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Abstract: An emergy-based comparison analysis is conducted for three typical mega cities in China, i.e., Beijing, Shanghai and Guangzhou, from 1990 to 2005 in four perspectives including emergy intensity, resource structure, environmental pressure and resource use efficiency. A new index of non-renewable emergy/money ratio is established to indicate the utilization efficiency of the non-renewable resources. The results show that for the three mega urban systems, Beijing, Shanghai and Guangzhou, the total emergy inputs were 3.76E+23, 3.54E+23, 2.52E+23sej in 2005, of which 64.88%, 91.45% and 72.28% were imported from the outsides, respectively. As to the indicators of emergy intensity involving the total emergy use, emergy density and emergy use per cap, three cities exhibited similar overall increase trends with annual fluctuations from 1990 to 2005. Shanghai achieved the highest level of economic development and non-renewable resource use efficiency, and meanwhile, lower proportion of renewable resource use and higher environmental pressure compared to those of Beijing and Guangzhou. Guangzhou has long term sustainability considering an amount of local renewable resources used, per capita emergy used, energy consumption per unit GDP and the ratio of waste to renewable emergy. It can be concluded that different emergy-based evaluation results arise from different geographical locations, resources endowments, industrial structures and urban orientations of the concerned mega cities. [Copyright &y& Elsevier]

Shading a greenhouse may have a time-dependent effect on fruit production and water and nutrient uptake in tomato plants (Solanum lycopersicum L.) as a result of acclimation to light and a dependence on stored carbohydrate and nutrients. In 2 years in the northeastern United States, shadecloth was applied at the start of warm weather in June and the houses were shaded until late August. Simultaneous comparisons were made among greenhouse sections that were either not shaded or covered with reflective aluminized shadecloth that blocked 0.15, 0.30, or 0.50 of direct sunlight. The amounts of water, nitrogen, and potassium taken up per day were calculated for successive 3-week intervals after shade was applied. The effect of shade on these uptake rates was compared with the effect on the rate of fruit production. There was a linear decline in water, nitrogen, and potassium uptake with increasing shade density. In each 3-week interval, water uptake under 0.5 shade density was 25% and 20% less than under no shade in 2004 and 2005, respectively. The uptake of nitrogen and potassium uptake under 0.5 shade density was ≈25% less than that under no shade. Shading did not affect the rate of fruit production within 3 weeks of application, but after more than 6 weeks, it was 30% less under 0.5 shade density than under no shade. The use efficiencies of radiation, water, and nutrients for fruit production increased with shade density immediately after shade were applied. These effects of shade on apparent resource use efficiencies dissipated from 3 to 6 weeks after shade was applied, because the effect of shade density on fruit production became proportionally the same as the effects on water and nutrient uptake. The water and nutrient uptake of greenhouse tomato acclimated to the change in irradiance resulting from shade within 3 weeks, but the full effect of shade on fruit production was not seen until 6 weeks after the application of shade. [ABSTRACT FROM AUTHOR]