Soil-nitrogen net mineralization increased after nearly six years of continuous nitrogen additions in a subtropical bamboo ecosystem

Abstract

In order to understand the effects of increasing atmospheric nitrogen (N) deposition on the subtropical bamboo ecosystem, a nearly six-year field experiment was conducted in a Pleioblastus amarus plantation in the rainy region of SW China, near the western edge of Sichuan Basin. Four N treatment levels-control (no N added), low-N (50 kg N ha -1 a -1 ), medium-N (150 kg N ha -1 a -1 ), and high-N (300 kg N ha -1 a -1 )-were applied monthly in the P. amarus plantation starting in November 2007. In June 2012, we collected intact soil cores in the bamboo plantation and conducted a 30-day laboratory incubation experiment. The results showed that the soil N net mineralization rate was 0.96 ± 0.10 mg N kg -1 day -1 , under control treatment. N additions stimulated the soil N net mineralization, and the high-N treatment significantly increased the soil N net mineralization rate compared with the control. Moreover, the soil N net mineralization rate was significantly and positively correlated with the fine root biomass, the soil microbial biomass nitrogen content and the soil initial inorganic N content, respectively, whereas it was negatively correlated with the soil pH value. There were no significant relationships between the soil N net mineralization rate and the soil total nitrogen (TN) content and the soil total organic carbon content and the soil C/N ratio and the soil microbial biomass carbon content, respectively. These results suggest that N additions would improve the mineral N availability in the topsoil of the P. amarus plantation through the effects of N additions on soil chemical and physical characteristics and fine-root biomass.

Soil biochemical responses to nitrogen addition in a secondary evergreen broad-leaved forest ecosystem

“…Nitrogen addition was associated with heightened soil NH 4 + concentration, which can be expected to accelerate nitrification 6, 43 . This is because NH 4 + is the substrate of nitrification and the nitrification rate depends on soil NH 4 + concentration.…”

“…Several previous studies reported that N deposition can result in soil acidification in terrestrial ecosystems 15 , 28 , 29 , 48 , which was confirmed by our study. Nitrogen addition was associated with heightened soil NH 4 + concentration, which can be expected to accelerate nitrification 6 , 43 . This is because NH 4 + is the substrate of nitrification and the nitrification rate depends on soil NH 4 + concentration.…”

“…The results from these studies indicated that N additions increased the rates of soil N mineralization and nitrification, the concentrations of NH 4 + and NO 3 − , microbial biomass carbon, fine root biomass, and mean annual soil respiration rate. On the other hand, litter decomposition rates and soil pH decreased, with mixed effects on soil enzyme activities 10 , 31 , 41 – 43 . These results indicate that such a high level of N deposition may have severely affected many ecosystem properties and processes in this area.…”

Effects of <i>Solidago canadensis</i> Invasion and Climate Warming on Soil Net N Mineralization

“…In our study, soil net N mineralization (SNmin) includes net mineralization (Nmin, inorganic N), net nitrification (NNmin, NO 3 --N)), and net ammonification (ANmin, NH 4 + -N). The Nmin, NNmin, and ANmin as the difference between planting and harvest (end-start) in soil [48,49]. All values were standard transformed using the min-max normalization method to satisfy the requirements of normality and homogeneity of variance.…”

“…Overall, Nmin, ANmin, and NNmin were not only suppressed by environmental factors, but also were affected by the enzyme and pH, which may even relate to N-fixing bacteria [30]. The previous study showed that ANmin and NNmin were significantly influenced by soil moisture and root biomass [49], and a significant positive correlation was also found between Nmin and fine-root biomass [48]. It was reported that the increase in fine-root biomass can lead to the increase of rootderived C, which is coupled with stimulating microbial activity and accelerating N transformation in the soils [79], even affecting the C:N soil [80].…”