Consequences of ten-year abandonment in a subalpine grassland: soil and litter decomposition changes

Woody species encroachment of grasslands is occurring worldwide with contrasting consequences for ecosystem processes. This work aims to describe the changes in soil and litter decomposition following the early stages of colonization in a subalpine grassland located in the Alps. We investigated soil properties onto O and A horizons, and carried out a 1-year decomposition experiment to quantify the decomposition rate and describe the qualitative features of the process through Fourier-transform infrared spectroscopy methodology. All the analyses were carried out in an encroached area and the adjacent grassland. Shrubland soil showed higher temperature and moisture compared to grassland, whereas no significant differences were found for pH, ammonium, nitrate, available P, total organic carbon, and total nitrogen, neither in the O nor in the A soil horizon. A significantly higher dissolved organic carbon content was observed in the shrubland A horizon, as well as a higher content of microbial C and N. The decomposition rate was significantly higher in the shrubland soil with no relevant differences about the qualitative aspects of the process. Our results showed that, even in the early stage of the process, when soil chemistry has not changed yet, woody encroachment caused an increase of soil moisture and microbial biomass, which favoured decomposition rate.