Long‐term and contemporary environmental conditions as determinants of the species composition of bog organisms

SUMMARY 1. Environmental change alters ecosystem processes, minding biogeochemical cycles. These changes are accompanied by shifts in species composition. We predicted that long-term averages of environmental variables would explain more of the variability in species composition than short-term assessments, but that this difference would be weaker for short-lived organisms. We further predicted that short-lived organisms with rapid dispersal would reflect recent environmental change. 2. In 51 plots of ombrotrophic summit bogs in two mountain ranges of Central Europe, we sampled the contemporary species composition of vascular plants, bryophytes, diatoms and testate amoebae. In the same plots, water chemistry (pH, conductivity, Ca, Mg, Na, K, Al, Fe, Pb, Hg, Zn, humic acids, ammonium, nitrates, nitrites, phosphates, sulphates and chlorides) and water level were monitored three times per year for 15 years. We tested species–environmental relationships using Mantel tests and canonical correspondence analyses with Monte Carlo permutation tests for overall, within-bog and between-bog effects. 3. The species composition of all four taxa changed along a natural gradient of water level. Diatoms and testate amoebae also changed along a pH/calcium gradient, which has appeared recently in one of the study regions because of aerial liming of forests. Only diatoms reflected variations in humic acid concentration. Spot measurements of environmental factors were sufficient to describe the general pattern while significant effects of phosphates for diatoms and bryophytes, nitrites for vascular plants, potassium for vascular plants and testate amoebae, sodium for all groups except diatoms and sulphates for bryophytes and testate amoebae were evident only by using medium- or long-term averages. 4. Although only long-term averages of some environmental variables were sufficient to explain species compositions, major patterns were revealed by single (spot) samples. The explanatory power of long- and short-term environmental conditions did not differ substantially between micro- and macroorganisms, although short-lived and well-dispersed microorganisms reflected the new pH/ calcium gradient.