Growth and Physiological Responses of Tundra Plants to Defoliation

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Abstract
Extreme abiotic conditions and biotic factors such as grazing influence the growth of tundra plants. Strategies of C assimilation, accumulation and utilization must not only satisfy the requirements of a rigorous physical environment, but must simultaneously adjust to the impacts associated with herbivory. Representatives of 4 growth forms found in northern Alaska, USA (a deciduous shrub, an evergreen shrub, a singleshooted graminoid and a tussock-forming graminoid) were subjected to various defoliation regimes and their physiological and morphological responses were documented. Apparently C allocation patterns are a function of growth form and dictate plant responses to defoliation, maximum photosynthetic rates are a function of growth form and are inversely related to leaf longevity, the impact of grazing is reduced in plant species with rapid leaf turnover and little supportive tissue, defoliation results in an immediate adjustment in C allocation pattern within the defoliated plant and C allocation to maintenance tissue or long-lived productive tissue is accompanied by mechanisms that reduce grazing.