Under climatic change, soil microbial community and variables relating to N-cycle are modulated by changes in the upper limit temperature

The effect of temperature increase and more specifically its upper and low level correlates on soil
microbial biomass, activity and N-cycle variables was studied in a Mediterranean shrubland.
Experimental manipulation succeeded in establishing three treatments which, in comparison with the
monthly ambient temperature, displayed an increase in mean monthly temperature by 2.1, 4.9 and
7.4 oC respectively. Also the upper limit temperature values (Tmax), but not the low limit counterparts
(Tmin), differed significantly among the three treatments. Tmax changes seemed to affect directly only
the microbial biomass, while it exerted an indirect effect on the majority of the other soil variables.
With increased Tmax the values of the estimated soil microbial variables (microbial biomass and
activity) increased, while other soil chemical variables, such as the inorganic forms of N, were found
reducing. Organic N was the only variable remaining independent from changing Tmax at any
treatment. The results of this paper indicate that the level of Tmax increase could be crucial for the
structure of the microbial community. A Tmax increase up to 7 oC induced by climate change could
favour the dominance of the soil bacterial populations, while larger increases could be in favour of
the fungal populations.