Simple measurements in a complex system: soil community responses to nitrogen amendment in a Pinus taeda forest

Journal Article · 05 April 2019 · Ecosphere

DOI: https://doi.org/10.1002/ecs2.2687 · OSTI ID:1505642

Kuske, Cheryl Rae  ^[1]; Sinsabaugh, Robert L. ^[2]; Gallegos‐Graves, La Verne ^[1]; Albright, Michaeline Burr Nelson  ^[1]; Mueller, Rebecca ^[1]; Dunbar, John Martin  ^[1]

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1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2. Univ. of New Mexico, Albuquerque, NM (United States)

Microorganisms regulate the decomposition of soil organic matter and the flow of plant–available nutrients. In a temperate pine forest in North Carolina, USA, where nitrogen (N) had been experimentally added for eight years, we combined DNA–based measures of fungal and bacterial biomass and composition with measures of seven extracellular enzymes (ecoenzymes). These measures were then correlated with soil chemistry. Our goals were to evaluate the relative sensitivity and repeatability of multiple structural and functional measures of community organization to long–term N deposition. Measurements were conducted at three litter/soil depths, corresponding to the litter, Oa, and mineral A horizons (max depth 10 cm) with ten spatial replicates per experimental plot. Soil chemistry differed significantly with soil depth and N amendment. Total biomass (soil DNA), as well as fungal and bacterial biomass (measured by qPCR), was greatest in the litter horizon and declined significantly with depth. Ecoenzyme activity patterns also changed with soil depth, transitioning from high levels of C, N, and P metabolizing activities in the litter horizon to increased oxidative activities at the lower depth. Under N amendment, soil pH decreased and nitrate concentrations increased in all three soil horizons. Correspondingly, the estimated microbial C use efficiency decreased in N–amended soils at all depths, despite differences in microbial biomass, community composition, and soil chemistry. Overall, bacterial composition was most responsive to nitrogen amendment, but the taxonomic context of the response varied with soil horizons in conjunction with shifts in soil chemistry and enzyme activities. While a single measure that would incorporate all of the C, N, and P metabolizing activities did not emerge, many measures correlated with each other, and/or with depth and/or N amendment.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: 89233218CNA000001
• OSTI ID: 1505642
• Alternate ID(s): OSTI ID: 1505643; OSTI ID: 1525839
• Report Number(s): LA-UR-18-23932
• Journal Information: Ecosphere, Vol. 10, Issue 4; ISSN 2150-8925
• Publisher: Ecological Society of AmericaCopyright Statement
• Country of Publication: United States
• Language: English