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Rhizosphere microbial communities are important components of the soil-plant-atmosphere continuum in paddy field ecosystems where they contribute to nutrient cycling and rice productivity. However, the rhizosphere microbial sensitivity to anthropic soil disturbance across plant growth stages remains little investigated. Here, we tracked the effects of long-term (> 25 years) N and NPK-fertilization on bacterial and archaeal community inhabiting the rice rhizosphere at three growth stages (tillering, panicle initiation and booting). Our results reveal that the effect of long-term inorganic fertilization on rhizosphere microbial communities varied with growth stage and that the bacterial and archaeal community differed in their response to N and NPK-fertilization. The microbial communities inhabiting the rice rhizosphere at the panicle initiation appear to be more sensitive to long-term inorganic fertilization than those at the tillering and booting stage. However, the effect of growth stage on microbial sensitivity to long-term inorganic fertilization was more strongly pronounced for bacterial than archaeal community. Furthermore, our results reveal dynamics of bacteria and archaea co-occurrence patterns in the rice rhizosphere, with differentiated bacterial and archaeal pivotal roles in the microbial inter-kingdom networks across growth stages. Hence, our study brings new insights on rhizosphere bacteria and archaea co-occurrence and sensitivity to long-term inorganic fertilization across growth stages in field-grown rice. By identifying one of the critical rice growth stages during which rhizosphere microbial communities are highly sensitive to inorganic fertilization, our results open new avenues for developing appropriate strategies in microbiome engineering to mitigate biotic and abiotic stress and improve crop yields.

The plant rhizosphere microorganisms having the phosphate solubilizing capacity can convert the insoluble soil organic and inorganic phosphates into a soluble form and make the phosphorus (P) available to the plant. With the objective of evaluating the phosphate solubilizing microorganism populations under the rice rhizosphere, soils samples were collected in three locations of two agro ecological zones of Cameroon and analyzed for their PSMs diversity. Isolation of microorganisms was made on non selective nutrient agar plates and the phosphate solubilizing activity of isolates was tested on National Botanical Research Institute’s Phosphate growth medium (NBRIP) amended with sparingly soluble rock phosphates of different origins. The morphological description of isolates allowed evaluating the phosphate solubilizing microorganism’s diversity under the rice rhizospheric soil. The most probable number of PSMs ranged between 22 and 53% with an average of 48%, 52.80% and 22.44% for Nkolbisson, Nyokon and Santchou respectively. The 65 isolates obtained from all locations were distributed in four diverse groups. The index of solubilization ranged between 2.70 and 7.24 depending on isolate. From a total of 65 isolates obtained from the three sampling sites, 46 were phosphate solubilizing isolates among which: 20 were of low solubilization, 16 of medium and 10 of high solubilization. This is the first work reporting phosphate solubilizing microorganisms on rice rhizosphere in Cameroon. However, the selection of phosphate solubilizing microorganisms as possible inoculation tools for phosphate-deficient soils should focus on the integral interpretation of laboratory assays, greenhouse experiments as well as field trials. © 2015 International Formulae Group. All rights reserved. Keywords: Diversity, index of solubilization, isolates, rice, rock phosphates