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The spatial distribution of alkaline phosphomonoesterase (ALP) activity in the rhizosphere and bulk soil of three plants (Zea mays, Medicago sativa, and Cyperus rotundus) grown in a karst soil (pH 8.27) was visualized using in situ soil zymography. According to the zymogram images, we identified and precisely collected soil samples from hotspots and non-hotspots of ALP activity, and then analyzed the phoD genes that encoded alkaline phosphomonoesterase and assessed the microbial community. The results showed that (1) the phoD abundance in the plant types varied and was highest in the alfalfa and lowest in the maize; (2) Proteobacteria dominated the phoD-harboring microbes in the rhizosphere and Actinobacteria dominated the phoD-harboring microbes in the bulk soil, and (3) the ALP activity was positively correlated with the relative abundance of the diazotrophic Azotobacter, but negatively correlated with the phoD gene abundance, microbial community richness, and diversity. By coupling zymography and microbial molecular approaches, we identified hotspots of enzymatic and microbial activity in rhizosphere soil and evaluated the relative contributions from potential active microorganisms. We found that the function of specific phoD-harboring microorganisms in these hotspots differed depending on the plant in the soil, which had implications for phosphorus (P) management in P-limited karst soils. The results also suggested that free-living N2-fixing bacteria (Azotobacter) might promote ALP activity, thereby emphasizing vital linkages between, and coupling of, the soil nutrient cycles. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Lentil and lupine, having contrasting root morphologies, were chosen to investigate the effects of plant growth and root morphology on the spatial distribution of β-glucosidase, cellobiohydrolase, leucine aminopeptidase, and acid phosphomonoesterase activities. Lentil kept as vegetative growth and the rhizosphere extent was constant, while the enzyme activities at the root surface kept increasing. Lupine entered reproductive growth in the seventh week after planting, the rhizosphere extent was broader in the eighth week than in the first and fourth weeks. However, enzyme activity at the root surface of lupine decreased by 10-50% in comparison to the preceding vegetative stage (first and fourth weeks). Lupine lateral roots accounted for 1.5-3.5 times more rhizosphere volume per root length than taproots, with 6-14-fold higher enzyme activity per root surface area. Therefore, we conclude that plant growth and root morphology influenced enzyme activity and shape the rhizosphere as follows: the enzyme activity in the rhizosphere increased with plant growth until reproductive stage; lateral roots have much larger rhizosphere volume per unit root length and higher enzyme activity per root surface area than the taproots. [ABSTRACT FROM AUTHOR]