Abstract:

Aims Collema tenax is a common N-fixing lichen in arid and semiarid grasslands, where range fire can be an important factor influencing ecosystem structure and function. The response of N-fixing activity of lichens to range fire has received little attention in ecological studies. Our purpose was to investigate the short-term effects of range fire on N fixation of C. tenax.

Methods Three months after a controlled burn at the Inner Mongolian semiarid grassland, we measured plant cover, litter cover and N-fixing activity of C. tenax in both burned plots and control plots. N-fixing activity was measured using acetylene reduction assay. One-Way ANOVA was applied to compare N-fixing activity between treatments.

Important findings At the individual scale, N-fixing activity of C. tenax decreased by 42.3% for individuals with a burned thallus, but increased by 28.4% for those with an intact one, as compared to that observed in unburned plots. These results show counteractive effects of burning on N fixation of C. tenax at individual scale, i.e., 1) negative effect through damage on lichen thallus and potential deterioration in surface water and temperature conditions and 2) positive effect as a result of increased light availability via removal of litter and plant biomass and, to a lesser extent, a fire-induced nutrient pulse on the soil surface. At the population scale, no significant effects of burning on N-fixing activity of this lichen were found, which may be attributable to the counteractive responses of N fixation of C. tenax at the individual scale.

Key words: grassland ecosystem, controlled burning, lichen, N fixation, acetylene reduction assay