Abstract:

The ecological distribution and temporal dynamics of soil bacterial physiological groups in subalpine timberline ecotone and its upper boundary of scree meadow and below boundary of fir forest in Western Sichuan were investigated and analyzed with the plate count and MPN methods. Results showed that populations of soil bacterial physiological groups decreased with increasing soil depth. In 0-30 cm soil layer, the quantities of nitrobacteria, denitrifying bacteria, aerobic nitrogen fixing bacteria, organic phosphorus-decomposing bacteria and aerobic cellulose-decomposing bacteria were in a sequence of timberline ecotone soil＞fir forest soil＞scree meadow soil. There was no significant difference for ammonifying bacteria, inorganic phosphorus-decomposing bacteria and anaerobic cellulose-decomposing bacteria between timberline ecotone and fir forest soil, while those bacteria in the two soils were more than that in scree meadow. The ammonifying bacteria, inorganic and organic phosphorus-decomposing bacteria were dominant physiological groups in each soil, while the cellulose-decomposing bacteria were the scarcest group. Furthermore, the populations of soil bacterial physiological groups were the least in 0-15 cm soil layer of scree meadow in April and the most in June, whereas the groups were also the least in the topsoil (0-30 cm) of timberline ecotone and fir forest, but all the most in August except denitrifying bacteria and anaerobic cellulose-decomposing bacteria which were the most in June. There was no significant temporal dynamics in the subsoil under three kinds of vegetations. In general, the spatial distribution patterns and temporal dynamics of various soil bacterial physiological groups in timberline ecotone and adjacent vegetations were to certain degree different, depending on the site condition, soil nutrition and water-heat conditions.

Key words: subalpine in Western Sichuan, timberline ecotone, bacterial physiological groups, population distribution