Respiration in the dark (RD) is a critical component of the carbon cycle, contributes approximately 60 Pg C y-1 to the atmosphere, and is incredibly sensitive to changes in temperature. Because climate change is increasing temperatures, as well as the frequency of extreme heat events around the globe, accurate parameterization of the short-term temperature response of RD is increasingly essential. Several large scale studies have highlighted that there is large global variation in RD among species, plant functional types and biomes. However, many species and plant functional types still remain underrepresented, carrying uncertainty forward into model predictions. Of particular note is the paucity of data on both tropical highland forests and conifer species. Here we present the first known respiration temperature (RT) curves of coniferous species growing in a tropical montane ecosystem in the Central Highlands of Vietnam. We place these species into the context of what is currently known about variability in the short-term RT response across biomes and conifer species. We also examine the effect of projected future temperature extremes on respiration in these species. RT curves were collected on detached sunlit upper-canopy foliage of 5 adult trees from each of 10 conifer species using a modified LI-6400 system that ramps temperature from 10 - 45°C while simultaneously recording gas exchange. A log-normal polynomial model was fit to each curve.
Results/Conclusions
Vietnamese conifers did not differ significantly in the parameterization of the RT response compared to 7 global biomes (P>0.05), confirming that species from underrepresented tropical montane forests also converge on a universal respiration temperature response. However, if Vietnamese conifers are compared to non-tropical conifers instead of biomes, Vietnamese species do have a significantly different parameterization of the RT response (P<0.05). Vietnamese species had significantly lower RD at a common T than non-tropical conifers (P<0.05), supporting global patterns of lower RD in species from warmer biomes when measured at a common temperature. Vietnamese species also had a significantly different shape of the RT response, indicating a more rapid increase in respiration for a given change in temperature, particularly at higher temperatures. This finding may indicate a greater vulnerability of these species to high temperature extremes predicted for Vietnam under future climate scenarios.