Temperature sensitivity of canopy photosynthesis phenology in northern ecosystems

Abstract

Northern Hemisphere terrestrial ecosystems have been recognized as areas with large carbon uptake capacity and sinks and are sensitive to temperature change. However, the temperature sensitivity of ecosystem carbon uptake phenology in different biomes of northern ecosystems has not been well explored. In this study, based on our previous effort in characterizing canopy photosynthesis phenology indices, we analyzed how these phenology indices responded to temperature changes by using spatial temperature variability in the temperate and boreal ecosystems in the north hemisphere. Eddy covariance flux measurements of canopy photosynthesis were used to examine the temperature sensitivity of canopy photosynthesis phenology in different biomes and seasons (spring and autumn). Over all the 68 sites, the upturning day, peak recovery day, peak recession day, and senescence day of canopy photosynthesis were all sensitive to mean annual air temperature. Sites with higher mean annual air temperature had earlier carbon uptake and peak recovery day, but later ending of carbon uptake and peak recession day. As a consequence, effective growing season length was linearly increased with temperature for all the biomes. Spring phenology indices were more sensitive to temperature change than fall phenology. Besides phenology, peak canopy photosynthesis capacity was also linearly increased with temperature, and contributed even more to annual carbon assimilation changes than growing season length. These findings suggest a predominant temperature controls on annual carbon assimilation in northern ecosystems by changing both canopy photosynthesis phenology and physiology. The temperature sensitivity of canopy photosynthesis phenology and physiology indices revealed in this study are helpful to develop better models to predict impacts of global climate change on vegetation activities.