The temperature acclimation potential of tropical bryophytes.

Bryophyte biomass and diversity in tropical moist forests decrease dramatically from higher altitudes towards the lowlands. High respiratory carbon losses at high temperatures may partly explain this pattern, if montane species are unable to acclimatise their metabolic rates to lowland temperatures. We transplanted ten bryophyte species from two altitudes (1200 and 500 m a.s.l.) to lower (warmer) altitudes (500 m and sea level) in Panama. We studied short-term temperature acclimation of CO2 exchange for 2.5 months, and survival and growth for 21 months following transplantation. Short-term acclimation did not occur, and on a longer time scale mortality was highest and growth lowest in the transplanted samples. A few transplanted samples of most species, however, survived the whole experiment and finished with growth rates similar to controls. This recovery of growth rate suggests temperature acclimation, in spite of no measurable metabolic changes in smaller random samples. This acclimation even compensated for shorter periods of CO2 uptake due to more rapid drying. Nevertheless, these species are not abundant in lowland forests, perhaps due to dispersal or establishment limitation. The apparent heterogeneity of the acclimation potential within species may allow populations to adapt locally and avoid being forced uphill under climatic warming.