A keystone microbial enzyme for nitrogen control of soil carbon storage
We used Web of Science (http://apps.webofknowledge.com/), google scholar (http://scholar.google.com/) and China National Knowledge Infrastructure (http://www.cnki.net/) for an exhaustive search of articles published before March 2018. The keywords and phrases used for literature research were: (1) “nitrogen addition” or “nitrogen amendment” or “nitrogen enrichment” or “nitrogen fertilizer” or “nitrogen elevated” or “nitrogen deposition”, and (2) “glucosidase” or “cellobiosidase” or “xylosidase” or “peroxidase” or “phenol oxidase” or “polyphenol oxidase” or “ligninase” or “cellulase”, and (3) “soil carbon”, and (4) “terrestrial” or “soil” or “land”.
To be included in our dataset, articles had to meet several requirements. First, we only considered experiments that lasted at least one year. Second, control and N addition treatments had to be applied at the same experimental site; that is, the microclimate, vegetation, and soil types were similar between treatments. Third, standard deviations and replicates had to be reported or could be derived from the results. Fourth, details on N addition methods (rate, frequency, form, and duration) had to be provided. We identified 40 papers that met these criteria.
For each study, we recorded linginase and cellulase activities, site location (longitude and latitude), climatic variables (mean annual precipitation (MAP), mean annual temperature (MAT)), elevation, background N deposition (BND), vegetation and soil types and N addition methods (rate, duration, frequency and form of N addition). If these data were not reported, we contacted the corresponding author for more information. Otherwise, we obtained MAT and MAP from WorldClim Database (http://www.worldclim.org/), BND from Global N deposition database (http://webmap.ornl.gov/), vegetation types from the Whittaker Biome Diagram, and soil types from FAO classification (http://www.fao.org/soils-portal/soil-survey/soil-classification/usda-soil-taxonomy/en). Where available, we also tabulated plant productivity, soil pH, soil C:N, microbial abundance, soil texture and recalcitrant C pool.
