COS 253-6 - Phosphate availability drives soil microbial P-cycling network across an elevational gradient

Thursday, August 10, 2023

11:15 AM – 11:30 AM PDT

Location: B116

Presenting Author(s)

HS

Hannah B. Shulman

University of Tennessee, United States

Coauthor(s)

JM

Jessica A. M. Moore

University of Tennessee, United States
SK

Stephanie Kivlin

University of Tennessee
Knoxville, Tennessee, United States
AC

Aimee T. Classen, PhD

University of Michigan
Ann Arbor, Michigan, United States
PS

Patrick Sorensen

Lawrence Berkeley National Laboratory, United States
DI

David W. Inouye

Rocky Mountain Biological Laboratory, United States
LS

Lara Souza

University of Oklahoma, United States
RS

Ruth Simberloff

University of Tennessee, United States

Abstract: Arbuscular mycorrhizal fungi (AMF) symbiosis involves the mutualistic transfer of nitrogen and phosphorus (P) in exchange for photosynthate carbon at the root-arbuscule interface. AMF scavenge for phosphate in the soil matrix, but do not themselves have the genetic inventory to create P- solubilizing or mineralizing enzymes. Instead, they rely on P-cycling bacteria to mineralize P from organic matter or solubilize it from mineral P sources. The functioning, diversity, and distribution of these bacteria can help us better understand how AMF and bacteria contribute to make P available for plant uptake.

To investigate the relationships among soil P, AMF, and P-cycling bacteria, we sampled soils collected across 5 elevation gradients in the Colorado Rocky Mountains and at 4 timepoints over a growing season. We tracked soil nutrient concentrations, AMF hyphal length density, and sequenced shotgun metagenomes and marker gene-inferred microbial communities (loci: 16S - bacteria, ITS - general fungi, SSU - AMF).

We hypothesized that greater AMF biomass would correlate with low soil P as well as high abundance and diversity of P-cycling bacterial genes: Lower P availability incentivizes a) more belowground carbon allocation by plants and subsequent hyphal growth and b) soil bacteria to invest more resources in P-mineralizing enzymes. In addition, AMF may directly affect P-cycling bacteria by priming them with sugar.

We found that with increasing elevation, AMF hyphal lengths increased, phosphate concentrations decreased, and the composition of bacterial phosphorus cycling genes shifted. Contrary to our hypothesis, higher AMF hyphal length density was negatively correlated to the genome diversity of P-mineralizing phosphatases and hydrolases, including Alkaline Phosphatase and 3-Phytase. However, AMF hyphal length density was not correlated with P-cycling gene abundance. We will present a soils-centric framework for contextualizing the high diversity of P-cycling bacterial genes recovered from these soils based on a) cellular responses to soil P status as well as a) the organic sources of soil P.

Overall, we will discuss how mechanisms of plant P-limitation influence the soil microbial capacity for organic matter mineralization and P transfer to AMF and plants.