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Environmental policy related to agriculture is generally administered by a government agency charged with achieving legislative objectives. The enabling legislation of an agency typically establishes a set of tools that the agency uses to influence the behavior on non-governmental agricultural producers who are pursuing their own objectives. This circumstance is recognizable as a bilevel optimization, or Stackelberg game. In the instance of agri-environmental policy, there is a single leader, the agency, and agricultural producers who are followers. The agency moves first, establishing a policy with the goal of optimizing its own objectives, and the producers respond by complying with the policy in a way that maximizes their individual profits. Almost all analysis and simulation of agri-environmental policy to date employ a single level of optimization. Comparison of scenarios where several agency policies are stipulated and the producers optimize with those constraints is a common approach. Many studies use a sequential optimization, where an agency optimizes, and then the producers optimize. We observe that in practice the agency and the producers are all solving their optimization problems at the same time, a crucial feature that is not represented by scenarios or sequential optimization. Our hypothesis is that bilevel optimization provides a better representation agri-environmental policy implementation, and will provide a better method of calculating optimal trade-offs among multiple objectives. We describe a hybrid genetic algorithm for solution of multiple objective bilevel optimization problems, and show how to incorporate data envelopment analysis (DEA) to simulate producer behavior, and include the Soil and Water Assessment Tool (SWAT) to provide the information about environmental effects required by the agency to specify their objectives. We applied the resulting integrated modeling system to the analysis of an incentive policy in the Calapooia watershed in Oregon, USA, using synthetic economic data generated from the Census of Agriculture. Through bilevel optimization, we were able to spatially target agri-environmental policy to find multiple objective Pareto frontiers that dominate those available from other methods.

Successful reintroduction of native species into landscapes requires an understanding of how introduced species invaded and became established. This study was conducted to determine the effect of temperature on interspecific seedling interference of two wetland grasses [sloughgrass (Beckmannia syzigachne Steud.) and tufted hairgrass (Deschampsia caespitosa L.)] native to the Pacific Northwest and tall fescue (Festuca arundinaceae Schreb. cv. Titan), a non-native grass species. The relationships of species interference to the thermal response of Photosystem II (PS II) fluorescence reappearance ratio (FRR) and glutathione reductase (GR) thermal stability were also investigated using the Mantel product moment correlation (r m ). Three combinations of two-species replacement series experiments (sloughgrass-hairgrass mixture, sloughgrass-tall fescue mixture, and hairgrass-tall fescue mixture) were conduced in growth chambers, planted in five proportions (0.0:1.0, 0.25:0.75, 0.5:0.5, 0.75:0.25, and 1.0:0.0), and grown at four temperatures (5, 10, 20, and 30°C). The FRR and GR were measured at eight temperatures ranging from 5 to 40°C. Tall fescue aggressiveness, relative to sloughgrass and hairgrass, increased with increasing temperature. Sloughgrass and hairgrass ranked second and third, respectively, and were only more aggressive than tall fescue at 5°C. Peak FRR occurred at 15, 20, and 22.5°C for sloughgrass, hairgrass, and tall fescue, respectively. Seedling dry mass of species was correlated with the stability of GR and the average efficiency of the PS II apparatus over the range of growing temperatures (r m = -1.00 and 0.96, respectively). Tall fescue had greater PS II efficiency and GR stability under elevated temperatures than sloughgrass and hairgrass, which may explain why tall fescue has been able to dominate some wetland landscapes of the temperate Pacific Northwest.

The thermal dependence of enzyme kinetic parameters has been presented as an indicator of species’ thermal optima and tolerance limits. Previous studies suggest the relationship between temperature and the apparent Michaelis–Menten constant (Km) of an enzyme system can be used to predict whole plant success at specific temperatures. The apparent Kmfor glutathione reductase (EC 1.6.4.2; GR) (oxidized glutathione as substrate) extracted from leaves of American sloughgrass (Beckmannia syzigachne Steud.), tufted hairgrass (Deschampsia caespitosa L.), tall fescue (Festuca arundinaceae Schreb. ‘Titan’), and maize (Zea mays L.), was determined over a range of temperatures (1–40 °C). For all species, minimum apparent Kmfor GR was observed at 1 °C, and Kmvalues increased as temperature increased. The apparent Kmvalues differed among all species at the lower temperatures (1–15 °C), but were similar at higher temperatures. The enzyme from tufted hairgrass had the lowest apparent Kmat low temperatures (

The contribution of potentially intense denitrification in the saturated zone of hydromorphic soils to atmospheric N2O levels is poorly understood because few data exist on shallow ground water N2O production, consumption and transport to the atmosphere. The objective of the present study was to investigate the contribution of the saturated zone to surface N2O emission for two fen soils and a Gleyic Luvisol with ground water tables at the surface during the experimental period. Total denitrification, denitrifier N2O production, ground water dissolved N2 and/or N2O, and surface N2O emissions were measured in situ. Concentrations of dissolved gases and surface emissions were also simulated with a simple process-based model assuming measured rates of N2and N2O production or constant profiles of dissolved N2O concentration. NO3 − and N2O were abundant in all samples of the three sites. Substantial N2O surface emission originating from the saturated zone was measured at both fen sites. Total denitrification ranged from 0.9 to 1.58 mg N l−1 day−1 in the 15 – 35-cm layer of the fen soils and from 0.005 to 0.13 mg N l−1 day−1 in the 50 – 100-cm layer of the Gleyic Luvisol. The ratio of N2O production to total denitrification ranged from 0.07 to 0.32 in the fen soils and from 0.06 to 0.08 in the Gleyic Luvisol. The ratio of N2O production to total denitrification ranged from 0.07 to 0.32, and from 0.06 to 0.08, respectively. Concentrations of dissolved N2O measured at the fen sites were 1 to 2 orders of magnitude lower than simulated concentrations. In contrast, measured N2O emissions were within the order of magnitude of emissions simulated assuming measured N2 and N2O production rates. The agreement between measured and simulated N2O concentrations and surface emissions was satisfactory when gas diffusivity was multiplied by 10 and N2O reduction rate was multiplied by 20 in the simulation. Simulation of diffusive N2O emission assuming constant values of measured N2O concentration profiles resulted in emissions approximately one order of magnitude lower than the measured values. At the Lake Creek site, the measured peak concentration of dissolved N2 and the concentration simulated assuming measured values of N2 production were relatively close with values of 2.4 and 3.5 times the atmospheric equilibrium concentration, respectively. It was concluded that the disagreements between measured and simulated values of N2O concentrations and emissions resulted from the underestimation of model parameters for gas transfer and/or for N2O reduction to N2,which were not measured. Future modeling attempts should include use of measured values for all model parameters to obtain a more realistic description of the dynamics of N2O emission from the saturated zone.

The adverse effect of lodging on grass seed yield may be attributed, in part, to assimilate limitation during the seed filling period. This investigation examined plant dry matter assimilate partitioning and seed yield as affected by lodging in three species that are closely related but phenotypically different: tall fescue (Festuca arundinacea Schreber.), Italian ryegrass (Lolium multiflorum Lam.), and perennial ryegrass (L. perenne L.). Studies were performed in field plots at Corvallis, Oregon, USA. Seed yield components (seed number per inflorescence, seed yield per inflorescence, and single seed mass) and leaf, stem (lower, middle, and peduncle) and seed inflorescence dry mass were measured just prior to anthesis to seed maturity. Dry mass and water soluble carbohydrates (WSC) were determined for shoot components. The reduction in dry mass and WSC in leaves and stem components following anthesis was often greater in lodged plants compared to upright plants. The relatively low seed yield depression in lodged tall fescue suggested a higher compensation potential for partitioning reserve assimilate from leaves and stems to support seed growth and development. This potential does not appear to be present to the same degree in Italian ryegrass and to an even lesser extent in perennial ryegrass. These findings suggest that the potential to compensate for reduced assimilate supply during the period of high assimilate demand by seeds may be attributed, in part, to the total assimilate reserve accumulated prior to photoassimilate reduction caused by the lodged condition.

The factors that affect denitrification of fertilizer N were determined in cultivated riparian (CR) soils cropped to perennial ryegrass (Lolium perenne L.) and noncultivated naturally vegetated riparian soils (NCR) of poorly drained grass cropping systems in western Oregon. Denitrification activity in the NCR was low compared with the CR using the Acetylene Inhibition method. The CR soil denitrification activity was consistent over the growing season, averaging between 269 and 280 g N 2 O-N ha -1 d -1 during the measurement period depending on soil type. Denitrification activity was positively correlated to soil NH 4 -N level in the CR. The greater denitrification activity of the CR likely reflects fertilizer applications in contrast to no fertilizer addition to the NCR. Nitrate-N levels in the CR averaged 5 to 12 times higher than those of the NCR. Nitrate did not appear to encroach from the CR into the NCR by subsurface water movement. The microbial biomass was four times larger in the NCR soils and may have functioned as a significant sink for N reducing denitrification activity. Multivariate factor analysis using orthogonal factor rotation showed that approximately 83% of the observed variance in denitrification was explained by grouping experimental variables by microbial activity, N 2 O-N emission, temperature, and nitrification. The grouping of soil variables was useful in explaining the importance of different soil processes in regulating denitrification. These denitrification activity data demonstrate the possibility for significant N losses, amounting to 12.5% of the applied fertilizer N, from poorly drained cropping systems.

Prescription based nitrogen (N) fertilization of crops in a given local environment begins by understanding factors affecting crop N use and relating these factors to a time scale most directly related to crop growth. For these reasons the following objectives were sought for an economically important grass seed crop in western Oregon, Italian ryegrass (Lolium multiflorum Lam.). One, to determine the influence of N source (NH4‐N and NO3‐N) on crop growth and seed yield. Second, to determine the relationship between accumulated growing degree days (GDD) and plant ontogeny and relate these findings to N‐source effects on growth and seed yield parameters. Field plots were established in 1991 and again in 1992. Five N‐source treatments were applied: calcium nitrate (CN), ammonium nitrate (AN), ammonium sulfate (AS), ammonium chloride (AC), and urea‐dicyandiamide (DCD). Nitrogen‐source treatments had no effect on root and shoot dry mass accumulation in either year. Ammonium‐N fertilization increased t...

To develop optimum nitrogen (N) fertilization practices with the least impact on environmental quality and with the greatest economic return, it is imperative that a greater understanding of crop and soil N dynamics be sought. This paper reports on research conducted with these objectives: (i) to determine the relationship between plant N and dry matter accumulation and soil N status as affected by N‐source fertilization as a function of accumulated growing degree days (GDD), and (ii) to determine if western Oregon soil conditions favor ammonium (NH4) over nitrate (NO3) nutrition during the period of grass seed crop growth. In a companion paper, plant growth and seed yield component data were discussed in relation to N‐source treatments and climatic year effects. Western Oregon field plots of Italian ryegrass (Lolium multiflorum Lam.) were fertilized with calcium nitrate, ammonium nitrate, ammonium sulfate, ammonium chloride, and urea‐dicyandiamide (DCD) to manipulate soil NH4 and NO3 ratios. Ita...

The role of chlorine atoms (Cl) in atmospheric oxidation was traditionally thought to be limited to the marine boundary layer, where they are produced through heterogeneous reactions involving sea salt. However, recent observation of photolytic Cl precursors (ClNO2 and Cl2) formed from anthropogenic pollution has expanded the potential importance of Cl to include coastal and continental urban areas. Measurements of ClNO2 in Los Angeles during CalNex showed it to be an important primary (first generation) radical source. Ratios of volatile organic compounds (VOCs) have been proposed as a sensitive method to quantify Cl oxidation, but have shown little evidence for a significant role of Cl outside of the Arctic. We used a box model with the Master Chemical Mechanism (MCM v3.2) chemistry scheme, constrained by observations in Los Angeles, to examine the Cl-sensitivity of the most commonly used VOC ratios (i-butane, n-butane, and propane) as a function of NOx and secondary radical production. Model results indicated these and faster reacting VOC tracer ratios could not detect the influence of Cl unless the sustained ratio of OH to Cl was below 200. However, the model results also show that secondary (second generation) OH production resulting from Cl oxidation of VOCs is strongly influenced by NOx, and that this effect can obscure the importance of Cl as a primary oxidant. Calculated concentrations of Cl showed a maximum in mid-morning due to a photolytic source from ClNO2 and loss primarily to reactions with VOCs. The OH to Cl ratio was below 200 for approximately three hours in the morning, but Cl oxidation was not evident from the measured ratios of VOCs. Instead, model simulations show that secondary OH production causes VOC ratios to follow the values expected for OH oxidation despite the significant input of primary Cl from ClNO2 photolysis in the morning. Despite the prevalence of secondary OH as an oxidant in Los Angeles, Cl may play an important role in tropospheric chemistry. The reactivity of Cl in Los Angeles during CalNex was more than an order of magnitude larger than that of OH. In addition, because of its reactivity toward different classes of VOCs and its greater propensity to participate in chain propagation rather than sink reactions, Cl atoms have a different impact on regional atmospheric oxidation than do OH radicals.

Biogenic volatile organic compounds (BVOCs) can react in the atmosphere to form organic nitrates, which serve as NOx (NO + NO2) reservoirs, impacting ozone and secondary organic aerosol production, the oxidative capacity of the atmosphere, and nitrogen availability to ecosystems. To examine the contributions of biogenic emissions and the formation and fate of organic nitrates in a forest environment, we simulated the oxidation of 57 individual BVOCs emitted from a rural mixed forest in northern Michigan. Key BVOC-oxidant reactions were identified for future laboratory and field investigations into reaction rate constants, yields, and speciation of oxidation products. Of the total simulated organic nitrates, monoterpenes contributed ~70% in the early morning at ~12 m above the forest canopy when isoprene emissions were low. In the afternoon, when vertical mixing and isoprene nitrate production were highest, the simulated contribution of isoprene-derived organic nitrates was greater than 90% at all altitudes, with the concentration of secondary isoprene nitrates increasing with altitude. Notably, reaction of isoprene with NO3 leading to isoprene nitrate formation was found to be significant (~8% of primary organic nitrate production) during the daytime, and monoterpene reactions with NO3 were simulated to comprise up to ~83% of primary organic nitrate production at night. Lastly, forest succession, wherein aspen trees are being replaced by pine and maple trees, was predicted to lead to increased afternoon concentrations of monoterpene-derived organic nitrates. This further underscores the need to understand the formation and fate of these species, which have different chemical pathways and oxidation products compared to isoprene-derived organic nitrates and can lead to secondary organic aerosol formation.

Nitrogen (N) is one of the most critical elements affecting grass seed yield. In soil and cropping conditions of Western Oregon, ammonium‐N may play an important role in the growth and development of ryegrass grown for seed. Our objectives were to determine the physiological and biochemical effects of ammonium and nitrate nutrition on ryegrass vegetative growth and subsequent expression of floral tillers, and changes in plant reduced‐N and carbohydrate composition. Plants were grown in hydroponics (active pH‐controlled) and fed nitrate and ammonium alone or in combination at 10 mM total N. The experiment was terminated at anthesis, which occurred at 68 days after planting (DAP). Changes in plant tiller number, height, dry weight, reduced‐N, and water‐soluble carbohydrates (WSC) were recorded. Vegetative growth rate of plants receiving lower ratios of nitrate/ammonium was up to twice those receiving total nitrate or 75/25 nitrate/ammonium. Total primary tiller number at 68 DAP (anthesis) was 30% g...

[1] Recent laboratory and field studies have indicated that glyoxal is a potentially large contributor to secondary organic aerosol mass. We present in situ glyoxal measurements acquired with a recently developed, high sensitivity spectroscopic instrument during the CalNex 2010 field campaign in Pasadena, California. We use three methods to quantify the production and loss of glyoxal in Los Angeles and its contribution to organic aerosol. First, we calculate the difference between steady state sources and sinks of glyoxal at the Pasadena site, assuming that the remainder is available for aerosol uptake. Second, we use the Master Chemical Mechanism to construct a two-dimensional model for gas-phase glyoxal chemistry in Los Angeles, assuming that the difference between the modeled and measured glyoxal concentration is available for aerosol uptake. Third, we examine the nighttime loss of glyoxal in the absence of its photochemical sources and sinks. Using these methods we constrain the glyoxal loss to aerosol to be 0–5 × 10−5 s−1 during clear days and (1 ± 0.3) × 10−5 s−1 at night. Between 07:00–15:00 local time, the diurnally averaged secondary organic aerosol mass increases from 3.2 μg m−3 to a maximum of 8.8 μg m−3. The constraints on the glyoxal budget from this analysis indicate that it contributes 0–0.2 μg m−3 or 0–4% of the secondary organic aerosol mass.

Stem carbohydrate reserves, in ryegrass grown for seed, may play a vital role in maintaining seed growth, especially under conditions of limited photosynthesis. Little is known concerning the processes controlling stem carbohydrate utilization and partitioning in ryegrass with respect to seed growth. The objective of this investigation was to determine detailed post-anthesis changes in stem and spikelet carbohydrates as affected by modification of source and sink strength. Source-sink relations were altered by imposing detillering or detillering-defoliation treatments at anthesis. Patterns of carbohydrate distribution of the ryegrass stem were different, both among positions within the stem and with age. Stem carbohydrates accumulated during early stages of seed growth and then declined as seeds matured. Reducing sugars comprised only a small fraction of the stem's total water soluble carbohydrates. Detillering induced the formation of new tiller sinks, thus increasing sink strength and reversing the carbohydrate gradient from spikelet (seed) sinks to new tiller sinks. Defoliation, combined with detillering, decreased source strength by reducing total stem carbohydrate. In control plants, carbohydrate levels appeared adequate to support maximum seed set, whereas conditions for reduced carbohydrate levels, resulting from detillering or detillering plus defoliation, lowered seed set. Results suggest that under conditions of limited source strength (e.g. reduced photosynthetic capacity), the stem plays a major role in partitioning assimilates to compensate for sink demand. New tiller growth during the period of seed development may out-compete seeds for available carbohydrate and thus reduce seed set

Aspartate aminotransferase (AAT) plays an important role in nitrogen metabolism in all plants and is particularly important in the assimilation of fixed N derived from the legume-Rhizoblum symbiosis. Two isozymes of AAT (AAT-1 and AAT-2) occur in alfalfa (Medicago sativa L.). Antibodies against alfalfa nodule AAT-2 do not recognize AAT-1, and these antibodies were used to study AAT-2 expression in different tissues and genotypes of alfalfa and also in other legume and nonlegume species. Rocket immunoelectrophoresis indicated that nodules of 38-day-old alfalfa plants contained about eight times more AAT-2 than did nodules of 7-day-old plants, confirming the nodule-enhanced nature of this isozyme. AAT-2 was estimated to make up 16, 15, 5, and 8 milligrams per gram of total soluble protein in mature nodules, roots, stems, and leaves, respectively, of effective N(2)-fixing alfalfa. The concentration of AAT-2 in nodules of ineffective non-N(2)-fixing alafalfa genotypes was about 70% less than that of effective nodules. Western blots of soluble protein from nodules of nine legume species indicated that a 40-kilodalton polypeptide that reacts strongly with AAT-2 antibodies is conserved in legumes. Nodule AAT-2 immunoprecipitation data suggested that amide- and ureide-type legumes may differ in expression and regulation of the enzyme. In addition, Western blotting and immunoprecipitations of AAT activity demonstrated that antibodies against alfalfa AAT-2 are highly cross-reactive with AAT enzyme protein in leaves of soybean (Glycine max L.), wheat (Triticum aestivum L.), and maize (Zea mays L.) and in roots of maize, but not with AAT in soybean and wheat roots. Results from this study indicate that AAT-2 is structurally conserved and localized in similar tissues among diverse species.

Aspartate aminotransferase (AAT), a key enzyme in the biosynthesis of aspartate and asparagine, occurs as two forms in alfalfa (Medicago sativa L.), AAT-1 and AAT-2. Both forms were purified to near homogeneity, and high titer polyclonal antibodies produced to the native proteins. Alfalfa AAT-1 was purified from root suspension culture cells, while AAT-2 was purified from effective root nodules. Antibodies prepared to AAT-1 and used as probes for western blots readily recognized native and SDS forms of AAT-1 but did not recognize either native or SDS forms of AAT-2. Conversely, antibodies to AAT-2 readily recognized native and SDS forms of AAT-2 but did not recognize AAT-1. Immunotitrations further confirmed the immunological distinction between AAT-1 and AAT-2. AAT-1 antibodies immunotitrated 100% of the in vitro activity of purified AAT-1 but had no effect on AAT-2 in vitro activity. Likewise, AAT-2 antibodies removed 100% of the in vitro activity of purified AAT-2 but did not affect AAT-1 in vitro activity. Sequential titration of total AAT activity from roots and nodules showed that AAT-1 comprised the major form (62%) of AAT in roots, while AAT-2 was the predominant form (90%) in nodules. Last, SDS-PAGE western blots showed that the molecular masses of AAT-1 and AAT-2 were 42 and 40 kilodaltons, respectively. These data indicate that AAT is under the control of at least two distinct genes in alfalfa.

Stands of native grasses along roadways, in buffer strips, riparian zones and grass prairies have potential utility as feedstock for bioenergy production. The sustainability of harvesting these stands is reliant, in part, on knowledge of the mineral concentration of the harvested grasses because removal of mineral nutrients such as phosphorus (P) and potassium (K) can impact subsequent biomass production and ecosystem services associated with these stands. Mineral content of biomass, particularly that of silicon (Si), chlorine (Cl), and sulfur (S) also impacts thermochemical conversion approaches that convert grasses into bioproducts. This study quantified Cl, S, Si, P and K in Bromus marginatus, Elymus glaucus, Poa secunda, Pseudoroegneria, Elymus lanceolatus, Elymus trachycaulus, Leymus cinereus, Leymus triticoides, and Pseudoroegneria spicata collected at three growth developmental stages from four plant introduction stations located in the western US. Differences (P< or =0.05) in mineral concentrations were associated with developmental stage, species, and location. Variability was greatest in Si concentrations which ranged from 1847 to 28620 mg kg(-1), similar to those recorded in other grasses. Variability in Cl and S concentrations also occurred, but at less magnitude than that of Si. Concentrations of P and K, two mineral fertilizer components, varied approximately threefold among these grasses. Differences in mineral concentrations among these grasses were not completely dependent upon soil mineral content. Long-term evaluations of available soil mineral concentrations under contrasting management practices are needed to quantify how local conditions impact mineral cycling, and in turn, the sustainability of harvesting these stands. The data presented here establish baselines for these species in locations subject to contrasting environmental and microbiological conditions that affect mineral cycling and availability.

Switchgrass (Panicum virgatum L.) is a warm season perennial grass with great potential as an energy crop in the USA. It is widely adapted to many regions of the country, produces large amounts of biomass, serves as a useful forage grass, and provides ecosystem services that benefit soil and water quality and wildlife. Biological and thermochemical technologies are being developed to convert herbaceous biomass, including switchgrass, to energy. The objective of this research was to determine the effect of genotype and production environment on the concentration of minerals that affect the suitability of switchgrass for thermochemical conversion and to quantify the amount of potassium (K) and phosphorus (P) removed from the production system by harvest of the aboveground biomass, a measure of the sustainability of the practice. Straw dry biomass contained from 1.3 to 6.4 kg Mg(-1) and from 6.2 to 15.8 kg Mg(-1) of P and K, respectively. Variability in aluminum (Al), calcium (Ca), chloride (Cl), K, P, silicon (Si), and sulfur (S) concentrations across locations was relatively high, ranging from twofold (Al) to eightfold (Cl). Location had a strong impact on mineral concentrations among switchgrass genotypes evaluated in this study. Latitude of origin impacted the Cl and Si concentrations measured in plant tissues, but none of the other minerals analyzed in this study. Upland and lowland cytotypes explained some of the observed differences, but populationxlocation interactions were the primary source of variability in the concentration of these minerals.

Oxalic acid is one of the most abundant dicarboxylic acids in the atmosphere, receiving a great deal of attention due to its potential influence on cloud condensation nucleus activities. In this work, we report 10 months of hourly oxalate measurements in particulate matter of less than 2.5 µm in aerodynamic diameter (PM2.5) by a Monitor for Aerosols and Gases in ambient Air at a suburban coastal site in Hong Kong from April 2012 to February 2013. A total of more than 6000 sets of oxalate and inorganic ion data were obtained. The mean (±SD) oxalate concentration was 0.34 (±0.18) µg m−3, accounting for 2.8% of the total ion mass and 1.5% of the PM2.5 mass. Seasonal variation showed higher concentrations in fall and winter (0.54 and 0.36 µg m−3, respectively) and lower concentrations in spring and summer (~0.26 µg m−3). Different from the inorganic ions, a shallow dip in the oxalate concentration consistently occurred in the morning after sunrise (around 9:00 A.M.) throughout all seasons. Our analysis suggests that this was likely due to photolysis of oxalate-Fe (III) complex under sunlight. In summer, a small daytime peak was discernable for oxalate and nitrate. This characteristic, together with a more evident diurnal variation of O3, indicates comparatively more active photochemical oxidation in summer than other seasons. High correlations were observed between oxalate and non-sea-salt SO42− (NSS) (R2 = 0.63) and Ox (O3 + NO2) (R2 = 0.48), indicating significant commonality in their secondary formation. Positive matrix factorization analysis of oxalate and other real-time gas and particle-phase component data estimates that secondary formation processes, including secondary gas or aqueous oxidation processes (49%), oxidation processes of biomass burning emissions (37%), accounted for the majority of PM2.5 oxalate. A backward trajectories cluster analysis found that higher oxalate/NSS ratios were associated with low pollution samples under the influence of marine air masses while the ratios were lower in high pollution samples that were typically associated with continental air masses passing through areas of high anthropogenic emissions. Isolating the “low pollution marine” aerosols across the entire data set indicates that oxalate production increased in the summer compared to other seasons, suggesting either more active marine emissions of oxalate precursors or stronger photochemical processes in the summer.

The amount of soil nitrogen (N) available to perennial ryegrass (Lolium perenne L.) will influence the distribution of N within the plant. At low amounts of plant available N the relative proportion of N in the roots will be high. As under conditions of high N availability, the proportion of N in vegetative and reproductive tillers as well as the number of vegetative and reproductive tillers will increase. However, the correlation between plant N content and tiller production is not known. Therefore, a growth chamber experiment was performed to investigate this relationship in perennial ryegrass. The relation is important to better predict the effect of N application on tiller production. Plants were grown in nutrient solutions containing diminishing amounts of N over 36 days. At the end of the growth period, N and carbon (C) concentrations of the plant tissues, as well as the tiller production, were analyzed. Higher N concentrations were found in leaves than in roots. Depending on the N concentr...

The Willamette Valley of Oregon has extensive areas of poorly drained, commercial grass seed lands. Little is known about the ability of riparian areas in these settings to reduce nitrate in water draining from grass seed fields. We established two study sites with similar soils and hydrology but contrasting riparian vegetation along an intermittent stream that drains perennial ryegrass (Lolium perenne L.) fields in the Willamette Valley of western Oregon. We installed a series of nested piezometers along three transects at each site to examine NO 3 -N in shallow ground water in grass seed fields and riparian areas. Results showed that a noncultivated riparian zone comprised of grasses and herbaceous vegetation significantly reduced NO 3 -N concentrations of shallow ground water moving from grass seed fields. Darcy's law-based estimates of shallow ground water flow through riparian zone A/E horizons revealed that this water flowpath could account for only a very small percentage of the streamflow. Even though there is great potential for NO 3 -N to be reduced as water moves through the noncultivated riparian zone with grass-herbaceous vegetation, the potential was not fully realized because only a small proportion of the stream flow interacts with riparian zone soils. Consequently, effective NO 3 -N water quality management in poorly drained landscapes similar to the study watershed is primarily dependent on implementation of sound agricultural practices within grass seed fields and is less influenced by riparian zone vegetation. Wise fertilizer application rates and timing are key management tools to reduce export of NO 3 -N in stream waters.

Grass seed cropping systems in the Pacific Northwest account for about half of the cool-season forage and turf grass seed production in the world. Grass seed cropping systems are intensely managed with inorganic fertilizers to sustain production. Much of the land where grass seed production occurs in western Oregon is marginally productive for most other crops because of the poorly drained soil conditions. The role of riparian areas bordering grass seed fields in moderating surface water and groundwater quality is not well understood. A study site in western Oregon was instrumented to determine how riparian areas bordering grass seed fields process N and thereby influence water quality. The site consisted of a perennial ryegrass (Lolium perenne L.) seed field, a grass riparian area, and an intermittent creek. Groundwater levels were monitored during the fall of 1995 to the late spring of 1996 and a complete set of samples were collected every two weeks from wells with water and analyzed for NO3- and NH4+. Total fertilizer applied to the crop was 200 kg N ha-1 yr-1. Data indicated a lateral subsurface hydrologic flow path from the cultivated field through the riparian zone, to the creek. Averaged over the season (November 1995 – June 1996), riparian zone A and C horizon groundwater mean NO3- concentration was mostly undetectable and less than 3.8 mg L-1 in the agricultural field. At all sampling dates, the NO3- concentration was higher in the field than in the riparian zone. Seasonal mean groundwater NH4+ concentrations for the riparian and field A and C horizons were ≤0.2 mg L-1. Annual crop net N accumulation was 144 kg N ha-1. Riparian soil electrode potentials (Eh) at 25 and 45 cm averaged -200 to -100 mV during the wet cycle, whereas the field ranged between 0 to +50 mV. Collectively, findings indicate that both crop and riparian processes at the Lake Creek site are responsible for reducing shallow groundwater NO3- to low levels.

Voles are well-known crop pests, especially when peak populations are present, but their role in soil fertility and impacts on agricultural sustainability are not well understood. Five months after the abrupt disappearance of a peak in a gray-tailed vole (Microtus canicaudus) population, we examined burrow structure, determined concentrations of trace elements, carbon and nitrogen in the soil immediately surrounding vole burrows, and compared soil chemical properties to a depth of 90 cm between areas with prior vole activity and areas of no activity. Vole tunneling activity was confined to the top 10 cm of the soil profile and was coincident with the majority of root biomass. Soil NH 4 +, NO 3 -, extractable organic carbon, and soil organic matter were greater below vole tunnels than above; however, due to small sample sizes, differences were not significant. There were no differences in trace elements with respect to position around vole tunnels. Vole activity was associated with increased soil nitrate concentrations and decreased soil pH to a depth of 90 cm, indicating that nitrification might be enhanced by vole activity, and that this effect continues after vole populations crash. Greater inorganic nitrogen could have long-term effects on ecosystem productivity. The effects voles have on soil processes that influence carbon and nutrient cycle requires further investigation.

Carbon metabolism in Bradyrhizobium japonicum bacteroids is reviewed. Additionally, the bacteroid tricarboxylic acid (TCA) cycle and its regulation under oxygen-limited conditions is considered, with emphasis on possible sites of TCA cycle rate-limiting reactions. Furthermore, we consider other adaptive pathways that may be employed by these organisms while in symbiosis. These pathways include: (1) a poly-β-hydroxy-butyrate shunt, (2) a malate-aspartate shuttle, (3) an α-ketoglutarate-glutamate shunt, (4) a modified dicarboxylic acid cycle, and (5) fermentation pathways leading to lactate, acetaldehyde and ethanol. The effects of oxygen limitation on host carbon metabolism are also considered briefly.

Stems of Vicia faba plants were used to study phloem unloading because they are hollow and have a simple anatomical structure that facilitates access to the unloading site. After pulse labeling of a source leaf with (14)CO(2), stem sections were cut and the efflux characteristics of (14)C-labeled sugars into various buffered solutions were determined. Radiolabeled sucrose was shown to remain localized in the phloem and adjacent phloem parenchyma tissues after a 2-hour chase. Therefore, sucrose leakage from stem segments prepared following a 75-minute chase period was assumed to be characteristic of phloem unloading. The efflux of (14)C assimilates from the phloem was enhanced by 1 millimolar p-chloromercuribenzene sulfonic acid (PCMBS) and by 5 micromolar carbonyl cyanide m-chlorophenly hydrazone (CCCP). However, PCMBS inhibited and CCCP enhanced general leakage of nonradioactive sugars from the stem segments. Sucrose at concentrations of 50 millimolar in the free space increased efflux of [(14)C]sucrose, presumably through an exchange mechanism. This exchange was inhibited by PCMBS and abolished by 0.2 molar mannitol. Increasing the osmotic concentration of the efflux medium with mannitol reduced [(14)C]sucrose efflux. However, this inhibition seems not to be specific to sucrose unloading since leakage of total sugars, nonlabeled sucrose, glucose, and amino acids from the bulk of the tissue was reduced in a similar manner. The data suggest that phloem unloading in cut stem segments is consistent with passive efflux of sucrose from the phloem to the apoplast and that sucrose exchange via a membrane carrier may be involved. This is consistent with the known conductive function of the stem tissues, and contrasts with the apparent nature and function of unloading in developing seeds.

In vitro sugar transport into developing isolated maize embryos was studied. Embryo fresh and dry weight increased concomitantly with endogenous sucrose concentration and glucose uptake throughout development. However, endogenous glucose and fructose concentration and sucrose uptake remained constant. The uptake kinetics of radiolabeled sucrose, glucose, and fructose showed a biphasic dependence on exogenous substrate concentration. Hexose uptake was four to six times greater than sucrose uptake throughout development. Carbonylcyanide-m-chlorophenylhydrazone and dinitrophenol inhibited sucrose and glucose uptake significantly, but 3-O-methyl glucose uptake was less affected. The uptake of 1 millimolar sucrose was strongly pH dependent while glucose was not. Glucose and fructose were readily converted to sucrose and insoluble products soon after absorption into the embryo. Thus, sucrose accumulated, while glucose pools remained low. Based on the findings of this and other studies a model for sugar transport in the developing maize kernel is presented.

Effective (N(2)-fixing) alfalfa (Medicago sativa L.) and plant-controlled ineffective (non-N(2)-fixing) alfalfa recessive for the in(1) gene were compared to determine the effects of the in(1) gene on nodule development, acetylene reduction activity (ARA), and nodule enzymes associated with N assimilation and disease resistance. Effective nodule ARA reached a maximum before activities of glutamine synthetase (GS), glutamate synthase (GOGAT), aspartate aminotransferase (AAT), asparagine synthetase (AS), and phosphoenolpyruvate carboxylase (PEPC) peaked. Ineffective nodule ARA was only 5% of effective nodule ARA. Developmental profiles of GS, GOGAT, AAT, and PEPC activities were similar for effective and ineffective nodules, but activities in ineffective nodules were lower and declined earlier. Little AS activity was detected in developing ineffective nodules. Changes in GS, GOGAT, AAT, and PEPC activities in developing and senescent effective and ineffective nodules generally paralleled amounts of immunologically detectable enzyme polypeptides. Effective nodule GS, GOGAT, AAT, AS, and PEPC activities declined after defoliation. Activities of glutamate dehydrogenase, malate dehydrogenase, phenylalanine ammonia lyase, and caffeic acid-o-methyltransferase were unrelated to nodule effectiveness. Maximum expression of nodule N-assimilating enzymes appeared to require the continued presence of a product associated with effective bacteroids that was lacking in in(1) effective nodules.

Aspartate aminotransferase (l-aspartate:2-oxoglutarate aminotransferase, EC 2.6.1.1 [AAT]), a key enzyme in the assimilation of C and N compounds, was purified from the cytosol of alfalfa (Medicago sativa L.) root nodules. Isoforms that increased during nodule development, AAT-2a, AAT-2b, and AAT-2c, were purified greater than 447-fold to apparent homogeneity, and high titer polyclonal antibodies were produced. The native molecular weight of the AAT-2 isoforms was approximately 80 kilodatons with a subunit molecular weight of 40 kilodatons, indicating that the holoenzymes are dimers. The AAT-2 isoforms comprised approximately 0.4% of the total soluble nodule protein. The AAT specific activity was measured in leaf, stem, root, and nodule organs, and zymograms of each were compared. Enzyme activity was 4- to 37-fold greater in effective (nitrogen fixing) nodules than in leaves, stems, and roots. Effective nodule AAT-specific activity was 3- to 8-fold greater than that of plant-controlled ineffective nodules. No differences in K(m) were observed between AAT-1 and AAT-2. Antibodies raised against AAT-2 were more selective against AAT-2 than AAT-1. Evidence obtained from zymograms suggests that the expression of alfalfa nodule AAT is controlled at two different gene loci, AAT-1 and AAT-2, resulting in different dimeric isoforms.