Comparison of the intrinsic optimum temperatures for seed germination between two bamboo species based on a thermodynamic model

Abstract

Alpine plants usually experience lower ambient temperatures than non-alpine plants. However, it is still not known whether the former have lower temperature thresholds and lower physiological optimum temperatures for development than the latter. We studied two native Chinese bamboo species that have different vertical distributions: Chimonobambusa utilis, which typically grows at altitudes of 1400–2200 m, and Phyllostachys edulis (i.e., moso), which typically grows at altitudes of 400–800 m. The seed germination times of both species at eight temperatures from 16 to 30 °C at 2 °C increments were observed. A thermodynamic model was used to calculate the intrinsic optimum temperature and upper developmental threshold for development of each of these two species, and a linear model was used to calculate their lower developmental threshold and the sum of effective temperatures required for completing seed germination. We found that the alpine bamboo species had a lower intrinsic optimum temperature and a lower low-temperature developmental threshold than the non-alpine moso (19.4 vs. 19.8 °C and 7.5 vs. 10.1 °C, respectively), although it should be noted that the difference between the intrinsic optimum temperatures of the two species was small. However, there was no significant difference between the upper developmental thresholds (31.6 vs. 31.0 °C) or the sum of effective temperatures (135.8 vs. 136.8 d °C) of the two species. The results of this study imply that climate warming might reduce the fitness of bamboos, especially the alpine species whose intrinsic optimum temperature was found to be approximately 20 °C, which is in accordance with results previously reported for terrestrial arthropods.