Carbon Mineralization and Microbial Attributes in Straw-Amended Soils as Affected by Moisture Levels.1

An 80-d incubation experiment was conducted to investigate straw decomposition, the priming effect and microbial characteristics in a non-fertilized soil （soil 1） and a long-term organic manure-fertilized soil （soil 2） with and without 13C-labeled maize straw amendment under different moisture levels. The soil 2 showed a markedly higher priming effect, microbial biomass C （Cmic）, and β-glucosidase activity, and more abundant populations of bacteria and fungi than the soil 1. Also, soil CO2 emission, Cmic, /3- glucosidase activity, and bacterial and fungal population sizes were substantially enhanced by straw amendment. In the presence of straw, the amount of straw mineralization and assimilation by microbes in the soil at 55% of water holding capacity （WHC） were significantly higher by 31% and 17%, respectively, compared to those at 25% of WHC. In contrast, β-glucosidase activity and fungal population size were both enhanced as the moisture content decreased. Cmic decreased as straw availability decreased, which was mainly attributed to the reduction of straw-derived Cmic. Amended soils, except the amended soil 2 at 25% of WHC, had a more abundant fungal population as straw availability decreased, indicating that fungal decomposability of added straw was independent of straw availability. Non-metric multidimensional scaling analysis based on fungal denatured gradient gel electrophoresis band patterns showed that shifts in the fungal community structure occurred as water and straw availability varied. The results indirectly suggest that soil fungi are able to adjust their degradation activity to water and straw availability by regulating their community structure.