Soil and biomass data from: Soil, competition, and niche shifts shape the floral mosaic of an annual plant diversity hotspot

Plant species with affinity for harsh substrates often have well-defined
edaphic (soil) niches and are ideal for exploring questions of community
assembly. Vertic clay soils are chemically and physically challenging to
plant establishment and productivity, and annual plant communities
associated with these soils of the San Joaquin Desert (California, USA)
form a distinctive mosaic pattern of species that reflects differences in
soil properties across the landscape. We conducted field sampling and a
pot study with 12 native annual forb species with an affinity for vertic
clay soils to determine how heterogeneous soils at two sites in the San
Joaquin Desert differed between realized niches of species, to test if
species differed in their realized and fundamental edaphic niches, and to
examine the competition effects of an invasive annual grass (Bromus
rubens) on these species’ edaphic niches. From our field study, we found
some differences in the vertic clay soils between the realized niches of
species at both sites. In our pot study, we found species exhibited
similar fundamental edaphic niche optima on our treatment soils, and that
species’ competitive ability differed across the gradient of edaphic
stress in our treatment soils. For some species, differences in
competitive ability led to shifts in edaphic niche optima, likely
contributing to more divergent realized niches. We found that the
combination of competitive pressure and abiotic stress drove differences
between the realized niche and fundamental niche for species in a novel,
heterogeneous study system.