Responses of temperate plants to drought conditions

Introduction

Environmental stress

Plants, especially those in temperate climates, live in an environment which can change not only seasonally, but also from moment to moment. Plants may face great variation, particularly in temperature and light conditions. Much of the time, the environment varies daily or seasonally in a way that is "predictable" for the plant. However, at times conditions arise that the plant is not fully adapted. These conditions are unfavorable for the plant, causing them "stress" (Gaspar et al. 2002). Generally biological stress is defined as a change in environmental conditions which might reduce or adversely change a plant's growth or development (Levitt 1980). However, physical stress is not all that plants may face in the environment, particularly in systems that are greatly influenced by humans. For example:

Table 1. Some of the sources of environmental stress in plants.
(Nilsen and Orcutt 1996)

Potential for water stress

Plant stressors are frequently discussed in terms of how they affect growth and productivity. Over large areas of the earth, water is the major factor limiting plant productivity. The difference in primary productivity between a desert environment, and one in which water is not limiting can be more than two orders of magnitude. However, even regions which have reasonably wet climates can experience periodic or seasonal droughts, which reduce productivity from that under optimal conditions (Jones 1992; Leuschner et al. 2001). Figure 1 shows the types of droughts that commonly occur across the United States.

Figure1. Map of the United States showing the distribution of forest ecosystems according to their current drought occurrence characteristics. Climate diagrams showing monthly precipitation and temperature are provided for selected locations within each zone to illustrate the seasonal nature of drought potential. (from Hanson and Weltzin 2000)