Global consistency in response of terrestrial ecosystem respiration to temperature

Abstract

Many studies have been carried out to quantify the trend of terrestrial ecosystem respiration (Re) in a warming world, but a conclusive answer has not yet been confirmed because the temperature sensitivity of Re was found inconsistent under different scales or regarding different types of respiratory flux. Aiming at reconciling the relationship between temperature and Re across different scales (i.e., short-term and site-to-site), we proposed a method to reduce noises of half-hourly Re measurements and applied nine empirical models to a 1387 site-year FLUXNET datasets. Regarding the temperature sensitivity of half-hourly Re records, we found a surprisingly consistent result that the sigmoid functions outcompeted other statistical models in 82% of site-year combinations, and on average, achieved a staggering R2 value of 0.92, indicating the positive correlation between Re and temperature on fine time scale (within one site-year dataset). Even though Re of all biomes followed sigmoid functions, the parameters of the S-curve varied strongly across sites or years. This explains why measured Q10 value (an index denote temperature sensitivity) largely depends on observation season and site. Furthermore, on the interannual variation of Re, we did not find any relationship between mean annual temperature (MAT) and mean annual Re within any site, which implies that the small year-to-year variation of the sigmoid pattern is large enough to counteract the warming effect on Re. This study brings up a conceptual framework to integrate the relationship between temperature and Re under short-term or site-to-site scales. It also provided evidence to support the argument that the relationship between MAT and mean annual Re by using data across multiple sites should not be used to interpret the response of respiration under global warming.