Resource Supply Conditions Research Articles

Assessment of Sustainable Supply Capability of Chinese Tin Resources Based on the Entropy Weight-TOPSIS Model

This study focuses on the issue of supply security in Chinese tin resources, conducting a comprehensive analysis encompassing supply security, demand conditions, market risk, and geopolitical stability. The study employs the AHP-Entropy Weight method to calculate the comprehensive weights of various indicators, revealing the sustainable supply capability of the resources and the challenges they confront. The research unveils that the domestic supply potential and the international commercial extraction environment are pivotal influences on the sustainable supply capability of tin resources. Firstly, since 2010, China has started to import net tin ores and concentrates, leading to a substantial increase in external dependency. However, China’s tin resource reserves have gradually decreased, posing challenges to the stability of the tin resource supply. Secondly, the stability of supply countries and the security of import channels critically affect the stability of the tin resource supply chain. A comprehensive analysis of the outcomes indicates a consistent decline in China’s sustainable tin resource supply capability since 2010, primarily due to the deterioration of resource supply conditions, growth in demand, and the escalation of geopolitical risks. Thus, the evolving foreign extraction environment, domestic resource supply potential, and the alteration in the global tin resource extraction landscape require significant attention.

Stoichiometric homeostasis in response to variable water and nutrient supply in a Robinia pseudoacacia plant–soil system

Abstract All organisms need elements in fixed proportions for carrying out normal metabolic processes and how flexible they are depends on how effective they are utilizing these resources from external sources. It is important to understand the interactions among plant, soil and microbial biomass carbon (C), nitrogen (N) and phosphorus (P) stoichiometry under different conditions of resource supply. We conducted a pot experiment on 1-year-old Robinia pseudoacacia seedlings for nearly 5 months under different water, nitrogen and phosphorus supplies, and we determined plant, soil and microbial biomass C, N and P stoichiometry. We found that plant, soil and microbial nutrients and stoichiometry exhibited a certain degree of plasticity in response to the changes in water and nutrient conditions in their environments. Variation partitioning analysis showed that root stoichiometry accounted for a large part of the variance in microbial stoichiometry. Structural equation modeling further revealed that root stoichiometry and leaf stoichiometry were two direct factors affecting microbial biomass C:N and C:P, and that root stoichiometry had the greatest direct effect. In addition, the degree of homeostasis for microbial biomass C and C:P was more sensitive to changes in soil nutrients than changes in other factors, and other elements and elemental ratios displayed strict homeostasis. These results highlight the importance of studying microbial stoichiometry in improving our understanding of nutrient cycling of the plant–soil system under different water and nutrient supply.

A Mechanistic Model of Macromolecular Allocation, Elemental Stoichiometry, and Growth Rate in Phytoplankton.

We present a model of the growth rate and elemental stoichiometry of phytoplankton as a function of resource allocation between and within broad macromolecular pools under a variety of resource supply conditions. The model is based on four, empirically-supported, cornerstone assumptions: that there is a saturating relationship between light and photosynthesis, a linear relationship between RNA/protein and growth rate, a linear relationship between biosynthetic proteins and growth rate, and a constant macromolecular composition of the light-harvesting machinery. We combine these assumptions with statements of conservation of carbon, nitrogen, phosphorus, and energy. The model can be solved algebraically for steady state conditions and constrained with data on elemental stoichiometry from published laboratory chemostat studies. It interprets the relationships between macromolecular and elemental stoichiometry and also provides quantitative predictions of the maximum growth rate at given light intensity and nutrient supply rates. The model is compatible with data sets from several laboratory studies characterizing both prokaryotic and eukaryotic phytoplankton from marine and freshwater environments. It is conceptually simple, yet mechanistic and quantitative. Here, the model is constrained only by elemental stoichiometry, but makes predictions about allocation to measurable macromolecular pools, which could be tested in the laboratory.

Interplay between r- and K-strategists leads to phytoplankton underyielding under pulsed resource supply.

Fluctuations in nutrient ratios over seasonal scales in aquatic ecosystems can result in overyielding, a condition arising when complementary life-history traits of coexisting phytoplankton species enables more complete use of resources. However, when nutrient concentrations fluctuate under short-period pulsed resource supply, the role of complementarity is less understood. We explore this using the framework of Resource Saturation Limitation Theory (r-strategists vs. K-strategists) to interpret findings from laboratory experiments. For these experiments, we isolated dominant species from a natural assemblage, stabilized to a state of coexistence in the laboratory and determined life-history traits for each species, important to categorize its competition strategy. Then, using monocultures we determined maximum biomass density under pulsed resource supply. These same conditions of resource supply were used with polycultures comprised of combinations of the isolated species. Our focal species were consistent of either r- or K-strategies and the biomass production achieved in monocultures depended on their efficiency to convert resources to biomass. For these species, the K-strategists were less efficient resource users. This affected biomass production in polycultures, which were characteristic of underyielding. In polycultures, K-strategists sequestered more resources than the r-strategists. This likely occurred because the intermittent periods of nutrient limitation that would have occurred just prior to the next nutrient supply pulse would have favored the K-strategists, leading to overall less efficient use of resources by the polyculture. This study provides evidence that fluctuation in resource concentrations resulting from pulsed resource supplies in aquatic ecosystems can result in phytoplankton assemblages' underyielding.

Optimal allocation of leaf‐level nitrogen: Implications for covariation of Vcmax and Jmax and photosynthetic downregulation

AbstractThe maximum rate of carboxylation, Vcmax, and the maximum rate of electron transport, Jmax, describe leaf‐level capacities of the photosynthetic system and are critical in determining the net fluxes of carbon dioxide and water vapor in the terrestrial biosphere. Although both Vcmax and Jmax exhibit high spatial and temporal variability, most descriptions of photosynthesis in terrestrial biosphere models assume constant values for Vcmax and Jmax at a reference temperature ignoring intraseasonal, interannual, and water stress‐induced variations. Although general patterns of variation of Vcmax and Jmax have been correlated across groups of species, climates, and nitrogen concentrations, scant theoretical support has been provided to explain these variations. We present a new approach to determine Vcmax and Jmax based on the assumption that a limited amount of leaf nitrogen is allocated optimally among the various components of the photosynthetic system in such a way that expected carbon assimilation is maximized. The optimal allocation is constrained by available nitrogen and responds dynamically to the near‐term environmental conditions of light and water supply and to their variability. The resulting optimal allocations of a finite supply of nitrogen replicate observed relationships in nature, including the ratio of Jmax/Vcmax, the relationship of leaf nitrogen to Vcmax, and the changes in nitrogen allocation under varying water availability and light environments. This optimal allocation approach provides a mechanism to describe the response of leaf‐level photosynthetic capacity to varying environmental and resource supply conditions that can be incorporated into terrestrial biosphere models providing improved estimates of carbon and water fluxes in the soil‐plant‐atmosphere continuum.

Complementarity among four highly productive grassland species depends on resource availability.

Positive species richness-productivity relationships are common in biodiversity experiments, but how resource availability modifies biodiversity effects in grass-legume mixtures composed of highly productive species is yet to be explicitly tested. We addressed this question by choosing two grasses (Arrhenatherum elatius and Dactylis glomerata) and two legumes (Medicago × varia and Onobrychis viciifolia) which are highly productive in monocultures and dominant in mixtures (the Jena Experiment). We established monocultures, all possible two- and three-species mixtures, and the four-species mixture under three different resource supply conditions (control, fertilization, and shading). Compared to the control, community biomass production decreased under shading (-56%) and increased under fertilization (+12%). Net diversity effects (i.e., mixture minus mean monoculture biomass) were positive in the control and under shading (on average +15 and +72%, respectively) and negative under fertilization (-10%). Positive complementarity effects in the control suggested resource partitioning and facilitation of growth through symbiotic N2 fixation by legumes. Positive complementarity effects under shading indicated that resource partitioning is also possible when growth is carbon-limited. Negative complementarity effects under fertilization suggested that external nutrient supply depressed facilitative grass-legume interactions due to increased competition for light. Selection effects, which quantify the dominance of species with particularly high monoculture biomasses in the mixture, were generally small compared to complementarity effects, and indicated that these species had comparable competitive strengths in the mixture. Our study shows that resource availability has a strong impact on the occurrence of positive diversity effects among tall and highly productive grass and legume species.

Resource supply alone explains the variability of marine phytoplankton size structure

AbstractDue to the covariation between temperature and resource availability in the surface ocean, a correct assessment of resource supply is crucial to determine if temperature has a direct effect on phytoplankton size structure. To remove the effect of resources, López‐Urrutia and Morán analyzed data subsets with narrow ranges of variation in Chlorophyll a (Chl a) concentration and found that temperature is correlated with Chl a partitioning among size classes, from which they concluded that temperature is an important variable to explain the variability of phytoplankton size structure. Our analysis, however, shows that resource supply varies widely also within these subsets and, importantly, that it is inversely correlated with temperature. Therefore, the relationship between temperature and size structure reflects instead the effect of resources. When groups of samples with similar resource supply conditions are considered, no correlation between temperature and phytoplankton size structure is observed, which invalidates the conclusion of López‐Urrutia and Morán. Even within restricted ranges of variation for phytoplankton biomass and production, changes in resource supply alone are sufficient to explain the variability of phytoplankton size structure in the sea.

Research on Project Scheduling Problem with Resource Constraints

Resource-constrained project scheduling problem is the traditional optimization problem considering constraint conditions of resource supply, which makes the problem more difficult to solve in real life. Resource- constrained project scheduling problem is a typical NP-hard problem, which is quite popular issue in recent years. This article firstly analyzes the literature review of resource- constrained project scheduling problem. And then, the mathematical model of this problem is established, and the solution via the genetic algorithm is also developed. Finally, the numerical experiment is adopted to verify the effectiveness and efficiency of the proposed model and algorithm.

The effect of species diversity on lipid production by micro-algal communities

Current research investigating the importance of diversity for biofuel lipid production remains limited. In contrast, the relationship between diversity and productivity within terrestrial and algal primary producers has been well documented in ecology. Hence, we set out to investigate, experimentally, whether diversity may also affect lipid production in micro-algae. We investigated the growth and lipid production of micro-algae using species from all major algal groups. Algae were grown in a large number of treatments differing in their diversity level. Additionally, we compared the growth and lipid production of laboratory communities to natural lake and pond phytoplankton communities of different diversity. Our results show that lipid production increased with increasing diversity in both natural and laboratory micro-algal communities. The underlying reason for the observed ‘diversity–productivity’ relationship seems to be resource use complementarity. We observed higher lipid production of highly diverse algal communities under the same growth and resource supply conditions compared to monocultures. Hence, the incorporation of the ecological advantages of diversity-related resource-use dynamics into algal biomass production may provide a powerful and cost effective way to improve biofuel production.

The evolution of silicification in diatoms: inescapable sinking and sinking as escape?

SummaryThe silicified bipartite cell walls of diatoms (Bacillariophyceae) are produced in intracellular compartments by precipitation from supersaturated Si(OH)4and are then externalized. Fossil evidence of silicification is for marine, probably neritic, centric diatoms from approx. 120 Mya. Regardless of the initial selective significance of silicification, and of other current roles of silicification, the increased density resulting from silicification increases the sinking rate of cells; this can be partly or wholly offset by regulation of the protoplast solute content. Acclimatory and regulatory changes in silicification (relatively slow), and intracellular solute composition (relatively rapid), and intracellular solute composition (relatively rapid) of marine diatoms alter cell density over periods of hours to days. Density changes via changes in resource supply and, probably, parasitism, would move cells into optimal resource supply conditions, and remove parasitized, infective cells from surface populations of uninfected cells. Regulation of sinking rate could have been the first function of external or internal silica if the earliest silicified diatoms were planktonic.ContentsI.Introduction46II.Phylogeny of diatoms and the habitat of the earliest diatoms46III.Origin of the silicon requirement in diatoms46IV.The phylogeny and ontogeny of turgor‐ resistant silicified walls47V.Possible selective advantages of silicified walls49VI.Conclusions57Acknowledgements57References57

Laboratorary Experiments with a Mixotrophic Chrysophyte and Obligately Phagotrophic and Photographic Competitors

Mixotrophic flagellates can compete with obligately heterotrophic flagellates for the uptake of food particles, whereas mixotrophs and obligately phototrophic phytoplankton can compete for soluble nutrients. Competition for soluble nutrients is expected when photosynthesis covers a significant portion of the mixotrophs' carbon metabolism. When heterotrophy predominates, however, mixotrophs may release soluble nutrients and facilitate phototrophs. Mechanistic resource competition theory predicts that, due to their ability to utilize substitutable C and P sources, mixotrophs should be able to coexist with their more specialized competitors under certain conditions of resource supply. In laboratory experiments, the mixotrophic flagellate Ochromonas excluded heterotrophic flagellates when only phototrophic growth was possible. However, Ochromonas was excluded by heterotrophic flagellates when only phagotrophic growth was possible. Both coexisted when food bacteria and light were supplied simultaneously. Ochromonas coexisted with a P—limited phytoplankter, Cryptomonas sp., when soluble reactive phosphorus (SRP) and bacterial phosphorus were available as alternative P sources. In nature, the mixotrophic strategy may be successful when resources are limiting. This is supported by published data on the occurrence of mixotrophic chrysophytes.

Oil Price Forecasting in the 1980s: What Went Wrong?*

This paper reviews forecasts of oil prices over the 1980s that were made in 1980. It identifies the sources of errors due to such factors as exogenous GNP assumptions, resource supply conditions outside the cartel, and demand adjustments to price changes. Through 1986, the first two factors account for most of the difference between projected and actual prices. After 1986, misspecification of the demand adjustments becomes a particularly troublesome problem.

Plywood Co-operatives in the United States: An Endangered Species

In addition to the familiar challenge of a highly volatile product market, the plywood co-operatives of the Pacific Northwest face a rapidly shrinking supply of timber. Their survival depends on their ability to concentrate on high-quality, high value-added segments of the market and on renewed investment. Investment has been difficult to sustain while owner-members' real incomes have been in decline. Industry and resource supply conditions and environmental regulation provide an increasingly difficult environment for this cluster of co-ops.