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Experimental warming increased soil nitrogen sink in the Tibetan permafrost
Author(s) -
Chang Ruiying,
Wang Genxu,
Yang Yuanhe,
Chen Xiaopeng
Publication year - 2017
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2017jg003827
Subject(s) - permafrost , nitrification , environmental science , nitrogen cycle , denitrification , soil science , nitrogen , sink (geography) , ecosystem , soil organic matter , soil water , agronomy , environmental chemistry , chemistry , ecology , cartography , organic chemistry , geography , biology
In permafrost soil, warming regulates the nitrogen (N) cycle either by stimulating N transformation or by enhancing cryoturbation, the mixture of soil layers due to repeated freeze thaw. Here N isotopic values (δ 15 N) of plants and the soil were investigated in a 7 year warming experiment in a permafrost‐affected alpine meadow on the Qinghai‐Tibetan Plateau. The results revealed that warming significantly decreased the δ 15 N in the plant (aboveground and belowground parts) and different soil fractions (clay and silt fraction, aggregate, and bulk soil). The decreased soil δ 15 N was associated with an increase in soil N stock due to greater N fixation. The incremental N retention in plants and soil mineral‐associated fractions from warming resulted in a decrease in soil inorganic N, which constrains the role of nitrification/denitrification in soil δ 15 N, suggesting a restrained rather than an open N cycle. Furthermore, enhanced cryoturbation under warming, identified by a downward redistribution of 137 Cs into deeper layers, promoted N protection from transformation. Overall, the decrease in soil δ 15 N indicated higher rates of N input through fixation relative to N loss through nitrification and denitrification in permafrost‐affected ecosystems under warming conditions.