Formation of catalytic metal-molecule contacts

We describe a new strategy for the in situ growth of molecular wires predicated on the synthesis of a trifunctional "primed" contact formed from metal-carbon multiple bonds. The ruthenium-carbon pi bond provides structural stability to the molecular linkages under ambient conditions, and density functional calculations indicate the formation of an efficient conduit for charge carriers to pass between the metal and the molecule. Moreover, the metal-carbon pi bond provides a chemically reactive site from which a conjugated molecular wire can be grown in situ through an olefin metathesis reaction.     

Another perspective on altitudinal limits of alpine timberlines

Recent hypotheses of timberline causation include the possibility that limitations to growth processes may be more limiting than restrictions on photosynthetic carbon gain, and that cold soil is a primary limiting factor at high altitude. However, almost all of the supporting data for timberline causation have come from studies on older trees, with little focus on the mechanisms of seedling establishment and the growth of saplings away from the forest edge into the treeline ecotone. We describe a conceptual model of timberline migration that invokes a strong dependence on ecological facilitation, beginning with seed germination and continuing through seedling establishment and sapling growth to the stage where trees with forest-like stature form new subalpine forest at a higher altitude. In addition to protection from severe mechanical damage, facilitation of photosynthetic carbon gain and carbon processing is enhanced by plasticity in plant form and microsite preference, enabling seedling survival and sapling growth inside and through the often severe boundary layer just above the ground cover. Several forms of facilitation (inanimate, interspecific, intraspecific and structural) result in substantial increases in photosynthetic carbon gain throughout the summer growth period, leading to enhanced root growth, subsequent amelioration of drought stress, and increased seedling survival. Avoidance of low temperatures and low-temperature photoinhibition of photosynthesis may be major benefits of the facilitation, enhancing photosynthetic carbon gain and respiratory-driven growth processes. We propose that the growth of vertical stems (flagged tree forms) from krummholz mats is analogous functionally to the facilitated growth of a seedling/sapling in and away from ground cover. Increasing abundance and growth of newly established trees in the treeline ecotone generates a structural and microsite facilitation characteristic of the subalpine forest below. This is followed by the formation of new subalpine forest with forest-like trees, and a new timberline at higher altitude.     

Evaluating unoccupied aerial systems (UAS) imagery as an alternative tool towards cotton-based management zones

Unoccupied aerial system (UAS) imagery may serve as an additional tool towards management zone delineation. This is because UAS data collection is relatively flexible. However, it is unclear how useful UASs can be towards generating management zones, relative to preexisting tools (e.g. apparent soil electrical conductivity or EC_a). The purpose of this study, therefore, was to evaluate UAS imagery, relative to EC_a, in terms of their ability to: 1) predict cotton traits (i.e. height, seed cotton yield), and 2) define cotton management zones based on these traits. Single-season UAS images from multispectral/thermal sensors were collected and processed into Normalized Difference Vegetation Index (NDVI) and radiometric surface temperature (T_r), respectively. Management zones were also delineated using digital camera (RGB) imagery collected at periods before planting and near harvest. RGB management zones were delineated by a novel open boll mapping approach. In-season NDVI and T_r layers were significant (P?<?0.01) predictors of canopy height. Additionally, NDVI and T_r maps produced statistically different management zones during flowering and boll filling growth stages in terms of yield (P?=?0.001 or less). Open boll layers were all more accurate predictors of cotton seed yield than EC_a data—these two layers also produced statistically distinct management zones. ANOVA tests revealed that, given EC_a alone, adding UAS information via the RGB open boll map resulted in a significantly different yield prediction model (P?<?0.001). These results suggest that UAS imagery can offer valuable information for cotton management zone delineation that other techniques cannot.

     

Estimating collateral mortality from towed fishing gear

More than 50% of the world's total marine catch (approximately 81 million tonnes) is harvested using towed fishing gears (i.e. Danish seines, dredges and otter and beam trawls). As for all methods, the total fishing mortality of these gears comprises the reported (landed) and unreported catch and other unaccounted, collateral deaths due to (i) avoiding, (ii) escaping, (iii) dropping out of the gear during fishing, (iv) discarding from the vessel, (v) ghost fishing of lost gear, (vi) habitat destruction or subsequent (vii) predation and (viii) infection from any of the above. The inherent poor selectivity of many towed gears, combined with their broad spatial deployment, means that there is considerable potential for cumulative effects of (i)–(viii) listed above on total fishing mortality, and subsequent wide‐scale negative impacts on stocks of important species. In this paper, we develop a strategy for minimizing this unwanted exploitation by reviewing all the primary literature studies that have estimated collateral, unaccounted fishing mortalities and identifying the key causal factors. We located more than 80 relevant published studies (between 1890 and early 2006) that quantified the mortalities of more than 120 species of escaping (26 papers) or discarded (62 papers) bivalves, cephalopods, crustaceans, echinoderms, elasmobranches, reptiles, teleosts and miscellaneous organisms. Seven of these studies also included the estimates of mortalities caused by dropping out of gears, predation and infection [(iii), (vii) and (viii) listed above]. Owing to several key biological (physiology, size and catch volume and composition), environmental (temperature, hypoxia, sea state and availability of light) and technical (gear design, tow duration and speed) factors, catch‐and‐escape or catch‐and‐discarding mechanisms were identified to evoke cumulative negative effects on the health of most organisms. We propose that because the mortalities of discards typically are much greater than escapees, the primary focus of efforts to mitigate unaccounted fishing mortalities should concentrate on the rapid, passive, size and species selection of non‐target organisms from the anterior sections of towed gears during fishing. Once maximum selection has been achieved and demonstrated to cause few mortalities, efforts should be made to modify other operational and/or post‐capture handling procedures that address the key causal factors listed above.     

Soil Acid-Base Chemistry of a High-Elevation Forest Watershed in the Great Smoky Mountains National Park: Influence of Acidic Deposition

Understanding the acid-base chemistry of soil and the soil processes related to the release or retention of sulfate and nitrate is important in order to predict watershed recovery from long-term acid deposition. Soils were sampled from the Noland Divide Watershed (NDW), a small, high-elevation watershed in the Great Smoky Mountains National Park receiving high rates of acid deposition over several decades. Soil samples were measured for chemical properties related to acidification and used to conduct sulfate adsorption and nitrogen (N) incubation experiments. Shallow soil was higher in acidic and basic ions than deeper soils, and the mean effective cation exchange capacity was 8.07, 5.06, and 3.57 cmol_c kg⁻¹ in the A, Bw, and Cb horizons, respectively. In all three soil horizons, the base saturation was equal to or below 7% and the ratio of Ca/Al was below 0.01, indicating that the NDW is very sensitive to acid deposition. Based on results from sulfate adsorption isotherms, the NDW has not reached its maximum sulfate adsorption saturation and is likely able to retain further additions of sulfate. Desorption of sulfate from NDW soils is expected if sulfate concentrations in soil solution drop below 50 μeq L⁻¹ but is highly dependent on soil pH and organic carbon content. Total soil organic N was 500 times greater than inorganic N in the A soil horizon, and net N mineralization and nitrification remained constant during a 28-day incubation indicating a large reservoir of N substrate for soil microbes. Nitrogen experiment results suggest that nitrate export from the watershed is largely controlled by biological processes rather than by nitrate deposition flux. Soil data collected in this study contributes to our understanding of biogeochemical processes affecting the response of acid-impacted ecosystems such as the NDW to future changes in atmospheric deposition.     

Evaluation of methanotroph (Methylococcus capsulatus,Bath) bacteria meal as an alternative protein source for growth performance,digestive enzymes,and health status of Pacific white shrimp (Litopenaeus vannamei)

Aquaculture International - The increasing cost of fishmeal (FM) with limited supply and the continuous development of aquaculture necessitate more economical FM substitutes. This study aimed to...