bold colonies under low-resource conditions. Thus, to understand selection on collective traits, it is insufficient to examine groups in isolation. The phenotypic environment in which groups reside and compete must also be considered.