Climate drivers of the terrestrial carbon cycle variability in Europe

Abstract

The terrestrial biosphere is a key component of the global carbon cycle and is heavily influenced by climate. Climate variability can be diagnosed through metrics ranging from individual environmental variables, to collections of variables, to the so-called climate modes of variability. Similarly, the impact of a given climate variation on the terrestrial carbon cycle can be described using several metrics, including vegetation indices, measures of ecosystem respiration and productivity and net biosphere-atmosphere fluxes. The wide range of temporal (from sub-daily to paleoclimatic) and spatial (from local to continental and global) scales involved requires a scale-dependent investigation of the interactions between the carbon cycle and climate. However, a comprehensive picture of the physical links and correlations between climate drivers and carbon cycle metrics at different scales remains elusive, framing the scope of this contribution. Here, we specifically explore how climate variability metrics (from single variables to complex indices) relate to the variability of the carbon cycle at sub-daily to interannual scales (i.e. excluding long-term trends). The focus is on the interactions most relevant to the European terrestrial carbon cycle. We underline the broad areas of agreement and disagreement in the literature, and conclude by outlining some existing knowledge gaps and by proposing avenues for improving our holistic understanding of the role of climate drivers in modulating the terrestrial carbon cycle.

Increasing Causal Effects of El Niño–Southern Oscillation on the Future Carbon Cycle of Terrestrial Ecosystems

“…We used monthly data of carbon mass flux out of atmosphere due to gross primary productivity (GPP), land carbon (i.e., total carbon stored in all terrestrial carbon pools including vegetation, litter, soil, forestry, and agricultural products; CLAND) and vegetation carbon (e.g., carbon content in trees, shrubs, grass; CVEG). The GPP is considered as a key metric for carbon fluxes in ecosystems (Betts et al., 2020; Keenan & Williams, 2018; Messori et al., 2019) while land carbon and vegetation carbon are used as metrics for terrestrial carbon stocks (Chaplin‐Kramer et al., 2015; Worden et al., 2021). The uncertainty of global carbon budget is mainly associated with the terrestrial carbon cycle (Tharammal et al., 2019) as the main contribution of CO 2 uptake from the atmosphere is from the land flux (Betts et al., 2020) and there is fluctuation of annual carbon uptake by land ecosystems (Le Quéré et al., 2013).…”

Rainfall intensification increases the contribution of rewetting pulses to soil heterotrophic respiration

“…Moreover, soil C substrates might be depleted through multiple drying and rewetting events -a behavior we do not consider in the proposed statistically stationary model. While some experiments show sustained rewetting pulses (Miller et al, 2005;Xiang et al, 2008), others show reduced total heterotrophic respiration with increasing frequency of drying and rewetting, possibly due to substrate depletion (Shi and Marschner, 2014). To capture these dynamics, a more complex model describing the changes in substrate and microbial compartments would be needed (e.g., Brangarí et al, 2018;Lawrence et al, 2009;Tang et al, 2019) at the cost of losing the analytical tractability.…”

“…The focus on the processes causing respiration pulses resulted in extensive work conducted under idealized laboratory conditions, in which soil moisture changes were controlled, typically following a regular pattern of drying and wetting (Fierer and Schimel, 2002;Miller et al, 2005;Marschner, 2014, 2015;Xiang et al, 2008). However, soil moisture varies randomly due to the stochastic nature of rainfall events (Katul et al, 2007;, and this temporal variability can either promote or decrease soil organic C storage depending on its effects on soil microbes (Lehmann et al, 2020).…”

Modes of climate variability bridge proximate and evolutionary mechanisms of masting

“…spring with the preceding winter NAO index (electronic supplementary material, figure S7b). In Central Europe periods of positive winter, NAO phases are associated with increased resource uptake in European forests [24,32,66]. Importantly, the lag-1 positive autocorrelation of the winter NAO index (electronic supplementary material, figure S7a) means that a positive winter NAO can persist for consecutive years, thus promoting a prolonged resource gain.…”