caa a22 4500 605517320 CHVBK 20210128100719.0 cr unu---uuuuu 210128e20151201xx s 000 0 eng 10.1007/s10533-015-0157-5 doi (NATIONALLICENCE)springer-10.1007/s10533-015-0157-5 Chronic nitrogen fertilization and carbon sequestration in grassland soils: evidence of a microbial enzyme link [Elektronische Daten] [Valeria Cenini, Dario Fornara, Geoffrey McMullan, Nigel Ternan, Kate Lajtha, Michael Crawley] Chronic nitrogen (N) fertilization can greatly affect soil carbon (C) sequestration by altering biochemical interactions between plant detritus and soil microbes. In lignin-rich forest soils, chronic N additions tend to increase soil C content partly by decreasing the activity of lignin-degrading enzymes. In cellulose-rich grassland soils it is not clear whether cellulose-degrading enzymes are also inhibited by N additions and what consequences this might have on changes in soil C content. Here we address whether chronic N fertilization has affected (1) the C content of light versus heavier soil fractions, and (2) the activity of four extracellular enzymes including the C-acquiring enzyme β-1,4-glucosidase (BG; necessary for cellulose hydrolysis). We found that 19years of chronic N-only addition to permanent grassland have significantly increased soil C sequestration in heavy but not in light soil density fractions, and this C accrual was associated with a significant increase (and not decrease) of BG activity. Chronic N fertilization may increase BG activity because greater N availability reduces root C:N ratios thus increasing microbial demand for C, which is met by C inputs from enhanced root C pools in N-only fertilized soils. However, BG activity and total root mass strongly decreased in high pH soils under the application of lime (i.e. CaCO3), which reduced the ability of these organo-mineral soils to gain more C per units of N added. Our study is the first to show a potential ‘enzyme link' between (1) long-term additions of inorganic N to grassland soils, and (2) the greater C content of organo-mineral soil fractions. Our new hypothesis is that the ‘enzyme link' occurs because (a) BG activity is stimulated by increased microbial C demand relative to N under chronic fertilization, and (b) increased BG activity causes more C from roots and from microbial metabolites to accumulate and stabilize into organo-mineral C fractions. We suggest that any combination of management practices that can influence the BG ‘enzyme link' will have far reaching implications for long-term C sequestration in grassland soils. The Author(s), 2015 Extracellular enzyme activity nationallicence β-1,4-Glucosidase nationallicence Fertilization nationallicence Liming nationallicence Soil carbon sequestration nationallicence Root C:N ratio nationallicence Cenini Valeria Environmental Sciences Research Institute, University of Ulster, BT52 1SA, Coleraine, UK aut Fornara Dario Agri-Food & Biosciences Institute, BT9 5PX, Belfast, UK aut McMullan Geoffrey School of Biomedical Sciences, University of Ulster, BT52 1SA, Coleraine, UK aut Ternan Nigel School of Biomedical Sciences, University of Ulster, BT52 1SA, Coleraine, UK aut Lajtha Kate Department of Crop and Soil Sciences, Oregon State University, 97331, Corvallis, OR, USA aut Crawley Michael Department of Life Sciences, Imperial College, Silwood Park, Ascot, SL5 7PY, Berkshire, UK aut Biogeochemistry Springer International Publishing 126/3(2015-12-01), 301-313 0168-2563 126:3<301 2015 126 10533 https://doi.org/10.1007/s10533-015-0157-5 text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s10533-015-0157-5 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Cenini Valeria Environmental Sciences Research Institute, University of Ulster, BT52 1SA, Coleraine, UK aut NATIONALLICENCE 700 1- Fornara Dario Agri-Food & Biosciences Institute, BT9 5PX, Belfast, UK aut NATIONALLICENCE 700 1- McMullan Geoffrey School of Biomedical Sciences, University of Ulster, BT52 1SA, Coleraine, UK aut NATIONALLICENCE 700 1- Ternan Nigel School of Biomedical Sciences, University of Ulster, BT52 1SA, Coleraine, UK aut NATIONALLICENCE 700 1- Lajtha Kate Department of Crop and Soil Sciences, Oregon State University, 97331, Corvallis, OR, USA aut NATIONALLICENCE 700 1- Crawley Michael Department of Life Sciences, Imperial College, Silwood Park, Ascot, SL5 7PY, Berkshire, UK aut NATIONALLICENCE 773 0- Biogeochemistry Springer International Publishing 126/3(2015-12-01), 301-313 0168-2563 126:3<301 2015 126 10533