TY - JOUR

T1 - From fibrous plant residues to mineral-associated organic carbon - the fate of organic matter in Arctic permafrost soils

AU - Prater, Isabel

AU - Zubrzycki, Sebastian

AU - Buegger, Franz

AU - Zoor-Fuellgraff, Lena Careen

AU - Angst, Gerrit

AU - Dannenmann, Michael

AU - Müller, Carsten W.

PY - 2020

Y1 - 2020

N2 - Permafrost-affected soils of the Arctic account for 70% or 727 Pg of the soil organic carbon (C) stored in the northern circumpolar permafrost region and therefore play a major role in the global C cycle. Most studies on the budgeting of C storage and the quality of soil organic matter (OM; SOM) in the northern circumpolar region focus on bulk soils. Thus, although there is a plethora of assumptions regarding differences in terms of C turnover or stability, little knowledge is available on the mechanisms stabilizing organic C in Arctic soils besides impaired decomposition due to low temperatures. To gain such knowledge, we investigated soils from Samoylov Island in the Lena River delta with respect to the composition and distribution of organic C among differently stabilized SOM fractions. The soils were fractionated according to density and particle size to obtain differently stabilized SOM fractions differing in chemical composition and thus bioavailability. To better understand the chemical alterations from plant-derived organic particles in these soils rich in fibrous plant residues to mineral-associated SOM, we analyzed the elemental, isotopic and chemical composition of particulate OM (POM) and clay-sized mineral-associated OM (MAOM). We demonstrate that the SOM fractions that contribute with about 17 kgCm(-3) for more than 60% of the C stock are highly bioavailable and that most of this labile C can be assumed to be prone to mineralization under warming conditions. Thus, the amount of relatively stable, small occluded POM and clay-sized MAOM that currently accounts with about 10 kgCm(-3) for about 40% of the C stock will most probably be crucial for the quantity of C protected from mineralization in these Arctic soils in a warmer future. Using delta N-15 as a proxy for nitrogen (N) balances indicated an important role of N inputs by biological N fixation, while gaseous N losses appeared less important. However, this could change, as with about 0.4 kgNm(-3) one third of the N is present in bioavailable SOM fractions, which could lead to increases in mineral N cycling and associated N losses under global warming. Our results highlight the vulnerability of SOM in Arctic permafrost-affected soils under rising temperatures, potentially leading to unparalleled greenhouse gas emissions from these soils.

AB - Permafrost-affected soils of the Arctic account for 70% or 727 Pg of the soil organic carbon (C) stored in the northern circumpolar permafrost region and therefore play a major role in the global C cycle. Most studies on the budgeting of C storage and the quality of soil organic matter (OM; SOM) in the northern circumpolar region focus on bulk soils. Thus, although there is a plethora of assumptions regarding differences in terms of C turnover or stability, little knowledge is available on the mechanisms stabilizing organic C in Arctic soils besides impaired decomposition due to low temperatures. To gain such knowledge, we investigated soils from Samoylov Island in the Lena River delta with respect to the composition and distribution of organic C among differently stabilized SOM fractions. The soils were fractionated according to density and particle size to obtain differently stabilized SOM fractions differing in chemical composition and thus bioavailability. To better understand the chemical alterations from plant-derived organic particles in these soils rich in fibrous plant residues to mineral-associated SOM, we analyzed the elemental, isotopic and chemical composition of particulate OM (POM) and clay-sized mineral-associated OM (MAOM). We demonstrate that the SOM fractions that contribute with about 17 kgCm(-3) for more than 60% of the C stock are highly bioavailable and that most of this labile C can be assumed to be prone to mineralization under warming conditions. Thus, the amount of relatively stable, small occluded POM and clay-sized MAOM that currently accounts with about 10 kgCm(-3) for about 40% of the C stock will most probably be crucial for the quantity of C protected from mineralization in these Arctic soils in a warmer future. Using delta N-15 as a proxy for nitrogen (N) balances indicated an important role of N inputs by biological N fixation, while gaseous N losses appeared less important. However, this could change, as with about 0.4 kgNm(-3) one third of the N is present in bioavailable SOM fractions, which could lead to increases in mineral N cycling and associated N losses under global warming. Our results highlight the vulnerability of SOM in Arctic permafrost-affected soils under rising temperatures, potentially leading to unparalleled greenhouse gas emissions from these soils.

KW - STATE C-13 NMR

KW - NITROGEN AVAILABILITY

KW - ISOTOPE FRACTIONATION

KW - TUNDRA SOIL

KW - DECOMPOSITION

KW - STABILIZATION

KW - CLIMATE

KW - STOCKS

KW - POOLS

KW - PARTICULATE

U2 - 10.5194/bg-17-3367-2020

DO - 10.5194/bg-17-3367-2020

M3 - Journal article

VL - 17

SP - 3367

EP - 3383

JO - Biogeosciences

JF - Biogeosciences

SN - 1726-4170

IS - 13

ER -