Physiological Ecology of Water Balance in Terrestrial Plants

Abstract

Water is one of the most important environmental factors limiting the growth and production of terrestrial (land) plants. Although water is essential for a number of metabolic, physiological, and growth processes in plants (e.g., turgor maintenance and cell elongation, transport of nutrients and carbohydrates, energy dissipation, and photosynthetic electron transport), most plants consume and store very little water. The vast majority of water that is absorbed by a plant’s root system moves through its vascular tissue (xylem) and is lost to the atmosphere as water vapor in the process of transpiration. It is the net difference between this uptake and loss that determines the overall water balance of a plant. Plant species vary considerably in their abilities to capture soil water, how efficiently they utilize water, and their tolerances to desiccation, and this variation has a number of ecological consequences at scales from individual plants to ecosystems, landscapes, and the globe. Historically, plant physiological ecologists studied the water relations of plant cells, tissues, and organs to better understand the molecular, physiological, anatomical, and morphological mechanisms by which plants have adapted to survive drought and cope with limited water availability. For obvious reasons, these studies were concentrated on plants in extreme moisture-limited ecosystems such as deserts, but water relations research was also conducted in other systems that experience intermittent and seasonal drought. Over time, physiological ecologists began to study the water relationships between plants and soil, examined how plants interacted with one another for this resource, and explored how temporal and spatial variation in soil moisture availability influences species distributions and community organization. The study of ecohydrology is a relatively recent interdisciplinary discipline that seeks to study how hydrological processes influence biological communities and also how these systems, in turn, influence the water cycle. Plant physiological ecologists play an important role in ecohydrology research by studying how water influences ecosystem function and quantifying the role of vegetation in influencing hydrological processes. Finally, plant physiological ecologists are increasingly interested in how changes in water availability driven by climate change affects plants and terrestrial ecosystems, how global change factors (e.g., atmospheric CO2) influence plant water relations, and what role vegetation itself plays in influencing the atmosphere and climate. Below are selected sources that highlight the full breadth of the study of the physiological ecology of water balance in plants. An emphasis is placed on terrestrial plants in non-hydric (i.e., non-flooded) environments and sources include a number of classical as well as contemporary publications.