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No abstract is provided for this article.

The aim of this study was to assess differences in rhizodeposition quantity and composition from maize cropped on soil or on 1:1 (w/w) soil–sand mixture and distribution of recently assimilated C between roots, shoots, soil, soil solution, and CO 2 from root respiration. Maize was labeled in 14 CO 2 atmosphere followed by subsequent simultaneous leaching and air flushing from soil. 14 C was traced after 7.5 h in roots and shoots, soil, soil solution, and soil‐borne CO 2 . Rhizodeposits in the leachate of the first 2 h after labeling were identified by high‐pressure liquid chromatography (HPLC) and pyrolysis–field ionization mass spectrometry (Py‐FIMS). Leachate from soil–sand contained more 14 C than from soil (0.6% vs. 0.4%) and more HPLC‐detectable carboxylates (4.36 vs. 2.69 μM), especially acetate and lactate. This is either because of root response to lower nutrient concentrations in the soil–sand mixture or decreasing structural integrity of the root cells during the leaching process, or because carboxylates were more strongly sorbed to the soil compared to carbohydrates and amino acids. In contrast, Py‐FIMS total ion intensity was more than 2 times higher in leachate from soil than from soil–sand, mainly due to signals from lignin monomers. HPLC‐measured concentrations of total amino acids (1.33 μM [soil] vs. 1.03 μM [soil–sand]) and total carbohydrates (0.73 vs. 0.34 μM) and 14 CO 2 from soil agreed with this pattern. Higher leachate concentrations from soil than from soil–sand for HPLC‐measured carbohydrates and amino acids and for the sum of substances detected by Py‐FIMS overcompensated the higher sorption in soil than in sand‐soil. A parallel treatment with blow‐out of the soil air but without leaching indicated that nearly all of the rhizodeposits in the treatment with leaching face decomposition to CO 2 . Simultaneous application of three methods— 14 C‐labeling and tracing, HPLC, and Py‐FIMS—enabled us to present the budget of rhizodeposition ( 14 C) and to analyze individual carbohydrates, carboxylates, and amino acids (HPLC) and to scan all dissolved organic substances in soil solution (Py‐FIMS) as dependent on nutrient status.

Organic carbon availability in soil is crucial for shaping microbial communities, yet, uncertainties persist concerning microbial adaptations to carbon levels and the ensuing ecological and evolutionary consequences. We investigated organic carbon metabolism, antibiotic resistance, and virus–host interactions in soils subjected to 40 y of chemical and organic fertilization that led to contrasting carbon availability: carbon-poor and carbon-rich soils, respectively. Carbon-poor soils drove the enrichment of putative genes involved in organic matter decomposition and exhibited specialization in utilizing complex organic compounds, reflecting scramble competition. This specialization confers a competitive advantage of microbial communities in carbon-poor soils but reduces their buffering capacity in terms of organic carbon metabolisms, making them more vulnerable to environmental fluctuations. Additionally, in carbon-poor soils, viral auxiliary metabolic genes linked to organic carbon metabolism increased host competitiveness and environmental adaptability through a strategy akin to “piggyback the winner.” Furthermore, putative antibiotic resistance genes, particularly in low-abundance drug categories, were enriched in carbon-poor soils as an evolutionary consequence of chemical warfare (i.e., interference competition). This raises concerns about the potential dissemination of antibiotic resistance from conventional agriculture that relies on chemical-only fertilization. Consequently, carbon starvation resulting from long-term chemical-only fertilization increases microbial adaptations to competition, underscoring the importance of implementing sustainable agricultural practices to mitigate the emergence and spread of antimicrobial resistance and to increase soil carbon storage.

The huge soil organic C (SOC) storage (around 34 Pg in the top 0.7 m) in Qinghai–Tibet Plateau (QTP) grasslands is commonly explained by slow decomposition of litter under cold climate therein, but this view may not be reliable as humidity also affects microbial activity. We sampled the 20 cm topsoil of grasslands along an altitudinal gradient from 1286 m on the western Loess Plateau (LP) to 4200 m above sea level on the northeastern QTP. The light-fraction SOC (LFOC), composition of non-cellulosic neutral carbohydrates, and amino sugars were used as biomarkers to investigate the intensity of microbial action on SOC as a function of climate along this altitudinal gradient. From the lowest-to the highest-humidity site with rising altitude, the root biomass tripled and the SOC content increased approximately sevenfold (from 13.5 g kg−1 to 93.3 g kg−1). The non-cellulosic neutral carbohydrate, microbial biomass C (MBC), and microbial necromass C (MNC) contents increased, but the LFOC content decreased. The contribution of MNC to the SOC and ratios between microbially- and plant-derived sugars in the non-cellulosic carbohydrate pool increased, but the proportion of LFOC in the SOC dropped. Consequently, besides the increased root biomass, the selective preservation of microbial compounds at colder and more humid sites contributed to SOC accruals in grasslands. The higher MBC in cold and humid grasslands perfectly explained the increased selective preservation of microbial derived C at the expense of plant C in higher-relative to lower-altitude areas. Importantly, the above humidity-controlled accumulations of microbial substances and SOC in grasslands were confirmed by results synthesized from published data across the LP and QTP. The higher SOC contents in cold and humid QTP grasslands relative to warm and dry regions were ascribed to the increased accumulation of microbial residues because of the increased humidity in QTP grasslands.

Despite the close interactions between carbon (C) and nutrients like nitrogen (N), phosphorus (P), and potassium (K), the consequences of N fertilization alone or in combination with P and K on soil organic matter (SOM) chemical composition remain unclear. Using solid-state 13C nuclear magnetic resonance spectroscopy data from 45 field studies, we meta-analyzed the effects of N alone and NPK fertilization on SOM content and chemical composition. Generally, mineral fertilization affects the SOM content and composition via three indirect processes: i) increasing litter input and rhizodeposition, ii) accelerating microbial decomposition of SOM, and iii) modifying the preservation of SOM by soil minerals. NPK fertilization (+12 %) increased organic C content more than N fertilization alone (+8.6 %). Alkyl and O-alkyl C increased at low-N rates (<50 kg N ha−1 yr−1) or after short-term (0–5 yrs) N fertilization alone, likely because improved N availability promoted bacterial residues rich in long-chain aliphatic C formation and carbohydrate-rich matter inputs. High-rate (>200 kg N ha−1 yr−1) or long-term (>25 yrs) NPK fertilization increased alkyl C but decreased aromatic C, likely due to reduced nutrient limitations and acidification. These factors promote aliphatic C-rich microbial biomass, accelerate the decomposition of stable compounds, and decrease the mineral protection of aromatic acids. The SOM chemical composition (excluding aromatic C) response to NPK fertilization decreased with increasing initial level. In contrast, the response of SOM raised with increasing initial content under N fertilization alone. The increase in organic C content was strongly linked to changes in SOM chemistry under NPK fertilization but not under N fertilization alone. In conclusion, NPK fertilization modified SOM chemistry and increased organic C accumulation more effectively than N fertilization alone, which was mediated by increasing plant growth, raising microbial biomass and activity, altering mineral protection, and initial soil C levels. Our findings provide critical insights for optimizing fertilization strategies to improve soil C sequestration capacity and fertility.

No abstract is provided for this article.

Livestock sheds are local and regional hotspots of greenhouse gases (GHG) emissions, but only very few studies analyse the intensities of GHG emissions from this source. The objective of this study was to quantify annual CH 4 , CO 2 and N 2 O emissions from inside and outside of sheepfolds and summer cattle sheds in a typical agro‐pastoral ecotone using static chamber technique. Both sheepfolds and cattle shed functioned as huge net sources of CH 4 and N 2 O at annual scale. Animal presence increased CH 4 , CO 2 and N 2 O effluxes for up to 1100 times compared to the animal sheds without animals. N 2 O emissions boosted for 160%–280% during and after rainfall and spring‐thaw events. The CH 4 and CO 2 fluxes increased exponentially with faeces temperature for the outside sheepfold and summer cattle shed. The annual GHG emissions from both sheepfolds and summer cattle shed were 56 t CO 2 equivalents ha −1 , of which N 2 O contributed to 94%. Sheepfold dominated the total GHG emissions from animal sheds and accounted for 83% of the annual GHG flux. Annual emission on a per animal basis was 15, 0.2 and 28 kg CO 2 eq year −1 sheep −1 and 26, 10 and 140 kg CO 2 eq year −1 cattle −1 for N 2 O, CH 4 and CO 2 , respectively. The annual N 2 O emissions from animal sheds were 70–250 times larger than nearby grassland soils, which were also net sink for atmospheric CH 4 . Concluding, animal sheds are very intensive local hotspots of GHG emissions, which should be considered at the local and regional scales.

No abstract is provided for this article.

The Earth's surface is in constant change due to biotic and abiotic processes. During the last decades awareness arose that these biotic and abiotic processes might intensely interfere. Biogenic weathering, the acceleration of mineral weathering by autotroph-symbiont couples fuelled by photoassimilates for the sake of an equilibrated nutrient supply of involved biota, potentially drives denudation rates at ecosystem level. Our experiment aimed to examine how aridity affects biogenic weathering. The study was conducted along a gradient in Chile from humid to hyperarid climate (Atacama Desert), where photoassimilate production is increasingly limited by water stress. We hypothesize that biogenic weathering would cease if a threshold between element loss from denudation and energy demand for additional nutrient element mobilization by biogenic weathering is crossed, as competition between life for these elements becomes less intense when water supply limits biomass growth increasingly. We buried mesh bags containing freshly broken minerals, including biotite, muscovite and apatite along the gradient in Chile on granitic bedrock. Unexpectedly and in contrast to our initial hypothesis, we found that mineral weathering rates driven by mycorrhizal fungi under arid conditions were even proportionally higher, indicating a comparatively higher investment of photoassimilates into biogenic weathering by desert plants than by mediterranean, suggesting an adaptive mechanism. Additionally, biogenic weathering occurred at constant rates over a depth of up to 2.3 m, illustrating the constant mining of mycorrhizal fungi, irrespective of overall biological activity along the soil profile. The relative importance of biogenic weathering in arid climates furthermore points towards a fundamental function of biogenic weathering beyond nutrient mobilization by suggesting a regulatory role in overcoming long periods of missing soil water that prevent nutrient exchange from the soil matrix.

Soil health is pivotal to sustain biological productivity, maintain environmental quality, and ensure the health of plants, animals, and ultimately humans. Global changes—such as climate warming, elevated CO₂ atmospheric concentration, droughts, and floods—as well as human impacts like land‐use change, chemical contamination, and application of fertilizer and pesticides, threaten soil health. Protecting soil health and raising global awareness on this topic are now critical to ensure sustainable management of natural and agricultural ecosystems under global change. This Special Issue includes 19 studies in three thematic groups. The first group includes methodological advances in the assessment of soil health, exploring new tools, techniques, and approaches for accurate evaluation. The second group encompasses studies examining how soil health responds to land‐use change, agricultural and forestry practices. The third group addresses human‐induced pollution and its effects on soil health. Overall, these studies provide contemporary insight into soil health in managed and natural ecosystems and methods for soil health evaluation. These contributions will shape strategies to sustain soil functions and preserve healthy soils for future generations, including efforts to meet Sustainable Development Goals for the 21st century.

Membrane zymography is commonly used in rhizosphere ecology to map enzyme activities in intact soil samples and plant roots. The method consists of incubating a membrane saturated with an enzyme-specific fluorogenic substrate on the soil/root surface followed by measurements of fluorescence intensity of the product in the membrane. The traditional zymography is based on assumptions that fluorescence on membrane images is linearly increasing with time during zymography and an increase in product content is numerically equal to enzyme activity in soil below the membrane. These assumptions are unlikely to hold in experimental settings. Here we introduce a new zymography technique, time-lapse zymography (TLZ); the approach that eliminates the need for assumptions of the traditional zymography and provides more realistic estimates of enzymatic activities. We assessed the new technique in a series of laboratory and modeling experiments, including quantification of the fluorescent product diffusion (e.g. MUF: 4-methylumbelliferone) from plant roots, enzyme activity measurements on the roots, and HYDRUS-2D & HP2 software calibration with obtained data. The calibrated model was used to analyze the processes governing spatial and temporal dynamics of MUF contents in the membrane. The results indicated that the enzyme diffusion within the membrane-soil system was negligible, and measured zymograms were adequately reproduced solely by accounting for substrate and product diffusions and for catalytic enzyme reaction described by the Michaelis-Menten equation. TLZ enabled identifying and using linear parts on MUF time series and accounting for MUF losses in each zymogram pixel, considerably improving the accuracy as compared to the traditional method. Results demonstrated that enzymatic activity from only a thin soil layer (~0.2 mm) is adequately represented in zymograms.

Soil organic carbon (SOC) stocks have been greatly depleted across the globe by conversion of wetlands to croplands, agroforestry, and urban areas. Here, we investigated SOC distribution and turnover in four land use types: a wetland, cropland, forestland, and construction land in the Baiyangdian Wetland, Northern China. The C : N ratios were up to 1.70‐times larger in cropland, forestland, and construction land than in the original wetland because of faster N losses compared to C following wetland conversion. The δ 13 C values of SOC increased with depth in wetland, and showed an overall depletion compared with the other three land use types. Acid‐to‐Aldehyde ratios of syringyl in wetland were 0.72–1.14‐, 0.72–1.72‐, and 1.18–1.43‐times, and cinnamyl/vanillyl ratios were 0.56–1.05‐, 0.22–0.48‐, and 0.40–0.76‐times those of cropland, forestland, and construction land, which reflects faster lignin decomposition rate in wetlands. The β value was defined by the slope of the linear regression between the logarithm of SOC and δ 13 SOC values, and decreased from cropland over construction land and forestland to wetland, reflecting the faster SOC turnover with the lower β values. However, SOC content and storage were up to 2.29‐ and 2.07‐times higher in wetlands than in soils of other land use types. The combination of C : N ratios, δ 13 C, and lignin monomer composition can explain the decrease of β value (corresponding to faster SOC turnover), and can be used as effective proxies to evaluate the sources and turnover of SOC in response to land use changes.