Land use alters relationships of grassland productivity with plant and arthropod diversity in Inner Mongolian grassland

The threats of land-use intensification to biodiversity have motivated
considerable research directed towards understanding the relationship
between biodiversity and ecosystem functioning (BEF). Functional diversity
is deemed a better indicator than species diversity to clarify the BEF
relationships. However, most tests of the BEF relationship have been
conducted in highly controlled plant communities, with terrestrial animal
communities largely unexplored. Additionally, most BEF studies examined
the effects of biodiversity on ecosystem functions, with the effects of
ecosystem functioning strength on biodiversity hardly considered. Based on
a 6-year long grassland experiment in the typical steppe region of Inner
Mongolia, we examined the variation of taxonomic diversity (TD) and
functional diversity (FD) of both plant and arthropod communities, and
their relations with grassland productivity, across three land management
types (moderate grazing, mowing and enclosure). We aimed to clarify the
interrelations among plant FD, arthropod FD, grassland productivity and
soil factors. We found that: (1) Grassland under mowing performs best in
terms of sustaining a high TD and FD of plants and arthropods compared to
that under grazing and enclosure. (2) The relationships between plant and
arthropod diversity and productivity varied with management types. Plant
TD and FD was negatively, whereas arthropod FD was positively, related
with productivity under enclosure; plant FD, but not arthropod FD, was
positively related with productivity under grazing; arthropod FD, but not
plant FD, was negatively related with productivity under mowing. (3)
Grassland productivity is positively interrelated with plant FD, but not
plant TD; and is negatively interrelated with arthropod TD, but not
arthropod FD across different management types. The respective positive
versus negative bi-directional relationships of productivity with plant
diversity versus arthropod diversity, was majorly a consequence of
divergent grazing/mowing effects on plant versus arthropod diversity. The
results indicate that grazing increases plant diversity, but decreases
arthropod diversity, whereas fall mowing provides a management strategy
for conservation of both trophic levels. These results also provide new
insights into the effects of land-use changes on biodiversity and
ecosystem processes, and indicate the importance of incorporating the
functional interrelations among different trophic groups in sustainable
grassland management.