Expansion of rice enzymatic rhizosphere: temporal dynamics in response to phosphorus and cellulose application

Aims The rhizosphere has ecological importance as a microbial hotspot to understand the 'real' processing rates of element cycles without being misled by inactive bulk soil. It is thus essential to estimate the rhizosphere size and its response to anthropogenic distribution during crop growth. Methods In situ beta-glucosidase, cellobiohydrolase (C-acquiring), and acid and alkaline phosphatase (P-acquiring) activity was examined using soil zymography in rice rhizosphere. Temporal dynamics of enzymatic rhizosphere size under phosphate and cellulose fertilization were calculated based on the expansion of enzyme activity hotspot. Results After 35 days of root development, radial expansion of cellobiohydrolase and acid phosphatase from the root centre to bulk soil was further than that of beta-glucosidase and alkaline phosphatase, respectively. Root development expanded beta-glucosidase hotspot in rhizosphere, but inhibited rhizosphere expansion of phosphatase activities. P fertilization caused strong N competition between plants and microorganisms, reducing rhizosphere expansion of all tested enzyme activities. Cellulose had no significant effects on C-acquiring enzyme activity expansion, but led to extended acid and alkaline phosphatase hotspots in the rice rhizosphere under P fertilization. Conclusion i) Plant growth stage affects the rice enzymatic rhizosphere size; ii) P fertilization in P-limited soil enhances rhizosphere enzyme activities but reduces the radial expansion; iii) non-labile C application affects enzymatic rhizosphere expansion in an enzyme-specific manner interactively with P fertilization.