Carbon use efficiency (CUE), defined as the proportion of net primary productivity (NPP) to gross primary production (GPP), is increasingly recognized as an important parameter describing ecosystem carbon storage (Collalti et al. 2020). As plant respiration (Ra) responds positively to temperature, a warming world may result in additional respiratory CO2 release, and hence further atmospheric warming. An accelerate positive feedback between climate warming and carbon cycle is therefore expected.
Fortunately, plant respiration can acclimate to altered temperatures to maintain their optimal photosynthetic capacity (Wang et al. 2020). The warming experiments has shown that acclimation eliminated 80% of the expected increase in leaf respiration of non-acclimated plants (Reich et al. 2016) (Fig.1), which weakens the positive feedback of plant respiration to rising global air temperature.
Fig.1 Increase in leaf dark respiration (Rd) with +3.4 °C experimental warming for acclimated and non-acclimated plants (Reich et al. 2016)
However, it is not clear how the sensitivity and magnitude of this acclimation change with environmental variations. Unlike photosynthesis with a well-established photosynthetic model (i.e. Farquhar-von Caemmerer-Berry model), there is no such theoretical model for respiration, especially for the stem and fine roots. Thus, land surface models still rely on the empirical relationship between respiration and temperature. For example, in Noah MP, respiration rate increases approximately exponentially with warming with a fixed thermal sensitivity. Lack of the respiratory acclimation, land surface models show that warming substantially enhances plant respiration and weakens CUE, which is contrary to the observation (Fig.2).
Fig.2. The responses of modelling (left panel) and observed (right panel) CUE to temperature (from He et al. (2018) and Collalti et al. (2020) ).
Lots of field experimental observations have suggested that plants can acclimate to the changing environment, and therefore reduce their thermal sensitivity, but it is still a huge gap in the understanding of the mechanisms of respiratory acclimation. Obviously, a robust theory of respiratory acclimation is a critical step towards better understanding of the biosphere-atmosphere carbon exchange under future climate change.
Collalti, A., A. Ibrom, A. Stockmarr, A. Cescatti, R. Alkama, M. Fernandez-Martinez, G. Matteucci, S. Sitch, P. Friedlingstein, P. Ciais, D. S. Goll, J. Nabel, J. Pongratz, A. Arneth, V. HaverdandI. C. Prentice. (2020). Forest production efficiency increases with growth temperature. Nat Commun, 11(1), 5322. 10.1038/s41467-020-19187-w
He, Y., S. Piao, X. Li, A. ChenandD. Qin. (2018). Global patterns of vegetation carbon use efficiency and their climate drivers deduced from MODIS satellite data and process-based models. Agricultural and Forest Meteorology, 256-257(150-158. 10.1016/j.agrformet.2018.03.009
Reich, P. B., K. M. Sendall, A. Stefanski, X. Wei, R. L. RichandR. A. Montgomery. (2016). Boreal and temperate trees show strong acclimation of respiration to warming. Nature, 531(7596), 633-6. 10.1038/nature17142
Wang, H., O. K. Atkin, T. F. Keenan, N. G. Smith, I. J. Wright, K. J. Bloomfield, J. Kattge, P. B. ReichandI. C. Prentice. (2020). Acclimation of leaf respiration consistent with optimal photosynthetic capacity. Glob Chang Biol. 10.1111/gcb.14980