Journal
GEODERMA
Volume 341, Issue -, Pages 1-9Publisher
ELSEVIER
DOI: 10.1016/j.geoderma.2019.01.034
Keywords
Gross N transformations; N cycling; Soil N status; N cycling-related enzymes; Karst region; Post-agricultural succession
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Funding
- National Key Research and Development Program of China [2016YFC0502404]
- National Key Basic Research Program of China [2015CB452703]
- National Natural Science Foundation of China [31460135, 41877094]
- Guangxi Bagui Scholarship Program
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Gross nitrogen (N) transformations are crucial in determining soil N status, but how gross N transformations change during post-agricultural succession remains poorly understood. Here, gross N transformations were measured using a N-15 isotope dilution technique in a subtropical karst region, southwest China. A stratified random sampling scheme was adopted and the succession sequence included grassland (similar to 4 years), shrubland (similar to 15 years) and secondary forest (similar to 30 years) with cropland as reference. The soil was leptosols (limestone soil). Soil total N concentrations were significantly (P < 0.05 hereafter) elevated in the shrubland and forest relative to the cropland and grassland. No clear pattern was found for NH4+ concentration, but NO3- concentration increased from the grassland to the forest. The gross rates of N mineralization and nitrification (GN) were significantly lower in the grassland than in the cropland, but increased significantly during post-agricultural succession. There were no clear patterns for the rates of dissimilatory NO3- reduction to NH4+ and gross NO3- immobilization. Gross NH4+ immobilization (GAI) in the forest was lowest but there was no significant difference among the cropland, grassland and shrubland. Gross N mineralization rate correlated significantly with protease activity, implying that the depolymerization of N-containing polymers was likely the rate-limiting step of gross N mineralization. Net nitrate production rate and GN:GAI ratio increased significantly from the grassland to the forest, supporting that soil N cycling likely became more open during post-agricultural succession in the karst region of southwest China.
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