Data from: Nonlinear responses of soil nematode community composition to increasing aridity

Aim: Increasing aridity under global change is predicted to have a
profound impact on the structure and functioning of terrestrial
ecosystems, yet we have poor understanding of how belowground communities
respond. In order to understand the longer-term responses of different
trophic levels in the soil food web to increasing aridity, we investigated
the abundance, richness and community similarity of the soil nematode
community along a 3200-km aridity gradient. Location: A transect across
semi-arid and arid grasslands in Northern China, where the aridity ranges
from 0.43 to 0.97. Time period: July and August 2012. Major taxa studied:
Soil-borne Nematoda. Methods: We used Generalized Additive (Mixed) Models
to analyze the abundance, richness and community similarity patterns of
soil nematodes. We used Structural Equation Modelling (SEM) to disentangle
the direct and indirect environmental drivers (aridity, soil and plant
variables) of the nematode community. Results: The abundance, richness and
similarity of nematode communities declined non-linearly with increasing
aridity. The most pronounced decline in nematode richness and community
similarity occurred under arid conditions (aridity > 0.80).
However, the shape of response to aridity differed among nematode feeding
groups. Under arid conditions, the abundance and richness of bacterial
feeders were less sensitive to changes in aridity than fungal feeders. The
SEM analysis revealed that nematode community responses to aridity were
not mediated via changes in plant and soil variables, but rather were
directly affected by aridity. Main conclusions: Our results show that in
mesic grasslands increasing aridity primarily caused decline in nematode
abundance, whereas increasing aridity in xeric grasslands led to loss of
nematode diversity. The non-linear responses of nematodes to aridity could
result in non-linear shifts in ecosystem functioning as well, because soil
nematodes operate at various trophic levels in the soil food web, thereby
influencing the performance of plants, soil biodiversity and
biogeochemical cycling.