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

Abstract

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.

Soil microorganisms respond distinctively to adaptive multi‐paddock and conventional grazing in the southeastern United States

“…The total amount of DNA per gram dry soil, measured as a surrogate for soil microbial biomass (Kuske et al., 2019), was 32% greater ( p = 0.012) under AMP compared to conventional management (Table 2). Analysis of variance main effects statistics are provided for all response variables in Table S5.…”

“…The abundance of rRNA genes was used to estimate the relative biomass of bacteria and fungi and to calculate fungal/bacterial (F:B) ratios, a potential indicator of land management (Kuske et al., 2019; Manter et al., 2021). In support of the total DNA assay results, there were 37% greater bacterial ( p = 0.001) and 33% greater fungal ( p = 0.009) ribosomal gene copies under AMP compared to conventional management (Table 2).…”

“…Fluorescence readings were acquired using a Biotek FLx800TBI microplate reader (excitation: 485/20, emission: 528/20). Total DNA (ng g −1 dry soil) was used as a proxy for microbial biomass (Kuske et al., 2019) and supported by biomass estimates of bacteria and fungi using quantitative polymerase chain reaction (qPCR) of rRNA genes (Kuske et al., 2019; Manter et al., 2021) as described below.…”

Impacts of winter wheat and cover crops on soil microbial diversity in a corn–soybean no‐till cropping system in Quebec (Canada)

“…Findings from this study suggest that neither crop rotation nor cover crops had an impact on molecular microbial biomass. Quantification with qPCR has only recently started being used to estimate molecular microbial biomass (Albright et al., 2020; Kuske et al., 2019). Data regarding the use of molecular biomass to evaluate the effects of cover crops on microbial communities are still scarce.…”

Quantificação dos efeitos da introdução de Pinus taeda nas comunidades microbianas do solo e no ciclo do nitrogênio em uma floresta tropical montana nativa com Araucaria angustifolia

“…angustifolia and P. taeda at the study site is not known. It has been proposed that a large proportion of the soil microbial biomass and necromass consists of mycelia of mycorrhizal fungi (Finlay and Söderström 1992;Kuske et al 2019). For AM fungi the estimated extra-radical hyphae in the standing crop, for a soil depth of 30 cm with a bulk density of 1.2 g cm -3…”