Elevated O 3 has stronger effects than CO 2 on soil nematode abundances but jointly inhibits their diversity in paddy soils.

Anthropogenic activities have resulted in rising atmospheric concentrations of carbon dioxide (CO ₂ ) and ozone (O ₃ ), exerting substantial direct and indirect impacts on soil biodiversity within agroecosystems. Despite the considerable attention given to the individual impacts of elevated CO ₂ and O ₃ levels, the combined effects on soil nematode communities have not been extensively explored. In this study, we investigated the interactive effects of elevated CO ₂ (+200 ppm, eCO ₂ ) and O ₃ (+40 ppb, eO ₃ ) levels on the abundance, diversity, and trophic composition of soil nematode communities associated with two rice cultivars (Nanjing 5055, NJ5055 and Wuyujing 3, WYJ3). Our findings revealed that soil nematodes had greater abundances under eO ₃ , whereas eCO ₂ had no significant impacts. Conversely, both eCO ₂ and eO ₃ , and their combination led to significant reductions in nematode generic richness, accompanied by a decline in the diversity particularly associated with the WYJ3 cultivar. Moreover, eCO ₂ and eO ₃ influenced nematode community composition and environmental factors, particularly for the WYJ3 cultivar. Both eCO ₂ and eO ₃ significantly increased soil nitrate levels. The changes in nematode community composition were related to soil nitrate levels, as well as nitrogen and carbon concentrations in rice plant roots. Furthermore, interactions between eCO ₂ and eO ₃ significantly impacted soil nematode abundance and trophic composition, revealing intricate consequences for soil nematode communities that transcend predictions based on single-factor experiments. This study unveils the potential impacts posed by eCO ₂ and eO ₃ on soil biodiversity mediated by rice cultivars, plant functional characteristics and soil feedback mechanisms, thereby underscoring the complex and interactive outcomes arising from concurrent drivers of climate change within the soil food web.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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