Data from: Soil biotic quality lacks spatial structure and is positively associated with fertility in a northern grassland

When placing roots in the soil, plants integrate information about soil
nutrients, plant neighbours and beneficial/detrimental soil organisms.
While the fine-scale spatial heterogeneity in soil nutrients and plant
neighbours have been described previously, virtually nothing is known
about the spatial structure in soil biotic quality (measured here as a
soil Biota-Induced plant Growth Response, or BIGR), or its correlation
with nutrients or neighbours. Such correlations could imply trade-offs in
root placement decisions. Theory would predict that soil BIGR is (1)
negatively related to soil fertility and (2) associated with plant
community structure, such that plants influence soil biota (and vice
versa) through plant-soil feedbacks. We would also expect that since
plants have species-specific impacts on soil organisms, spatially
homogeneous plant communities should also homogenize soil BIGR. Here, we
test these hypotheses in a semiarid grassland by (1) characterizing the
spatial structure of soil BIGR at a scale experienced by an individual
plant and (2) correlating it to soil abiotic properties and plant
community structure. We do so in two types of plant communities: (1)
low-diversity patches dominated by an invasive grass (Bromus inermis
Leyss.) and (2) patches covered mostly by native vegetation, with the
expectation that dominance by Bromus would homogenize soil BIGR. Soil BIGR
was spatially heterogeneous, but not autocorrelated. This was true in both
vegetation types (Bromus-invaded vs. native patches). Conversely, soil
abiotic properties and plant community structure were frequently spatially
autocorrelated at similar scales. Also, contrary to many studies, we found
a positive correlation between soil BIGR and soil fertility. Soil BIGR was
also associated with plant community structure. Synthesis. The positive
correlation between soil BIGR and some soil nutrient levels suggests that
plants don't necessarily trade-off between foraging for nutrients vs.
biotic interactions: nutritional cues could rather indicate the presence
of beneficial soil biota. Moreover, the spatial structure in plant
communities, coupled with their correlation with soil BIGR, jointly
suggest that plant-soil feedbacks operate at local scales in the field:
this has been identified in modelling studies as an important driver of
plant coexistence.