Soil Pools Research Articles

Primary productivity regulates rhizosphere soil organic carbon: Evidence from a chronosequence of subtropical Chinese fir (Cunninghamia lanceolata) plantation

Tree plantations worldwide are a large terrestrial carbon sink. Previous studies on the carbon sequestration capacity of plantations mainly focused on tree biomass carbon sequestration, but the importance of soil organic carbon (SOC) was relatively unclear. Living root carbon inputs influence SOC via plant-microbe interactions in the rhizosphere and play an essential role in nutrient cycling. Here, we compared SOC, including its fractions, microbial properties, and major nutrients in rhizosphere and bulk soils, and examined their relationships to net primary productivity (NPP) across three developmental stages of Chinese fir (Cunninghamia lanceolata) plantations (6, 18, and 42 years old) in subtropical China. Although NPP differed among the three plantations, SOC concentration in bulk soils did not vary significantly among them. However, SOC concentration and labile C pool I and recalcitrant C pool in rhizosphere soils were significantly (p < 0.05) higher in the young (6-year) and mature (42-year) plantations, both of which had lower (p < 0.05) NPP (−37.71 % and − 42.67 %) compared to the middle-aged (18-year) plantation, suggesting a decoupling of NPP from rhizosphere SOC in the plantations. The decoupling of NPP from rhizosphere SOC concentrations may be driven by nitrogen (N) and phosphorus (P) tree growth requirements, belowground C allocation, and resultant microbial activity in this highly weathered subtropical soil. Our study provides field-based evidence suggesting that rhizosphere SOC changes are primarily regulated by net primary production in subtropical forest plantations. We propose that accurate predictions of SOC dynamics in forest plantations require an improved understanding of rhizosphere processes during plantation development.

MiPrime: A model for the microbially mediated impacts of organic amendments on measurable soil organic carbon fractions and associated priming effects

Priming effects can influence the efficiency with which organic amendments sequester carbon in the soil. Yet, few soil models currently include priming effects. Those models that do are often based on operationally defined soil pools and implicitly allow only for positive priming effects. This limits the verification of model processes with experimental data and hinders the optimization of our carbon sequestration strategies. To address these shortcomings, we developed MiPrime, which offers a framework for the mechanistic modelling of organic amendment impacts on microbially mediated transformation of carbon fractions that are quantifiable through parsimonious soil extraction methods. MiPrime allows for assessment of organic amendment impacts on soil carbon dynamics, including priming effects, by simulating changes in mineralized, microbial biomass, dissolvable, hot water extractable and insoluble carbon fractions in soil exogenous (i.e. organic amendment-derived) and endogenous (i.e. soil) pools. After calibration of model parameters using Markov Chain Monte Carlo methods to incubation data of three types of isotopically labelled roadside grasses (a fresh grass product, a compost thereof, and a Bokashi-fermented product thereof), MiPrime was able to simulate changes in carbon fractions of the soil with a good degree of accuracy for five compositionally complex organic amendments, namely the three types of roadside grasses, as well as non-isotopically labelled wood chips and water weeds and reeds. Validation of the model results with experimental data demonstrates that changes in total carbon were very well predicted but that there is room for improvement in predicting mineralization rates and changes in dissolvable, hot water extractable and insoluble carbon fractions in the soil endogenous pool. MiPrime thus offers an initial step towards the mechanistic modelling of organic amendment impacts on measurable soil carbon fractions and can operate as a new tool for designing effective carbon sequestration strategies and understanding organic amendment impacts.

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.

Ammonium nutrition enhances rhizosphere mobilization and uptake of silicon in white lupin grown in low phosphorus soil

Abstract Background and Aims While nitrogen (N) supply can enhance plant silicon (Si) accumulation, the mechanisms by which different forms of N affect Si mobilization in the rhizosphere are not well understood. This study aims to elucidate how pH changes induced by ammonium (NH4+) and nitrate (NO3−) affect Si availability in the rhizosphere, especially under low phosphorus (P) conditions. Methods White lupin (Lupinus albus) plants were grown in non-fertilized low-P soil, supplied with a low dose of N, either as NH4+ or NO3−, with or without supply of monosilicic acid. We measured Si levels in various rhizosphere soil pools, along with different plant and rhizosphere soil parameters. Results The addition of NH4+ significantly lowered rhizosphere pH and decreased both Si adsorbed to pedogenic Fe/Mn oxides and amorphous phytogenic Si, resulting in higher concentrations of plant available Si in the white lupin rhizosphere. This led to greater Si uptake and improved plant growth compared to both the –N and + NO3− treatments. The supply of Si further enhanced these effects, with NH4+ showing a consistently different pattern of influence compared to NO3−. Additionally, –N white lupin plants accumulated more P than those treated with N, while Si supply significantly improved P acquisition across all treatments. Conclusions Our study demonstrates that rhizosphere acidification induced by NH4+ nutrition can significantly enhance Si mobilization from the rhizosphere soil in the absence of Si supply and reduce Si adsorption when Si is applied. These findings may have practical implications for improving both Si mobilization in the rhizosphere and the effectiveness of Si fertilizers.

Isotope Evidence for Rice Accumulation of Newly Deposited and Soil Legacy Cadmium: A Three-Year Field Study.

Biogeochemical processes of atmospherically deposited cadmium (Cd) in soils and accumulation in rice were investigated through a three-year fully factorial atmospheric exposure experiment using Cd stable isotopes and diffusive gradients in thin films (DGT). Our results showed that approximately 37-79% of Cd in rice grains was contributed by atmospheric deposition through root and foliar uptake during the rice growing season, while the deposited Cd accounted for a small proportion of the soil pools. The highly bioavailable metals in atmospheric deposition significantly increased the soil DGT-measured bioavailable fraction; yet, this fraction rapidly aged following a first-order exponential decay model, leading to similar percentages of the bioavailable fraction in soils exposed for 1-3 years. The enrichment of light Cd isotopes in the atmospheric deposition resulted in a significant shift toward lighter Cd isotopes in rice plants. Using a modified isotopic mass balance model, foliar and root uptake of deposited Cd accounted for 47-51% and 28-36% in leaves, 41-45% and 22-30% in stems, and 45-49% and 26-30% in grains, respectively. The implications of this study are that new atmospheric deposition disproportionately contributes to the uptake of Cd in rice, and managing emissions thus becomes very important versus remediation of impacted soils.

Soil phosphorus fractionations as affected by cropping systems in the central mid-hills region of Nepal.

Soil plays a critical role as the primary reservoir of phosphorus (P) in terrestrial ecosystems. Sequential fractionation has been extensively utilized to gain insights into the characteristics and dynamics of soil P. However, there is a knowledge gap regarding the different P pools in Nepalese soils. Therefore, this study aimed to investigate the impact of cropping systems on soil P fractions in the central mid-hills of Nepal. The study focused on four cropping systems: vegetable, fruit, rice, and maize-based systems, which exhibited variations in nutrient management, topography, and cropping intensity. A total of 240 soil samples (60 samples from each cropping system) were collected from multiple sites within the central mid-hill region. Standard analytical methods were used to determine the general parameters of the soils, while the sequential fractionation method was employed to assess the organic and inorganic P pools. The results indicated that the effect of cropping systems on soil pH, calcium carbonate (CaCO3) content, and the proportion of sand, silt, and clay was not statistically significant in terms of general parameters. However, significant differences were observed among the different cropping systems in organic matter (OM), electrical conductivity (EC), cation exchange capacity (CEC), and available phosphorus. Similarly, in terms of inorganic phosphorus fractions, loosely bound P (LB-P), aluminum bound P (Al-P), iron bound P (Fe-P), and reductant soluble P (RS-P) were significantly affected, while calcium bound P (Ca-P) did not show a significant difference. Furthermore, in terms of organic phosphorus fractions, labile organic P (L-Po), fluvic acid organic P (FA-Po), and non-labile organic P (NL-Po) exhibited significant differences, whereas moderately labile organic P (ML-Po) and humic acid organic P (HA-Po) did not show a significant difference. Additionally, reductant soluble P showed a significant difference, while total P did not differ significantly. The vegetable-based system exhibited higher levels of the majority of P fractions, followed by the fruit-based, maize-based, and rice-based systems. These findings emphasize the importance of considering cropping systems and their response to different phosphorus pools, as this knowledge can contribute to the development of improved soil phosphorus management strategies and promote sustainable agricultural practices in the region.

Biochar and Straw Amendments over a Decade Divergently Alter Soil Organic Carbon Accumulation Pathways

Exogenous organic carbon (C) inputs and their subsequent microbial and mineral transformation affect the accumulation process of soil organic C (SOC) pool. Nevertheless, knowledge gaps exist on how different long-term forms of crop straw incorporation (direct straw return or pyrolyzed to biochar) modifies SOC composition and stabilization. This study investigated, in a 13-year long-term field experiment, the functional fractions and composition of SOC and the protection of organic C by iron (Fe) oxide minerals in soils amended with straw or biochar. Under the equal C input, SOC accumulation was enhanced with both direct straw return (by 43%) and biochar incorporation (by 85%) compared to non-amended conventional fertilization, but by different pathways. Biochar had greater efficiency in increasing SOC through stable exogenous C inputs and inhibition of soil respiration. Moreover, biochar-amended soils contained 5.0-fold greater SOCs in particulate organic matter (POM) and 1.2-fold more in mineral-associated organic matter (MAOM) relative to conventionally fertilized soils. Comparatively, although the magnitude of the effect was smaller, straw-derived OC was preserved preferentially the most in the MAOM. Straw incorporation increased the soil nutrient content and stimulated the microbial activity, resulting in greater increases in microbial necromass C accumulation in POM and MAOM (by 117% and 43%, respectively) compared to biochar (by 72% and 18%). Moreover, straw incorporation promoted poorly crystalline (Feo) and organically complexed (Fep) Fe oxides accumulation, and both were significantly and positively correlated with MAOM and SOC. The results address the decadal-scale effects of biochar and straw application on the formation of the stable organic C pool in soil, and understanding the causal mechanisms can allow field practices to maximize SOC content. These results are of great implications for better predicting and accurately controlling the response of SOC pools in agroecosystems to future changes and disturbances and for maintaining regional C balance.

Early-stage soil organic carbon stabilization in conservation agriculture-based cereal systems

In South Asia, the sustainability of conventional tillage and input-intensive cereal-based cropping systems (such as rice-rice and rice-wheat) is under scrutiny due to soil organic carbon depletion, stagnant productivity, and adverse environmental impacts stemming from greenhouse gas emissions (N2O, CH4, and CO2). Against this backdrop, a long-term field experiment was initiated in 2009 at three sites in India (Karnal, Patna, and Aduthurai) and one site in Bangladesh (Gazipur) to assess four scenarios (S) reflecting current and future diversified crop rotations and conservation agriculture (CA) practices: S1 - double cereal rotation with conventional practices; S2 - double cereal plus legume rotation with partial CA; S3 - double cereal plus legume rotation with full CA; and S4 - futuristic diversified cereal-legume rotations with full CA. This study delved into the dynamics and stabilization of soil organic carbon across all scenarios and sites. Replicated soil samples were collected from depths of 0–15 cm and 15–30 cm after two crop cycles. We analyzed Walkley-Black carbon (WBC), total organic carbon (TOC), and various carbon pools with different oxidizability, determining the amount of carbon stabilized under CA-based scenarios and identifying optimal systems for carbon economy in South Asia. On average, active and passive carbon pools, TOC, and WBC stocks followed the order: S4 > S3 > S2 > S1 at all sites, except Gazipur, where the order was S3 > S4 > S2 > S1. CA practices stabilized applied carbon inputs to soil organic carbon at an annual rate of 1.7 %, with greater stabilization observed under S4 (11.7 %) > S3 (10.6 %) > S2 (7.8 %), regardless of location. Rice-rice sites exhibited a higher carbon stabilization rate (13.4 %) compared to rice-wheat sites (6.7 %). A significant proportion of stabilized carbon (63 %) was allocated to passive pools in soils under S2, S3, and S4, highlighting CA's potential to enhance carbon stability. Using a linear indexing technique, we identified that both S3 and S4 are conducive to better carbon stabilization, yield sustainability, and environmental co-benefits. Consequently, full CA systems with best management practices (S3) and best management practices with crop diversification (S4) are recommended for sustainable crop production in the major double cereal growing regions of South Asia, including India and Bangladesh.

Modified biochar affects CO2 and N2O emissions from coastal saline soil by altering soil pH and elemental stoichiometry

The application of biochar in degraded farmland improves soil productivity while achieving the recycling of agricultural waste. The collapse of the physical structure of coastal saline soils will greatly reduce the carbon sequestration potential of biochar. Phosphorus- and magnesium-modified biochar greatly improve the stability of biochar, which endows them with the potential to greatly improve the organic carbon pool of coastal saline soil. However, changes in the properties of modified biochar increase the uncertainty of microbial driven CO2 and N2O release by affecting soil chemistry properties. In this study, through laboratory soil microcosmic experiment, we investigated the effects of magnesium-modified biochar (BCMg) and phosphorus-modified biochar (BCP) on CO2 and N2O releases from coastal saline soils, and further uncovered their potential mechanisms. Compared with unapplied biochar (CK) and unmodified biochar (BC) treatment, BCMg reduced both the releases of CO2 and N2O, and BCP decreased N2O release but enhanced CO2 release. pH is the medium through which BCMg affects the release of CO2 and N2O. Specifically, BCMg increased soil pH above 8.5, which reduced the metabolic activity of the microbial community, and the abundance of bacteria directly or indirectly involved in N2O production, thereby decreasing the releases of CO2 and N2O. The amendment of BCP changed soil elemental stoichiometry causing microbial N-limitation. Increasing CO2 release and decreasing N2O release were strategies for microorganisms to cope with N-limitation. These findings suggested that BCMg is superior to BCP in mitigating greenhouse gas emissions, providing a basis for the application of modified biochar to improve the carbon pool and reduce greenhouse gas emissions of coastal saline soil.

Microplastic fate in a chronosequence of biosolid‐amended agricultural soil in Southern Ontario, Canada

AbstractMunicipally sourced biosolids are commonly used as cost‐effective fertilizers, diverting material from landfills and contributing to the circular economy. However, biosolids contain high concentrations of microplastics (MPs), which are emerging contaminants of concern due to their ubiquity in the environment. Despite this, there is a lack of environmentally relevant field studies. In 2022, composite topsoil samples (0–15 cm depth) were collected from seven agricultural fields in Southern Ontario, Canada, representing a chronosequence of biosolid applications ranging from 1 to 9 years since amendment and a control (untreated) field. MP particles down to 20 μm in size were extracted by density separation, enumerated, characterized by stereomicroscope and polymers identified using attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy. Here, we report on the characteristics, abundance and polymer type of MP particles in the study area to assess their fate in biosolid‐amended soils. The average MP concentration among fields was 6.87 ± 1.47 MP g−1 (3.43 ± 0.74 mg MP kg−1). Additionally, the MP soil pool increased with repeated applications of biosolids. The dewatered biosolid plastic content of 8816 ± 1809 MP g−1 dry weight (11.6 ± 17.5 g MP kg−1 dry weight) was used to estimate a mean MP loading of 94.5 ± 10.9 kg ha−1 to each field per application, suggesting that 7% of the MP soil pool persisted over time. Quantifying the MP pool in biosolid‐amended agricultural soil will inform evidence‐based plastic policy changes in our global effort to understand and reduce plastic pollution.

Assessing extraradical mycelium of mycorrhizal fungi in tropical forests using armored in-growth mesh bags

The extraradical mycelium of mycorrhizal fungi is among the major carbon pools in soil that is hard to quantitatively assess in-situ. Established method of in-growth mesh bags in temperate ecosystems is difficult to apply in the tropics, where mesh bags are often damaged by termites. Here we introduce a modification of the in-growth mesh bag technique, in which mesh bags are enforced by stainless steel mesh. Its performance was tested in the Đồng Nai (Cát Tiên) National Park in Vietnam across two monsoon tropical forests, dominated by tree species associated with either ectomycorrhizal (ECM) or arbuscular mycorrhizal (AM) fungi. Armored in-growth mesh bags remained intact, while about 60 % of non-armored mesh bags were damaged by termites after 180 days of exposure. The biomass of extraradical mycelium of ectomycorrhizal fungi estimated by PLFA analysis was similar in the armored and non-armored mesh bags and did not differ between studied forests. However, fungal community composition slightly differed between armored and non-armored mesh bags in the ECM- but not in the AM-dominated forest. Fungal mycelium gathered in the AM-dominated forest was depleted in 15N compared to that collected in the ECM-dominated forest. Overall, our results argue for using armored mesh bags as a robust tool for harvesting the biomass of extraradical mycelium of mycorrhizal fungi in tropical ecosystems.

Dynamics of structural indices and organic carbon pool across a haplic acrisol under secondary tropical rainforest at Umudike Abia State

Differences in vegetation types over a landscape influences the structural behaviour and organic carbon pool of soils thereby affecting site-specific management decisions. This study aimed at establishing the differences in structural indices and organic carbon pool across a soil under secondary rainforest vegetation. Nine replicates of auger and core soil samples were randomly collected from the site at 0 – 20 cm depth. Soil samples were prepared and analysed at a laboratory. Data obtained were subjected to geospatial analysis using a Geographical Information System (GIS) software package. Results showed that changes in organic carbon storage ranged from 40 – 48 ton / ha, BD ranged from 1.39 – 1.42 mg / m3, clay flocculation index ranged from 50 – 68 %, aggregated silt + clay ranged from 9 – 12 %, clay dispersion index ranged from 32 – 42 %, dispersion ratio ranged from 26 – 32 %, mean weight diameter ranged from 0.75 – 1.05 mm, saturated hydraulic conductivity ranged from 3.1 – 3.8 cm / mins and total porosity ranged from 46.4 – 47.6 %. Regions of weak micro aggregaion dominated the land while regions of increased stability of macro aggregates were dominant. Regions of increased soil organic carbon storage occupied about half portion of the land. Greater portion of the land was noted for increased bulk density, reduced total porosity and saturated hydraulic conductivity. Consequently, there were changes in soil structural properties and organic carbon storage across the studied area.

Positive Effect of Biochar Application on Soil Properties: Solubility and Speciation of Heavy Metals in Non-Acidic Contaminated Soils near a Steel Metallurgical Plant in Southeastern Europe

Neutral and slightly alkaline arable soils from the vicinity of the former and the biggest metallurgical plant in southeastern Europe were analyzed for the status of the water soluble pool of heavy metals in 1–20% w/w biochar (BC)-amended contaminated soils. Heavy metal solubility was monitored over a 6-month period. The metals (Fe, Mn, Cu, Zn, Cd, Pb and Ba) exhibited significant relationships between each other and exceeded the maximum permissible concentrations (MPC) in surface waters for domestic and drinking purposes. In most of the investigated sites and BC treatments, metal concentrations decreased with time due to the transfer to more resistant soil pools. Cation exchange capacity, exchangeable Ca and pH increased after BC application, while electrical conductivity decreased. BC amendment led to the prevalence of humic acids (HAs) over fulvic acids (FAs) and increased the fraction of refractory organic carbon. The share of metal–organic complexes increased for the metals Zn, Cd, Mn and Ba in the BC-amended soils, and the share of free Me2+ species decreased. This trend was especially pronounced in the soils with the lowest pH of 6.4–6.9. In addition to improving soil physicochemical and ecochemical properties, biochar application contributed to metal species in solutions that were less mobile and bioavailable.

Earthworm influence on soil aggregate distribution and protected carbon at managed forest sites in Vermont, USA

The long-term effect of non-native earthworm species on forest soil carbon storage is not clear. While initial invasion into earthworm-free soils stimulates carbon losses, there is evidence that carbon stabilization in soil aggregates is enhanced. Fourteen managed forest sites throughout Vermont were sampled to identify and enumerate earthworms, and determine soil aggregate distribution and physically protected carbon. Most of these sites were northern hardwoods reforested in the mid-20th century after agricultural land use. Soil at six 50 × 50 cm subplots at each site was sampled to a depth of 20 cm below the Oe horizon and the mineral soil fractionated into free microaggregates (<250 μm), small macroaggregates (250–2000 μm), and large macroaggregates (>2000 μm). Microaggregates were then isolated from the macroaggregates and organic carbon determined. Mean earthworm numbers below the Oe horizon at each site ranged from 0 to 313 individuals m−2 and ten different species were identified, representing all earthworm ecotypes. Four sites had no earthworms in the soil layer sampled, three sites had earthworms in every subplot with up to six different species, and seven sites had subplots both with and without earthworms. When subplots were grouped by number of species present, there was a trend towards a greater fraction of the mineral soil in macroaggregates containing greater protected carbon, and a lower fraction of free microaggregates. A paired t-test of subplots from the seven sites with variable earthworm presence showed significant differences in the same trends and there was significantly greater mineral soil total carbon and protected carbon in the subplots with earthworms. These results are consistent with recent research into earthworm effects on soil carbon stabilization. While initial invasion likely resulted in a negative carbon balance, our findings suggest that earthworms can enhance transfer of carbon into physically protected pools in these forest soils.

Legacy soil phosphorus bioavailability in tropical and temperate soils: Implications for sustainable crop production

Improving phosphorus (P) use efficiency is key to improving the productivity and sustainability of cropping systems and slowing the exploitation rate of mineral P resources required for fertilizer production. At present, large amounts of added P in fertilizers and manure each year are retained in the soil and are not used by the crop. This ‘legacy P’ progressively accumulates in soil and represents an untapped P resource in tropical soils while in temperate soils it contributes to eutrophication. In the context of legacy P, the aim of this study was to quantify changes in soil P pools of contrasting bioavailability (determined using conventional chemical extraction procedures) during 12 successive brachiaria (Urochloa ruziziensis) cropping cycles in which no additional P was added. The study was undertaken in the greenhouse with 10 tropical (Brazil) and 6 temperate (UK) agricultural topsoils. Above-ground dry matter yield (DM) and P offtake was measured at each harvest alongside operationally-defined measures of the labile, moderately-labile and non-labile P pools at the start and end of the experiment. Over twelve repeated cultivation cycles, brachiaria demonstrated an ability to efficiently mine legacy P from all measurable soil pools across both sets of soils. This included the depletion of up to 87 % of non-labile soil P in some soils from the UK and up to 66 % from soils in Brazil after one year. While the amounts of initial labile P showed the closest positive relationship with plant P export, contrary to expectation the non-labile P pool also clearly contributed to plant nutrition across all the soils. As a cover crop, brachiaria clearly possesses traits which enable both the solubilization and efficient capture of soil P that can be harnessed to actively recycle historically non recalcitrant soil P fractions. Incorporating brachiaria into crop rotations or intercropping systems therefore shows promise as a strategy to enhance the longer-term sustainability of soil P management.

Green Infrastructure Microbial Community Response to Simulated Pulse Precipitation Events in the Semi-Arid Western United States

Processes driving nutrient retention in stormwater green infrastructure (SGI) are not well quantified in water-limited biomes. We examined the role of plant diversity and physiochemistry as drivers of microbial community physiology and soil N dynamics post precipitation pulses in a semi-arid region experiencing drought. We conducted our study in bioswales receiving experimental water additions and a montane meadow intercepting natural rainfall. Pulses of water generally elevated soil moisture and pH, stimulated ecoenzyme activity (EEA), and increased the concentration of organic matter, proteins, and N pools in both bioswale and meadow soils. Microbial community growth was static, and N assimilation into biomass was limited across pulse events. Unvegetated plots had greater soil moisture than vegetated plots at the bioswale site, yet we detected no clear effect of plant diversity on microbial C:N ratios, EEAs, organic matter content, and N pools. Differences in soil N concentrations in bioswales and the meadow were most directly correlated to changes in organic matter content mediated by ecoenzyme expression and the balance of C, N, and P resources available to microbial communities. Our results add to growing evidence that SGI ecological function is largely comparable to neighboring natural vegetated systems, particularly when soil media and water availability are similar.

Long-term different fertilization practices restructured the functional carbon pools in a paddy soil through distinct mechanisms

Fertilization is a common management practice for improving soil organic matter (SOM), which is a crucial indicator of soil fertility. Nevertheless, how long-term fertilization affects functional SOM fractions and its mechanisms remain unclear. In this study, a 12-year field experiment, initiated in 2011, was conducted in Xinzhu village, Zhejiang province, China. Four different fertilizer treatments (without any fertilizers application, Control; sole application of inorganic fertilizers, NPK; combined application of NPK with cattle manure, NPKM; and combination of NPK fertilizers and return of rice straw, NPKS) were selected in this field trial. Functional carbon (C) pools, microbial community structure and SOM composition in both topsoil (0−15 cm) and subsoil (15−30 cm) were explored using the physical and chemical fractionation, phospholipid fatty acids (PLFA) analysis and solid-state 13C-Nuclear Magnetic Resonance Spectrometry (13C NMR) assays. Compared to the control, the NPK combined with organic amendments had significantly higher organic carbon contents of unprotected pools (cPOM and fPOM) in both topsoil (39−277 %) and subsoil (43.1−91.3 %), respectively. Organic carbon accumulated the most within iPOM (1.99 g kg−1 soil) and H-d(Silt+Clay) fractions (1.41 g kg−1 soil) under NPKM in the topsoil, suggesting that physical and chemical protection played the pivotal role after manure addition. Furthermore, NPKM increased the abundance of bacterial and fungal PLFAs in both topsoil (31.4 % and 24.5 %) and subsoil (173 % and 175 %), while NPKS elevated the alkyl/O-alkyl C ratio but reduced the aromaticity in topsoil, compared to inorganic fertilization alone. Partial least squares path modelling showed that fertilization had a direct impact on silt+clay associated C (0.6) in topsoil, POM-C (0.76) in subsoil, and microbial community structure (0.88 and 0.87) in both soil layers. Redundancy analysis revealed that in the NPKM treatment, the key factors affecting functional carbon pools were the total PLFA and the ratio of gram-positive to gram-negative bacterial PLFA, while for the NPKS treatment, it was the alkyl C/O-alkyl C ratio. In conclusion, long-term fertilization had a strong effect on functional carbon fractions through multiple mechanisms in different soil layers, involving changing microbial community and SOM composition.

Patterns and drivers of atmospheric nitrogen deposition retention in global forests.

Forests are the largest carbon sink in terrestrial ecosystems, and the impact of nitrogen (N) deposition on this carbon sink depends on the fate of external N inputs. However, the patterns and driving factors of N retention in different forest compartments remain elusive. In this study, we synthesized 408 observations from global forest 15N tracer experiments to reveal the variation and underlying mechanisms of 15N retention in plants and soils. The results showed that the average total ecosystem 15N retention in global forests was 63.04 ± 1.23%, with the soil pool being the main N sink (45.76 ± 1.29%). Plants absorbed 17.28 ± 0.83% of 15N, with more allocated to leaves (5.83 ± 0.63%) and roots (5.84 ± 0.44%). In subtropical and tropical forests, 15N was mainly absorbed by plants and mineral soils, while the organic soil layer in temperate forests retained more 15N. Additionally, forests retained more than , primarily due to the stronger capacity of the organic soil layer to retain . The mechanisms of 15N retention varied among ecosystem compartments, with total ecosystem 15N retention affected by N deposition. Plant 15N retention was influenced by vegetative and microbial nutrient demands, while soil 15N retention was regulated by climate factors and soil nutrient supply. Overall, this study emphasizes the importance of climate and nutrient supply and demand in regulating forest N retention and provides data to further explore the impacts of N deposition on forest carbon sequestration.

Determination of Soil Carbon Pools in Selected Soils of Abia State, Nigeria

Soil carbon pools exist in Abia State soils but variation, quantification and speciation remain unascertained. This study was carried out on soils collected from two locations (Umuahia North and Ikwuano LGAs) under three land use systems: arable land (AL), forest land (FL) and palm plantation (PP). The aim of the study was to assess carbon pools in the study soil. Laboratory data was subjected to analysis of variance (ANOVA) in Randomized Complete Block Design (RCBD). Significantly different means were separated using Fisher’s least significant difference (F-LSD) at 5% level of probability (p≤0.05). Correlation analysis was used to assess the relationship between the selected soil properties. It was observed that organic carbon increased significantly (p&lt;0.05) 2.47 under forest land in Umuahia North and decreased to 0.97 under arable land in Ikwuano, permanganate oxidizable carbon (POC) increased significantly in Umuahia North (p&lt;0.05) while decreasing in Ikwuano, the POC interaction on the both locations were significant, water soluble organic carbon (WSOC) and microbial biomass carbon (MBC) were neither significant in location, land use or their interaction.

Organic carbon in Mollisols of the world − A review

Mollisols represent 29 % of agricultural land and they are considered to be one of the most fertile soils in the world. Here, we compare soil organic carbon (SOC) concentrations and pools of Mollisols for the globe, the USA and Poland, and review how differences are caused by climate, land use, and key environmental factors. Globally, the mean thickness of the A horizon in Mollisols is 50 cm. At 0–30 cm the mean SOC concentration is 2.3 %, SOC pool is 84 t ha−1, and clay content calculated at 0–50 cm soil depth is 21 %. Mollisols in the USA have an A horizon thickness of 36 cm and have a mean clay content of 27 % (0–50 cm). SOC concentrations are 2.0 and 1.7 % and SOC pools are 85 and 116 t ha−1 at 0–30 and 0–50 cm soil depth, respectively. Mollisols in Poland have SOC concentrations of 1.8 and 1.5 % at 0–30 and 0–50 cm soil depth, respectively, and lower clay content (17 %) at 0–50 cm depth. The SOC pool at 0–30 cm depth is 74 t ha−1 whereas it is 106 t ha−1 at 0–50 cm. At the global scale, the highest SOC concentrations and pools are in Mollisols from Eastern Europe (including Ukraine and Western Russia) and Asia, while the lowest SOC pools are found in Mollisols from South America. The Mollisols in Western and Central Europe and North America have similar SOC pools, although Mollisols in North America have higher SOC concentrations and lower A horizon thickness. Globally, the mean pH value of Mollisols is 7.1, and the pH is slightly lower in Mollisols of the USA (6.9 ± 0.9). The SOC concentrations and pools are strongly and positively correlated with clay content. Soil moisture and temperature regimes determine SOC concentration and pools in Mollisols, and higher SOC concentrations and pools are in Mollisols with frigid and frigid-cryic soil temperature regimes as well as aquic, xeric, and aridic soil moisture regimes. Mollisols under grassland have the largest SOC pools compared to those cultivated or under forest. The important environmental factors on SOC concentrations and pools in Mollisols worldwide are soil texture, land use, and soil temperature regime.