Abstract
Microbial processes, including extracellular enzyme (exoenzyme) production, are a major driver of decomposition and a current topic of interest in Arctic soils due to the effects of climate warming. While enzyme activity levels are often assessed, we lack information on the specific location of these exoenzymes within the soil matrix. Identifying the locations of different soil enzymes is needed to improve our understanding of microbial and overall ecosystem function. Using soil obtained from Utqiaġvik, Alaska, our objectives in the study are (1) to measure the activity of enzymes in soil pore water, (2) to examine the distribution of activity among soil particle size fractions using filtration, and (3) to cross these particle size fraction analyses with disruption techniques (blending to shred and sonication to further separate clumped/aggregated soil materials) to assess how tightly bound the enzymes are to the particles. The results of the soil pore water assays showed little to no enzyme activity (<0.05 nmol g soil–1 h–1), suggesting that enzymes are not abundant in soil pore water. In the soil cores, we detected activity for most of the hydrolytic enzymes, and there were clear differences among the particle size and disruption treatments. Higher activities in unfiltered and 50-µm filters relative to much finer 2-µm filters suggested that the enzymes were preferentially associated with larger particles in the soil, likely the organic material that makes up the bulk of these Arctic soils. Furthermore, in the sonication + blending treatment with no filter, 5 of 6 hydrolytic enzymes showed higher activity compared to blending only (and much higher than sonication only), further indicating that enzyme–substrate complexes throughout the organic matter component of the soil matrix are the sites of hydrolytic enzyme activity. These results suggest that the enzymes are likely bound to either the producing microbes, which are bound to the substrates, or directly to the larger organic substrates they are decomposing. This close-proximity binding may potentially minimize the transport of decomposition products away from the microbes that produce them.
Highlights
Decomposition of organic matter in soils is driven by microbial biochemical activity, by producing hydrolytic and oxidative enzymes (Skujinscaron and Burns, 1976; Burns, 1982)
This study aims to explore the possible location of Arctic soil enzymes within the soil matrix using various separation techniques
Soil pore water enzyme assay Activities of 4 of the 6 enzymes were detectable from the assays conducted on soil water from the rhizon sampler technique used to collect soil pore water (Figure 3)
Summary
Decomposition of organic matter in soils is driven by microbial biochemical activity, by producing hydrolytic and oxidative enzymes (Skujinscaron and Burns, 1976; Burns, 1982). There are many distinct locations within the soil matrix where these enzymes might operate, such as free-floating in soil pore water, attached to the microbial cells, linked with enzyme–substrate complexes, associated with soil organic matter (SOM; Burns, 1982), or associated with clay–enzyme or tannin–enzyme complexes (Burns, 1986; Marx et al, 2005). Arctic soils are an especially relevant system to study the location of enzyme activities because of the possibility for accelerated decomposition due to climate change (Schuur et al, 2015) These soils remain frozen for most of the year, and the low temperatures preserve decomposed material in the surface layers (Weintraub and Schimel, 2003; Walz et al, 2017).
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
