Alonso-Crespo, I. M. | bioRxiv Science

bioRxiv2023

Exploring priority and year effects on plant diversity, productivity and vertical root distribution: first insights from a grassland field experiment

O_LIThe order of arrival of plant species during community assembly can affect how species interact with each other. These so-called priority effects can have strong implications for the structure and functioning of plant communities. However, the extent to which the strength, direction, and persistence of priority effects are modulated by weather conditions during plant establishment ( year effects) is not well known. C_LIO_LIHere we present the first results from a long-term field experiment (POEM: PriOrity Effects Mechanisms) initiated in 2020 in Northern Germany to test how plant functional group (PFG) order of arrival and the year of initiation of an experiment interactively affect the structure and functioning of nutrient-poor dry acidic grasslands, both above and belowground. To do this, we established the same experiment, manipulating the order of arrival of forbs, grasses and legumes on the same site, but in different years. C_LIO_LIWe found that time since establishment was a stronger driver of plant community composition than PFG order of arrival and year of initiation. These three factors interactively affected plant species diversity, with the effect of PFG order of arrival on plant species richness depending on time since establishment. Year of initiation, not PFG order of arrival, was the strongest driver of aboveground community productivity. Although we did not find any effect of PFG order of arrival on root productivity, it had a strong impact on the vertical distribution of roots. Communities where grasses were sown first rooted more shallowly than communities in which forbs or legumes were sown first. C_LIO_LISynthesis: Our results demonstrate that plant order of arrival and year effects jointly affect plant diversity and species composition, with time since establishment also playing an important role. While year effects were more important than plant order of arrival in modulating aboveground biomass production in our nutrient-poor grassland, we showed that plant order of arrival can strongly affect the vertical distribution of roots, with communities in which forbs or legumes were sown first rooting deeper than grasses-first communities. These results suggest that a deeper understanding of priority and year effects is needed to better predict restoration outcomes. C_LI

ecology↗

bioRxiv2021

Assembly history modulates vertical root distribution in a grassland experiment

The order of arrival of plant species during assembly can affect the structure and functioning of grassland communities. These so-called priority effects have been extensively studied aboveground, but we still do not know how they affect the vertical distribution of roots in the soil and the rooting depth of plant communities. To test this hypothesis, we manipulated the order of arrival of three plant functional groups (forbs, grasses and legumes) in a rhizobox experiment. Priority effects were created by sowing one functional group 10 days before the other two. Rhizoboxes in which all functional groups were sown simultaneously were used as controls. During the experiment, the mean rooting depth of plant communities was monitored using image analysis and a new methodological approach using deep learning (RootPainter) for root segmentation. At harvest, we measured aboveground (community and species level) and belowground (community level) biomass, and assessed the vertical distribution of the root biomass in different soil layers. At the community level, all scenarios where one functional group was sown before the other two had similar shoot and root productivity. At the species level, two forbs (Achillea millefolium and Centaurea jacea) benefited from arriving early, and one legume (Trifolium pratense) had a disadvantage when it was sown after the grasses. Priority effect treatments also affected the vertical distribution of roots. When grasses were sown first, plant communities rooted more shallowly than when forbs or legumes were sown first. In addition, roots moved down the soil profile 24% more slowly in grasses-first communities. Our results highlight that plant functional group order of arrival in grassland communities can affect the vertical distribution of roots in the soil and this may have implications for species coexistence.

ecology↗