Plant nutritional and structural diversity shape multitrophic arthropod communities and grassland productivity

Arthropod communities, comprising diverse trophic groups such as
herbivores, predators, and parasitoids, are intricately linked to plant
traits that provide food and habitat.  While it is
well-established that changes in plant functional diversity (e.g., trait
identity and diversity) can significantly alter arthropod diversity across
trophic levels, the cascading effects on ecosystem functions remain less
understood.  Particularly, the role of multitrophic arthropod
diversity in mediating the relationship between plant functional diversity
and grassland productivity presents a critical knowledge gap in ecosystem
ecology. We employed a long-term plant removal experiment in the Inner
Mongolian grassland to systematically investigate how variations in the
community-weight mean and diversity of multiple plant traits influence the
diversity (measured by taxon richness and abundance) of herbivores and
their natural enemies.  Furthermore, we explored how trophic
interactions between herbivores and their natural enemies influence plant
community productivity. Our findings indicate that high diversity in plant
nutritional traits (e.g., nitrogen, phosphorus, and sodium contents)
negatively impacts plant productivity through both direct and indirect
pathways.  The adverse effect was mediated by an increase in the
richness of sucking and chewing herbivores, which exploited high resource
complementarity yet collectively suppressed plant productivity.
  In contrast, higher community-weighted means of plant
structural traits (e.g., vegetative height and leaf lateral spread) were
associated with greater plant productivity.  This positive effect
appears to arise from enhanced top-down control, whereby
predators—particularly spiders—reduced both the richness and abundance of
herbivores. Synthesis. Our study reveals that herbivores and their natural
enemies respond distinctly to the variation in the composition and
diversity of plant nutritional and structural traits.  We show
that cross-trophic interactions—specifically, diversity within herbivore
and predator guilds—constitute a primary pathway through which plant
functional diversity influences grassland productivity.  By
disentangling the links between plant trait spectra, arthropod community
structure, and ecosystem functioning, our findings provide key insights
for biodiversity conservation and the design of ecosystem management
strategies in grasslands.