CAN PLANTS STIMULATE SOIL MICROBES AND THEIR OWN NUTRIENT SUPPLY? EVIDENCE FROM A GRAZING TOLERANT GRASS

TLDR

Mineral nutrients for plants mainly arise from microbial decomposition of organic matter, yet plants have traditionally been viewed as passive participants that cannot significantly influence this process. The study aimed to trace carbon movement into the rhizosphere and microbial biomass of Poa pratensis using a 13C pulse‑chase experiment, and to assess its impact on soil nitrogen availability and plant nitrogen dynamics. Researchers applied a 13C pulse‑chase to Poa pratensis in Yellowstone National Park, monitoring carbon incorporation into rhizosphere microbes and subsequent changes in soil nitrogen pools and plant nitrogen uptake. Grazing stimulated root exudation, rapidly fueling rhizosphere microbes, which in turn enhanced soil inorganic nitrogen, plant nitrogen uptake, leaf nitrogen content, and photosynthesis, providing the first evidence that herbivory can promote microbial‑mediated nutrient acquisition and a positive feedback loop supporting plant regrowth.

Abstract

The primary source of mineral nutrients for plants is the decomposition of organic matter by soil microbes. Plants are traditionally viewed as largely passive participants in the decomposition process, incapable of directly affecting rates of decomposition significantly and primarily assimilating nutrients unused by the microbial pool. We performed a 13C pulse-chase experiment on a common grazing tolerant grass, Poa pratensis L., of Yellowstone National Park, to follow carbon flow into the soil rhizosphere and microbial biomass and the associated effects on soil N availability and plant N dynamics. Grazing promoted root exudation of carbon, which was quickly assimilated into a burgeoning microbial population in the rhizosphere of clipped plants. Moreover, these facilitating effects of defoliation on rhizospheric processes positively fed back on soil inorganic N pools, plant N uptake, leaf N content, and photosynthesis. Such findings are the first evidence, to our knowledge, that suggest (1) plants are capable of promoting rhizospheric microbial populations to facilitate uptake of a limiting soil resource and (2) that there is a general positive feedback mechanism by which herbivory promotes plant regrowth as well as energy and nutrient flows in grazed landscapes.