Influence Soil Organic Matter Research Articles

Soil organic matter and aggregate stability dynamics under major no-till crop rotations on the Canadian prairies

There is a need to develop and adopt novel, more resilient, or “climate-smart” cropping strategies on the Canadian prairies, which are crucial for sustainable agroecosystem management. To examine how crop rotation influences soil organic matter and aggregate stability (AS) dynamics, six crop rotations: (i) conventional (control), (ii) pulse/oilseed intensified, (iii) diversified, (iv) market-driven, (v) high-risk and high-reward, and (vi) soil health-enhanced were established in 2018 at three field sites: Lethbridge, Alberta and Swift Current and Scott, Saskatchewan under no-till management. After 4-year, soil organic carbon (SOC), total nitrogen (TN), particulate organic matter carbon (POM-C) and nitrogen (POM-N), or mineral-associated organic matter C (MAOM-C) and N (MAOM-N) concentrations were not significantly affected by crop rotation in the 0–7.5 cm soil depth. However, crop rotation significantly altered AS at two of three sites, with both soil health-enhanced and high-risk and high-reward rotations having the highest AS at Lethbridge and Swift Current. Across all three sites, strong positive correlations were found among SOC, TN, MAOM, and AS. Moreover, MAOM-C and MAOM-N showed stronger relationships with AS than POM, perhaps suggesting a positive feedback loop on the stability of SOC and aggregation. Overall, the inclusion of pulses in rotations showed the potential to sustain soil quality, likely by offsetting low residue quantity with better residue quality and diversity, thereby supporting SOC accrual and AS similar to or greater than conventional cereal- or oilseed-dominated rotations.

Impacts of Forest Fires on Soil: Exploring the Effects on Biotic and Abiotic Components

Forest fires are a widespread occurrence in ecosystems worldwide, impacting both vegetation and soil. The effects of forest fires, as well as prescribed fires, on forest soil are complex, influencing soil organic matter, macro and micro-nutrients, and physical properties such as texture, color, pH, and bulk density, along with soil biota. The magnitude of the impact on forest soil depends on factors such as fire intensity, fuel load, and soil moisture. The severity and frequency of fire determine whether it is beneficial or harmful to the soil. Low-intensity fires can enhance plant available nutrients through the combustion of litter and soil organic matter, promoting rapid growth of herbaceous plants and increased nutrient storage. Conversely, high intensity fires can lead to complete loss of soil organic matter, volatilization of vital elements (N, P, S, K), and microbial death. Additionally, intense forest fires generate hydrophobic organic compounds that result in water-repellent soils. Forest fires also have long-term effects on forest soil. This paper aims to review the impacts of forest fires on various soil properties crucial for maintaining a healthy ecosystem.

Uncovering the dominant role of root metabolism in shaping rhizosphere metabolome under drought in tropical rainforest plants

Plant-soil-microbe interactions are crucial for driving rhizosphere processes that contribute to metabolite turnover and nutrient cycling. With the increasing frequency and severity of water scarcity due to climate warming, understanding how plant-mediated processes, such as root exudation, influence soil organic matter turnover in the rhizosphere is essential. In this study, we used 16S rRNA gene amplicon sequencing, rhizosphere metabolomics, and position-specific 13C-pyruvate labeling to examine the effects of three different plant species (Piper auritum, Hibiscus rosa sinensis, and Clitoria fairchildiana) and their associated microbial communities on soil organic carbon turnover in the rhizosphere. Our findings indicate that in these tropical plants, the rhizosphere metabolome is primarily shaped by the response of roots to drought rather than direct shifts in the rhizosphere bacterial community composition. Specifically, the reduced exudation of plant roots had a notable effect on the metabolome of the rhizosphere of P. auritum, with less reliance on neighboring microbes. Contrary to P. auritum, H. rosa sinensis and C. fairchildiana experienced changes in their exudate composition during drought, causing alterations to the bacterial communities in the rhizosphere. This, in turn, had a collective impact on the rhizosphere's metabolome. Furthermore, the exclusion of phylogenetically distant microbes from the rhizosphere led to shifts in its metabolome. Additionally, C. fairchildiana appeared to be associated with only a subset of symbiotic bacteria under drought conditions. These results indicate that plant species-specific microbial interactions systematically change with the root metabolome. As roots respond to drought, their associated microbial communities adapt, potentially reinforcing the drought tolerance strategies of plant roots. These findings have significant implications for maintaining plant health and preference during drought stress and improving plant performance under climate change.

Climate, soil mineralogy and mycorrhizal fungi influence soil organic matter fractions in eastern US temperate forests

Abstract Identifying the primary controls of particulate (POM) and mineral‐associated organic matter (MAOM) content in soils is critical for determining future stocks of soil carbon (C) and nitrogen (N) across the globe. However, drivers of these soil organic matter fractions are likely to vary among ecosystems in response to climate, soil type and the composition of local biological communities. We tested how soil factors, climate and plant–fungal associations influenced the distribution and concentrations of C and N in MAOM and POM in seven temperate forests in the National Ecological Observatory Network (NEON) across the eastern United States. Samples of upper mineral horizon soil within each forest were collected in plots representing a gradient of dominant tree–mycorrhizal association, allowing us to test how plant and microbial communities influenced POM and MAOM across sites differing in climate and soil conditions. We found that concentrations of C and N in soil organic matter were primarily driven by soil mineralogy, but the relative abundance of MAOM versus POM C was strongly linked to plot‐level mycorrhizal dominance. Furthermore, the effect of dominant tree mycorrhizal type on the distribution of N among POM and MAOM fractions was sensitive to local climate: in cooler sites, an increasing proportion of ectomycorrhizal‐associated trees was associated with lower proportions of N in MAOM, but in warmer sites, we found the reverse. As an indicator of soil carbon age, we measured radiocarbon in the MAOM fraction but found that within and across sites, Δ14C was unrelated to mycorrhizal dominance, climate, or soil factors, suggesting that additional site‐specific factors may be primary determinants of long‐term SOM persistence. Synthesis. Our results indicate that while soil mineralogy primarily controls SOM C and N concentrations, the distribution of SOM among density fractions depends on the composition of vegetation and microbial communities, with these effects varying across sites with distinct climates. We also suggest that within biomes, the age of mineral‐associated soil carbon is not clearly linked to the factors that control concentrations of MAOM C and N.

Yield and Quality of Winter Jujube under Different Fertilizer Applications: A Field Investigation in the Yellow River Delta

Winter jujube (Ziziphus jujuba Mill. cv. Dongzao) is highly popular due to its attractive taste and flavor of fruits. However, its cultivation is facing a serious obstacle for the substantial decrease in fruit soluble solids contents. In this study, four commonly-used fertilization types, including organic manure application (OM), combined application of manure and NPK fertilizer (OC), NPK fertilizer application at high rate (HC) and NPK fertilizer application at low rate (LC) were selected to investigate their effects on soil and fruit properties. Results showed that fertilization influenced soil organic matter (SOM) and NPK contents. Fruit yield decreased as HC (3.37tha−1) > OC (2.81tha−1) > OM (2.14tha−1) > LC (1.92tha−1).Total soluble solids (TSS), protein contents, and the ratio of TSS to titratable acid (TA) were highest in OM, followed by OC, LC and HC. TSS and TSS/TA ratio in OM were 23.0% and 27.0% higher than those in HC. Fruit yield was significantly positively correlated with soil available N, vegetative shoot leaf N, and total topsoil P contents. TSS and TSS/TA ratio both significantly positively correlated with SOM of topsoil and leaf P contents. Combined application of organic and inorganic fertilizers should be the optimal mode for winter jujube production.

Do model choice and sample ratios separately or simultaneously influence soil organic matter prediction?

This study was performed to examine the separate and simultaneous influence of predictive models’ choice alongside sample ratios selection in soil organic matter (SOM). The research was carried out in northern Morocco, characterized by relatively cold weather and diverse geological conditions. The dataset herein used accounted for 1591 soil samples, which were randomly split into the following ratios: 10% (∼150 sample ratio), 20% (∼250 sample ratio), 35% (∼450 sample ratio), 50% (∼600 sample ratio) and 95% (∼1200 sample ratio). Models herein involved were ordinary kriging (OK), regression kriging (RK), multiple linear regression (MLR), random forest (RF), quantile regression forest (QRF), Gaussian process regression (GPR) and an ensemble model. The findings in the study showed that the accuracy of SOM prediction is sensitive to both predictive models and sample ratios. OK combined with 95% sample ratio performed equally to RF in conjunction with all the sample ratios, as the latter did not show much sensitivity to sample ratios. ANOVA results revealed that RF with a ∼10% sample ratio could also be optimum for predicting SOM in the study area. In conclusion, the findings herein reported could be instrumental for producing cost-effective detailed and accurate spatial estimation of SOM in other sites. Furthermore, they could serve as a baseline study for future research in the region or elsewhere. Therefore, we recommend conducting series of simulation of all possible combinations between various predictive models and sample ratios as a preliminary step in soil organic matter prediction.

Long-term effects of tillage and nitrogen fertilization on soil C and N fractions in a corn–soybean rotation

Tillage and nitrogen (N) fertilization can influence soil organic matter (SOM) dynamics, but their interactive effects remain contradictory. A long-term (25 yr) corn (Zea mays L.)-soybean (Glycine max L. Merr.) rotation was used to investigate the effect of tillage [moldboard plow (MP) and no-till (NT)] and N rates (0, 80, and 160 kg N·ha−1) on soil organic carbon (SOC), total N (STN), respiration, and SOM fractions [particulate organic matter (POMC, POMN), mineral-associated organic matter (MAOMC, MAOMN), and microbial biomass (MBC, MBN)]. Results indicate that NT had 27% higher SOC and 24% higher STN than MP in the 0–20 cm depth. Furthermore, SOC and STN stocks (0–20 cm) were 22% and 20% higher, respectively, under NT than MP. There was significant stratification under NT, with a rather uniform distribution under MP. The SOM fractions and soil respiration were 28%–275% and 20%–83% higher at the 0–5 and 5–10 cm depths, respectively, under NT than MP. Interestingly, N fertilizer rate or its interaction with tillage had no impact, except for respiration (tillage × N rate and N rate × depth). Hence, while N addition was required for adequate grain production and increased cumulative plant C and N inputs, our findings indicate that the vertical distribution of SOC, STN, and SOM fractions was affected by tillage, thereby influencing resource accessibility and subsequent dynamics of SOM fractions. Taken together, our results support the adoption of NT and judicious use of N fertilizers for enhancing topsoil SOM storage and fertility under humid temperate conditions.

Variation of soil organic matter depends on light-fraction organic matter under long-term monocropping of different crops

Cultivating crops influences soil organic matter (SOM), but the effect of different crops remains unclear, particularly under long-term monocropping. The objective of this study was to identify how different crops influence the content and chemical structures of SOM under long-term monocropping. Here, soils were sampled (0–20 cm) under 27-year soybean and maize monocropping and separated into different physical fractions. The content and chemical structures of SOM in all fractions were determined. SOM contents were higher under soybean than maize in bulk soil and macroaggregates and their light-fractions instead of microaggregates and silt and clay. The difference in SOM chemical structure was observed in aggregates and density fractions rather than bulk soils and supported by the result of principal component analysis. The proportion of O-alkyl C in macro- and microaggregates and all free light fractions and that of aromatic C in mineral-associated fractions were higher, while that of carbonyl C was lower under maize than soybean. These results demonstrated that different crops monocropping influences the content and chemical structures of SOM, and the variations were mainly in the light-fraction SOM and highlight a higher sensitivity of physical fractions than bulk soil to different crops.

Arbuscular mycorrhizal trees cause a higher carbon to nitrogen ratio of soil organic matter decomposition via rhizosphere priming than ectomycorrhizal trees

Tree roots and their associated microbes can significantly influence soil organic matter (SOM) decomposition, i.e., the rhizosphere priming effect. This effect is expected to be greater in trees associated with arbuscular mycorrhizal (AM) fungi, which produce higher extracellular enzymes especially surrounding hyphae, than in trees associated with ectomycorrhizal (ECM) fungi. Here, we selected five tree species associated with AM (Juglans mandshurica Maxim. and Cunninghamia lanceolata (Lamb.) Hook.) or ECM (Picea koraiensis Nakai, Quercus mongolica Fischer ex Turcz. and Larix kaempferi (Lamb.) Carriere). We grew tree seedlings inside of cores lined with different mesh sizes to investigate how roots, hyphae and exudates influence soil carbon (C) and nitrogen (N) mineralization via the rhizosphere priming effect, using a13C natural abundance approach and a15N pool dilution method, concurrently. We found that tree seedlings significantly accelerated soil C decomposition by on average 78%, i.e., positive priming, compared to unplanted control pots. AM-associated trees induced 2.1 times greater soil C decomposition than ECM-associated trees across all mesh sizes. In contrast, gross N mineralization did not differ between tree-mycorrhizal associations. Compared to ECM counterparts, AM-associated trees had higher C- and lower N-degrading enzyme activities. Consequently, AM-associated trees induced a significantly higher C:N ratio of SOM decomposition than their ECM counterparts, which could be associated with the differences in soil enzyme activities for C and N degradation. Further, for both AM- and ECM-associated trees, we found no significant influences of mesh size on soil C decomposition, suggesting that the rhizosphere priming effect of mycorrhizal symbiosis was predominantly driven by root exudates. We conclude that SOM decomposition caused by AM-associated trees may have a higher C:N ratio than that by ECM-associated trees mainly due to differences in microbial enzyme investment. Our findings imply that tree-mycorrhizal associations are capable of modulating soil biogeochemical cycling via the rhizosphere priming effect.

Assessment of soil microbial and enzyme activity in the rhizosphere zone under different land use/cover of a semiarid region, India

BackgroundLand use/cover and management practices are widely known to influence soil organic matter (SOM) quality and quantity. The present study investigated the effect of different land use, i.e., forests viz. mixed forest cover (MFC), Prosopis juliflora (Sw.) DC-dominated forest cover (PFC), and cultivated sites viz. agriculture field (AF), vegetable field (VF), respectively, on soil parameter, microbial activity, and enzymes involved in soil nutrient cycle in a semiarid region of India.ResultsThe results showed a significant reduction (P < 0.05) in soil carbon (SC), soil nitrogen (SN) content (~ 30–80%) and consequently the soil microbial biomass carbon (SMBC) (~ 70–80%), soil basal respiration (SBR), soil substrate-induced respiration (SSIR), and soil enzyme activities (β-glucosidase, acid phosphatase, and dehydrogenase) under cultivated sites in comparison with forest sites. Pearson’s correlation showed that a positive correlation of SC with SMBC, SBR, SSIR (P < 0.01), and enzymatic activities (i.e., β-glucosidase, dehydrogenase) (P < 0.05) may imply the critical role of SC in regulating microbial and enzymatic activity. Also, a positive correlation of soil moisture with urease activity (P < 0.01) was found suggesting it as a significant abiotic factor for soil biological functions. Additionally, based on the PCA analysis, we observed the clustering of SMBC/SC ratio and qCO2 nearby AF.ConclusionOur study suggests that soil microbial parameters (SMBC, SBR, SSIR, SMBC/SC, qCO2) and enzyme activity are key indicators of soil health and fertility. Land use/cover alters the SOM content and soil microbial functions. The management strategies focusing on the conservation of natural forest and minimizing the land disturbances will be effective in preventing soil carbon flux as CO2 and maintaining the SC stock.

Soil carbon dynamics during drying vs. rewetting: Importance of antecedent moisture conditions

Soil moisture influences soil carbon dynamics, including microbial growth and respiration. The response of such ‘soil respiration’ to moisture changes is generally assumed to be linear and reversible, i.e. to depend only on the current moisture state. Current models thus do not account for antecedent soil moisture conditions when determining soil respiration or the available substrate pool. We conducted a laboratory incubation to determine how the antecedent conditions of drought and flood influenced soil organic matter (SOM) chemistry, bioavailability, and respiration. We sampled soils from an upland coastal forest, Beaver Creek, WA USA, and subjected them to drying and rewetting treatments. For the drying treatment, field moist soils were saturated and then dried to 75, 50, 35, and 5% saturation. In the rewetting treatment, field moist soils were air-dried and then rewet to 35, 50, 75, and 100% saturation. We measured respiration and water extractable organic carbon (WEOC) concentrations and used 1H-NMR and FT-ICR-MS to characterize the WEOC pool across the treatments. The drying vs. wetting treatment strongly influenced SOM bioavailability, as rewet soils (with antecedent drought) had greater WEOC concentrations and respiration fluxes compared to the drying soils (with antecedent flood). In addition, air-dry soils had the highest WEOC concentrations, and the NMR-resolved peaks showed a strong contribution of protein groups in these soils. Both NMR and FT-ICR-MS analyses indicated increased contribution of complex aromatic groups/molecules in the rewet soils, compared to the drying soils. We suggest that drying introduced organic matter into the WEOC pool via desorption of aromatic molecules and/or by microbial cell lysis, and this stimulated microbial mineralization rates. Our work indicates that even short-term shifts in antecedent moisture conditions can strongly influence soil C dynamics at the core scale. The predictive uncertainties in current soil models may be reduced by a more accurate representation of soil water and C persistence that includes a mechanistic and quantitative understanding of the impact of antecedent moisture conditions.

Prostorno mapiranje kemijskih svojstava tla koristeći multivarijatnu geostatistiku. Studija s oraničnih tala u istočnoj Hrvatskoj

The spatial variability of soil chemical properties is affected by factors of soil formation and human activities. Understanding their spatial variability will improve agricultural production, reduce environmental problems (e.g., soil pollution, offsite effects), and achieve sustainable agroecosystems. The main objective was to study the spatial variability of pH, soil organic matter, available phosphorus, and available potassium using univariate and multivariate methods in cropland fields in eastern Croatia. For the study, 169 (0-30 cm) soil samples were collected in a 911 ha study area. The results showed that soils had slightly acidic pH, adequate available phosphorus and potassium values for crop production, and low soil organic matter concentration. The variability was high in available phosphorus and low in pH. Soil pH, soil organic matter, available phosphorus, and potassium nugget/sill ratio was 0.00, 2.79, 18.68, and 22.08, respectively. Auxiliary variables increased the accuracy of the predictions. Soil organic matter levels were below the recommendable, and this is very likely an anthropogenic effect, even though the intrinsic process influences soil organic matter. The heterogeneous distribution of phosphorus and potassium highlighted the necessity of fertilization in some areas. For the sustainability of agroecosystems, adaptable site-specific soil management strategies need to be implemented.

Continuous Monoculture of Alfalfa and Annual Crops Influence Soil Organic Matter and Microbial Communities in the Rainfed Loess Plateau of China

Cropping systems are structured to maximize crop yields and increase sustainability in agricultural production. A field study was conducted to investigate different long-term cropping systems on soil organic matter and microbial communities. The cropping systems studied were: (i) a 14-year continuous alfalfa (Medicago sativa L.) (CA), (ii) a 9-year alfalfa removed and rotated with 4–5 years continuous annual crops (spring wheat (Triticum aestivum L.), maize (Zea mays L.), potato (Solanum tuberosum L.), and millet (Panicum miliaceum L.)), and (iii) a 5-year field fallow after alfalfa. Results showed that continued annual crops decreased total organic C and labile organic C by 10 to 20% and 17 to 34% in the topsoil (0–30 cm), and by 15 to 35% and 20 to 46% in the subsoil (30–60 cm), respectively, compared with CA. Similar trends were found in soil total N concentration, which decreased by 7 to 20% in the topsoil. Highest microbial biomass C was found in CA. Shannon-Wiener diversity and substrate richness of soil microbes measured by Biolog EcoPlates was significantly affected by cropping system with CA exhibiting a higher degree of soil microbial functional diversity in the topsoil, while the lowest values were found in the alfalfa-potato system. The higher soil organic matter content and functional diversity of soil microbe in CA indicates that soil nutrition and microbial activity did not limit alfalfa development and growth in the dryland area. The lower microbial activity and functional diversity observed in the potato field indicates the importance of crop selection in cropping systems.

Nutrient cycling and soil-related processes under different land covers of semi-arid rangeland ecosystems in northern Iran

There are contrasting reports about whether and how land covers influence soil organic matter fractions and microbial activities. To the best of the authors’ knowledge, the relationship between above-ground plant cover and the nutrient cycling in semi-arid areas, which are often considered as especially fragile and sensitive ecosystems, are almost unknown. The purpose of this research was to evaluate the influence of different shrub and grasslands located in northern Iran on the fractions of soil particulate and dissolved organic matter, microbial/enzyme activities. In this study, a total of 15 soil samples (30 × 30 × 10 cm) from each vegetation type [i.e. (1) Crataegus microphylla C. Koch., (2) Berberis integerrima Bunge., (3) Ribes Uva – crispa L., (4) Prunus spinosa L., (5) rangeland cover with dominant Lecokia cretica (Lam.) DC., Orchis mascula L., Cardamine bulbifera (L.) Crantz, and (6) rangeland cover with the dominance of Fragaria vesca L.] were transferred to the laboratory. Berberis significantly increased soil particulate organic C (2.26 g kg−1), but the maximum particulate organic N (0.27 g kg−1) was found under the Cratagus plant type. Soil dissolved organic C content was found to be significantly higher under Berberis (38.08 mg kg−1) ≈ Cratagus (34.81 mg kg−1), whereas the soil dissolved organic N was enhanced in Cratagus (22.84 mg kg−1) land cover. Significantly higher values of basal and substrate induced respiration (0.27 and 1.22 mg CO2 g−1 day−1, respectively) were found under Berberis when compared with the other land covers. Soil microbial biomass C and P were found to be significantly higher under Cratagus (259.90 and 61.00 mg kg−1) and Berberis (273.72 and 54.80 mg kg−1), whereas microbial biomass of N was enhanced under Cratagus (36.88 mg kg−1) plant type. Soil urease (18.22 µg NH4+–N g−1 2 h−1), acid phosphatase (305.66 µg PNP g−1 h−1), arylsulfatase (90.60 µg PNP g−1 h−1), invertase (97.53 µg Glucose g−1 3 h−1), geometric mean (4.73) and Shannon's diversity index (0.15) of enzyme activities were significantly increased in the topsoil of Cratagus compared with the other vegetation types. Based on principal component analysis (PCA), Cratagus, Berberis, and Ribes enhanced soil organic matter fractions, microbial and enzyme activities and were related to higher amounts of soil moisture, pH, organic C, total N, available P, fulvic/humic acids, and root biomass. Pasture and Prunus decreased the fractions of organic matter and soil microbial activities and most often affected the stoichiometry of carbon sources. It was concluded that shrubs (especially Cratagus and Berberis) can play a crucial role in nutrient cycling and soil-related processes in semi-arid rangeland ecosystems.

Integrated farming systems influence soil organic matter dynamics in southeastern Brazil

Integrated farming systems are sustainable strategies to intensify land productivity by combining annual crop, livestock and/or forestry activities in different spatio-temporal arrangements. Therefore, they may help tackle global food and energy insecurity and climate change in the coming decades. We investigated the effects of integrated crop-livestock (ICL) and integrated crop-livestock-forestry (ICLF) systems on quantity, quality, and origin of soil organic matter (SOM) in southeastern Brazil. A native forest and an extensive low-grazing intensity pasture system were used as references. In integrated systems, corn (Zea mays) was alternated with two consecutive years of piatã grass (Urochloa bryzantha) for cattle grazing. In ICLF, eucalyptus trees (Eucalyptus urograndis) were planted in simple rows of 15 × 2 m. Soil sampling was performed three times; in 2014, after two years of grazing; in 2015, after crop cultivation; and in 2016, after a successive grazing year, to evaluate chemical and physical composition changes of organic matter (C, N, δ13C, δ15N, and organic matter fractions) with time. Our findings showed that from 2010 to 2016, all systems (extensive grazing, ICL and ICLF) promoted increments on soil C and N stocks. However, land intensification converting extensive low-grazing intensity pasture to ICL was the most promising strategy, increasing soil C stocks at the rate of 0.28 Mg C ha−1 yr−1 from 2010 to 2016. Annual crop cultivation (corn intercropped with piatã grass) promoted high organic matter inputs on the soil, increasing the amount of soil labile organic matter fractions, which presented higher δ13C and lower δ15N values over time. SOM in the integrated farming systems was originated mainly from C4 plants. Therefore, optimizing development of piatã grass and corn increases organic residue inputs and then, soil C and N stocks. In addition, the crop period increased soil fertility parameters, which favors plant growth, thus providing high labile C inputs to the soil. In contrast, land intensification by adding the forestry component into the system (i.e., conversion from ICL to ICLF) reduced soil C (-0.22 Mg C ha−1 yr−1) and N (-0.03 Mg N ha−1 yr−1) stocks from 2010 to 2016, likely due to the reduction of C and N inputs to the soil caused by limited growth of annual crop and grass species under tree shades. In conclusion, land use intensification through ICL system contributes towards a more efficient and low-C agriculture, whereas the studied ICLF system did not bring further benefits to increase the quantity and/or quality of SOM.

Prevalent root-derived phenolics drive shifts in microbial community composition and prime decomposition in forest soil

Phenolic compounds perform various functions in soil ranging from microbial substrate to toxin and form the basis of several plant-mediated processes. The aim of this study was to investigate how phenolics commonly exuded by tree roots influence soil organic matter (SOM) decomposition and interact with other labile forms of carbon (C) abundant in root exudates. Therefore, we performed a 38-day incubation experiment and assessed whether phenolic compounds (benzoic acid, caffeic acid and catechin) facilitated or inhibited SOM decomposition in a glucose-amended forest soil. Changes in decomposition, substrate use, fungal and bacterial community composition, and microbial abundance and activity were measured over time using 13C-stable-isotope tracing, DNA-based molecular methods and enzyme assays. Our findings showed that phenolics inhibited microbial activity and abundance to varying degrees. Yet, benzoic acid was the only compound producing a substantial priming effect leading to a 21% increase in SOM decomposition, which was amplified in glucose-amended soils. This stimulation in microbial activity was associated with an increase in β-1,4-glucosidase activity and the bacterial genera Paraburkholderia and Caballeronia of the Burkholderiaceae family. Phenolics drove microbial community shifts in glucose-amended soils with negligible interactive effects. In conclusion, phenolic priming of SOM decomposition is associated with microbial community shifts and amplified in the presence of glucose. This evidence emphasizes the need for considering phenolics and interactions among root exudates as priming mechanisms in the rhizosphere and other soil environments where aromatics and phenolic compounds are abundant.

The Influence of the Rotation Length of Eucalypt Plantations on Soil Organic Matter Dynamics in Southern Brazil

The rotation length of forest plantations can influence soil organic matter (SOM) pools. However, this is not well documented in eucalypt systems in Brazil. Therefore, we assessed the total organic carbon (TOC), total nitrogen (TN), and SOM fractions with different turnover rates (i.e., light organic matter [LOM], alkali extractable [AE], and nonextractable [ANE]) in the top 1 m of soil of 10‐, 13‐, and 22‐yr eucalypt rotations, and compared them with those of a native grassland in southern Brazil. The 22‐yr rotation yielded greater TOC stocks in the 0‐ to 60‐cm soil depth (107.2 Mg ha−1) than the grassland (86.7 Mg ha−1). Total N stocks were lower in the upper soil layers (0‐ to 40‐cm depth interval) in the eucalypts than in the grassland, except for the 10‐yr rotation. The changes in TOC and TN resulted in wider soil C/N ratios in the soil (0‐ to 100‐cm depth interval) in longer rotations (13 and 22 yr). The LOM‐C and LOM‐N fractions were similar between the grassland and longer rotations but were reduced in the 10‐yr stand. Overall, afforestation increased AE‐C stocks; the 10‐ and 13‐yr stands yielded the greatest AE‐C stocks at the 0‐ to 60‐cm and 0‐ to 100‐cm soil depths, respectively. For ANE‐C, the 22‐yr stand yielded the greatest stock at the 0‐ to 100‐cm depth (88.8 Mg ha−1). Our study showed that longer eucalypt rotations promoted soil C accrual compared with the grassland and shorter rotations; however, TN stocks were less affected, resulting in wider soil C/N ratio as rotation length increased.

Soil Chemical Properties and Nutrient Composition of Cocoyam Grown in an Organically Fertilized Soil

ABSTRACTField experiments were conducted for two consecutive years to evaluate the influence of cow dung and rice husk application rates on soil chemical properties and nutrient composition of cocoyam cormels. The treatments comprised four rates each of cow dung and rice husk (0, 10, 20, and 30 t/ha) arranged as a factorial experiment using randomized complete block design with three replicates. The treatments were incorporated into the soil 2 weeks before planting of cocoyam each year. After 2 years of cropping, soil samples were collected from the respective plots and analyzed so also cocoyam cormels. Cow dung application positively and significantly (P < .05) affected soil pH, organic matter (OM), and the soil nutrients (r = 0.95, 0.98, and 0.94–1.00, respectively) while rice husk application significantly and positively influenced soil OM, nitrogen and phosphorus (r = 0.98, 0.95, and 0.98, respectively). Aside potassium content that was enhanced, cow dung application did not significantly affect the nutrient composition of the cocoyam cormels. However, 30 t/ha of applied rice husk caused significant reduction in crude protein and fiber contents but significant increase in carbohydrate. There was negative and significant correlation between rice husk and the cormels crude protein (r = −0.97). A total of 20 t/ha each of the organic fertilizers was found to be optimum for improving soil fertility and invariably yield without compromising the nutrient content of the cocoyam cormels.

Characterization of Dark Septate Endophytic Fungi and Improve the Performance of Liquorice Under Organic Residue Treatment.

Dark septate endophytic (DSE) fungi is a diverse group of Ascomycetes fungi that colonize the plants roots, and may facilitate plant growth and fitness, however, their ecological roles need further clarification. This study aimed to evaluate the growth promoting effects of DSE fungi in a medicinal plant, liquorice (Glycyrrhiza uralensis), under additional organic residues. First, we isolated, identified and characterized, two DSE fungal species (Acrocalymma vagum and Paraboeremia putaminum) harboring inside the roots of liquorice growing in arid areas of China. Second, we examined the performance and rhizosphere soil parameters of liquorice plants inoculated with these fungi under additional sterilized organic residues and unsterilized organic residue (containing Trichoderma viride population) in a growth chamber. The results showed that two DSE strains could effectively colonize plant roots and formed a strain-dependent symbiosis with liquorice. DSE inoculation alone increased the plant biomass, and glycyrrhizic acid and glycyrrhizin content. It also improved the root system and N and P absorption by plants, consequently depleting these macronutrients in the soil. Residues alone increased soil organic matter, available phosphorus (P), and available nitrogen (N) content, and plant biomass, N, P, glycyrrhizic acid, and glycyrrhizin content. Mantel test and structural equation model (SEM) analysis demonstrated that DSE associated with residues significantly positively influenced soil organic matter, available P and available N, and plant biomass, glycyrrhizin, N, P, and root surface area. Variation in plant growth and glycyrrhizic acid and glycyrrhizin accumulation can be attributed to the effects of DSE inoculation. DSE associated with residues exhibited a general synergistic effect on the growth and accumulation of glycyrrhizic acid and glycyrrhizin of liquorice. We demonstrate for the first time, two DSE fungi in the liquorice roots that have potential use as promoter for the cultivation of medicinal plant.

Impacts of land use change on soil organic matter chemistry in the Everglades, Florida - a characterization with pyrolysis-gas chromatography–mass spectrometry

Reclamation of marshlands for agricultural land use is widespread. An example of large-scale land use shifts is evident in the Everglades Agricultural Area of Florida where freshwater wetlands were converted to sugarcane (Saccharum officinarum) production. Such land-use shifts can markedly influence soil organic matter cycling and processes. The effect of such land use change on molecular characteristics of soil organic carbon is unknown. In this study, three surface soils cores (0–5 cm, 5–10 cm, and 10–19 cm) from a representative marsh and a sugarcane field in the Florida Everglades with known land use history and management practices were characterized using pyrolysis-gas chromatography–mass spectrometry (Py-GC/MS) to investigate molecular characteristics of soil organic matter. Soil organic carbon (SOC), total nitrogen, total sulfur, and water extractable organic carbon contents in sugarcane soil were 37.02%, 2.44%, 0.46% and 0.11%, while they were 44.57%, 2.62%, 0.73% and 0.38%, respectively. On the whole, marshland reclamation to sugarcane caused increase of aromatics (from 11.37% to 13.20%), polyaromatic hydrocarbon (from 0% to 1.63%), n-alkanes (from 8.90% to 16.17%), n-alkenes (from 25.10% to 28.77%), other aliphatics (from 7.33% to 11.77%) and fatty acids (from 1.93% to 3.87%) in pyrolysis products of soil organic matter (SOM), whereas this shift reduced lignin (from 12.87% to 2.47%), phenols (from 23.33% to 16.13%), polysaccharides (from 2.40% to 1.03%), benzofuran (from 1.67% to 0.27) and nitrogen containing compounds (from 5.07% to 4.67%), respectively. Overall, the conversion of marsh to sugarcane land use not only reduced total SOC contents but also altered molecular features of SOM with significant increases in aliphatic fractions and almost complete exhaustion of lignin fractions, signifying SOC dynamic shift due to land change in the Everglades.