Benefit to N<Subscript>2</Subscript>-fixing alder of extending growth period at the cost of leaf nitrogen loss without resorption

This study examines the adaptive role of not resorbing N in N₂-fixing deciduous trees in terms of their energy balance. The autumnal growth of N₂-fixing Alnus firma Sieb. et Zucc. (alder) was compared with that of the non-N₂-fixing Morus bombycis Koizumi (mulberry), which resorbs leaf N. The freezing resistance of leaves of both species was –2°C. Mulberry seedlings lost their photosynthetic ability in mid-October, although the minimum temperature was still above 0°C. Thereafter, their leaves turned yellow and were gradually shed. In contrast, seedlings of the alder maintained their photosynthetic ability until mid-November, when the minimum temperature fell to the freezing resistance limit. Thereafter, their leaves were shed quickly without an autumn tint. The mulberry resorbed 48.9% of leaf N, whereas the alder resorbed hardly any. These results show that, compared with the mulberry tree, the alder extended its growth period for 1 month in return for losing leaf N without resorption. The amount of energy assimilated by the alder in the extended growth period was about six times that required for compensating for the nitrogen loss, if the compensation is dependent only on the tree's own nitrogen fixation. This surplus energy balance has probably allowed N₂-fixing deciduous trees to evolve their non-N-resorbing trait.     

Energy Intensities and Carbon Dioxide Emissions in a Social Accounting Matrix Model of the Andalusian Economy

The aim of this article is to calculate energy intensity and carbon dioxide (CO₂) emissions in Andalusia, the largest and most populated region of Spain. Energy intensities for five energy commodities used in production activities are calculated using a social accounting matrix (SAM) model with three alternative scenarios, each utilizing differing closure rules. More interestingly, by using 2005 data and updating the values of exogenous accounts, the article also provides estimates of CO₂ emissions ten years out from the 1995 base year. Finally, counterfactual experiments are performed to quantify the overall reduction in direct energy coefficients that would have made it possible to maintain constant production‐sector emissions from 1995 to 2005. The results indicate that there is a strong interdependence among energy sectors and the most intensive energy users; they also indicate the importance of induced effects when factor accounts and private consumption are endogenous. The estimates obtained concerning CO₂ emissions are close to official estimates, both from 1995 and 2005. The counterfactual experiments indicate that a 26.5% cut in the size of direct energy requirements would have made it possible to maintain constant emissions. They also indicate that efforts to curtail emissions should be focused on improving efficiency in coal extraction and combustion and oil refining.     

A hybrid material flow analysis for quantifying multilevel anthropogenic resources

This study develops a hybrid material flow analysis (HMFA) method to evaluate the annual additional quantity of material stock, known as net additions to stock (NAS) at both micro‐ and macro‐levels through analyzing the fixed capital formation (FCF) and total supply in input‐output tables (IOTs). HMFA turns NAS from a balance indicator in the top‐down approach to an indicator with meaningful value in terms of urban ore evaluation. To verify the validity of HMFA, this study compares the developed HMFA with a top‐down approach and a bottom‐up approach through assessing the NAS of Taiwan and Germany. The quantity of NAS estimated by HMFA is considered as a more conservative upper bound than that by the top‐down approach, while underestimation often occurs with a bottom‐up approach. HMFA has been proven as an efficient and rational evaluation method which overcomes a key limitation in assessing micro‐level material stock by a top‐down approach, and solves the data demanding problem of the bottom‐up approach for quantifying material stock.     

A Review and Typology of Circular Economy Business Model Patterns

The circular economy (CE) requires companies to rethink their supply chains and business models. Several frameworks found in the academic and practitioner literature propose circular economy business models (CEBMs) to redefine how companies create value while adhering to CE principles. A review of these frameworks shows that some models are frequently discussed, some are framework specific, and some use a different wording to refer to similar CEBMs, pointing to the need to consolidate the current state of the art. We conduct a morphological analysis of 26 current CEBMs from the literature, which includes defining their major business model dimensions and identifying the specific characteristics of these dimensions. Based on this analysis, we identify a broad range of business model design options and propose six major CEBM patterns with the potential to support the closing of resource flows: repair and maintenance; reuse and redistribution; refurbishment and remanufacturing; recycling; cascading and repurposing; and organic feedstock business model patterns. We also discuss different design strategies to support the development of these CEBMs.     

Nitrogen and phosphorus economy of the riparian shrub <Emphasis Type="Italic">Salix gracilistyla</Emphasis> in western Japan

Salix gracilistyla is one of the dominant plants in the riparian vegetation of the upper-middle reaches of rivers in western Japan. This species colonizes mainly sandy habitats, where soil nutrient levels are low, but shows high potential for production. We hypothesized that S.␣gracilistyla uses nutrients conservatively within stands, showing a high resorption efficiency during leaf senescence. To test this hypothesis, we examined seasonal changes in nitrogen (N) and phosphorus (P) concentrations in aboveground organs of S. gracilistyla stands on a fluvial bar in the Ohtagawa River, western Japan. The concentrations in leaves decreased from April to May as leaves expanded. Thereafter, the concentrations showed little fluctuation until September. They declined considerably in autumn, possibly owing to nutrient resorption. We converted the nutrient concentrations in each organ to nutrient amounts per stand area on the basis of the biomass of each organ. The resorption efficiency of N and P in leaves during senescence were estimated to be 44 and 46%, respectively. Annual net increments of N and P in aboveground organs, calculated by adding the amounts in inflorescences and leaf litter to the annual increments in perennial organs, were estimated to be 9.9 g and 0.83 g m⁻² year⁻¹, respectively. The amounts released in leaf litter were 6.7 g N and 0.44 g P m⁻². These values are comparable to or larger than those of other deciduous trees. We conclude that S. gracilistyla stands acquire large amounts of nutrients and release a large proportion in leaf litter.     

Ecological accounting for an integrated “pig–biogas–fish” system based on emergetic indicators

With the expansion of urbanization in China, the integrated biogas-utilization system has gained its popularity for both renewable energy production and multi-level utilization of organic waste. To appraise the ecological performance of the integrated biogas system, systematic accounting is undertaken for an integrated “pig–biogas–fish” system in Hubei province, China. Based on Odum's concept of embodied solar energy as a unified measure for environmental resources, human labors and purchased goods, a set of emergetic indicators are employed to quantify the system sustainability. The results reveal that in a 20-year designed lifetime scenario, 94.69% of the total emergy inputs for the “pig–biogas–fish” system are attributed to purchased social resources. Three kinds of products, namely pig, biogas, fish are taken into consideration, and transformity of the “pig–biogas–fish” system is calculated as 1.26E + 05 seJ/J. Compared with the Chinese conventional agriculture system, the integrated biogas system shows a higher sustainability. Given that most biogas systems have a lifespan less than 20 years, for the “pig–biogas–fish” system, six other scenarios with different lifespans are studied to investigate the impact of the lifespan on sustainability. The findings suggest that the “pig–biogas–fish” system should be well operated for at least 8 years to prove its advantage in ecological economy over the conventional agriculture system. This has essential policy implications that local government should strengthen subsequent management on biogas production to extend the practical service life of the biogas system.     

Modelling carbon stocks and fluxes in the wood product sector: a comparative review

In addition to forest ecosystems, wood products are carbon pools that can be strategically managed to mitigate climate change. Wood product models (WPMs) simulating the carbon balance of wood production, use and end of life can complement forest growth models to evaluate the mitigation potential of the forest sector as a whole. WPMs can be used to compare scenarios of product use and explore mitigation strategies. A considerable number of WPMs have been developed in the last three decades, but there is no review available analysing their functionality and performance. This study analyses and compares 41 WPMs. One surprising initial result was that we discovered the erroneous implementation of a few concepts and assumptions in some of the models. We further described and compared the models using six model characteristics (bucking allocation, industrial processes, carbon pools, product removal, recycling and substitution effects) and three model‐use characteristics (system boundaries, model initialization and evaluation of results). Using a set of indicators based on the model characteristics, we classified models using a hierarchical clustering technique and differentiated them according to their increasing degrees of complexity and varying levels of user support. For purposes of simulating carbon stock in wood products, models with a simple structure may be sufficient, but to compare climate change mitigation options, complex models are needed. The number of models has increased substantially over the last ten years, introducing more diversity and accuracy. Calculation of substitution effects and recycling has also become more prominent. However, the lack of data is still an important constraint for a more realistic estimation of carbon stocks and fluxes. Therefore, if the sector wants to demonstrate the environmental quality of its products, it should make it a priority to provide reliable life cycle inventory data, particularly regarding aspects of time and location.     

循环经济——可持续的经济发展模式

循环经济是经济效益与环境效益有机结合的一种新的经济发展模式,将经济发展推向循环经济的轨道是保证可持续发展的重要举措。循环经济具有深刻的经济学基础和生态学基础,发展循环经济具有重要的现实意义,它是生态社会最适宜的经济发展模式,世界发达国家已在发展循环经济领域取得了较大成就。本文从循环经济的基础理论入手,阐述了我国发展循环经济的现状、重要意义和所面临的问题,提出我国发展循环经济的对策,并指出循环经济是中国21世纪经济可持续发展模式的必然选择。     

湖南主要经济蛇类养殖场的设计与建造调查研究

目的研究出一种适合湖南地域理想的科学经济蛇类人工养殖场。方法采用调查研究法、试验法、归纳总结法等研究方法。结果总结出湖南省经济蛇类养殖场主要有蛇房、露天蛇场、室内外结合蛇场等3种模式,首创了“湖南立体蛇场”模式。结论在湖南省境内采用“湖南立体蛇场”模式进行经济蛇类的养殖效果较好,不仅简单易建、经济合算,而且科学合理、实用方便,达到了预期的目的。     

A paradox of leaf-trait convergence: why is leaf nitrogen concentration higher in species with higher photosynthetic capacity?

It is well known that leaf photosynthesis per unit dry mass (A_mass) is positively correlated with nitrogen concentration (N_mass) across naturally growing plants. In this article we show that this relationship is paradoxical because, if other traits are identical among species, plants with a higher A_mass should have a lower N_mass, because of dilution by the assimilated carbon. To find a factor to overcome the dilution effect, we analyze the N_mass–A_mass relationship using simple mathematical models and literature data. We propose two equations derived from plant-growth models. Model prediction is compared with the data set of leaf trait spectrum obtained on a global scale. The model predicts that plants with a higher A_mass should have a higher specific nitrogen absorption rate in roots (SAR), less biomass allocation to leaves, and/or greater nitrogen allocation to leaves. From the literature survey, SAR is suggested as the most likely factor. If SAR is the sole factor maintaining the positive relationship between N_mass and A_mass, the variation in SAR is predicted to be much greater than that in A_mass; given that A_mass varies 130-fold, SAR may vary more than 2000-fold. We predict that there is coordination between leaf and root activities among species on a global scale. Kouki Hikosaka is the recipient of the BSJ Award for Young Scientist, 2006.