Impact of litter quality on soil nematode communities with the intensifies of grassland degradation: Shifting from resource input to environmental stress

Abstract

Litter quality determines the resource input from aboveground processes in regulating soil biota function in degraded grassland. However, the knowledge of litter quality along with the degradation on the contribution to the soil biota remains sparse, particularly across different trophic groups, given their varying demands for food resources. A 240-day decomposition experiment was conducted to investigate the effect of the litter quality (high-quality and low-quality litters) on soil nematode communities at different intensities of grassland degradation (light, moderate and heavy). The results showed that, even though degradation induced the abundance of microbivorous nematode, the high trophic group nematode reduction was the primary factor that caused the decrease of top-down control from omnivore-predator (OP). Moreover, the metabolic footprint of omnivore-predator was more sensitive than its abundance with OP footprint taking over 40 % of the total footprint while its abundance taking 15 % of total abundance at the light degradation. At the light degraded level, high-quality litter promoted abundance and metabolic footprint of OP nematodes by 69.37 % and 88.27 %, respectively, compared to low-quality litter. These changes in the nematode communities and functions were primarily determined by the N resource change resulting from litter quality. On the contrary, at the moderate and heavy degraded levels, the execrable soil conditions, characterized by high soil pH, simplified the nematode food web. Therefore, the environmental stress screening on soil nematode communities from degradation exceeded the bottom-up effect from litter input. These results suggested that the community structure determined by long-term harsh soil conditions required more attention on the fundamental approach to soil quality rather than litter quality alone. It is critical to adapt appropriate management practices for rehabilitation in the maintenance of belowground communities in grassland restoration.