Photoinhibition is a central problem for the understanding of plasticity in photosynthesis vs. irradiance response. It effectively reduces the photosynthetic rate. In this contribution, we present a mechanistic model of algal photoinhibition induced by photodamage to photosystem-II. Photosystem-IIs (PSIIs) are assumed to exist in three states: open, closed and inhibited. Photosynthesis is closely associated with the transitions between the three states. The present model is defned by four parameters: effective cross section of PSII, number of PSIIs, turnover time of electron transfer chains and the ratio of rate constant of damage to that of repair of D1 proteins in PSIIs. It gives a photosynthetic response curve of phytoplankton to irradiance (PI-curve). Without photoinhibition, the PI-curve is in hyperbola with the first three parameters. The PI-curve with photoinhibition can be simplified to the same form as the hyperbola by replacing either the number of PSIIs with the number of functional PSIIs or the turnover time of electron transfer chains with the average turnover time.

The paper analyzes the overall diversity of trophic structures and processes at the organizational level of ecosystems. The overall diversity based on Lindeman's trophic dynamics is considered as one-dimensional diversity. By unfolding ecosystems, trophic structures and processes of ecosystems are expressed in two-dimensional space along compartment and trophic level axes. By use of the Shannon-Weaver diversity index, the overall diversity of two-dimensional distributions of standing stocks or throughflows, which are significantly different from those defined in one-dimensional space, is determined. When flows between compartments are partitioned across trophic levels we can determine the overall diversity of three-dimensional distribution of throughflows over two compartment axes and a trophic level axis. The relationships between these overall diversity indexes defined in the different dimensional spaces are formulated by use of trophic niches and trophic functions as suggested by Higashi et al. (1992). The three-dimensional diversity of throughflows fall into three parts. The first identifies the overall diversity of two-dimensional distribution along compartment and trophic level axes. The second indicates the average diversity of resources utilized in an ecosystem. The third specifies the transfer efficiency of flows in an ecosystem. The three-dimensional diversity of throughflows may support a new framework to understand trophic structures and processes. Two real ecosystems are examined through the calculation of overall diversity indexes. The results confirm the differences between diversity indexes defined in different dimensions. Out of all the diversity indexes, those related to paths (to the third-dimension) are more powerful to reveal differences in trophic structures and processes between the two ecosystems.

Empirical biomass spectra in which biomass is measured in logarithmically equal body size intervals are different from those measured in linearly equal size intervals. Moreover, the scales of body size used by different authors may differ, e. g., length, volume, equivalent!sphere diameter and body mass. The discrete models derived to explain the regularity of the empirical spectra are dependent on the choice of size-scales and size!intervals. Hence, evaluating the effect of size scales and intervals on biomass spectra is helpful for understanding the size!structures of ecosystems. In the present contribution, we analyse the relationships between the size measures used frequently in expressing the empirical data and discuss the difference between the biomass spectra organized in logarithmically equal size intervals and those in linearly equal size intervals. On this basis, we present the distribution function of biomass spectral density and transformation to different size scales. After dexthe effect of size intervals on the distribution functions of biomass spectral density, we give an example of the calculation of this effect by assuming that the distribution function of biomass spectral density is an allometric relationship. Finally, we explore the influence of size intervals on the validity of three discrete models developed by Kerr, Sheldon and co!workers and Borgman.

In consequence of interactions between compartments, the matter or energy residence time in an econetwork is in nature distinct from that in a compartment. Based on the analysis of econetwork structure, a strategy is developed to calculate the matter or energy residence time in a general econetwork and the effects of self-, direct-and indirect interaction on econetwork residence time. Two typical examples are used to illustrate the strategy, the results show that total residence time equals the ratio of total standing stock to total system outflow or total system inflow instead of the ratio of total standing stock to total system throughput.

We explore control mechanisms underlying the vertical migration of zooplankton in the water column under the predator-avoidance hypothesis. Two groups of assumptions in which the organisms are assumed to migrate vertically in order to minimize realized or effective predation pressure (type-I) and to minimize changes in realized or e!ective predation pressure (type-II), respectively, are investigated. Realized predation pressure is defined as the product of light intensity and relative predation abundance and the part of realized predation pressure that really affects organisms is termed as effective predation pressure. Although both types of assumptions can lead to the migration of zooplankton to avoid the mortality from predators, only the mechanisms based on type-II assumptions permit zooplankton to undergo a normal diel vertical migration (morning descent and evening ascent). The assumption of minimizing changes in realized predation pressure is based on consideration of DVM induction only by light intensity and predators. The assumption of minimizing changes in effective predation pressure takes into account, apart from light and predators also the effects of food and temperature. The latter assumption results in the same expression of migration velocity as the former one when both food and temperature are constant over water depth. A significant characteristic of the two type-II assumptions is that the relative change in light intensity plays a primary role in determining the migration velocity. The photoresponse is modified by other environmental variables: predation pressure, food and temperature. Both light and predation pressure are necessary for organisms to undertake DVM. We analyse the effect of each single variable. The modification of the phototaxis of migratory organisms depends on the vertical distribution of these variables.