Development and assessment of a coupled crop–climate model

It is well established that crop production is inherently vulnerable to variations in the weather and climate. More recently the influence of vegetation on the state of the atmosphere has been recognized. The seasonal growth of crops can influence the atmosphere and have local impacts on the weather, which in turn affects the rate of seasonal crop growth and development. Considering the coupled nature of the crop–climate system, and the fact that a significant proportion of land is devoted to the cultivation of crops, important interactions may be missed when studying crops and the climate system in isolation, particularly in the context of land use and climate change.
To represent the two-way interactions between seasonal crop growth and atmospheric variability, we integrate a crop model developed specifically to operate at large spatial scales (General Large Area Model for annual crops) into the land surface component of a global climate model (GCM; HadAM3). In the new coupled crop–climate model, the simulated environment (atmosphere and soil states) influences growth and development of the crop, while simultaneously the temporal variations in crop leaf area and height across its growing season alter the characteristics of the land surface that are important determinants of surface fluxes of heat and moisture, as well as other aspects of the land-surface hydrological cycle. The coupled model realistically simulates the seasonal growth of a summer annual crop in response to the GCM's simulated weather and climate. The model also reproduces the observed relationship between seasonal rainfall and crop yield. The integration of a large-scale single crop model into a GCM, as described here, represents a first step towards the development of fully coupled crop and climate models. Future development priorities and challenges related to coupling crop and climate models are discussed.     

Variation in Copper Tolerance among Homokaryotic and Dikaryotic Mycelia of Polyporus palustris Berk. et Curt.

Investigations were made of the variation in copper toleranceamong homokaryons and dikaryons originating from one dikaryoticisolate of Polyporus palustris, as shown by their growth onnutrient agar containing copper sulphate, usually at 0.32 Mconcentration (c. 8 per cent of CuSO₄.5H₂O). Homokaryons obtainedby monobasidiospore isolation were crossed and further homokaryonsobtained in the same way. Selection for copper tolerance gavean increase in the second generation, but no further increasein the third; whilst selection for copper sensitivity gave substantialincreases in both second and third generations. It is concludedthat copper tolerance in this fungus is controlled by a numberof genes. It was found that, in this fungus, the copper toleranceof a dikaryon was substantially greater than that of eitherof its constituent homokaryons. It was also found that differentisolates of P. palustris varied very widely in copper tolerance.     

Photon requirement for growth of the diatom Phaeodactylum tricornutum Bohlin (Bacillariophyceae)

Abstract Photon requirements for growth (φ_g^?1) of the diatom Phaeodactylum tricornutum were determined under nutrient-sufficient conditions at two photon flux densities corresponding to light limited and near-saturating conditions for growth. The value of φ_g^?1 based on assimilated carbon was light-dependent and varied from 8.8 to 14.0 mol photon mol C^?1 with the minimum value at the lowest photon flux density. These results are lower than might be predicted for microalgal growth based on the Z scheme of photosynthesis. Conversion of these values for carbon fixation to estimates based on oxygen evolution is problematical due to uncertainty over the appropriate assimilatory quotient (Q_a= mol O₂ mol C^?1). Minimum values based on oxygen evolution rates ranged from 6.2 to 7.6 mol photon mol O₂^?1 using a Q_a of 1.41 mol O₂ mol C^?1 obtained by Myers (1980). These estimates are similar to our previous measurements for photosynthesis and indicate a high efficiency for light energy transforming reactions during growth. The values of (φ_g^?1 obtained in this work indicate a number of inadequacies in our understanding of the energetics of microalgal growth and are inconsistent with our present knowledge of photosynthetic energy coupling in plant cells.     

Estimating Culicoides sonorensis biting midge abundance using digital image analysis

ImageJ is an open‐source software tool used for a variety of scientific objectives including cell counting, shape analysis and image correction. This technology has previously been used to estimate mosquito abundance in surveillance efforts. However, the utility of this application for estimating abundance or parity in the surveillance of Culicoides spp. (Diptera: Ceratopogonidae) has not yet been tested. Culicoides sonorensis (Wirth and Jones), a biting midge often measuring 2.0–2.5 mm in length, is an economically important vector of ruminant arboviruses in California. Current surveillance methods use visual sorting for the characteristics of midges and are very time‐intensive for large studies. This project tested the utility of ImageJ as a tool to assist in gross trap enumeration as well as in parity analysis of C. sonorensis in comparison with traditional visual methods of enumeration using a dissecting microscope. Results confirmed that automated counting of midges is a reliable means of approximating midge numbers under certain conditions. Further evaluation confirmed accurate and time‐efficient parity analysis in comparison with hand sorting. The ImageJ software shows promise as a tool that can assist and expedite C. sonorensis surveillance. Further, these methods may be useful in other insect surveillance activities.     

The Effects of Feeding Tetracycline, Nitrovin and Quindoxin on the Drug-Resistance of Coli-aerogenes Bacteria from Calves and Pigs

A study of calves and pigs was made to compare the effects on intestinal coli-aerogenes bacteria of feeding diets medicated with tetracycline, nitrovin or quindoxin. Results showed that even before the introduction of medicated diets, drug-resistant coli-aerogenes bacteria were present in surprisingly high numbers. However, it was clear with both animal species that only tetracycline had a selective effect. With calves a resistance to furazolidone was frequently present in tetracycline-resistant organisms. Analysis of the resistance patterns supported the contention that the dominant coli-aerogenes bacteria in the gut flora following use of certain growth-promoters, resulted from suppression of fully sensitive organisms: the distribution of the various resistance patterns was independent of the agent used and whether or not the diet was medicated. There was no significant difference in the trans-missibility of resistance genes between calves and pigs receiving either tetracycline or quindoxin or neither treatment. Results obtained with nitrovin were thought to be similar but, inexplicably, the control animals all gave low values.