Publications

Manure is an important source of nutrients for plants and stimulates a wide range of enzyme-mediated microbial processes. Such stimulation, however, depends on manure distribution and the duration of its decomposition in soil. For the first time, we investigated the spatio-temporal patterns of enzyme activities as affected by manure application strategies: 1) Localized manure: manure application as a layer in the upper soil; 2) Homogenized manure: mixing manure throughout the soil; and 3) Control without manure. Tibetan barley was planted on soil managed with yak manure from the Tibetan Plateau. Soil zymography was used to visualize the two-dimensional distribution and dynamics of the activities of three enzymes responsible for cycling of carbon (β-glucosidase), nitrogen (N-acetylglucosaminidase) and phosphorus (phosphomonoesterase) over 45 days. The manure detritusphere increased enzyme activities relative to the control (which had only the rhizosphere effect of barley) and this stimulation lasted less than 45 days. Enzyme activities in the manure-induced hotspots were higher than on the barley rhizoplane, indicating that the detritusphere stimulated microbial activities more strongly than roots. Homogenized manure led to 3–29% higher enzyme activities than localized manure, but shoot and root biomass was respectively 3.1 and 6.7 times higher with localized manure application. Nutrients released by high enzyme activities within the whole soil volume will be efficiently trapped by microorganisms. In contrast, nutrients released from manure locally are in excess for microbial uptake and remain available for roots. Consequently, microorganisms were successful competitors for nutrients from homogeneous manure application, while plants benefited more from localized manure application. We conclude that localized manure application decreases competition for nutrients between the microbial community of manure and the roots, and thereby increases plant performance.

Microbial carbon (C) use efficiency (CUE) delineates the proportion of organic C used by microorganisms for anabolism and ultimately influences the amount of C sequestered in soils. However, the key factors controlling CUE remain enigmatic, leading to considerable uncertainty in understanding soil C retention and predicting its responses to global change factors. Here, we investigate the global patterns of CUE estimate by stoichiometric modeling in surface soils of natural ecosystems, and examine its associations with temperature, precipitation, plant‐derived C and soil nutrient availability. We found that CUE is determined by the most limiting resource among these four basic environmental resources within specific climate zones (i.e., tropical, temperate, arid, and cold zones). Higher CUE is common in arid and cold zones and corresponds to limitations in temperature, water, and plant‐derived C input, while lower CUE is observed in tropical and temperate zones with widespread limitation of nutrients (e.g., nitrogen or phosphorus) in soil. The contrasting resource limitations among climate zones led to an apparent increase in CUE with increasing latitude. The resource‐specific dependence of CUE implies that soils in high latitudes with arid and cold environments may retain less organic C in the future, as warming and increased precipitation can reduce CUE. In contrast, oligotrophic soils in low latitudes may increase organic C retention, as CUE could be increased with concurrent anthropogenic nutrient inputs. The findings underscore the importance of resource limitations for CUE and suggest asymmetric responses of organic C retention in soils across latitudes to global change factors.

Global warming increases belowground carbon (C) input as plant litterfall, root biomass and rhizodeposition, which influences the stocks and dynamics of soil organic matter. To clarify the effects of labile C availability (biochemical factor) and temperature (environmental factor) on enzyme activities, we incubated typical paddy soil for 75 d at four temperatures (5, 15, 25, and 35 °C) under anaerobic conditions. Acetate was used as the source of labile C and methane. The potential activities of three hydrolases (β-glucosidase, chitinase, and xylanase) were analysed on days 3, 15, and 75 after acetate addition. Activity of β-glucosidase and chitinase in soil without acetate addition was 2.1–2.7 times higher than that with acetate. Xylanase activity increased with temperature and incubation period. The enzymes involved in the C cycle were sensitive to temperature, whereas chitinase (responsible for N cycle) activity became temperature sensitive only after acetate addition (Q 10-V max ≥ 1). Organic C mineralisation (CO2 release) was more sensitive at low temperature with Q 10 values 1.1–3.4 times higher at 5–15 °C than at 25–35 °C. The Q 10 values for methane (CH4) emission were 2.8–13.5 times higher at 5–15 °C than at 25–35 °C. Organic matter decomposition in paddy soil was more sensitive to temperature (Q 10 of CO2 and CH4 emission ≥ 1) than enzyme activities. Comparison of abiotic (temperature) and biochemical (C availability) effects indicated that warming has limited effects on hydrolase activities in paddy soil. The increase in labile C remarkably stimulated microbial activity and soil organic matter turnover. We conclude that: i) enzyme activities are more sensitive to C addition than to temperature; ii) and SOM decomposition is accelerated by both C input and warming, especially at low temperatures.

No abstract is provided for this article.

No abstract is provided for this article.

Abstract Phosphorus is a critical factor limiting ecosystem productivity in subtropical ecosystems. Deforestation alters element stocks and cycling, leading to changes in the soil microbiome. However, the impacts of native forest conversion on the capacity of microbes to support phosphorus availability remain unknown. Here, we investigate the responses of soil microbial phosphorus cycling after native subtropical forests conversion to plantations and croplands across southern China. Increases in soil pH and phosphorus content after forest conversion alter microbial phosphorus cycling in plantations and croplands. Croplands have the declined functional potentials for phosphorus solubilization and mineralization, and the diversity of the key phosphorus-solubilizing bacterial taxa in Burkholderiaceae and Enterobacteriaceae is reduced. Our work highlights the importance of conserving soil phosphorus biogeochemical cycles to support the restoration of deforested environments and the sustainability of managed ecosystems.

Microbial necromass is a major contributor to mineral-associated organic carbon (MAOC), widely recognized as the primary and stable carbon (C) pool in soils. Nevertheless, long-term land use changes modify MAOC content and composition, including its fungal and bacterial contributions, which depend on soil types, particularly its hydraulic properties. Here, the impacts of over 30 years of land use, encompassing dryland pasture (DryPast), irrigated-pasture (IrrPast) and cropland (IrrCrop), on MAOC were evaluated across three representative soils with varying drainage characteristics: well-drained Lismore soil (LIS), moderately drained Templeton soil (TEM), and poorly drained Waterton/Temuka soil (WAT). Soil organic carbon (SOC) content and MAOC content decreased in order of IrrPast > DryPast > IrrCrop. MAOC determined the total SOC gains and losses after DryPast conversion to IrrPast and IrrCrop, respectively. Land use change had varying impacts on MAOC, which were influenced by the specific soil types. The well-drained LIS soil showed the highest MAOC increase, rising by 26 % following the conversion from DryPast to IrrPast. In contrast, the poorly drained WAT soil experienced the most significant MAOC reduction, decreasing by 22 % after the conversion to IrrCrop. Fungal necromass dominated MAOC gains, while bacterial necromass drove MAOC losses. Furthermore, the response of MAOC to land uses was primarily affected by labile C as the major source of microbial activity and binding agents. The stabilized fungal necromass is primarily protected within micropores of 0.2–3 µm. In contrast, bacterial necromass is largely constrained by the availability of labile nitrogen. Overall, the increase in fungal necromass and the decrease in bacterial necromass, driven by the interplay between specific management (e.g., irrigation or cultivation) and soil type (e.g., hydraulic properties), are important to interpret MAOC responses to changes in land use.

Microbial processes mediated by soil enzymes are crucial in soil organic matter decomposition, resulting in release of nutrients that become available for plant and microbial uptake. Therefore, it is crucial to know the sensitivity of enzyme activities (EA) along soil depths at distinct plant vegetation stages, and how the availability of mineral nitrogen (N) alters EA. We studied effects of N fertilization (0 and 160 kg N ha−1), soil depth (0–35 cm), and plant-phenological stage (silking and maturity) on microbial biomass C (Cmic) and potential activities of C-, N- and P-acquiring enzymes in the field under Zea mays L. Nitrogen fertilization increased shoot biomass by more than 80% compared to unfertilized plants. Maize roots triggered increases in Cmic and EA for all measured enzymes compared to bare fallow. Stimulating effect of plant roots on EA was enzyme specific and stronger at silking than maturity stage of maize. The down-regulating effect of N fertilization on EA involved in acquiring N was most pronounced on the activity of L-leucine aminopeptidase and β-1,4-N-acetylglucosaminidase. Soil depth was the primary determinant of EA, explaining up to 51% of the variation. Depth-dependent EA changes were stronger in rooted soil. A pronounced biotic control on EA was demonstrated by higher EA in rooted soil than in bare fallow. This confirmed root-mediated microbial activation. Stronger effect of silking vs. maturity stage on EA indicated that actively growing roots fuel microorganisms via root-derived organics. Thus, soil depth and plant roots were major factors controlling microbial activity in arable soil.

This study assessed the carbon (C) budget and the C stocks in major compartments of the soil food web (bacteria, fungi, protists, nematodes, meso- and macrofauna) in an arable field with/without litter addition. The C stocks in the food web were more than three times higher in topsoil (0–10 cm) compared to subsoil (>40 cm). Microorganisms contained over 95% of food web C, with similar contributions of bacteria and fungi in topsoil. Litter addition did not alter C pools of soil biota after one growing season, except for the increase of fungi and fungal feeding nematodes in the topsoil. However, the C budget for functional groups changed with depth, particularly in the microfauna. This suggests food web resilience to litter amendment in terms of C pool sizes after one growing season. In contrast, the distinct depth dependent pattern indicates specific metacommunities, likely shaped by dominant abiotic and biotic habitat properties.

The effects of organic and mineral fertilization on four soil organic matter (SOM) fractions (non-protected, physically protected, chemically protected, an

The aim of the study: Analysis of carbon stocks in soils and vegetation on the territory of the Pilot Carbon Polygon “Ugra”. Location and time of the study. Kaluga region, Ugra National Park, March–October, 2020. Methodology. The study was carried out on soils of four land use types: i) arable lands, ii) abandoned arable lands under grassland vegetation, iii) young forest vegetation (25–30 years old), and iv) mature mixed forest (75–80 years old). Two-four plots were located in each land use type. Soil samples were taken up to 50 cm by 10 cm layers. The content of organic carbon (Corg), total nitrogen (N), and the C/N ratio were determined. Considering soil density, the Corg and N stocks were calculated in the top 20 and top 50 cm. In the top 20 cm, the particle size distribution, pH(KCl), water holding capacity (WHC), and microbial properties (basal respiration, BR and content of microbial biomass, Cmic) were determined. Based on the forest inventory, the carbon stocks in phytomass and mortmass (dead trees) were estimated. Main results. The Retisols of the Carbon Polygon “Ugra” are characterized by a sandy loamy texture and slightly acidic (arable and abandoned lands) or acidic (forest areas) reaction. Microbial activity in the top 20 cm of soil decreases in the following order: abandoned lands under grassland > young forest stands (25–30 years old) > arable lands > mature mixed forest. The BR variability was determined by 86–90 % by the Cmic content. The highest Corg stock in the 0–50 cm layer was in the arable soils (65.4±4.4 t C/ha), and the lowest Corg stock (41.4±0.4 t C/ha) was observed in the soils under young forest. The C/N ratio in the top 10 cm varied from 8.9 to 17.6 and depended on the composition of plant litter at the soil surface. The main C pool in the forest ecosystems, regardless of their age, was the phytomass of woody plants. This C pool exceeded the total Corg stocks in the 50-cm soil layer by 1.6 and 4 times in young forest and mature mixed forest, respectively. The total C stocks in the mature mixed forest were 3 times larger than in young forest stands. Conclusions. The C stocks and the state of the soils of the Carbon Polygon “Ugra” depend on the current land use type, which in turn determines the composition of plant residues input on and in the soil. This is the reason for the most distinct differences between the studied soils in terms of Corg and N content, C/N ratio, and microbial characteristics. The age of forest stands is a key factor determining the total C stocks in soils and forest biomass.

<p>Thermokarst lakes of permafrost peatlands in Western Siberia are among the most important sources of greenhouse gases (GHG) such as CO<sub>2</sub> and CH<sub>4</sub> because of current permafrost thawing due to climate change. Field measurements demonstrated the increase of dissolved GHG concentrations with the decreasing lake size due to higher concentration of coastal-derived organic C in water of small lakes. However, the size-dependent mechanisms of the GHG production and consumption (e.g. CH<sub>4</sub> oxidation) in the sediments of these lakes remain poorly known. We estimated aerobic CO<sub>2</sub> production and CH<sub>4</sub> oxidation potentials based on natural <sup>13</sup>C abundance and <sup>13</sup>C labeling in two layers of upper 20 cm sediments of three thermokarst lakes: small (~ 300 m<sup>2</sup>), medium (~ 3000 m<sup>2</sup>) and large (~ 1 km<sup>2</sup>). We hypothesized that i) specific CO<sub>2</sub> production (per gram of sediment) decreases with increasing lake size, but CH<sub>4</sub> oxidation increases, and ii) both processes are more intensive in the upper 10 cm of sediments than in deeper 10–20 cm, due to naturally occurring O<sub>2</sub> gradients and the available C. As expected, CO<sub>2</sub> production in the upper layer was 1.4–3.5 times higher than in the deeper layer and the rate of production increased from large (170 nmol CO<sub>2</sub> g<sup>-1</sup> d.w. h<sup>-1</sup>) to medium (182) and small (234) lakes. In contrast to CO<sub>2</sub>, CH<sub>4</sub> oxidation in the uppermost sediment layer was similar between lakes, while the deeper layer in the large lakes had 12- and 73-fold higher oxidation rates (5.1 nmol CH<sub>4</sub>-derived CO<sub>2</sub> g<sup>-1</sup> d.w. h<sup>–1</sup>) than in small and medium lakes, respectively. This was attributed to the fact that the O<sub>2</sub> concentration in the water of large lakes is higher than in smaller lakes due to the intense turbulence caused by wind and waves. Due to the ongoing and future thawing of permafrost, smaller lakes will increase in size, so that a large part of the CH<sub>4</sub> produced in the sediments will be oxidized. However, this process can be (over)compensated by the increased formation of new small lakes. From an ecological perspective, the sediments of shallow thermokarst lakes in the discontinuous permafrost zone of Western Siberia could oxidize up to 0.48 Tg C as CH<sub>4</sub> in the summer period, with the largest contribution coming from the large lakes. This confirms the key role of the thermokarst lake ecosystems as a global hotspot of GHG turnover.</p><p><strong>Acknowledgement.</strong> This work was supported by RSF grant No. 21-77-10067 and the German Academic Exchange Service (DAAD).</p>

<p>Microbial carbon use efficiency (CUE), a key regulator of soil organic carbon (SOC) dynamics, reflects carbon allocation between microbial growth and respiration. Separate investigation of microbial growth and respiration helps to clarify the role of CUE in the carbon balance and consequently, in the carbon cycle in soil. First, in terms of microbial resource acquisition, the drivers of microbial growth and respiration differ: microbial growth is primarily regulated by synergistic availability of carbon, nitrogen, and phosphorus, whereas respiration is more strongly influenced by substrate quality, such as the carbon-to-nitrogen ratio. Second, synchronized responses of microbial growth and respiration rates under climate change (e.g., warming, drought, elevated CO<sub>2</sub>) often mask underlying CUE regulatory mechanisms. Thus, we propose: (1) explicitly representing microbial growth and respiration in models to raise the precision of SOC dynamics predictions; and (2) applying approaches such as isotope probing and metagenomic functional annotation to resolve CUE mechanisms from the community to the single-species level. Overall, decoupling CUE into its growth and respiration components establishes a mechanistic framework that explicitly links CUE to microbially mediated SOC dynamics.</p>