THIS paper is concerned with those actions of business firms which have harmful effects on others. The standard example is that of a factory the smoke from which has harmful effects on those occupying neighbouring properties. The economic analysis of such a situation has usually proceeded in terms of a divergence between the private and social product of the far' ory, in which economists have largely followed the treatment of Pigou in The Economics of Welfare. The conclusions to which this kind of analyris seems to have led most economists is that it would be desirable to make the owner of the factory liable for the damage caused to those injured by the smoke, or alternatively, to place a tax on the factory owner varying with the amount of smoke produced and equivalent in money terms to the damage it would cause, or finally, to exclude the factory from residential districts (and presumably from other

闡釋《社會成本問題》[The Problem of Social Cost]

Redesigning agrosystems to include more ecological regulations can help feed a growing human population, preserve soils for future productivity, limit dependency on synthetic fertilizers, and reduce agriculture contribution to global changes such as eutrophication and warming. However, guidelines for redesigning cropping systems from natural systems to make them more sustainable remain limited. Synthetizing the knowledge on biogeochemical cycles in natural ecosystems, we outline four ecological systems that synchronize the supply of soluble nutrients by soil biota with the fluctuating nutrient demand of plants. This synchrony limits deficiencies and excesses of soluble nutrients, which usually penalize both production and regulating services of agrosystems such as nutrient retention and soil carbon storage. In the ecological systems outlined, synchrony emerges from plant–soil and plant–plant interactions, eco‐physiological processes, soil physicochemical processes, and the dynamics of various nutrient reservoirs, including soil organic matter, soil minerals, atmosphere, and a common market. We discuss the relative importance of these ecological systems in regulating nutrient cycles depending on the pedoclimatic context and on the functional diversity of plants and microbes. We offer ideas about how these systems could be stimulated within agrosystems to improve their sustainability. A review of the latest advances in agronomy shows that some of the practices suggested to promote synchrony (e.g., reduced tillage, rotation with perennial plant cover, crop diversification) have already been tested and shown to be effective in reducing nutrient losses, fertilizer use, and N2O emissions and/or improving biomass production and soil carbon storage. Our framework also highlights new management strategies and defines the conditions for the success of these nature‐based practices allowing for site‐specific modifications. This new synthetized knowledge should help practitioners to improve the long‐term productivity of agrosystems while reducing the negative impact of agriculture on the environment and the climate.

Plant–soil synchrony in nutrient cycles: Learning from ecosystems to design sustainable agrosystems

Ulvan, extracted from the marine green algae belonging to the genus Ulva, is mainly composed of four monosaccharides consisting of rhamnose, xylose, glucuronic acid and iduronic acid. It has great potential in the fields of food, pharmaceuticals and chemistry. It can be degraded by ulvan lyase with a β-elimination mechanism, which cleaves the β-glycosidic bond between sulfated rhamnose and glucuronic acid/iduronic acid, thereby producing an Ulva oligosaccharide with unsaturated bond. These oligosaccharides have several pleasing functions, including antioxidant, antiviral, antilipidic, antibacterial, and other effects. The latest CAZy data shows that ulvan lyases are composed of four families of lyases: PL24, PL25, PL28, and PL40. The structural features of some enzymes have been fully demonstrated, which is highly helpful in understanding their catalytic mechanisms. This review summarizes key sources, classifications, and key research advances in the biochemical properties of enzymes. In addition, its structural features and catalytic mechanism have been organized. Finally, we briefly summarized the potential of various active functional oligosaccharides produced by degrading ulvan in future applications. This detailed information can give us a better understanding of ulvan.

Ulvan polysaccharide-degrading enzymes: An updated and comprehensive review of sources category, property, structure, and applications of ulvan lyases

Ulvan lyase, specifically depolymerizing ulvan to unsaturated sulfated oligosaccharides with diverse biological activities, is becoming more and more popular. To provide an economical fermentative strategy, Catenovulum sp. LP cultured in low-cost medium that directly used Ulva prolifera as the main carbon source was used to produce ulvan lyase. The fermentation conditions were established in a shake flask containing 5% (w/v) U. prolifera powder, 0.2% K2HPO4, 0.4% NH4Cl, 0.5% NaCl, and 0.05% MgSO4. In a 5-L fermentor, series of strategies were used to systematically discuss the fermentation process. The enzyme with the best activity was obtained by the condition of a two-stage temperature (28–32 °C), initial pH 7.0, 1.5 vvm and two-stage agitation (200–400 rpm). The fermentation kinetic model of substrate consumption indicated that a shorter culture time may improve the ulvan lyase activity. Moreover, 10.09% improvement in enzyme activity was observed in a 30-L fermentor by shortening the fermentation time to 20 h. This fermentation method offers a promising prospect to enlarge the production of ulvan lyase and also provides a potential possibility to mildly prepare bioactive unsaturated oligosaccharides.

Efficient production of ulvan lyase from Ulva prolifera by Catenovulum sp. LP based on stage-controlled fermentation strategy

Extraction and identification of toxic organic substances from decaying green alga Ulva prolifera.

Economic assessment and environmental management of green tides in the Chinese Yellow Sea

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Economic assessment and environmental management of green tides in the Chinese Yellow Sea