Alaskan carbon-climate feedbacks will be weaker than inferred from short-term experiments

Abstract

Climate warming is occurring fastest at high latitudes. Based on short-term field experiments, this warming is projected to stimulate soil organic matter decomposition, and promote a positive feedback to climate change. We show here that the tightly coupled, nonlinear nature of high-latitude ecosystems implies that short-term (<10 year) warming experiments produce emergent ecosystem carbon stock temperature sensitivities inconsistent with emergent multi-decadal responses. We first demonstrate that a well-tested mechanistic ecosystem model accurately represents observed carbon cycle and active layer depth responses to short-term summer warming in four diverse Alaskan sites. We then show that short-term warming manipulations do not capture the non-linear, long-term dynamics of vegetation, and thereby soil organic matter, that occur in response to thermal, hydrological, and nutrient transformations belowground. Our results demonstrate significant spatial heterogeneity in multi-decadal Arctic carbon cycle trajectories and argue for more mechanistic models to improve predictive capabilities.

Enhanced plant leaf P and unchanged soil P stocks after a quarter century of warming in the arctic tundra

“…In contrast, soil P stocks summarize the net effect of plant inputs and microbial activity. Our lack of response with P stocks is consistent with no response after 2 and 10 yr of warming in alpine meadow or 5 yr in Swedish heath tundra (Jonasson et al 1999, Wang et al 2014) and indicate that warming has no longterm net effect on belowground P. This is consistent with growing global evidence that long-term warming does not alter C stocks in ways that are predicted from short-term warming manipulations (van Gestel et al 2018, Bouskill et al 2020, Jian et al 2020. Therefore, we suggest that inconsistencies between tundra systems in response to warming encompass both seasonal variation, ecosystem specificity, and differences in duration of warming.…”

Microbial contribution to post-fire tundra ecosystem recovery over the 21st century

“…These results, and previously described evaluations of the model against diurnal, seasonal, and inter-annual variability of high-latitude ecosystems with 39 and without fire [43][44][45][46] , and the review of previous comparisons provided above, demonstrate that ecosys provides a reasonable representation of tundra ecosystems, and can be extended to our 21 st century model experiments.…”

“…were tested using an analysis of variance test. Finally, we used an information theory approach (transfer entropy; 43 ) to examine directional impacts from one variable (e.g., soil nutrient cycling) to another (e.g., net primary productivity). These relationships were inferred by Shannon information entropy (H) and its transfer (TE) (unit bits), as previously described 103 .…”

“…However, while there exists observational evidence 33,34,60 and model simulations 43 for the expansion of shrubs across tundra ecosystems, the majority of these studies attribute the expansion to deciduous shrubs, such as dwarf shrubs or willow 34 . At the northern Anaktuvuk River site, evergreen shrubs were observed and modeled to be significant contributors to ecosystem biomass and NPP at the beginning of the 21 st century 17 , and modeled to increase over time.…”

Coupling plant litter quantity to a novel metric for litter quality explains C storage changes in a thawing permafrost peatland

“…Thus, our study shows the importance of including plant community transition, in addition to within-community growth patterns, when quantifying changes in NPP, biomass, and soil C resulting from climate change. It will be important for models of ecosystem response to include such shifts in plant community composition in order to accurately predict warming-induced changes to C cycling (Bouskill et al, 2020). It should also be noted that the lack of significant differences in aboveground biomass and photosynthetic tissue was partly due to high heterogeneity in plant growth patterns at our site, particularly in the density and composition of aboveground biomass.…”