Plant nitrogen retention in alpine grasslands of the Tibetan Plateau under multi-level nitrogen addition.

Nitrogen (N) deposition might alleviate degradation of alpine grassland caused by N limitation on the Tibetan Plateau (TP). To determine such limitation and quantify the N-induced N retention in plant, a six-year fertilization experiment with six levels of N addition rates (0, 1, 2, 4, 8 and 16 g N m-2 yr-1) was conducted in the Namco alpine steppe and additional 89 experiments with multi-level N addition were also synthesized worldwide among which 27 sites were on the TP. In general, N addition promoted N retention in plants, and this increasing trend diminished at the critical N rate (Ncr). The maximum N retention capacity (MNRC) of plants at Ncr was strongly correlated with initial aboveground net primary productivity with a slope of 0.02, and the MNRC of grasslands globally ranged from 0.35 to 42.59 g N m-2 yr-1, approximately account for 39% of Ncr. Tibetan alpine grassland had a low average MNRC (2.24 g N m-2 yr-1) with distinct regional characteristic, which was much lower in the western TP (0.80 g N m-2 yr-1) than the eastern TP (4.10 g N m-2 yr-1). Our results inferred 0.33-1.21 Tg N yr-1 (0.22-0.79 g N m-2 yr-1) can be retained and 5.65-20.11 Tg C yr-1 (3.67-13.06 g C m-2 yr-1) can be gained by Tibetan alpine grasslands under current N deposition level. With the aggravation of N deposition, the alpine steppe ecosystem might continuously absorb N and C until N deposition reaches Ncr.

Nitrogen deposition accelerates greenhouse gas emissions at an alpine steppe site on the Tibetan Plateau.

The increase in atmospheric N deposition can alter the exchange of greenhouse gas (GHG) between the biosphere and atmosphere. The effect of N deposition on GHG is poorly understood in alpine steppe. Therefore, we conducted a 4-year experiment with multilevel N addition of 0, 10, 20, 40, 80, 160 kg N ha-1 using the static chamber and gas chromatography method to quantify responses of GHG fluxes and characterize the relationship between GHG fluxes and N addition rate in Namco located in the alpine steppe in the central Tibetan Plateau (TP). The mean CO2 efflux, CH4 uptake, N2O emission during growing seasons across four years were 33.59 ± 16.41 mg C m-2 h-1, -56.42 ± 29.20 µg C m-2 h-1, 0.67 ± 4.40 µg N m-2 h-1 respectively. CO2 efflux increased 1.55-22.6%, CH4 uptake decreased 5.96-20.1%, N2O emission increased 37.3-133.5% with N addition. We also observed a critical threshold of 40 kg N ha-1 a-1 of N addition above which the increase rate of N2O emission would diminish. Our current results implied that under the background of future N deposition, N induced C sequestration might be offset by GHG balance causing a heating effect to the climate.

Fermentation characteristics and bacterial dynamics during Chinese sauerkraut fermentation by Lactobacillus curvatus LC-20 under varied salt concentrations reveal its potential in low-salt suan cai production.

Salt profoundly affects the physicochemical properties and microbial abundance of fermented foods such as suan cai, a popular traditional fermented food in China. It is vital to systematically investigate the effects of salt concentrations on fermented suan cai for high fermentation quality and large-scale production. We elucidated the effects of salt concentrations on Lactobacillus curvatus (LC-20) and suan cai during fermentation, and found that salt (0-1%) favoured an increase in LC-20 growth and a decrease in pH (salt: 0-2%). For suan cai fermentation, the results from sensory scoring judged 1% salt treatment the highest. Salt concentration also affected the nitrite content of the fermentation system with peak nitrite values in low salt treatments being significantly higher on the first day, and gradually decreasing to similar levels. After fermentation, the total titratable acid and lactic acid concentrations in the 0-1% treatments were higher (p < 0.05) than those in 2-5% treatments. The colony forming units of lactic acid bacteria increased initially and then decreased after 6 d of fermentation. At the phylum level, Firmicutes and Proteobacteria were predominant in all treatments, and at the genus level, Lactobacillus dominated the fermentation. Other lactic acid bacteria such as Lactococcus and Weissella were also detected. Quantitative PCR showed DNA concentration of LC-20 at 0.5-2% salt treatments were higher than that in other treatments and L. curvatus was the dominant microorganism during fermentation. Hence, we conclude that L. curvatus could be used for suan cai product at low salt concentrations.

Complete Genome Sequence of Lactobacillus nenjiangensis SH-Y15, Isolated from Sauerkraut.

We isolated a strain of Lactobacillus nenjiangensis named SH-Y15 from traditional suan-cai used in northeastern China because it has a high capacity for degrading nitrites at low temperatures. The complete genome of SH-Y15 contains a single circular chromosome and a plasmid. The complete length is 2,249,893 bp, and the G+C content is 39.68%.