Oat straw, hay, and alfalfa litter, differing in microbial colonization and recalcitrance, were added to organic matter-free quartz sand (5 mg C [g material](-1)) and incubated in the laboratory at 5 degrees C, 10 degrees C, 15 degrees C, 20 degrees C, and 25 degrees C. Different incubation periods were chosen so that theoretically the same amounts of CO(2) would be produced and the same amounts of O(2) would be consumed for each litter type. It was investigated whether Q(10) values (change in respiration rate between two temperatures) increase with decreasing temperature and how much these Q(10) values and also the respiratory quotient (RQ: mol CO(2)/mol O(2)) depend on the litter type. The sums of CO(2)-C evolved and O(2) consumed, but also the contents of microbial biomass C and microbial biomass N showed a nearly 7-fold increase in the order oat straw < hay < alfalfa litter. In contrast, the ratio of the fungal cell-membrane component ergosterol to microbial biomass C was highest in the oat straw (4.1 parts per thousand) and lowest in the alfalfa litter (0.2 parts per thousand). This ratio reached a similar level between 5 degrees C and 15 degrees C (1.9 parts per thousand), significantly higher (p = 0.01) than the level at 20 degrees C (0.9 parts per thousand). Respiration was similar between 20 degrees C and 25 degrees C, with a mean Q(10) value of 1.9. The use of temperature rate-modifying factors suggested by the carbon-turnover model ROTHC revealed that the incubation period for similar respiration rates was underestimated at 5 degrees C and overestimated at 25 degrees C. The lignin-poor and protein-rich alfalfa litter showed the highest Q(10) values of the three litter types in the medium temperature range of 10 degrees C to 20 degrees C. In contrast, the lignin-rich and protein-poor oat straw showed significantly highest Q(10) values at 5 degrees C and 25 degrees C in comparison with the other two litter types. The RQ was significantly highest in the hay litter (1.05) and in comparison with alfalfa litter (0.97) and oat straw (0.92). Strong temperature-dependent variations in Q(10) values and respiratory quotients suggest interactions between litter quality, microbial colonization of litter, and temperature, which warrants further investigation.
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