Long-term different fertilization regimes impact on the fate of root-derived C and microbial community structure in paddy soil

It is known that fertilization pattern could alter soil nutrient and organic matter status. However, it is still unclear how photosynthesized C is distributed in rice-rhizosphere soil-microbial system and its influencing factors due to fertilization pattern and subsequent changes in soil fertility. This study examined the allocation of rice photosynthetic C in rice-rhizosphere soil-microbial systems and the changes in microbial community under three longterm fertilizer regimes. Rice was grown in soils with 8-year history of no fertilizer, inorganic fertilizer (NPK) or NPK fertilizer plus cattle manure (NPK + CM), and was pulse-labelled with 13CO2 at rice tillering stage. The results showed that 13C incorporation in rice-rhizosphere soil system was the highest in the NPK + CM treatment, increased by 489% and 28.9% compared to unfertilized control and the NPK alone. In the >2 mm aggregate fraction, the 13C enrichment was higher in NPK + CM compared to no-fertilized control and NPK treatments. Total PLFA and PLFA groups contents in all aggregate size fractions were the greatest in the NPK + CM treatment. Partial least squares path modelling analysis revealed that microbial community in large macroaggregate (>2 mm) was significantly (P < 0.05) affected by root properties, while soil fertility had a significant (P < 0.01) impact on microbial community in microaggregate (<0.25 mm). The redundancy analysis showed that soil parameters except soil alkali-hydro nitrogen (AN) significantly impacted the soil microbial communities. Through canonical variation partitioning analysis, soil available K was the most important factor leading to variance (11.4%) in microbial community composition. On the other hand, soil pH significantly (P < 0.05) affected the distribution of 13C in microbe community. More than 20% of 13C was incorporated into G- and G+ bacteria across all treatments. Overall, it was observed the NPK fertilizer plus cattle manure treatment was most conducive to retain C from root exudates in the rice-rhizosphere soil-microbial system.