Estimation of oxygen consumption of lithobiid field populations from laboratory measurements.

The oxygen consumption of two lithobiid populations in an old beech stand in the Solling is estimated. Respiration of single individuals was determined at different temperatures in a Warburg respirometer. Respiration rate depends exponentially on temperature (Q10 about 3). Respiration per unit weight decreases considerably with increasing weight in Lithobius mutabilis, whereas in Lithobius curtipes these differences are much lower. With regard to the transferability of the laboratory values to field conditions, the error introduced by use of an arithmetic temperature mean instead of integration over the actual temperature cycle is estimated. Respiration values determined with arithmetic and biological (after Nielsen 1978) temperature means are compared. It is shown that under the temperature conditions in the Solling the use of an arithmetic instead of a biological daily temperature mean (based on hourly temperature readings), and the use of an arithmetic instead of a biological monthly temperature mean (based on arithmetic daily means) only give slight underestimates, about 0.8% and 1.2% respectively. The use of an arithmetic instead of a biological annual mean (based on arithmetic monthly means) gives an underestimate of 14%. The influence of other factors affecting the Warburg apparatus is discussed. It is concluded that the metabolism of L. mutabilis and L. curtipes measured in a Warburg respirometer should be multiplied by a factor of about 1.75 to give an estimate of respiration in the field. The population of L. mutabilis respires 5.5×1.75=9.63 kJm-2 year-1, the population of L. curtipes 2.2×1.75=3.85 kJ m-2 year-1. The results obtained are compared with a short-cut method proposed by Phillipson (1970), the "best estimate". Possible improvements of the method are discussed.