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Ammonium nitrogen (NH 4 + -N) at high concentrations is toxic to plants. In order to explore the NH 4 + ) and its ability of nitrogen (N) and phosphorus (P) uptake, this study used a nutrient solution with three NH Myriophyllum aquaticum ( M. aquaticum ) and its ability of nitrogen (N) and phosphorus (P) uptake, this study used a nutrient solution with three NH 4 + -N levels (70, 210, 420 mg·L -1 ) to incubate M. aquaticum for 21 d. The characteristics of plant physiology and N and P uptake of M. aquaticum were measured. At NH 4 + -N of 70 mg·L -1 ammonium, malondialdehyde (MDA) content of M. aquaticum grew healthily, and shoot height and biomass linearly increased with the increase incubation time. Relative shoot height and biomass of M. aquaticum were 40.56 cm and 17.82 g·hole -1 on day 21, respectively. Compared to the control with 70 mg·L -1 ammonium, malondialdehyde (MDA) content of M. aquaticum was significantly increased; chlorophyll and soluble sugar contents were also high at NH 4 + -N of 210 mg·L -1 . M. aquaticum suffered from the NH 4 + -N stress. However, the stress of 210 mg·L -1 NH 4 + -N did not affect its normal growth and there was no significant difference in the relative growth rate of the shoot height and biomass compared with the control. At NH 4 + -N of 420 mg·L -1 , MDA contents of M. aquaticum doubled and the shoot height and biomass growth rate were only 27.4% and 17.9% of those for 70 mg·L -1 NH 4 + -N, indicating that M. aquaticum was subjected to serious stress that caused unhealthy growth or even death. At three NH 4 + -N levels, the ranges of N and P content of M. aquaticum were 30.7-53.4 mg·g -1 and 3.8-7.7 mg·g -1 , respectively, which indicated that M. aquaticum had a high uptake capacity of N and P. M. aquaticum is an ideal wetland plant that has a good application prospect for constructed wetlands in biological treatment of high-ammonia wastewater.

Digested piggery wastewater(DPW) contains high concentrations of nitrogen and phosphorus which could be used as a cost-effective culture medium for Spirulina platensis . However, Spirulina platensis would be limited by many factors in the complex composition of DPW, especially the high concentration of ammonium. In this paper, a traditional sequencing batch reactor(SBR) was used to remove these inhibitors in DPW. The retention of nitrate and nitrite in the effluent, which was used as nitrogen source for cultivating Spirulina platensis , was studied at different ratios of chemical oxygen demand(COD) to total nitrogen(TN) in the influent. By comparing the growth of Spirulina platensis in the related effluents, the operation condition of SBR was optimized. The lab-scale cultivation results showed that Spirulina platensis possessed a high biomass yield of 0.084 g·(L·d) -1 in the effluent when the COD/TN ratio of SBR influent was 3.0. In particular, the concentrations of ammonium, nitrate and nitrite in the effluent were 51.2 mg·L -1 , 91.6 mg·L -1 and 213.1 mg·L -1 , respectively. Furthermore, the aforementioned effluent was also used to culture Spirulina platensis in a 120 L outdoor raceway pond, and the growth rate of Spirulina platensis reached(0.075±0.003)g·(L·d) -1 after 10-day culture. The protein content of Spirulina platensis was approximately 60% and the removal efficiency of ammonium was 99%. This study provides an alternative method for the utilization of DPW.

Warming-induced decrease in seasonal snow cover has a great potential to affect soil nitrogen cycle in alpine cold forest ecosystems. In this study, a wooden-shelter method was used to remove the snow accumulation. Soil nitrogen pools and mineralization rates in the snow removal and control plots were measured synchronously in three critical periods (early snow cover, deep snow cover and snow cover melting) in a subalpine spruce forest of western Sichuan, China. Seasonal snow cover kept soil from cold air temperature. Snow removal decreased average and minimum soil temperatures (5 cm) by 0.33 and 1.17 ℃, respectively. In addition, snow removal caused a positive effect on soil frost depth and freeze-thaw cycle. There was a significant dynamic in soil labile nitrogen pool among different periods. Snow removal on average increased NH 4 + -N and dissolved organic nitrogen (DON) contents by 38.6%, 23.5% and 57.3%, respectively, over the winter. Moreover, snow removal increased soil net nitrification and mineralization rates in the snow co-ver melting period. Overall, warming-induced decrease in snow cover could stimulate winter soil nitrogen cycle of subalpine forests.3 - -N and dissolved organic nitrogen (DON) contents by 38.6%, 23.5% and 57.3%, respectively, over the winter. Moreover, snow removal increased soil net nitrification and mineralization rates in the snow co-ver melting period. Overall, warming-induced decrease in snow cover could stimulate winter soil nitrogen cycle of subalpine forests.

[Objective] The study aimed to investigate the effects of nitrogen application rate on soil inorganic nitrogen content, cotton yield, nutrient absorption and utilization in cotton field in Southern Xinjiang. [Method] Taken Xinluzao 66 as the material, five nitrogen application treatments ( 0, 150, 225, 300, 450 kg N/hm2, respectively expressed as NO, N150, N225, N300, N450) were set, and field tests in Shaya county, Aksu Prefecture, Xinjiang in 2021 were conducted. The content of nitrate nitrogen, ammonium nitrogen, dry matter quality, nitrogen accumulation and yield of cotton in 0 - 60 cm soil layer were measured. [Result] ( i) The content of nitrate nitrogen and anunonium nitrogen in soil of each treatment decreased with soil deepening. With the increase of nitrogen application level, the contents of nitrate nitrogen and ammonium nitrogen in 0 - 60 cm soil layers were significantly increased. The nitrate nitrogen in 0 - 20 cm soil layers at bud stage was significantly different ( P < 0. 05, the same as below), and the fertilization treatment increased I. 54 - 2. 47 times compared with NO; There was no significant difference in ammonium nitrogen content between N225 and N300 treatments in 0 - 20 cm soil layer at seedling stage ( P >0. 05, the same as below), and N450 treatment significantly increased 57% -140% compared with other treatments. The anunonium nitrogen content was abundant at the seedling stage, but it was obviously lacking in the peak bell stage. The nitrate nitrogen content was lacking in the seedling stage and abundant at the peak bell stage. (ii) The dry matter quality, nitrogen content, lint yield, nitrogen fertilizer utilization rate and agronomic utilization rate of cotton all increased first and then decreased with the increase of fertilization amount, and reached the maximum under N300 treatment. The maximum dry matter accumulation of cotton roots, stems, leaves, buds, flowers and bolls under N300 treatment were 4. 16, 20. 33, 7. 47 and 10. 84 g/ plant, respectively; The nitrogen accumulation amount of cotton at N300 treatment was 304. 00 kg/hm2, and the nitrogen accumulation amount of the boll at N300 treatment was 32.17%, which increased by 3. 95% - 5. 27% compared to other treatments; The lint yield at N300 treatment reached 6574. 8 kg/hm2, which increased by 21. 23% -67. 54% compared to other treatments, the nitrogen fertilizer utilization rate increased by 6. 85 % - 20. 88 %, and the agronomic utilization rate 2. 86% -6. 66%. [ Conclusion] The best amount of nitrogen fertilizer is 300 kg/hm² . When the nitrogen application rate exceeds 300 kg/ hm², the dry matter quality and nitrogen accumulation of cotton decrease, the soil nitrate nitrogen ammonium nitrogen content is higher, the nitrogen use efficiency decreases, and the yield increase effect is not obvious. [ABSTRACT FROM AUTHOR]

The aim of the present study was to explore the effects of dicyandiamide（DCD）and surfactant on the form and content of nitro⁃ gen in digested slurry, using a laboratory simulation experiment with different combinations of application of the treatments. Six treatments were used：single application of digested slurry, digested slurry+8%DCD, digested slurry+16%DCD, digested slurry+surfactant, digested slurry+8%DCD+surfactant, and digested slurry+16%DCD+sufactant. The total nitrogen（TN）, total Kjeldahl nitrogen（TKN）, ammonium ni⁃ trogen（NH4+-N）, and nitrate nitrogen（NO3--N）content of digested slurry were measured at 10, 30 min, and 1, 3, 10, 24, 48 h. The results revealed that, in the digested slurry+8%DCD and digested slurry+16%DCD treatments, the concentrations of NH4+-N, TKN, and NO3--N in⁃ creased by 0.74%~8.96%, 24.67~59.70 mg·L-1, 13.42~145.88 times, respectively, and the concentrations of all three increased with the quantity of DCD. The addition of surfactant had little effect on the form and concentration of nitrogen in digested slurry. [ABSTRACT FROM AUTHOR]

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