Plant Rhizosphere Contributions to Soil Aggregation in a Riparian Buffer
Grant Falvo1*
1Arizona State University, Tempe, Arizona, USA; gfalvo@asu.edu
Grazed riparian buffers are implicated in the filling of reservoirs with sediment and the loss of topsoil from ranches. Plants and the microbial symbionts found in their rhizospheres are implicated in the causal chain for soil aggregation, which confers resistance to erosive forces. Soils were sampled from the rhizosphere of the grass, Nassella leucotricha, as well as the surrounding top and subsoil, in the riparian buffer of a semi-arid cattle grazing ranch. Results showed that the rhizosphere had significantly (p0.05) greater degrees of soil aggregation than the top and subsoil as measured by mean weight diameter. This was due, in part, to the significantly (p0.05) higher concentrations of organic carbon and glomalin related soil protein, which is produced by the arbuscular mycorrhizal fungi directly associated with the plant. An active microbiome was identified by the significantly (p0.05) lower carbon to nitrogen ratio found in the rhizosphere soils. These points of evidence show a functioning exchange economy between the Nassella leucotricha and the arbuscular mycorrhizal fungi where Nassella leucotricha exudes photosynthates to feed the arbuscular mycorrhizal fungi which in turn, scavenges nitrogen and produces glomalin, a known soil aggregator with relatively high nitrogen content. Increased soil aggregation facilitates root penetration and reduces soil erodibility for the plant’s descendants, which confers increased fitness for the plant and increased resistance to erosive forces for the riparian habitat. This means that Nassella leucotricha cooperates with its microbial symbionts to augment the suitability and stability of its own niche while preventing excess sediment from entering the river and subsequently, downstream reservoirs.