Organic Nitrogen Content Research Articles

Influence of landscape patterns on nitrate and particulate organic nitrogen inputs to urban stormwater runoff

This study investigated the effect of the landscape pattern of permeable/impermeable patches on NO3−-N and particulate organic nitrogen (PON) concentrations during stormwater runoff transport and their source contributions. Six landscape pattern indices, namely, mean proximity index (MPI), largest patch index (LPI), mean shape index (MSI), landscape shape index (LSI), connect index (CONNECT), and splitting index (SPLIT), were selected to reflect the fragmentation, complexity, and connectivity of permeable patches in urban catchments. The results show that lower fragmentation, higher complexity, and greater connectivity can reduce NO3−-N concentrations in road runoff and drainage flow (i.e., the flow in the stormwater drainage network), as well as PON concentrations in road runoff. Further, the above landscape pattern is effective for mitigating the contributions of NO3--N and PON from road runoff. Low impact development (LID) can be incorporated with the landscape pattern of permeable/impermeable patches to mitigate nitrogen pollution in urban stormwater at the catchment scale by optimizing the spatial arrangement.

Effects of Long-term Tillage on Soil Bacterial Community Structure and Physicochemical Properties of Dryland Wheat Fields in Northern China

To explore the effects of long-term tillage on bacterial community structure in different soil layers of dryland wheat fields and its relationship with soil physicochemical properties, a long-term field experiment was conducted from 2016 to 2021 in Wenxi Experimental Demonstration Base of Shanxi Agricultural University, Shanxi Province. We studied the effects of no-tillage (NT), subsoiling-tillage (ST), and deep plowing (DP) on soil physicochemical properties; α and β diversity of the bacterial community; and dominant and different species of phyla and genera in different soil layers. Additionally, PICRUSt2 was used to predict the metabolic function of soil bacterial community. The results revealed that subsoiling-tillage and deep plowing significantly increased the soil water content in the 20-40 cm soil layer and significantly decreased the soil organic carbon content in the 0-20 cm soil layer compared with that under no-tillage for five consecutive years. Compared with that under deep plowing, subsoiling-tillage significantly increased soil water content, soil organic carbon content, dissolved organic carbon content, and dissolved organic nitrogen content in the 0-20 cm soil layer. Compared with that under no-tillage, subsoiling-tillage and deep plowing increased the α diversity of the soil bacterial community in the 0-40 cm soil layer, and subsoiling-tillage was higher than deep plowing. Compared with that under no-tillage, subsoiling-tillage and deep plowing significantly increased the relative abundances of Acidobacteria and Nitrospirae in the 0-20 cm soil layer and Acidobacteria, Chloroflexi, Gemmatimonadetes, Rokubacteria, GAL15, and Nitrospirae in the 20-40 cm soil layer. Compared with that under no-tillage, subsoiling-tillage and deep plowing significantly increased the relative abundance of Nitrospira in the 0-20 cm soil layer and Rubrobacter and Streptomyces in the 20-40 cm soil layer. Compared with that under deep plowing, subsoiling-tillage significantly increased the relative abundance of Acidobacteria and Gemmatimonadetes in the 0-40 cm soil layer. Redundancy analysis demonstrated that the contents of soil organic carbon, dissolved organic carbon, and dissolved organic nitrogen in the 0-20 cm soil layer exerted positive effects on Actinobacteria and Blastococcus, and the soil water content in the 0-40 cm soil layer exerted positive effects on Acidobacteria, Chloroflexi, and Gemmatimonadetes under subsoiling-tillage. The results of PICRUSt2 prediction showed that subsoiling-tillage and deep plowing significantly increased the relative abundance of amino acid metabolism and the metabolism of cofactors and vitamins but decreased the relative abundance of lipid metabolism of bacterial communities in the 20-40 cm soil layer compared with that under no-tillage. Compared with that under deep plowing, subsoiling-tillage significantly increased the relative abundances of amino acid metabolism in the 0-40 cm soil layer and other amino acid metabolism in the 0-20 cm soil layer. In conclusion, subsoiling-tillage or deep plowing could increase the soil water content, α diversity of the soil bacterial community, and their metabolic capacity in the dryland wheat fields during the summer fallow period. The relative abundance of Acidobacteria and Gemmatimonadetes and the ability of amino acid metabolism of the bacterial community were increased by subsoiling-tillage, and thus the contents of soil dissolved organic carbon and dissolved nitrogen can be increased.

EFFICIENCY OF UTILIZATION OF ORGANIC SUBSTANCES PRODUCED FROM ORGANIC WASTE ON ORDINARY CHERNOZEM

The authors presented in the article the results of studying the effect of solid and liquid organic fertilisers obtained at their installation and when composting from agricultural waste on spring wheat yield and quality in a laboratory experiment on ordinary chernozems of the Orenburg region. The effectiveness of using the obtained substances as liquid and solid organic fertilisers was assessed. The authors substantiated that according to all options for studying the norms and types of organic fertilisers in the soil, the content of organic matter, ammonium nitrogen, mobile phosphorus and potassium increased. The data on the green mass of spring wheat for all research options in the laboratory experiment are given. It has been established that when liquid organic fertilisers are applied to the soil, ammonium nitrogen is highly mobile and available to plants, so plants become taller at the initial vegetation stage. The authors determined the lower efficiency of applying solid organic fertilisers in short-term laboratory studies. As a result, it has been established that 4 t/ ha for solid organic fertilisers and 8 t/ha for liquid organic fertilisers is the most effective. With such a rate of application of liquid organic fertilisers, the germination of spring wheat reaches 98.7%, and the yield of green mass of plants increases by three times compared to the control. In addition, the trend of the highest efficiency of applying liquid organic fertilisers compared to solid ones was noted.

Responses of wheat nitrogen uptake and utilization, rhizosphere bacterial composition and nitrogen-cycling functional genes to nitrogen application rate, planting density and their interactions

The nitrogen application rate and planting density affect soil physiochemical properties, plant physiological characteristics, and soil bacterial community composition. In this study, a two-factor randomized block design was adopted with two planting density levels (high density, HD and low density, LD), and three nitrogen application rate levels (no nitrogen application, N0, low nitrogen application, LN and high nitrogen application, HN). The results showed that the highest yield was produced by LDHN and HDLN, while HDLN had the highest nitrogen use efficiency. Root dry weight was highest in HDHN, followed by HDLN, LDHN and LDLN, while the root nitrogen content was highest in LDHN and HDLN. In the 0–20 cm soil, LDLN had the highest pH and lowest nitrate nitrogen content, HDHN had the lowest pH, and HDLN had the highest content of soluble organic nitrogen and free amino acids. In addition, compared to LDHN, the bacterial community in HDLN and LDLN had higher α diversity and a higher relative abundance of functional genes involved in nitrate reduction. However, HDHN was the opposite. Additionally, correlation analysis also found that the abundance of some bacterial modules was significantly correlated with wheat nitrogen partial factor productivity. Overall, nitrogen application rates and planting density, through changing the physicochemical properties of rhizosphere soil, bacterial composition and function, and wheat root physiological properties, changed the nitrogen utilization and yield of wheat.

Inoculation of cold-adapted microbial consortium screened from alpine meadows promotes the growth of mixed grasses by changing soil properties and enzyme activity

The objective of this study was to investigate the effect of co-inoculation of three PGPR strains and inoculation ratio on the growth characteristics and soil properties of mixed grasses. In this study, we used 3 strains of PGPR for the material, which were Acinetobacter calcoaceticus called HMAJ1, Pseudomonas piscium called HMAJ5, and Pseudarthrobacter psychrotolerans called NCZ1, with nitrogen fixation and phosphorus solubilization ability. By mixing the bacteria in a different ratio, the effect of inoculating with a microbial consortium on the plant and soil properties of mixed grasses (Elymus nutans Griseb, Festuca sinensis, and Poa pratensis L.) was evaluated and the best microbial inoculants ratio was selected. The results showed that inoculating with a microbial consortium increased the soil organic carbon , available phosphorus, ammonium and nitrate nitrogen content, and the activities of soil alkaline phosphatase, sucrase, peroxidase, and urease, which promoted the plant height and biomass of mixed grasses. Pearson correlation analysis showed that plant characteristics were differently correlated with soil properties. Grey correlation analysis of plant biomass, soil properties, and soil enzyme activity revealed that T7 (HMAJ1:NCZ1 = 3:7) was the most effective in improving mixed-grasses biomass and soil quality. Our results indicated that the positive interaction of nitrogen-fixing bacteria with phosphorus-solubilizing strains may become a novel and effective bio-inoculant to achieve sustainable pulse productivity.

Effect of ocean warming on pigment and photosynthetic carbon fixation of plankton assemblage in Pingtan Island of Southeast China

Temperature plays an important role in affecting the physiological traits of marine plankton. In this study, we conducted an outdoor incubation experiment to investigate the effects of elevated temperature on Chl a, photosynthetic carbon fixation and the composition of plankton communities in the surface seawater around Pingtan Island, the northwest Taiwan Strait in Autumn 2022. After 3–4 days of incubation, elevated temperature (1–4 °C higher than ambient temperature) led to a decrease in Chl a concentration across all three stations, did not result in significant increases in the particulate organic carbon (POC) and nitrogen (PON) concentrations in seawater with high nitrate concentrations, whereas increased POC and PON concentrations in nitrate-limited seawater. These findings suggest that the effect of temperature on the POC and PON contents of plankton is affected by the availability of nitrate. Diatoms were the dominant phytoplankton group in all three stations. Our results indicate that ocean warming has a potential to increase the POC contents of marine plankton per volume of seawater, which may increase the ability of phytoplankton to absorb atmospheric CO2 and to alleviate global warming.

The importance of transparent exopolymer particles over ballast in determining both sinking and suspension of small particles during late summer in the Northeast Pacific Ocean

Gravitational sinking of particles is a key pathway for the transport of particulate organic carbon (POC) to the deep ocean. Particle size and composition influence particle sinking velocity and thus play a critical role in controlling particle flux. Canonically, sinking particles that reach the mesopelagic are expected to be either large or ballasted by minerals. However, the presence of transparent exopolymer particles (TEP), which are positively buoyant, may also influence particle sinking velocity. We investigated the relationship between particle composition and sinking velocity during the Export Processes in the Ocean from RemoTe Sensing (EXPORTS) campaign in the Northeast Pacific Ocean using Marine Snow Catchers. Suspended and sinking particles were sized using FlowCam for particle imaging, and their biogeochemical composition was assessed by measuring the concentration of particulate organic carbon (POC) and nitrogen, particulate inorganic carbon, biogenic and lithogenic silica, and TEP. Sinking fluxes were also calculated. Overall, both suspended and sinking particles were small (<51 μm, diameter) in this late summer, oligotrophic system. Contrary to expectation, the ratio of ballast minerals to POC was higher for suspended particles than sinking particles. Further, suspended particles showed TEP-to-POC ratios three times higher than sinking particles. These ratios suggest that TEP content and not ballast dictated whether particles in this system would sink (low TEP) or remain suspended (high TEP). Fluxes of POC averaged 4.3 ± 2.5 mmol C m−2 d−1 at 50 m (n = 9) and decreased to 3.1 ± 1.1 mmol C m−2 d−1 at 300–500 m (n = 6). These flux estimates were slightly higher than fluxes measured during EXPORTS with drifting sediment traps and Thorium-234. A comparison between these approaches illustrates that small sinking particles were an important component of the POC flux in the mesopelagic of this late summer oligotrophic system.

The effect of catchment load reductions on water quality in the crown-of-thorn starfish outbreak initiation zone

Crown-of-Thorns Starfish (CoTS) population outbreaks contribute to coral cover decline on Indo-Pacific reefs. On the Great Barrier Reef (GBR), enhanced catchment nutrient loads are hypothesised to increase phytoplankton food for CoTS larvae in the outbreak initiation zone. This study examines whether catchment load reductions will improve water quality in this zone during the larval period. We defined the i) initiation zone's spatial extent; ii) larval stage's temporal extent; and iii) water quality thresholds related to larval food, from published information. We applied these to model simulations, developed to quantify the effect of catchment load reductions on GBR water quality (Baird et al., 2021), and found a consistently weak response of chlorophyll-a, total organic nitrogen and large zooplankton concentrations in the initiation zone. Model results indicate marine and atmospheric forcing are more likely to control the planktonic biomass in this zone, even during major flooding events purported to precede CoTS outbreaks.

Selected Properties of Soil-like Substrates Made from Mine Coal Waste and Their Effect on Plant Yields

To reduce the environmental damage caused by coal waste landfills, it is necessary to look for rational methods for their management. One method for their development is the creation of soil-like substrates. This study aimed to assess the properties of soil-like substrates from coal mining waste, combined with a varied sample of sewage sludge and waste mineral wool. The properties of the substrates were evaluated in a pot experiment. The properties of the substrates and their yield potential were determined. Coal mining waste as a substrate, compared to anthropogenic soil, was characterized by a significantly higher sorption capacity; the content of alkaline cations and pH; significantly higher contents of organic carbon, nitrogen, and available forms of K and Mg; and a lower content of available P. The substrates enriched with sewage sludge showed a significant increase in content of organic carbon, nitrogen, and assimilable forms of P and Mg, as well as the optimization of sorption properties. Extending the composition of substrates with mineral wool resulted in further improvement of their properties. The yields of plants grown on coal mining waste were significantly lower than those of those grown on anthropogenic soil. Substrates with sewage sludge and mineral wool had a significantly higher yield potential.

Dissolved organic matter movements from forests influence downstream soil CO2 flux during thawing

Soil CO2 flux is critical for atmospheric carbon emissions and is highly influenced by soil respiration. Dissolved organic matter (DOM) from upland forests can transport to downstream wetlands and then influence soil respiration during thawing. Current studies have mainly focused on a uniform forest or wetland, whereas the soil CO2 flux changing characteristics affected by watershed DOM movements within the forest wetland catchment during thawing are rarely understood. In this study, the in situ measurement, field sampling, and multiple analysis methods were adopted. First, the soil CO2 flux and soil respiration rates were acquired by eddy covariance tower and portable greenhouse analyzer, respectively. The higher soil CO2 flux occurred during thawing might be partly attributed to the bursts of stored CO2. Then, the relationship between dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentrations in water samples, and soil CO2 flux was analyzed by linear regression analysis. DOM from forests can be transported to downstream wetlands via surface runoff, and then promotes soil CO2 flux during thawing. Finally, the soil microbial abundances near the in situ measured sites of forests and wetlands were also compared with the corresponding soil respiration rates. LMWs contains in DOM inputs may influence soil respiration rates by altering soil microbial abundance. Overall, watershed DOM movement from forests can influence downstream soil CO2 flux during thawing in which microbes might exert effects via altering soil respiration rates.

Organic Amendments promote saline-alkali soil desalinization and enhance maize growth.

Secondary soil salinization in arid and semi-arid regions is a serious problem that severely hampers local agricultural productivity and poses a threat to the long-term sustainability of food production. the utilization of organic soil amendments presents a promising approach to mitigate yield losses and promote sustainable agricultural production in saline-alkali soil. In this study, we established four distinct treatments, chemical fertilizer (CK), humic acid with chemical fertilizer (HA), carboxymethyl cellulose with chemical fertilizer (CMC), and amino acid with chemical fertilizer (AA), to elucidate their respective impacts on the reclamation of saline soil and the growth of maize. The findings of our study reveal notable variations in desalination rates within the 0-40 cm soil layer due to the application of distinct soil amendments, ranging from 11.66% to 37.17%. Moreover, application of amendments significantly increased the percentage of soil macro-aggregates as compared to the CK treatment. Furthermore, HA and AA treatments significantly augmented soil nutrient content (HA: 48.07%; AA: 39.50%), net photosynthetic rate (HA: 12.68%; AA: 13.94%), intercellular CO2 concentration (HA: 57.20%; AA: 35.93%) and maize yield (HA:18.32%; AA:16.81%). Correlation analysis and structural equation modeling unveiled diverse mechanisms of yield enhancement for HA, CMC, and AA treatments. HA enhanced yield by increasing organic matter and promoting soil aggregate formation, CMC improved soil water content and facilitated salt leaching due to its excellent water-holding properties, while AA increased yield by elevating soil organic matter and effective nitrogen content. Among the array of soil amendment materials scrutinized, HA treatment emerged as the most promising agent for enhancing soil conditions and is thus recommended as the preferred choice for treating local saline soils.

The effects of Eisenia fetida and Metaphire guillelmi on the soil micro-food web in a microcosm experiment.

Numerous studies have shown that the function of earthworms may depend on their ecotype and density, which affects how they impact soil microbial and nematode communities. However, it is unclear how different earthworm species and densities alter the composition of soil microbial and nematode communities and how these modifications impact the soil micro-food web. The structural equation model (SEM) is a more accurate tool for identifying the intricate relationships between various trophic levels in the soil micro-food webs than the widely used bivariate data analysis. In order to ascertain the effects of earthworm species, including epigeic earthworm Eisenia fetida and anecic earthworm Metaphire guillelmi, as well as varying densities on the composition of main microbial groups, soil nematodes and their relationships, a microcosm experiment was conducted in a greenhouse. After nine weeks of observation, compared with the control treatments, Eisenia fetida increased the biomasses of total microorganism and bacteria, whereas Metaphire guillelmi decreased the biomasses of total microorganism, bacteria, and gram-positive bacteria, but showed an increase in AMF biomass. Additionally, both two earthworm species decreased the abundance of total soil nematode, bacterivores, and omnivore-predators, which is in contrast with the control treatments. The SEM results indicated that the addition of Eisenia fetida at different densities had indirect negative effects on the abundance of omnivore-predators, as it significantly increased the content of soil organic carbon, ammonium nitrogen, and nitrate nitrogen. The bottom-up effects were found to be the dominant forces, which promoted bacterial-dominated decomposition channels. The addition of Metaphire guillelmi with different density had direct negative impact on bacterivores and fungivores. Moreover, it had indirect negative effects on omnivore-predators by altering the soil properties. The dominant forces were still the bottom-up effects. Our study suggests that different earthworm species have distinct mechanisms that affect the soil micro-food web in different ways.

Contrasting response of soil microbiomes to long-term fertilization in various highland cropping systems

Soil microbiomes play important roles in supporting agricultural ecosystems. However, it is still not well-known how soil microbiomes and their functionality respond to fertilization in various cropping systems. Here we examined the effects of 36 years of phosphorus, nitrogen, and manure application on soil bacterial communities, functionality and crop productivity in three contrasting cropping systems (i.e., continuous leguminous alfalfa (AC), continuous winter wheat (WC), and grain-legume rotation of winter wheat + millet - pea - winter wheat (GLR)) in a highland region of China’s Loess Plateau. We showed that long-term fertilization significantly affected soil bacterial communities and that the effects varied with cropping system. Compared with the unfertilized control, fertilization increased soil bacterial richness and diversity in the leguminous AC system, whereas it decreased those in the GLR system. Fertilization, particularly manure application, enlarged the differences in soil bacterial communities among cropping systems. Soil bacterial communities were mostly affected by the soil organic carbon and nitrogen contents in the WC and GLR systems, but by the soil available phosphorous content in the AC system. Crop productivity was closely associated with the abundance of fertilization-responsive taxa in the three cropping systems. Our study highlights that legume and non-legume cropping systems should be disentangled when assessing the responses of soil microbial communities to long-term fertilizer application.

Fog and rain water chemistry in a tea plantation of northern Taiwan.

Tea plantations are expanding globally and many are in mountainous areas with frequent fog but few studies have examined fog chemistry in these areas. We examined chemical composition of fog and rain water at a tea plantation in northern Taiwan. Fog water was collected using a Kroneis passive cylindrical fog-water collector and rain water was collected using a 20-cm-diameter funnel. The most abundant ions were Cl- and Na+ in both fog and rain waters due to the proximity of the site to the coast. The order of abundance of other ions was NO3- > Mg2+ > SO42- > Ca2+ > NH4+ > K+ > H+ in fog water and SO42- > K+ > NO3- > NH4+ > Ca2+ > Mg2+ > H+ in rain water. The concentration enrichment ratio (fog to rain) ranged between 2.2 (K+) and 22 (Mg2+) lying between sites near major emission sources and sites in remote areas, possibly because the immediate surrounding landscape is covered with secondary forests although it is near large cities. Factor analysis highlights the influences of sea-salt aerosols on the variation of fog and rain water chemistry. Sea-salt corrections using Na+ as the sea salt tracer led to negative concentrations of Cl- and Mg2+ suggesting that assumptions involved in sea-salt corrections were not satisfied. Agriculture influence is identified as a unique factor for explaining variance of K+, NH4+, and dissolved organic nitrogen (DON) concentrations in fog water but not rain water. Ion concentrations in fog and rain water were generally higher in the weekly samples associated with air trajectories passing through the continental East Asia than those associated with oceanic trajectories pointing to the role of regional pollution sources in affecting local fog and rain water chemistry. Our study highlights greater effects of tea agriculture on fog than rain water chemistry.

Response of soil microbial community diversity to continuous cucumber cropping in facilities along the Yellow River irrigation area.

Cucumber is an important cash crop; however, continuous cropping obstacles readily occur within the intensive production processes of facility horticulture. This study aimed to determine the effects of continuous cropping on soil quality and the microbial community in the rhizosphere soil of cucumbers. Rhizosphere soil of cucumber planted continuously for 4, 8, and 12 years was investigated, and soil that was not continuously planted was used as the control. Soil physicochemical properties, enzyme activity, microbial diversity, and richness were determined. The results showed that with the increase in continuous cropping years (0, 4, 8, and 12 years), soil total salt content continuously increased, while the pH value significantly decreased. Compared with the control, soil organic matter, alkali-hydrolyzed nitrogen, available phosphorus, available potassium, and nitrate nitrogen contents increased significantly after 4 and 8 years of continuous cropping. Spearman correlation analysis showed that pH was negatively correlated with sucrase or sucrose and available phosphorus was positively correlated with alkaline phosphatase. Compared with the control, the diversity and abundance of bacterial and fungal communities in cucumber rhizosphere soil decreased after 4 and 12 years of continuous cropping. Continuous cropping led to a significant increase in the richness of the dominant phylum of cucumber rhizosphere soil. Principal coordinates analysis showed that, compared with the control, the soil microbial community structure was significantly separated after 4, 8, and 12 years of continuous cropping, and the microbial community structure was most similar after 4 and 8 years of continuous cropping. In addition, redundancy analysis showed that pH was the main driver of soil microbial dominance. In conclusion, continuous cropping of cucumber along the Yellow River irrigation area has led to the deterioration of soil nutrients and microbial communities in that region. This experiment provides a theoretical foundation for addressing the challenges associated with continuous cropping in cucumber cultivation.

Soil organic nitrogen content and composition in different wetland habitat types along the south-east coast of China

Soil organic nitrogen (SON) turnover regulates soil nitrogen (N) storage and availability. The coastal mudflats (MFs) in China have undergone drastic transformation due to invasive Spartina alterniflora (SAs) and subsequent reclamation of Spartina marshes to create aquaculture ponds (APs), but the impact on the amounts and compositions of soil nitrogen remains unclear. This study measured the topsoil total nitrogen (STN) and organic nitrogen (SON) compositions in 21 coastal wetlands in southeastern China. Results show that conversion of MFs to SAs increased STN by 38.5%, whereas subsequent conversion to APs decreased it by 16.4%, and the effect was consistent across the broad geographic and climate gradients. Most of the change occurred in the non-acid-hydrolysable fraction of SON, which accounted for 32–42% of STN. Within the acid-hydrolysable fraction, amino acid N, ammonia N and amino sugar N together accounted for about 57%, with the remaining 43% unidentified chemically. Our results suggest that invasion by S. alterniflora was the overwhelming driver to increase bioavailability of nitrogen and related biogeochemical processes in coastal soil, and the effects were partly reversed in subsequent reclamation of Spartina marshes to create aquaculture ponds.

Effects of thaw slump on soil bacterial communities on the Qinghai-Tibet Plateau

The rapid permafrost degradation caused by climate warming can lead to thermokarst development, which in turn greatly alter soil parameters and impact the soil bacterial communities. However, the effects of thermokarst development on soil bacterial communities largely remain unclear. Here we selected a typical thaw slump in the Qinghai-Tibet Plateau. We classified three microfeatures in the thaw slump areas, i.e., control, slumping and exposed and collected surface 30 cm soils at a depth interval of 10 cm using a soil auger. The results showed that thaw slump decreased soil carbon and nitrogen contents especially for the topsoil (0–10 cm). Thaw slump increased the relative abundance of Gemmatimonadaceae, but decreased the relative abundance of Micrococcaceae. The richness indices including OTU numbers, Ace, Chao 1 and Simpson indices were the largest in the exposed area and lowest in the slumped area, and these trends were opposite to the Shannon index. Correlation analysis revealed that the relative abundance of Micrococcaceae was negatively correlated with moisture, Anaerolineaceae was positively correlated with organic carbon content. The Nitrospira, RB41 and Gemmatimonadaceae were negatively associated with total nitrogen, but Anaerolineaceae and JG30-KF-CM45 were positivity correlated with total nitrogen. C/N ratio was positively correlated with RB41 but negatively correlated with JG30-KF-CM45. We concluded that soil organic carbon, total nitrogen and C/N ratio were the most important factors shaping the bacterial community structure among the three microfeatures. The bacterial community diversity was the highest in the exposed area and lowest in the slumping area. The bacterial structure community was related with total nitrogen, soil organic carbon contents and C/N ratios. Overall, our findings showed thaw slump can decrease soil organic carbon and nitrogen content for the surface soils in the alpine meadow and further change the soil bacterial communities.

Effect of Different Soil Treatments on Production and Chemical Composition of Essential Oils Extracted from Foeniculum vulgare Mill., Origanum vulgare L. and Thymus vulgaris L.

The aim of the study was to investigate how essential oil production and associated chemical composition and related biological activity could be influenced by different cultivation treatments and distillation methods. Foeniculum vulgare Mill. (fennel), Origanum vulgare L. (oregano) and Thymus vulgaris L. (thyme) were cultivated in absence of any fertilizer (control) and in presence of three different fertilizers: a chemical one with augmented mineral phosphorus and potassium, a second added with hydrolyzed organic substance and mineral phosphorus and potassium (organic-mineral) and a third one treated with a high content of organic nitrogen of protein origin (organic). The plants were subjected to steam distillation using two modalities, recycled and continuous, to obtain 32 essential oil samples. Chemical composition analysis was performed using gas chromatography-mass spectrometry; in vitro antimicrobial activity was evaluated using a broth microdilution method. In general, the recycled distillation method appeared to have a slightly higher yield than the continuous method. The "mineral" and "organic-mineral" treatments resulted in a higher yield compared to the "organic" or "control" treatments, and this was particularly evident in the recycled method. The "control" plants had a lower yield of essential oils. Anethole (13.9-59.5%) and estragole (13.4-52.2%) were the main constituents of the fennel oils; p-cymene and its derivatives carvacrol and thymol were the main constituents of the oregano and thyme samples. The antimicrobial activity of the thyme oils on Staphylococcus aureus ranged from 0.31 to 0.16% (v/v); a lower effect of the oregano samples and no activity of the fennel samples were observed. The essential oils failed to inhibit the growth of Pseudomonas aeruginosa strains.

Response of Strawberry Fruit Yield, Soil Chemical and Microbial Properties to Anaerobic Soil Disinfestation with Biochar and Rice Bran

Organic materials added to soil create anaerobic conditions that can reduce soil-borne pathogens that reduce the yield and quality of agricultural crops. Anaerobic soil disinfestation (ASD) requires relatively large quantities of readily available, inexpensive organic materials. We evaluated the impact of ASD with rice bran and biochar organic materials on changes to the soil’s physicochemical properties, microbial taxa, and strawberry fruit yield. We found that the organic materials applied at different dose rates significantly increased the control effect of the soil Fusarium spp. and Phytophthora spp. to 69–99% and 63–98%, respectively. In addition, ASD significantly increased soil organic matter and ammonium nitrogen contents. Strawberry yield also increased significantly after ASD treatment with biochar applied at 10 t/ha, which was positively correlated with increased soil nutrients and a significant reduction in pathogens. High-throughput gene sequencing showed that ASD significantly increased the abundance of some beneficial microorganisms such as Bacillus, Pseudomonas, and Mortierella, possibly due to changes in the soil’s physicochemical properties that favored their survival. We found for the first time that biochar applied at 10 t/ha could create anaerobic conditions that effectively reduced soil-borne pathogens and increased crop yield.

Medium-term associations of soil properties and plant diversity in a semi-arid pine forest after post-wildfire management

The medium- and long-term studies about the effectiveness of post-fire management techniques on soil and plant ecology are scarce, although the effects of wildfire and subsequent management can be long lasting. This study has evaluated the changes in the main physico-chemical properties of soil and plant diversity six years after a wildfire and post-fire treatments using contour felled log debris (CFD) and log erosion barriers (LEB) in a Mediterranean pine forest in comparison to unburnt (UB), and burnt but untreated (BNA) sites. Soil texture and pH did not generally change after wildfire and treatments, while organic matter and nutrients were significantly different between the treated soils and the other sites. Herbaceous plants were found only in UB and LEB sites, the latter showing the lowest number of tree species. Shrubs were equally distributed among the four soil conditions. Resprouting and germinating plants increased in the treated sites compared to BNA area, which however showed a higher number of facultative resprouters. The analysis of relationships between soil properties and plant diversity showed that, when organic matter (CFD plots) and nitrogen (LEB plots) contents are noticeably higher compared to BNA soils, more resprouting species are detected. Moreover, significant increases in pH (UB and BNA plots) and organic matter (CFD plots) are associated to more abundant tree and herbaceous species. The study also indicates to forest managers the most resilient plant species after post-fire restoration several years after a wildfire under Mediterranean conditions.