Decay rates as a function of water availability and temperature for extracellular enzymes from mesophiles and thermophiles at three different soils. Figrure 2 [Dataset]

Besides the effect of temperature, EEA decay is also affected by water availability (Figure 2). At low aw values (i.e., under dry conditions) an increased variability in the decay response of the enzymes was observed. Significant ifferences of decay rates were observed for glucosidase, phosphatase and protease activities at different water activities (P< 0.005, 0.005 and 0.04, respectively. MRPP analysis). The response of the three tested EEAs was significantly different (P< 0.001. MRPP analysis). For example, at aw 0.5 (which represent conditions below the potential growth of any microorganism; Stevenson et al. 2015) maximum decay rates were frequently observed for different enzymes in distinct soils indicating adverse conditions for both microorganisms and their extracellular enzymes (Figure 2). Most enzymes in different soils presented lowest decay rates at aw 0.7 which represents quite dry conditions close to the lowest aw limit for microbial growth. The lowest aw value assayed (aw 0.3; extreme dry soil conditions) presented very low decay rates as a consequence of very poor measurable EEA indicating that at these conditions a residual activity of microbial extracellular enzymes is maintained in soils. Ordination by NMDS analysis of the different parameters tested (i.e., temperature, water availability, soils) for the decay of studied EEAs confirmed increased differentiation on decay rates when reducing water availability (Figure 3). In most casesdecay rates at aw 1 and aw 0.7 were located in proximity whereas the highest divergence was observed for aw 0.5 and aw 0.3 (the most dried conditions). NMDS stress values for glucosidase, phosphatase and protease activities were 0.07, 0.06 and 0.04, respectively, suggesting excellent representations of decay rates observed for the tested enzymes under the variety of analyzed conditions. The decay at 60ºC of enzymes from thermophiles showed minimum distance among the three EEAs tested. Generally, the most dispersed decays between the different soils were observed for EEA decay at 20ºC for mesophilic and thermophilic microorganisms. These results suggested an homogeneous behavior of hightemperature enzymes under elevated temperatures showing high persistence. At moderate temperature (20ºC) the results for EEA decay from mesophilic and thermophilic microorganisms showed different responses.