Elevated CO₂ and temperature increase soil C losses from a soybean–maize ecosystem

Abstract

Warming temperatures and increasing CO are likely to have large effects on the amount of carbon stored in soil, but predictions of these effects are poorly constrained. We elevated temperature (canopy: +2.8 °C; soil growing season: +1.8 °C; soil fallow: +2.3 °C) for 3 years within the 9th-11th years of an elevated CO (+200 ppm) experiment on a maize-soybean agroecosystem, measured respiration by roots and soil microbes, and then used a process-based ecosystem model (DayCent) to simulate the decadal effects of warming and CO enrichment on soil C. Both heating and elevated CO increased respiration from soil microbes by ~20%, but heating reduced respiration from roots and rhizosphere by ~25%. The effects were additive, with no heat × CO interactions. Particulate organic matter and total soil C declined over time in all treatments and were lower in elevated CO plots than in ambient plots, but did not differ between heat treatments. We speculate that these declines indicate a priming effect, with increased C inputs under elevated CO fueling a loss of old soil carbon. Model simulations of heated plots agreed with our observations and predicted loss of ~15% of soil organic C after 100 years of heating, but simulations of elevated CO failed to predict the observed C losses and instead predicted a ~4% gain in soil organic C under any heating conditions. Despite model uncertainty, our empirical results suggest that combined, elevated CO and temperature will lead to long-term declines in the amount of carbon stored in agricultural soils.

Increased temperatures may safeguard the nutritional quality of crops under future elevated CO2 concentrations

“…Alternatively, a ‘dilution’ of nutrients by elevated CO 2 has been proposed as another potential mechanism driving the decrease in nutrition in crops (Chaturvedi et al ., ), and may contribute to our observed responses. Warmer soils associated with the heating treatment (Black et al ., ) may also increase the rate at which soil nutrients are taken up by roots through a variety of mechanistic chemical, physical and biological responses to temperature (Pregitzer and King, ). It is likely that the observed responses are driven by a complex interaction involving plant and soil responses to the treatments, necessitating more research to fully refine the underlying mechanisms.…”

Soil moisture controls the spatio-temporal pattern of soil respiration under different land use systems in a semi-arid ecosystem of Delhi, India

“…S R is considered a key process in the terrestrial C cycle, and it releases 98 Pg C per year into the atmosphere (Bilandžija et al 2016;Zhao et al 2017). Any small variation in S R has a significant impact on the carbon dioxide (CO 2 ) concentration in the atmosphere which in turn affects the global C cycle (Black et al 2017). Therefore, understanding the dynamics of the S R in any ecosystem is critical for combatting climate change.…”

Impact of plant species and atmospheric CO2 concentration on rhizodeposition and soil microbial activity and community composition

“…Generally, easily accessible C in form of root exudates can enhance growth and stimulate activity of soil microorganisms, leading to decomposition of more polymerized SOM (rhizosphere priming effect (RPE); Kuzyakov , ). As a result, both the increase in root biomass ( Allard et al, ) and the increase in the amount of C exuded ( Allard et al, ) may enhance soil microbial growth ( Blagodatskaya et al, ) and activity ( Allard et al, ; Black et al, ) under eCO 2 leading to increased SOM mineralization. Moreover, plant species can also strongly influence the mineralization of SOM.…”