University of Maine

About: University of Maine is a education organization based out in Orono, Maine, United States. It is known for research contribution in the topics: Population & Ice sheet. The organization has 8637 authors who have published 16932 publications receiving 590124 citations. The organization is also known as: University of Maine at Orono.

Brassica cover cropping: I. Effects on weed and crop establishment

Abstract: The Brassicaceae contain glucosinolates, which hydrolyze to form compounds toxic to plants, fungi, nematodes, and certain insects. Lower weed density and biomass in crops grown following incorporation of brassica cover crops suggest that they may contribute to weed management in agricultural systems. Field experiments were conducted to determine whether incorporated brassica cover crops, including canola, rapeseed, and yellow mustard, reduce subsequent weed and crop establishment; a companion paper describes separate but related field experiments that examined the influence of brassica cover crops on plant growth. Emergence rate and total emergence of sixteen weed and crop bioassay species were measured following brassica cover crops, fallow, or incorporated residues of other short-season cover crops including oat, crimson clover, and buckwheat. The bioassay species, representing a range of seed sizes, were chosen to determine whether larger seed size confers protection from residue-mediated effe...

Annual cycles of ecological disturbance and recovery underlying the subarctic Atlantic spring plankton bloom

Abstract: Received 27 November 2012; revised 1 April 2013; accepted 15 May 2013; published 20 June 2013. [1] Satellite measurements allow global assessments of phytoplankton concentrations and, from observed temporal changes in biomass, direct access to net biomass accumulation rates (r). For the subarctic Atlantic basin, analysis of annual cycles in r reveals that initiation of the annual blooming phase does not occur in spring after stratification surpasses a critical threshold but rather occurs in early winter when growth conditions for phytoplankton are deteriorating. This finding has been confirmed with in situ profiling float data. The objective of the current study was to test whether satellite-based annual cycles in r are reproduced by the Biogeochemical Element Cycling–Community Climate System Model and, if so, to use the additional ecosystem properties resolved by the model to better understand factors controlling phytoplankton blooms. We find that the model gives a similar early onset time for the blooming phase, that this initiation is largely due to the physical disruption of phytoplankton-grazer interactions during mixed layer deepening, and that parallel increases in phytoplankton-specific division and loss rates during spring maintain the subtle disruption in food web equilibrium that ultimately yields the spring bloom climax. The link between winter mixing and bloom dynamics is illustrated by contrasting annual plankton cycles between regions with deeper and shallower mixing. We show that maximum water column inventories of phytoplankton vary in proportion to maximum winter mixing depth, implying that future reductions in winter mixing may dampen plankton cycles in the subarctic Atlantic. We propose that ecosystem disturbance-recovery sequences are a unifying property of global ocean plankton blooms.

Humble persons are more helpful than less humble persons: Evidence from three studies

Abstract: Connections between humility and other prosocial qualities led us to develop a humility–helpfulness hypothesis. In three studies, humble persons were more helpful than less humble persons. In Study 1, participants (n = 117) completed self-report measures of humility, the Big Five, and helpfulness. In Study 2, participants (n = 90) completed an implicit measure of humility and were presented with an unexpected opportunity to help someone in need. In Study 3, participants (n = 103) completed self-report and implicit measures of humility and were presented a similar helping opportunity. Humility and helpfulness correlated positively when personality and impression management were controlled. Humble participants helped more than did less humble participants even when agreeableness and desirable responding were statistically controlled. Further, implicit humility uniquely predicted helping behavior in an altruistic motivation condition.

Stress tolerance and reactive oxygen metabolism in the intertidal red seaweeds Mastocarpus stellatus and Chondrus crispus

Abstract: Mastocarpus stellatus and Chondrus crispus are morphologically similar red seaweeds that co-occur on rocky intertidal seashores in the Northern Atlantic. Mastocarpus stellatus grows higher on the shore and is more tolerant of environmental stress, caused by factors such as freezing and desiccation, than C. crispus. Here we report a correlation between reactive oxygen metabolism and stress tolerance, which suggests that reactive oxygen metabolism may play a role in stress tolerance of intertidal red seaweeds. Mastocarpus stellatus scavenged added H 2 O 2 slightly faster, and was more resistant to oxidative stress induced by addition of H 2 O 2 and Rose Bengal, than C. crispus. These data were consistent with higher levels of ascorbate and β-carotene and higher activities of catalase and glutathione reductase, in M. stellatus. Tocopherol content and activities of superoxide dismutase and ascorbate peroxidase were similar in both species. Activities of reactive oxygen scavenging enzymes generally increased with tidal height in M. stellatus; this was, however, not a consistent trend in C. crispus.

Survival and Recovery of Methanotrophic Bacteria Starved under Oxic and Anoxic Conditions

Abstract: The effects of carbon deprivation on survival of methanotrophic bacteria were compared in cultures incubated in the presence and absence of oxygen in the starvation medium. Survival and recovery of the examined methanotrophs were generally highest for cultures starved under anoxic conditions as indicated by poststarvation measurements of methane oxidation, tetrazolium salt reduction, plate counts, and protein synthesis. Methylosinus trichosporium OB3b survived up to 6 weeks of carbon deprivation under anoxic conditions while maintaining a physiological state that allowed relatively rapid (hours) methane oxidation after substrate addition. A small fraction of cells starved under oxic and anoxic conditions (4 and 10%, respectively) survived more than 10 weeks but required several days for recovery on plates and in liquid medium. A non-spore-forming methanotroph, strain WP 12, displayed 36 to 118% of its initial methane oxidation capacity after 5 days of carbon deprivation. Oxidation rates varied with growth history prior to the experiments as well as with starvation conditions. Strain WP 12 starved under anoxic conditions showed up to 90% higher methane oxidation activity and 46% higher protein production after starvation than did cultures starved under oxic conditions. Only minor changes in biomass and morphology were seen for methanotrophic bacteria starved under anoxic conditions. In contrast, starvation under oxic conditions resulted in morphology changes and an initial 28 to 35% loss of cell protein. These data suggest that methanotrophic bacteria can survive carbon deprivation under anoxic conditions by using maintenance energy derived solely from an anaerobic endogenous metabolism. This capability could partly explain a significant potential for methane oxidation in environments not continuously supporting aerobic methanotrophic growth.