Hydrogen Bonding between the Q_B Site Ubisemiquinone and Ser-L223 in the Bacterial Reaction Center: A Combined Spectroscopic and Computational Perspective

In the Q_B site of the <i>Rhodobacter sphaeroides</i> photosynthetic reaction center, the donation of a hydrogen bond from the hydroxyl group of Ser-L223 to the ubisemiquinone formed after the first flash is debatable. In this study, we use a combination of spectroscopy and quantum mechanics/molecular mechanics (QM/MM) calculations to comprehensively explore this topic. We show that ENDOR, ESEEM, and HYSCORE spectroscopic differences between mutant L223SA and the wild-type sample (WT) are negligible, indicating only minor perturbations in the ubisemiquinone spin density for the mutant sample. Qualitatively, this suggests that a strong hydrogen bond does not exist in the WT between the Ser-L223 hydroxyl group and the semiquinone O₁ atom, as removal of this hydrogen bond in the mutant should cause a significant redistribution of spin density in the semiquinone. We show quantitatively, using QM/MM calculations, that a WT model in which the Ser-L223 hydroxyl group is rotated to prevent hydrogen bond formation with the O₁ atom of the semiquinone predicts negligible change for the L223SA mutant. This, together with the better agreement between key QM/MM calculated and experimental hyperfine couplings for the non-hydrogen-bonded model, leads us to conclude that no strong hydrogen bond is formed between the Ser-L223 hydroxyl group and the semiquinone O₁ atom after the first flash. The implications of this finding for quinone reduction in photosynthetic reaction centers are discussed

Spatial planning for a green economy: National-level hydrologic ecosystem services priority areas for Gabon

<div><p>Rapidly developing countries contain both the bulk of intact natural areas and biodiversity, and the greatest untapped natural resource stocks, placing them at the forefront of “green” economic development opportunities. However, most lack scientific tools to create development plans that account for biodiversity and ecosystem services, diminishing the real potential to be sustainable. Existing methods focus on biodiversity and carbon priority areas across large geographies (e.g., countries, states/provinces), leaving out essential services associated with water supplies, among others. These hydrologic ecosystem services (HES) are especially absent from methods applied at large geographies and in data-limited contexts. Here, we present a novel, spatially explicit, and relatively simple methodology to identify countrywide HES priority areas. We applied our methodology to the Gabonese Republic, a country undergoing a major economic transformation under a governmental commitment to balance conservation and development goals. We present the first national-scale maps of HES priority areas across Gabon for erosion control, nutrient retention, and groundwater recharge. Priority sub-watersheds covered 44% of the country’s extent. Only 3% of the country was identified as a priority area for all HES simultaneously, highlighting the need to conserve different areas for each different hydrologic service. While spatial tradeoffs occur amongst HES, we identified synergies with two other conservation values, given that 66% of HES priority areas intersect regions of above average area-weighted (by sub-watersheds) total forest carbon stocks and 38% intersect with terrestrial national parks. Considering implications for development, we identified HES priority areas overlapping current or proposed major roads, forestry concessions, and active mining concessions, highlighting the need for proactive planning for avoidance areas and compensatory offsets to mitigate potential conflicts. Collectively, our results provide insight into strategies to protect HES as part of Gabon’s development strategy, while providing a replicable methodology for application to new scales, geographies, and policy contexts.</p></div

Spatial biophysical inputs for hydrologic ecosystem services modeling.

<p>Data sources are described in the main text.</p

The portfolio of combined hydrologic ecosystem services priority areas.

<p>(A) “All population” scenario. (B) “Rural-weighted” scenario. (C) Overlap between these scenarios. For (A) and (B), percentage areas (of the total country area) are reported for each unique combination of the HES objectives. For (C), the percentage area of overlap and separation is reported across the two scenarios.</p

Land use/land cover map for Gabon used in the analysis.

<p>Land use/land cover map for Gabon used in the analysis.</p

Servicesheds for erosion control, nitrogen retention, and phosphorus retention weighted by downstream beneficiary population size.

<p>(A) “All population” serviceshed. (B) “Rural-weighted” serviceshed. Pixel values represent the number of downstream people within each serviceshed that would benefit from a watershed conservation activity on that pixel. Therefore, pixels with the highest values are those with the largest downstream population.</p

Priority areas of sub-watersheds (top 20% by area) for each hydrologic ecosystem service.

<p>(A-C) Erosion control, nitrogen retention, and phosphorous retention for the “all population” scenario. (D-F) Erosion control, nitrogen retention, and phosphorous retention for the “rural-weighted” scenario. (G) Groundwater recharge for the single scenario (i.e., not weighted by population distribution). Grey lines show the boundary of all the sub-watershed polygons.</p

Overlap of hydrologic ecosystem services priority areas with other indicators of conservation value.

<p>Overlap with national parks (shown in black outline) for (A) “all population” and (B) “rural-weighted” scenarios. All other colors represent portfolio sub-watersheds as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0179008#pone.0179008.g005" target="_blank">Fig 5</a>. Overlap with forest carbon stocks below or equal to (orange color) or above (purple color) the average sub-watershed total carbon stock across the country (154 MgC ha^-1) for (C) “all population” and (D) “rural-weighted” scenarios.</p

Presentation1_Balancing renewable energy and river resources by moving from individual assessments of hydropower projects to energy system planning.pdf

As governments and non-state actors strive to minimize global warming, a primary strategy is the decarbonization of power systems which will require a massive increase in renewable electricity generation. Leading energy agencies forecast a doubling of global hydropower capacity as part of that necessary expansion of renewables. While hydropower provides generally low-carbon generation and can integrate variable renewables, such as wind and solar, into electrical grids, hydropower dams are one of the primary reasons that only one-third of the world’s major rivers remain free-flowing. This loss of free-flowing rivers has contributed to dramatic declines of migratory fish and sediment delivery to agriculturally productive deltas. Further, the reservoirs behind dams have displaced tens of millions of people. Thus, hydropower challenges the world’s efforts to meet climate targets while simultaneously achieving other Sustainable Development Goals. In this paper, we explore strategies to achieve the needed renewable energy expansion while sustaining the diverse social and environmental benefits of rivers. These strategies can be implemented at scales ranging from the individual project (environmental flows, fish passage and other site-level mitigation) to hydropower cascades to river basins and regional electrical power systems. While we review evidence that project-level management and mitigation can reduce environmental and social costs, we posit that the most effective scale for finding balanced solutions occurs at the scale of power systems. We further hypothesize that the pursuit of solutions at the system scale can also provide benefits for investors, developers and governments; evidence of benefits to these actors will be necessary for achieving broad uptake of the approaches described in this paper. We test this hypothesis through cases from Chile and Uganda that demonstrate the potential for system-scale power planning to allow countries to meet low-carbon energy targets with power systems that avoid damming high priority rivers (e.g., those that would cause conflicts with other social and environmental benefits) for a similar system cost as status quo approaches. We also show that, through reduction of risk and potential conflict, strategic planning of hydropower site selection can improve financial performance for investors and developers, with a case study from Colombia.</p

DataSheet1_Balancing renewable energy and river resources by moving from individual assessments of hydropower projects to energy system planning.docx

As governments and non-state actors strive to minimize global warming, a primary strategy is the decarbonization of power systems which will require a massive increase in renewable electricity generation. Leading energy agencies forecast a doubling of global hydropower capacity as part of that necessary expansion of renewables. While hydropower provides generally low-carbon generation and can integrate variable renewables, such as wind and solar, into electrical grids, hydropower dams are one of the primary reasons that only one-third of the world’s major rivers remain free-flowing. This loss of free-flowing rivers has contributed to dramatic declines of migratory fish and sediment delivery to agriculturally productive deltas. Further, the reservoirs behind dams have displaced tens of millions of people. Thus, hydropower challenges the world’s efforts to meet climate targets while simultaneously achieving other Sustainable Development Goals. In this paper, we explore strategies to achieve the needed renewable energy expansion while sustaining the diverse social and environmental benefits of rivers. These strategies can be implemented at scales ranging from the individual project (environmental flows, fish passage and other site-level mitigation) to hydropower cascades to river basins and regional electrical power systems. While we review evidence that project-level management and mitigation can reduce environmental and social costs, we posit that the most effective scale for finding balanced solutions occurs at the scale of power systems. We further hypothesize that the pursuit of solutions at the system scale can also provide benefits for investors, developers and governments; evidence of benefits to these actors will be necessary for achieving broad uptake of the approaches described in this paper. We test this hypothesis through cases from Chile and Uganda that demonstrate the potential for system-scale power planning to allow countries to meet low-carbon energy targets with power systems that avoid damming high priority rivers (e.g., those that would cause conflicts with other social and environmental benefits) for a similar system cost as status quo approaches. We also show that, through reduction of risk and potential conflict, strategic planning of hydropower site selection can improve financial performance for investors and developers, with a case study from Colombia.</p