Plant life in cold climates.

Structural and functional features of plants from cold regions such as high mountain and tundra environments are characterized. Cold climates are not necessarily cold for plants at all times and influences of plant-growth form on canopy climate are substantial. Extreme low temperatures can cause temporal cessation of metabolic processes or partial tissue losses, but rarely represent an existential problem for plants native to cold regions. Low temperatures induce drastic changes in plant physiognomy and leaf anatomy, but dry matter allocation to the different plant compartments does not show a uniform trend. This suggests that generalizations of optimization and adaptation theories are not appropriate in this respect and that the functional importance of carbohydrate budgets is commonly over-estimated. Inconsistent with widespread beliefs, photosynthetic capacity in plants from cold regions is not essentially different from that in temperate regions, when comparable life forms are considered. Prevailing leaf temperatures exert minor limitations to seasonal photosynthetic carbon gain. Low temperatures come into play primarily in two ways: indirectly, via the length of the growing season and perhaps mineral nutrient availability, and directly, through influences on the growth process per se. Inherited slow or temporally restricted growth resembles an evolutionary response to long-term expectations of low resource availability. Within these genetic constraints the mitotic rate seems to be an essential point of action where low temperature determines the growth of an individual under respective local climates. Evidence is provided to support this view of an overruling significance of developmental processes in plant performance under cold conditions.