Abstract:

Aims: This study aimed to investigate the cascading effects of plant diversity-grasshoppers-carabids across four types of temperate grasslands in Ningxia, China, and to assess their impacts on primary productivity. 

Methods: A total of 42 sampling plots were established across four grassland types: Temperature meadow steppe, temperature typical steppe, temperature desert steppe, and temperature steppe desert. Plant species richness and coverage were measured using quadrats, and primary productivity was estimated accordingly. Grasshopper richness and abundance were assessed sampled via sweep-netting, while carabid beetle richness and abundance were determined using pitfall trapping. All data were analyzed to identify correlations among the studied variables. 

Results: The plant species richness in the temperature meadow steppe, temperature typical steppe, temperature desert steppe, and temperature steppe desert was 41, 35, 22, and 16 species. Grasshopper (Orthoptera) richness was 9, 12, 16, and 6 species, while carabid beetle (Coleoptera: Carabidae) species richness was 8, 12, 12, and 3 species, respectively. In the temperature meadow steppe, there were no significant pairwise correlations were found among plant diversity, grasshopper abundance (richness), carabid abundance (richness), and primary productivity. In the temperature typical steppe, primary productivity was positively correlated with plant diversity, carabid abundance, and carabid species richness. In the temperature desert steppe, primary productivity was positively correlated with plant diversity but negatively correlated with carabid richness. In the temperature steppe desert, both grasshopper richness and abundance were positively correlated with plant diversity, and carabid abundance was positively correlated with grasshopper abundance. However, primary productivity was negatively correlated with plant diversity, grasshopper richness, and abundance. 

Conclusion: Among the four grassland types, the strongest cascading effect of plant diversity-grasshoppers-carabids was observed in the steppe desert, where increased plant diversity significantly promoted grasshopper outbreaks and ultimately reduced primary productivity. These findings suggest that enhancing plant diversity for vegetation restoration in steppe deserts must be carefully managed, considering the trophic interactions between herbivores and their natural enemies, as well as the potential consequences for grassland productivity.

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