C/P stoichiometry of dying rice root defines the spatial distribution and dynamics of enzyme activities in root-detritusphere
As the primary microbial substrate after shoot cutting, the element stoichiometry of root-detritus (dying or dead roots) influences the enzyme activity in root-detritusphere. However, the effect of the C/P ratio of root-detritus on the dynamics and distribution of enzyme activities is little revealed. We hypothesised that P fertilisation would decrease the C/P ratio of root-detritus, therefore affecting the hotspot areas and hot moments of C-acquiring and P-acquiring enzyme activities, as well as their activity ratio (C/P acquisition ratio). Root-detritus of low (59.0) and high (170.8) C/P ratios was produced in P-poor soil with and without P fertilisation, respectively. In situ soil zymography showed that the distribution of C-acquiring enzymes (β-glucosidase and cellobiohydrolase) was more associated with root-detritus than P-acquiring enzymes (acid and alkaline phosphomonoesterase). P fertilisation increased the hotspot areas of C-acquiring enzyme activities over the experiment, without influencing their temporal dynamics. However, its effect on phosphomonoesterase activities depended on the decomposition and delayed the appearance of the highest hotspot areas. P supply met the microbial demand in P-fertilised soil, with high C/P acquisition ratio and constant stoichiometry of microbial biomass C (MBC)/microbial biomass P (MBP). A low C/P acquisition ratio and high MBC/MBP in non-fertilised soil was observed, indicating P limitation for microorganisms. After the 150-day incubation, Olsen P significantly increased in P-fertilised soil (P < 0.05), whereas it decreased in the root-detritusphere of non-fertilised soil. We conclude that the decomposition of root-detritus with a low C/P ratio has potential to improve soil P availability; however, C-P imbalance may increase during the decomposition of root-detritus with a high C/P ratio.
KeywordsP fertilisation Root-detritus C/P ratio C/P acquisition ratio Hotspot areas Hot moments Root-detritusphere Soil zymography
We thank the Public Service Technology Center, Institute of Subtropical Agriculture and Chinese Academy of Sciences for technical assistance. The work was performed according to the Government Program of Competitive Growth of Kazan Federal University.
This study was supported by the National Key Research and Development Program of China (2016YFE0101100; 2017YFD0800104),the National Natural Science Foundation of China (41430860, 41811540031 and 41761134095), the Youth Innovation Team Project of the Institute of Subtropical Agriculture, Chinese Academy of Sciences (2017QNCXTD_GTD), Hunan Province Base for Scientific and Technological Innovation Cooperation (2018WK4012) and Chinese Academy of Sciences President’s International Fellowship Initiative to Bahar S. Razavi (2018VCC0011).
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