Variations in the Soil Microbial Community Structure, Abundance and Function Amended with Biochar in Legume-Cereal Cropping Pattern.

Biochar is being evaluated globally as a means to improve soil fertility and to mitigate climate change. However, the long term effects of plant-based biochar on soil microbial communities have received much less attention than its effects on soil biological properties. The present study was conducted in the arid zone agricultural region of Pakistan to investigate the impact of biochar on the soil microbial community structure, abundance and activity in the rhizosphere of legume-cereal cropping system. For this, pyrolyzed biochar of sugarcane bagasse was prepared and applied at rates of 0, 0.25 and 0.5%-C (C-equivalent basis) with and without NPK fertilization (23N, 45P, 25k, Kg ha^-1). Biochar treatments were applied before sowing of mash bean, after which the residual effects of the treatments were investigated on wheat. Soil samples were collected from each treatment plot at maturity for each crop. Soil microbial communities were analyzed using PLFA profiling. Gene copy numbers of bacterial 16S rRNA were significantly increased with biochar (132%) and NPK fertilization (27%) in mash bean, while 18S rRNA was significantly decreased with biochar application by 22%. However, 18S abundance was increased (20%) when biochar was applied along with chemical fertilizer. In wheat crop, 16S rRNA and 18S rRNA gene was significantly increased by 32% and 104% with biochar and NPK, fertilization. PLFA profiling revealed significant shifts in the microbial communities in legume-cereal cropping systems. The increase in PLFAs was attributed to Gram positive and Gram negative bacteria and Pseudomonas in the mash bean and wheat while only mycorrhizae were significantly increased in the wheat crop. Urease and dehydrogenase activity was significantly increased with biochar applied at 0.5%-C and NPK fertilization in mash bean crop and that of urease activity decreased in wheat crop while dehydrogenase activity remained unchanged. In conclusion, biochar application significantly changed the soil microbial community structure, increased the abundance and microbial activity in the legume-cereal cropping system of an arid climate.