Sichuan Agriculture University,Sichuan Agriculture University,Sichuan Agriculture University,,,Sichuan Agriculture University
Foliar litter humification is one of the main mechanisms of carbon sequestration, and is essential in forming soil organic matter from foliar litter. Soil fauna is a type of decomposer that can influence litter humification. It was previously believed that soil fauna were dormant during the winter in cold biomes, and thus their activities were not considered to affect litter humification. However, recent studies have documented that some cold tolerant soil fauna remain active during the winter. However, little is known about the effects of soil fauna on litter humification during the winter in cold biomes. Therefore, a field experiment with different sizes of litterbags was conducted on three cold biomes along different altitudinal gradients in the eastern Tibet Plateau. Two species were selected to study litter decomposition at each of the three biomes:Betula albo-sinensis and Abies faxoniana in the subalpine forest at 3000 m, Sabina saltuaria and Salix paraplesia in the alpine forest at 3600m, and Ajania nubigena and Carex atrofusca in the alpine meadow at 4000 m. Litterbags were placed before the soil completely froze in November, 2013. Litterbags were sampled at the onset of three stages-freezing, deep freezing, and thawing-from 2013 to 2014. Tone coefficient (ΔlogK) and optical density value (E4/E6) were analyzed to determine the litter humification levels. The results showed that soil fauna promoted leaf litter humification as the temperature decreased, and suppressed leaf litter humification as the temperature increased during the winter in cold ecosystems. The effects of soil fauna on the process of leaf litter were regulated by altitude and litter species. The effect of soil fauna on leaf litter humification decreased as the altitude increased. Soil fauna increased litter humification at 3000m during the deep freezing stage and at 3600m at the onset of the freezing stage. However, soil fauna inhibited litter humification at 4000m during the thawing stage. Furthermore, soil fauna did not affect litter humification at other altitudes and sampling stages. The effects of soil fauna on litter humification rate at the onset of freezing stage were higher than those of the deep freezing stage and thawing stage, and humification rate peaked during the deep freezing stage. These results suggest that the activities of soil animals could promote humus formation from litter as the temperature decreases, indicating a possible increase in soil carbon sequestration. Together, these data provide a new understanding of soil organic matter formation and the carbon budget in cold ecosystems.