Transition From Sagebrush Steppe to Annual Grass (Bromus tectorum): Influence on Belowground Carbon and Nitrogen

Vegetation changes associated with climate shifts and anthropogenic disturbance have major impacts on biogeochemical cycling. Much of the interior western United States currently is dominated by sagebrush (Artemisia tridentata Nutt.) ecosystems. At low to intermediate elevations, sagebrush ecosystems increasingly are influenced by cheatgrass (Bromus tectorum L.) invasion. Little currently is known about the distribution of belowground organic carbon (OC) on these changing landscapes, how annual grass invasion affects OC pools, or the role that nitrogen (N) plays in carbon (C) retention. As part of a Joint Fire Sciences-funded project called the Sagebrush Treatment Evaluation Project (SageSTEP), we quantified the depth distribution of soil OC and N at seven sites experiencing cheatgrass invasion. We sampled plots that retained sagebrush, but represented a continuum of cheatgrass invasion into the understory. Eighty-four soil cores were taken using a mechanically driven diamond-tipped core drill to a depth of 90 cm, or until bedrock or a restrictive layer was encountered. Samples were taken in 15-cm increments, and soil, rocks, and roots were analyzed for OC and total N. We determined that cheatgrass influences the vertical distribution of OC and N within the soil profile and might result in decreased soil OC content below 60  cm. We also found that OC and total N associated with coarse fragments accounted for at least 10% of belowground pools. This emphasizes the need for researchers to quantify nutrients in deep soil horizons and coarse fragments.     

Impact of coal combustion waste on the microbiology of a model aquifer

The effects of water infiltration into an alkaline coal combustion waste burial site on the chemical and microbiological aspects of a meso-scale (2.44 m diameter × 4.6 m, height, 65 tonne) model aquifer were analyzed. The spatial and temporal effects of the alkaline leachate on microbial activity, numbers and diversity were examined in the model and compared with uncontaminated control materials. Within the saturated zone below the waste there was a pH gradient from 12.4 at the water table, immediately below the waste, to 6.0 at 3.5 meters from the waste, and elevated levels of arsenic and strontium in the pore waters. Microtox testing of the contaminated pore waters indicated high toxicity (a gamma value of 1 at dilutions of 45 to 110 fold). The leachate contamination was associated with a reduction in bacterial [³H] leucine incorporation from a high of 267 fmol g^?1 h^?1 in sediments below the contaminant plume to undetectable in the contaminated zone. In comparison, leucine incorporation rates in control column sediments were 899 fmol g^?1 h^?1. Similar toxic effects were evident in reduced total direct and culturable counts of bacteria. Observations also indicated a reduction in microbial diversity and development of alkaline-tolerant microbial communities. These results indicated that any failure of confinement technologies at disposal sites would adversely affect both the chemistry and microbiology of the underlying saturated zone.     

Effects of vegetation regime on denitrification potential in two tropical volcanic soils

Effects of vegetation and nutrient availability on potentail denitrification rates were studied in two volcanic, alluvial-terrace soils in lowland Costa Rica that differ greatly in weathering stage and thus in availability of P and base cations. Potential denitrification rates were significantly higher in plots where vegetation had been left undisturbed than in plots where all vegetation had been removed continuously, and were higher on the less fertile of the two soils. The potential denitrification rates were correlated strongly with respiration rates, levels of mineralizable N, microbial biomass, and moisture content, and moderately well with concentrations of extractable NH _inf4 ^sup+ , Kjeldahl N, and total C. In all plots, denitrification rates were stimulated by the removal of O₂ and by the addition of glucose but not by the addition of water or NO _inf3 ^sup- .This is Paper 2772 of the Forest Research Laboratory, Oregon State University     

Effect of temperature, elevated carbon dioxide, and drought during seed development on the isoflavone content of dwarf soybean [Glycine max (L.) Merrill] grown in controlled environments

The effects of elevated temperature, carbon dioxide, and water stress on the isoflavone content of seed from a dwarf soybean line [Glycine max (L.) Merrill] were determined, using controlled environment chambers. Increasing the temperature from 18 degrees C during seed development to 23 degrees C decreased total isoflavone content by about 65%. A further 5 degrees C increase to 28 degrees C decreased the total isoflavone content by about 90%. Combining treatments at elevated temperature with elevated CO(2) (700 ppm) and water stress to determine the possible consequences of global climate change on soybean seed isoflavone content indicated that elevated CO(2) at elevated temperatures could partially reverse the effects of temperature on soybean seed isoflavone content. The addition of drought stress to plants grown at 23 degrees C and elevated CO(2) returned the total isoflavone levels to the control values obtained at 18 degrees C and 400 ppm CO(2). The promotive effects of drought and elevated CO(2) at 23 degrees C on the 6' '-O-malonygenistin and genistin levels were additive. The individual isoflavones often had different responses to the various growth conditions during seed maturation, modifying the proportions of the principal isoflavones. Therefore, subtle changes in certain environmental factors may change the isoflavone content of commercially grown soybean, altering the nutritional values of soy products.     

Uptake and nutrient balance of nitrogen,sulfur, and boron for optimal canola production in eastern Canada

Balanced plant nutrition is essential to achieve high yields of canola (Brassica napus L.) and get the best economic return from applied fertilizers. A field study was conducted at nine site‐years across eastern Canada to investigate the effects of nitrogen (N), sulfur (S) and boron (B) fertilization on canola nutrient uptake, nutrient balance, and their relationship to canola yields. The factorial experiment consisted of four N rates of 0 (N0), 50 (N50), 100 (N100), and 150 (N150) kg ha^?1, two S rates of 0 (S0) and 20 (S20) kg ha^?1, and three B treatments of 0 (B0), 2 kg ha^?1 at preplant (B2.0P), and 0.5 kg B ha^?1 foliar‐applied at early flowering stage (B0.5F). Each site‐year used the same experimental design and assigned treatments in a randomized complete block design with four replications. Fertilizer S application greatly improved seed yields at six out of nine site‐years, and the highest N use efficiency was in the N150+S20 treatment. Sulfur application generally increased seed S concentration, seed S removal, and plant total S uptake, while B fertilization mainly elevated straw B concentration and content, with minimal effect on seed yields. At the early flowering stage, plant tissue S ranged from 2.2 to 6.6 mg S g^?1, but the N : S ratio was over or close to the critical value of 12 in the N150+S0 combination at five site‐years. On average across nine site‐years, canola reached a plateau yield of 3580 kg ha^?1 when plants contained 197 kg N ha^?1, 33 kg S ha^?1 and 200 g B ha^?1, with a seed B content of 60 g B ha^?1. The critical N, S, and B values identified in this work and their potential for a posteriori nutrient diagnosis of canola should be useful to validate fertilizer requirements for canola production in eastern Canada.     

Revisiting two sympatric European seahorse species: apparent decline in the absence of exploitation

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Closing the compliance gap in marine protected areas with human behavioural sciences

Advocates, practitioners and policy-makers continue to use and advocate for marine protected areas (MPAs) to meet global ocean protection targets. Yet many of the worlds MPAs, and especially no-take MPAs, are plagued by poaching and ineffective governance. Using a global dataset on coral reefs as an example, we quantify the potential ecological gains of governing MPAs to increase compliance, which we call the ‘compliance gap’. Using ecological simulations based on model posteriors of joint Bayesian hierarchical models, we demonstrate how increased compliance in no-take MPAs could nearly double target fish biomass (91% increases in median fish biomass), and result in a 292% higher likelihood of encountering top predators. Achieving these gains and closing the compliance gap necessitates a substantial shift in approach and practice to go beyond optimizing enforcement, and towards governing for compliance. This will require engaging and integrating a broad suite of actors, principles, and practices across three key domains: (i)) harnessing social influence, (ii) integrating equity principles, and (iii) aligning incentives through market-based instruments. Empowering and shaping communication between actor groups (e.g., between fishers, practitioners, and policy-makers) using theoretically underpinned approaches from the behavioural sciences is one of the most essential, but often underserved aspects of governing MPAs. We therefore close by highlighting how this cross-cutting tool could be further integrated in governance to bolster high levels of compliance in MPAs.     

Cation exchange capacity of density fractions from paired conifer/grassland soils

The cation exchange capacity (CEC) of a soil depends on the type and amount of both mineral and organic surfaces. Previous studies that have sought to determine the relative contribution of organic matter to total soil CEC have not addressed differences in soil organic matter (SOM) composition that could lead to differences in CEC. The objectives of this study were (1) to compare the CEC of two distinct SOM pools, the “light fraction (LF)” composed of particulate plant, animal, and microbial debris, and the “heavy fraction (HF)” composed of mineral-bound organic matter; and (2) to examine the effects of differences in aboveground vegetation on CEC. Soil samples were collected from four paired grassland/conifer sites within a single forested area and density fractionated. LF CEC was higher in conifer soils than in grassland soils, but there was no evidence of an effect of vegetation on CEC for the HF or bulk soil. LF CEC (but not HF CEC) correlated well with the C concentration in the fraction. The mean CEC of both fractions (per kg fraction) exceeded that of the bulk soil; thus, when the LF and HF CEC were combined mathematically by weighting values for each fraction in proportion to dry mass, the resulting value was nearly twice the measured CEC of bulk soil. On a whole soil basis, the HF contributed on average 97% of the CEC of the whole soil, although this conclusion must be tempered given the inflation of CEC values by the density fractionation procedure.