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The response of old-field vegetation to fertilization at the rate of 450 kg·N·ha under different application schedules was evaluated using measurements of plant species number, biomass accumulation and structurefunction group productivity. Application of fertilizer under differing schedules at the same seasonal rate differentially affected plant species number, but not biomass accumulation. The structure-function groups productivities were differentially stimulated in response to fertilization under different schedules. These responses are discussed in terms of generated dominance and site resource availability.Structure-function groups are defined as a level of biological organization greater than the population, but less than the community. The use of such groupings is discussed as a means of viewing community interactions at a level higher than the population.

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Plants with the C dicarboxylic acid pathway of photosynthetic CO fixation are generally nutritionally inferior to C (Calvin cycle) plants as foodstuff for herbivores. A possible contributing factor to this nutritional inferiority is the concentration, in C plants, of large quantities of nutritional material in very tough, thick-walled vascular bundle sheath cells which herbivores may not be able to break down. Experiments with 10 species of grass-hoppers from different areas in the United States revealed large numbers of unbroken bundle sheath cells, contents intact, in fecal pellets produced when the grasshoppers were fed C vegetation. We conclude that the material stored in C bundle sheath cells is at least partially unavailable to herbivores, and that this may contribute to the observed nutritional inferiority of C vegetation.

Decomposition of terrestrial litterfall, that could enter a lake, was investigated at three depths within the lake in question using leaves of red maple (Acer rubrum). Sixty litter bags each containing 1o g dry weight of maple leaves were anchored at 1 m, 4 m and 12 m in East Twin Lake. At monthly intervals five bags were harvested at each level and dry weight changes noted. Results indicate little difference in decomposition between depths over the winter months . Beginning in May, however, significant differences were noted between i m and all other depths for the remainder of the experimental period . Maples lost too% of weight at I m, 54% at 4 m, and 55% at 12 m over the experimental period . The rate of decomposition over the total experiment period was approximately .03 g da 1 at i m and .015 g da 1 at the 4 and 12 m depths . These results are discussed in terms of regulation of decomposition, position of decomposition and contribution to lake metabolism.