Changming Fang

Similar response of labile and resistant soil organic matter pools to changes in temperature

Our understanding of the relationship between the decomposition of soil organic matter (SOM) and soil temperature affects our predictions of the impact of climate change on soil-stored carbon. One current opinion is that the decomposition of soil labile carbon is sensitive to temperature variation whereas resistant components are insensitive. The resistant carbon or organic matter in mineral soil is then assumed to be unresponsive to global warming. But the global pattern and magnitude of the predicted future soil carbon stock will mainly rely on the temperature sensitivity of these resistant carbon pools. To investigate this sensitivity, we have incubated soils under changing temperature. Here we report that SOM decomposition or soil basal respiration rate was significantly affected by changes in SOM components associated with soil depth, sampling method and incubation time. We find, however, that the temperature sensitivity for SOM decomposition was not affected, suggesting that the temperature sensitivity for resistant organic matter pools does not differ significantly from that of labile pools, and that both types of SOM will therefore respond similarly to global warming.

Impact of Global Warming on Soil Organic Carbon

Soils contain a stock of carbon that is about twice as large as that in the atmosphere and about three times that in vegetation. Small losses from this large pool could have significant impacts on future atmospheric carbon dioxide concentrations, so the response of soils to global warming is of critical importance when assessing climate carbon cycle feedbacks. Models that have coupled climate and carbon cycles show a large divergence in the size of the predicted biospheric feedback to the atmosphere. Central questions that still remain when attempting to reduce this uncertainty in the response of soils to global warming are (1) the temperature sensitivity of soil organic matter, especially the more recalcitrant pools; (2) the balance between increased carbon inputs to the soil from increased production and increased losses due to increased rates of decomposition; and (3) interactions between global warming and other aspects of global change, including other climatic effects (e.g., changes in water balance), changes in atmospheric composition (e.g., increasing atmospheric carbon dioxide concentration) and land‐use change. In this chapter, we review trends in warming, factors affecting the response of soil carbon to global warming, evidence on the balance between changes in production and soil organic matter decomposition, recent research on the temperature sensitivity of soil organic carbon pools, methods for measuring soil responses to global warming, approaches to modeling soil responses to global warming, regions/ecosystems likely to be most vulnerable to future warming, and available technologies to reduce vulnerability of soil carbon to the impacts of future global warming.

An improved dynamic chamber technique for measuring CO2 efflux from the surface of soil

1. A new dynamic chamber has been developed with the aim of improving the performance of existing techniques for measuring CO 2 efflux from the soil surface. It has been shown that differences in the flow rates of incoming and outgoing air can be balanced quickly with this new chamber, consequently reducing the pressure difference between the inside and outside of the chamber. In the new chamber, the pressure difference varied within ± 0.2 Pa at flow rates of up to 4 litres min -1 when placed on the soil surface, whereas the corresponding value for an earlier design of chamber was about ± 1.0 Pa. The improved chamber can give a better and a more reliable estimation of CO 2 evolution from the soil surface compared to existing dynamic chambers, as demonstrated by either the magnitude or the trend of daily variation of measured CO2 effluxes. 2. In a dynamic chamber technique, the pressure difference depends mainly upon the flow rate of sample air and the length and diameter of inlet or outlet tubing through which air passes into or out of the chamber. It is difficult to obtain a steady and negligible pressure difference with a normal dynamic chamber, especially if the method employs simultaneously blowing and drawing air, as the pressure difference is very changeable.

Carbon cycle: A warm response by soils

The flux of carbon from soils to the atmosphere has apparently increased with climate warming. But does this reflect a net loss of carbon to the atmosphere that could exacerbate climate change?

Corrigendum: Similar response of labile and resistant soil organic matter pools to changes in temperature

Nature 433, 57–59 (2005) The x axis of Fig. 1 of this Letter was mislabelled. The correct tick labels (from left to right) should read: ‘Root-free soil 0–10 cm’; ‘Intact soil 0–10 cm’; ‘Root-free soil 20–30 cm’; and ‘Intact soil 20–30 cm’. These errors do not affect any of our conclusions.

Similar response of labile and resistant soil organic matter pools to changes in temperature (vol 433, pg 57, 2005)

Nature 433, 57–59 (2005) The x axis of Fig. 1 of this Letter was mislabelled. The correct tick labels (from left to right) should read: ‘Root-free soil 0–10 cm’; ‘Intact soil 0–10 cm’; ‘Root-free soil 20–30 cm’; and ‘Intact soil 20–30 cm’. These errors do not affect any of our conclusions.

Erratum: Similar response of labile and resistant soil organic matter pools to changes in temperature: Corrigendum

Nature 433, 57–59 (2005) The x axis of Fig. 1 of this Letter was mislabelled. The correct tick labels (from left to right) should read: ‘Root-free soil 0–10 cm’; ‘Intact soil 0–10 cm’; ‘Root-free soil 20–30 cm’; and ‘Intact soil 20–30 cm’. These errors do not affect any of our conclusions.