Seasonal variation in enzyme activities and temperature sensitivities in Arctic tundra soils

Abstract

Arctic soils contain large amounts of organic matter due to very slow rates of detritus decomposition. The first step in decomposition results from the activity of extracellular enzymes produced by soil microbes. We hypothesized that potential enzyme activities are low relative to the large stocks of organic matter in Arctic tundra soils, and that enzyme activity is low at in situ temperatures. We measured the potential activity of six hydrolytic enzymes at 4 and 20 1C on four sampling dates in tussock, intertussock, shrub organic, and shrub mineral soils at Toolik Lake, Alaska. Potential activities of N-acetyl glucosaminidase, b-glucosidase, and peptidase tended to be greatest at the end of winter, suggesting that microbes produced enzymes while soils were frozen. In general, enzyme activities did not increase during the Arctic summer, suggesting that enzyme production is N-limited during the period when temperatures would otherwise drive higher enzyme activity in situ. We also detected seasonal variations in the temperature sensitivity (Q 10 ) of soil enzymes. In general, soil enzyme pools were more sensitive to temperature at the end of the winter than during the summer. We modeled potential in situ b-glucosidase activities for tussock and shrub organic soils based on measured enzyme activities, temperature sensitivities, and daily soil temperature data. Modeled in situ enzyme activity in tussock soils increased briefly during the spring, then declined through the summer. In shrub soils, modeled enzyme activities increased through the spring thaw into early August, and then declined through the late summer and into winter. Overall, temperature is the strongest factor driving low in situ enzyme activities in the Arctic. However, enzyme activity was low during the summer, possibly due to N-limitation of enzyme production, which would constrain enzyme activity during the brief period when temperatures would otherwise drive higher rates of decomposition.

Enzymes in the rhizosphere of plants growing in the vicinity of the Polish Arctowski Antarctic Station

“…The enzyme most sensitive to the temperature change was b-glucosidase (68-78% reduction with temperature decrease) and the least sensitive was urease (55-56% reduction). It has been observed in Alpine and Arctic tundra soils that C mineralization is more sensitive to low temperatures than N mineralization, which is a result of different sensitivities of the enzymes participating in the cycles of these elements (Koch et al 2007;Wallenstein et al 2009;2011;Jing et al 2014 …”

Lasting effect of soil warming on organic matter decomposition depends on tillage practices

“…Numerous studies have reported that increased temperature significantly alters microbial community structure and functioning by affecting substrate and nitrogen availability (Melillo et al, 2011;Bradford, 2013;Steinweg et al, 2013;DeAngelis et al, 2015). However, an understanding of microbial feedback to global warming remains limited, especially for the utilization of substrate and microbial activity associated with soil C cycling (Wallenstein et al, 2009).…”

High-throughput Fluorometric Measurement of Potential Soil Extracellular Enzyme Activities

“…The abundance of different C-, N-, and P-degrading enzymes in soils is controlled by numerous factors including microbial biomass, community composition, substrate availability, microclimate, and stoichiometric demands 5,6 . However, in situ EEAs within the soil environment are also affected by temperature 7,8 , the binding of enzymes to soil clays and humic properties 18,19 . MUC-linked substrates are commonly associated with N-rich synthetic substrates such as proteins and/or amino acids.…”