Spatial correlation network characteristics and influencing factors of urban ecological vulnerability in the Yellow River Basin, China.

To elucidate the effects of fire on soil nematode community structure and energy flow within the soil micro-food web across different forest types in the subtropical-temperate transition zone, we investigated soil nematode communities in broadleaf forest, mixed coniferous-broadleaf forest, and coniferous forest in the Xianshan forest area near Henan Dabie Mountains National Forest Ecosystem Field Observation and Research Station. We analyzed soil nematode community structure and micro-food web energy flow between burned and unburned plots, and explored the key driving factors. The results showed that fire significantly reduced the average total soil nematode abundance and the relative abundance of omnivore-predator nematodes across the three forest types by 30.3% and 58.9%, respectively. Meanwhile, fire significantly decreased the soil nematode maturity index and channel index by 10.9% and 22.6%, respectively. There were no significant changes in the relative abundance of microbe-feeding nematodes, plant-parasitic nematodes, or diversity indices. For broadleaf forests, fire significantly increased the Shannon diversity index, richness index, and enrichment index of soil nematodes by 9.5%, 26.9%, and 44.5%, whereas the maturity index and channel index decreased by 19.5% and 41.3%, respectively. Post-fire soil organic matter decomposition was predominantly mediated by the bacterial channel, and no changes were found in total nematode abundance or the relative abundance of any trophic group. In mixed coniferous-broadleaf forests, fire significantly reduced the relative abundance of omnivore-predator nematodes by 61.9%, but did not affect the relative abundance of microbe-feeding nematodes, plant-parasitic nematodes, or ecological indices. For coniferous forests, fire did not alter total nematode abundance, the relative abundance of any trophic group, or ecological indices. Nematode faunal analysis showed that fire increased the functional metabolic footprint of soil nematodes in broadleaf forests, but reduced that in mixed coniferous-broadleaf and coniferous forests. Fire resulted in more uniform energy flow distribution among different energy channels in the micro-food web of mixed coniferous-broadleaf forests. In contrast, energy flow through organic matter decomposition channels and predation channels in the micro-food web was inhi-bited in broadleaf and coniferous forests, with energy concentrated in the plant-parasitic channel and energy flow uniformity decreasing. Litter quality, soil available nitrogen content, and soil water content were the key environmental factors affecting soil nematode community composition. In conclusion, soil nematode communities in different forest types exhibited divergent responses to fire. Broadleaf forests showed stronger potential for biodiversity recovery and nutrient enrichment, mixed forests had improved energy flow uniformity in the micro-food web, and coniferous forests exhibited characteristics of functional inhibition and reduced metabolic activity. These results provide a scientific basis for regional ecological restoration and soil health assessment of burned forests in the subtropical-temperate transition zone.