Mesquite Plants Research Articles

Customized biochar for soil applications in arid land: Effect of feedstock type and pyrolysis temperature on soil microbial enumeration and respiration

Biochar is rapidly gaining worldwide interest as an agro-technology for increasing soil health and carbon storage. This study investigated the physicochemical characteristics and impact on soil microbes of biochar amendments from three feedstock sources: date palm leaves (D), mesquite plants (M) and sludge compost (S.C.); pyrolyzed at 450 ℃, 600 ℃ and 750 ℃. Scanning electron microscopy images showed an apparent pore size increase with increasing pyrolysis temperature. The increase in pyrolysis temperature decreased O-H and C-O bonds and increased the proportion of C-C bonds, as obtained from the Fourier transform infrared spectroscopy studies. Thermostability was highest at a pyrolysis temperature of 750 ℃, with distinct thermal decomposition profiles for each of the three feedstock materials used, as indicated by the dynamic thermal gravimetric analysis. The SC biochars showed the highest mineral content (45–66%) with significantly higher water-soluble and total concentrations of mineral elements. The SC samples also showed the presence of possible soil contaminants such as Pb and As, and its use as a soil amendment is not recommended, even though the SC at 450 ℃ was the only nonalkaline biochar in this study. The M feedstock produced biochar with the highest surface area (600 m2 g−1) and carbon content based on loss on ignition (94.98%); nevertheless, the M biochar reduced soil microbial enumeration and respiration. This reduction increased with increasing pyrolysis temperature. Therefore, the M biochar feedstocks are not recommended for improving soil health and may be tested in the future as a microbial inhibitor for soil-borne plant pathogens. Considering the physicochemical properties and the biochar impact on soil, D at 600 ℃ was the best biochar selected for further studies as a soil amendment. The large differences in biochar physicochemical properties and their effect on soil microbes observed in this study suggest that the feedstock type and pyrolysis temperatures must be considered during biochar amendment production for improving soil health in arid-land agroecosystems.

Characterization and in vitro spread of mesquite (Prosopis laevigata (Humb. & Bonpl. ex Willd.) M.C.Johnst.)

Objective: To analyze fruit characteristics, genetic diversity, and in vitro spread of mesquite genotypes (Prosopis laevigata (Humb. & Bonpl.) ex Willd.) from the plains of Ojuelos-Aguascalientes, Mexico. Design/Methodology/Approach: Fruit and leaf samples were collected from 20 mesquite genotypes to analyze and extract DNA to determine their diversity using RAPDs. Simultaneously, in vitro spread tests were performed. Results: The Ojuelos de Jalisco genotype stood out for the weight of its fruits, while La Presa genotype stood out for its degrees Brix. Genotypes were grouped according to their best growth condition for their genetic analysis. In in vitro spread, AG3 with IBA allowed stem/shoot elongation and root formation; meanwhile, AgNO3 prevents leaf fall, allowing rooting and transfer to the soil. Study Implications/Limitations: This study about mesquite (P. laevigata) was limited to the plains of Ojuelos-Aguascalientes. Findings/Conclusions: Mesquite plants from the Ojuelos-Aguascalientes subregion, Mexico, were identified and georeferenced; likewise, a methodology for its in vitro spread was developed.

Silver nanoparticles from Hpytus suaveolens and their effect on biochemical and physiological parameter in mesquite plants

In this study, a simple and economical procedure to obtain silver nanoparticles using leaf-extract of Hpytus sauveolens (AgNPs) and their effect in chlorophyll, nitrogen balance index and epidermal polyphenols contents, photochemical efficiency and phenylalanine ammonia lyase (PAL) activity in Prosopis juliflora is reported. Synthesized nanoparticles were characterized by ultraviolet (UV) spectroscopy, DLS analyzer, FTIR spectroscopy, Scanning electron microscopy (SEM) and energy dispersive analysis X-ray (EDX). The results showed that AgNPs contained bioactive molecules, which had important function in the reduction of Ag ion. The AgNPs had mean particle size, zeta potential conductivity of 22 nm, 29.50 mv and 1.394 mS/cm, respectively according to DLS analysis. Different doses of AgNPs (100, 75, 50 and 25 ppm) showed positive effects on phenylalanine ammonia lyase (PAL) activity and neutral effect in chlorophyll, nitrogen balance index and epidermal polyphenols contents on plants. Only higher doses (100 ppm) caused negative effects in photochemical efficiency in Prosopis juliflora . Hence future studies are necessary to elucidate the participation of green AgNPs as exogenous inducers of PAL enzyme involved in the phenylpropanoid pathway in Prosopis juliflora in the reduction of stress oxidative in plants. • Synthesis of green silver nanoparticles from native plants using Hpytus suaveolens . • The applications of AgNPs produce changes biochemical in Prosopis juliflora . • Higher doses AgNPs produce negative effects on physiological status. • Green AgNPs increased the PAL activity in plants.

Aplicación de ethephon en una población de mezquite (Prosopis spp.) para la extracción de goma en Naica, Chihuahua, México

The objective of the research was to extract gum from the mesquite plant, for this, a plant hormone in concentration of 10%, 10.85, 15%, 20%, 25% was used. It was applied to cuts of trunk and secondary branches of trees. The results indicated that 100% of the treated plants produced gum. The duration of the hormone's effect on gum production was nine weeks. Harvests were made every three weeks. No plant showed signs of damage or deterioration. It was observed that as the tree has a greater perimeter of the stem, it produces a greater amount of gum. It was also observed that the plant hormone apparently did not cause biological damage to the leaves and pods according to visual observation compared to other trees without treatment. The proximal chemical analysis that both mesquite and huizache gums have similarity and even improve the parameters required by the Food and Drug Administration for the use of gum arabic in the food industry. The production and harvest periods are from February to June and from September to December. There is an estimated average production of around 180 gr per tree production season.

Extracción de goma en mezquite (Prosopis spp) nativo usando etileno como hormona vegetal

El objetivo de la investigación fue extraer goma de la planta de mezquite, para ello, se utilizó una hormona vegetal en concentración al 10%, 10.85, 15%, 20%, 25%. Se aplicó en cortes de tronco y ramas secundarias de los árboles. Los resultados indicaron que el 100% de las plantas tratadas produjeron goma. La duración del efecto de la hormona en la producción de goma fue de nueve semanas. Las cosechas se realizaron cada tres semanas. Ninguna planta manifestó signos de daño o deterioro. Se observó que conforme el árbol tiene mayor perímetro de fuste produce mayor cantidad de goma. Se observó además que la hormona vegetal aparentemente no causó daño biológico en las hojas y en las vainas de acuerdo a la observación visual comparándolo con otros árboles sin tratamiento. El análisis químico proximal que ambas gomas de mezquite y huizache tienen semejanza e incluso mejoran los parámetros requeridos por la Food and Drug Administration para el uso de la goma arábiga en la industria alimenticia. Los periodos de producción y cosecha son de febrero a junio y de septiembre a diciembre. Se tiene una producción promedio estimado de alrededor de 180 gr por árbol temporada de producción.

High-performance thin-layer chromatography fingerprinting, total phenolic and total flavonoid contents and anti-platelet-aggregation activities of Prosopis farcta extracts

Cardiovascular diseases are a leading cause of worldwide death and excessive platelet is closely related with their pathogenesis. Different plants and natural compounds have demonstrated anti-platelet effects. The aim of this study was to report the high-performance thin-layer chromatography (HPTLC) fingerprinting and anti-platelet-aggregation activities of different leaf extracts (n-hexane, chloroform, ethyl acetate, methanol and aqueous) of Prosopis farcta (Syrian mesquite) plant. The results showed a 100% inhibition of aggregation activity after plasmatic adenosine diphosphate (ADP) aggregation activation of ethyl acetate, ethanolic, methanolic and aqueous extracts, at 60 mg/mL concentration. The IC50 ADP value of these extracts ranged between 4.07 and 11.39 mg/mL. Moreover, these extracts reported the highest amounts of phenolic and flavonoid contents. In conclusion, phytochemicals present in P. farcta leaves have anti-platelet-aggregation activities. Future studies are needed to identify the compounds with anti-platelet potential present in P. farcta.

Consumption of the Syrian mesquite plant (Prosopis farcta) fruit and seed lyophilized extracts may have both protective and toxic effects in STZ-induced diabetic rats

The aim of study was to investigate the antidiabetic and antioxidant properties of extracts obtained from dried Prosopis farcta fruit and seeds against streptozotocin-induced diabetes in rats. According to the results, glucose, haemoglobin A1c, α-glycosidase activity, liver and kidney damage biomarkers, and malondialdehyde contents of all of the diabetic groups were found to have increased significantly according to the control group. Furthermore, the insulin and C-peptide secretions increased, and liver malondialdehyde level decreased, which were determined as the result of fluctuations in the antioxidant enzyme activities with a dose of 400 mg/kg fruit extract, while seed extract dosages of 100 and 400 mg/kg caused an increase in hepatic demage biomarkers. It was concluded that fruit extract may have insulin secretion stimulating and lipid peroxidation inhibitory effects, whereas seed extract might have caused hepatocyte damage changes to the transport functions and membrane permeability of these cells, thus causing enzymes to leak.

Molecular identification of Botryosphaeria dothidea as a fungal associate of the gall midge Asphondylia prosopidis on mesquite in the United States

The gall midge, Asphondylia prosopidis Cockerell, is considered a potential biological control agent for invasive mesquite (Prosopis species) populations in South Africa. Asphondylia species induce galls on mesquite plants by inserting an egg into a bud, and also carry conidia of specific fungal associates in their mycangia that are transferred into the galls. However, fungal associates have not been characterized in flower bud galls formed by A. prosopidis on mesquite. It is essential to identify the fungal associates in the galls formed on natural populations of mesquite prior to host specificity testing. In this study, we showed that Botryosphaeria dothidea (Moug. ex Fr.) Ces. & De Not. is the fungal associate in the flower bud galls on mesquite induced by A. prosopidis in New Mexico by characterization of the internal transcribed spacer (ITS) region. Further, isolates of B. dothidea in A. prosopidis galls formed on mesquite were genetically identical to isolates of B. dothidea carried by other Asphondylia species, particularly on the confamilial Acacia species in South Africa. Our result suggests that A. prosopidis is safe to utilize as a biological control agent for mesquite, if A. prosopidis shows a narrow host range in the pre-release risk assessment, since B. dothidea appears to be ubiquitous. To our knowledge, this is the first report of the association between Asphondylia species and B. dothidea in the United States. We anticipate that A. prosopidis will associate with indigenous B. dothidea in South Africa.

Influence of biochar and compost on phytoremediation of oil-contaminated soil

ABSTRACTThe use of pyrolyzed carbon, biochar, as a soil amendment is of potential interest for improving phytoremediation of soil that has been contaminated by petroleum hydrocarbons. To examine this question, the research reported here compared the effects of biochar, plants (mesquite tree seedlings), compost and combinations of these treatments on the rate of biodegradation of oil in a contaminated soil and the population size of oil-degrading bacteria. The presence of mesquite plants significantly enhanced oil degradation in all treatments except when biochar was used as the sole amendment without compost. The greatest extent of oil degradation was achieved in soil planted with mesquite and amended with compost (44% of the light hydrocarbon fraction). Most probable number assays showed that biochar generally reduced the population size of the oil-degrading community. The results of this study suggest that biochar addition to petroleum-contaminated soils does not improve the rate of bioremediation. In contrast, the use of plants and compost additions to soil are confirmed as important bioremediation technologies.

Mesquite (Prosopis juliflora) plant prevalence in different districts of Balochistan & antibacterial activity of its pods

This study was conducted to evaluate in vivo multiple uses of mesquite plant, identification of selected areas in Balochistan and anti-bacterial activity of mesquite pods (alkaloid-enriched extracts). For this purpose a survey was conducted in areas where mesquite plant prevails. Pods of mesquite were collected from different trees standing at Yaro Pishin Roadside Plantation and were brought to the physiology laboratory of Centre for Advanced Studies in Vaccinology & Biotechnology (CASVAB) University of Balochistan Quetta. Pods were dried and extract was obtained which was subjected to check antibacterial activity through two different methods. The inhibition zones of bacteria were measured in mm. It was concluded that mesquite, which was once viewed as weed, its pods have antibacterial components. Furthermore, this study indicated that mesquite is a useful plant if properly managed. Keywords: Prosopis juliflora; Pods; Balochistan; Antibacterial activity http://dx.doi.org/10.19045/bspab.2017.600162

Allelopathic effects of mesquite (Prosopis juliflora) aqueous extracts on seeds germination and seedlings growth of alfalfa, sesame and sorghum

Abstract. Omer HHM, Mohammed IS. 2017. Allelopathic effects mesquite (Prosopis juliflora) aqueous extracts on seeds germination and seedling growth of alfalfa, sesame and sorghum. Cell Biol Dev 1: 51-54. Mesquite plant [Prosopis juliflora (Swartz) DC] is an invasive tree or shrub native to South America. Unfortunately, the plant threatens biodiversity and agriculture due to deliberate distribution within Sudan. Furthermore, this plant has an allopathic potential that may be caused by falling leaves, fruits, root exudates, or plant leachates. These allelochemicals may inhibit the germination and growth of agricultural crops. This study was conducted in the Laboratory of Plant Pathology, College of Agricultural Studies, Sudan University of Science and Technology, Khartoum, in January-February 2016. The aim of this study was to elucidate the potential of allopathic effects of aqueous extract of different parts of mesquite plant, i.e., leaves, fruits, bark, and roots, on germination and early seedlings growth of alfalfa, sesame, and sorghum. The results indicated that the aqueous extracts of different parts of the mesquite plant significantly ( P ? 0. 05) inhibited the seeds' germination and reduced the early growth of the seedlings. These suggest that the inhibitory substance (s) were widely distributed in mesquite plants but to varying extents. Moreover, fruits and leaves extracts were more pronounced and consistent than bark and roots. That could be attributed to the mesquite fruits and leaves aqueous extracts containing more water-soluble allelochemicals than roots and bark. They gave 0.0% germination in alfalfa and sesame and 47.6-86.7% in sorghum, respectively, compared to control. At the same time, the length of hypocotyl and radical was reduced to 0.0 cm and up to 2.7 cm depending on the efficacy of extract and the response of the test crop. Thus, it is recommended to study the nature of inhibitors to determine whether allelopathic is the cause of the extraordinary success of mesquite on the flat plains of agricultural land in Sudan.

Visualization of copper(II) in velvet mesquite (Prosopis Juliflora-Velutina) and soybeans (Glycine max) by earth field magnetic resonance imaging

ABSTRACTThe goal of this research was to visualize the uptake of copper by plants to promote phytoremediation. The hypothesis was that regions of the plant that contain more copper have enhanced nuclear magnetic resonance using copper as a paramagnetic contrast agent. Earth field magnetic resonance imaging (EFMRI) spectrometry uses a magnetic field 300,000 times weaker than a 600 MHz nuclear magnetic resonance spectrometer. As in conventional human MRI, this portable instrument is capable of recording one-, two-, and three-dimensional images, although the sample size is reduced. The enhancement of signal was first demonstrated recording the two dimensional images of different concentrations of aqueous copper sulfate. The study also focused on growing mesquite and soybean plants in hydroponic media containing 0.25 mM copper nitrate for four and three weeks, respectively, and recording their EFMRI images with plants grown without copper nitrate. The results showed that EFMRI allows the probing the plant absorption of copper without having to dissect the specimen and therefore requires less sample preparation and time than current techniques. This technique may be beneficial to phytoremediation by imaging plants to evaluate their copper accumulation.

Estimate of Damage on Mesquite Pods and Seeds (<i>Prosopis laevigata</i> (Willd) M.C. Johnst) (Mimosoideae) Caused by Bruchids (COLEOPTERA) in the Municipality of Durango, Durango, Mexico

Damage caused by weevils or bruchids in mesquite plants (Prosopis laevigata), in the municipality of Durango was established by infestation index. Immature and mature pods were obtained from 22 bushes during the months of June to September 2013. The pods were placed in emergence chambers, maintained at a temperature of 35±2°C and 70±10% RH, until adults were obtained. In June, 1,761 immature pods were obtained of which 76% were damaged (perforations); in August 713 mature pods were obtained with 90% damage. Observed bruchids species feeding on the pods and seed of mesquite were Algarobius prosopis and Mimosestes amicus (Bruchinae) with relative abundance of 76 and 19% respectively and an average infestation index of 83,2% on pods. Natural enemies that were present were the parasitoids Urosigalphus sp. (Braconidae) and Horismenus missouriensis (Chalcidoidea: Eulophidae) with 2% relative abundance. From the total 105 pods damaged by insects, 1, 188 seeds had 69, 2% bruchid damage. Bruchids control is necessary in order to be able to obtain benefits from the mesquite pods and this can be done mainly through parasitoids that are associated with them. This electronic document is a “live” template. The various components of your paper [title, text, tables, figures and references] are already defined on the style sheet, as illustrated by the portions given in this document.

Interactions between CeO2 Nanoparticles and the Desert Plant Mesquite: A Spectroscopy Approach

Exploring the effects of ecosystem exposure to unusual concentrations of engineered nanoparticles (ENP) is a critical issue in current environmental research. Nanotoxicological studies on plants have focused on model and crop plants, leaving plants from desert ecosystems virtually ignored. This research was designed to explore the interactions between CeO2 ENP and the desert plant mesquite (Prosopis juliflora velutina). Mesquite plantlets were grown for 15 days in a hydroponic CeO2 ENP-nutrient suspension at concentrations ranging from 500 to 4000 mg L–1. Biochemical assays showed that ascorbate-peroxidase activity in roots increased when exposed to 2000 and 4000 mg CeO2 L–1; whereas in leaves, catalase presented an increasing trend associated with the external concentration of the ENP. However, mesquite plants exhibited no visible signs of stress. At all CeO2 ENP treatments, the accumulation of Ce in root tissue was much higher (≥79%) than in the aerial part of the plant (≤21%). X-ray absorption near edg...

Population-level consequences of herbivory, changing climate, and source-sink dynamics on a long-lived invasive shrub.

Long-lived plant species are highly valued environmentally, economically, and socially, but can also cause substantial harm as invaders. Realistic demographic predictions can guide management decisions, and are particularly valuable for long-lived species where population response times can be long. Long-lived species are also challenging, given population dynamics can be affected by factors as diverse as herbivory, climate, and dispersal. We developed a matrix model to evaluate the effects of herbivory by a leaf-feeding biological control agent released in Australia against a long-lived invasive shrub (mesquite, Leguminoseae: Prosopis spp.). The stage-structured, density-dependent model used an annual time step and 10 climatically diverse years of field data. Mesquite population demography is sensitive to source-sink dynamics as most seeds are consumed and redistributed spatially by livestock. In addition, individual mesquite plants, because they are long lived, experience natural climate variation that cycles over decadal scales, as well as anthropogenic climate change. The model therefore explicitly considered the effects of both net dispersal and climate variation. Herbivory strongly regulated mesquite populations through reduced growth and fertility, but additional mortality of older plants will be required to reach management goals within a reasonable time frame. Growth and survival of seeds and seedlings were correlated with daily soil moisture. As a result, population dynamics were sensitive to rainfall scenario, but population response times were typically slow (20-800 years to reach equilibrium or extinction) due to adult longevity. Equilibrium population densities were expected to remain 5% higher, and be more dynamic, if historical multi-decadal climate patterns persist, the effect being dampened by herbivory suppressing seed production irrespective of preceding rainfall. Dense infestations were unlikely to form under a drier climate, and required net dispersal under the current climate. Seed input wasn't required to form dense infestations under a wetter climate. Each factor we considered (ongoing herbivory, changing climate, and source-sink dynamics) has a strong bearing on how this invasive species should be managed, highlighting the need for considering both ecological context (in this case, source-sink dynamics) and the effect of climate variability at relevant temporal scales (daily, multi-decadal, and anthropogenic) when deriving management recommendations for long-lived species.

Spatial patterns of grassland–shrubland state transitions: a 74‐year record on grazed and protected areas.

Tree and shrub abundance has increased in many grasslands causing changes in ecosystem carbon and nitrogen pools that are related to patterns of woody plant distribution. However, with regard to spatial patterns of shrub proliferation, little is known about how they are influenced by grazing or the extent to which they are influenced by intraspecific interactions. We addressed these questions by quantifying changes in the spatial distribution of Prosopis velutina (mesquite) shrubs over 74 years on grazed and protected grasslands. Livestock are effective agents of mesquite dispersal and mesquite plants have lateral roots extending well beyond the canopy. We therefore hypothesized that mesquite distributions would be random on grazed areas mainly due to cattle dispersion and clustered on protected areas due to decreased dispersal and interspecific interference with grasses; and that clustered or random distributions at early stages of encroachment would give way to regular distributions as stands matured and density-dependent interactions intensified. Assessments in 1932, 1948, and 2006 supported the first hypothesis, but we found no support for the second. In fact, clustering intensified with time on the protected area and the pattern remained random on the grazed site. Although shrub density increased on both areas between 1932 and 2006, we saw no progression toward a regular distribution indicative of density-dependent interactions. We propose that processes related to seed dispersal, grass–shrub seedling interactions, and hydrological constraints on shrub size interact to determine vegetation structure in grassland-to-shrubland state changes with implications for ecosystem function and management.

Green leaf volatiles and oxygenated metabolite emission bursts from mesquite branches following light–dark transitions

Green leaf volatiles (GLVs) are a diverse group of fatty acid-derived compounds emitted by all plants and are involved in a wide variety of developmental and stress-related biological functions. Recently, GLV emission bursts from leaves were reported following light-dark transitions and hypothesized to be related to the stress response while acetaldehyde bursts were hypothesized to be due to the 'pyruvate overflow' mechanism. In this study, branch emissions of GLVs and a group of oxygenated metabolites (acetaldehyde, ethanol, acetic acid, and acetone) derived from the pyruvate dehydrogenase (PDH) bypass pathway were quantified from mesquite plants following light-dark transitions using a coupled GC-MS, PTR-MS, and photosynthesis system. Within the first minute after darkening following a light period, large emission bursts of both C(5) and C(6) GLVs dominated by (Z)-3-hexen-1-yl acetate together with the PDH bypass metabolites are reported for the first time. We found that branches exposed to CO(2)-free air lacked significant GLV and PDH bypass bursts while O(2)-free atmospheres eliminated the GLV burst but stimulated the PDH bypass burst. A positive relationship was observed between photosynthetic activity prior to darkening and the magnitude of the GLV and PDH bursts. Photosynthesis under (13)CO(2) resulted in bursts with extensive labeling of acetaldehyde, ethanol, and the acetate but not the C(6)-alcohol moiety of (Z)-3-hexen-1-yl acetate. Our observations are consistent with (1) the "pyruvate overflow" mechanism with a fast turnover time (<1h) as part of the PDH bypass pathway, which may contribute to the acetyl-CoA used for the acetate moiety of (Z)-3-hexen-1-yl acetate, and (2) a pool of fatty acids with a slow turnover time (>3h) responsible for the C(6) alcohol moiety of (Z)-3-hexen-1-yl acetate via the 13-lipoxygenase pathway. We conclude that our non-invasive method may provide a new valuable in vivo tool for studies of acetyl-CoA and fatty acid metabolism in plants at a variety of spatial scales.

Arsenic Localization and Speciation in the Root–Soil Interface of the Desert Plant Prosopis juliflora-velutina

The bioavailability and mobility of arsenic (As) in soils depends on several factors such as pH, organic matter content, speciation, and the concentration of oxides and clay minerals, among others. Plants modify As bioavailability in the rhizosphere; thus, the biogeochemical processes of As in vegetated and non-vegetated soils are different. Changes in As speciation induced by the rhizosphere can be monitored using micro-focused synchrotron-based X-ray fluorescence (μXRF) combined with μX-ray absorption near-edge spectroscopy (μXANES). This research investigated As speciation in the rhizosphere of mesquite (Prosopis juliflora-velutina) plants grown in a sandy clay loam treated with As(III) and As(V) at 40 mg kg(-1). Rhizosphere soil and freeze-dried root tissues of one-month-old plants were analyzed by bulk XAS. Bulk XAS results showed that As(V) was the predominant species in the soil (rhizosphere and non-vegetated), whereas As(III) was dominant in the root tissues from both As(V) and As(III) treated plants. μXAS and μXRF studies of thin sections from resin embedded soil cores revealed the As(III)-S interactions in root tissues and a predominant As-Fe interaction in the soil. This research demonstrated that the combination of bulk XAS and μXAS techniques is a powerful analytical technique for the study of As speciation in soil and plant samples.

Spatial variation of soil δ13C and its relation to carbon input and soil texture in a subtropical lowland woodland

Spatial patterns of soil δ13C were quantified in a subtropical C3 woodland in the Rio Grande Plains of southern Texas, USA that developed during the past 100 yrs on a lowland site that was once C4 grassland. A 50 × 30 m plot and two transects were established, and soil cores (0–15 cm, n = 207) were collected, spatially referenced, and analyzed for δ13C, soil organic carbon (SOC), and soil particle size distribution. Cross-variogram analysis indicated that SOC remaining from the past C4 grassland community co-varied with soil texture over a distance of 23.7 m. In contrast, newer SOC derived from C3 woody plants was spatially correlated with root biomass within a range of 7.1 m. Although mesquite trees initiate grassland-to-woodland succession and create well-defined islands of soil modification in adjoining upland areas at this site, direct gradient and proximity analyses accounting for the number, size, and distance of mesquite plants in the vicinity of soil sample points failed to reveal any relationship between mesquite tree abundance and soil properties. Variogram analysis further indicated soil δ13C, texture and organic carbon content were spatially autocorrelated over distances (ranges = 15.6, 16.2 and 18.7 m, respectively) far greater than that of individual tree canopy diameters in these lowland communities. Cross-variogram analysis also revealed that δ13C – SOC and δ13C-texture relationships were spatially structured at distances much greater than that of mesquite canopies (range = 17.6 and 16.5 m, respectively). These results suggest fundamental differences in the functional nature and consequences of shrub encroachment between upland and lowland landscapes and challenge us to identify the earth system processes and ecosystem structures that are driving carbon cycling at these contrasting scales. Improvements in our understanding how controls over soil carbon cycling change with spatial scale will enhance our ability to design vegetation and soil sampling schemes; and to more effectively use soil δ13C as a tool to infer vegetation and soil organic carbon dynamics in ecosystems where C3–C4 transitions and changes in structure and function are occurring.

Toxicity and biotransformation of uncoated and coated nickel hydroxide nanoparticles on mesquite plants

Nanomaterials are of particular interest in environmental chemistry due to their unknown toxicity to living organisms. Reports indicate that nanoparticles (NPs) affect seed germination, but the uptake and biotransformation of metal nanoparticles is not well understood. The present study investigated the toxicity and biotransformation of Ni(OH)2 NPs by mesquite plants (Prosopis sp.). Three sets of plants were treated for four weeks with 0.01, 0.05, or 0.10 g of either uncoated or sodium citrate coated NPs before and after synthesis. Nickel concentrations in plants were determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES) and the form and oxidation state of Ni was determined using X-ray absorption spectroscopy (XAS). Results showed that uncoated NPs had an average size of 8.7 nm, whereas coated NPs before and after synthesis had an average of 2.5 and 0.9 nm, respectively. The ICP-OES results showed that plants treated with 0.10 g of uncoated and coated NPs before and after synthesis had 803, 764, and 400 mg Ni kg dry weight, in the leaves, respectively. The XAS analyses showed Ni NPs in roots and shoots of plants treated with uncoated NPs, whereas leaves showed a Ni(II)-organic acid type complex. However, plants treated with coated NPs before or after synthesis showed Ni NPs only in roots and a Ni(II)-organic acid complex in shoots and leaves. Results also showed that none of the treatments reduced plant size or chlorophyll production. To the authors' knowledge, this is the first time that the biotransformation of nanoparticles by a plant system is reported.