University of New Hampshire

About: University of New Hampshire is a education organization based out in Durham, New Hampshire, United States. It is known for research contribution in the topics: Population & Solar wind. The organization has 9379 authors who have published 24025 publications receiving 1020112 citations. The organization is also known as: UNH.

Photosynthesis and photoprotection in symbiotic corals

Abstract: In zooxanthellate corals, excess excitation energy can be dissipated as heat (nonphotochemical quenching), thereby providing protection against oxidative damage by supraoptimal light in shallow reefs. To identify and quantify the photoprotective mechanisms, we studied the diel variability of chlorophyll fluorescence yields and photosynthetic parameters in situ in corals, using moored and SCUBA-based fast-repetition-rate fluorometers. The results reveal that nonphotochemical quenching is triggered prior to saturation of photosynthetic electron transport by downregulation of the reaction centers of Photosystem II (PSII). This process dissipates up to 80% of the excitation energy. On a sunny day in shallow waters, the daily integrated flux of photons absorbed, and subsequently dissipated as heat, is ;4 times that used for photosynthesis. Fluorescence quenching is further accompanied by a slight reduction in the functional absorption cross section for PSII that results from thermal dissipation of excitation energy in the light-harvesting antennae. These two processes are highly dynamic and adjust to irradiance changes on timescales consistent with the passage of clouds across the sky. Under supraoptimal irradiance, however, up to 30% of PSII reaction centers become photoinhibited, and these are repaired only after several hours of low irradiance. In shallow corals, between 10% and 20% of the reactions centers are chronically photoinhibited and appear to remain permanently nonfunctional throughout the year. Our results establish, for the first time, the suite of biophysical mechanisms that optimize photosynthesis while simultaneously providing photoprotection in symbiotic corals in situ.

Estimation of tropical forest height and biomass dynamics using lidar remote sensing at La Selva, Costa Rica

Abstract: [1] In this paper we present the results of an experiment to measure forest structure and biomass dynamics over the tropical forests of La Selva Biological Station in Costa Rica using a medium resolution lidar. Our main objective was to observe changes in forest canopy height, related height metrics, and biomass, and from these map sources and sinks of carbon across the landscape. The Laser Vegetation Imaging Sensor (LVIS) measured canopy structure over La Selva in 1998 and again in 2005. Changes in waveform metrics were related to field-derived changes in estimated aboveground biomass from a series of old growth and secondary forest plots. Pairwise comparisons of nearly coincident lidar footprints between years showed canopy top height changes that coincided with expected changes based on land cover types. Old growth forests had a net loss in height of −0.33 m, while secondary forests had net gain of 2.08 m. Multiple linear regression was used to relate lidar metrics with biomass changes for combined old growth and secondary forest plots, giving an r2 of 0.65 and an RSE of 10.5 Mg/ha, but both parametric and bootstrapped confidence intervals were wide, suggesting weaker model performance. The plot level relationships were then used to map biomass changes across La Selva using LVIS at a 1 ha scale. The spatial patterns of biomass changes matched expected patterns given the distribution of land cover types at La Selva, with secondary forests showing a gain of 25 Mg/ha and old growth forests showing little change (2 Mg/ha). Prediction intervals were calculated to assess uncertainty for each 1 ha cell to ascertain whether the data and methods used could confidently estimate the sign (source or sink) of the biomass changes. The resulting map showed most of the old growth areas as neutral (no net biomass change), with widely scattered and isolated sources and sinks. Secondary forests in contrast were mostly sinks or neutral, but were never sources. By quantifying both the magnitude of biomass changes and the sensitivity of lidar to detect them, this work will help inform the formulation of future space missions focused on biomass dynamics, such as NASA's Deformation Ecosystem Structure and Dynamics of Ice mission.

Coastal Acidification by Rivers: A Threat to Shellfish?

Abstract: Increasing atmospheric CO2 is likely to cause a corresponding increase in oceanic acidity by lowering pH by 0.20.5 pH units by the end of the 21st century [Royal Society, 2005]. In light of increasing acidity, there are growing concerns about the future health of a variety of marine organisms, particularly shellfish, which in the United States is a $1.6 billion industry. Shellfish predominantly inhabit coastal regions, and in addition to the projected stress caused by the global trend in ocean acidification, some coastal ecosystems receive persistent or episodic acid inputs as a result of interactions with river water, bottom sediments, or atmospheric deposition of terrigenous materials. Most river plumes are acidic relative to the receiving ocean, and river water is mixed extensively over the continental shelf. Moreover, the chemical nature and magnitude of discharge are changing rapidly due to climate change and land-use practices.

Determinants of a sustainable competitive advantage due to an IT-enabled strategy

Abstract: Information technology (IT) has been asserted to be a source of sustainable competitive advantage. Empirical evidence has shown that IT can improve a company's performance and competitive position. We examine the factors that are believed to lead to a sustainable competitive advantage due to an IT-enabled strategy, and test these factors empirically. Our findings show that managerial IT skills are positively related to sustainability, and competitor's knowledge of competitive advantage is negatively related to sustainability. There was no support for technical IT skills or IT infrastructure as a source of sustainable competitive advantage.