Abstract: As a key component of carbon cycling in terrestrial ecosystems, the production of fine roots is regulated by both environmental and biological factors. Herbivorous soil animals are an important factor influencing fine root turnover. To elucidate the mechanisms by which herbivorous soil animals influence fine root production across broad geographical gradients, we established 17 plots in natural secondary forests spanning a latitudinal range of 18°36′N-53°26′N in eastern China. We manipulated herbivorous soil animal activity by applying insecticides to control their feeding on roots. Following one-year treatment, fine roots were collected from the 0-20 cm soil layer, classified using the root order classification approach, and their production was quantified to examine differential responses of absorptive fine root (AFR) and transport fine root (TFR) yields to herbivory disturbance. The results showed that: (1) under natural conditions, both AFR and TFR production exhibited a significant increasing trend from north to south sites, with yields in tropical and subtropical regions being significantly higher than those in temperate and cold-temperate regions. Specifically, AFR production in tropical forests was 1.5-2.1 times of that in cold-temperate plots (78-94 g·m^-2), and TFR production was 3-4 times of that in cold-temperate plots (138-150 g·m^-2). Some mid-subtropical plots had lower yields than adjacent areas in the same climatic zone due to micro-environmental differences. (2) After excluding herbivorous soil animals, AFR and TFR production significantly increased  in half of the plots, but the magnitude of response differed significantly across latitude zones. AFR production increased by 20%-25% and TFR production by 25%-30% in low-latitude tropical and subtropical regions, with AFR yields in some subtropical plots being the highest among adjacent latitudes after treatment. AFR production increased by only 10%-15% in high-latitude cold-temperate to temperate regions, with cold-temperate plots becoming low-yield areas and showing no significant geographical gradient. Two-way ANOVA Showed that there was a significant interaction between treatment effects and latitude zones (P<0.05), with a stronger regulatory effect of soil animals on fine root production in low-latitude regions. (3) Fine root production was highly significantly negatively correlated with latitude and significantly positively correlated with mean annual temperature and annual precipitation, confirming that hydrothermal condition is the fundamental driver of geographical differentiation of fine root production. The regulatory effect of herbivorous soil animals showed latitudinal dependency. Low-latitude regions induced plant compensatory growth through feeding pressure, while high-latitude low-temperature environments inhibited soil animal activity, masking their effects by climatic factors. This study provides an important reference for further exploring the relationship between herbivorous soil animals and fine root production in forests, and has important theoretical significance for understanding the relationship between energy flow and material cycling in forest ecosystems.

Key words: fine root production, herbivorous soil animal, root order classification method, ingrowth method, natural secondary forest