Temperature sensitivity of mineral soil carbon decomposition in shrub and graminoid tundra, west Greenland

Abstract

Background: Shrub expansion is transforming Arctic tundra landscapes, but the impact on the large pool of carbon stored in high-latitude soils is poorly understood. Soil carbon decomposition is a potentially important source of greenhouse gases, which could create a positive feedback to atmospheric temperature. Decomposition is temperature sensitive, but the response to temperature can be altered by environmental variables. We focus on mineral soils, which can comprise a substantial part of the near-surface carbon stock at the landscape scale and have physiochemical characteristics that influence temperature sensitivity. We conducted a soil incubation experiment to measure carbon dioxide (CO 2) emissions from tundra soils collected from west Greenland at two depths of mineral soils (0-20 cm and 20-40 cm below the surface organic horizon) incubated at five temperatures (4, 8, 12, 16, 24°C) and two moisture levels (40 % and 60 % water holding capacity). We used an information theoretic model comparison approach to evaluate temperature, moisture and depth effects, and associated interactions, on carbon losses through respiration and to determine the temperature sensitivity of decomposition in shrub-and graminoid-dominated soils. Results: We measured ecologically important differences in heterotrophic respiration and temperature sensitivity of decomposition between vegetation types. Graminoid soils had 1.8 times higher cumulative respiration and higher temperature sensitivity (expressed as Q-10) in the shallow depths (Q-10 graminoid = 2.3, Q-10 shrub = 1.8) compared to shrub soils. Higher Q-10 in graminoid soils was also observed for the initial incubation measurements (Q-10 graminoid = 2.4, Q-10 shrub = 1.9). Cumulative respiration was also higher for shallow soils, increased with moisture level, and had a temperature-depth interaction. Increasing soil moisture had a positive effect on temperature sensitivity in graminoid soils, but not in shrub soils. Conclusion: Mineral soil associated with graminoid-dominated vegetation had greater carbon losses from decomposition and a higher temperature sensitivity than shrub-dominated soils. An extrapolation of our incubation study suggests that organic carbon decomposition in western Greenland soils will likely increase with warming and with an increase in soil moisture content. Our results indicate that landscape level changes in vegetation and soil heterogeneity are important for understanding climate feedbacks between tundra and the atmosphere.

Phosphorus rather than nitrogen enhances CO2 emissions in tropical forest soils: Evidence from a laboratory incubation study

“…With C addition, CO 2 emission rate increased dramatically and showed a pulse response, whereas a monotonic declining pattern was observed for all soils without C addition (Figures 1 and 3). This supports the idea that the microorganisms in the soils collected from the field might have limited access to readily available C. The pulse response pattern is common in response to C substrate addition (Cleveland et al, 2002;Kuzyakov, 2010;Tian et al, 2014), although some incubation studies report a decline of CO 2 emission rates due to rapid metabolism of the labile C substrate (e.g., Bradley-Cook, Petrenko, Friedland, & Viginia, 2016;Jing et al, 2017;Tian et al, 2014;Zhou, Hui, & Shen, 2014). Increasing emissions with C addition could indicate the growth of the microbial population, decomposition of the added labile substrate and/or increasing microbial activity through the priming (Blagodatskaya & Kuzyakov, 2008;Blagodatsky et al 2010;Mehnaz et al 2019).…”

Impact of understory vegetation on soil carbon and nitrogen dynamic in aerially seeded Pinus massoniana plantations

“…Understory vegetation participates in the nutrient cycling of soil C and N process through several different ways. The graminoid vegetation has a fibrous root system, with higher decomposition rates compared with the rhizomes of Dicranopteris , which would potentially increase soil organic matter inputs [ 40 , 41 ]. Additionally, due to differences in functional traits, understory vegetation types might alter litter decomposition rates and microbial activities by affecting soil moisture, temperature, and other environmental factors [ 42 , 43 ].…”

Comparison of carbon and nitrogen storage in mineral soils of graminoid and shrub tundra sites, western Greenland

“…Johnson et al (2011) reported higher C pools under graminoid than shrub vegetation for both organic and mineral soil. Furthermore, Bradley-Cook et al (2016) found that microbial respiration in graminoid mineral soils is more sensitive to increases in temperature than shrub mineral soils, suggesting vulnerability of the graminoid soil C pool to changes in climate. This study contributes an original data set on mineral soil C and N pools in two dominant Arctic tundra vegetation types and provides baseline data to which future shifts in vegetation and changes in C and N pools can be compared.…”