Abstract:

Aims: To reveal the cascading effects of plant diversity-grasshoppers-carabids across grassland types and their influences on primary productivity. 

Methods: In Ningxia’s four temperate grassland types, 42 research sites were established to assess plant diversity (quadrat-based species composition and cover degree) and primary productivity. Concurrently, the abundance and richness of grasshoppers were sampled via sweep-netting, the abundance and richness of carabids were sampled via pitfall traps, with subsequent multivariate analysis of all datasets. 

Results: The plant species richness in meadow steppe, typical steppe, desert steppe, and steppe desert was 41, 35, 22, and 16 species, respectively; grasshopper (Orthoptera) species richness was 9, 12, 16, and 6 species, while carabid beetle (Coleoptera: Carabidae) species richness was 8, 12, 12, and 3 species. In the meadow steppe, no significant pairwise correlations were found among plant diversity, grasshoppers, carabids, and primary productivity. In the typical steppe, primary productivity exhibited significant positive correlations with plant diversity, carabid abundance, and carabid species richness. In the desert steppe, primary productivity showed significant positive correlation with plant diversity, but carabid species richness showed significant negative correlation with plant diversity. However, in the steppe desert, not only were grasshopper species richness and abundance significantly positively correlated with plant diversity, but carabid abundance was also significantly positively correlated with grasshopper abundance, while primary productivity demonstrated significant negative correlations with plant diversity, grasshopper abundance, and species richness. 

Conclusion: Therefore, among the four grassland types, the steppe desert exhibited the strongest cascading effects of plant diversity-grasshoppers-carabids, but increased plant diversity promotes locust proliferation and leads to a decline in primary productivity. This study highlights that elevated plant diversity may trigger locust outbreaks and reduce ecosystem productivity. Therefore, when using plant diversity to restore steppe deserts, it is necessary to consider the grassland type and its impact on the interactions between pests and natural enemies and thereby on the primary productivity of the grassland.

Key words: grassland plant diversity, grasshopper, carabid beetle, primary productivity, cascading effect