Rhizosphere processes are driven by roots and soil microorganisms. Microbial activity in the rhizosphere increase nutrient mobilization and consequently net primary productivity of plants. Rhizodeposition is intimately linked to root morphology. The presence of root hairs, for instance, increases root exudation. Furthermore, root hairs play a crucial role for nutrients’ acquisition, but their effects on SOM turnover and nutrient cycling in soil still remains unknown.
Material and Methods
We investigated the effects of root hairs, with or without P-fertilization, on maize biomass production and nutrient cycling in soil. We hypothesized that 1) root hairs increase rhizodeposition, which stimulates microbial activity and enhance nutrient turnover, and 2) in P-limited soils, microbes mine for P by producing exoenzymes mineralizing SOM.
Maize (Wild type and roothairless 3 mutants) was grown in P-limited soil with or without P-fertilization. Plants were harvested at 3 phenological stages. Plant biomass, microbial biomass (Cmic, Nmic, Pmic), and exoenzyme activities were determined.
P-fertilization increased plant biomass similarly for the wild type and mutants. Root activity increased microbial biomass. P-fertilization decreased Pmic and Nmic especially at later stages for wild type and mutants. When plants are sufficiently supplied with nutrients, no change or downregulation of enzyme activities in rhizosphere soils demonstrates microbial utilization of available nutrients. When nutrients become scarce (stem elongation and heading), root hairs intensified plant-microbial competition for P and N, which is shown by higher enzyme activities under the wild type especially in unfertilized soils.
Our study supports the theory of microbial activation through living roots by the release of rhizodeposits. In nutrient poor soils, root hairs enhance net primary production, intensify plant-microbial interactions and regulate nutrient cycling.