First insights into 6PPD-quinone formation from 6PPD photodegradation in water environment.

p-Phenylenediamines (PPDs), an important type of rubber antioxidants, have received little study on their environmental fate, particularly for their vital photodegradation process in water environment. Accordingly, N-(1,3-dimethylbutyl)-N'-phenyl-1,4-phenylenediamine (6PPD), as a representative of PPDs, was investigated experimentally and theoretically for its photodegradation in water. Rapid photodegradation occurred when 6PPD was exposed to illumination especially UV region irradiation. Under acidic conditions, the photodegradation of 6PPD accelerated mainly due to the increased absorption of long wavelength irradiation by ionized 6PPD. Nine photodegradation products (e.g., 6PPD-quinone (6PPDQ)) of 6PPD were identified by an ultra-performance liquid chromatography QTOF mass spectrometry. Molar yields of photoproducts such as 6PPDQ, aniline, 4-aminodiphenylamine, and 4-hydroxydiphenylamine were 0.03 ± 0.00, 0.10 ± 0.01, 0.03 ± 0.02, and 0.08 ± 0.01, respectively. Mechanisms involved in 6PPD photodegradation include photoexcitation, direct photolysis, self-sensitized photodegradation, and 1O2 oxidation, as demonstrated by electron paramagnetic resonance (EPR) analysis, scavenging experiments, and the time-dependent density functional theory (TD-DFT). Notably, the toxicity of the reaction solution formed during the photodegradation of 6PPD was increased by the formation of highly toxic products (e.g., 6PPDQ). This study provides the first explanation for photodegradation mechanisms of 6PPD and confirms the pathway of 6PPDQ produced by the photoreaction in water environment.

Research review on the pollution of antibiotic resistance genes in livestock and poultry farming environments.

Increasingly serious pollution of antibiotic resistance genes (ARGs) caused by the abuse of antibiotics in livestock and poultry industry has raised worldwide concerns. ARGs could spread among various farming environmental media through adsorption, desorption, migration, and also could transfer into human gut microbiome by hori-zontal gene transfer (HGT), posing potential threats to public health. However, the comprehensive review on the pollution patterns, environmental behaviors, and control techniques of ARGs in livestock and poultry environments in view of One Health is still inadequate, resulting in the difficulties in effectively assessing ARGs transmission risk and developing the efficient control strategies. Here, we analyzed the pollution characteristics of typical ARGs in various countries, regions, livestock species, and environmental media, reviewed the critical environmental fate and influencing factors, control strategies, and the shortcomings of current researches about ARGs in the livestock and poultry farming industry combined with One Health philosophy. In particular, we addressed the importance and urgency of identifying the distribution characteristics and environmental process mechanisms of ARGs, and developing green and efficient ARG control means in livestock farming environments. We further proposed gaps and prospects for the future research. It would provide theoretical basis for the research on health risk assessment and technology exploitation of alleviating ARG pollution in livestock farming environment.

Hormetic Effect of Pyroligneous Acids on Conjugative Transfer of Plasmid-mediated Multi-antibiotic Resistance Genes within Bacterial Genus.

Spread of antibiotic resistance genes (ARGs) by conjugation poses great challenges to public health. Application of pyroligneous acids (PA) as soil amendments has been evidenced as a practical strategy to remediate pollution of ARGs in soils. However, little is known about PA effects on horizontal gene transfer (HGT) of ARGs by conjugation. This study investigated the effects of a woody waste-derived PA prepared at 450°C and its three distillation components (F1, F2, and F3) at different temperatures (98, 130, and 220°C) on conjugative transfer of plasmid RP4 within Escherichia coli. PA at relatively high amount (40-100 µL) in a 30-mL mating system inhibited conjugation by 74-85%, following an order of PA > F3 ≈ F2 ≈ F1, proving the hypothesis that PA amendments may mitigate soil ARG pollution by inhibiting HGT. The bacteriostasis caused by antibacterial components of PA, including acids, phenols, and alcohols, as well as its acidity (pH 2.81) contributed to the inhibited conjugation. However, a relatively low amount (10-20 µL) of PA in the same mating system enhanced ARG transfer by 26-47%, following an order of PA > F3 ≈ F2 > F1. The opposite effect at low amount is mainly attributed to the increased intracellular reactive oxygen species production, enhanced cell membrane permeability, increased extracellular polymeric substance contents, and reduced cell surface charge. Our findings highlight the hormesis (low-amount promotion and high-amount inhibition) of PA amendments on ARG conjugation and provide evidence for selecting an appropriate amount of PA amendment to control the dissemination of soil ARGs. Moreover, the promoted conjugation also triggers questions regarding the potential risks of soil amendments (e.g., PA) in the spread of ARGs via HGT.

Pyroligneous acid mitigated dissemination of antibiotic resistance genes in soil.

Strategies to mitigate the spread of antibiotic resistance genes (ARGs) in soils are urgently needed. Therefore, a pristine pyroligneous acid (PA) from pyrolyzing blended woody waste at 450 °C and its three fractions distilled at 98, 130, and 220 °C (F1, F2, and F3) were used to evaluate their feasibility of reducing ARGs in soil. Application of PA, F2, and F3 effectively decreased the relative ARG abundance by 22.4-75.4% and 39.7-66.7% in the rhizosphere and bulk soil relative to control, respectively, and the removal efficiency followed an order of F3 > PA > F2. Contrarily, F1 increased the abundance of ARGs. The decreased abundance of two mobile genetic elements and impaired conjugative transfer of RP4 plasmid in the presence of PA, F2 and F3 demonstrated that the weakened horizontal gene transfer (HGT) contributed to the reduced ARG level. Variation partitioning analysis and structural equation models confirmed that ARG reduction was primarily driven by the weakened HGT, followed by the decreased co-selection of heavy metals and shifted bacterial community (e.g., reduced potential host bacteria of ARGs). Our findings provide practical and technical support for developing PA-based technology in remediating ARG-contaminated soil to ensure food safety and protect human health.

[Effect of Pyrolytic Temperature and Time on Characteristics of Typha angustifolia Derived Biochar and Preliminary Assessment of the Ecological Risk].

A batch of biochar was produced from pyrolysis of Typha angustifolia (TBCs) at 200-500℃ for 2 h and 6 h to investigate the effects of pyrolytic temperature and heating retention time on the physico-chemical properties. Moreover, Escherichia coli (E. coli) HB101 and the seeds of Helianthus annuus were used to preliminarily test the ecological risk of the TBCs. Results showed that the heating retention time (i.e., 2 and 6 h) had no significant effect on the properties of TBCs, while pyrolytic temperature significantly affected TBCs' characteristics. As the pyrolysis temperature increased from 200 to 500℃, the mass yield and contents of hydrogen (H) and oxygen (O) decreased, while the contents of carbon (C) and ash increased. The pH and surface pores also increased with increasing pyrolytic temperature, whereas the O-containing functional group (e.g., -COOH and -OH) decreased. These results indicated the increased carbonization and aromatization of the TBCs. For the inherent nutrients of TBCs, the total phosphorus (TP) and available potassium (K) contents significantly increased as temperature increased. The main components of dissolved organic matter (DOM) of TBCs were humic acid-like and fulvic acid-like organic compounds. As the pyrolysis temperature increased, the content of humic acid-like organic compounds decreased, while the content of fulvic acid-like organic compounds increased. All the TBCs had no significant effect on the growth of E. coli HB101 and the seed germination of Helianthus annuus, indicating the little ecological risk of TBCs under the experimental conditions. These findings provide an alternative way for resource utilization of waste wetland biomass and provide important theoretical data for screening biochar in soil reclamation.

Photodegradation Elevated the Toxicity of Polystyrene Microplastics to Grouper (Epinephelus moara) through Disrupting Hepatic Lipid Homeostasis.

Microplastics (MPs) have caused increasing global concerns due to their detrimental effects on marine ecosystems. However, the role of photodegradation in altering toxicity of MPs to marine organisms is poorly understood. We therefore investigated the photolytic transformation of pristine polystyrene fragments (P-PS) by 60-day ultraviolet (UV) irradiation, and compared the toxicity of P-PS, photodegraded PS (PD-PS), and commercially available polystyrene microbeads (C-PS) to juvenile grouper (Epinephelus moara). Photodegradation reduced the size from ∼55.9 µm of P-PS to ∼38.6 µm of PD-PS, even produced nanoparticles (∼75 nm) with a yield of 7.03 ± 0.37% (w/w), and induced surface oxidation and formation of persistent free radicals (e.g., CO•, COO•). Also, endogenous pollutants (chemical additives and polymer fragments) were leached out. Thus, PD-PS had the highest growth inhibition and lipidosis-driven hepatic lesions of grouper, followed by P-PS and C-PS, which was mainly explained by increased hepatic bioaccumulation of MPs/NPs and released endogenous toxicants. Furthermore, oxidative stress-triggered mitochondrial depolarization, suppression of fatty acid oxidation and transport, and promotion of inflammation were identified as the key mechanisms for the enhanced hepatotoxicity after photodegradation. This work provides new insight into the potential hazard and harm of MPs in marine environments after photodegradation.

Comparative study of individual and Co-Application of biochar and wood vinegar on blueberry fruit yield and nutritional quality.

Biochar and its by-product, wood vinegar, have attracted extensive attention owing to their great potentials in improving degraded soil, which is a global concern because of the threats to soil productivity and food security. However, the effect of biochar or wood vinegar on blueberry production is unknown. Therefore, a field trial was conducted to investigate the effects of individual and co-application of biochar (BC450) and wood vinegar (WV450) derived from blended wood waste on the blueberry tree (Vaccinium corymbosum L.) growth, fruit yield, appearance, and nutritional quality as well as the soil properties and nutrient availability. Regardless of individual or co-application, all the amendments had little effect on tree growth. Although BC450 and WV450 increased the fruit yield, the differences between the amended treatments were non-significant. Both the amendments had little effect on the apparent fruit quality, but improved the nutritional quality has been improved (e.g., increased vitamin C and decreased titratable acidity). Additionally, the individual or co-application of BC450 and WV450 had little effect on soil properties (except for soil organic matter), but increased the soil nutrient availability (e.g., NH4+-N, NO3⁻-N, and Mg). The enhancement in the nutritional quality of the blueberry fruit can be mainly attributed to the increased nutrient availability. This is the first preliminary study that demonstrates that the individual or co-application of biochar and wood vinegar can be a potential strategy for reclaiming degraded soil and enhancing blueberry production.

Polystyrene microplastics impaired the feeding and swimming behavior of mysid shrimp Neomysis japonica.

Growing evidences revealed the deleterious impacts of microplastics (MPs) on marine organisms. However, the effects of MPs on the movement behavior of marine crustacean is poorly understood. Therefore, this study aims to evaluate the physiological and behavioral responses of mysid shrimp (Neomysis japonica) larvae to polystyrene (PS) and carboxylated polystyrene (PS-COOH). PS-COOH presented a greater physiological toxicity to shrimp larvae compared to PS, causing significant lethal and growth inhibition effect, owing to bioaccumulation of MPs inside stomach. Both two MPs decreased the feeding efficiency of larvae, showing weakened predation competence. Moreover, reduced hunting and/or explorative ability of shrimps caused by MPs was also identified, which was evidenced by an overall decrease in swimming activity, range and frequency after exposure. Our study firstly highlighted that micron-sized polystyrene particles had the negative effects on the movement behavior of mysid shrimp larvae, thus posing potential hazard to population dynamics and ecological function of marine crustacean.

Comparison of efficacies of peanut shell biochar and biochar-based compost on two leafy vegetable productivity in an infertile land.

The soils in northwest China are severely stressed with nutrient deficiency and water depletion, thus limiting crop production and sustainable agricultural development. Biochar-based amendments, tailored for specific soil issues, have raised great public interest for soil improvement and carbon sequestration. Peanut shell-derived biochar (PBC) and PBC-based amendment (PAD) obtained from composting were added at concentrations of 0%, 1.5%, 3%, and 5% (w/w) into light sierozem soil to compare their effects on growth of crown daisy (Chrysanthemum coronarium L.) and leaf lettuce (Lactuca sativa var longifoliaf L.). PBC had no significant effect on the yields of the two vegetables due to the second season growth, while addition of low concentrations of PAD (≤3%) significantly increased their yields by 15.8%-107%. The positive effect of PAD was primarily attributed to the improved soil qualities (e.g., water holding capacity (WHC), soil organic matter (SOM), electrical conductivity (EC)) and increased contents of available macronutrients (e.g., P and K), and micronutrients (e.g., B, Zn and Mn). However, addition of 5% PAD decreased the yield of crown daisy by 26.9% compared to that grown in untreated soil because of surplus nutrient input resulting in high EC. Overall, our findings demonstrated that the designed PAD synthesized from PBC compost had the potential to ameliorate the infertility in the soil and thus to improve vegetable yield.

Differential toxicity of functionalized polystyrene microplastics to clams (Meretrix meretrix) at three key development stages of life history.

Little knowledge is available on impact of microplastics (MPs) on the bivalve larvae at different developmental stages throughout their life history, especially for metamorphic stage. Therefore, this study aims to evaluate the toxic responses of carboxylated (PS-COOH) and amino (PS-NH2) polystyrene MPs on the developing clam larvae at three key life stages, i.e., fertilized eggs, D-veliger larvae, and umbo larvae. PS-COOH and PS-NH2 significantly decreased the hatching rates by 5.79-39.5% and developmental rates by 4.78-7.86% of the clam larvae relative to the unexposed clam larvae. The toxicity of MPs followed the order: hatching stage > metamorphosis > D-veliger larvae stage, showing stage-dependent toxic effects. Moreover, PS-NH2 with a smaller hydrodynamic diameter showed a greater toxicity to the developing larvae compared to PS-COOH. Our study highlighted the stage-dependent toxic effects of MPs on the developing clam larvae, thus posing ecological risks to population succession of marine bivalves and aquatic ecosystems.

Characteristics and mechanisms of chlorpyrifos and chlorpyrifos-methyl adsorption onto biochars: Influence of deashing and low molecular weight organic acid (LMWOA) aging and co-existence.

The effects of inherent minerals in biochars and low molecular weight organic acids (LMWOAs) on chlorpyrifos and chlorpyrifos-methyl adsorption by biochars are unclear. We examined the sorption of chlorpyrifos and chlorpyrifos-methyl onto giant reed-derived biochars before and after deashing or LMWOA aging. The effect of citric acid (CA) as a co-solute on the sorption of chlorpyrifos and chlorpyrifos-methyl was also investigated. With increasing temperature (300-600 °C), the adsorption capacity of biochars increased from 4.32 to 14.8 mg/g for chlorpyrifos and from 15.0 to 50.5 mg/g for chlorpyrifos-methyl. This can be explained by the fact that higher temperature biochar had more aromatic units and pores for capturing more sorbates. The deashing and LMWOA aging treatments exposed more carbon surfaces and improved the porosity of biochar, thus favoring sorption. Further, the deashing treatment resulted in greater sorption enhancement, when compared with the LMWOA aging treatment. At pH 6.5, CA2- and CA3- chelated Ca2+ via bridging at CA concentration below 10 mmol/L, thus reducing the competition of Ca2+ for aromatic surfaces and COO-/OH groups. When the CA concentration was above 20 mmol/L, CA2-, CA3-, and [Ca(CA)2]x- inhibited the sorption of chlorpyrifos and chlorpyrifos-methyl by competing for carbon sites and pores of biochar. These findings will help guide the practical application of biochar in pesticide-contaminated water and soil, and to better understand the role of biochar in the transport, fate, and bioavailability of organophosphorus pesticides in the rhizosphere.

Fate of four phthalate esters with presence of Karenia brevis: Uptake and biodegradation.

Phthalate esters (PAEs), one class of the most frequently detected endocrine-disrupting chemicals (EDCs) in marine environment, have aroused wide public concerns because of their carcinogenicity, teratogenicity, and mutagenicity. However, the environmental fate of PAEs in the occurrence of harmful algal blooms remains unclear. In this research, four PAEs with different alkyl chains, i.e., dimethyl phthalate (DMP), diethyl phthalate (DEP), diallyl phthalate (DAP), and dipropyl phtalate (DPrP) were selected as models to investigate toxicity, uptake, and degradation of PAEs in seawater grown with K. brevis, one of the common harmful red tide species. The 96-h median effective concentration (96h-EC50) values followed the order of DMP (over 0.257 mmol L-1) > DEP (0.178 mmol L-1) > DAP (0.136 mmol L-1) > DPrP (0.095 mmol L-1), and the bio-concentration factors (BCFs) were positively correlated to the alkyl chain length. These results indicate that the toxicity of PAEs and their accumulation in K. brevis increased with increasing alkyl chains, due to the higher lipophicity of the longer chain PAEs. With growth of K. brevis for 96 h, the content of DMP, DEP, DAP, and DPrP decreased by 93.3%, 68.2%, 57.4% and 46.7%, respectively, mainly attributed to their biodegradation by K. brevis, accounting for 87.1%, 61%, 46%, 40% of their initial contents, respectively. It was noticed that abiotic degradation had little contribution to the total reduction of PAEs in the algal cultivation systems. Moreover, five metabolites were detected in the K. brevis when exposed to DEP including dimethyl phthalate (DMP), monoethyl phthalate (MEP), mono-methyl phthalate (MMP), phthalic acid (PA), and protocatechuic acid (PrA). While when exposed with to DPrP, one additional intermediate compound diethyl phthalate (DEP) was detected in the cells of K. brevis in addition to the five metabolites mentioned above. These results confirm that the main biodegradation pathways of DEP and DPrP by K. brevis included de-esterification, demethylation or transesterification. These findings will provide valuable evidences for predicting the environmental fate and assessing potential risk of PAEs in the occurrence of harmful algal blooms in marine environment.

Comparison of six digestion methods on fluorescent intensity and morphology of the fluorescent polystyrene beads.

Effect of digestion methods on fluorescence intensity of fluorescent polystyrene (PS) beads was poorly understood, which may affect the accuracy of toxicity test of the fluorescent PS beads exposed to marine organisms. Therefore, six digestion approaches were compared on fluorescence intensities and properties of three commercial fluorescent PS beads. Among all the protocols, the digestion using KOH (10% w/v, 60 °C) (KOH-digestion) had no effect on the fluorescence intensity, morphology and composition of the three fluorescent PS beads. Moreover, the extraction efficiency ≥ 95.3 ±â€¯0.2% of fluorescent PS beads in Daphnia magna and zebrafish, confirming its feasibility in fluorescent PS beads quantitative analysis. However, the fluorescence intensities of fluorescent PS beads digested by other five protocols were significantly decreased, as well as the change of morphology and composition on fluorescent PS beads. Overall, the KOH-digestion is an optimal protocol for extracting fluorescent PS beads in biological samples.

Enhanced growth of halophyte plants in biochar-amended coastal soil: roles of nutrient availability and rhizosphere microbial modulation.

Soil health is essential and irreplaceable for plant growth and global food production, which has been threatened by climate change and soil degradation. Degraded coastal soils are urgently required to reclaim using new sustainable technologies. Interest in applying biochar to improve soil health and promote crop yield has rapidly increased because of its multiple benefits. However, effects of biochar addition on the saline-sodic coastal soil health and halophyte growth were poorly understood. Response of two halophytes, Sesbania (Sesbania cannabina) and Seashore mallow (Kosteletzkya virginica), to the individual or co-application of biochar and inorganic fertilizer into a coastal soil was investigated using a 52 d pot experiment. The biochar alone or co-application stimulated the plant growth (germination, root development, and biomass), primarily attributed to the enhanced nutrient availability from the biochar-improved soil health. Additionally, the promoted microbial activities and bacterial community shift towards the beneficial taxa (e.g. Pseudomonas and Bacillus) in the rhizosphere also contributed to the enhanced plant growth and biomass. Our findings showed the promising significance because biochar added at an optimal level (≤5%) could be a feasible option to reclaim the degraded coastal soil, enhance plant growth and production, and increase soil health and food security.

Biochar-induced negative carbon mineralization priming effects in a coastal wetland soil: Roles of soil aggregation and microbial modulation.

Biochar can sequestrate carbon (C) in soils and affect native soil organic carbon (SOC) mineralization via priming effects. However, the roles of soil aggregation and microbial regulation in priming effects of biochars on SOC in coastal wetland soils are poorly understood. Thus, a coastal wetland soil (δ13C -22‰) was separated into macro-micro aggregates (53-2000µm, MA) and silt-clay fractions (<53µm, SF) to investigate the priming effect using two 13C enriched biochars produced from corn straw (δ13C -11.58‰) at 350 and 550°C. The two biochars induced negative priming effect on the native SOC mineralization in the both soil aggregate size fractions, attributed to the enhanced stability of the soil aggregates resulting from the intimate physico-chemical associations between the soil minerals and biochar particles. Additionally, biochar amendments increased soil microbial biomass C and resulted in a lower metabolic quotient, suggesting that microbes in biochar amended aggregates could likely incorporate biomass C rather than mineralize it. Moreover, the biochar amendments induced obvious shifts of the bacterial community towards low C turnover bacteria taxa (e.g., Actinobacteria and Deltaproteobacteria) and the bacteria taxa responsible for stabilizing soil aggregates (e.g., Actinobacteria and Acidobacteria), which also accounted for the negative priming effect. Overall, these results suggested that biochar had considerable merit for stabilizing SOC in the coastal soil and thus has potential to restore and/or enhance "blue C" sink in the degraded coastal wetland ecosystem.

Aging impacts of low molecular weight organic acids (LMWOAs) on furfural production residue-derived biochars: Porosity, functional properties, and inorganic minerals.

The aging of biochar by low molecular weight organic acids (LMWOAs), which are typical root-derived exudates, is not well understood. Three LMWOAs (ethanoic, malic, and citric acids) were employed to investigate their aging impacts on the biochars from furfural production residues at 300-600°C (BC300-600). The LMWOAs created abundant macropores in BC300, whereas they significantly increased the mesoporosity and surface area of BC600 by 13.5-27.0% and 44.6-61.5%, respectively. After LMWOA aging, the content of C and H of the biochars increased from 51.3-60.2% and 1.87-3.45% to 56.8-69.9% and 2.06-4.45%, respectively, but the O content decreased from 13.8-24.8% to 7.82-19.4% (except BC300). For carbon fraction in the biochars, the LMWOAs barely altered the bulk and surface functional properties during short-term aging. The LMWOAs facilitated the dissolution of minerals (e.g., K2Mg(PO3)4, AlPO4, and Pb2P2O7) and correspondingly promoted the release of not only plant nutrients (K+, Ca2+, Mg2+, Fe3+, PO43-, and SO42-) but also toxic metals (Al3+ and Pb2+). This research provided systematic insights on the responses of biochar properties to LMWOAs and presented direct evidence for acid activation of inorganic minerals in the biochars by LMWOAs, which could enhance the understanding of environmental behaviors of biochars in rhizosphere soils.

Efficacies of biochar and biochar-based amendment on vegetable yield and nitrogen utilization in four consecutive planting seasons.

Biochar has been suggested as a potential tailored technology for mediating soil conditions and improving crop yields. However, the efficacies of biochar and biochar-based amendments (e.g., composted biochar) in agricultural soils under a rotation system remain uncertain. In this study, an arable soil was subjected to peanut shell biochar (PBC) and biochar-based amendment (PAD) combined with or without nitrogen (N) fertilizer to evaluate their effects on vegetable yield, N bioavailability, and their relative contribution to vegetable biomass in four consecutive planting seasons. PBC alone or in co-application with N fertilizer had little effect on vegetable yield, while PAD co-application with N fertilizer decreased vegetable biomass because of the inhibition of root morphology by excessive nutrient supply. PBC and PAD applications increased rhizosphere soil pH due to OH- and HCO3- release and NO3--N uptake. Although the addition of PAD increased soil N contents due to its high contents in PAD, it had little effects on N utilization efficiency (NUE) in the four seasons. The relative contribution of PBC, PAD, and their interaction with N fertilizer to biomass yield was maintained at a low level. Our results indicated that a biochar-based amendment (e.g., PAD) was a potential alternative to N fertilizer, but the ratio of biochar to additives should be managed carefully to generate optimal benefits. Notably, the efficacy of PAD on plant growth was closely associated with plant species, and further related research on different plants is encouraged.

[In situ dynamics of phosphorus in the rhizosphere solution and organic acids exudation of two aquatic plants].

A mini-rhizotron experiment with Alternanthera philoxeroides and Typha latifolia was conducted to measure the spatial and temporal dynamics of phosphorus in the rhizosphere solution. The organic acids in the in situ rhizosphere soil solution were analyzed. A decreasing phosphorus concentration gradient in soil solution toward the root was observed for both A. philoxeroides and T. latifolia. The phosphorus concentration in the rhizosphere soil solution of A. philoxeroides (2.53 mg x L(-1)) was lower than that of T. latifolia (5.43 mg x L(-1)) in the forth sampling day. Compared to T. latifolia, A. philoxeroides released more malic acid (27.33 umol x L(-1)) which was more efficient in phosphorus mobilization. A. philoxeroides was more effective in phosphorus uptake in the rhizosphere than T. latifolia.