Plant Leachate Research Articles

Leaching of per- and polyfluoroalkyl substances (PFAS) from food contact materials with implications for waste disposal

Leaching of per- and polyfluoroalkyl substances (PFAS) during the post-consumer disposal of food contact materials (FCMs) poses a potential environmental threat but has seldom been evaluated. This study characterized the leaching behavior of PFAS and unidentified precursors from six common FCMs and assessed the impact of environmental conditions on PFAS release during disposal. The total concentration of 21 PFAS ranged from 3.2 to 377 ng/g in FCMs, with PFAS leachability into water varying between 1.1–42.8 %. Increasing temperature promoted PFAS leaching, with leached nine primary PFAS (∑9PFAS) reaching 46.3, 70.4, and 102 ng/L at 35, 45, and 55 ℃, respectively. Thermodynamic analysis (∆G>0, ∆H>0, and ∆S<0) indicated hydrophobic interactions control PFAS leaching. The presence of dissolved organic matter in synthetic leachate increased the leached ∑9PFAS from 47.1 to 103 ng/L but decreased PFBS, PFOS, and 6:2 FTS leaching. The total release of seven perfluorocarboxylic acids (∑7PFCAs) from takeaway food packaging waste was estimated to be 0.3–8.2 kg/y to landfill leachate and 0.6–15.4 kg/y to incineration plant leachate, contributing 0.2–4.8 % and 0.1–3.2 % of total ∑7PFCAs in each leachate type. While the study presents a refined methodology for estimating PFAS release during disposal, future research is needed on the indirect contribution from precursors.

Insights into priming effects of dissolved organic matter degradation in urban lakes with different trophic states

Priming effect (PE) is recognized as an important potential mechanism for dissolved organic matter (DOM) degradation in aquatic ecosystems. However, the priming effects (PEs) of various priming substances on the degradation of DOM pools in urban lakes along diverse trophic states remain unknown. To address this knowledge gap, the PEs and drivers of glucose and plant leachate of lake water with three trophic states were investigated. We reveal differences in the bioavailability of DOM in lake water, glucose, and plant leachate. The PE of the same priming substance was significantly higher in highly-eutrophic lake water than in mesotrophic lake. The priming intensity induced by glucose was significantly higher when compared to plant leachate. Regarding the addition of glucose, humic-like components (C1 and C3) showed slight PE, while the tyrosine-like component C2 showed negative PE. However, the positive PEs were observed on three components after adding plant leachate. The driver of PE by glucose shifted from nutrients to DOM components with increasing trophic levels. The PEs induced by plant leachate were affected by nutrients, chlorophyll-a (Chl-a), water chemistry, and DOM components in lightly/moderately-eutrophic lake water. This study revealed the intensities, directions, and drivers of PEs, providing essential insights into uncovering the DOM biogeochemical process in urban lakes.

Chitosan immobilized Chinese gallotannin: A potential adsorbent to enrich the rare metals Ge (Ⅳ), Ga (Ⅲ), and In (Ⅲ)

In this study, a solid adsorbent based on Chinese gallotannin and chitosan was generated and applied to adsorb rare and scattered metals, including Ge (Ⅳ), Ga (Ⅲ), and In (Ⅲ), from simulated zinc plant leachates. Fourier-transform infrared spectroscopy (FTIR) and solid state nuclear magnetic resonance (SSNMR) were performed to characterize the grafting way of Chinese gallotannin on the chitosan matrix. It was clearly showed that Chinese gallotannin was immobilized on the chitosan by Schiff-base condensation and phenol-formaldehyde reaction at the molar ratio of glutaraldehyde to tannin of 2:1. And the amount of chitosan amino groups was ten times that of tannin, with an initial pH of 4. The adsorption experiments showed that an appropriate increase in pH was more beneficial to enhance the adsorption capacity of immobilized Chinese gallotannin (ICGT). At a temperature exceeding 30 °C, the immobilized tannin became less sensitive to temperature. Adsorption kinetics studies showed that the adsorption of the three scattered metals by ICGT followed a quasi-second-order kinetic equation, with chemisorption as the mechanism. The adsorption isotherm was well fitted by the Langmuir model, indicating uniform adsorption sites on the surface of ICGT. The adsorption capacities of Ge (Ⅳ), Ga (Ⅲ), and In (Ⅲ) in solution by the adsorption model of monolayer were 61.39 mg/g, 63.82 mg/g, and 59.92 mg/g, respectively. Mechanical property and stability tests showed that ICGT had good resistance to harsh adsorption conditions of scattered metal ions.

Less is more: partial larvicidal efficacy of plant leachate leads to larger Aedes aegypti mosquitoes.

Major efforts to control the population of Aedes aegypti mosquitoes involve the use of synthetic insecticides, which can be harmful to the environment. Most plant compounds are eco-friendly and some of them have biocontrol potential, whereas a fraction of these compounds is released into the environment through the leaf-leaching process. We evaluated the effects of secondary compounds from Ateleia glazioviana and Eucalyptus grandis senescent leaf leachates on Ae. aegypti larval mortality, adult emergence time, and wing size using a microcosm approach. The microcosms consisted of 10 larvae kept in water (control) and under four treatments with leachates from a combination of plant species and leaching time (7 or 14 days). Chemical analyses of the leachates showed the presence of carboxaldehyde and Heptatriocotanol, which have antimicrobial properties, potentially reducing the food available for larvae. β-Sitosterol, Stigmasterol, α-Amyrin, and Lupeol are compounds with inhibitory, neurotoxic, and larvicidal effects. Both plant species' leachates increased larval mortality and decreased emergence time due to the presence of compounds toxic to the larvae. Larger organisms emerged in treatments with 7-days leachates, likely due to the high concentration of dissolved organic matter in the leachates. The higher mortality in 7-days leachates may also increase the organic matter from co-specific decomposition, improving adult size. Therefore, if the mosquito population is not locally extinct, compounds present in leaf leachates may act as a resource enhancing larvae growth, potentially increasing survivors' fitness. In conclusion, biocontrol attempts using urban green spaces may have unexpected outcomes, such as resulting in larger pest organisms.

The priming effects of plant leachates on dissolved organic matter degradation in water depend on leachate type and water stability

The modification of dissolved organic matter (DOM) degradation by plant carbon inputs represents a critical biogeochemical process that controls carbon dynamics. However, the priming effects (PEs) different plant tissues induce on the degradation of DOM pools with different stabilities remain unknown. In this study, PEs, induced by different tissue leachates of Phragmites australis, were evaluated via changes in DOM components and properties of both fresh and tidal water (with different stabilities). The results showed that DOM derived from different plant tissue leachates differed in composition and bioavailability. Inputs of tissue leachates induced PEs with different intensities and directions (negative or positive) on DOM degradation of fresh and tidal water. In fresh water, the PEs of leaf and root leachates were significantly higher than those of stem and rhizome leachates. The PE direction changed for DOM degradation between fresh and tidal water. The addition of leaf and root leachates tended to induce positive PEs on DOM degradation of fresh water, while resulting in negative PEs on DOM degradation of tidal water. Negative PEs for tidal water DOM may be due to preferential utilization of microbes, high salinity, and/or the promotion of exogenous DOM production from plant tissues. The results indicate that intensity and direction of PEs induced by plant leachates depend on both leachate type and water stability. The findings highlight the necessity to examine the nature of exogenous and native DOM when interpreting the interactive processes that regulate DOM degradation.

Structuring Life After Death: Plant Leachates Promote CO2 Uptake by Regulating Microbial Biofilm Interactions in a Northern Peatland Ecosystem

Shifts in plant functional groups associated with climate change have the potential to influence peatland carbon storage by altering the amount and composition of organic matter available to aquatic microbial biofilms. The goal of this study was to evaluate the potential for plant subsidies to regulate ecosystem carbon flux (CO2) by governing the relative proportion of primary producers (microalgae) and heterotrophic decomposers (heterotrophic bacteria) during aquatic biofilm development in an Alaskan fen. We evaluated biofilm composition and CO2 flux inside mesocosms with and without nutrients (both nitrogen and phosphorus), organic carbon (glucose), and leachates from common peatland plants (moss, sedge, shrub, horsetail). Experimental mesocosms were exposed to either natural sunlight or placed under a dark canopy to evaluate the response of decomposers to nutrients and carbon subsidies with and without algae, respectively. Algae were limited by inorganic nutrients and heterotrophic bacteria were limited by organic carbon. The quality of organic matter varied widely among plants and leachate nutrient content, more so than carbon quality, influenced biofilm composition. By alleviating nutrient limitation of algae, plant leachates shifted the biofilm community toward autotrophy in the light-transparent treatments, resulting in a significant reduction in CO2 emissions compared to the control. Without the counterbalance from algal photosynthesis, a heterotrophic biofilm significantly enhanced CO2 emissions in the presence of plant leachates in the dark. These results show that plants not only promote carbon uptake directly through photosynthesis, but also indirectly through a surrogate, the phototrophic microbes.

Effects of Photodegradation on the Optical Indices of Chromophoric Dissolved Organic Matter from Typical Sources.

Chromophoric dissolved organic matter (CDOM) plays important roles in aquatic environments, and its optical properties provide a series of indices for evaluating the source and composition of dissolved organic matter (DOM). However, little is known about the varying photodegradation of CDOM from different sources and the effects on the optical indices of DOM composition. This was studied for typical natural and anthropogenic sources (plant and leaf litter leachates, the influent and effluent of a wastewater treatment plant, and a river). The CDOM absorption (a280) showed a lower degradability for the plant leachate than other sources, mainly due to its low molecular weight and aromaticity. Four fluorescent components were identified with excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC), namely benzoic acid/monolignol-like C1, humic-like C2 and C3, and tryptophan-like C4. The plant leachate contained mainly C1, which was photodegraded moderately, while other sources had more C2 and C3 with higher photodegradability. C4 was photodegraded in most sources but was photoproduced in the leaf litter leachate. The absorption slope (S275-295) and slope ratio (SR) increased while the humification index (HIX) decreased, suggesting a decreasing molecular weight and humic content by photodegradation. This was consistent with the decreasing %C2 and %C3 but increasing %C4, which indicated preferential removal of humic-like components. The %C1, %C2, biological index (BIX), and fluorescence index (FI) were less affected by photodegradation than other indices for most sources. These results have implications for a better understanding of the photochemistry of CDOM and the applications of optical indices.

Relationship between the Antioxidant Activity and Allelopathic Activities of 55 Chinese Pharmaceutical Plants.

Pharmaceutical plants contain several phytochemicals that are sources of myriad biological activities. These biological activities can be explored in multiple fields for the benefit of mankind. Pharmaceutical plants with high ethnobotanical indices (i.e., use value and relative frequency of citation) were reported with the potential to inhibit lettuce elongation through leachates and volatiles. The focus of the study was to assess Chinese pharmaceutical plants for both antioxidants, as well as allelopathic potentials to explore any underlying relationship. The estimation of antioxidative capacity and content of total phenolics (TPC) for the 55 Chinese pharmaceutical plants was conducted by the assays of DPPH radical scavenging activity (DPPH-RSA), oxygen radical absorbance capacity (ORAC) and the means of Folin–Ciocalteu. The estimation of the activity of allelopathy for collected medicinal plants was done by adopting the sandwich method for plant leachates and the dishpack method for volatile constituents, respectively. The fruits of sea buckthorn (Hippophae rhamnoides) had the most remarkable ORAC value (168 ± 7.04 μmol TE/g) and DPPH radical scavenging activity (440 ± 7.32 μmol TE/g) and contained the highest contents of total phenolic compounds (236 ± 7.62 mg GAE/g) in the 55 pharmaceutical plant species according to the results. In addition, sea buckthorn showed dominant allelopathic potential through plant leachates evaluated by using the sandwich method. Star anise (Illicium verum Hook. f.) showed conspicuous allelopathic activity through plant volatiles assessed by the dishpack bioassay method. Among the same plant species, antioxidative ability and total phenolics, in comparison with potential allelopathy of medicinal herbs indicated that volatile allelochemical had a weak active effect (r = 0.407 to 0.472, p < 0.01), with antioxidant capacity by the dishpack method. However, the evaluation by the sandwich method showed a significant positive correlation (r = 0.718 to 0.809, p < 0.001) with antioxidant capacity. Based on these results, a new hypothesis is that the antioxidant activity of plants may have an involvement with the potential allelopathic activity.

Massive warming-induced carbon loss from subalpine grassland soils in an altitudinal transplantation experiment

Abstract. Climate change is associated with a change in soil organic carbon (SOC) stocks, implying a feedback mechanism on global warming. Grassland soils represent 28 % of the global soil C sink and are therefore important for the atmospheric greenhouse gas concentration. In a field experiment in the Swiss Alps we recorded changes in the ecosystem organic carbon stock under climate change conditions, while quantifying the ecosystem C fluxes at the same time (ecosystem respiration, gross primary productivity, C export in plant material and leachate water). We exposed 216 grassland monoliths to six different climate scenarios (CSs) in an altitudinal transplantation experiment. In addition, we applied an irrigation treatment (+12 % to 21 % annual precipitation) and an N deposition treatment (+3 and +15 kg N ha−1 yr−1) in a factorial design, simulating summer-drought mitigation and atmospheric N pollution. In 5 years the ecosystem C stock, consisting of plant C and SOC, dropped dramatically by about −14 % (-1034±610 g C m−2) with the CS treatment representing a +3.0 ∘C seasonal (April–October) warming. N deposition and the irrigation treatment caused no significant effects. Measurements of C fluxes revealed that ecosystem respiration increased by 10 % at the +1.5 ∘C warmer CS site and by 38 % at the +3 ∘C warmer CS site (P≤0.001 each), compared to the CS reference site with no warming. However, gross primary productivity was unaffected by warming, as were the amounts of exported C in harvested plant material and leachate water (dissolved organic C). As a result, the 5-year C flux balance resulted in a climate scenario effect of -936±138 g C m−2 at the +3.0 ∘C CS, similar to the C stock climate scenario effect. It is likely that this dramatic C loss of the grassland is a transient effect before a new, climate-adjusted steady state is reached.

Intraspecific Variation in Responses of a Montane Grass, Festuca thurberi, to Simulated Biological Invasion

High elevation plant populations, such as those found in sub-alpine meadows, are at the forefront of climate change and likely to experience novel interactions with migrating plants from lower elevations, including non-native species. Some of these non-native plants, particularly members of the Brassicaceae, produce secondary metabolites that have been shown to inhibit root fungi in other ecosystems. We conducted a growth experiment with plant leachates in order to evaluate the degree to which the dominant high elevation grass species, Festuca thurberi would be affected by future novel interactions with the non-native mustard, Thlaspi arvense, relative to a native mustard (Noccaea fendleri). We assessed growth, chlorophyll content, biomass, mortality, and percent colonization of arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE) in different genotypes of F. thurberi exposed to leachates from native and non-native mustards as well as F. thurberi leachate and a deionized (DI) water control. New growth and mortality varied more by genotype than by treatment with leachate of F. thurberi, T. arvense, and N. fendleri. Treatment, genotype, and the treatment × genotype interaction all had significant effects on chlorophyll content, with N. fendleri treatments demonstrating higher relative greenness levels than control treatments. Percent of fine roots with dark septate endophytes was significantly affected by individual genotype and treatment × genotype interaction, but there were no effects of treatment, genotype, or their interaction on percent root colonization by arbuscules or vesicles. Overall, we show that performance of a dominant high-altitude grass species varies in its response to the presence of an expanding, non-native plant, which may become increasingly common due to climate change.

Allelopathic effects of Androstachys johnsonii Prain on germination and growth of Zea mays L. and Vigna subterranea (L.) Verdc.

Allelopathic effects of the donor plants are mostly regarded as harmful to target plants such as traditional crops. Traditional crops play pivotal role as staple food for rural communities and hence ensuring food security. Study of the allelopathic effects of Androstachys johnsonii Prain on the germination and growth of Zea mays L. and Vigna subterranea (L.) Verdc was conducted. Different plant leachates concentrations of 0.675%, 1.25%, 2.5% and 5% were prepared through serial dilutions. Germination bioassays were arranged in a complete randomized setup of three replicates for each treatment for seven days. Germination rates were calculated, radicle and hypocotyl lengths were also measured. Germination rates of Z. mays L. and V. subterranea (L.) Verdc. ranged from 50 - 100% and 18 - 76%, respectively. Significant differences of P&lt; 0.005 were noticed from the germination rates of V. subterranea (L.) Verdc subjected to high concentrations of different extracts used. Statistically there was no significant differences between germination rates of Z. mays L. treated with all concentrations of leaf leachates against germination rates of the seeds treated with distilled water. Outstandingly, the germination rate and early growth of Z. mays L. were promoted by less concentrated extracts of leaf, root, stem bark and soil which then suggest future use of allelochemicals from Androstachys johnsonii Prain for promotion of maize plant productions. Based on the beneficial attributes of allelochemicals from Androstachys johnsonii on the germination and growth of Z. mays L., planting of Androstachys johnsonii Prain in maize fields is highly recommended.

Diversity of resident plant communities could weaken their allelopathic resistance against alien and native invaders

Elton’s classic diversity-invasibility hypothesis posits that diversity of resident communities increases resistance against invaders. We tested whether the diversity-invasibility relationsip might be mediated by allelopathic effects of the resident species. In a large germination experiment, we exposed seeds of six alien and six native test species to leachates of one, three, six or twelve species. The leachates tended to slightly delay germination, and almost all single-species leachates reduced the proportion of germinated seeds. Nevertheless, the overall effect of the plant leachate mixtures on the proportion of germinated seeds was not significant. This was because a higher diversity of the leachates increased the proportion of germinated seeds, particularly for native test species. Among the six alien test species, it was only the most invasive one that benefited from increased diversity of the leachates, just like the natives did. Overall, our findings suggest that allelopathy of diverse communities does not provide resistance but could actually facilitate the germination of invaders.

THE ALLELOPATHICITY OF RED SPRANGLETOP (Leptochloa chinensis L.) AGAINST GERMINATION AND SEEDLING GROWTH OF RICE (Oryza sativa L.)

Red sprangletop (Leptochloa chinensis L.) is a problematic weed of aerobic rice (Oryza sativa L.) that greatly reduces in yield. The laboratory studies were undertaken to confirm allelopathicity of its plant leachates and soil-decomposition plant residues towards emergence and seedling growth of rice. In first experiment, aqueous extracts from various plant parts of red sprangletop (stem, root, leaves, flower and entire plant) at their 5% (w/v) concentration were applied to germinating rice seeds. In second experiment, soil-decomposed red sprangletop plant residues of variable concentrations (2, 4 and 6% w/w) were used as germination media for rice. Among plant parts, red sprangletop leaves showed maximum allelopathic effect by fully inhibiting the germination of rice while its stem could be positioned at second situation as it caused 60, 73, 84.13 and 86 % reductions in germination percentage, germination index, seedling length and seedling dry biomass of rice as compared with control, respectively. This treatment also resulted in maximum delays in mean germination time (up to 4.80 days) and days taken to 50% germination (up to 4.40 days) of rice. The highest concentrated (6%) soil-decomposed plant residue of red sprangletop significantly diminished the germination percentage, germination index, seedling length and seedling vigor index that were 35.13, 23.26 and 41.61% lower than control. It very well may be presumed that liquid concentrates of leave and stem soil-decomposed plant residues of 6% concentration had different kind of allelochemicals that inhibited the germination, seedling growth and development of rice.

Antibiotics in the municipal solid waste incineration plant leachate treatment process

ABSTRACT At present, the distribution of antibiotics in wastewater is mainly concentrated in municipal sewage treatment plants, and little attention is paid to the distribution and removal of antibiotics in landfill leachate. The concentrations of five sulfonamide, three tetracycline, and two macrolide antibiotics in leachate from a solid waste incineration plant were measured and the efficiency of the leachate treatment process in removing them was investigated. All target antibiotics were detected in the raw leachate samples. The total sulfonamide, tetracycline, and macrolide concentrations in the raw leachate ranged from 0.98 to 90.25, 1.90 to 50.64, and 146.41 to 382.90 ng/L, respectively. The leachate treatment process simultaneously removed all ten antibiotics with high removal efficiencies ranged from 96.0% to 100%. Biological and physical processes affected the removal of different types of antibiotics differently, with macrolides being more difficult for microorganisms to degrade than the other two categories. Leachate contaminants correlated to antibiotics suggesting environmental factors impact the removal of antibiotics. The accumulation of antibiotics in the leachate treatment process may create environmental problems.

Do experimental conditions bias plankton responses to increased concentration of dissolved organic matter (DOM)? A meta-analytical synthesis of the published results

The concentration of dissolved organic matter (DOM) in aquatic ecosystems has manifold direct and indirect consequences for primary and secondary production. Theoretical approaches suggest a negative effect of DOM on phytoplankton and a positive effect on bacteria, both of which alter the development of metazooplankton, the main consumer of bacteria and phytoplankton. However, experimental observations give heterogeneous results on the effect sizes of plankton in relation to DOM addition. Here, the synthesis of 411 effect sizes of plankton in response to DOM is presented from 59 studies. The referenced studies display effect sizes in relation to various DOM sources and different experimental designs. Thus, the hypothesis that neither DOM quality nor the type of experiment bias the effect size response of plankton was tested; the hypothesis was tested separately for bacterioplankton, phytoplankton and metazooplankton with the use of a meta-analytical approach. DOM quality was represented by the five different sources of DOM that are used most often in these experiments, i.e., natural water, bog leachate, glucose/sucrose, terrestrial plant leachate, and soil leachate. The experiment types comprised in situ experiments, i.e., experiments taking place under manipulated conditions in a natural ecosystem, and ex situ experiments, i.e., those taking place outside of a natural ecosystem. The meta-analyses showed that, although total DOM had a positive influence on the effect size of bacterioplankton and an insignificant influence on metazooplankton, the effect sizes differed significantly in relation to DOM source and the type of experiment. The effect size of phytoplankton, although not significantly related with total DOM, differed in response to DOM source but not experiment type. The results suggest that experimental conditions may produce artifacts in the strength of responses of aquatic biota to DOM concentrations.

Effect of allelopathy on plant performance: a meta-analysis.

Allelopathy (i.e. chemical interactions between plants) is known to affect individual performance, community structure and plant invasions. Yet, a quantitative synthesis is lacking. Here, we performed a meta-analysis of 384 studies that measured allelopathic effects of one species (allelopathy plant) on another species or itself (test plant). Overall, allelopathy reduced plant performance by 25%, but the variation in allelopathy was high. The type of method affected the allelopathic effect: compared to leachates, allelopathy was more negative when residues of allelopathy plants were applied, and less negative when soil conditioned by allelopathy plants was applied. The negative effects of allelopathy diminished with study duration, and increased with concentrations of leachates or residues. Although allelopathy was not significantly related to lifespan, life form or domestication of the interacting plants, it became more negative with increasing phylogenetic distance. Moreover, native plants suffered more from leachates of naturalised alien plants than from leachates of other native plants. Our synthesis reveals that allelopathy could contribute to success of alien plants. The negative relationship between phylogenetic distance and allelopathy indicates that allelopathy might contribute to coexistence of closely related species (i.e. convergence) or dominance of single species.

Assessing the priming effect of dissolved organic matter from typical sources using fluorescence EEMs-PARAFAC

Priming effect (PE) is increasingly recognized as an important mechanism in the microbial degradation of dissolved organic matter (DOM) from freshwater to the ocean. However, potential PE during the mixing of DOM from different sources and the effects on different DOM constituents are still largely unknown. This study examined the PE after adding DOM from typical natural and anthropogenic sources (rainwater, fresh plant, leaf litter, and wastewater) into pre-aged river DOM, using dissolved organic carbon (DOC) measurement, absorption spectroscopy, and fluorescence excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC). The plant-derived DOM had a low humic content and was dominated by benzoic acid-like and tyrosine-like fluorescent components (C4 and C5), which showed a high DOC bioavailability of 80%. DOC in rainwater and wastewater also had high bioavailabilities (45%–50%), while DOM in the leaf litter leachate showed high aromaticity, average molecular weight, and humic content but low DOC bioavailability (12%). There was generally limited PE (<5% of the initial values) on the degradation of DOC and chromophoric DOM (CDOM) for most samples. Two humic-like components (C2 and C3) showed little PE, while the humic-like C1 and C6, tyrosine-like C5, and tryptophan-like C7 showed variable PE after adding rainwater, wastewater, and plant leachate. Overall, the results revealed that the DOM from typical natural and anthropogenic sources had different composition and bioavailability, and their inputs to aquatic environments would result in variable PE on the bulk DOC and different DOM components.

Towards more realistic estimates of DOM decay in streams: Incubation methods, light, and non-additive effects

Dissolved organic matter (DOM) is the largest pool of organic matter in aquatic ecosystems and is a primary substrate for microbial respiration in streams. However, understanding the controls on DOM processing by microbes remains limited, and DOM decay rates remain largely unconstrained. Many DOM decay rates are quantified with bioassays in dark bottles, which may underestimate DOM decay in streams because these bioassays do not include a benthic zone and do not account for abiotic factors of DOM loss, such as photodegradation and volatilization. We measured decay of labile and semi-labile DOM over 3 d in experimental streams and bottle bioassays. Incubations included 3 types of labile DOM (algal, light-degraded soil, and light-degraded plant leachates) and 2 types of semi-labile DOM (plant and soil leachates). We also quantified decay rates when labile and semi-labile DOM were mixed to test for non-additive effects, or priming, of semi-labile DOM by labile DOM. We converted dissolved organic carbon (DOC) decay rates to half-lives and uptake velocities and compared these metrics to previous studies that quantified DOC loss in bioassays or real streams. Percent DOC lost over time, or biodegradable DOC, was greater in experimental streams than in bioassays. DOC decay rates and uptake velocities did not differ between bioassays and experimental streams but were lower than in real streams. Mixing of labile and semi-labile DOM resulted in both positive and negative non-additive effects. Consistent non-additive effects were difficult to quantify because decay rates were not constant over the course of each incubation, as shown by faster decay rates calculated over the first 6 h of incubation compared to >70 h. Decay rates of leachates from natural substrates (e.g., algae and soil) incubated over short periods of time (hours–days) are needed for models that aim to quantify organic matter transformation in aquatic ecosystems with short residence times, such as rivers and streams.

Optical properties of chromophoric dissolved organic matter (CDOM) and dissolved organic carbon (DOC) levels in constructed water treatment wetland systems in southern California, USA

Many removal mechanisms in treatment wetlands involve absorption to organic matter. Optical properties and DOC levels of waters entering and exiting 4 treatment wetland systems in Orange County, Southern California, were measured to characterize the dissolved organic matter pool. Average DOC levels decreased between the inlets and outlets, except for Forge Street (FS), which increased. For 3 wetlands, absorption coefficients decreased between inlet and outlet; the exception was FS, which increased. Average spectral slopes for the inlets and outlets were similar. Average intensities of terrestrial humic peaks A and C from 3D EEM fluorescence spectra decreased between the inlets and outlets for most wetlands. No EEM protein peaks were observed. Average flu/abs ratios for inlets and outlets were similar (high point for FS inlet excluded), suggesting chromophoric dissolved organic matter (CDOM) of a similar composition was present. The average FI value for the inlets and outlets was ∼1.5, consistent with terrestrial sources of CDOM. Average BIX values for the inlets and outlets were ∼0.8, suggesting limited contributions from autochthonous production of CDOM. Dominant plant species in the wetlands were cattail and bulrush. Humic peaks A and C, along with protein peaks, were observed in plant leachates. Protein peaks rapidly degraded with solar simulator irradiation. Results indicate that most of the wetlands are a net sink for CDOM, possibly due to absorption to sediments. The FS wetland appears to have a source of non-CDOM optically active organic carbon, possibly from a pollutant.

Organic acids combined with Fe-chelate improves ferric nutrition in tomato grown in calcisol soil

Plants developed in calcisol soils have limitations in iron nutrition, so exogenous applications of organic acids plus iron chelate can be an alternative. With the objective of knowing the answer of adding organic acids in the fertilizer solution plus a ferric chelate on the characteristics of the ferric nutrition of tomato plants developed in the calcisol soil the present experiment was established. We conducted the experiment in two stages, in the first stage studied different concentration of some organic acids: citric acid (CA), oxalic acid (OA), salicylic acid (SA), and humic complexes (HCs) combined with a FeEDDHA iron chelate, we included treatment control FeEDTA and FeEDDHA and treatment without iron in the fertilizer solution. In the second stage, we compared the best concentrations of organic acids in combination with FeEDTA iron chelate; we used to treatment control FeEDTA and FeEDDHA, and a control treatment without iron in the fertilizer solution. The best concentrations were CA 10−4 M, OA 10−4 M, SA 10−5 M, and HC 0.4 ml l−1. In the second stage, the addition of CA+FeEDTA and HC+FeEDTA increased SPAD units, chlorophyll and vitamin C contents and fruit quality improved. An increase content of Fe, Zn, and Mn in leaves was presented with treatment CA+FeEDTA and HC+FeEDTA. Addition of CA+FeEDTA improved the oxidation-reduction potential, pH and electrical conductivity (EC) of plant leachates, followed by HC+FeEDTA. Applications of CA and HC in the nutrient solution in combination with EDTA-type chelate improved the characteristics of the ferric nutrition of tomato plants developed in calcisol soil.