Linking Soil Microbial Diversity to Nitrogen and Phosphorus Dynamics

Changes in the soil microbial community for studies of different novel communities can be promoted by different methodologies, among which soil autoclaving stands out as a quick and readily available tool. However, this procedure may also directly or indirectly alter nitrogen (N) and phosphorus (P) dynamics. The purposes of this study were as follows: (i) to characterize microbial activity after soil autoclaving through microbial 14CO2-respiration; and (ii) to evaluate the effect of microbial manipulation and autoclaving on soil N and 33P dynamics. For this, two sets of soil samples from two areas (forest and cultivated area) were used in the laboratory. Firstly, 14C-glucose was added to the soils and after 24 h five soil microbiomes were generated: AS (autoclaved soil), and AS re-inoculated with serial dilutions (w/v) prepared by successive mixing of soil suspensions in sterile deionized water obtaining 10−1, 10−3, and 10−6, which generated the treatments AS + 10−1, AS + 10−3, and AS + 10−6; and the treatment NS (non-autoclaved control), all incubated for 28 d. 14CO2 emission was used to characterize microbial activity; additionally, N dynamics were assessed at the end of incubation. In a second assay, 33P was applied to the soil before autoclaving and re-inoculation. Following further incubation (14 d), a 33P chemical fractionation was performed. The following are based on the results: (i) 14CO2 emission: microbial activity in the autoclaved soil is null, but after a reinoculation of AS + 10−1 and AS + 10−3 soil dilution suspension, the 14CO2-respiration is higher than in an NS. (ii) regarding the N dynamics, in autoclaved soils, the microbial levels increased N-NH4+ concentration, with an evident increase in the AS + 10−3 and AS + 10−1, and a reduction in the N-NO3− concentration in comparison to the NS. For 33P, the autoclaving procedure itself reduced the 33P lability, regardless of the levels of microbial community reinoculated.