Microbial CO2 production from surface and subsurface soil as affected by temperature, moisture, and nitrogen fertilisation

Abstract

The Sanjiang Plain of north-east China is presently the second largest freshwater marsh in China. The drainage and use of marshes for agricultural fields occurred in the past 50 years, resulting in the increase in cultivated land from about 2.9 × 108 m2 in 1893 to 4.57 × 1010 m2 in 1994. Under human disturbance in the past half century, the environment in Sanjiang Plain has had significant change. We hypothesised that environmental factors such as soil moisture, soil temperature, and soil N levels affect the rates of soil organic C mineralisation and the nature of the controls on microbial CO2 production to change with depth through the soil profile in the freshwater marsh in the Sanjiang Plain. In a series of experiments, we measured the influence of soil temperature, soil water content, and nitrogen additions on soil microbial CO2 production rates. The results showed that Q10 values (the factor by which the CO2 production rate increases when the temperature is increased by 10°C) significantly increased with soil depth through the soil profile (P < 0.05). The average Q10 values for the surface soils were 2.7 (0–0.2 m), significantly lower than that (average Q10 values 3.3) for the subsurface samples (0.2–0.6 m) (P < 0.05), indicating that C mineralisation rates were more sensitive to temperature in subsurface soil horizons than in surface horizons. The maximum respiration rate was measured at 60% water hold capacity for each sample. The quadratic equation function adequately describes the relationship between soil respiration and soil water content, and the R2 values were > 0.80. The sensitivity of microbial CO2 production rate response to soil water content for surface soils (0–0.2 m) was slightly lower than for subsurface soils (0.2–0.6 m). The responses of actual soil respiration rates to nitrogen fertilisation were different for surface and subsurface soils. In the surface soils (0–0.2 m), the addition of N caused a slight decreased in respiration rates compared with the control, whereas, in the subsurface soils (0.2–0.6 m), the addition of N tended to increase microbial CO2 production rates, and the addition of 10 µg N/g soil treatment caused twice the increase in C mineralisation rates of the control. Our results suggested that the responses of microbial CO2 production to changes in soil moisture, soil temperature, and soil N levels varied with soil depth through the profile, and subsurface soil organic C was more sensitive to temperature increase and nitrogen inputs in the freshwater marsh of the Sanjiang Plain.

Labile substrate availability controls temperature sensitivity of organic carbon decomposition at different soil depths

“…However, previous studies have shown inconsistent patterns of Q 10 values of soil respiration with soil depth. Increase (Lomander et al 1998;Fierer et al 2003;Jin et al 2008;Karhu et al 2010), decrease (Winkler et al 1996;MacDonald et al 1999;Gillabel et al 2010), or no changes (Fang et al 2005;Leifeld and Fuhrer 2005;Rey et al 2008) in apparent Q 10 values with increasing soil depth have been observed in different studies. Much of the variation in the apparent temperature sensitivity of SOC decomposition may be related to the fact that labile substrate availability is often unaccounted for in these studies Gershenson et al 2009;Conant et al 2011).…”

The Role of Soil CO2 Efflux in the Global Carbon Cycle: An Evaluation of Importance and Controls

“…Serving primarily as a determinant of respiration rates, both for autotrophic and heterotrophic biomass, increases in soil and air temperature have demonstrated exponential increases in the associated CO 2 efflux (Jin et al, 2008). Figure 6 demonstrates the diurnal fluctuation of soil temperature and soil respiration; as seen, these two factors display covariance, maintaining approximate similarity throughout the sample period.…”

“…Climate change scenarios also predict an increase in the demand for key nutrients (van Veen et al, 1991); initial increases in N may result in rapid yet unstable consumption of soil organic matter that would lead to an overall reduction in soil respiration rates with time (Jin et al, 2008). This situation raises questions about the sensitivity of soil communities, with primary focus being given to subsurface soils.…”

“…In the face of climate change, mineralization rates are expected to increase as a result of increased temperature (Jin et al, 2008). Higher rates of respiration coincide with shorter turnover times and increased availability of key nutrients.…”

“…Figure 6 demonstrates the diurnal fluctuation of soil temperature and soil respiration; as seen, these two factors display covariance, maintaining approximate similarity throughout the sample period. When plotted against there exists a large degree of heterogeneity within soil horizons (Pumpanen et al, 2003); temperature means and maxima within each horizon can dictate the production of both aboveground and belowground biomass as well as determine microbial community structures within the soil (Jin et al, 2008).…”