High-Temperature Responses of North American Cacti

Smith, Stanley; Didden-Zopfy, Brigitte; Nobel, Park

High-temperature tolerances of 14 spp. of North American cacti (carnegiea gigantea, Lophocereus schottii, Stenocereus titurberi, Ferocactus acanthodes, F. covillei, F. viridescens, F. wislizenii, Opuntia acanthocarpa, O. bigelovii, O. ramosissima, O. basilaris, O. chlorotica, Coryphantha vivipara, Mammillaria dioica) were investigated. A reduction in the production of chlorenchyma cells taking up a vital stain (neutral red) and reduced nocturnal acid accumulation were used as indicators of high-temperature damage. All species tolerated relatively high tissue temperatures, the mean maximum tolerance being 64 deg. C, with an absolute maximum of 69 deg. for 2 spp. of Ferocatus. Such tissue tolerances to high temperature may be unsurpassed on vascular plants. Morphological features can affect tissue temperatures. Specifically, thin-stemmed species such as the cylindrupontias attain lower maximum temperatures under identical microclimate conditions than do more massive species; they also tend to be less tolerant to high-temperature stress. Stem diameter changes of 3 spp. of columnar ceroid cacti along a Sonoran Desert latitudinal transect were previously attributed to adaptation to progressively colder temperatures northward. Such changes can also be interpreted as morphological adaptation to high temperatures, particularly in the southern Sonoran Desert. Interspecific differences in high-temperature tolerance may account for distributional differences among other speices, e.g., the coastal-stage inhibiting F. viridescens was less tolerant of high. temperature than were the 3 Ferocactus species that inhabit warmer desert regions. Acclimation of high-temperature tolerances in response to increasing day/night air temperatures was observed in all 14 spp., especially at higher growth temperatures. From 40 deg. day/30 deg. night to 50 deg./40 deg., the tolerable tissue temperatures increased an average of 6 deg. Half-times for the acclimation shifts were 1-3 d (day). Although cacti attain extremely high tissue temperatures in desert habitats, tolerance of high temperatures and pronounced acclimation potental allow them to occur in some of ther hottest habitats of North America.

High-Temperature Responses of North American Cacti

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