Organic Nutrients Induced Coupled C- and P-Cycling Enzyme Activities During Microbial Growth in Forest Soils

Besides environmental and soil physical drivers, the functional properties of microbial populations, i. e., growth rate, enzyme production, and maintenance requirements are dependent on the microbes' environment. The soil nutrition status and the quantity and quality of the substrate input, both infer different growth strategies of microorganisms. It is uncertain, how enzyme systems respond during the different phases of microbial growth and retardation in soil. The objective of this study was to uncover the changes of microbial functioning and their related enzyme systems in nutrient-poor and nutrient-rich beech forest soil during the phases of microbial growth. We determined microbial growth via kinetic approach by substrate-induced respiratory response of microorganisms, enabling the estimation of total, and growing biomass of the microbial community. To induce microbial growth we used glucose, while yeast extract simulated additional input of nutrients and factors indicating microbial residues (i.e., necromass compounds). Microbial growth on glucose showed a 12–18 h delay in associated enzyme activity increase or the absence of distinct activity responses (Vmax). β-glucosidase and chitinase (NAG) demonstrated clear differences of Vmax in time and between P-rich and P-poor soils. However, during microbial growth on glucose + yeast extract, the exponential increase in enzymatic activity was clearly stimulated accompanied by a delay of 8–12 h, smoothing the differences in nutrient-acquisition dynamics between the two soils. Furthermore, cross-correlation of β-glucosidase and acid phosphatase between the two sites demonstrated harmonized time constraints, which reflected the establishment of comparable and balanced enzymatic systems within the decomposition network

Functional soil organic matter fractions in response to long-term fertilization in upland and paddy systems in South China

Soil organic matter (SOM) and its fractions play key roles in optimizing crop yield and improving soil quality. However, how functional SOM fractions responded to long-term fertilization and their relative importance for C sequestration were less addressed. In this study, we determined the effects of long-term fertilization on six functional SOM fractions (unprotected, physically protected, physico-biochemically protected, physico-chemically protected, chemically protected, and biochemically protected) based on two long-term fertilization experiments carried out in South China. The unprotected coarse particulate organic matter (cPOM), the biochemically and chemically protected silt-sized fractions (NH-dSilt and H-dSilt) were the primary C storage fractions under long-term fertilization, accounting for 23.6–46.2%, 15.7–19.4%, and 14.4–17.4% of the total soil organic carbon (SOC) content in upland soil and 19.5–29.3%, 9.9–15.5%, and 14.2–17.2% of the total SOC content in paddy soil, respectively. Compared with the control treatment (CK) in upland soil, the application of manure combined with mineral NPK (NPKM) resulted in an increase in the SOC content in the cPOM, pure physically protected fraction (iPOM), the physico-chemically protected (H-μSilt), and the chemically protected (H-dSilt) fraction by 233%, 166%, 124%, and 58%, respectively. Besides, the SOC increase in upland soil expressed as SOC content per unit of total SOC for iPOM, H-μSilt, cPOM and H-dSilt were the highest and as large as 283%, 248%, 194%, and 105% respectively. In paddy soil, the highest increase per unit of total SOC was H-dSilt (190%), followed by H-dClay (156%) and H-μSilt (155%). These results suggested that the upland soil could stabilize more C through the pure physical, whereas the chemical protection mechanism played a more important role in paddy soil. Chemical protection mechanism within the microaggregates played important roles in sequestrating C in both upland and paddy soils. Overall, the different responses of functional SOM fractions to long-term fertilization indicate different mechanisms for SOM cycling in terms of C sequestration under upland and paddy systems

New perspectives on microbiome and nutrient sequestration in soil aggregates during long-term grazing exclusion

15 páginas.- 5 figuras.- referencias.-Grazing exclusion alters grassland soil aggregation, microbiome composition, and biogeochemical processes. However, the long-term effects of grazing exclusion on the microbial communities and nutrient dynamics within soil aggregates remain unclear. We conducted a 36-year exclusion experiment to investigate how grazing exclusion affects the soil microbial community and the associated soil functions within soil aggregates in a semiarid grassland. Long-term (36 years) grazing exclusion induced a shift in microbial communities, especially in the 2 mm aggregates, and reduced carbon (C) sequestration potential thus revealing a negative impact of long-term GE. In contrast, 11–26 years of grazing exclusion greatly increased C sequestration and promoted nutrient cycling in soil aggregates and associated microbial functional genes. Moreover, the environmental characteristics of microhabitats (e.g., soil pH) altered the soil microbiome and strongly contributed to C sequestration. Our findings reveal new evidence from soil microbiology for optimizing grazing exclusion duration to maintain multiple belowground ecosystem functions, providing promising suggestions for climate-smart and resource-efficient grasslands.This work was financially supported by the National Natural Science Foundation of China (32061123007, 41977031), the Strategic Priority Research Program of Chinese Academy of Sciences (XDB40020202), and the Natural Science Foundation of Hubei Province, China (2020CFA013). Manuel Delgado-Baquerizo acknowledges support from the Spanish Ministry of Science and Innovation for the I+D+i project PID2020-115813RA-I00 and TED2021-130908B-C41 funded by MCIN/AEI/10.13039/501100011033.Peer reviewe

Management of grasslands by mowing versus grazing – impacts on soil organic matter quality and microbial functioning

International audienceAlthough 30% of the European surface area is covered with grasslands, little is known about the effect of their management on soil quality and biogeochemical cycling. Here, we analysed soil from an experimental site in Western France, which had been under either grazing or mowing regime for 13 years. We aimed to assess the effect of the two management practices on the biogeochemical functioning of the soil system. To this end we compared soil organic matter (SOM) composition and microbial properties at two depths. We analysed for elemental, lignin and non-cellulosic polysaccharide content and composition, microbial biomass, soil microbial respiration and enzyme activities. Our results showed higher soil organic carbon (SOC) and nitrogen contents in the surface soil under grazing as compared to mowing. Soil biogeochemical properties also differed between grazing and mowing treatments. In particular, soil under grazing showed lower lignin and higher microbial biomass. Despite the similar non-cellulosic polysaccharide content under both treatments, microbial community under mowing was characterised by higher enzyme production per microbial biomass, leading to more degraded SOM in the mowing system as compared to grazing. We conclude that grazing and mowing regimes impact differently biogeochemical soil functioning. Higher and more diverse carbon input under grazing compared to mowing may lead to enhanced substrate availability and thus more efficient microbial functioning, which could favour SOC sequestration through formation of microbial products

Fertilization promotes microbial growth and minimum tillage increases nutrient-acquiring enzyme activities in a semiarid agro-ecosystem

Microorganisms respiratory and enzymatic activities provide sensitive indicators of changes in soil properties, such as those caused by interactive effects of tillage and fertilization regimes or other agricultural practices. However, the rapid, adaptive microbial growth, respiratory and enzymatic responses to changes in soil environments induced by specific agricultural practices are not well understood. Thus, to explore these adaptations we compared effects of contrasting environments on functional microbial traits (growth and enzyme kinetic parameters) in a Mediterranean agro-ecosystem. These environments differed in long-term disturbance (no, minimum, or conventional tillage), nitrogen-richness (fertilization with 90 kg N ha−1 versus no fertilization), and resource scarcity (increasing with soil depth in 0–30, 30–60 and 60–90 cm layers). Reducing soil disturbance from conventional to minimum tillage promoted microbial growth through shorter Tlag and larger active biomass fraction and induced increases in N- and P-acquiring enzyme activities by increasing nutrients limitation. Fertilization stimulated increases in fast-growing microorganisms with low substrate-affinity enzyme systems, microbial biomass, enzymatic activities, and turnover rates of soil organics. In contrast, increasing scarcity of resources with soil depth strongly reduced microbial biomass and activity. A lack of correlation between soil and enzymatic stoichiometric ratios raises concern regarding the applicability of eco-enzymatic stoichiometric indexes in Mediterranean agro-ecosystems. We conclude that decomposition and turnover of organic substrates under contrasting agricultural practices are mediated by microbial communities with distinct functional traits (active fraction, growth parameters) and enzyme properties (Vmax, Km), which need to be considered in smart land use regimes

Microbial growth and carbon use efficiency in the rhizosphere and root-free soil.

Plant-microbial interactions alter C and N balance in the rhizosphere and affect the microbial carbon use efficiency (CUE)-the fundamental characteristic of microbial metabolism. Estimation of CUE in microbial hotspots with high dynamics of activity and changes of microbial physiological state from dormancy to activity is a challenge in soil microbiology. We analyzed respiratory activity, microbial DNA content and CUE by manipulation the C and nutrients availability in the soil under Beta vulgaris. All measurements were done in root-free and rhizosphere soil under steady-state conditions and during microbial growth induced by addition of glucose. Microorganisms in the rhizosphere and root-free soil differed in their CUE dynamics due to varying time delays between respiration burst and DNA increase. Constant CUE in an exponentially-growing microbial community in rhizosphere demonstrated the balanced growth. In contrast, the CUE in the root-free soil increased more than three times at the end of exponential growth and was 1.5 times higher than in the rhizosphere. Plants alter the dynamics of microbial CUE by balancing the catabolic and anabolic processes, which were decoupled in the root-free soil. The effects of N and C availability on CUE in rhizosphere and root-free soil are discussed

Обзор и обобщение воздействия повышенного уровня атмосферного углекислого газа на почвенные процессы: никаких изменений в водоемах не зафиксировано, однако отмечено увеличение потоков и ускорение циклов.

Atmospheric change encompassing a rising carbon dioxide (CO2) concentration is one component of Global Change that affects various ecosystem processes and functions. The effects of elevated CO2 (eCO2) on belowground processes are incompletely understood due to complex interactions among various ecosystem fluxes and components such as net primary productivity, carbon (C) inputs to soil, and the living and dead soil C and nutrient pools. Here we summarize the literature on the impacts of eCO2 on 1) cycling of C and nitrogen (N), 2) microbial growth and enzyme activities, 3) turnover of soil organic matter (SOM) and induced priming effects including N mobilization/immobilization processes, and 4) associated nutrient mobilization from organic sources, 5) water budget with consequences for soil moisture, 6) formation and leaching of pedogenic carbonates, as well as 7) mobilization of nutrients and nonessential elements through accelerated weathering. We show that all effects in soil are indirect: they are mediated by plants through increased net primary production and C inputs by roots that foster intensive competition between plants and microorganisms for nutrients. Higher belowground C input from plants under eCO is compensated by faster C turnover due to accelerated microbial growth, metabolism and respiration, higher enzymatic activities, and priming of soil C, N and P pools. We compare the effects of eCO2 on pool size and associated fluxes in: soil C stocks vs. belowground C input, microbial biomass vs. CO soil efflux vs. various microbial activities and functions, dissolved organic matter content vs. its production, nutrient stocks vs. fluxes etc. Based on these comparisons, we generalize that eCO will have little impacts on pool size but will strongly accelerate the fluxes in biologically active and stable pools and consequently will accelerates biogeochemical cycles of C, nutrients and nonessential elements.Атмосферные изменения, такие как растущая концентрация углекислого газа (CO2) - один из компонентов глобальных изменений климата, которые, в свою очередь, влияют на различные процессы и функции экосистем. Влияние повышенного уровня CO2 на подземные процессы не до конца понятно из-за сложных взаимодействий между различными компонентами экосистемы. Изучению данного взаимодействия и посвящена эта статья

Effects of Elevated CO2 in the Atmosphere on Soil C and N Turnover

Rising atmospheric carbon dioxide (CO2) concentration affects various soil processes especially related to carbon (C) and nutrient turnover. The methods to study the effects of elevated CO2 (eCO2) were shortly presented. All effects of eCO2 on soil are indirect: by plants through increased net primary production and belowground C inputs due to higher photosynthesis under eCO2. We summarized the impacts of eCO2 on (1) cycling of C and nitrogen (N), (2) microbial growth and enzyme activities, (3) turnover of soil organic matter and induced priming effects including N mobilization/immobilization processes, and (4) associated nutrient mobilization from organic sources. Higher C input from plants under eCO2 leads to faster C turnover due to high microbial activities including respiration, enzymatic activities, and priming effect of soil organic matter. Comparing the effects of eCO2 on changes in pools with that in fluxes we conclude that eCO2 in the atmosphere will have small (or no) effects on the C pools but will strongly increase the fluxes. The stable pools but intensified fluxes will accelerate biogeochemical cycles under elevated CO2