Effects of climate change on soil factors and metazoan microfauna (nematodes, tardigrades and rotifers) in a Swedish tundra soil – a soil transplantation experiment
Introduction
Expected changes in climate due to increased amounts of greenhouse-gases are likely to influence animal and plant communities especially strongly in polar areas. Although changes in the soil system will primarily be caused by changes in vegetation and primary production, there are also direct climatic effects on soil organisms (Whitford, 1992). In tundra soils, significant quantities of nutrients are bound in the peat because of low temperatures and permafrost. An increase in temperature is therefore expected to have dramatic influences on soil organisms and mineralization processes (Billings and Peterson, 1992).
To study the effects of climate change on metazoan microfauna (nematodes, rotifers and tardigrades), microorganisms and mineralization, a soil transplantation experiment was undertaken. Soil blocks were taken from a tundra soil at Abisko, northern Sweden and transferred to nine warmer places in the country.
The changes in soil life induced by such transplantation may be of different kinds. Responses of soil animals to transplantation of soil cores to warmer places have been described by Briones et al. (1997). Changes of substrate properties, vegetation and liberation of bound nutrients may, apart from the direct influences of moisture and temperature, influence performance of various species of soil organisms differently. This can be expected to influence food webs, competitive ability etc., resulting in changes in microfaunal structure, microbial biomass, and amount of mineralized carbon and nitrogen (Clarholm et al., 1981; Ingham et al., 1985; Coleman and Crossley, 1996).
It is well known from various laboratory experiments that microbial feeding nematodes can influence microbial biomass and rate of mineralization (Ingham et al., 1985). When blocks of tundra soil are transferred to warmer places, this should result in an increased rate of mineralization reflected by the increased numbers of certain groups of nematodes and accumulation of inorganic nutrients. The bacterial feeding nematodes have been shown to reflect C and N mineralization rates (Mikola and Setälä, 1998). Little is known about the rates of these changes and how the temperature and moisture will influence them.
In this paper the overall effects of climate change on microfauna, microbial biomass and nitrogen mineralization will be analysed. Increased rates of mineralization were anticipated, especially at warmer sites. It was expected that such changes should stimulate nematodes such as Rhabditida which require a rapid microbial production.
The study is included in the EC-project Diversity effects in grassland ecosystems of Europe (DEGREE). Analysis of data from all participants is found in Ekschmitt et al. (in press).
Section snippets
Transplantation experiment
On the 3–4 June 1996, 18 blocks of peat were taken from the Stordalen mire in the north and transplanted on 5–12 June to nine sites along temperature and moisture gradients in Sweden (Fig. 1). The blocks, measuring 55 cm × 35 cm × 22 cm, were placed in plastic boxes. In the bottom of each box 24 holes (diameter 8 mm) were drilled for drainage and a net (mesh size 1 mm) covered the bottom to prevent larger animals and roots from entering the box from below. The boxes were dug into the soil so that the
Temperature and moisture at the different transplantation sites
Mean and maximum values of soil temperature measurements, and mean and minimum water contents from the blocks are indicated in Table 1 together with measurements of soil temperatures and daily mean precipitation for the period before sampling obtained from the weather stations.
The variation of soil temperature and soil water contents between different sites was large during the summer. These factors did not vary with the latitude but rather with local climate at the sites (Fig. 2). Thus, at
Fluctuations in various components
Multiple linear regression analysis yielded no correlations among nematodes, microbial parameters and nitrogen pools (Ekschmitt et al., in press). The failure of this analysis to reveal causal relationships that may have existed is almost certainly due to the great spatial and temporal variation in the parameters sometimes coupled with pronounced time lags. Thus, for instance conditions that promoted nematode growth or nitrogen mineralization were probably not reflected in the data until some
Acknowledgements
The study was supported by a grant from the European Commission to the project Diversity Effects in Grassland Ecosystems of Europe (ENV4-CT95-0029). The partners in the project are thanked for fruitful cooperation and we are especially grateful to the German and Greek colleagues, who carried out the analyses of microbial and fungal biomass, and inorganic nitrogen. Many people have assisted us in various ways whilst we performed the transplantation experiment and they are all gratefully
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