Labile Soil Research Articles

Vegetation degradation reduces aggregate associated carbon by reducing both labile and stable carbon fraction in Northeast China

Vegetation changes can affect soil organic carbon (SOC) content and storage by altering the inputs of plant biomass and the catabolism and anabolism of soil microorganisms. However, influence of vegetation degradation on aggregate associated carbon fractions and the contribution of different aggregates to total SOC in bulk soil remains poorly understood. In this study, undisturbed soil samples were collected from three types of grassland in Songnen grassland: an undegraded grassland (LEY, Leymus chinensis), a moderately degraded grassland (CHL, Chloris virgata), and a severely degraded grassland (SUA, Suaeda heteroptera). Three soil aggregates including macroaggregate (> 0.25 mm), microaggregate (0.053–0.25 mm) and silt and clay fraction (< 0.053 mm) were separated using wet sieving. Contents of total SOC, soil labile and stable carbon in bulk soil and different soil aggregates were measured. Compared with LEY, the mean weight diameter and geometric mean diameter under the degraded vegetation communities reduced by 39.42 % and 28.47 %, respectively. The reduction in SOC contents in bulk soil, macroaggregate, microaggregate and silt and clay fraction resulting from vegetation degradation was 49.81 %, 26.00 %, 76.17 % and 43.65 %, respectively. Under the degraded vegetation communities, contents of soil labile and stable carbon in bulk soil (45.73 % and 52.61 %, respectively), macroaggregate (17.38 % and 31.61 %, respectively), microaggregate (77.83 % and 74.18 %, respectively), and silt and clay fraction (21.20 % and 53.45 %, respectively) were significantly lower than those under LEY. The contribution of macroaggregate, microaggregate and silt and clay fraction to total SOC was 13.27 %, 23.61 % and 63.12 %, respectively. The contribution of soil aggregates to total SOC following vegetation degradation reduced by 53.63 % for microaggregate, but increased by 47.10 % for silt and clay fraction. These findings collectively indicate that vegetation degradation reduces the aggregate associated carbon content by reducing both labile and stable carbon fraction in Songnen grassland, and sustainable vegetation restoration strategies are need to enhance soil carbon storage in Northeast China.

Tillage and cover cropping influence phosphorus dynamics in soil and water pools

AbstractWinter cover crops (CCs) have the potential to reduce phosphorus (P) loss by temporarily fixing P into CC biomass. A field experiment with no‐tillage (NT) and conventional tillage (CT) was used to study the ability of different CC species planted after corn (Zea mays L.) and soybean (Glycine max L.) harvests to reduce the P availability in soil solution. The effect of three crop rotations (corn–no CC–soybean–no CC [C–S], corn–cereal rye (Secale cereale)–soybean–hairy vetch (Vicia villosa) [C–R–S–HV], corn–cereal rye–soybean–oats (Avena sativa)+ radish (Raphanus sativus L.) [C–R–S–OR]) and two tillage (NT and CT) treatments was determined on soil available P and soil solution P content through pan (A horizon) and tension (100‐cm depth) cup lysimeters. The experiment was set up as a randomized complete block design with tillage as a split factor with three replicates. Over the study period, incorporating hairy vetch in C–R–S–HV rotation reduced the Mehlich‐3 P content in soil by 26%–29% compared to the C–S and C–R–S–OR rotation. Both CC rotations (C–R–S–HV and C–R–S–OR) were effective in reducing dissolved reactive P (DRP) concentration in pan and tension cup lysimeters compared to the C–S in both CT and NT systems. However, these results varied with CC species grown and seasonal variability in precipitation. A significantly lower DRP load with crop rotation and tillage treatments was observed mainly during the CC growing season. During the study period, crop rotations with reduced labile soil P content and DRP loss were ranked in an order of C–R–S–HV &gt; C–R–S–OR &gt; C–S. Overall, this study showed that CCs have the potential in both CT and NT systems to significantly reduce P in soil and soil solution, and these effects are resilient to a wide range of precipitation conditions.

Soil labile organic carbon and nitrate nitrogen are the main factors driving carbon-fixing pathways during vegetation restoration in the Loess Plateau, China

Although the microbial fixation of CO2 is a key process in regulating soil carbon cycling, the effects of vegetation type on microbial carbon-fixing pathways and their driving factors in soils have yet to be sufficiently established. In this study, based on macro-genome sequencing and other analytical methods, we sought to determine the soil physicochemical properties, soil organic carbon contents, carbon-fixing microorganisms, and carbon-fixing genes in areas of farmland (FL), grassland (GL). Robinia pseudoacacia (RP), Caragana korshinskii (CAK), and Prunus sibirica (PS) in the Wuliwan watershed of the Loess Plateau region of China. Our findings revealed that the organic carbon contents of the assessed soils increased in the following order: FL < GL∼PS < CAK < RP (P < 0.05). Re-vegetation-based restoration was found to enhance soil organic carbon pool stability. Compared with farmland soil, the proportions of recalcitrant organic carbon had increased by 6 % and 9 % in the soil at sites that had undergone restoration with C. korshinskii and R. pseudoacacia respectively. Among the identified carbon fixation pathways, the DC/4-HB cycle had the highest relative abundance of 25.10–25.52 %. The dominant groups of carbon-fixing microorganisms were identified as Actinobacteria and Proteobacteria, accounting for over 60 % of the total abundance. Furthermore, analysis based on a partial least squares path model revealed labile organic carbon and soil nitrate nitrogen as the primary drivers of carbon fixation pathways. Collectively, our findings in this study provide evidence to indicate that restoration of vegetation on the Loess Plateau can contribute to increases in soil organic carbon content and stability and the abundance of carbon-fixing microorganisms, with R. pseudoacacia and C. korshinskii having the most significant effects in this regard. These findings have important implications for restorative vegetation carbon pool management and provide additional perspectives for understanding global carbon cycling.

Differential responses of soil phosphorus fractions to varied nitrogen compound additions in a meadow steppe

Nitrogen (N) addition can greatly influence soil inorganic phosphorus (Pi) and organic phosphorus (Po) transformations. However, whether and how the N compound forms may differentially affect the soil P fractions remain unclear. Here, we investigated the responses of soil Pi (labile Pi, moderately-occluded Pi, and recalcitrant Pi) and Po fractions (labile Po and stable Po) to varying addition rates of three N compounds ((NH4)2SO4, NH4NO3, and urea) in a meadow steppe in northern China. Our studies revealed that with increasing N addition rate, soil labile and moderately-occluded Pi increased, accompanied by decreases in soil recalcitrant Pi. This shift was attributed to N-induced soil acidification, which accelerated the conversion of recalcitrant Pi into labile and moderately-occluded Pi. Soil labile Po decreased with increasing rate of N addition, whilst soil stable Po was not affected. Regardless of the compound forms, N addition increased soil Olsen-P, suggesting a potential alleviation of P limitation in this grassland ecosystem. The effect of N addition on soil labile Pi was significantly greater with addition of urea than with addition of either (NH4)2SO4 or NH4NO3, indicating that urea was more efficient in enhancing soil P availability. Addition of (NH4)2SO4 imposed a more pronounced positive effect on soil moderately-occluded Pi than the addition of either NH4NO3 or urea, mainly due to the greater mobilization of recalcitrant Pi as a result of higher soil acidification strength of (NH4)2SO4. These findings underscore the importance of considering the distinct effects of different N compounds when studying grassland soil P dynamics and availability in response to N addition.

Temperature sensitivity of soil respiration to elevated temperature and nitrogen availability

Plastic film mulching (PFM) and nitrogen (N) fertilization are two important agricultural management methods that are used to enhance crop yields in semi-arid dryland agriculture. However, the impacts of PFM and N fertilization on the temperature sensitivity (Q10) of soil respiration (Rt), particularly its heterotrophic (Rh) and autotrophic (Ra) components, remain unclear. To investigate this, a trenching experiment was carried out between 2019 and 2021 in a rainfed maize-cultivated cropland that had been under cultivation for 7 years. There were four treatments: no PFM and N fertilization (control), full PFM without N fertilization (PFM), 150 kg N ha–1 fertilization without PFM (Nfer), and full PFM with 150 kg N ha–1 fertilization (PFM+Nfer). PFM and N fertilization not only enhanced crop yield and root biomass but also increased soil total respiration (Rt) and its components, due to improved soil hydrothermal conditions with PFM and increased N availability with N fertilization. Soil hydrothermal conditions and root biomass were identified as the most important factors influencing Rh and Ra, respectively. The greater increase in Ra (84 %–212 %) compared to Rh (9 %–29 %) resulted in a decrease in the proportion of Rh in Rt decreasing from 81.2 % in the control to 58 % under the PFM+Nfer treatment. The Rh/Rt ratio decreased in all three treatments compared to the control (p < 0.05). The increase in Rh under PFM led to a decrease in soil organic carbon (SOC) by 17 %. Specifically, the soil labile C content (i.e. LFOC 44 %) decreased more under PFM and PFM+Nfer (p < 0.05) compared to control, but not under the Nfer treatment (p > 0.05). Plastic film mulching increased the Q10 of Rh (p < 0.05) through decrease the content of soil labile C, whereas N fertilization had no effect (p > 0.05). Both PFM and N fertilization increased the Q10 of Ra (p < 0.05) by increasing root biomass. The impact of Ra’s Q10 (0.66) on Rt’s Q10 is greater compared to Rh’s Q10 (0.31). To our knowledge, this is the first long-term field study to examine the response of Rt components and their Q10 to PFM and N fertilization. Our results highlight that soil labile C and root biomass are the determining factors for the Q10 of Rh and Ra, respectively. We emphasize the importance of accurately modeling the temperature responses of Rh and Ra when predicting Rt under climate change scenarios.

Labile not stable SOC fractions constitute the manageable drivers of soil health advances in carbon farming

The assessment of soil health and the determination of carbon stability in soils are current challenges that have gained momentum through initiatives at national as well as international scales. However, inferring universally valid soil health parameters that are directly linked to carbon permanence remains challenging. Our aim was to evaluate the potential of simultaneous thermal analysis (STA) for an improved monitoring of soil health advances in the context of carbon farming strategies. For this purpose, an on-farm comparison of soil health in ten conservation agricultural systems with adjacent conventional farms was performed based on STA and thermal measures were related to key biological and physical indicators for monitoring soil functions. Using an autocorrelation-based approach, we identified independent thermal indicators, revealing that carbon farming efforts predominantly increased labile soil organic matter fractions in the range of 300–400 °C, while thermally more recalcitrant fractions did not respond to farming system transformation. Similarly, most soil health indicators revealed highest correlation with temperature ranges of mass loss of labile organic matter fractions. The relation of STA with commonly used soil health indicators was highest for soil organic carbon (SOC, r=0.971) and total nitrogen (TN, r=0.981). However, also inference on microbial activity parameters such as dimethylsulfoxid reduction, microbial biomass carbon and substrate-induced respiration could be demonstrated with r>0.663. The results thus highlight key temperature ranges of organic matter stability for future soil monitoring tasks of climate change mitigation potentials of carbon farming and related advances in soil health.

How nitrate and ammonium impact soil organic carbon transformation with reference to aggregate size

While nitrogen (N) deposition and over-fertilization enrich N in soil, it is unclear how it impacts soil organic carbon (SOC) transformation at the aggregate scale. Herein, a 90-day study reveals the transformation mechanisms of SOC in soil aggregates under nitrate and ammonium enrichment conditions. Results showed that nitrate treatment (NT) and ammonium treatment (AT) significantly increased SOC content by 15.6 % and 18.9 %, respectively. In addition, NT increased SOC accrual in large macro-aggregates (LMA), while AT increased SOC accrual in small macro-aggregates (SMA) and micro-aggregates (MA). Further analysis of pyrolysis products showed that N enrichment drove the transformation of labile soil organic matter (SOM) composition into recalcitrant SOM, with polysaccharides declining from 19–30 % to 2–13 %, while lipids rose from 18–27 % to 33–45 %. LMA and SMA contained more aromatic compounds than MA. This is linked to the inhibition of the expression of C degradation function genes, while almost all genes encoding SOC degradation are down-regulated under N enrichment. In the meantime, NT increased the abundance of genes encoding the degradation of N-containing compounds in LMA. Moreover, NO3− enrichment exerted a higher inhibitory effect on labile SOC degradation while NH4+ enrichment substantially inhibited recalcitrant SOC. Finally, Random Forest analysis confirmed that N enrichment elevated the importance of N-containing compounds' metabolism, which diminished when the size of soil aggregates decreased. In contrast, the importance of genes encoding saccharides and cellulose metabolism increased in smaller aggregates. This study highlights that both N type and aggregate size were determining factors in shaping SOC transformation in the N enrichment process.

Frass deposition from pest outbreaks affects soil organic carbon and its relationship with environmental factors in a deciduous broad-leaved forest

Forest defoliators are one of the major biological disturbances to forest ecosystems. As one of the abnormal nutrient input paths into forest ecosystems, frass deposition from the pest outbreak plays a critical role in regulating soil organic carbon (SOC) in forest ecosystems. However, how frass deposition affects SOC and its fractions in forests remains unclear. Based on a severe outbreak of defoliator in an oak-sweetgum mixed forest in Jigong Mountain in 2014, we compared the difference in SOC between plots with and without frass deposition for 4 consecutive years. The results showed that frass deposition led to a significant increase of 25.1 % in soil microbial biomass C (MBC) and 32.0 % in dissolved organic C (DOC) in 2014, which further escalated to 50.4 % and 50.6 % in the subsequent year (2015), respectively. The response of SOC to frass deposition lagged behind MBC and DOC. Specifically, there was no change in SOC in 2014, but a significant increase (50.9 %) was observed in the subsequent 2–3 years. The positive dependences of MBC and DOC upon fine root biomass were negated under frass deposition, while the relationship between SOC and fine root biomass remained unaffected. Soil organic carbon and DOC showed non-linear responses to frass amount and the changed soil nitrogen content. Our finding that the response of SOC to frass deposition lagged behind soil labile C indicates that SOC exhibits a certain resilience towards forest disturbance. The findings also imply that investigating the long-term impacts of frass deposition on SOC in forests would contribute to the scientific assessment of forest C cycling under disturbance.

Influence of nature reserve road traffic disturbance on soil carbon

PurposeRoad traffic has long been recognized as a considerable source of ecological disturbance, compromising the integrity of natural ecosystems from their pristine baseline state. Pollutant deposition from vehicular emissions significantly contributes to environmental contamination, while associated human activities exacerbate ecosystem disruptions. In designated conservation zones, including nature reserves, land-use practices such as pastoralism and agriculture are subject to regulation. Nevertheless, the influence of road traffic on ecosystem structure and processes, particularly concerning carbon (C) sequestration and its spatial heterogeneity, warrants further research. This consideration is critically relevant in the understanding the intricate C fractions and their dynamic interplay with environmental factors. Materials and methodsIn this study, we meticulously selected four distinct locations along a principal roadway within a national reserve. For each site, experimental measuring 2 m * 2 m were established at intervals of 2 m, 10 m, 20 m, 30 m, 40 m, and 50 m from the road's edge. Observational data were accrued during the peak of the vegetative growth seasons in August of both 2020 and 2021. Within each plot, soil and cut-ring samples were procured for comprehensive analysis of soil carbon fractions (Total Carbon, TC, g/kg; Carbon Density, g/m2; Readily Oxidizable Carbon, ROC, g/kg; Dissolved Organic Carbon, DOC, mg/kg; Microbial Biomass Carbon, MBC, mg/kg; Cumulative Mineralization Carbon, CMC, mg(CO2-C)*(kg*soil)−1; Soil Inorganic Carbon, SIC, g/kg), chemical properties (pH; Electrical Conductivity, EC, us/cm; Soil Organic Matter, SOM), and physical properties (Soil Water, SW, %; Bulk Density, BD, g/cm3; area conditions). Vegetation metrics, including above-ground biomass (AGB) and below-ground biomass (BGB), species composition, height, and coverage, were meticulously documented. The four sites were replicated, culminating in 24 uniformly oriented plots to mitigate wind influence. ResultsOur analysis revealed that C stock, as determined by TC and C density increased with distance from the road edge, reaching a peak at approximately 30 m (TC: 19.43 g/kg, C density: 39.26 g/m2, SOM: 27.57 g/kg), followed by a subsequent decline. At the 30 m distance, there was a 60.6 %, 41.2 %, and 38.7 % enhancement in TC, C density, and SOM, respectively, compared to the 2 m distance, and a 23.9 %, 25.9 %, and 19.8 % increase relative to the 50 m distance. Levels of DOC, MBC, and CMC exhibited an upward trend from the road edge to 50 m, suggesting more favorable microbiological conditions in less disturbed locales. SEM demonstrated that SIC is directly influenced by BGB (β = −0.31), pH (β = 0.46), and labile C components (β = 0.56), culminating in a reduction of total C storage (total effect, β = −0.28). The dynamic changes of soil C stocks were primarily explained directly by soil labile C (β = 0.475, p < 0.001), and indirectly by vegetation biomass (β = 0.460) and pH (β = −0.570), and were closely correlated with ROC (0.54, the highest eigenvalue among Labile_C). ConclusionThe findings suggest that the buffering effect of the roadside in these nature reserves up to a distance of 30 m has an signficant impact on C stock, and that C losses attributable to biochemical processes and laible soil C fractions may contribute to diminished C levels in less disturbed zones 50 m away from the road. Our findings also substantiate the moderate disturbance hypothesis, particularly in the milieu of road traffic within the Hulunbuir Nature Reserve, Mongolia. A moderate distance from roadways enhances soil C storage compared to areas near the road or undisturbed natural landscapes.

Phosphorus acquisition by faba bean, blue lupin, and chickpea in relation to soil phosphorus status

AbstractThe efficiency of soil phosphorus (P) mobilization and uptake by plants depends on a complex combination of factors, including plant P acquisition strategies and soil P availability. The objective of this study was to assess and compare the capabilities of three legume species (blue lupin (Lupinus angustifolius L.), faba bean (Vicia faba L.), and chickpea (Cicer arietinum L.)), which may be used as green manures in temperate crop systems to acquire P from a soil with different levels of plant‐available P. Three cycles of each legume were grown in a glasshouse over a 6 month period in the same soil type with high (Olsen P: 47 mg kg−1) and low (Olsen P: 9 mg kg−1) levels of plant‐available P. Measurements included above—and below—ground plant biomass and P uptake, in addition to determination of acid and alkaline phosphomonoesterase activities, microbial P, and P fractions in soil at the end of the experiment. In both soils, plant biomass, P uptake, and microbial P were all higher under faba bean compared to blue lupin and chickpea (p &lt; .05). In the low‐P soil, faba bean increased alkaline phosphomonoesterase activity (p &lt; .05). Significant depletion of inorganic P in the soluble (46%–69%), labile (29%–42%), and moderately labile (15%–16%) pools and increase of organic P in the labile (13%–18%) and total (7%–13%) pools occurred under faba bean compared with blue lupin, while changes under chickpea were between those determined for faba bean and blue lupin (p &lt; .05). The findings of this study indicated that inclusion of faba bean green manure may have the potential to improve overall P use efficiency by enhancing mobilization of labile soil inorganic P, although further research is required to investigate mobilization of more stable forms of soil legacy P and quantify the potential of faba bean as a green manure crop under field conditions.

Exploring the Influence of Natural and Agricultural Land Use Systems on the Different Lability Organic Carbon Compounds in Eutric Endocalcaric Arenosol

It is important to ensure the ratio of stable and labile soil organic carbon (SOC) compounds in the soil as this influences ecosystem functions and the sustainability of soil management. The aim of this investigation was to determine the changes in SOC compounds and soil quality improvement in Arenosol soil after the conversion of arable land to natural and agricultural land use. The land use types included pine afforestation (PA), uncultivated abandoned land (UAL), unfertilised and fertilised cropland (CLunf, CLf), and unfertilised and fertilised grassland (GRunf, GRf). To assess the lability of organic carbon (OC) compounds, levels of mobile humic substances (MHSs), mobile humic acids (MHAs), mobile fulvic acids (MFAs), active C pool (POXC), and water-soluble C (WEOC) compounds were determined. It was found that faster OC accumulation occurs in PA soil than in CLf, and is somewhat slower in grassland uses (GRf and UAL). As the amount of SOC increased, more MHS formed. A significant increase in their quantity was found in PA (+92.2%) and CRf and UAL (+51.5–52.7%). The application of mineral fertilisers promoted the formation of MHSs in CLf and GRf. PA, GRunf, and GRf soils had more suitable conditions for MHA formation (MHA/MFA &gt; 1.3), whereas CLunf soil contained more MFAs. The POXC pool was insensitive to land-use changes in the Arenosol. After land-use conversion, POXC amounts were significantly (p &lt; 0.05) higher in natural ecosystems (UAL and PA) and fertiliser perennial grasses than in CL. The amount of WEOC increased the most in UAL, PA, and GRf (7.4–71.1%). The sequence of decrease in land use was GRf, UAL, and PA &gt; CLunf, CLf, and GRunf. The decreasing order of the carbon management index (CMI) of different land uses (PA &gt; UAL &gt; GRf &gt; GRunf &gt; Clunf) confirms that faster OC accumulation in Arenosol soil occurred in PA and grassland land uses (GRf and UAL). The values of the carbon lability index (CLI) variation (CLunf &gt; GRunf GRf &gt; UAL &gt; PA) show that in PA, UAL, and GRf land uses, mobile organic matter (OM) forms are relatively less formed, which stabilises OC accumulation in the soil. The CMI showed that UAL and GRf were the most suitable soil uses for Arenosol soils.

Spatiotemporal investigation of geochemical and hydrological controls on release of soluble reactive phosphorus from the shallow aquifer of a riparian zone.

Phosphorus (P) that accumulates in agricultural riparian zones can be released under certain hydrological and biogeochemical conditions, thereby limiting the effectiveness of these zones in reducing P loads from field to stream. The study objective was to explore factors that may be contributing to, or limiting, high soluble reactive phosphorus (SRP) concentrations in the shallow aquifer of an alluvial upland riparian zone located in a continental climate. Field investigations including porewater sampling from six vertical nests, soil sampling, and continuous soil moisture, groundwater table, and redox measurements were conducted over 19 months. Porewater SRP concentrations were generally low in the aquifer considering all sampling times (median=14.7µg/L; interquartile range [IQR]=11.1µg/L, 287 samples). The overall low SRP may be due to low reducible labile soil P (median=21.1 µgP/g dw, IQR=10.9 µgP/g dw, 21 samples). However, high SRP concentrations(>52µg/L, 95% quartile) did occur intermittently in space and time with no clear spatial or temporal patterns. Analyses indicate that most high concentrations were likely not associated with factors previously reported to influence SRP release in riparian aquifers, including redox conditions, pH, and soil drying and wetting. Further, data indicate that internally released or externally supplied SRP may undergo rapid (re-) sequestration within the aquifer, limiting its vertical or horizontal transport. The study findings highlight the complexity of P behavior in riparian zones and the need for caution when assessing the effectiveness of conservation practices and in interpreting potential impacts of subsurface water quality on stream water quality when monitoring locations are distant from the stream.

Returning Different Organic Materials to the Field: Effects on Labile Soil Nitrogen Pool under Drip Irrigation with Film Mulching in a Semi-Arid Soil

The purpose of this study was to observe the changes in soil nitrogen pools (active organic and inorganic nitrogen fractions) after applying organic materials under drip irrigation with film mulching in a semi-arid soil. The two-year field experiment included four fertilization treatments: maize straw, fodder grass, sheep manure, and a control treatment with no organic material applied (CK). The results showed that the application of maize straw and sheep manure significantly increased the soil total nitrogen content by 9.02~13.33% and 11.02~17.27%, respectively, while no significant improvement was found with the use of fodder grass. Compared with CK, returning organic materials to the field increased the soil active nitrogen pools, except for ammonium nitrogen content. Meanwhile, the content of particulate organic nitrogen was significantly increased by 42.11~78.85% under the application of organic materials, which took the highest proportion of active nitrogen pools and was sensitive to fertilization treatments. Among the three organic materials, maize straw and sheep manure increased the soil active nitrogen content the most. In conclusion, both maize straw and sheep manure are the optimum organic materials, which could be applied for improving soil nitrogen storage under drip irrigation with film mulching within semi-arid areas.

Responses of vascular plant fine roots and associated microbial communities to whole-ecosystem warming and elevated CO2 in northern peatlands.

Warming and elevated CO2 (eCO2) are expected to facilitate vascular plant encroachment in peatlands. The rhizosphere, where microbial activity is fueled by root turnover and exudates, plays a crucial role in biogeochemical cycling, and will likely at least partially dictate the response of the belowground carbon cycle to climate changes. We leveraged the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment, to explore the effects of a whole-ecosystem warming gradient (+0°C to 9°C) and eCO2 on vascular plant fine roots and their associated microbes. We combined trait-based approaches with the profiling of fungal and prokaryote communities in plant roots and rhizospheres, through amplicon sequencing. Warming promoted self-reliance for resource uptake in trees and shrubs, while saprophytic fungi and putative chemoorganoheterotrophic bacteria utilizing plant-derived carbon substrates were favored in the root zone. Conversely, eCO2 promoted associations between trees and ectomycorrhizal fungi. Trees mostly associated with short-distance exploration-type fungi that preferentially use labile soil N. Additionally, eCO2 decreased the relative abundance of saprotrophs in tree roots. Our results indicate that plant fine-root trait variation is a crucial mechanism through which vascular plants in peatlands respond to climate change via their influence on microbial communities that regulate biogeochemical cycles.

Some biological properties of the Kuidusun depression soils of Oymyakon

The aim of the study. To investigate some microbiological properties of the catenal series of soils in the Kuidusun depression of the Oymyakon Highlands. Location and time of the study. The study area is located in the vicinity of the Tomtor village (N63°15'41.94''; E143°10'26.91'') of the Oymyakonsky district of the Republic of Sakha (Yakutia, Russia). Soil samples were collected in the fall of 2011 at the main positions of the catena. The length of the catena is 38 km, the altitude a.s.l. is 727–821m. Soils are classified as Cambic Cryosols (fragic, мurshic), (forest); Skeletic Cryosols (aridic), (steppe meadow), Cambic Cryosols (fluvic), (typical meadow); Folic Cryosols (swampy meadow). Methods. The content of labile soil organic matter (LOC) was determined photocalorimetrically in soil extracts with phosphate buffer (1/15 M, pH 6,8). The number of colony-forming units (CFU) was determined using standard MPA, KAA, and Czapek media. The functional spectrum of the soil microbiota was assessed using the community level physiological profile (CLPP) method. All properties were studied in 10 cm thick layers to a depth of 40 cm. Soil urease activity was assessed by ammonium production from urea. Results. At the time of sampling moisture content of soil samples down the catena increased from 5 to 20%, whereas the LOC content increased from 2 to 6 g C /kg. In the 0–10 cm layer, the greatest accumulation of LOC was observed in the soil under a typical meadow. The highest number of CFU (150 million/g soil) in a dilute MPA medium was also found there. An increase in the proportion of CFU in the dormant state was revealed in the soil series from the lower position of the catena to the upper one. In the same series, an increase in the oligotrophic index of the community was noted. The highest metabolic activity was observed in the soil under a swampy meadow, whereas the lowest was shown by the soil under a forest. The enrichment of soil organic matter with microbiota cells increased in the series of soils f in the following order: a swampy meadow – a typical meadow – a steppe meadow, whereas the specific activity of the microbiota decreased. Urease activity of the soil was detected mainly in the 0–10 cm layer; in the underlying layers the activity was more than 500 times lower. Conclusions. The biological properties of the studied soils corresponded to the known patterns established for the catenal series of soils in other soil and climatic conditions. The peculiarity of the studied soils was related to the extremely sharp differentiation of the microbiological profile. The absolute predominance of actinomycetes CFU in the soil under the steppe meadow was the major characteristic feature of the culturable part of the soil microbial community.

Insight into the availability and desorption kinetics of Se and Cd in naturally-rich soils using diffusive gradients in thin-films technique

Cadmium (Cd) contamination of selenium (Se)-rich soils may jeopardize the nutritional benefits of Se-biofortified crops. This study employed diffusive gradients in thin-films (DGT) technique and DIFS (DGT-induced fluxes in soils) model to understand the interdependency and driving factors of Se and Cd distribution and desorption kinetics across 50 soils from south China with naturally elevated levels. DGT-labile Se was the highest (up to 2.66 μg L−1) in non-carbonate/shale-derived soils, while Cd was maximal (5.53 μg L−1) in carbonate-based soils, reflecting soil background concentrations and soil characteristics. Over one-third of the soils showed labile Se:Cd molar ratio below 0.7, suggesting Cd phytotoxicity risks. The DIFS-derived response times (Tc) and desorption rate constants (k−1) suggested that Se was resupplied to the soil solution faster than Cd in soils with higher pH and SOM level, but Se resupply was still restricted due to the rapid depletion of its labile pool. As the first study of Se and Cd release kinetics in soils, our results reveal dependence on soil parent materials, with low labile Se:Cd soils presenting greater Cd hazards. By elucidating Se and Cd lability and interactions in soils, our findings help to inform management strategies to balance reduced Cd risk with adequate Se availability.

A comparison of characterisation and modelling approaches to predict dissolved metal concentrations in soils

Environmental context It is useful to know the concentration of ‘labile’, or chemically active, metal in soils because it can be used to predict metal solubility and environmental impact. Several methods for extracting the labile metal from soils have been proposed, and here we have tested two of these to see how well the resulting data can be used to model metal solubility. Such mixed approaches can be applied to different soil types with the potential to model metal solubility over large areas. Rationale Predicting terrestrial metal dynamics requires modelling of metal solubility in soils. Here, we test the ability of two geochemical speciation models that differ in complexity and data requirements (WHAM/Model VII and POSSMs), to predict metal solubility across a broad range of soil properties, using differing estimates of the labile soil metal concentration. Methodology Using a dataset of UK soils, we characterised basic properties including pH and the concentrations of humic substances, mineral oxides and metals. We estimated labile metal by extraction with 0.05 mol L−1 Na2H2EDTA and by multi-element isotopic dilution (E-value). Dissolved concentrations of Ni, Cu, Zn, Cd and Pb were estimated in 0.01 mol L−1 Ca(NO3)2 soil suspensions using the total metal ({M}total), the EDTA-extracted pool ({M}EDTA) and the E-value ({M}E) as alternative estimates of the chemically reactive metal concentration. Results Concentrations of {M}EDTA were highly correlated with values of {M}E, although some systematic overestimation was seen. Both WHAM/Model VII and POSSMs provided reasonable predictions when {M}EDTA or {M}E were used as input. WHAM/Model VII predictions were improved by fixing soil humic acid to a constant proportion of the soil organic matter, instead of the measured humic and fulvic acid concentrations. Discussion This work provides further evidence for the usefulness of speciation modelling for predicting soil metal solubility, and for the usefulness of EDTA-extracted metal as a surrogate for the labile metal pool. Predictions may be improved by more robust characterisation of the soil and porewater humic substance content and quality.

Effects of Rice Straw Return on Soil Labile Organic Carbon and β-Glucosidase Activity in Paddy Soil

Effects of Rice Straw Return on Soil Labile Organic Carbon and β-Glucosidase Activity in Paddy Soil

Soil Microbial Community in Relation to Soil Organic Carbon and Labile Soil Organic Carbon Fractions under Detritus Treatments in a Subtropical Karst Region during the Rainy and Dry Seasons

Climate and detritus influence soil organic carbon (SOC) and labile SOC fractions by affecting soil microbial communities. However, it is not clear how, or to what extent, different detritus treatments affect soil microbial communities and SOC content in karst landscapes during different seasons. Plots in a karst landscape were treated with different detritus input regimes (control, no litter, no roots, no litter or roots, and double litter), and samples were collected during the dry and rainy seasons. We used Illumina sequencing of 16S rRNA to examine shifts in the diversity and composition of the associated soil microbial communities. Additionally, labile SOC fractions, including dissolved organic carbon (DOC) and microbial biomass carbon (MBC), along with soil physicochemical properties and C-degrading enzyme activities, were analyzed. The results revealed that the responses of soil properties and labile SOC fractions to detritus treatments were more pronounced during the rainy season than during the dry season, which mainly reflected that the levels of available potassium (AK), DOC, and MBC were significantly increased during the rainy season. Moreover, SOC and total nitrogen (TN) demonstrated significant changes with the double litter (DL) treatment during the rainy season. The responses of soil microbial communities to detritus treatments varied with the season, as reflected primarily in changes in the relative abundance of Ascomycota, unclassified_K_fungi, Proteobacteria, and Actinobacteriota. Climate, detritus treatments, and their interactions had significant effects on the species richness of soil bacterial communities, but did not influence fungal community diversity. Furthermore, structural equation modeling (SEM) revealed that the soil bacterial composition had the largest total effects on SOC, DOC, and MBC. In addition to directly influencing SOC, DOC, and MBC, soil properties (TN, AK, and pH) indirectly affected SOC, DOC, and MBC by altering C-degrading enzyme activity and the microbial community. We conclude that detritus treatments affect the soil microbial community and labile carbon fractions during both the rainy and dry seasons. Relationships among SOC, labile SOC fractions, enzyme activities, microbial communities, and function differed between seasons and among treatment types. This research advances our knowledge of how variation in detritus treatments affects biogeochemical cycling in karst soils during the rainy and dry seasons.

Divergent effects of biochar amendment and replacing mineral fertilizer with manure on soil respiration in a subtropical tea plantation

Applying biochar amendment and manure in tea plantation ecosystems can diminish soil acidification and degradation. However, the impact of these practices on soil respiration and associated mechanisms remains unclear. In this study, we combined a two-year field experiment and laboratory analyses based on soil properties, functional genes, and microbial co-occurrence networks to explore the determinants of soil respiration intensity in a subtropical tea plantation with biochar amendment and manure application. The results showed that the effect of biochar amendment on soil respiration was unconspicuous. Although biochar amendment increased bacterial richness and Shannon index, biochar amendment did not alter the abundance of species associated with C-cycling functional genes. Besides directly adding recalcitrant C to the soil, biochar also indirectly enhanced C sequestration by weakly increasing soil carbon dioxide (CO2) emissions. However, replacing mineral fertilizer with manure significantly stimulated soil respiration in the tea plantation, resulting in a 36% increase in CO2 emissions over two years. The increase in CO2 emissions under the manure treatment was mainly attributed to the increased soil labile C pool, the activity of hydrolytic enzymes (e.g., cellobiohydrolase and acetylglucosaminidase), and the relative abundance of functional genes associated with the C-cycle. This may also be related to the application of manure that increased the abundance of Gemmatimonadetes and altered ecological clusters in bacterial co-occurrence networks. Our correlation network analysis suggested that Gemmatimonadetes might be the potential hosts for C-cycling genes due to their strong positive correlation with the abundance of C-cycling genes. Overall, these findings provide new insights into soil respiration under biochar amendment and manure application in tea plantations and broaden the options for carbon sequestration in soils.Graphical