Title: Root exudates shift how N mineralization and N fixation contribute to the plant-available N supply in low fertility soils

Abstract

Nitrogen (N) availability is a primary constraint to plant productivity, especially in marginal lands with inherently low fertility. Root exudates change with plant nutrient status, and are expected to affect the microbially-mediated N transformations (gross N mineralization vs N fixation) in low fertility soil (low soil organic matter). To explore this possibility, we sampled soils from two monoculture switchgrass (var. Cave-In-Rock) plot with and without N addition at two marginal land sites in Michigan, USA. In a two-week lab incubation, we quantified the effect of different root exudates on gross N mineralization and N fixation by adding simulated root exudates (carbohydrates, organic acids) at a rate of 100 μg C g^–1 day^–1. On average, adding carbohydrates to low fertility soil increased the soil respiration by 254%, the dissolved organic carbon (DOC) by 366% and reduced dissolved organic N (DON) by 40%. In contrast, soils receiving organic acids had 159% more soil respiration, 163% higher DOC concentration and the DON concentration increased by 49%. Analysis of the C recovery in measured pools revealed that root exudates C inputs were nearly equivalent to the DOC, microbial biomass carbon (MBC), and soil respiration in sandy soil, but only 45–74% of the root exudatemore » C was recovered in these pools in the sandy loam soil. This suggests that root exudate C may be adsorbed to mineral particles in the sandy loam soil. Soil treated with organic acids had higher gross N mineralization and N immobilization rates than soil with carbohydrates addition. Adding carbohydrates significantly increased the free-living N fixation rates, compared to organic acid addition. Changes in soil pH, and DON induced by root exudate addition had strong association with N transformation rates and N availability. Gross N mineralization produced more plant-available N than N fixation, as evidenced by higher inorganic N concentration in soils receiving organic acids than carbohydrates. Here, by quantifying how different root exudates affect the contribution of N mineralization and N fixation to the plant-available N pool in low fertility soils, this study enhances our understanding of the “C for N” exchange in the plant rhizosphere.« less

Authors:

Liu, Yuan  ^[1];

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• Search DOE PAGES for ORCID "0000-0001-8350-5773"

Evans, Sarah E. ^[2]; Friesen, Maren L.  ^[3];

• Search DOE PAGES for author "Friesen, Maren L."
• Search DOE PAGES for ORCID "0000-0002-4274-8928"

Tiemann, Lisa K.  ^[1]

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• Search DOE PAGES for ORCID "0000-0003-0514-6503"

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+ Show Author Affiliations

1. Michigan State Univ., East Lansing, MI (United States)
2. Michigan State Univ., Hickory Corners, MI (United States)
3. Washington State Univ., Pullman, WA (United States)

Publication Date:

Tue Dec 28 00:00:00 EST 2021

Research Org.:

Great Lakes Bioenergy Research Center (GLBRC), Madison, WI (United States); Michigan State Univ., East Lansing, MI (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER)

OSTI Identifier:

1845450

Grant/Contract Number:  

SC0014108; SC0018409; FC02-07ER64494

Resource Type:

Accepted Manuscript

Journal Name:

Soil Biology and Biochemistry

Additional Journal Information:

Journal Volume: 165; Journal ID: ISSN 0038-0717

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; Marginal lands; Root exudates; N fixation; Gross N mineralization; Plant-microbe interactions