Abstract
Atmospheric nitrogen (N) deposition increases N availability in soils, with consequences affecting the decomposition of soil carbon (C). The impacts of increasing N availability on surface soil C dynamics are well studied. However, subsurface soils have been paid less attention although more than 50% soil C stock is present below this depth (below 20 cm). This study was designed to investigate the response of surface (0–20 cm) and subsurface (20–40 cm and 40–60 cm) C dynamics to 0 (0 kg N ha−1), low (70 kg N ha−1) and high (120 kg N ha−1) levels of N enrichment. The soils were sampled from a cropland and a grass lawn and incubated at 25 °C and 60% water holding capacity for 45 days. Results showed that N enrichment significantly decreased soil C mineralization (Rs) in all the three soil layers in the two studied sites (p < 0.05). The mineralization per unit soil organic carbon (SOC) increased with profile depth in both soils, indicating the higher decomposability of soil C down the soil profile. Moreover, high N level exhibited stronger suppression effect on Rs than low N level. Rs was significantly and positively correlated with microbial biomass carbon explaining 80% of variation in Rs. Overall; these results suggest that N enrichment may increase C sequestration both in surface and subsurface layers, by reducing C loss through mineralization.
Highlights
Nitrogen (N) is one of the most important elements in nature
The soil organic carbon (SOC) content, initial microbial biomass carbon (MBC) and total N decreased with the profile depth in both soils, and were significantly higher in grass lawn than those in cropland (p < 0.05)
The results showed that cumulative soil C mineralization, reduced soil C mineralization (Rs) from different layers in grass lawn was significantly higher than corresponding values in cropland during the 45-days incubation period (Fig. 1)
Summary
Nitrogen (N) is one of the most important elements in nature. human activities such as fossil fuel combustion, food and energy production and land use change have greatly accelerated the atmospheric deposition of reactive N to the biosphere (Vitousek et al, 1997; Galloway et al, 2004). This N enrichment has negative impacts on ecosystem functioning, biotic diversity and terrestrial carbon (C) cycling (Vitousek et al, 1997; Bobbink, Hornung & Roelofs, 1998; Stevens et al, 2004; Perveen et al, 2014) with consequent feedbacks on global climate change
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