Germination sensitivities to water potential among co-existing C-3 and C-4 grasses of cool semi-arid prairie grasslands

摘要

An untested theory states that C-4 grass seeds could germinate under lower water potentials () than C-3 grass seeds. We used hydrotime modelling to study seed water relations of C-4 and C-3 Canadian prairie grasses to address divergent sensitivities and germination strategies along a risk-spreading continuum of responses to limited water. C-4 grasses were Bouteloua gracilis, Calamovilfa longifolia and Schizachyrium scoparium; C-3 grasses were Bromus carinatus, Elymus trachycaulus, Festuca hallii and Koeleria macrantha. Hydrotime parameters were obtained after incubation of non-dormant seeds under different PEG 6000 solutions. A t-test between C-3 and C-4 grasses did not find statistical differences in population mean base ((b)(50)). We found idiosyncratic responses of C-4 grasses along the risk-spreading continuum. B.gracilis showed a risk-taker strategy of a species able to quickly germinate in a dry soil due to its low (b)(50) and hydrotime ((H)). The high (b)(50) of S.scoparium indicates it follows the risk-averse strategy so it can only germinate in wet soils. C.longifolia showed an intermediate strategy: the lowest (b)(50) yet the highest (H). K.macrantha, a C-3 grass which thrives in dry habitats, had the highest (b)(50), suggesting a risk-averse strategy for a C-3 species. Other C-3 species showed intermediate germination patterns in response to relative to C-4 species. Our results indicate that grasses display germination sensitivities to across the risk-spreading continuum of responses. Thus seed water relations may be poor predictors to explain differential recruitment and distribution of C-3 and C-4 grasses in the Canadian prairies.