4.1 Overall biomass
While we found differences in community biomass across our climates
characterized by different soils, the species-specific contributions to
community biomass within these climates were consistent: as expected,D. glomerata , the graminoid species, typically produced the most
biomass with P. lanceolata and L. corniculatus being less
productive. Species-specific biomass scaled with the community biomass
across climates. While this may suggest that species do have consistent
contributions to community biomass, comparing individual biomasses
across species and climates offers a different perspective.
Individual biomass analysis revealed a similar overall relationship as
species biomass between climates, showing community hierarchies were
largely maintained when accounting for survivorship. However, when
looking at individual biomass, different intra-climate hierarchies
emerge than when looking at species biomass. While D. glomerataconsistently dominated species biomass, either P. lanceolata orL. corniculatus demonstrated higher individual biomass at all
climates except one. This in part is due to high survival rates ofD. glomerata , contrasting with fewer surviving individuals ofP. lanceolata and L. corniculatus . Thus, low survivorship
led to higher individual competitiveness, and survival is not solely
determinant of biomass dominance.
Species generally maintained their biomass hierarchies across
communities while having different individual biomass hierarchies. This
relationship reveals that survivorship is differentially affecting the
study species within the same communities. While warming is known to
influence the stability of biomass production because species respond
asynchronously (Z. Ma et al. 2017), our findings do not support this.
Instead, we find that species contributions to community productivity is
relatively stable across climates. Mortality was closely associated with
reference soil in our study – this trend may therefore be an
experimental artifact. The reference soil treatment led to higher
community biomass, root biomass, and mortality compared to local soils.
High root biomass can indicate stronger belowground competition, with
increases in belowground biomass typically being symmetric for
neighboring individuals (Cahill and Casper 2000; Broadbent et al. 2018),
but this effect was not quantified here. With limited resources
available in each pot, intensive root competition may have resulted in
decreased species abundance, however overall higher productivity (Tilman
1990; Rajaniemi, Allison, and Goldberg 2003), explaining how species
with lower survivorship were able to increase their individual biomass
to maintain overall community hierarchies. This demonstrates how
competition for space strongly affects community productivity (Schmid,
Huth, and Taubert 2021), while also agreeing with past studies finding
that net primary production can be maintained even with shifts in
community composition (Liu et al. 2018). Nevertheless, this observation
underscores the role of mortality and individual species dynamics in
contributing to overall community biomass.
Individual biomass experienced the strongest positive relationship with
species biomass in cases where survival was low. This reveals a
mortality influenced trade-off, where high total species biomass is
achieved with the loss of individual biomass. Thus, an individual-rich
community leads to higher net productivity in plant-model communities.
While this trade-off has been documented in grassland monocultures
(Heisse et al. 2007; Chalmandrier, Albouy, and Pellissier 2017), this is
the first documentation in plant-model communities. High species
evenness is considered critical in maintaining community biomass (Rohr
et al. 2016). In our study, community biomass was maintained across
communities of varying species evenness, due to the limited ability of
species experiencing high relative mortality to produce larger
individuals.