Identifying mechanisms of tolerance to herbivore damage will facilitate attempts to understand the role of tolerance in the evolutionary and ecological dynamics of plants and herbivores. Several external factors, such as water availability, nutrient availability, intensity of damage, and timing of damage, will affect the ability of individual plants to tolerate damage by mediating internal mechanisms. Though interspecific comparisons are useful for identifying possible mechanisms, direct comparisons between tolerance and putative mechanism have been made almost exclusively in interspecies or interpopulation studies.
This study compared the compensatory responses of Avena sativa and Brassica campestris, which belong to different growth forms, to clipping under two fertilization treatments. The results showed that, for Avena sativa, under no fertilization treatment, the biomass, total biomass, fruit weight and number of fruits were greater than in the control, but only some aspects resulted in overcompensation. Under fertilized conditions, clipping treatments did not cause any overcompensation. Whether fertilized or not, the index of compensation during the tillering stage and jointing stage were both higher than during the flowering stage. Thus, under the no fertilization treatment, the low clipping treatment during the vegetative stage was shown to benefit Avena sativa. With respect to Brassica campestris, the index of compensation was greatest in the low clipping treatment during the flower bud stage, and was enhanced under fertilization. These results indicate that clipping during the reproductive stage can help compensatory growth in Brassica campestris. The different responses to clipping were attributed to the different growth forms, which had different positions and activities of dormant buds.