Contrasting mechanisms underlie short‐ and longer‐term soil respiration responses to experimental warming in a dryland ecosystem

Abstract

Soil carbon losses to the atmosphere through soil respiration are expected to rise with ongoing temperature increases, but available evidence from mesic biomes suggests that such response disappears after a few years of experimental warming. However, there is lack of empirical basis for these temporal dynamics in soil respiration responses, and for the mechanisms underlying them, in drylands, which collectively form the largest biome on Earth and store 32% of the global soil organic carbon pool. We coupled data from a ten-year warming experiment in a biocrust-dominated dryland ecosystem with laboratory incubations to confront 0-2 years (short-term hereafter) vs. 8-10 years (longer-term hereafter) soil respiration responses to warming. Our results showed that increased soil respiration rates with short-term warming observed in areas with high biocrust cover returned to control levels in the longer-term. Warming-induced increases in soil temperature were the main driver of the short-term soil respiration responses, whereas longer-term soil respiration responses to warming were primarily driven by thermal acclimation and warming-induced reductions in biocrust cover. Our results highlight the importance of evaluating short and longer-term soil respiration responses to warming as a mean to reduce the uncertainty in predicting the soil carbon-climate feedback in drylands.

Species‐specific effects of biocrust‐forming lichens on soil properties under simulated climate change are driven by functional traits

“…δ 13 C in soil organic matter (SOM) is c. −26, while in atmospheric CO 2 it is c. −8; Lakatos et al, 2007). Increased soil respiration in biocrust-dominated soils has been reported during the first years of simulated warming and rainfall reduction (Maestre et al, 2013;Escolar et al, 2015;Dacal et al, 2020). However, it would then be expected that P. decipiens, characterized by discontinuous darker squamules (small, scale-like thallus units), should also have higher evaporation rates under these experimental conditions and, simultaneously, capture more water from nonliquid precipitation than more continuous species because of its higher surface area (Raggio et al, 2014).…”

“…total C and N) of both biocrust‐forming lichens and mosses is expected to be reduced with increased temperature and altered rainfall regimes as a result of reduced physiological performance (Reed et al ., 2012), as has been shown along climatic gradients in the field (Concostrina‐Zubiri et al ., 2018). Thus, lichens are expected to play an important role in modulating climate change effects on soil diversity and functioning (Maestre et al ., 2015; Liu et al ., 2016; Dacal et al ., 2020). Understanding how climate change will differentially impact dominant biocrust‐forming lichen species is critical to better forecasting how climate change will impact ecosystem functioning in drylands.…”

Relative humidity predominantly determines long‐term biocrust‐forming lichen cover in drylands under climate change

“…The first one (hereafter Experiment 1) in El Cautivo, where we assessed the sensitivity of lichen physiological processes and cover towards systematic changes in single and combined climate variables. The second experiment (hereafter Experiment 2) mimicked and extended an ongoing climate change experiment in Aranjuez (Dacal et al, 2020;Maestre et al, 2013) to determine the mechanisms leading to the observed changes in biocrust cover and to see how well the model can be transferred to other sites despite the intra-specific physiological variability of D. diacapsis (Lange et al, 1997;Pintado et al, 2005).…”

“…Considering the temporal and spatial scales at which climate change is operating, experiments and field studies have some major limitations. First, they are restricted to relatively small research areas and short time-scales: all experiments conducted to date have been running for 15 years or less (Dacal et al, 2020;Ferrenberg et al, 2015). Second, manipulative climate change treatments potentially introduce unintended side effects that can influence the results (Carlyle et al, 2011) and different manipulation methods can hamper the comparison between studies (Bokhorst et al, 2013;Klein et al, 2005;Ladrón de Guevara et al, 2018).…”

Changes in above‐/below‐ground biodiversity and plant functional composition mediate soil respiration response to nitrogen input

“…To adequately explore the potential mechanisms shaping the responses of autotrophic and heterotrophic respiration to N input, we also evaluated the effects of other environmental (soil temperature, pH, etc. ; Dacal et al., 2020; Luo & Zhou, 2006), plant (gross primary productivity, root biomass, plant functional traits, etc. ; Bardgett et al., 2014) and microbial (soil total phospholipid fatty acids [PLFAs], extracellular enzyme activity, etc.…”