The Aquatic Species Program was a relatively small research effort intended to look at the use of aquatic plants as sources of energy. Its history dates back to 1978, but much of the research from 1978 to 1982 focused on using algae to produce hydrogen. The program switched emphasis to other transportation fuels, particularly biodiesel, beginning in the early 1980's. This report summarizes the research activities carried out from 1980 to 1996, with an emphasis on algae for biodiesel production.

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Look Back at the U.S. Department of Energy's Aquatic Species Program: Biodiesel from Algae; Close-Out Report

The structure of the light-harvesting chlorophyll a/b-protein complex, an integral membrane protein, has been determined at 3.4 A resolution by electron crystallography of two-dimensional crystals. Two of the three membrane-spanning alpha-helices are held together by ion pairs formed by charged residues that also serve as chlorophyll ligands. In the centre of the complex, chlorophyll a is in close contact with chlorophyll b for rapid energy transfer, and with two carotenoids that prevent the formation of toxic singlet oxygen.

Atomic model of plant light-harvesting complex by electron crystallography

Whole-plant energy capture depends not only on the photosynthetic response of individual leaves, but also on their integration into an effective canopy, and on the costs of producing and maintaining their photosynthetic capacity. This paper explores adaptation to irradiance level in this context, focusing on traits whose significance would be elusive if considered in terms of their impact at the leaf level alone. I review traditional approaches used to demonstrate or suggest adaptation to irradiance level, and outline three energetic tradeoffs likely to shape such adaptation, involving the economics of gas exchange, support, and biotic interactions. Recent models using these tradeoffs to account for trends in leaf nitrogen content, stornatal conductance, phyllotaxis, and defensive allocations in sun v. shade are evaluated. A re-evaluation of the classic study of acclimation of the photosynthetic light response in Atriplex, crucial to interpreting adaptation to irradiance in many traits, shows that it does not completely support the central dogma of adaptation to sun v. shade unless the results are analysed in terms of whole-plant energy capture. Calculations for Liriodendron show that the traditional light compensation point has little meaning for net carbon gain, and that the effective compensation point is profoundly influenced by the costs of night leaf respiration, leaf construction, and the construction of associated support and root tissue. The costs of support tissue are especially important, raising the effective compensation point by 140 pmol m- s - ' in trees 1 m tall, and by nearly 1350 pmol m - s - ' in trees 30 m tall. Effective compensation points give maximum tree heights as a function of irradiance, and shade tolerance as a function of tree height; calculations of maximum permissible height in Liriodendron correspond roughly with the height of the tallest known individual. Finally, new models for the evolution of canopy width/height ratio in response to irradiance and coverage within a tree stratum, and for the evolution of mottled leaves as a defensive measure in understory herbs, are outlined.

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Adaptation to Sun and Shade: a Whole-Plant Perspective

Ecosystem management is management driven by explicit goals, executed by policies, protocols, and practices, and made adaptable by monitoring and research based on our best understanding of the ecological interactions and processes necessary to sustain ecosystem composition, structure, and function. In recent years, sustainability has become an explicitly stated, even legislatively mandated, goal of natural resource management agencies. In practice, however, management approaches have often focused on maximizing short-term yield and economic gain rather than long-term sustainability. Several obstacles contribute to this disparity, including: (1) inadequate information on the biological diversity of environments; (2) widespread ignorance of the function and dynamics of ecosystems; (3) the openness and interconnectedness of ecosystems on scales that transcend management boundaries; (4) a prevailing public perception that the immediate economic and social value of supposedly renewable resources outweighs the risk of future ecosystem damage or the benefits of alternative management approaches. The goal of ecosystem management is to overcome these obstacles. Ecosystem management includes the following elements: (1) Sustainability. Ecosystem management does not focus primarily on deliverables" but rather regards intergenerational sustainability as a precondition. (2) Goals. Ecosystem management establishes measurable goals that specify future processes and outcomes necessary for sustainability. (3) Sound ecological models and understanding. Ecosystem management relies on research performed at all levels of ecological organization. (4) Complexity and connectedness. Ecosystem management recognizes that biological diversity and structural complexity strengthen ecosystems against disturbance and supply the genetic resources necessary to adapt to long-term change. (5) The dynamic character of ecosystems. Recognizing that change and evolution are inherent in ecosystem sustainability, ecosystem management avoids attempts to freeze" ecosystems in a particular state or configuration. (6) Context and scale. Ecosystem processes operate over a wide range of spatial and temporal scales, and their behavior at any given location is greatly affected by surrounding systems. Thus, there is no single appropriate scale or time frame for management. (7) Humans as ecosystem components. Ecosystem management values the active role of humans in achieving sustainable management goals. (8) Adaptability and accountability. Ecosystem management acknowledges that current knowledge and paradigms of ecosystem function are provisional, incomplete, and subject to change. Management approaches must be viewed as hypotheses to be tested by research and monitoring programs. The following are fundamental scientific precepts for ecosystem management. (1) Spatial and temporal scale are critical. Ecosystem function includes inputs, outputs, cycling of materials and energy, and the interactions of organisms. Boundaries defined for the study or management of one process are often inappropriate for the study of others; thus, ecosystem management requires a broad view. (2) Ecosystem function depends on its structure, diversity, and integrity. Ecosystem management seeks to maintain biological diversity as a critical component in strengthening ecosystems against disturbance. Thus, management of biological diversity requires a broad perspective and recognition that the complexity and function of any particular location is influenced heavily by the surrounding system. (3) Ecosystems are dynamic in space and time. Ecosystem management is challenging in part because ecosystems are constantly changing. Over time scales of decades or centuries, many landscapes are altered by natural disturbances that lead to mosaics of successional patches of different ages. Such patch dynamics are critical to ecosystem structure and function. (4) Uncertainty, surprise, and limits to knowledge. Ecosystem management acknowledges that, given sufficient time and space, unlikely events are certain to occur. Adaptive management addresses this uncertainty by combining democratic principles, scientific analysis, education, and institutional learning to increase our understanding of ecosystem processes and the consequences of management interventions, and to improve the quality of data upon which decisions must be made. Ecosystem management requires application of ecological science to natural resource actions. Moving from concepts to practice is a daunting challenge and will require the following steps and actions. (1) Defining sustainable goals and objectives. Sustainable strategies for the provision of ecosystem goods and services cannot take as their starting points statements of need or want such as mandated timber supply, water demand, or arbitrarily set harvests of shrimp or fish. Rather, sustainability must be the primary objective, and levels of commodity and amenity provision must be adjusted to meet that goal. (2) Reconciling spatial scales. Implementation of ecosystem management would be greatly simplified if management jurisdictions were spatially congruent with the behavior of ecosystem processes. Given the variation in spatial domain among processes, one perfect fit for all processes is virtually impossible; rather, ecosystem management must seek consensus among the various stakeholders within each ecosystem. (3) Reconciling temporal scales. Whereas management agencies are often forced to make decisions on a fiscal-year basis, ecosystem management must deal with time scales that transcend human lifetimes. Ecosystem management requires long-term planning and commitment. (4) Making the system adaptable and accountable. Successful ecosystem management requires institutions that are adaptable to changes in ecosystem characteristics and in our knowledge base. Adaptive management by definition requires the scientist's ongoing interaction with managers and the public. Communication must flow in both directions, and scientists must be willing to prioritize their research with regard to critical management needs. Scientists have much to offer in the development of monitoring programs, particularly in creating sampling approaches, statistical analyses, and scientific models. As our knowledge base evolves, scientists must develop new mechanisms to communicate research and management results. More professionals with an understanding of scientific, management, and social issues, and the ability to communicate with scientists, managers, and the public are needed. Ecosystem management is not a rejection of an anthropocentric for a totally biocentric worldview. Rather it is management that acknowledges the importance of human needs while at the same time confronting the reality that the capacity of our world to meet those needs in perpetuity has limits and depends on the functioning of ecosystems.

The Report of the Ecological Society of America Committee on the Scientific Basis for Ecosystem Management

Growth of autotrophic plants is directly and dramatically influenced by the intensity of light — the driving force of photosynthesis — which provides nearly all of the carbon and chemical energy needed for plant growth. Moreover, light intensity (quantum flux density) is perhaps the most conspicuous environmental variable with which plants must cope. Contrasting terrestrial habitats may differ by at least two orders of magnitude in the daily quantum flux available for photosynthesis. In any habitat the quantum flux density varies seasonally, diurnally, and spatially (such as within a canopy of a given plant stand).

Responses to Different Quantum Flux Densities

Photosynthesis, biomass and growth characteristics of the temperate seagrass, Zostera marina L. (eelgrass), were examined in a meadow in Great Harbor, Woods Hole, Massachusetts during June and August, 1982. Underwater lamps and light shading screens were placed at shallow (1.3 m) and deep (5.5 m) stations to lengthen and shorten daily light periods. The portion of the day (H,,,) that light intensities saturated Z. marina photosynthesis was lengthened by 4 to 6 h and shortened by 3 to 5 h. Photosynthesis vs irradiance relations, leaf chlorophyll content, photosynthetic unit size and density, shoot size, specific leaf area, leaf biomass, and production rates were determined at the end of 30 d experiments. Cellular photosynthetic adjustment (photosynthesis vs irradiance relationships, chlorophyll and photosynthetic unit characteristics) to the H,,, manipulations occurred only in June, however biomass and growth adjustments occurred both in June and August. Photosynthesis and respiration rates, and H,,, regimes, were used to calculate daily leaf carbon balances. Daily carbon balance was an accurate predictor of plant survival. Plant responses to manipulations indicate that growth is light limited for eelgrass growing near the deep edge of the meadow, and that these plants appear to be living near the minimum light regime for growth and survival (H,,, = 6 to 8 h) . Maximum depth distribution of this species appears to be controlled principally by daily light periods.

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Role of daily light period in the depth distribution of Zostera marina (eelgrass)

Photosynthetic responses of the temperate seagrass, Zostera marina L., were examined by manipulations of photon flux density in an eelgrass bed in Great Harbor, Woods Hole, MA during August 1981. Sun reflectors and light shading screens were placed at shallow (1.3 m) and deep (5.5 m) stations in the eelgrass bed to increase (+35% to +40%) and decrease (-55%) ambient photon flux densities. The portion of the day that light intensities exceeding the light compensation point for Z. marina (H
comp) and the light saturation point (H
sat) were determined to assess the impact of the reflectors and shades. The H
comp and H
sat periods at the deep station shading screen were most strongly affected; H
comp was reduced by 11% and H
sat was reduced by 52%. Light-saturated photosynthetic rates, dark respiration rates, leaf chlorophyll content, chlorophyll a/b, PSUO
2 size, PSU density, leaf area, specific leaf area, leaf turnover times and leaf production rates were determined at the end of three sets of 1- to 2-week experiments. None of the measured parameters were affected by the photon flux density manipulations at the shallow station; however, at the deep station leaf production rates were significantly reduced under the shading screen and chlorophyll a/b ratios were higher at the reflector. These results indicate that adjustment to short-term changes in light regime in Z. marina is largely by leaf production rates. Further, the most dramatic changes in the periods of compensating or saturating photon flux densities had the greatest impact on the measured photosynthetic responses.

Photosynthetic responses of Zostera marina L. (Eelgrass) to in situ manipulations of light intensity

Effects of temperature on photosynthesis and respiration in eelgrass (Zostera marina L.)

A number of species of macroalagae possess a flat, strap-like blade morphology in habitats exposed to rapidly-moving water whereas those at protected sites have a wider, undulate blade shape. We have explored the functional consequences of flat, narrow vs. wide, undulate blade morphologies in the giant bull kelpNereocystis luetkeana. Our study focused on the behavior of blades in ambient water currents and the consequences of that behavior to breakage and to photosynthesis. In flowing water, the narrow, flat blades flap with lower amplitude and collapse together into a more streamlined bundle than do wide, undulate blades, and hence experience lower drag per blade area at a given flow velocity. If the algae at current-swept sites had ruffled blades, drag forces would sometimes be sufficient to break the stipes. However, flat blades in a streamlined bundle experience more self-shading than do undulate blades, which remain spread out in water currents. Thus, there is a morphological trade-off between reducing drag and reducing self-shading. Photosynthetic14C-HCO3 uptake rates decrease in slow flow when the boundary layer along the blade surface across which diffusion takes place is relatively thick. However, blade flapping, which stirs water near the blade surface, enhances carbon uptake rates in slow water currents for both the undulate and the flat morphologies.

Randall S. Alberte

Papers

Role of daily light period in the depth distribution of Zostera marina (eelgrass)

Photosynthetic responses of Zostera marina L. (Eelgrass) to in situ manipulations of light intensity

Effects of temperature on photosynthesis and respiration in eelgrass (Zostera marina L.)

Flow, flapping, and photosynthesis ofNereocystis leutkeana: a functional comparison of undulate and flat blade morphologies

Photoadaptation and growth of Zostera marina L. (eelgrass) transplants along a depth gradient