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Agricultural Ecosystems (agricultural + ecosystem)
Selected AbstractsThe conversion of the corn/soybean ecosystem to no-till agriculture may result in a carbon sinkGLOBAL CHANGE BIOLOGY, Issue 11 2005Carl J. Bernacchi Abstract Mitigating or slowing an increase in atmospheric carbon dioxide concentration ([CO2]) has been the focus of international efforts, most apparent with the development of the Kyoto Protocol. Sequestration of carbon (C) in agricultural soils is being advocated as a method to assist in meeting the demands of an international C credit system. The conversion of conventionally tilled agricultural lands to no till is widely accepted as having a large-scale sequestration potential. In this study, C flux measurements over a no-till corn/soybean agricultural ecosystem over 6 years were coupled with estimates of C release associated with agricultural practices to assess the net biome productivity (NBP) of this no-till ecosystem. Estimates of NBP were also calculated for the conventionally tilled corn/soybean ecosystem assuming net ecosystem exchange is C neutral. These measurements were scaled to the US as a whole to determine the sequestration potential of corn/soybean ecosystems, under current practices where 10% of agricultural land devoted to this ecosystem is no-tilled and under a hypothetical scenario where 100% of the land is not tilled. The estimates of this analysis show that current corn/soybean agriculture in the US releases ,7.2 Tg C annually, with no-till sequestering ,2.2 Tg and conventional-till releasing ,9.4 Tg. The complete conversion of land area to no till might result in 21.7 Tg C sequestered annually, representing a net C flux difference of ,29 Tg C. These results demonstrate that large-scale conversion to no-till practices, at least for the corn/soybean ecosystem, could potentially offset ca. 2% of annual US carbon emissions. [source] Residual toxicity of two insecticides on three field populations of Lygus lineolaris (Hemiptera: Miridae) collected along the St Lawrence valley in eastern CanadaPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 5 2007Dominique Fleury Abstract Insecticides are still the single main pest control method employed today by most growers to mitigate damage done by the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae). In eastern Canada, the complex agricultural ecosystem, which may be described as a mosaic of farmlands dispersed among natural habitats (forest, prairies), allows tarnished plant bug adults to fly and move from sprayed to non-sprayed areas. In 2004 (late August to early September), three populations of L. lineolaris were collected from three mixed vegetation strips adjacent to orchards and vineyards along the St Lawrence valley: the Niagara Peninsula (Ontario), Dunham (Quebec) and La Pocatière (Quebec). Assays were done in the laboratory by confining adults in glass vials coated with dried residues. The estimated LC50 values for the three populations varied from 11.2 to 16.8 × 10,5 g L,1 for azinphos-methyl and from 0.8 to 1.4 × 10,5 g L,1 for cypermethrin. In contrast to the Mississippi delta, no tolerance to insecticides was found in the populations collected. Possible explanations for this non-tolerance to insecticides includes a very low selection pressure as a result of the reduced number of insecticide treatments done in the context of the diversified agricultural landscapes encountered in eastern Canada which allow movements of adults from treated to non-treated areas. Copyright © 2007 Society of Chemical Industry [source] Sublethal responses of wolf spiders (Lycosidae) to organophosphorous insecticidesENVIRONMENTAL TOXICOLOGY, Issue 5 2002S. Van Erp Abstract The activities of cholinesterase (ChE) and glutathione S -transferase (GST) enzymes were assessed in the wolf spider (Lycosa hilaris) as biomarkers of organophosphate contamination in agricultural ecosystems. Spiders were exposed to simulated field rates of two commercially available organophosphorous insecticides [Basudin (diazinon) and Lorsban (chlorpyrifos)] under laboratory conditions. In terms of survival, chlorpyrifos and diazinon were more toxic to male than to female wolf spiders, but gender-specific differences in ChE activities were not evident. Cholinesterase activity in male spiders was inhibited to 14% and 61% of control activity by Basudin and Lorsban, respectively. Gluthathione S -transferase activity was not affected by either pesticide. Mortality and biomarker responses in the wolf spider were further investigated following the application of Basudin to pasture. Wolf spiders were deployed into field mesocosms; after 24 h mortality was 40%, and surviving spiders displayed significant inhibition of ChE activity (87%) compared with controls. Cholinesterase activity in spiders exposed for subsequent 24- or 48-h time periods was monitored until it returned to control levels 8 days post-application. Inhibition of ChE activity after a single application of Basudin indicate the potential use of this enzyme in wolf spiders as a biomarker for evaluating organophosphate contamination. © 2002 Wiley Periodicals, Inc. Environ Toxicol 17: 449,456, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/tox.10078 [source] Effects of terrestrial pollutants on insect parasitoids,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2009Casey D. Butler Abstract Parasitoids are important organisms in the regulation of insect herbivores in natural, urban, and agricultural ecosystems. The impact of pollutants acting on parasitoids has not been extensively reviewed. This prompted us to propose a falsifiable null hypothesis (pollutants have no effects on parasitoids) and two alternative hypotheses (pollution negatively or positively affects parasitoids) to assess in the available literature the effects of pollutants acting on parasitoids. We found 26 studies examining 39 biological systems that met our criteria for inclusion. Of these studies, 18 of the 39 biological systems (46.2%) supported the null hypothesis while 18 (46.2%) supported the first alternative hypothesis in which pollutants exhibited negative effects on parasitoids. Only a small percentage of the studies (7.6%, 3 of 39) supported the second alternative hypothesis suggesting that pollutants had positive effects on parasitoids. We provide a synthesis of the available data by pollution type, summarize trends for different pollutants, and suggest future areas of research. [source] Molecular weight and humification index as predictors of adsorption for plant- and manure-derived dissolved organic matter to goethiteEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2007T. Ohno Summary Sorptive retention of organic matter is important in maintaining the fertility and quality of soils in agricultural ecosystems. However, few sorption studies have been conducted that use dissolved organic matter (DOM) characteristic of agricultural amendments. We investigated the sorption to goethite (,-FeOOH) of DOM extracted from: (i) above-ground biomass of wheat straw (Triticum aestivum L.), maize residue (Zea mays L.), soybean residue (Glycine max (L.) Merr.), and hairy vetch residue (Vivia billosa L.); (ii) below-ground biomass from maize, soybean, canola (Brassica napus L.), and green bean (Phaseolus vulgaris L.); and (iii) beef, dairy, poultry, and pig animal manures. The apparent molecular weight (MWAP) of the DOM was measured by high performance-size exclusion chromatography and ranged from 312 to 1074 g mol,1. The carboxyl-group content of the DOM measured by potentiometric titration ranged from 4.84 to 21.38 mmol(,) g,1 carbon. The humification index (HIX) determined by fluorescence spectrometry varied from 1.15 to 4.33. Sorption was directly related to both MWAP and HIX values of the DOM. Molecular weight analysis of the solution prior to and after sorption indicated that the DOM molecules > 1800 g mol,1 were preferentially sorbed, resulting in fractionation of the DOM upon reaction with goethite. The multiple regression equation, based only on MWAP and HIX parameters, explained 76% of the variance in amount of DOM sorbed. The results indicate that MWAP and HIX are important factors in controlling the sorption of DOM to mineral surfaces. Amendment with materials that release DOM of higher molecular weight and greater humification will result in enhanced initial sorption of DOM to soil solids, thereby contributing to accumulation of a larger soil organic C pool. [source] Effects of inoculation with plant growth-promoting rhizobacteria on resident rhizosphere microorganismsFEMS MICROBIOLOGY LETTERS, Issue 1 2007Susana Castro-Sowinski Abstract Plant growth-promoting rhizobacteria (PGPR) are exogenous bacteria introduced into agricultural ecosystems that act positively upon plant development. However, amendment reproducibility as well as the potential effects of inoculation upon plant root-associated microbial communities can be sources of concern. To address these questions, an understanding of mutual interactions between inoculants and resident rhizosphere microorganisms is required. Mechanisms used by PGPR can be direct or indirect; the former entails the secretion of growth regulators and the latter occurs through the production of antimicrobial compounds that reduce the deleterious effects of phytopathogens. The different modes of action may lead to different relationships between an inoculant and root microbial communities. Rhizobacterial communities are also affected by the plant, engineered genes, environmental stresses and agricultural practices. These factors appear to determine community structure more than an exogenous, active PGPR introduced at high levels. [source] Impact of land use and land cover change on groundwater recharge and quality in the southwestern USGLOBAL CHANGE BIOLOGY, Issue 10 2005Bridget R. Scanlon Abstract Humans have exerted large-scale changes on the terrestrial biosphere, primarily through agriculture; however, the impacts of such changes on the hydrologic cycle are poorly understood. The purpose of this study was to test the hypothesis that the conversion of natural rangeland ecosystems to agricultural ecosystems impacts the subsurface portion of the hydrologic cycle by changing groundwater recharge and flushing salts to underlying aquifers. The hypothesis was examined through point and areal studies investigating the effects of land use/land cover (LU/LC) changes on groundwater recharge and solute transport in the Amargosa Desert (AD) in Nevada and in the High Plains (HP) in Texas, US. Studies use the fact that matric (pore-water-pressure) potential and environmental-tracer profiles in thick unsaturated zones archive past changes in recharging fluxes. Results show that recharge is related to LU/LC as follows: discharge through evapotranspiration (i.e., no recharge; upward fluxes <0.1 mm yr,1) in natural rangeland ecosystems (low matric potentials; high chloride and nitrate concentrations); moderate-to-high recharge in irrigated agricultural ecosystems (high matric potentials; low-to-moderate chloride and nitrate concentrations) (AD recharge: ,130,640 mm yr,1); and moderate recharge in nonirrigated (dryland) agricultural ecosystems (high matric potentials; low chloride and nitrate concentrations, and increasing groundwater levels) (HP recharge: ,9,32 mm yr,1). Replacement of rangeland with agriculture changed flow directions from upward (discharge) to downward (recharge). Recent replacement of rangeland with irrigated ecosystems was documented through downward displacement of chloride and nitrate fronts. Thick unsaturated zones contain a reservoir of salts that are readily mobilized under increased recharge related to LU/LC changes, potentially degrading groundwater quality. Sustainable land use requires quantitative knowledge of the linkages between ecosystem change, recharge, and groundwater quality. [source] Nonlinear response of N2O flux to incremental fertilizer addition in a continuous maize (Zea mays L.) cropping systemGLOBAL CHANGE BIOLOGY, Issue 10 2005Claire P. McSwiney Abstract The relationship between nitrous oxide (N2O) flux and N availability in agricultural ecosystems is usually assumed to be linear, with the same proportion of nitrogen lost as N2O regardless of input level. We conducted a 3-year, high-resolution N fertilizer response study in southwest Michigan USA to test the hypothesis that N2O fluxes increase mainly in response to N additions that exceed crop N needs. We added urea ammonium nitrate or granular urea at nine levels (0,292 kg N ha,1) to four replicate plots of continuous maize. We measured N2O fluxes and available soil N biweekly following fertilization and grain yields at the end of the growing season. From 2001 to 2003 N2O fluxes were moderately low (ca. 20 g N2O-N ha,1 day,1) at levels of N addition to 101 kg N ha,1, where grain yields were maximized, after which fluxes more than doubled (to >50 g N2O-N ha,1 day,1). This threshold N2O response to N fertilization suggests that agricultural N2O fluxes could be reduced with no or little yield penalty by reducing N fertilizer inputs to levels that just satisfy crop needs. [source] From agriculture based on fossil fuel resources to agriculture based on biological interactions and matter cycling in agroecosystemsGRASSLAND SCIENCE, Issue 1 2005Masae Shiyomi Abstract The modern system of agriculture, which depends on the consumption of large quantities of fossil fuel, will be forced to change to a system in which matter cycling and the various interactions operating among organisms and between organisms and their environment are effectively used. Three key factors will necessitate this change: the depletion of readily available fossil fuel resources; the leveling-off of the growth and yield response of crops in response to the increase in the use of fertilizers, agrochemicals and big machinery; and the degradation of the environment associated with the consumption of fossil fuels and derived agrochemicals. Therefore, it is essential to further promote the following two types of study: (i) the elucidation of the structure and use of complex biological interactions, and the cause-and-effect relationships among and between organisms in relation to their environment; and (ii) the effective use of matter cycling in agricultural ecosystems. Efficient use of biological interactions and matter cycling will reduce the dependence of agriculture on fossil fuel. [source] Mycorrhizal fungi as mediators of defence against insect pests in agricultural systemsAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 4 2009Rachel L. Vannette Abstract 1Below-ground organisms influence above-ground interactions in both natural and agricultural ecosystems. Among the most important below-ground organisms are mycorrhizal fungi, comprising ubiquitous and ancient plant mutualists that have significant effects on plant growth and fitness mediated by resource exchange with plants. In the present study, we focus on the effects of arbuscular mycorrhizal fungi (AMF) on crop defence against insect pests. 2AMF alter the availability of resources used by crop plants to manufacture defences against pests and to compensate for pest damage. However, AMF also provide plants with nutrients that are known to increase insect performance. Through potentially opposing effects on plant nutritional quality and defence, mycorrhizal fungi can positively or negatively affect pest performance. 3Additionally, AMF may directly affect gene expression and plant defence signalling pathways involved in the construction and induction of plant defences, and these effects are apparently independent of those caused by nutrient availability. In this way, AMF may still influence plant defences in the fertilized and highly managed systems typical of agribusiness. 4Because AMF can affect plant tolerance to pest damage, they may have a significant impact on the shape of damage,yield relationships in crops. Potential mechanisms for this effect are suggested. 5We highlight the need for continuing research on the effects of AMF identity and the abundance on crop defences and tolerance to pest attack. Much work is needed on the potential effects of mycorrhizal colonization on plant signalling and the induction of direct and indirect defences that may protect against pest damage. [source] Wild mammals and the human food chainMAMMAL REVIEW, Issue 2-3 2008PIRAN C. L. WHITE ABSTRACT 1Wild mammals have a long history of association with the human food chain, with some being the source for domesticated animals and others being considered traditionally as game species. Wild mammals are of negligible importance in terms of overall energy flows in agricultural ecosystems in Britain, but some wild mammals can have detrimental effects on the human food chain through predation, competition and disease transmission. 2Understanding these ecological processes at the level of populations and individuals can assist with devising appropriate management strategies to reduce human,wildlife conflict over limited resources. There remains a dearth of reliable information on the economic impacts of wild mammals on human food production, although the available quantified evidence suggests that the impacts are generally minor and localized, and are far outweighed by the wider public benefits associated with wild mammals. 3Greater public awareness of environmental and animal welfare issues, together with changes to rural communities resulting from human population movements, are changing the social landscape of interactions between people and wild mammals in the British countryside, and leading to an increase in more ambivalent attitudes towards wild mammals than has typically been the case in the past. 4Reform of agricultural policy is placing greater emphasis on the management of the land for biodiversity and environmental protection. While the benefits deriving from many previous agri-environment schemes have been mixed, there is increasing evidence that an emphasis on targeted and coordinated management at the landscape scale can enhance success. This type of approach is essential if some of the major threats facing declining wild mammal populations, such as population fragmentation, are to be overcome. 5There is an increasing divergence between regulation of agricultural ecosystems for food production and disease minimization and regulation of the land for biodiversity production via agri-environment schemes. The resolution of these tensions at the policy level will have major implications for future interactions between wild mammals and the human food chain. [source] Geographical variation in resistance to acetyl-coenzyme A carboxylase-inhibiting herbicides across the range of the arable weed Alopecurus myosuroides (black-grass)NEW PHYTOLOGIST, Issue 4 2010Christophe Délye Summary ,The geographical structure of resistance to herbicides inhibiting acetyl-coenzyme A carboxylase (ACCase) was investigated in the weed Alopecurus myosuroides (black-grass) across its geographical range to gain insight into the process of plant adaptation in response to anthropogenic selective pressures occurring in agricultural ecosystems. ,We analysed 297 populations distributed across six countries in A. myosuroides' main area of occupancy. The frequencies of plants resistant to two broadly used ACCase inhibitors and of seven mutant, resistant ACCase alleles were assessed using bioassays and genotyping, respectively. ,Most of the resistance was not endowed by mutant ACCase alleles. Resistance and ACCase allele distribution patterns were characterized by mosaicism. The prevalence of resistance and of ACCase alleles differed among countries. ,Resistance clearly evolved by redundant evolution of a set of resistance alleles or genes, most of which remain unidentified. Resistance in A. myosuroides was shaped by variation in the herbicide selective pressure at both the individual field level and the national level. [source] Multi-scale responses of plant species diversity in semi-natural buffer strips to agricultural landscapesAPPLIED VEGETATION SCIENCE, Issue 2 2008Maohua Ma Question: How does agricultural land usage affect plant species diversity in semi-natural buffer strips at multiple scales? Location: Lepsämä River watershed, Nurmijärvi, Southern Finland. Methods: Species diversity indicators included both richness and evenness. Plant communities in buffer strips were surveyed in 29 sampling sites. Using ArcGIS Desktop 9.0 (ArcInfo) and Fragstats 3.3 for GIS analysis, the landscape composition around each sampling site was characterized by seven parameters in square sectors at five scales: 4, 36, 100, 196, and 324ha. For each scale, Principle Component Analysis was used to examine the importance of each structural metric to diversity indicators using multiple regression and other simple analyses. Results: For all but the smallest scales (4 ha), two structural metrics including the diversity of land cover types and percentage of arable land were positively and negatively correlated with species richness, respectively. Both metrics had the highest correlation coefficients for species richness at the second largest scale (196 ha). The density of arable field edges between the fields was the only metric that correlated with species evenness for all scales, which had highest predictive power at the second smallest scale (36 ha). Conclusions: Species richness and evenness of buffer strips had scale-dependent relationships to land use in agricultural ecosystems. The results of this study indicated that species richness depends on the pattern of arable land use at large scales, which may relate to the regional species pool. Meanwhile, species evenness depended on the level of field edge density at small scales, which relates to how the nearby farmland was divided by the edges (e.g. many small-scale fields with high edge density or a few big-scale fields with low edge density). This implies that it is important to manage the biodiversity of buffer strips within a landscape context at multiple scales. [source] | |||||||||||||