restricted access I.3 Physiological Ecology: Plants
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I.3 Physiological Ecology: Plants David D. Ackerly and Stephanie A. Stuart OUTLINE 1. Introduction 2. Resource acquisition 3. Resource allocation and growth 4. Responses to environmental conditions 5. Ecophysiology, distributions, and global climate change Plant physiological ecology addresses the physiological interactions of plants with the abiotic and biotic environment and the consequences for plant growth, distributions, and responses to changing conditions. Plants have three unique features that influence their physiological ecology: they are autotrophs (obtaining energy from the sun), they are sessile and unable to move, and they are modular, exhibiting indeterminate growth. Plant growth dependson acquisition of four critical resources: light, CO2, mineral nutrients, and water. Light together with nitrogen-rich enzymes in the leaf drive photosynthetic assimilation of CO2 intocarbohydrates.Uptake of nitrogen and phosphorus, the elements most often limiting growth, is facilitated by symbiotic associations on plant roots with bacteria and fungi, respectively. Most water acquired by plants is lost in transpiration in exchange for CO2 uptake through stomata. Water moves through a plant by cohesiontension , drawn upward as a result of evaporation from leaves. Excessive tension can lead to embolism, in which air bubbles enter the water column and block water transport. Within the plant, allocation of resources to alternative functions creates important trade-offs that critically influence plant responses and performance in contrasting environments. Physiological ecology plays a critical role in understanding the distributions of individual species and of major biomes at a global scale and is vital to understand the potential impacts of global climate change on vegetation and biodiversity. GLOSSARY acquisition. The processes of acquiring resources from the environment, such as photosynthesis in leaves and nutrient uptake by roots. allocation. The partitioning of resources among alternative structures or functions within a plant. The principle of allocation states that resources used for one purpose will be unavailable for other purposes, creating trade-offs that strongly influence plant growth and life cycles. conditions. Factors of the environment that influence an organism but cannot be consumed or competed for (e.g., temperature, pH). embolism (or cavitation). The blockage of water transport by air bubbles in the xylem (water-transporting cells), causing reduced water transport and, potentially , plant death. leaf energy balance. The balance of energy inputs and outputs that influence leaf temperature. Solar radiation is the most important input, and transpirational cooling and convective heat loss are the most important outputs. photosynthetic pathway. Plants exhibit three alternative photosynthetic pathways (C3, C4, and CAM) that differ in underlying biochemical and physiological mechanisms, resulting in contrasting performance depending on temperature and the availability of light, water, and nutrients. resources. Aspects of the environment that are consumed during growth and that plants compete for. The most important are light, water, nutrients, and space. water and nutrient use efficiency. The efficiency of photosynthesis relative to investment of water or nutrients , respectively. 1. INTRODUCTION Physiological ecology examines how plants acquire and utilize resources, tolerate and adapt to abiotic conditions , and respond to changes in their environment. The study of physiological ecology considers plant physiology in relation to the physics and chemistry of the abiotic world on one hand, and a broad ecological and evolutionary context on the other. Plant physio- logical ecology provides the basic sciences with essential information about plant evolution, biodiversity, ecosystem productivity, and carbon and nutrient cycling . It also plays an instrumental role in a wide range of applied sciences, including agriculture, forestry, management of invasive species, restoration ecology, and global change biology. In its early years, plant ecophysiology addressed two broad themes. One was the effort beginning in the midnineteenth century to understand the global distribution of major biomes and vegetation types, led by pioneering plant geographers such as A. von Humboldt , A.F.W. Schimper, and their followers. These workers recognized that similar vegetation types arise under similar climates in different parts of the world, and they developed basic principles of plant form and function that could explain these global patterns. This led to a subsequent emphasis, in the early twentieth century, on the question of how plants survive in extreme environments. Principles of physiology and biophysics were applied in natural settings to understand how plants can tolerate and even thrive from the heat of the desert to the extreme cold of the high arctic and the upper limits of vegetation on high mountains. Both of these traditions combined the mechanistic view of the physiologist with the idea of evolutionary adaptation to understand why species with different physiological...