Soluble organic C and N and their relationships with soil organic C and N and microbial characteristics in moso bamboo (Phyllostachys edulis) plantations along an elevation gradient in Central Taiwan

摘要

Purpose Moso bamboo (Phyllostachys edulis), an important economic crop, is distributed from low- to medium-elevation mountains in Taiwan. Bamboo is a fast-growing herbaceous species with an extensive rhizome structure. With the hypothesis that the characteristics of soil organic matter and microbes might change after long-term bamboo plantation, we investigated different fractions of organic C and N as well as soil microbial biomass and activities in five moso bamboo plantations along an elevation gradient in Central Taiwan. Materials and methods Five soil samples (top 10 cm of soil) were collected from each bamboo plantation (600,800,1,000, 1,200, and 1,400 m above sea level (asl)) in January 2011. Soil was processed and analyzed for soil total C and N contents, biologically available C, potentially mineralizable N, soil microbial biomass and soil respiration (CO_2). Two extraction methods (2 M KC1 and hot-water extraction) were used to estimate soil soluble organic C and N (S_bOC and S_bON) and soil inorganic N (NH_4~+ and NO_3~-) concentrations to evaluate the relationship with soil organic matter and microbe characteristics in bamboo plantations. Results and discussion Soil total C and N contents as well as soil microbial biomass and soil respiration (CO_2) of the bamboo plantations increased along the elevation gradient. Temperature changes along elevation contributed to such variations observed among the selected bamboo plantations. The S_bON in hot-water extracts was highest in the 1,200-m plantation, then in the 1,400-m plantation, and lowest in the low-elevation plantations (600, 800, and 1,000 m). However, S_bON in 2 M KCl extracts did not differ by elevation. The S_bON was strongly correlated with soil total N in both 2 M KC1 and hot-water extracts, but only S_bON in hot-water extracts was strongly correlated with microbial biomass N and potentially mineralizable N. S_bOC was strongly correlated with soil total C content, microbial biomass C, and biologically available C in both 2 M K.C1 and hot-water extracts. Conclusions Soil total C and N, S_bOC and S_bON, and microbial biomass characteristics increased in the moso bamboo plantations with increasing elevation. No altitudinal difference in specific soil respiration (CO_2) rate suggested that the enhanced potentially mineralizable N and soil respiration (CO_2) in the high-elevation plantations were associated with increased microbial biomass rather than microbial activities.