Seed germination and seedling growth response of Leymus chinensis to the allelopathic influence of grassland plants.

Allelopathy has a profound impact on the germination and growth of plants, influencing the establishment of plant populations and shaping community ecological patterns. However, the allelopathic potential of many grassland species remains poorly understood. In this study, we prepared aqueous extracts from 17 herbaceous plants to investigate their allelopathic effects on the seed germination and seedling growth of Leymus chinensis, a dominant grassland species. Our results revealed that the response of L. chinensis to allelopathic compounds was dependent on the specific plant species, extract concentration, and target plant organ. Notably, Fabaceae plants exhibited a stronger allelopathic potential than Poaceae, Asteraceae, and other plant families. Moreover, we observed that root growth of L. chinensis was more sensitive to allelopathy than shoot growth, and seed germination was more affected than seedling growth. Generally, the germination of L. chinensis was strongly inhibited as the donor plant extract concentration increased. The leachate of Fabaceae plants inhibited the seedling growth of L. chinensis at concentrations ranging from 0.025 to 0.1 g mL-1. On the other hand, the leachate from other families' plants exhibited either inhibitory or hormetic effects on the early growth of L. chinensis, promoting growth at 0.025 g mL-1 and hindering it at concentrations between 0.05 and 0.1 g mL-1. These findings highlight the significant allelopathic potential of grassland plants, which plays a critical role in establishing plant populations and associated ecological processes. In addition, they shed light on the coexistence of other plants with dominant plants in the community.

Soil properties and fungal community jointly explain N2O emissions following N and P enrichment in an alpine meadow.

Nutrient enrichment, such as nitrogen (N) and phosphorus (P), typically affects nitrous oxide (N2O) emissions in terrestrial ecosystems, predominantly via microbial nitrification and denitrification processes in the soil. However, the specific impact of soil property and microbial community alterations under N and P enrichment on grassland N2O emissions remains unclear. To address this, a field experiment was conducted in an alpine meadow of the northeastern Qinghai-Tibetan Plateau. This study aimed to unravel the mechanisms underlying N and P enrichment effects on N2O emissions by monitoring N2O fluxes, along with analyzing associated microbial communities and soil physicochemical properties. We observed that N enrichment individually or in combination with P enrichment, escalated N2O emissions. P enrichment dampened the stimulatory effect of N enrichment on N2O emissions, indicative of an antagonistic effect. Structural equation modeling (SEM) revealed that N enrichment enhanced N2O emissions through alterations in fungal community composition and key soil physicochemical properties such as pH, ammonium nitrogen (NH4+-N), available phosphorus (AP), microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN)). Notably, our findings demonstrated that N2O emissions were significantly more influenced by fungal activities, particularly genera like Fusarium, rather than bacterial processes in response to N enrichment. Overall, the study highlights that N enrichment intensifies the role of fungal attributes and soil properties in driving N2O emissions. In contrast, P enrichment exhibited a non-significant effect on N2O emissions, which highlights the critical role of the fungal community in N2O emissions responses to nutrient enrichments in alpine grassland ecosystems.

Drought is threatening plant growth and soil nutrients of grassland ecosystems: A meta-analysis.

As a widespread direct effect of global warming, drought is currently wreaking havoc on terrestrial ecosystems' structure and function, however, the synthesized analysis is lacked to explore the general rules between drought changes and main functional factors of grassland ecosystems. In this work, meta-analysis was used to examine the impacts of drought on grassland ecosystems in recent decades. According to the results, drought greatly reduced aboveground biomass (AGB), aboveground net primary production (ANPP), height, belowground biomass (BGB), belowground net primary production (BNPP), microbial biomass nitrogen (MBN), microbial biomass carbon (MBC) and soil respiration (SR), and increased dissolved organic carbon (DOC), total nitrogen (TN), total phosphorus (TP), nitrate nitrogen (NO3--N), and the ratio of microbial biomass carbon and nitrogen (MBC/MBN). The drought-related environmental factor mean annual temperature (MAT) was negatively correlated with AGB, height, ANPP, BNPP, MBC, and MBN, however, mean annual precipitation (MAP) had positive effect on these variables. These findings indicate that drought is threatening the biotic environment of grassland ecosystem, and the positive steps should be taken to address the negative effects of drought on grassland ecosystems due to climate change.

Calcium-modified biochar rather than original biochar decreases salinization indexes of saline-alkaline soil.

We investigated the improvement effects of herbaceous (corn) and woody (oak sawdust) biochar with their calcium modification on saline alkali soil. The addition of unmodified biochar regardless of types had no significant effect on the soluble cations (Na+, Ca2+, and Mg2+) and the main indicators of soil salinity and alkalinity (pH, sodium adsorption ratio (SAR), exchangeable sodium percentage (ESP), and total alkalinity (TA)), but the addition of calcium modified biochar decreased these soluble cations and indicators, especially the addition of modified woody biochar (PBM). Compared to CK, TA decreased by 70.02% and 89.25% in PBM with 2% and 4% addition, respectively. Soil ESP and SAR showed a significantly positive correlation with pH and TA, which indicated that soil salinization and alkalization were synchronized. These results showed that the calcium modified biochar, especially the modified woody biochar, instead of the original biochar could be potential soil amendments for the improvement of saline-alkali soil.

Effective microorganisms input efficiently improves the vegetation and microbial community of degraded alpine grassland.

Soil beneficial microorganism deficiency in the degraded grasslands have emerged as the major factors negatively impacting soil quality and vegetation productivity. EM (effective microorganisms) has been regarded as a good ameliorant in improving microbial communities and restoring degraded soil of agricultural systems. However, knowledge was inadequate regarding the effects of adding EM on the degraded alpine grassland. Four levels of EM addition (0, 150, 200, 250 mL m-2) were conducted to investigate the effects of EM addition on soil properties and microorganisms of degraded alpine grassland. The addition of EM increased aboveground biomass, soil organic carbon, total nitrogen, available phosphorus, and microbial biomass, but decreased soil electric conductivity. Meanwhile, the relative biomasses of gram-negative bacteria decreased, while the ectomycorrhizal fungi and arbuscular mycorrhizal fungi increased after EM addition. The relationship between microbial communities and environmental factors has been changed. The restore effect of EM increased with the increase of addition time. These results indicated that EM addition could be a good practice to restore the health of the degraded alpine grassland ecosystem.

Soil properties rather than plant diversity mediate the response of soil bacterial community to N and P additions in an alpine meadow.

The alpine meadow on the Qinghai-Tibetan Plateau, which is susceptible to global climate change and human activities, is subject to nutrient addition such as nitrogen (N) and phosphorus (P) to enhance soil available nutrients and ecosystem productivity. Soil bacterial community partly drivers the effects of nutrient additions on ecosystem processes, whereas the factors influencing N and P additions on bacterial community in alpine meadows are not well documented. We conducted a N and P addition experiment in an alpine meadow ecosystem on the Qinghai-Tibetan Plateau with four treatments: untreated control (CK), N addition (N), P addition (P), and NP addition (NP). We employed a high-throughput Illumina Miseq sequencing technology to investigate the response of soil bacterial community to short-term N and P additions. N and P additions decreased soil bacterial richness (OTU numbers and Chao 1 index), and P addition decreased soil bacterial diversity (Shannon and Simpson indices). N addition directly induced the change of soil N H 4 + - N , and decreased plant diversity. The N and P additions reduced soil bacterial community diversity, whose response was independent with plant diversity. Additionally, nutrient additions altered soil bacterial community composition, which were highly correlated with soil properties (i.e. pH, N H 4 + - N , and TP) as shown by RDA. Consistently, structural equation modeling results revealed that N addition indirectly acted on soil bacterial community through altering soil available nutrients and pH, while P addition indirectly affected bacterial community by increasing soil P availability. These findings imply that more attention should be paid to soil properties in regulating belowground biodiversity process in alpine meadows under future environmental change scenario.

Precipitation increase counteracts warming effects on plant and soil C:N:P stoichiometry in an alpine meadow.

Temperature and precipitation are expected to increase in the forthcoming decades in the northeastern Qinghai-Tibetan Plateau, with uncertain effects of their interaction on plant and soil carbon:nitrogen:phosphorus (C:N:P) stoichiometry in alpine ecosystems. A two-year field experiment was conducted to examine the effects of warming, precipitation increase, and their interaction on soil and plant C:N:P stoichiometry at functional groups and community level in an alpine meadow. Warming increased aboveground biomass of legumes and N:P ratios of grasses and community, but did not affect soil C:N:P stoichiometry. The piecewise structural equation model (SEM) indicated that the positive effect of warming on community N:P ratio was mainly resulted from its positive influence on the aboveground biomass of functional groups. Precipitation increase reduced C:N ratios of soil, grasses, and community, indicating the alleviation in soil N-limitation and the reduction in N use efficiency of plant. SEM also demonstrated the decisive role of grasses C:N:P stoichiometry on the response of community C:N:P stoichiometry to precipitation increase. The interaction of warming and precipitation increase did not alter plant community and soil, N:P and C:P ratios, which was resulting from their antagonistic effects. The stable soil and plant community C:N:P stoichiometry raised important implications that the effect of warming was offset by precipitation increase. Our study highlights the importance of considering the interaction between warming and precipitation increase when predicting the impacts of climate change on biogeochemical cycles in alpine meadow ecosystems.

Mycorrhizal Inoculation Enhances Nutrient Absorption and Induces Insect-Resistant Defense of Elymus nutans.

The majority of terrestrial plants can form symbiotic associations on their roots with arbuscular mycorrhizal fungi (AMF) in the soil to stimulate the growth and nutrient uptake of the host plant and to improve plant resistance to insects and disease. However, the use of AMF for insect control on gramineous forages requires further study. Here, we evaluated the effects of AMF (Funneliformis mosseae) inoculation on the defense against Locusta migratoria attack in Elymus nutans. Inoculation assays showed that mycorrhizal plants had a higher resistance than non-inoculated plants, as evidenced by plants having more plant biomass, a higher nitrogen and phosphorus content, and greater lipoxygenase (LOX) activity. The results of insect damage showed that in addition to a decrease in the enzyme phenylalanine-ammonia-lyase, the activities of other plant defense-related enzymes (including polyphenol oxidase and ß-1,3-glucanase) were increased. A key enzyme, LOX, belonging to the jasmonic acid (JA) signaling pathway was notably increased in mycorrhizal treatment. Volatile organic compounds (VOCs) were identified using gas chromatography mass spectrometry and the results showed that several metabolites with insect-resistant properties, including D-Limonene, p-Xylene, 1,3-Diethylbenzene were detected in mycorrhizal plants. These findings suggest that mycorrhizal inoculation has potential applications in insect management on forage grasses and demonstrates that the JA signaling pathway is essential for insect resistance in Elymus nutans.

Spatial variations of root-associated bacterial communities of alpine plants in the Qinghai-Tibet Plateau.

Exploring the geospatial variation of root-associated microbiomes is critical for understanding plant-microbe-environment interactions and plant environmental adaptability. Root-associated bacterial communities from the three compartments [rhizosphere surrounding soil (RSS), rhizosphere soil (rhizosphere), and root endosphere (endophytic)] are influenced by multiple factors, including plant species and geographical locations. Nonetheless, these communities remain poorly understood under harsh conditions. In this study, we selected four dominant alpine plants on the Qinghai-Tibet Plateau (i.e., Elymus nutans, Festuca sinensis, Kobresia pygmaea, and Kobresia humilis) to investigate their root-associated bacterial communities across 11 geographical locations and determine the factors driving spatial variation. The results showed that the microbiota of the three compartments had significantly different community compositions, with more Pseudomonadaceae and Enterobacteriaceae present in the endosphere. Spatial variations in root endophytic microbiota were mainly governed by stochastic processes, which were different from the deterministic processes in the other two compartments. Meanwhile, the geographical location had greater effects on bacterial communities than plant species, and the spatial variation of α-diversity in the endosphere was much higher than that in the RSS and rhizosphere. We further found that the differentiation of bacterial diversity in the endosphere among sympatric plant species was enhanced by higher annual precipitation, lower soil nutrients (carbon and nitrogen), and pH. For example, the coefficient of variation of endosphere Pseudomonadaceae abundance was positively correlated with annual mean precipitation, whereas that of Enterobacteriaceae abundance was negatively correlated with soil pH. The co-occurrence network analysis identified a higher proportion of bacterial coexistence in the endosphere (70.9%) than in the RSS (49.5%) and rhizosphere soil (50.9%). Finally, we revealed the relative convergence of endophytic communities among sympatric plant species in the alpine grasslands.

Cooperation between arbuscular mycorrhizal fungi and plant growth-promoting bacteria and their effects on plant growth and soil quality.

The roles of arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) in improving nutrition uptake and soil quality have been well documented. However, few studies have explored their effects on root morphology and soil properties. In this study, we inoculated Elymus nutans Griseb with AMF and/or PGPR in order to explore their effects on plant growth, soil physicochemical properties, and soil enzyme activities. The results showed that AMF and/or PGPR inoculation significantly enhanced aboveground and belowground vegetation biomass. Both single and dual inoculations were beneficial for plant root length, surface area, root branches, stem diameter, height, and the ratio of shoot to root, but decreased root volume and root average diameter. Soil total nitrogen, alkaline phosphatase, and urease activities showed significant growth, and soil electrical conductivity and pH significantly declined under the inoculation treatments. Specific root length showed a negative correlation with belowground biomass, but a positive correlation with root length and root branches. These results indicated that AMF and PGPR had synergetic effects on root morphology, soil nutrient availability, and plant growth.

The Mixed Addition of Biochar and Nitrogen Improves Soil Properties and Microbial Structure of Moderate-Severe Degraded Alpine Grassland in Qinghai-Tibet Plateau.

The degradation of the grassland system has severely threatened the safety of the ecological environment and animal husbandry. The supplement of key substances lost due to degradation is widely used to accelerate the restoration of the degraded grassland ecosystem. In this study, we investigated the effects of biochar and nitrogen addition on soil properties and microorganisms of degraded alpine grassland. The experimental treatments consisted of the control without any addition, only nitrogen addition (10 gN/m2), only biochar addition (4.00 kg/m2 biochar), and the mixed addition of biochar and nitrogen (4.00 kg/m2 biochar and 10 gN/m2 nitrogen, respectively). Adding N alone did not significantly change the pH, total organic carbon (TOC), total nitrogen (TN), microbial biomass (MB), and the composition proportion of microbes of the soil, but increased the contents of soil water content (SWC), NH4 +-N, NO3 --N, available phosphorus (AP), and the biomass of bacteria and fungi. The addition of biochar or the mixture of biochar and nitrogen increased the contents of pH, TOC, TN, MB, SWC, NH4 +-N, NO3 --N, AP, bacteria, and fungi in the soil and changed the structure of the soil microbial community. The increasing intensity of AP, bacteria, and fungi under the addition of biochar or the mixture of biochar and nitrogen was significantly greater than that under N addition alone. These results indicated that the separated addition of nitrogen and biochar and the mixed addition of biochar and nitrogen all improved the soil condition of the moderate-severe degraded alpine grassland, but the mixed addition of biochar and nitrogen could be a better strategy to remediate the degraded alpine grassland.

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Stellera chamaejasme is one of most common poisonous plant species in degraded grasslands of China. S. chamaejasme could dominate the community in some severely degraded grasslands, which is a serious threat to the sustainable development of animal husbandry in natural grasslands. In this study, S. chamaejasme population was divided into 10 age classes according to the number of branches. We investigated the age structure of S. chamaejasme population and population dynamic indices, and quantified the survival status of S. chamaejasme population by compiling a static life table, drawing a survival curve, conducting survival analysis. The age structure of S. chamaejasme population in the study area was growth type. The number of individuals in Ⅰ age class was sufficient but with relatively low survival rate. The population structure of S. chamaejasme was fitted the growing type. The development process of population was fluctuating. The number of individuals would drop sharply in Ⅱ and Ⅷ, indicating that these two age classes were the bottleneck period in the development of S. chamaejasme population. The survival curves of S. chamaejasme population was the Deevey-Ⅱ type. The results of survival analysis showed that the population had a sharp decrease in the early stage and was stable in the later stage, which was because the value of fx and λx of S. chamaejasme in Ⅰ or Ⅱ age class were the highest. In conclusion, sufficient young individuals (Ⅰ) was the basis for the expansion of S. chamaejasme population in the degraded typical steppe. The low transformation rate of young individuals to adults might be one of the reasons explaining why S. chamaejasme population could not expand rapidly in the early stage of grassland degradation. Therefore, it was suggested to intervene early when the number of S. chamaejasme was limited.

Spatial patterns in soil physicochemical and microbiological properties in a grassland adjacent to a newly built lake.

Soil water content (SWC) is an important determinant for nutrient cycling and microorganism activity in the grassland ecosystem. Lakes have a positive effect on the water supply of the neighboring ecosystem. However, information evaluating whether newly built lakes improve the physiochemical properties and microorganism activity of adjacent grassland soil is rare. A 15-hectare artificial lake with a 2 m depth was built on grazed grassland to determine whether the change of soil physiochemical properties and microorganism activity of the adjacent grassland depended on the distance from the lake. SWC and total nitrogen (TN) were greater within 150 m of the lake than at distances over 150 m from the lake. The total organic carbon (TOC) increased first at 100-150 m from the lake and then decreased. The soil microbial biomass and the bacterial and fungal contents increased with increasing years after the construction of the lake. Gram-negative bacteria and methanotrophic bacteria were greater within a 30 m distance of the lake. Over 60 m away from the lake, Actinobacteria, gram-positive bacteria, and anaerobic bacteria showed higher abundances. In the area near the lake (<250 m distance), microorganisms were strongly correlated with SWC, EC, TN, and TOC and greatly correlated with the changes of total phosphorous (TP) and pH when the distance from the lake was over 250 m. The results indicated that the newly built lake could be a driving factor for improving the physiochemical properties and microorganism activity of adjacent grassland soil within a certain range.

Grazing and Cultivated Grasslands Cause Different Spatial Redistributions of Soil Particles.

The distribution of soil particle sizes is closely related to soil health condition. In this study, grasslands under different grazing intensities and different cultivation ages grasslands were selected to evaluate the dynamics of soil particle size redistribution in different soil layers. When the grazing intensity increased, the percentage of 2000~150-µm soil particles in the 0-10-cm soil layer decreased; 150~53-µm soil particles remained relatively stable among the grazing intensities-approximately 28.52%~35.39%. However, the percentage of less than 53-µm soil particles increased. In cultivated grasslands, the larger sizes (>53 µm) of soil particles increased and the smaller sizes (<53 µm) decreased significantly (p < 0.05) in the 0-10 cm-soil layer with increasing cultivation ages. The increase in small soil particles (<53 µm) in topsoil associated with grazing intensity increased the potential risk of further degradation by wind erosion. The increase in big soil particles (>53 µm) in topsoil associated with cultivation ages decreased the soil capacity of holding water and nutrient. Therefore, to maintain the sustainability of grassland uses, grazing grasslands need to avoid heavy grazing, and cultivated grasslands need to change current cultivation practices.

Effects of species-dominated patches on soil organic carbon and total nitrogen storage in a degraded grassland in China.

BACKGROUND: Patchy vegetation is a very common phenomenon due to long-term overgrazing in degraded steppe grasslands, which results in substantial uncertainty associated with soil carbon (C) and nitrogen (N) dynamics because of changes in the amount of litter accumulation and nutrition input into soil. METHODS: We investigated soil C and N stocks beneath three types of monodominant species patches according to community dominance. Stipa krylovii patches, Artemisia frigida patches, and Potentilla acaulis patches represent better to worse vegetation conditions in a grassland in northern China. RESULTS: The results revealed that the soil C stock (0-40 cm) changed significantly, from 84.7 to 95.7 Mg ha-1, and that the soil organic carbon content (0-10 cm) and microbial biomass carbon (0-10 and 10-20 cm) varied remarkably among the different monodominant species communities (P < 0.05). However, soil total nitrogen and microbial biomass nitrogen showed no significant differences among different plant patches in the top 0-20 cm of topsoil. The soil C stocks under the P. acaulis and S. krylovii patches were greater than that under the A. frigida patch. Our study implies that accurate estimates of soil C and N storage in degenerated grassland require integrated analyses of the concurrent effects of differences in plant community composition.

Colloidal stability and aggregation kinetics of biochar colloids: Effects of pyrolysis temperature, cation type, and humic acid concentrations.

An understanding of biochar colloid aggregation and stability in aqueous environments is critical for assessing biochar fate and mobility in the soil. The aggregation kinetics of wheat straw-derived biochar colloids pyrolyzed at two temperatures 300 and 600 °C (WB300 and WB600 colloids, respectively) were investigated in monovalent and divalent electrolyte solutions in absence/presence of humic acid (HA). Results show that the critical coagulation concentrations (CCCs) of WB300 colloids in NaCl and CaCl2 solutions were 274 and 61.4 mM, which were higher than those (183 mM for NaCl and 38.1 mM for CaCl2) of WB600 colloids. WB300 had more oxygen-containing functional groups than WB600, which induced more negative surface charge on WB300. HA of 5 mg L-1 greatly increased the CCCs of WB300 and WB600 colloids to 1288 and 806 mM in NaCl solutions, but decreased the CCCs to 54.6 and 37.0 mM in CaCl2 solutions because of strong bridging between HA and Ca2+. In CaCl2 solutions with high salt concentrations (near to the CCCs), different HA concentrations caused distinct effects on the aggregation of biochar colloids. The aggregation of biochar colloids was accelerated by HA with the concentration higher than 5 mg L-1 through cation-bridging while the aggregation was inhibited in the presence of <2.5 mg L-1 HA. Our findings show that pyrolysis temperature used for biochar production had a large effect on the aggregation of biochar colloids in the aqueous environment and that cation type and dissolved natural organic matter are controlling variables.

Uranium (VI) transport in saturated heterogeneous media: Influence of kaolinite and humic acid.

Natural aquifers typically exhibit a variety of structural heterogeneities. However, the effect of mineral colloids and natural organic matter on the transport behavior of uranium (U) in saturated heterogeneous media are not totally understood. In this study, heterogeneous column experiments were conducted, and the constructed columns contained a fast-flow domain (FFD) and a slow-flow domain (SFD). The effect of kaolinite, humic acid (HA), and kaolinite/HA mixture on U(VI) retention and release in saturated heterogeneous media was examined. Media heterogeneity significantly influenced U fate and transport behavior in saturated subsurface environment. The presence of kaolinite, HA, and kaolinite/HA enhanced the mobility of U in heterogeneous media, and the mobility of U was the highest in the presence of kaolinite/HA and the lowest in the presence of kaolinite. In the presence of kaolinite, there was no difference in the amount of U released from the FFD and SFD. However, in the presence of HA and kaolinite/HA, a higher amount of U was released from the FFD. The findings in this study showed that medium structure and mineral colloids, as well as natural organic matter in the aqueous phase had significant effects on U transport and fate in subsurface environment.

Effect of physicochemical factors on transport and retention of graphene oxide in saturated media.

Fate and transport of graphene oxide (GO) have received much attention recently with the increase of GO applications. This study investigated the effect of salt concentration on the transport and retention behavior of GO particles in heterogeneous saturated porous media. Transport experiments were conducted in NaCl solutions with three concentrations (1, 20, and 50 mM) using six structurally packed columns (two homogeneous and four heterogeneous) which were made of fine and coarse grains. The results showed that GO particles had high mobility in all the homogeneous and heterogeneous columns when solution ionic strength (IS) was low. When IS was high, GO particles showed distinct transport ability in six structurally heterogeneous porous media. In homogeneous columns, decreasing ionic strength and increasing grain size increased the mobility of GO. For the column containing coarse-grained channel, the preferential flow path resulted in an early breakthrough of GO, and further larger contact area between coarse and fine grains caused a lower breakthrough peak and a stronger tailing at different IS. In the layered column, there was significant GO retention at coarse-fine grain interface where water flowed from coarse grain to fine grain. Our results indicated that the fate and transport of GO particles in the natural heterogeneous porous media was highly related to the coupled effect of medium structure and salt solution concentration.

Antagonistic effect of humic acid and naphthalene on biochar colloid transport in saturated porous media.

Biochar is a carbon-enriched material derived from organic material pyrolysis under no/limited oxygen, which is widely used for soil amendment, carbon sequestration, and contaminated soil remediation. This study aims to explore the interplay effect of humic acid (HA) and naphthalene on transport of biochar colloid (BC) in saturated porous media. A series of column experiments were conducted to study BC mobility at different concentrations of HA (0, 10, and 20 mg L-1) and naphthalene (0, 0.1, and 0.2 mg L-1). The results showed that increasing HA concentration promoted BCs mobility in porous media by increasing the electrostatic and steric interaction between BCs and collectors. However, the presence of naphthalene reduced the mobility of BCs with naphthalene increasing from 0 to 0.2 mg L-1, because the nonpolar naphthalene adsorbed onto the biochar surface and shielded the negative charge of BCs. The maximum breakthrough C/C0 of BCs was increased from 0.7 to 0.8 with increasing HA concentration from 0 to 20 mg L-1 in the presence of 0.1 mg L-1 naphthalene. This meant that HA still played the role to increase the electrostatic repulsion between BCs with HA and collectors when naphthalene was adsorbed on BCs. BCs breakthrough curves were well described by the two-site kinetic retention model including one reversible retention site and another irreversible retention site. The antagonistic effects of naphthalene and HA on BC transport suggested that the mobility of colloidal biochar particles in naphthalene-polluted soil was dependent on the coupled effects of naphthalene and natural organic matter.

Leaching potential of phosphorus from cattle excreta patches in the central highlands of Florida.

Research is limited for cow-calf operations as a potential nonpoint source of P within Florida's central highlands region (CHR). The study was conducted in a bahiagrass ( Flügge) pasture. The soil is an excessively drained 'Candler' sand. In dung-designated plots, 2 kg of fresh cattle dung was deposited across the surface of a 15-cm-radius circular zone (Zone 1 [Z1]) centered within 3 × 3 m plots. In urine plots, 1 L of urine was deposited on Z1 and 1 L on Zone 2 (Z2), an area extending outward from Z1 to 30 cm from plot center. In dung and urine plots, Zone 3 (Z3) extended from Z2 to 45 cm from plot center and Zone 4 (Z4) from Z3 to 60 cm. Excreta deposition frequencies (DFs) were 0, 1, 2, and 3 times per year during 2006 and 2007. Total apparent remaining P (ARP = [fertilizer P + excreta P] - forage P removal) for Z1 of dung plots was 21, 447, 905, and 1249 kg ha for DF0, DF1, DF2, and DF3, respectively. In 2008, soil was incrementally sampled to a depth of 120 cm in all zones. Urine deposition did not increase soil P. Soil P levels and the degree of P saturation percentages increased with DF but only in the upper 10 cm of topsoil beneath Z1 of dung plots. Our results suggest that the risk of dung P reaching groundwater is low due to a considerable P retention capacity within the rooting zone of the Candler soil.