Hans Göransson (Bangor University, United Kingdom), Harry Olde Venterink & Erland Bååth
"Bacterial growth limitation during primary succession in the Alps"


During stages of primary succession there are only small amounts of C and N available for bacteria and plants. In this study we investigated which factor (C, N or P) limits bacterial growth along a 138 year long chronosequence formed by a glacier retreat. This was done by adding labile sources of C, N and P to soil samples and measuring the bacterial growth response (Leucine incorporation) after a 40 h incubation period. The bacteria were never found to be limited by N or P. On the youngest soils nor C, N or P induced a bacterial growth which indicate co-limitation. On older soils the bacteria was found to be C-limited. The shift from where the bacteria did not respond to C to being C-limited was related to the C:N ratio in the soil where the C-limitation occurring only on soils with a C:N ratio below 13.4 (w/w). The increase in growth response to C addition with increasing soil age suggests that N becomes relatively more available to bacteria as compared to C as the soil develops.