Metal co-tolerances in the grass Deschampsia cespitosa

Abstract

METAL tolerance in plants growing on metal-contaminated soils around mines^1–3, smelters⁴ and refineries⁵ have been reported. While metal tolerances in many dicotyledonous species, such as Becium homblei⁶, Mimulus guttatus⁷ and Silene cucubalus⁸, have been found, the emphasis has largely been placed on the study of populations of a limited number of grass species, especially Agrostis tenuis^1,2,9–11, Agrostis stolonifera^5,12, Festuca ovina³ and Anthoxanthum odoratum^13,14. (Adaptive population responses to a number of elements high in soils were recorded for lead, zinc, copper and nickel, reviewed by Antonovics et al.¹⁵.) In addition, tolerances to cadmium⁴ and arsenic¹⁶ have been investigated. Jowett¹⁷ and Bradshaw et al.¹¹ have postulated that tolerance to more than one element is dependent on the presence of these elements at elevated levels in the soil, that is, tolerance is specific. A few exceptions to this ‘rule’ have been noted, such as the apparent enhancement of nickel tolerance in a zinc-tolerant population of Agrostis tenuis despite the absence of elevated soil nickel¹¹. We present here evidence of the evolution of co-tolerances to copper, nickel and aluminium in a population of Deschampsia cespitosa (L.) Beauv. Also, the occurrence of co-tolerances for lead and zinc, which were not elevated in the soils from which the population was obtained. A limited number of cadmium-tolerant clones were also found in both populations.