Allelopathic Effects of Artemisia tridentata Leaves on Germination and Growth of two Grass Species

Abstract

Volatile substances and aqueous extracts from Artemisia tridentata leaves were tested for their effects on germination, shoot growth and radicle growth o? Elymus cinereus and Agropyron cristatum. Germination of E. cinereus and A. cristatum seeds was significantly inhibited by both uncrushed and crushed A. tridentata leaves, as well as by aqueous extracts from the latter. Crushed A. tridentata leaves significantly reduced shoot and radicle growth of A. cristatum seedlings and radicle growth of E. cinereus seedlings. Introduction The role of chemical inhibition (allelopathy) in patterning of vegetation has been extensively studied in shrub communities of the western United States (Rice, 1974, 1979). Numerous studies have presented evidence that Artemisia sp. have allelopathic effects against neighboring species. Artemisia tridentata, big sagebrush, is the most widespread and common shrub of western North America, and it is particularly abundant in the Great Basin (McArthur et ai, 1979). The success of A. tridentata may partly depend on its production of allelopathic substances which inhibit the germination and growth of potential competitors (Weaver and Klarich, 1977). Hoffman and Hazlett (1977) and M?ller (1966) have implied that allelopathy may be a predominant influence in A. tridentata-dominated vegetation of the Great Basin, although the latter presented no data. Phytotoxins may be either volatile or water-transported. Aqueous extracts of litter and leaves (Schlatterer and Tisdale, 1969; Hoffman and Hazlett, 1977), as well as volatile substances (M?ller, 1966; Klarich and Weaver, 1973; McCahon et ai, 1973) from Artemisia tridentata have been shown to inhibit germination, shoot growth and radicle growth of several grass and herbaceous species. Klarich and Weaver (1973) stated that smaller amounts of volatile materials were released from uncrushed A. tridentata leaves than from crushed leaves. Their results indicated that growth of plants exposed to vapors from crushed leaves was always significantly less than that of plants exposed to uncrushed leaves. Additionally, Muller et al. (1964) indicated that root growth inhibition of test species was directly proportional (logarithmically) to increasing amounts of crushed A. californica leaves. Klarich and Weaver (1973) reported a similar finding with increasing amounts of crushed A. tridentata leaves, but presented no data. The purpose of the present investigation was to test the hypothesis that allelopathic substances from Artemisia tridentata inhibit germination, shoot growth and root growth of two test species, Agropyron cristatum (crested wheat grass) and Elymus cinereus (giant wild rye). The investigation was designed to overcome the problems of insufficient sample sizes, inadequate controls, improper test species and lack of statistical treatment of data which have occurred in previous allelopathic studies of Artemisia tridentata. Agropyron cristatum and E. cinereus were chosen as test species because they are grasses often found in close association with Artemisia tridentata in the Great Basin. Although Agropyron cristatum is an introduced species, it has been widely planted in sagebrush regions where invasion of such seeded areas by Artemisia tridentata is common. Materials and Methods Sagebrush plants {Artemisia tridentata ssp. tridentata), each approximately 15-20 cm in height, were transplanted during January 1980, from the Gibson Jack Creek Watershed (Pocatello, Idaho) to growth chambers at Idaho State University. Each plant was potted in a 15-cm clay pot with Bacto^ soil and acclimated for 3 weeks from a winter photoperiod and temperatures (12L/12D, 15 C day/8 C night) to a summer