Changes in microbial heterotrophic diversity along five plant successional sequences

Abstract

Little is known about the changes in microbial diversity associated with ecosystem development. We measured microbial heterotrophic evenness (a component of diversity) and other soil/humus properties (including basal respiration, substrate-induced respiration, pH, total C, N and P) at different stages in the development of five different ecosystems, with plant assemblages being used to define the phase in the successional sequence. Our objectives were to determine whether there were common patterns in establishment of microbial heterotrophic evenness with ecosystem development and whether changes in evenness were correlated to soil properties. Samples were collected from five sequences: Gisborne land slips (a chronosequence of re-vegetating landslip scars); Mount Tarawera (primary succession on aerially-deposited ash from a volcanic eruption); Rangitoto island (primary succession on a lava flow from a volcanic eruption); Franz Josef (primary succession initiated on gravels after the retreat of a glacier); and Swedish islands (a series of islands of differing size supporting different stages of plant succession). Heterotrophic diversity was measured using the catabolic response profile technique where CO2 efflux is measured during a 4-h incubation of samples amended with 25 different carbon substrates. Heterotrophic evenness was calculated from the CO2 responses using the Simpson–Yule index (maximum possible is 25). For Tarawera and Gisborne sequences, heterotrophic evenness was significantly lower at the first stage of succession (11.5 and 19.9, respectively), but subsequently plateaued, ranging between 21 and 23. Heterotrophic evenness declined significantly with succession at Rangitoto and Franz Josef sequences, but there was no trend along the Swedish island sequence. Despite the lack of a common pattern of heterotrophic evenness along all the sequences, there were significant linear correlations between heterotrophic evenness and basal respiration for Rangitoto (r=0.51, P<0.01), Gisborne (r=0.88, P<0.01) and the Swedish islands sequences (r=0.52, P<0.01), while the relationship was marginal at Franz Josef (r=0.69, P<0.06), but not significant at the Tarawera sequence. Plant evenness along two sequences (Rangitoto and Swedish islands) was not correlated with heterotrophic evenness. These data suggest that heterotrophic evenness re-establishes rapidly following major disturbance once organic matter inputs occur then subsequently declines. Patterns of change in heterotrophic evenness may, in part, be dependent on changes in the availability of organic carbon or resources to heterotrophs.