Effects of Long-Term Preconditioning on Growth and Flowering of Some Snow Tussock (Chionochloa Spp.) Populations in Otago, New Zealand

Abstract

Clone members of each of three altitudinal populations (910-1590 m) of two ecologically important snow tussocks (Chionochloa macra and C. rigida) reciprocally transplanted to four sites (10-1590 m) in 1960 were further subdivided and re-reciprocally transplanted to the same four sites in 1974 and their subsequent growth and flowering behaviour followed over two seasons. Interpopulation differences in stature and growth rates remained distinct after the 14-year intervening period, reinforcing earlier evidence for some genetic control of these characters. In contrast, the flowering of each population at each site had converged towards that of the resident plants, which indicated some adjustment to the critical threshold temperature for flowering. Interpopulation differences in flowering behaviour could not, therefore, be strictly controlled genetically as had been previously assumed. No interpopulation differences emerged as a result of 14 years of preconditioning in diverse environments. Furthermore, the preconditioning had a negligible effect on the subsequent perfor- mance of each population in a wide range of temperature environments. Distinct differences in growth rates between a lowland coastal population of C. rigida and its alpine counterparts appear adaptive, suggesting differentiation of a lowland ecotype. The high degree of physiological plasticity inherent in all populations of snow tussock studied may have its origin in the climatically diverse post-Pleistocene period when genotypes with maximum flexibility may have been selected preferentially. Since then, probably as a result of expansion of snow tussock grasslands within the last millenium, local adaptive variants have evolved.