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A Proposed Mechanism for the Pulse in Carbon Dioxide Production Commonly Observed Following the Rapid Rewetting of a Dry Soil

Dep. of Ecology, Evolution, and Marine Biology, Univ. of California, Santa Barbara, CA 93106

View larger version (14K): [in a new window]   Fig. 1. A schematic diagram (not to scale) illustrating the time course of events and the soil water potentials during the experiment. Oak and grass soil samples were adjusted to identical soil water potentials. * equals a set of samples were destructively harvested for unfumigated and fumigated extractions. Dashed lines indicate the time periods during which we monitored CO2 and 14C-CO2 production.

View larger version (16K): [in a new window]   Fig. 2. Rates of total CO2 production before and after rewetting. Carbon dioxide production was not monitored during the drying period, Day 11 to Day 13. Error bars represent ±1 standard error of the means (N = 4).

View larger version (20K): [in a new window]   Fig. 3. Carbon-14 labeled CO2 release rates (2a) and the enrichment of respired CO2 (2b) before and after rewetting. Error bars represent ±1 standard error of the means (N = 4).

View larger version (30K): [in a new window]   Fig. 4. The amount (3a) and enrichment (3b) of extractable microbial biomass C recovered from oak and grass soils at three time points during the experiment. Error bars represent 1 standard error of the means (N = 4). Means denoted by the same letter do not differ significantly (P > 0.05).

View larger version (23K): [in a new window]   Fig. 5. The total amount (4a) of extractable-organic C from an unfumigated extraction with 0.5 M K2SO4 and the enrichment of the extracted C (4b). Error bars represent 1 standard error of the means (N = 4). Means denoted by the same letter do not differ significantly (P < 0.05).

View larger version (23K): [in a new window]   Fig. 6. A schematic diagram illustrating the changes in C pools before drying and after the rewetting of the dried soil. The carbon pools and the arrows showing the contribution of each of these C pools to total CO2 production are conceptual representations of the hypotheses presented in this paper. Carbon pool size, in micrograms of C per gram of soil (µg C g soil-1)(values not in parentheses), and 14C enrichment, in becquerels of 14C per gram of C (Bq 14C g C-1)(values in parentheses), are indicated for each box. The size and enrichment of each C pool are estimated based on our measurements for the oak soil. The size of each box is equivalent to the estimated size of the carbon pool. We hypothesize that cytoplasmic solutes (indicated by the dashed box) are the major source of C mineralized after rewetting, however, the size and enrichment of this pool could not be directly measured.