Research

Organic matter flow in the food web at a temperate heath under multifactorial climate change

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Abstract

The rising atmospheric CO2 concentration, increasing temperature and changed patterns of precipitation currently expose terrestrial ecosystems to altered environmental conditions. This may affect belowground nutrient cycling through its intimate relationship with the belowground decomposers. Three climate change factors (elevated CO2, increased temperature and drought) were investigated in a full factorial field experiment at a temperate heathland location. The combined effect of biotic and abiotic factors on nitrogen and carbon flows was traced in plant root → litter → microbe → detritivore/omnivore → predator food‐web for one year after amendment with 15N13C2‐glycine. Isotope ratio mass spectrometry (IRMS) measurement of 15N/14N and 13C/12C in soil extracts and functional ecosystem compartments revealed that the recovery of 15N sometimes decreased through the chain of consumption, with the largest amount of bioactive 15N label pool accumulated in the microbial biomass. The elevated CO2 concentration at the site for 2 years increased the biomass, the 15N enrichment and the 15N recovery in detritivores. This suggests that detritivore consumption was controlled by both the availability of the microbial biomass, a likely major food source, and the climatic factors. Furthermore, the natural abundance δ13C of enchytraeids was significantly altered in CO2‐fumigated plots, showing that even small changes in δ13C‐CO2 can be used to detect transfer of carbon from primary producers to detritivores. We conclude that, in the short term, the climate change treatments affected soil organism activity, possibly with labile carbohydrate production controlling the microbial and detritivore biomass, with potential consequences for the decomposition of detritus and nutrient cycling. Hence, there appears to be a strong coupling of responses in carbon and nitrogen cycling at this temperate heath. Copyright © 2011 John Wiley & Sons, Ltd.