Rural Households' Demand Status for Mitigation of Prosopis juliflora (Sw.) DC Invasion and Its Determinant Factors in Ethiopia: Empirical Evidence from Afar National Regional State.

Ethiopia is among the world's poorest nations, and its economy is growing extremely slowly; thus, the government's budget to manage environmental amenities is not always sufficient. Thus, for the provision of environmental management services such as the eradication of Prosopis juliflora, the participation of local households and other stakeholders is crucial. This study is therefore initiated with the objective of assessing rural households' demands for mitigating Prosopis juliflora invasion in the Afar Region of Ethiopia. A multistage sampling technique was employed to obtain the 313 sample rural households that were used in the analysis, and those sample households were selected randomly and independently from the Amibara and Awash Fentale districts of Afar National Regional State, Ethiopia. In doing this, a seemingly unrelated bivariate probit model was used to determine factors affecting rural households' demands for mitigating Prosopis juliflora invasion. Consequently, as per the inferential statistical results, there was a significant mean/percentage difference between willing and nonwilling households for the hypothesized variables, except for some variables such as farm experience; years lived in the area, distance from the market, and dependency ratio. Furthermore, the seemingly unrelated bivariate probit model result indicates that sex, family size, tenure security, livestock holding, frequency of extension contact, and years lived in the area were important factors influencing the willingness to participate in Prosopis juliflora management practices positively, whereas age, off-farm/nonincome, and bid value affected willingness to pay negatively and significantly. Hence, to improve the participation level of households, policymakers should target these variables.

Community perceptions towards invasion of Prosopis juliflora, utilization, and its control options in Afar region, Northeast Ethiopia.

This study aimed to assess community perceptions towards invasion of Prosopis juliflora, utilization, and its control options in Afar region, Northern Ethiopia. Using purposive sampling and stratified random methods, 20 members of key informants and 154 households from four sites of Awash Fentale and Amibara Districts were selected. For data analysis, we used Kruskal Wallis non-parametric tests of K independent samples. About 30% of respondents in Amibara and 29% in Awash Fentale reported that Prosopis juliflora was largely introduced into their landscape by livestock. It showed that 29% of the respondents in Awash Fentale and 41% in Amibara responded that Prosopis juliflora largely invaded and affected rangelands. Morevover, about 1% of respondents in Awash Fentale and 14% in Amibara argued that Prosopis juliflora hindered movements of livestock. In addition, 30% of respondents in Amibara and 29% in Awash Fentale believe that Prosopis juliflora was largely dispersed by livestock. It showed that 20% of households in Awash Fentale and 41% in Amibara have the notion that Prosopis juliflora majorly impacted rangelands. Whereas 1.3% of respondents in Awash Fentale and 14% in Amibara argued that Prosopis juliflora have hampered the movement of livestock. Thus, the afromentioned findings are implications for management of rangelands. With regard to the control of Prosopis juliflora invasions, 12% of respondents in Awash Fentale and 33% in Amibara District tried control its expansion by fire. About 10% of respondents in Awash Fentale and 9% in Amibara district managed Prosopis juliflora expansion by its utilization, whereas, in Awash Fentale (11%) and Amibara (8%) households indicated that invasion of Prosopis juliflora could be controlled by mechanical methods. It is advisable to do some managerial work to reverse these impacts as perceived by local communities in the study area to avert the aggressive proliferation of Prosopis juliflora in the region.

Implications of land use/land cover dynamics and Prosopis invasion on ecosystem service values in Afar Region, Ethiopia.

Land use/land cover (LULC) dynamics and the resulting changes in ecosystems, as well as the services they provide, are a consequence of human activities and environmental drivers, such as invasive alien plant species. This study assessed the changes in LULC and ecosystem service values (ESVs) in the Afar National Regional State, Ethiopia, which experiences a rapid invasion by the alien tree Prosopis juliflora (Swartz DC). Landsat satellite data of 1986, 2000 and 2017 were used in Random Forest algorithm to assess LULC changes in the last 31 years, to calculate net changes for different LULC types and the associated changes in ESVs. Kappa accuracies of 88% and higher were obtained for the three LULC classifications. Post-classification change analyses for the period between 1986 and 2017 revealed a positive net change for Prosopis invaded areas, cropland, salt flats, settlements and waterbodies. The rate of Prosopis invasion was estimated at 31,127 ha per year. Negative net changes were found for grassland, bareland, bush-shrub-woodland, and natural forests. According to the local community representatives, the four most important drivers of LULC dynamics were climate change, frequent droughts, invasive species and weak traditional law. Based on two different ESVs estimations, the ecosystem changes caused by LULC changes resulted in an average loss of ESVs in the study area of about US$ 602 million (range US$ 112 to 1091 million) over the last 31 years. With an increase in area by 965,000 ha, Prosopis-invaded land was the highest net change during the study period, followed by grassland (-599,000 ha), bareland (-329,000 ha) and bush-shrub-woodland (-327,000 ha). Our study provides evidence that LULC changes in the Afar Region have led to a significant loss in ESVs, with serious consequences for the livelihoods of the rural people.

Effect of Fe3O4 NPs application on fluoride (F) accumulation efficiency of Prosopis juliflora.

Fluoride (F) pollution is a major worldwide problem affecting approximately 200 million people. Hyperaccumulator plant Prosopis juliflora has been used for the removal of F from contaminated soils; however it's low F accumulation efficiency and low biomass limits the phytoremediation efficiency. Present study deals with enhancement of F uptake efficiency of plant P. juliflora through iron oxide nanoparticles (Fe3O4 NPs) application for remediation of agricultural soils. For the study, Fe3O4 NPs were synthesized through green route using waste jojoba leaves. The application of Fe3O4 NPs significantly increased the shoot and root length of plant P. juliflora. Fe3O4 NPs treatment also promoted the F accumulation in shoot and root tissues upto 28.43 and 34.64 mg kg-1, respectively. Microscopic (FESEM and light microscopic) and EDX spectrum analysis of plant tissues confirmed the accumulation and translocation of Fe3O4 NPs and F in plant tissues This nano-phytoremediation approach could be a better option for F remediation for agricultural and commercial purpose.

Biological Invasion Influences the Outcome of Plant-Soil Feedback in the Invasive Plant Species from the Brazilian Semi-arid.

Plant-soil feedback is recognized as the mutual interaction between plants and soil microorganisms, but its role on the biological invasion of the Brazilian tropical seasonal dry forest by invasive plants still remains unclear. Here, we analyzed and compared the arbuscular mycorrhizal fungi (AMF) communities and soil characteristics from the root zone of invasive and native plants, and tested how these AMF communities affect the development of four invasive plant species (Cryptostegia madagascariensis, Parkinsonia aculeata, Prosopis juliflora, and Sesbania virgata). Our field sampling revealed that AMF diversity and frequency of the Order Diversisporales were positively correlated with the root zone of the native plants, whereas AMF dominance and frequency of the Order Glomerales were positively correlated with the root zone of invasive plants. We grew the invasive plants in soil inoculated with AMF species from the root zone of invasive (I changed) and native (I unaltered) plant species. We also performed a third treatment with sterilized soil inoculum (control). We examined the effects of these three AMF inoculums on plant dry biomass, root colonization, plant phosphorous concentration, and plant responsiveness to mycorrhizas. We found that I unaltered and I changed promoted the growth of all invasive plants and led to a higher plant dry biomass, mycorrhizal colonization, and P uptake than control, but I changed showed better results on these variables than I unaltered. For plant responsiveness to mycorrhizas and fungal inoculum effect on plant P concentration, we found positive feedback between changed-AMF community (I changed) and three of the studied invasive plants: C. madagascariensis, P. aculeata, and S. virgata.

Isolation by distance and stochastic migration in a fragmented population of Prosopis alba.

PREMISE OF THE STUDY: Gene flow through dispersal of seeds and pollen is a fundamental determinant of spatial genetic structure (SGS) in natural populations of trees at different spatial scales. Within continuous populations, restrictions to gene flow should be manifested in a process of local genetic differentiation, known as isolation by distance. The present work examines the SGS of a Prosopis alba population in a patchy region where urban, forest, and agricultural areas coexist. The analysis discussed here expands our knowledge about the processes affecting the distribution of the genetic variability in populations of disturbed landscapes. METHODS: Three sites with different landscape and demographic characteristics were analyzed. Seven highly variable microsatellite markers were used to survey the relevance of both isolation by distance and stochastic migration in the SGS of the population. KEY RESULTS: The analyses showed that (1) the genetic similarity declined with increasing geographic distance, (2) the population may be conceived as a single genetically continuous unit showing spatial differentiation as consequence of isolation by distance, rather than a structured population following the island model, and (3) there is evidence supporting a past immigration event into one of the study sites, which promoted a local pattern of genetic structure. CONCLUSIONS: These results indicate that in spite of the population fragmentation produced by land-use changes, P. alba maintains the genetic cohesion and a continuous genetic structure in the analyzed area.

A novel heavy metal ATPase peptide from Prosopis juliflora is involved in metal uptake in yeast and tobacco.

Heavy metal pollution of agricultural soils is one of the most severe ecological problems in the world. Prosopis juliflora, a phreatophytic tree species, grows well in heavy metal laden industrial sites and is known to accumulate heavy metals. Heavy Metal ATPases (HMAs) are ATP driven heavy metal pumps that translocate heavy metals across biological membranes thus helping the plant in heavy metal tolerance and phytoremediation. In the present study we have isolated and characterized a novel 28.9 kDa heavy metal ATPase peptide (PjHMT) from P. juliflora which shows high similarity to the C-terminal region of P1B ATPase HMA1. It also shows the absence of the invariant signature sequence DKTGT, and the metal binding CPX motif but the presence of conserved regions like MVGEGINDAPAL (ATP binding consensus sequence), HEGGTLLVCLNS (metal binding domain) and MLTGD, GEGIND and HEGG motifs which play important roles in metal transport or ATP binding. PjHMT, was found to be upregulated under cadmium and zinc stress. Heterologous expression of PjHMT in yeast showed a higher accumulation and tolerance of heavy metals in yeast. Further, transgenic tobacco plants constitutively expressing PjHMT also showed increased accumulation and tolerance to cadmium. Thus, this study suggests that the transport peptide from P. juliflora may have an important role in Cd uptake and thus in phytoremediation.

Metabolomic profiling of the halophyte Prosopis strombulifera shows sodium salt- specific response.

Primary and secondary metabolite profiles were analyzed in roots and leaves of the halophytic shrub Prosopis strombulifera in response to control plants (no salt added in the growing media) and to lowering the osmotic potential to -1.0, -1.9, and -2.6 MPa generated by NaCl, Na2SO4, and the iso-osmotic combination of them at 24 h after reaching such potential. A rapid production of metabolites in response to sodium salt was found, which was correlated with modifications in growth parameters. Analysis of polar metabolite profiles by GC-MS rendered a total of 108 significantly altered compounds including 18 amino acids, 19 secondary metabolites, 23 carbohydrates, 13 organic acids, 4 indole acids, among others. Primary metabolites showed a differential response under the salt treatments, which was dependent on salt type and concentration, organ and age of plants. Most of identified compounds showed the strongest accumulation at the highest salt concentration assayed for Na2SO4-treated plants, which was correlated with damaging effects of sulfate anion on plant growth. Roots of NaCl-treated plants showed a higher number of altered metabolites (analyzed by UPLC-ESI-QqTOF-MS) compared to other treatments, while leaves of Na2SO4-treated plants showed the highest number of altered signals. A low degree of overlapping between secondary metabolites altered in roots and leaves of NaCl and Na2SO4-treated plants was found. However, when both NaCl and Na2SO4 salts were present plants always showed a lower number of altered metabolites. Three compounds were tentatively identified: tryptophan, lysophosphatidylcoline and 13-hydroxyoctadecadienoic acid. Increasing knowledge on P. strombulifera metabolism will contribute to unravel the underlying biochemical mechanism of salt tolerance.

Biomass yielding potential of naturally regenerated Prosopis juliflora tree stands at three varied ecosystems in southern districts of Tamil Nadu, India.

Fuel energy demand is of great concern in recent times due to the depletion of fossil fuel resources. Biomass serves as widely available primary renewable energy source. Hence, a study was performed to assess the above-ground biomass yielding capability of fuel wood tree Prosopis juliflora in three varied ecosystems viz., coastal, fallow land and riparian ecosystems in southern districts of Tamil Nadu. The results showed that the biomass production potential and above-ground net primary productivity of P. juliflora depend on the age of the tree stands and the nature of ecosystem. A higher biomass yield was observed for P. juliflora trees with 5 to 10 years old when compared to less than 5 years of their age. Among the three ecosystems, the maximum biomass production was recorded in riparian ecosystem. The stands with less than 5-year-old P. juliflora trees gave 1.40 t/ha, and 5- to 10-year-old tree stands produced 27.69 t/ha in riparian ecosystem. Above-ground net primary productivity of both the age groups was high in fallow land ecosystem. In riparian ecosystem, the wood showed high density and low sulphur content than the other two ecosystems. Hence, P. juliflora biomass can serve as an environmentally and economically feasible fuel as well as their utilization proffers an effective means to control its invasiveness.

Is control through utilization a cost effective Prosopis juliflora management strategy?

The invasive tree Prosopis juliflora is known to cause negative impacts on invaded ranges. High P. juliflora eradication costs have swayed developing countries to follow a new and less expensive approach known as control through utilization. However, the net benefits of this new approach have not been thoroughly evaluated. Our objective was to assess the economic feasibility of selected P. juliflora eradication and utilization approaches that are currently practiced in one of the severely affected developing countries, Ethiopia. The selected approaches include converting P. juliflora infested lands into irrigated farms (conversion), charcoal production, and seed flour production. We estimate the costs and revenues of the selected P. juliflora eradication and utilization approaches by interviewing 19 enterprise owners. We assess the economic feasibility of the enterprises by performing enterprise, break-even, investment, sensitivity, and risk analyses. Our results show that conversion to irrigated cotton is economically profitable, with Net Present Value (NPV) of 5234 US$/ha over 10 years and an interest rate of 10% per year. Conversion greatly reduces the spread of P. juliflora on farmlands. Managing P. juliflora infested lands for charcoal production with a four-year harvest cycle is profitable, with NPV of 805 US$/ha. However, the production process needs vigilant regulation to protect native plants from exploitation and caution should be taken to prevent charcoal production sites from becoming potential seed sources. Though flour from P. juliflora pods can reduce invasions by destroying viable seeds, flour enterprises in Ethiopia are unprofitable. Conversion and charcoal production can be undertaken with small investment costs, while flour production requires high investment costs. Introducing new changes in the production and management steps of P. juliflora flour might be considered to make the enterprise profitable. Our study shows that control through utilization may be a viable P. juliflora management strategy under the right environmental setting.

Effect of co-inoculations of native PGPR with nitrogen fixing bacteria on seedling traits in Prosopis cineraria.

Prosopis cineraria significantly contribute to sand dune stabilization, soil fertility rejuvenation and is an integral component of agro-forestry systems in arid regions of India. Effect of different rhizobacterial seed treatments on seed germination and seedling traits in two genotypes of P. cineraria (HPY-1) and (FG-1) were tested. Observations on seed germination (%) and seedling traits viz., root length (cm), shoot length (cm), seedling weight (g) and seedling length of different treatments were recorded. Whereas, germination index (GI), seedling vigour index (SVI) and root/shoot length ratio were derived from the observed data. The scarification treatment with sulphuric acid for 10 minutes substantially enhanced germination from < 20% to 80-82% in control treatments. Treatments with co-inoculations of Bacillus licheniformis and Sinorhizobium kostiense or S. saheli supported the maximum seed germination and seedling growth and vigour. The maximum germination per cent (92.5%), seedling length (10.94 cm), seedling vigour index (10.12) and germination index (7.97) were recorded with treatment (V2T6) wherein seeds of high pod yielding genotype were co-inoculated with Bacillus licheniformis and S. kostiense. The higher positive correlations of seedling length v/s shoot length followed by SVI v/s seedling length, SVI v/s root length and seedling length v/s root length is a fair indicative of inter dependency of these characteristics. Higher R2 values of root length v/s shoot length followed by that of SVI v/s GI indicates that a regression line fits the data well and future outcomes of observed seedling traits are likely to be predicted by the model.

The introduced tree Prosopis juliflora is a serious threat to native species of the Brazilian Caatinga vegetation.

Despite its economic importance in the rural context, the Prosopis juliflora tree species has already invaded millions of hectares globally (particularly rangelands), threatening native biodiversity and rural sustainability. Here we examine seedling growth (leaf area, stem diameter, plant height) and seedling mortality across five native plant species of the Caatinga vegetation in response to competition with P. juliflora. Two sowing treatments with 10 replications were adopted within a factorial 2 × 5 randomized block design. Treatments consisted of P. juliflora seeds sowed with seeds of Caesalpinia ferrea, Caesalpinia microphylla, Erythrina velutina, Mimosa bimucronata and Mimosa tenuiflora (one single native species per treatment), while seeds of native species sowed without P. juliflora were adopted as controls. Overall, our results suggest that P. juliflora can reduce seedling growth by half and cause increased seedling mortality among woody plant species. Moreover, native species exhibit different levels of susceptibility to competition with P. juliflora, particularly in terms of plant growth. Such a superior competitive ability apparently permits P. juliflora to establish monospecific stands of adult trees, locally displacing native species or limiting their recruitment. The use of less sensitive species, such as C. ferrea and M. tenuiflora, to restore native vegetation before intensive colonization by P. juliflora should be investigated as an effective approach for avoiding its continuous spread across the Caatinga region.

Seedling responses to water pulses in shrubs with contrasting histories of grassland encroachment.

Woody plant encroachment into grasslands has occurred worldwide, but it is unclear why some tree and shrub species have been markedly more successful than others. For example, Prosopis velutina has proliferated in many grasslands of the Sonoran Desert in North America over the past century, while other shrub species with similar growth form and life history, such as Acacia greggii, have not. We conducted a glasshouse experiment to assess whether differences in early seedling development could help explain why one species and not the other came to dominate many Sonoran Desert grasslands. We established eight watering treatments mimicking a range of natural precipitation patterns and harvested seedlings 16 or 17 days after germination. A. greggii had nearly 7 times more seed mass than P. velutina, but P. velutina emerged earlier (by 3.0±0.3 d) and grew faster (by 8.7±0.5 mg d⁻¹). Shoot mass at harvest was higher in A. greggii (99±6 mg seedling⁻¹) than in P. velutina (74±2 mg seedling⁻¹), but there was no significant difference in root mass (54±3 and 49±2 mg seedling⁻¹, respectively). Taproot elongation was differentially sensitive to water supply: under the highest initial watering pulse, taproots were 52±19 mm longer in P. velutina than in A. greggii. Enhanced taproot elongation under favorable rainfall conditions could give nascent P. velutina seedlings growth and survivorship advantages by helping reduce competition with grasses and maintain contact with soil water during drought. Conversely, A. greggii's greater investment in mass per seed appeared to provide little return in early seedling growth. We suggest that such differences in recruitment traits and their sensitivities to environmental conditions may help explain ecological differences between species that are highly similar as adults and help identify pivotal drivers of shrub encroachment into grasslands.

Growth responses and ion accumulation in the halophytic legume Prosopis strombulifera are determined by Na2SO4 and NaCl.

Halophytes are potential gene sources for genetic manipulation of economically important crop species. This study addresses the physiological responses of a widespread halophyte, Prosopis strombulifera (Lam.) Benth to salinity. We hypothesised that increasing concentrations of the two major salts present in soils of central Argentina (Na2SO4, NaCl, or their iso-osmotic mixture) would produce distinct physiological responses. We used hydroponically grown P. strombulifera to test this hypothesis, analysing growth parameters, water relations, photosynthetic pigments, cations and anions. These plants showed a halophytic response to NaCl, but strong general inhibition of growth in response to iso-osmotic solutions containing Na2SO4. The explanation for the adaptive success of P. strombulifera in high NaCl conditions seems to be related to a delicate balance between Na(+) accumulation (and its use for osmotic adjustment) and efficient compartmentalisation in vacuoles, the ability of the whole plant to ensure sufficient K(+) supply by maintaining high K(+)/Na(+) discrimination, and maintenance of normal Ca(2+) levels in leaves. The three salt treatments had different effects on the accumulation of ions. Findings in bi-saline-treated plants were of particular interest, where most of the physiological parameters studied showed partial alleviation of SO4(2-)-induced toxicity by Cl(-). Thus, discussions on physiological responses to salinity could be further expanded in a way that more closely mimics natural salt environments.

Resource assurance predicts specialist and generalist bee activity in drought.

Many short-lived desert organisms remain in diapause during drought. Theoretically, the cues desert species use to continue diapause through drought should differ depending on the availability of critical resources, but the unpredictability and infrequent occurrence of climate extremes and reduced insect activity during such events make empirical tests of this prediction difficult. An intensive study of a diverse bee-plant community through a drought event found that bee specialists of a drought-sensitive host plant were absent in the drought year in contrast to generalist bees and to specialist bees of a drought-insensitive host plant. Different responses of bee species to drought indicate that the diapause cues used by bee species allow them to reliably predict host availability. Species composition of the bee community in drought shifted towards mostly generalist species. However, we predict that more frequent and extended drought, predicted by climate change models for southwest North America, will result in bee communities that are species-poor and dominated by specialist species, as found today in the most arid desert region of North America.

Analysis of the invasion rate, impacts and control measures of Prosopis juliflora: a case study of Amibara District, Eastern Ethiopia.

The tree Prosopis juliflora, introduced to Ethiopia in the 1970s to curb desertification, is imposing significant ecosystem and socioeconomic challenges. The objectives of this study are therefore to analyze the dynamics and associated impacts of the P. juliflora invasion over the period 1973-2004 and to evaluate the effectiveness of the management measures implemented to date. This required the analysis of Landsat images, field surveys, the use of structured questionnaires, and interviews. P. juliflora was found to invade new areas at an average rate of 3.48 km(2)/annum over the period 1973-2004. The high germination nature of the seed, mechanisms of seed dispersal, and its wide-range ecological adaptability are the main drivers for the high invasion rate. By the year 2020, approximately 30.89 % of the study area is projected to be covered by P. juliflora. The expansion has affected human health, suppressed indigenous plants, and decreased livestock productivity. The management measures that have been implemented are not able to yield the desirable results because of the limited spatial scale, cost, and/or improper planning and implementation. Therefore, the formulation of a strategy for management approaches that include the engagement of the community and the limiting of the number of vector animals within the framework of the current villagization program remain important. Moreover, risk assessment should be completed in the future before an exotic species is introduced into a certain area.

Effects of fluoride on germination, early growth and antioxidant enzyme activities of legume plant species Prosopis juliflora.

Prosopis juliflora (Mimosoideae) is a fast growing and drought resistant tree of semi-arid region of India where fluoride (F) toxicity is a common problem. In the present investigations this species was fluoride tested to check their capacity as bioindicator plant and its efficiency to accumulate. To achieve this aim, P. juliflora seedlings grown in hydroponic culture containing different concentrations of F were analyzed for germination percentage together with some biochemical parameters viz, antioxidant enzyme activities, total chlorophyll and accumulation of F in different plant parts. After 15 days of treatment, root growth (r = -0.928, p < 0.01), shoot growth (r = -0.976, p < 0.01), vigor index (r = -0.984, p < 0.01) were in decreasing trend with increasing concentration of NaF. Both catalase (3.2 folds) and peroxidase (2.7 folds) enzymes activity increased with increase in F concentration. Plant accumulated larger portion of the F in the roots (1024.63 microg g(-1) d.wt.) followed by shoot (492.30 microg g(-1) d.wt.). As P. juliflora did not show any morphological changes (marginal and tip chlorosis of leaf portions, necrosis and together these features are referred to as leaf "tip-burn") therefore, this species may be used as suitable bioindicator species for potentially F affected areas. Further, higher accumulation of F in roots indicates that P. juliflora is a suitable species for the removal of F in phytoremediation purposes.

A test of critical thresholds and their indicators in a desertification-prone ecosystem: more resilience than we thought.

Theoretical models predict that drylands can cross critical thresholds, but experimental manipulations to evaluate them are non-existent. We used a long-term (13-year) pulse-perturbation experiment featuring heavy grazing and shrub removal to determine if critical thresholds and their determinants can be demonstrated in Chihuahuan Desert grasslands. We asked if cover values or patch-size metrics could predict vegetation recovery, supporting their use as early-warning indicators. We found that season of grazing, but not the presence of competing shrubs, mediated the severity of grazing impacts on dominant grasses. Recovery occurred at the same rate irrespective of grazing history, suggesting that critical thresholds were not crossed, even at low cover levels. Grass cover, but not patch size metrics, predicted variation in recovery rates. Some transition-prone ecosystems are surprisingly resilient; management of grazing impacts and simple cover measurements can be used to avert undesired transitions and initiate restoration.

Community impacts of Prosopis juliflora invasion: biogeographic and congeneric comparisons.

We coordinated biogeographical comparisons of the impacts of an exotic invasive tree in its native and non-native ranges with a congeneric comparison in the non-native range. Prosopis juliflora is taxonomically complicated and with P. pallida forms the P. juliflora complex. Thus we sampled P. juliflora in its native Venezuela, and also located two field sites in Peru, the native range of Prosopis pallida. Canopies of Prosopis juliflora, a native of the New World but an invader in many other regions, had facilitative effects on the diversity of other species in its native Venezuela, and P. pallida had both negative and positive effects depending on the year, (overall neutral effects) in its native Peru. However, in India and Hawaii, USA, where P. juliflora is an aggressive invader, canopy effects were consistently and strongly negative on species richness. Prosopis cineraria, a native to India, had much weaker effects on species richness in India than P. juliflora. We carried out multiple congeneric comparisons between P. juliflora and P. cineraria, and found that soil from the rhizosphere of P. juliflora had higher extractable phosphorus, soluble salts and total phenolics than P. cineraria rhizosphere soils. Experimentally applied P. juliflora litter caused far greater mortality of native Indian species than litter from P. cineraria. Prosopis juliflora leaf leachate had neutral to negative effects on root growth of three common crop species of north-west India whereas P. cineraria leaf leachate had positive effects. Prosopis juliflora leaf leachate also had higher concentrations of total phenolics and L-tryptophan than P. cineraria, suggesting a potential allelopathic mechanism for the congeneric differences. Our results also suggest the possibility of regional evolutionary trajectories among competitors and that recent mixing of species from different trajectories has the potential to disrupt evolved interactions among native species.

Organ-wise accumulation of fluoride in Prosopis juliflora and its potential for phytoremediation of fluoride contaminated soil.

Fluoride (F) contamination is a global environmental problem, as there is no cure of fluorosis available yet. Prosopis juliflora is a leguminous perennial, phreatophyte tree, widely distributed in arid and semi-arid regions of world. It extensively grows in F endemic areas of Rajasthan (India) and has been known as a "green" solution to decontaminate cadmium, chromium and copper contaminated soils. This study aims to check the tolerance potential of P. juliflora to accumulate fluoride. For this work, P. juliflora seedlings were grown for 75 d on soilrite under five different concentrations of F viz., control, 25, 50, 75 and 100 mg NaF kg(-1). Organ-wise accumulation of F, bioaccumulation factor (BF), translocation factor (TF), growth ratio (GR) and F tolerance index (TI) were examined. Plant accumulated high amounts of F in roots. The organ-wise distribution showed an accumulation 4.41 mg kg(-1)dw, 12.97 mg kg(-1)dw and 16.75 mg kg(-1)dw F, in stem, leaves and roots respectively. The results indicated significant translocation of F from root into aerial parts. The bioaccumulation and translocation factor values (>1.0) showed high accumulation efficiency and tolerance of P. juliflora to F. It is concluded that P. juliflora is a suitable candidate for phytoremediation purpose and can be explored further for the decontamination of F polluted soils.