Soil Biomass Research Articles

Nitrogen induced soil carbon gains are resistant to loss after the cessation of excess nitrogen inputs

Nitrogen (N) deposition has increased soil carbon (C) storage across eastern US temperate forests by reducing microbial decomposition. However, the fate of these N-induced soil C gains are uncertain given strong declines in N-deposition rates and rising soil temperatures. As N deposition has reduced soil pH and plant C investments into the rhizosphere, we compared the extent to which removing limitations to microbial decomposition by increasing soil pH, adding artificial root exudates, or elevating soil temperature would increase microbial decomposition in soils that have and have not received excess N inputs. We hypothesized that alleviating these microbial decomposition limitations would prime soil C losses from soils that have received excess N inputs. To test this hypothesis, we conducted a soil microcosm experiment where we compared microbial respiration, microbial biomass, and soil enzyme activity in soils from an unfertilized watershed and a previously N-fertilized watershed 4 years after the end of a 30-year N deposition experiment at the Fernow Experimental Forest in West Virginia. In both watersheds, we found that removing pH, plant carbon, or temperature limitations to decomposition stimulated microbial respiration. However, microbial decomposition and soil C losses were consistently lower in the previously N-fertilized watershed across all treatments. This response, coupled with a lack of differences in microbial biomass between watersheds and treatments, suggests that long-term N fertilization has fundamentally altered soil microbial communities and has led to a sustained impairment of the ability of the microbial community to decompose soil organic matter. Collectively, our results indicate that the legacy effect of N deposition on microbial communities may influence the persistence of soil C stocks in the face of global change.

A Treasure Trove of Urban Microbial Diversity: Community and Diversity Characteristics of Urban Ancient Ginkgo biloba Rhizosphere Microorganisms in Shanghai.

Rapid urbanization has exerted immense pressure on urban environments, severely constraining the growth of ancient trees. The growth of ancient trees is closely linked to the microbial communities in their rhizospheres, and studying their community characteristics may provide new insights into promoting the growth and rejuvenation of ancient trees. In this study, the rhizosphere soil and root systems of ancient Ginkgo biloba trees (approximately 200 years old) and adult G. biloba trees (approximately 50 years old) in Shanghai were selected as research subjects. Phospholipid fatty acid (PLFA) analysis and high-throughput sequencing were employed to investigate the diversity of microbial communities in the G. biloba rhizosphere. The results indicated that the 19 PLFA species selected to characterize the soil microbial community structure and biomass were present in the rhizosphere soil of both ancient and adult G. biloba trees. However, the total microbial biomass and the microbial biomass in the rhizosphere soil of ancient G. biloba were lower than the microbial biomass in the rhizosphere soil of adult G. biloba. The biomasses of Gram-negative bacteria (G-), arbuscular mycorrhizal fungi (AMF), and protozoans (P) were significantly different. Total phosphorus, organic matter, and pH may be the key factors influencing the soil microbial community in the rhizosphere zone of ancient G. biloba. An in-depth study of AMF showed that the roots and rhizosphere soil of G. biloba contained abundant AMF resources, which were assigned to 224 virtual taxa using the MaarjAM reference database, belonging to four orders, ten families, and nineteen genera. The first and second most dominant genera were Glomus and Paraglomus, respectively. Archaeospora and Ambispora were more dominant in the rhizosphere than the roots. Furthermore, the abundance of live AMF was significantly higher in ancient G. biloba than in adult G. biloba. Therefore, future research should focus on the improvement of soil environmental characteristics and the identification and cultivation of indigenous dominant AMF in the rhizosphere of ancient G. biloba, aiming for their effective application in the rejuvenation of ancient trees.

Phytotoxicity of single and mixed rare earth element (La, Nd and Sm) exposures on Lactuca sativa seed germination and growth.

The mode of action, bioaccumulation potential and toxicity of Rare Earth Elements (REE), with several applications in the technology, medical and agricultural fields, are still understudied. The nitrates acute effects on single exposures, binary and ternary mixtures of lanthanum (La), neodymium (Nd) and samarium (Sm) on Lactuca sativa lettuce seed germination and wet biomass in an artificial soil (AS) and an Ultisol were assessed. Germination (EC50), wet biomass (IC50) and germination inhibition (% GI) were evaluated. EC50 values show La was the most toxic in Ultisol, Sm in AS, and Nd appears with intermediate values on both substrates. The IC50, both single and mixed, decreased from 3- to 181-fold with increasing test concentrations in relation to the control in AS, while increases in Ultisol were observed, followed by decreases at higher doses which may be associated with the low-dose stimulation effect (hormesis). Our findings may be used to subsidize REE risk assessment studies and reinforce the hormesis effect to prevent the use of high application of REE fertilizers, avoiding the accumulation of REE in agricultural soils.

Native tree promotes invasion when native grasses are absent

Despite the expected co‐occurrence of effects from resident species, the environment, and disturbance on non‐natives, these factors have largely been treated as acting separately. Co‐occurring factors may, however, act in combination to result in a powerful, yet little explored, mechanism of invasion. Here, we addressed three hypotheses to explain the localized invasion of the non‐native Chenopodium album (Chenopodium) under the canopy of the dominant native tree Neltuma caldenia (Neltuma) in central Argentina. First, we evaluated that Neltuma favors Chenopodium by modifying environmental conditions, and specifically assessed the importance of soil versus that of the microclimate created by Neltuma shade. Second, we tested that Neltuma benefits Chenopodium by promoting under its canopy (calden microsite) the dominance of a grass species, Nassella tenuissima (Nassella), that exerts weaker competitive effects on Chenopodium than those exerted by the dominant grass, Piptochaetium napostaense (Piptochaetium), in adjacent communities free of the tree (open microsite). Lastly, we explored that the invasion of Chenopodium is mediated by disturbance. Chenopodium displayed increased biomass and fecundity (performance) in soil from calden relative to that from open microsites, whereas it exhibited no response to shade treatments. Also, Chenopodium performance in pots with Nassella was similar to that in pots with Piptochaetium. Finally, Chenopodium performance was much greater in pots with no initial plants than in those with grasses. Importantly, in pots without plants, Chenopodium performed much better in calden than open microsites, but in pots with grasses, Chenopodium performance exhibited no differences between microsites. These findings suggest that disturbance mediates Chenopodium invasion in calden microsites. Specifically, disturbance may weaken strong competitive effects from native grasses on Chenopodium, allowing this non‐native herb to benefit from favorable soil conditions under Neltuma. The combined action of natives enhancing resource levels and disturbance providing access to them could be a general mechanism of invasion.

Does the presence of mineral nutrient enhance the carbon sequestration, soil aggregation, and microbial biomass in the subtropical clay soil?

Crop residue incorporation is considered as a promising approach for improving carbon sequestration coupling with soil aggregation (MWD). However, better understanding is needed regarding to the mechanism of carbon sequestration and aggregation following crop residue return in subtropical clay soil. A short-term field experiment (1.5 years) was conducted to explore the underlaying potential mechanism of carbon sequestration after crop residues return in the subtropical clay soil. Four treatments were applied as follows: (1) Control, (2) Inorganic fertilization (NPK), (3) Crop residue at 8-ton ha−1, (6) NPK + Crop residue at 8-ton ha−1. MWD, soil organic carbon (SOC), microbial biomass carbon (MBC), glomalin protein (GRSP), mineral and aggregate-associated SOC, and Fe oxides were determined. Results exhibited that the mineral nutrients with or without crop residue enhanced the SOC significantly in comparison to the only straw and control treatments (P < 0.05). The short-term residue return enhanced the MWD compared to the baseline soil, which was less than control due to the greater concentration of amorphous Fe oxides. Moreover, GRSP and MBC were significantly increased upon crop residue return in presence of mineral nutrients treatment (P < 0.01). SOC was reduced in the order of NPK > NPK + Crop residue > Crop residue > control, while MBC and GRSP were increased in the order of control < Crop residue < NPK < Crop residue + NPK. Aggregate-associated and mineral-associated SOC of aggregates were enhanced in presence of mineral nutrients (P < 0.001). Our results suggest that the nutrients addition in presence or absence of crop residue return under short-term field experiment is considered as a promising and sustainable clay soil management approach for enhancing carbon sequestration to mitigate climate change.

Transformation of Biochar from Plant Biomass in Gray Forest Soil: Evaluation by Isotopic Labeling Method

Pyrolysis is considered to be one of promising methods for processing agricultural waste and for producing fertilizers. The efficiency of the resulting biochar as a fertilizer has been proven, but the preferential way of decomposition of organic substances in it—biotic or abiotic—is still open to argument. The ways of transformation of biochar obtained from corn (a plant of the C4 type of photosynthesis with an increased 13C content) were assessed in this work, using the solid-phase CP/MAS 13C NMR spectroscopy. Biochar was placed into the top layer of a monolith of gray forest soil, and the precipitation regime characteristic of Central Russia was simulated for 90 days. The peak at 129 ppm typical for aromatic compounds increased during the experiment in the obtained NMR spectra of soil samples with biochar in the upper soil layer, but not in other layers. This testifies that biochar particles do not migrate down the soil profile during one season. The intensity of cumulative microbial respiration in the presence of biochar increases from 85.0 g CO2 kg–1 in the control sample to 201.4 g CO2 kg–1 in the sample with biochar (the topsoil). According to the NMR spectra of the salt formed during mineralization of carbon dioxide released from the soil, it contains labeled carbon: there is a peak at 169 ppm characteristic of carbonates. The cumulative volume of CO2 released from the soil with biochar is 1.9 times greater as compared to the control soil. The addition of microorganisms-decomposers caused an additional increase in the CO2 volume: 2.4 times relative to the control, which indicates the role of microorganisms in the destruction of soil organic matter and of biochar. However, based on the stability of the total carbon content in the soil, it can be concluded that only a small proportion of biochar components is susceptible to biotic decomposition.

Increasing Ages of Inga punctata Tree Soils Facilitate Greater Fungal Community Abundance and Successional Development, and Efficiency of Microbial Organic Carbon Utilization

Leguminous Inga trees are thought to enhance soil carbon (C) accumulation following reforestation, through mostly unknown mechanisms. This study amplified soil DNA using the ITS1F and ITS4 primers for PCR and Illumina MiSeq methods to identify fungal taxa, and traditional C analysis methods to evaluate how planted 4-, 8-, and 11-year-old Inga punctata trees affected soil fungal community compositions and C utilization patterns compared to old-growth I. punctata trees and an adjacent unplanted pasture within the same reforestation zone in Monteverde, Costa Rica. Along the tree age gradient, the planted I. punctata trees enhanced the tree soil C capture capacity, as indicated by increased levels of soil biomass C, Respiration, and efficiency of organic C use (with lower qCO2 values), and development of increasingly more abundant, stable, and successionally developed fungal communities, including those associated with the decomposition of complex organic C compounds. The level and strength of differences coincided with differences in the time of separation between the pasture and tree age or between the different tree ages. Fungal taxa were also identified as potential indicators of the early and late stages of soil recovery. Thus, planting I. punctata should be part of future reforestation strategies used in this region of the Monteverde Cloud Forest in Costa Rica.

Different seasons and vegetation cover more than fire control nutrient stoichiometry and biological activities in Mediterranean soils

Mediterranean soils are affected by degradation phenomena, exacerbated by anthropic disturbance. These ecosystems are affected by peculiar climatic conditions, characteristic vegetation and frequent fire that with the anthropic activities can compromise soil nutrient status. Studies concerning the nutrients stoichiometry in Mediterranean area are scarce, therefore the present research aim to fill the gap about the effect of seasonal variations, vegetation cover and fire occurrences on soil nutrient balance and microbial biomass and activity. The sampling was performed inside the Vesuvius National Park across 24 sites during two seasons (Fall and Spring), under trees and shrubs and in burned and unburned areas. Soils were characterized for carbon (C), nitrogen (N), phosphorous (P) and potassium (K) concentrations, for bacterial and fungal biomass (Eub and Fungi) and for microbial activities (respiration, hydrolase: HA, dehydrogenase: DHA, β-glucosidase: β-glu and urease: U). The results showed that, both in Fall and Spring, high C:N (18.7), C:P (130) and N:P (6.74) ratios were observed in soils under trees. Both in soils under trees and shrubs, low eubacterial biomass (trees: 90.2 ng g−1 w.w.; shrubs: 44.4 ng g−1 w.w.), respiration (trees: 0.24 mg CO2 g−1 d.w. min−1; shrubs: 0.14 mg CO2 g−1 d.w. min−1) and hydrolase (trees: 37.0 mmol FDA g−1 d.w. min−1; shrubs: 11.9 mmol FDA g−1 d.w. min−1) activities were observed in Spring. Fire effect was evident only in Fall where low values of eubacterial biomass (667 ng g−1 w.w.) and respiration activity (0.60 mg CO2 g−1 d.w. min−1) were observed in burnt soils. In conclusion, the seasonal variations and the vegetation cover appeared the main environmental factors that affect nutrient stoichiometry and microbial biomass and activity in Mediterranean soils. It is necessary to monitor Mediterranean soils during different seasons and encourage the growth of native vegetation to enhance nutrient cycling and maintain soil health.

Intra‐annual dynamics of soil and microbial C, N, and P pools in a Central Amazon Terra Firme forest

AbstractBackgroundTropical ecosystem functioning is influenced by seasonal fluctuations in precipitation, but the impact on soil nutrient cycling and microbial stoichiometry is not fully understood.AimThis study investigates the magnitude of intra‐annual fluctuations in nutrient availability and microbial biomass in a tropical forest soil by examining carbon (C), nitrogen (N), and phosphorus (P) pools.MethodsWe analyzed the total, extractable, and microbial C, N, and P contents and their stoichiometry in Terra Firme Ferralsols, representative for the central Amazon basin.ResultsWe observed intra‐annual variations in resource availability, particularly between wet and dry seasons. Despite relatively stable total C, N, and P stocks throughout the year, we observed a decrease in extractable organic C and available (Olsen) P and an increase in extractable N in the dry season compared to the wet season. Microbial biomass pools and stoichiometry also varied across sampling dates and soil depths: relative to microbial‐C and ‐N, microbial‐P decreased in both wet and dry season and increased in the transition from wet to dry season.ConclusionsOur research highlights intra‐annual variation in nutrient pools, particularly dynamic microbial carbon and nutrient fractions, in weathered tropical forest soils.

Residual effect of biochar on microbial biomass and enzyme activities of soil cultivated with grape varieties: a two -year field assessment

Biochar has received increasing attention as a soil conditioner, being known for its ability to confer numerous benefits to the soil. Derived from the thermal decomposition of organic materials under low levels of oxygen, biochar concentrates essential nutrients and carbon while having low carbon dioxide emissions. Our hypothesis is that biochar applied as a top dressing can improve soil microbial attributes even after two years in a soil cultivated with different grape varieties. To test this hypothesis, we conducted a field experiment using different doses of cashew wood biochar applied to two grape varieties and evaluated its residual effect on microbial biomass and soil enzymatic activities. The design used was a randomized block design, in a 4 x 2 factorial scheme, with five replications: four doses of biochar (0, 5, 10 and 15 ton ha-1) and two grape varieties (Cabernet sauvignon and Malbec). Soil collection was carried out at a depth of 0-20 cm, to evaluate total organic carbon, microbial biomass carbon and soil enzymatic activities. Our findings revealed that the effect of grape varieties on soil biological properties was more pronounced than the biochar dose, indicating that there is a small residual effect of biochar doses after 2 years of application. Overall, our study provides important insights into the residual effect of biochar on soil microbial attributes and is considered an ecologically sustainable alternative, as it solves the problem of waste reuse and provides a disposal that brings benefits to soil properties.

Biomass and Carbon Stock Capacity of Robinia pseudoacacia Plantations at Different Densities on the Loess Plateau

Forests make an important contribution to the global carbon cycle and climate regulation. Caijiachuan watershed false acacia (Robinia pseudoacacia Linn.) plantation forests have been created for 30 years, but a series of problems have arisen due to the irrationality of the density involved at that time. To precisely assess the contribution of R. pseudoacacia plantations with different densities to this cycle, we measured the diameter at breast height (DBH), tree height (H), biomass, and carbon stocks in trees, shrubs, herbs, litter, and soil across different density ranges, denoted as D1 = 900–1400, D2 = 1401–1900, D3 = 1901–2400, D4 = 2401–2900, and D5 = 2901–3400 trees ha−1. In order to achieve the purpose of accurately estimating the biomass, carbon stocks and the contribution rate of each part in different densities of R. pseudoacacia plantations were measured. The results are as follows: (1) Both DBH and H decreased with increasing density, and field surveys were much more difficult and less accurate for H than DBH. Based on the two allometric growth models, it was found that the determination coefficient of the biomass model that incorporated both H and DBH (0.90) closely resembled that of the model using only DBH (0.89), with an error margin of only 0.04%. (2) At the sample scale, stand density significantly affected R. pseudoacacia stem biomass and total biomass. At the individual plant scale, stand density significantly affected R. pseudoacacia organ biomass. Increasing stand densities promoted the accumulation of vegetation biomass within the sample plot but did not improve the growth of individual R. pseudoacacia trees. The stem biomass constituted the majority of the total R. pseudoacacia biomass (58.25%–60.62%); the total R. pseudoacacia biomass represented a significant portion of the vegetation biomass (93.02%–97.37%). (3) The total carbon stock in the sample plots tended to increase with increasing stand density, indicating a positive correlation between density and the carbon stock of the whole plantation forest ecosystem. Hence, in future R. pseudoacacia plantations, appropriate densities should be selected based on specific objectives. For wood utilization, a planting density of 900–1400 trees ha−1 should be controlled. For carbon fixation, an initial planting density of 2900–3400 trees ha−1 should be selected for R. pseudoacacia. This study provides theoretical support for local forest management and how to better sequester carbon.

Once in Three-Year Deep-Banding and Annual Shallow-Banding of P, K and Cu Fertilizer Effects on Crops and Soil Nutrients

Deep-banding of the immobile nutrients (P, K, and Cu) is considered one technique that may improve crop production under temperate dryland systems, where moister soil conditions prevail at seeding followed by relatively drier soil during the growing period. The objectives were to compare growth and yield of canola (Brassica napus L.), field pea&amp;rsquo;s (Pisum sativum L.) and wheat (Triticum aestivum L.); and nutrient concentrations in crops and soil from once in three-year deep-banding (12.5-15 cm) and annual shallow-banding (3.75 to 5 cm diagonally deeper than seeding depth) of P, K and Cu under direct seeding systems. Small plot trials were conducted at the three sites; representing Brown (Dark Brown Chernozem), Black (Black Chernozem), and Grey (Dark Grey Luvisol) soil zones in Alberta, Canada; which represent crop growing conditions for most areas of western Canada. The nine treatments were annual shallow-banding and once in three year deep-banding of P, K, Cu and PKCU nutrients plus a control (no P, K, or Cu fertilizer). Applied thrice the recommended rate for deep-banding (in 2018) treatments and the recommended rate for the annual shallow-banding treatments in 2018, 2019 and 2020. All three phases of pea&amp;rsquo;s-wheat-canola rotation were grown at each site to generate nine years of data for each crop. The density, height, NDVI (normalized difference vegetation index) and biomass of plants, yield for crops and nutrient concentrations in seed and biomass of crops and soil showed significantly positive responses to P, K, and PKCu additions in some cases; generally not linked to the deep or shallow placement of tested nutrients. Changes in nutrient concentrations in seed and biomass of crops in response to nutrient additions were not consistent. Treatments with P showed response more often than with the K and Cu. The soil P and Cu concentrations increased in response to their additions in some cases, but no change was observed from the K addition. Once in three-year deep-banding or annual shallow-banding methods were equally effective. The findings provide another option (once in three year deep-banding) for applying the P, K and Cu fertilizers.

The Effect of Organic and Biofertilizers on Carbon and Nitrogen of Biomass in Soil Seasoned with Broccoli

The Effect of Organic and Biofertilizers on Carbon and Nitrogen of Biomass in Soil Seasoned with Broccoli

Problems of Estimation of Microbial Biomass in Soddy-Podzolic Soils (Forests of the Protected Areas of Moscow Region)

Problems of Estimation of Microbial Biomass in Soddy-Podzolic Soils (Forests of the Protected Areas of Moscow Region)

Assessing the Impacts of land Use Change on Carbon Sequestration: A Comprehensive Analysis for Kochi City, India

Land use typologies play a pivotal role in determining the carbon sequestration capacity of urban ecosystems. Ashuman activities continue to reshape landscapes, understanding the impact of different land uses on carbon storageis crucial for developing effective climate change mitigation strategies for cities. This paper aims to analyse therelationship between land use typologies and carbon sequestration. Carbon sequestered in the selected city i.e., Kochiis quantified using the InVEST Carbon Storage and Sequestration model (Integrated Valuation of Ecosystem Servicesand Tradeoffs), coupled with remote sensing. The model uses input data on carbon pools including above-ground,below-ground, soil biomass, and dead carbon matter. The change in carbon sequestration with change in land usebetween 2003 and 2023 is calculated. The study reveals that there has been a reduction in wetland areas by 59 %which leads to 63% less sequestration of carbon highlighting the implication of land use on carbon sequestration.

Linking nematode trophic diversity to plantation identity and soil nutrient cycling

Ecological services provided by forest plantations depend on soil biodiversity, which encompasses taxonomic and functional diversity. These diversity components may respond specifically to environmental changes with consequences for soil functions. Given the large differences in plant-derived resource input between coniferous and broadleaved plantations, we investigated their impact on nematode species and trophic diversity, and on the soil nutrient cycling. The establishment of plantations (Larix gmelinii, Pinus tabuliformis, and Cercidiphyllum japonicum) 30 years ago led to a 31 %-37 % reduction in nematode species diversity, which is connected with decreased microbial biomass in soil. The reduced species diversity, however, was not linked to the cycling of organic matter, nitrogen, or phosphorus. Coniferous plantations (Larix gmelinii and Pinus tabuliformis) reduced nematode trophic diversity (34 %-55 %), indicating a strong decline in herbivorous and omnivorous-predatory groups of the food webs. This decline was primarily attributed to moisture limitations and reduced litter quality, and decreased nutrient cycling within the coniferous plantations. Conversely, the broadleaved plantation (Cercidiphyllum japonicum) maintained a complex nematode trophic structure with intensive nutrient cycling. Consequently, the trophic functional traits of nematode communities were determined by resource availability and linked to nutrient cycling in soil after plantation establishment.

PENDAMPINGAN MASYARAKAT DESA HUTAN (BINAAN PT. WWI) DALAM PENERAPAN METODE PENGUKURAN CADANGAN KARBON DI DESA WAPSALIT KABUPATEN BURU

Carbon reserves in forests play a crucial role in climate change mitigation and the preservation of global ecosystems. Forests act as primary absorbers of carbon dioxide (CO2) from the atmosphere, storing carbon in the biomass of trees, soil, and leaf litter. This community service aims to provide understanding and education to the public about carbon storage, factors influencing storage capacity, and the implications of sustainable forest management. The methodology used includes direct measurement of carbon reserves in various forest types and the analysis of secondary data from scientific literature. Survey results indicate that the village forest of Wapkalit still has significant potential, emphasizing the need for community awareness to continue managing and preserving the forest. Socialization conducted through the FGD (Focus Group Discussion) method can directly impart knowledge to the community.

Co-application of Green Manure and Trichoderma spp. Induced Plant Growth Promotion by Nutrient Improvement and Increased Fungal Biomass in Soil

Co-application of Green Manure and Trichoderma spp. Induced Plant Growth Promotion by Nutrient Improvement and Increased Fungal Biomass in Soil

The relationship between soil biomass and soil quality index for Kafr El-Dawar region, Beheira Governorate

The current investigation was conducted in the Kafr El-Dawar region to study the relationship between soil microbial biomass and soil quality index. Thirty-nine soil samples were taken for the chemical characteristics used to determine the soil quality index by the Soil Management Assessment Framework (SMAF) procedures. Pearson correlation relationship and Principal components analysis (PCA) between soil quality index and soil parameters were done as well as regression between soil quality index and microbial biomass. For the soil microbial biomass, the lowest value was about 186 mg kg-1 (5% of the total samples). The highest value was about 387 mg kg-1 (5% of the total samples). The average microbial biomass of the samples was about 299 mg kg 1. Approximately 50% of the total samples have a value equal to the average sample value. Higher significant correlation was observed among soil pH with CaCO3 content. Significant correlation was observed among soil pH with Fe and Mn. Soil quality index had a higher significant correlation with Ca, Mg, N, K, Cu, and Zn. P was a more effective factor on soil quality index. The chemical properties had the most impact on the soil quality index. All samples have a soil quality index score of less than 50%. About 69.2% were poor quality (SQI less than 40%), and the rest were moderate quality (SQI between 40 and 60%). Microbial biomass is a key soil characteristic that influences soil quality according to the regression result. Further research should include biological and other physicochemical soil properties to enlarge soil quality index.

Aggregate stability and carbon and N dymamics in macroaggregate size fractions with different soil texture

Soil nutrient cycling, the distribution of soil aggregates, and their stability are directly influenced by soil texture. Different sizes of soil aggregates provide microhabitats for microorganisms and therefore influence soil carbon (C) and nitrogen (N) mineralization. The purpose of the present study was to assess the aggregate stability and dynamics of carbon and nitrogen in macroaggregate size fractions (1-8 mm) with different clay content from meadow soils. Surface soil samples (0-15 cm) were collected from 4- to 5-year-old forage crops. Four macroaggregate size classes were isolated by dry sieving and analyzed for their mass proportions: fine macroaggregates (FM) (less than 1 mm), medium-fine macroaggregates (MFM) (1-2 mm), medium-coarse macroaggregates (MCM) (2-4 mm), and large-coarse macroaggregates (LCM) (4-8 mm). The dry mean weight diameter (MWD), organic carbon (OC), total nitrogen (TN), carbon and nitrogen of microbial biomass (C-MB, N-MB) were determined. CO2 emission and net nitrogen mineralized (NM) were measured after 14 weeks of incubation. The amounts of FM were significantly lower than those of intermediate macroaggregates (MCM and MFM) and decreased markedly with increasing clay content within soil macroaggregates. In general, the amounts of macroaggregate size fractions were lowest in soils with high clay content. MWD exhibited a significant correlation with particle size distribution, OC, and MB-C. OC, TN, MB-C, and MB-N contents within macroaggregates increased with decreasing macroaggregate size and increasing clay content of macroaggregate fractions. The CO2 emission and NM content increased with increasing macroaggregate size, indicating higher organic C and N mineralization activity in larger macroaggregates. Mineralization of OC was lowest in macroaggregate fractions with the highest clay content. We conclude that clay content can increase the protection of microbial biomass in meadow soils. Small macroaggregates tend to contain more recalcitrant organic matter compared to larger macroaggregates.