Contribution of Root and Rhizosphere Respiration of Haloxylon ammodendron to Seasonal Variation of Soil Respiration in the Central Asian Desert

Soil respiration originates from both soil organic matter decomposition (Rd) and root and rhizosphere respiration (Rr). In order to evaluate implications of soil biotic and abiotic variables for soil carbon cycling and sequestration, a better understanding how the contributions of these two components to soil respiration is required. Furthermore, quantifying the components of net soil respiration is essential for understanding soil biological processes response to climate change.

The gap formation method is a procedure that indirectly estimates Rr from the difference in soil respiration rates between the plot under the crown and a plot between in the gap. In the Central Asian desert, the sparse distribution of Haloxylon ammodendron provides a natural gap for studying CO2 flux from roots and its associated rhizosphere microbial organisms. A research team from Xinjiang Institute of Ecology and Geography took the H. ammodendron as an example to explore a gap formation approach and measure Rr originating from soil organic matter decomposition (Rd) and quantify the contribution of Rr and Rd to total soil respiration or response to soil variables on seasonal time scales.

Soil CO2 efflux rate in situ was correlated with key soil biotic (e.g. fungal, bacterial and actinomycetes populations) and abiotic (e.g. soil moisture, temperature, pH and organic carbon concentration) variables. Root and rhizosphere respiration originating from soil organic matter decomposition (Rd) were estimated from Rc (soil respiration under the crowns of H. ammodendron) and Rg (soil respiration in the gaps between H. ammodendron) of H. ammodendron. Contribution of Rr to total soil respiration ranged from 13% to 94% during the growing season. Correlations of Rr with soil temperature and moisture were significant, but Rd was not significantly correlated with soil temperature and moisture. Microbial biomass, pH, soil organic carbon (SOC), total nitrogen (TN) and calcium carbonate (CaCO3) were analyzed in the soil. Rd with soil biomass and SOC were significantly correlated, whereas Rr was not significantly correlated with soil biomass and SOC. Effects of pH value, TN and CaCO3 on the two components of soil respiration (Rr and Rd) were not significant. Taken together, the data suggest that factors affecting seasonal changes of respiration were different between the two components of soil respiration: Rr was more sensitive to changes of temperature and moisture than Rd.

The study was supported by the National 973 project, the National Project and the Key National Natural Science Foundation. This work has been published on Quaternary International, 2011, 244(2): 304-309. This paper is also archived at http://www.sciencedirect.com/science/article/pii/S1040618210004337.