Part II

Physiological and biophysical plant ecology investigates abiotic conditions, the responses of plant species to abiotic factors, and the transport of carbon, water and nutrients between plants and the surrounding soil or atmosphere. The range of possible responses of plants to the environment is wide and includes molecular, cellular and structural changes. The relationships between plants with soils and the atmosphere also include (bio)physical processes, for example the energy balance of plants. Plants have been very successful at adapting even to extreme environments. During the course of evolution, plants have occupied every terrestrial habitat, ranging from tropical climates to the eternal ice, from bogs to deserts, from extremely saline to nutrient-limited habitats. Plants have also developed manifold interactions with other organisms, ranging from mutualism with pollinators to antagonism with herbivores, and pathogen defence. These adjustments range from reversible acclimations (e.g. leaf movements) to non-reversible modifications (phenotypic plasticity) and long-term evolutionary adaptations. The latter occur as genetic changes in individuals of a population that may not even be phenotypically visible and that are not necessarily disadvantageous under the prevailing conditions of competition and stress in the habitat. However, if conditions change, for example, climate, supply of nutrients or competition, then individual plants with certain advantageous traits are able to compete better, have a better chance of survival, to maintain or enlarge the area they occupy, and to increase their fitness. This process is called pre-adaptation. Traits that are “advantageous” for certain habitats develop before the actual change of growth conditions and are the precondition for the colonisation of new habitats.

Plants occur in a wide variety of forms, from giant trees hundreds of years old, with a life cycle from germination to the flowering age of decades to centuries, to annual species in arid regions, with a life cycle from seed to seed of only a few days. Thus, plant responses to the environment not only occur at the biochemical level but also include structural changes and adjustments of the life span. The physiological ecology (also called ecophysiology) of plants considers the reactions at the level of individual organs (e.g. height of shoot, size of leaf, depth of root) or relationships between organs (e.g. distribution of resources between shoot and root, regulation of coordination between shoot and root). Biophysical ecology includes the laws of physics that control the fluxes of material between the plant individual and its environment. Thus, this section of the textbook provides the connection between Molecular Ecology (Part I) and Community Ecology (Part IV).