Potential phytoremediation of Pampa biome native and invasive grass species cohabiting vineyards contaminated with Cu in Southern Brazil.

The objectives were (a) to evaluate whether grasses native to the Pampa biome, Axonopus affinis Chase, Paspalum notatum Flüggé and Paspalum plicatulum Michx, and the invasive grass Cynodon dactylon (L.). Pers have the potential to phytoremediate soil contaminated with Cu (0, 35 and 70 mg Cu kg-1); (b) assess whether the growth of these species is compromised by the excess of Cu available in the soil; and (c) determine the impact of excess Cu on the physiological responses of the studied species. C. dactylon presented the best performance in soil contaminated with 35 mg of Cu kg-1. In C. dactylon, the concentrations of chlorophyll b and carotenoids increased, as did the photosynthetic rate and plant growth. Phytotoxic effects of Cu in soil contaminated with 70 mg of Cu kg-1 were more severe on A. affinis and led to plant death. The other species presented reduced photosynthetic and growth rates, as well as increased activity of antioxidant enzymes such as superoxide dismutase and guaiacol peroxidase. This very same Cu level has decreased photosynthetic pigment concentrations in P. notatum and P. plicatulum. On the other hand, it did not change chlorophyll a and b concentrations in C. dactylon and increased carotenoid concentrations in it. High values recorded for Cu bioaccumulation-in-grass-root factor, mainly in P. plicatulum, have indicated that the investigated plants are potential phytostabilizers. High C. dactylon biomass production-in comparison to other species-compensates for the relatively low metal concentration in its tissues by increasing metal extraction from the soil. This makes C. dactylon more efficient in the phytoremediation process than other species.

The tolerance of grapevine rootstocks to copper excess and to the use of calcium and phosphorus to mitigate its phytotoxicity.

High soil copper (Cu) concentrations in vineyards can cause phytotoxicity to grapevine rootstocks. In order to mitigate toxicity, the use of grapevine rootstock genetic variation and the application of amendments are possible strategies. The aim of this study is to assess the tolerance of grapevine rootstocks to Cu excess and whether phosphorus (P) and calcium (Ca) can reduce phytotoxicity caused by Cu. Grapevine rootstock seedlings were produced from selected stakes: Paulsen 1103 (Vitis berlandieri × Vitis rupestris); SO4 (Vitis berlandieri × Vitis riparia); IAC 572 ((Vitis Riparia × Vitis rupestris) × Vitis caribaea); and Isabel (Vitis labrusca). Seedlings were grown in nutrition solution added with the following treatments: 0.3 µM Cu (control); 60 µM Cu; 60 µM Cu and 62 mg L-1 P; 60 µM Cu and 400 mg L-1 Ca. High Cu concentration caused phytotoxicity in all rootstocks, impairing their growth and decreasing nutrient concentration and photosynthetic activity. P and Ca addition had positive effect on the photosynthetic activity of all rootstocks, although it was not enough to revert growth to levels comparable with controls. Overall, based on the results, the application of P and Ca was not efficient in mitigating Cu phytotoxicity in grapevine plants grown in solution. Isabel was the most sensitive rootstock to Cu phytotoxicity, whereas Paulsen 1103 and SO4 presented more tolerance and can be used, together with other management strategies, in contaminated vineyard areas. Therefore, careful genotype rootstock selection for use in high Cu soils is important, while Ca and P are not efficient mitigators of Cu toxicity.

Physiological responses of beet and cabbage plants exposed to copper and their potential insertion in human food chain.

Copper (Cu) can be toxic to vegetables when it is absorbed and accumulated at large concentrations, a fact that increases the risk of excessive addition of this metal to the human food chain. The aims of the current study are (1) to determine the Cu concentrations that have critical toxic effects on beet and cabbage plants, and the potential of these plants to enter the human food chain, as well as (2) to assess the physiological and biochemical responses of representatives of these vegetables grown in nutrient solution presenting increasing Cu concentrations. Beet and cabbage plants were grown for 75 days in pots filled with sand added with nutrient solution presenting six Cu concentrations: 0.00, 0.52, 1.02, 1.52, 2.02 and 2.52 mg Cu L-1. Dry matter yield and Cu accumulation in different plant organs were evaluated. Photosynthetic pigment contents, lipid peroxidation levels (TBARs), superoxide dismutase (SOD) and peroxidase (POD) activity and hydrogen peroxide (H2O2) concentrations in leaves were evaluated. Critical Cu concentrations that led to toxicity in plant organs such as beetroot and cabbage head, which are often found in human diets, corresponded to 1.43 mg Cu L-1 and 1.59 mg Cu L-1, respectively. High Cu concentrations in the nutrient solution have increased Cu concentrations and accumulation in plant tissues. This outcome justified the increased POD and SOD enzyme activity in the leaves of beet and cabbage plants, respectively, and was the cause of reduced plant growth in both crops. Cabbage plants presented higher tolerance to increased Cu levels in the growing environment than beet plants. However, it is necessary being careful at the time to consume both vegetables, when they are grown in Cu-enriched environments.

Soil tillage affects soybean growth and promotes heavy metal accumulation in seeds.

When soybean is grown in soils with high heavy metal concentrations, it may introduce those contaminants into the human food chain, posing risks to human health. This study evaluated the effect of tilling the soil with high Cu, Zn, and Mn levels on soybean physiology and metal accumulation in seeds. Disturbed and undisturbed soil samples were collected in two different sites: a vineyard with high heavy metal concentration and a grassland area, containing natural vegetation. Two soybean cultivars were sown and grown in the greenhouse. Photosynthetic parameters and biochemical analysis of oxidative stress were performed. Cu, Zn, and Mn in leaves and seeds, dry mass, and weight of seeds were evaluated. Soil structure had a high influence on plant growth and physiology, while soil site had a high impact on heavy metal accumulation in leaves and seeds. Soybean plants that grown in vineyard soils with high heavy metal concentrations, accumulated 50% more Zn in leaves and seeds, 70% more Cu in leaves, and 90% more Cu in seeds, than those plants grown in grassland soils. Besides, Zn concentration in seeds was higher than the permissible limit. Moreover, the disturbance of both vineyard soil and grassland soil was not good for plant growth and physiology, which have increased TBARS and H2O2 concentration in plants, transpiration rate, metal concentration in leaves and seeds. Soil disturbance may have caused organic matter oxidation and changes in the composition and quantity of soil microorganisms and it affects the availability of other nutrients in the soil.

Tolerance and phytoremediation potential of grass species native to South American grasslands to copper-contaminated soils.

Grass species native to South American can have mechanisms to tolerate copper (Cu) excess, which improves their use to phytoremediate Cu-contaminated soils . The aims of the present study are to assess the tolerance of grass species native to South American grasslands to copper-contaminated soils, as well as their adaptive responses under high Cu-stressed condition and to identify native grass species presenting the highest potential to be used for phytoremediation purposes. Soil samples were air-dried and their acidity, phosphorus and potassium levels were corrected, and the samples were incubated. Three Cu levels were used in the experiment: natural (Dose 0), with added of 40 mg kg-1 of Cu and with added of 80 mg kg-1 of Cu. Three Axonopus affinis, Paspalum notatum and Paspalum plicatulum seedlings were transferred to 5-L pots filled with soil in August and grown for 121 days. Soil solution was collected during cultivation with the aid of Rhizon lysimeters. Main concentrations of cations and anions, dissolved organic carbon and pH in the soil solution were analyzed and the ionic speciation was carried out. Cu toxicity impaired the growth of grass species native to South America, since Cu excess led to both changes in root morphology and nutritional unbalance. Among all assessed native species, Paspalum plicatulum was the one presenting the greatest potential to phytostabilize in Cu-contaminated soils, since it mainly accumulates Cu absorbed in the roots; therefore, its intercropping with grapevines is can be beneficial in Cu-contaminated soils.

The copper economy response is partially conserved in rice (Oryza sativa L.).

Copper (Cu) is an essential element for plants, especially in photosynthesis, as it is required for plastocyanin function in electron transfer reactions at thylakoid membranes. In Arabidopsis thaliana, Cu deficiency leads to the Cu economy response, in which plants prioritize Cu usage by plastocyanin in detriment of non-essential cupric proteins. In rice (Oryza sativa), however, this response has not been characterized. Rice OsHMA5 is a Cu xylem-loading transporter involved in Cu translocation from roots to shoots, as suggested by the analysis of oshma5 mutant plants. Aiming to understand how rice plants respond to Cu deficiency and how decreased Cu translocation to shoots can affect this response, we characterized the physiological and molecular responses of WT and oshma5 plants under control and Cu deficiency treatments. We found evidence that shoots of oshma5 plants are more prone to Cu deficiency compared to shoots of WT plants, as demonstrated by decreased chlorophyll and Cu concentrations, and electron transport rate. Gene expression analysis revealed that Cu high-affinity transporters OsCOPT1 and OsCOPT5, along with a set of miRNAs and three Cu/Zn superoxide dismutases are responsive to Cu deficiency in both WT and oshma5 plants, suggesting their involvement in the Cu economy response. However, Fe superoxide dismutase was not up-regulated in rice, indicating a difference compared to the A. thaliana Cu economy model. Therefore, we provide evidence for a partially conserved Cu economy response in rice, in comparison to A. thaliana.

Physiological responses of rice (Oryza sativa L.) oszip7 loss-of-function plants exposed to varying Zn concentrations.

Rice is a daily staple for half of the world's population. However, rice grains are poor in micronutrients such as Fe and Zn, the two most commonly deficient minerals in the human diet. In plants, Fe and Zn must be absorbed from the soil, distributed and stored, so that their concentrations are maintained at sufficient but non-toxic levels. The understanding of mechanisms of Fe and Zn homeostasis in plants has the potential to benefit agriculture, improving the use of micronutrients by plants, as well as to indicate approaches that aim at biofortification of the grains. ZIP transporters are commonly associated with Zn uptake, but there are few reports about their physiological relevance in planta. Here we describe a Tos17 loss-of-function line for the Zn plasma membrane transporter OsZIP7 (oszip7). We showed that the absence of functional OsZIP7 leads to deregulated Zn partitioning, increasing Zn accumulation in roots but decreasing in shoots and seeds. We also demonstrated that, upon Zn deficiency, oszip7 plants slightly increase their photosynthetic performance, suggesting that these plants might be primed for Zn deficiency which makes them more tolerant. On the other hand, we found that Zn excess is more deleterious to oszip7 plants compared to wild type, which may be linked to secondary effects in concentrations of other elements such as Fe. Our data suggest that OsZIP7 is important for Zn homeostasis under physiological Zn concentrations, and that Fe homeostasis might be affected due to loss of function of OsZIP7.

Barnyardgrass control using tank-mixed herbicides with saflufenacil and its influence in photosynthesis and chlorophyll fluorescence / Controle de capim-arroz mediante associações de herbicidas com saflufenacil e influência na fotossíntese e fluorescência de clorofila

ABSTRACT: The objectives of this research were to evaluate the interaction between herbicides mixed with saflufenacil for the control of barnyardgrass and to determine the effect on photosynthetic and chlorophyll fluorescence parameters. The experiment was conducted in a greenhouse in a 2x8 factorial scheme, whose factor A tested resistant and susceptible biotypes; and factor B the herbicides: saflufenacil (70 g a.i. ha-1), clomazone (180 g a.i. ha-1), imazapyr + imazapic (73.5 + 24.5 g a.i. ha-1), and cyhalofop (360 g a.i. ha-1), the mixtures of these herbicides with saflufenacil, and control without treatment. Weed control was assessed 7, 14, 21 and 28 days after herbicide application (DAA), as well as shoot dry matter at 28 DAA, photosynthetic parameters using infrared gas analyzer (IRGA), and emission of chlorophyll a fluorescence after 24 and 28 hours of application of treatments, respectively, and interaction of herbicides. Combination of saflufenacil with the herbicides tested in general did not change the response of both barnyardgrass biotypes to the herbicides used. The resistant biotype showed a lower negative effect on chlorophyll fluorescence and photosynthesis parameters in the combination of herbicides with saflufenacil. The herbicide cyhalofop was effective for the control of ALS-susceptible and resistant barnyardgrass.

RESUMO: O objetivo deste trabalho foi avaliar a interação entre herbicidas associados ao saflufenacil para o controle de capim-arroz e a determinação do efeito dos herbicidas sobre os parâmetros fotossintéticos e de fluorescência de clorofila. O experimento foi conduzido em casa de vegetação em esquema fatorial 2x8, cujo fator A testou os biótipos resistente e suscetível; e o fator B os herbicidas: saflufenacil (70 g i.a. ha-1), clomazone (180 g i.a. ha-1), imazapyr+imazapic (73,5+24,5 g i.a. ha-1), cyhalofop (360 g i.a. ha-1), as associações desses com saflufenacil, e testemunha sem tratamento. Foi avaliado o controle aos 7, 14, 21 e 28 dias após a aplicação dos herbicidas (DAA), massa seca da parte aérea aos 28 DAA, avaliação de parâmetros fotossintéticos com analisador de gás infravermelho (IRGA) e emissão de fluorescência da clorofila a 24 e 48 horas após aplicação dos tratamentos, respectivamente, e interação dos herbicidas. A associação de saflufenacil com herbicidas testados na maior parte não modificou a resposta dos herbicidas para o controle de capim-arroz em ambos os biótipos. O biótipo resistente apresentou menor efeito negativo nos processos de fluorescência de clorofila e parâmetros de fotossíntese na associação de herbicidas com saflufenacil. O herbicida cyhalofop associado ao saflufenacil demonstra ser eficiente para o controle de capim-arroz suscetível e resistente a ALS.

Earthworms and mycorrhization increase copper phytoextraction by Canavalia ensiformis in sandy soil.

Phytoremediation is an alternative for remediating soil contamination by copper, and its efficiency has been shown to increase when arbuscular mycorrhizal fungi (AMF) and earthworms are separately inoculated into the soil. This study evaluated the isolated and combined effects of inoculating earthworms and arbuscular mycorrhizal fungi into a sandy soil on copper phytoremediation by Canavalia ensiformis. The plants were grown in a greenhouse in soil contaminated with 100 mg Cu kg-1 with and without being inoculated with the arbuscular mycorrhizal fungus Rhizoglomus clarum and the earthworm Eisenia andrei. The availabilities of solid-phase Cu and other nutrients in the soil solution and plant growth were evaluated along with Cu phytotoxicity based on photochemical efficiency and oxidative stress enzyme activity. Accumulation of Cu and other nutrients in the shoots and roots; mycorrhizal colonization, nodulation, and reproduction; and Cu accumulation in the earthworm tissues were also evaluated. The copper caused photosynthetic and biochemical damage that reduced the shoot dry weight by 44% and the root dry weight by 29%. However, the arbuscular mycorrhizal fungus alleviated the Cu toxicity to the plant and increased the shoot dry weight by 81% in the contaminated soil. The earthworms increased the Cu uptake and translocation to the shoot by 31%. The combined presence of the arbuscular mycorrhizal fungus and earthworms in the contaminated soil increased the growth and Cu content of the aerial plant tissues, yielding a 200% increase in Cu accumulation (metal content × biomass) in the C. ensiformis shoots. Combined inoculation with earthworms and arbuscular mycorrhizal fungi increased copper phytoextraction by Canavalia ensiformis in a sandy soil.

Potential of vermicompost and limestone in reducing copper toxicity in young grapevines grown in Cu-contaminated vineyard soil.

Foliar fungicide application in grapevines increases the content of heavy metals such as copper (Cu) in vineyard soils, which may reach phytotoxic levels. The application of soil amendments such as limestone and vermicompost may reduce Cu availability and phytotoxicity. The study aimed to assess growth, physiological status and changes in root morphology in young grapevines grown for 12 months in Cu-contaminated soil with and without the application of soil amendments. Samples of a Typic Hapludalf soil were collected in a vineyard with more than 30 years of cultivation. The following treatments were used: 1) control (without amendment), 2) application of organic vermicompost (86.7 g kg-1) and 3) application of limestone (3 Mg ha-1). Grapevines (Paulsen 1103 rootstock) were transplanted and grown for 12 months in PVC soil columns. We assessed parameters of growth, photosynthesis and root morphology. Grapevines grown in soil treated with limestone showed increased growth, dry matter yield and photosynthetic efficiency. The highest Cu concentrations in root tissue were found in grapevines grown in control soil. The application of vermicompost in this study did not alleviate Cu toxicity. Grapevines grown in soil treated with vermicompost showed high manganese (Mn) concentration in shoots before the winter pruning, reflecting the high Mn concentrations in soil solution that caused Mn phytotoxicity, resulting in plant death after the winter pruning. The vermicompost used in this study is not suitable for agronomic use. The use of limestone was an effective strategy to reduce Cu availability and phytotoxicity.

Effects of Rhizophagus clarus and P availability in the tolerance and physiological response of Mucuna cinereum to copper.

Arbuscular mycorrhizal fungi (AMF) improve plant ability to uptake P and tolerate heavy metals. This study aimed to evaluate the effect of available P and the inoculation of Rhizophagus clarus in a Cu-contaminated soil (i) on the activity of acid phosphatases (soil and plant), the presence of glomalin, and (ii) in the biochemical and physiological status of Mucuna cinereum. A Typic Hapludalf soil artificially contaminated by adding 60 mg kg-1 Cu was used in a 3 × 2 factorial design with three replicates. Treatments consisted of three P levels: 0, 40, and 100 mg kg-1 P. Each P treatment level was inoculated (+AMF)/non-inoculated (-AMF) with 200 spores of R. clarus per pot, and plants grown for 45 days. The addition of at least 40 mg kg-1 P and the inoculation of plants with R. clarus proved to be efficient to reduce Cu phytotoxicity and increase dry matter yield. Mycorrhization and phosphate fertilization reduced the activity of enzymes regulating oxidative stress (SOD and POD), and altered the chlorophyll a fluorescence parameters, due to the lower stress caused by available Cu. These results suggest a synergism between the application of P and the inoculation with R. clarus, favoring the growth of M. cinereum in a Cu-contaminated soil. This study shows that AMF inoculation represents an interesting alternative to P fertilization to improve plant development when exposed to excess Cu.

Growth, biochemical response and nutritional status of Angico-Vermelho (Parapiptadenia rigida (Bentham) Brenan) under the application of soil amendment in Cu-contaminated soil.

Forest species Angico-Vermelho (Parapiptadenia rigida (Bentham) Brenan) is an alternative for the revegetation of areas contaminated with high levels of heavy metals such as copper (Cu). However, excess Cu may cause toxicity to plants, which is why the use of soil amendments can facilitate cultivation by reducing the availability of Cu in the soil. The aim of this study was to assess how the use of amendment can contribute to growth and nutritional status as well as reduce oxidative stress in Angico-Vermelho grown in Cu-contaminated soil. Samples of a Typic Hapludalf soil containing high Cu content were used for the application of four amendments (limestone, organic compost, Ca silicate and zeolite), in addition to a control treatment. The treatments were arranged in a completely randomized design, with four replicates. The use of amendments decreased Cu content available in soil and contributed to improve both plant nutritional status and its antioxidant response expressed by enzymatic activity. The application of the amendments, especially zeolite and Ca silicate, increased dry matter yield of Angico-Vermelho. Thus, the results presented here suggest that the use of amendments contributes to improving Cu-contaminated soils and favors revegetation with Angico-Vermelho.

Relationship between root exudation of organic carbon and physiological variables of irrigated rice cultivars / Relação entre exsudação radicular de carbono orgânico e variáveis fisiológicas de cultivares de arroz irrigado

ABSTRACT: Rhizospheric carbon resulting from root exudation is one of the substrates used by the soil microbiota, and reflects methane (CH4) emissions in anoxic environments such as irrigated rice cultivation. With the increase of the photosynthetic capacity of the plant in the reproductive period, there is greater accumulation of biomass which, in turn, increases the rate of root exudation. However, genotypic variations in the physiological aspects of rice plants may be related to the amount of root exudates. Ten cultivars of irrigated rice were evaluated for the exudation rate of total organic carbon (EXRToc), shoot dry matter (SDM), and physiological variables related to photosynthesis during the full flowering (blooming) period. Two experiments were conducted in the greenhouse of the Department of Soils of the UFSM (University of Santa Maria, Santa Maria, RS, Brazil) in a completely randomized experimental design. The cultivars presented significant differences in EXRToc, SDM, and all physiological variables as well as positive and significant correlations between EXRToc and physiological variables. Early cultivars were more inefficient in the physiological variables reflecting reduced values of EXRToc and SDM whereas medium-cycle cultivars were more efficient with larger EXRToc and SDM reflections.

RESUMO: O carbono rizosférico resultado da exsudação radicular é um dos substratos utilizados pela microbiota do solo, refletindo-se nas emissões de metano (CH4) em ambientes anóxicos, como no cultivo de arroz irrigado. Com o aumento da capacidade fotossintética da planta no período reprodutivo, ocorre acúmulo maior de biomassa, que por sua vez, impulsiona aumento na taxa de exsudação radicular. Entretanto, variações genotípicas nos aspectos fisiológicos das plantas de arroz podem se relacionar com a quantidade de exsudatos radiculares. Foram avaliadas dez cultivares de arroz irrigado quanto a taxa de exsudação de carbono orgânico total (TEXCOT), matéria seca da parte aérea (MSPA) e variáveis fisiológicas relacionadas com a fotossíntese no período de florescimento pleno. Dois experimentos foram conduzidos na casa de vegetação do Departamento de Solos da UFSM em delineamento experimental inteiramente casualizado. As cultivares apresentaram diferenças significativas na TEXCOT, na MSPA e em todas as variáveis fisiológicas, bem como, correlações positivas e significantes entre TEXCOT e as variáveis fisiológicas, sendo que as cultivares de ciclo precoce se mostraram mais ineficientes nas variáveis fisiológicas refletindo em valores reduzidos de TEXCOT e MSPA, enquanto que as cultivares de ciclo médio se mostraram mais eficientes com reflexos em maiores TEXCOT e MSPA.