Organic matter dynamics along a salinity gradient in Siberian
Norbert Bischoff1, Robert Mikutta2, Olga Shibistova1,3, Reiner Dohrmann4, Daniel Herdtle1, Lukas Gerhard1, Franziska Fritzsche1, Alexander Puzanov5, Marina Silanteva6, Anna Grebennikova6, and Georg Guggenberger11Institute of Soil Science, Leibniz University Hannover, Herrenhäuser Straße 2, 30419 Hannover, Germany 2Soil Science and Soil Protection, Martin Luther University Halle-Wittenberg, Von-Seckendorff-Platz 3, 06120 Halle (Saale), Germany 3VN Sukachev Institute of Forest, Siberian Branch of the Russian Academy of Sciences, Akademgorodok 50, 660036 Krasnoyarsk, Russian Federation 4Federal Institute for Geosciences and Natural Resources, Stilleweg 2, 30655 Hannover, Germany 5Institute for Water and Environmental Problems, Siberian Branch of the Russian Academy of Sciences, Molodezhnaya Street 1, 656038 Barnaul, Russian Federation 6Faculty of Biology, Altai State University, Prospekt Lenina 61a, 656049 Barnaul, Russian Federation
Received: 17 Feb 2017 – Accepted for review: 20 Feb 2017 – Discussion started: 21 Feb 2017
Abstract. Salt-affected soils will become increasingly important in the next decades as arid and semi-arid ecosystems are predicted to expand as a result of climate change. Nevertheless, little is known about organic matter (OM) dynamics in these soils, though OM is largely controlling soil fertility and represents an important C sink. We aimed at investigating OM dynamics along a salinity and sodicity gradient in soils of the south-western Siberian Kulunda steppe (Kastanozem, Non-sodic Solonchak, Sodic Solonchak) by assessing the organic carbon (OC) stocks, the quantity and quality of particulate and mineral-associated OM in terms of non-cellulosic neutral sugar contents and carbon isotopes (δ13C, 14C activity), and the microbial community composition based on phospholipid fatty acid (PLFA) patterns. Our hypotheses were that (i) soil OC stocks decrease along the salinity gradient, (ii) the proportion and stability of particulate OM is larger in salt-affected Solonchaks as compared to non-salt-affected Kastanozems, and (iii) sodicity reduces the proportion and stability of mineral-associated OM. Against our first hypothesis, OC stocks increased along the salinity gradient with most pronounced differences between topsoils. In contrast to our second hypothesis, the proportion of particulate OM was unaffected by salinity, thereby accounting for only < 10 % in all three soil types, while mineral-associated OM contributed to > 90 %. Isotopic data (δ13C, 14C activity) and neutral sugars in the OM fractions indicated a comparable degree of OM transformation along the salinity gradient, thus particulate OM was not more persistent under saline conditions. This we attribute to a resilient microbial community composition and function, which was nearly unaffected by salt occurrence, and capable of decomposing OM at a similar rate in salt-affected and non-salt-affected soils. Also our third hypothesis was rejected, as saline-sodic soils contained more than twice as much mineral-bound OC than non-salt-affected soils, what we ascribe to the flocculation of OM and mineral components under higher ionic strength conditions. We conclude that salt-affected soils contribute significantly to the OC storage in the semi-arid soils of the Kulunda steppe while most of the OC is associated to minerals and therefore effectively sequestered in the long-term.
Bischoff, N., Mikutta, R., Shibistova, O., Dohrmann, R., Herdtle, D., Gerhard, L., Fritzsche, F., Puzanov, A., Silanteva, M., Grebennikova, A., and Guggenberger, G.: Organic matter dynamics along a salinity gradient in Siberian
steppe soils, Biogeosciences Discuss., doi:10.5194/bg-2017-53, in review, 2017.