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Controls on Natural Nitrogen‐15 and Carbon‐13 Abundances in Forest Soil Organic Matter
Author(s) -
Natelhoffer K. J.,
Fry B.
Publication year - 1988
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1988.03615995005200060024x
Subject(s) - subsoil , soil water , litter , organic matter , plant litter , fractionation , soil organic matter , chemistry , decomposition , nitrogen , environmental chemistry , soil carbon , environmental science , agronomy , soil science , nutrient , biology , organic chemistry
We used δ 15 N and δ 13 C measurements to study formation and decay of soil organic matter in surface soils of two oak ( Quercus spp.) forests in Wisconsin. There were two controls of soil isotopic compositions: new litter inputs and overall isotopic fractionation during decomposition. Litter inputs lowered soil δ 15 N and δ 13 C values while decomposition increased δ 15 N and δ 13 C values. Leaf and root litter inputs averaged −3.8 and −1.6‰ δ 15 N and −27.3 and −28.2‰ δ 13 C, respectively. Field experiments showed that low surface soil δ 15 N and δ 13 C values resulted when litter inputs were high. Laboratory experiments showed that overall isotopic fractionation during decomposition left residual soil N and C enriched in 15 N and 13 C, and could explain the high δ 15 N and δ 13 C values observed in deeper forest soils (+5.9‰ δ 15 N and −23.6‰ δ 13 C for 10 to 20 cm soils). Our results suggest two pools of naturally labeled N in forest soils: surface N with low δ 15 N values and subsoil N with high δ 15 N values. Natural abundance measurements of soil N may be useful for following the importance of these two N pools in forest N cycles. We found no evidence for selective preservation of 13 C depleted litter components, such as lignin, during long‐term decomposition in forest soils.