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Soil N mineralization is critical for designing appropriate N management strategies, though it has been seldom studied in plasticmulched croplands. We evaluated plastic mulch e ect on N mineralization in urea-amended furrow-ridge plots with and without maize (Zea mays L.) planting at a semiarid rain-fed site, China. Clear lm covered all soil surfaces in the mulched treatments and maize was seeded in furrows in the cropped treatments. Mulch increased daytime soil temperature in the 0 to 15 cm throughout the season without maize but only in the seedling and elongation stages with maize, compared with no mulch. Mulch increased soil moisture in the whole season without maize but only in the early growth with maize, compared with no mulch in 2011. However, the mulch in uence on soil moisture was independent on the presence of maize in 2012. Compared with non-mulched soils, N mineralization rate increased in mulched soils throughout the season in 2011 and 2012. By harvest, in 2011 total N mineralized averaged 112 kg ha -1 in mulched soils, contrasting to 54 kg N ha -1 immobilized in non-mulched soils; in 2012 total N mineralization was 348 kg ha -1 in mulched soils whereas it was 116 kg ha -1 in non-mulched soils. Maize increased N mineralization in the tasseling and silking stages compared with no maize. However, the mulch e ect on N mineralization rate was independent on the presence of maize. We concluded that plastic mulch increased N mineralization in urea-amended soils by increasing soil temperature and moisture.

Soil and water conservation is an important function of forest ecosystems; however, it remains unclear which forest type is best suited for water and soil conservation under the same site conditions. In order to clarify the soil and water conservation function of different plantations in the northern and southern mountains of Lanzhou city, we investigated several soil and water conservation function indicators (thickness and accumulation of litter, maximum water holding capacity and rate of litter, water holding capacity and water absorption rate of litter, soil infiltration rates, soil water content, soil bulk density, soil porosity, and soil water storage) of five plantation types (Platycladus orientalis plantations (Po), Robinia pseudoacacia plantations (Rp), Populus alba var. pyramidalis plantations (Pa), P. alba var. pyramidalis + R. pseudoacacia mixed plantations (Pa + Rp), and P. orientalis + R. pseudoacacia mixed plantations (Po + Rp)) and evaluated them using the gray correlation method. The results indicated the accumulation of litter varied from 13.50 to 47.01 t·hm−2 and increased in the order of Pa < Rp < Po < Po + Rp < Pa + Rp. The maximum water holding capacity of litter varied from 35.29 to 123.59 t·hm−2 and increased in the order of Pa < Rp < Po < Po + Rp < Pa + Rp. The soil physical properties (soil infiltration, porosity, and bulk density) of mixed plantations were better than those of pure plantations. The soil maximum water storage was significantly different among plantation types (p < 0.05), with an average varying from 3930.87 to 4307.45 t·hm−2, and was greater in mixed plantations than in pure plantations. Gray correlation analysis revealed that mixed plantations had the best conservation function of the five plantation types, followed by broad-leaved plantations and coniferous plantations. This suggests that the planting of mixed plantations dominated by Pa + Rp is therefore recommended in the future construction of plantations in the northern and southern mountains of Lanzhou to realize sustainable forest development.

Soil salinization is an important environmental problem worldwide and has a significant impact on the growth of plants. In recent years, the mechanisms of plant salt tolerance have received extensive attention from researchers. In this paper, an experiment was implemented to assess the potential effect of different NaCl and NaHCO3 (sodium bicarbonate—an alkaline salt) concentrations (25 mmol·L−1, 50 mmol·L−1, 100 mmol·L−1, 150 mmol·L−1 and 200 mmol·L−1) on the growth, antioxidant enzymes, osmoprotectants, photosynthetic pigments and MDA of Viola tricolor L. to reveal the physiological response and explore the maximum concentrations of NaCl and NaHCO3 stress that V. tricolor can tolerate. The results showed that NaCl and NaHCO3 treatments had significant effects on osmoprotectants, antioxidant enzymes, photosynthetic pigments, MDA content and the plant height growth of V. tricolor. On day 14 of the NaCl and NaHCO3 stress, the height growth of V. tricolor was significantly greater than CK when the concentration of NaCl and NaHCO3 was less than 100 mmol·L−1. Soluble protein (SP) was significantly greater than CK when the NaCl concentration was less than 150 mmol·L−1 and the NaHCO3 concentration was less than 200 mmol·L−1; soluble sugar (SS) was significantly greater than CK under all NaCl and NaHCO3 treatments; proline (Pro) was significantly greater than CK when the NaCl concentration was 150 mmol·L−1 and the NaHCO3 concentration were 150 and 200 mmol·L−1 , respectively. Peroxidase (POD) was significantly greater than CK when the NaCl concentration was less than 200 mmol·L−1 and the NaHCO3 concentration was less than 150 mmol·L−1; superoxide dismutase (SOD) was significantly greater than CK when the NaCl concentration was 50 mmol·L−1 and the NaHCO3 concentrations were 50, 100 and 150 mmol·L−1 , respectively; catalase (CAT) was significantly greater than CK when the NaCl and NaHCO3 concentrations were 25, 50 and 100 mmol·L−1 , respectively. Chlorophyll (Chl) was significantly lower than CK when the NaCl and NaHCO3 concentrations were greater than 100 mmol·L−1. Malondialdehyde (MDA) gradually increased with the increase in the NaCl and NaHCO3 concentrations. Membership function analysis showed that the concentrations of NaCl and NaHCO3 that V. tricolor was able to tolerate were 150 mmol·L−1 and 200 mmol·L−1, respectively. Beyond these thresholds, osmoprotectants and antioxidant enzymes were seriously affected, Chl degradation intensified, the photosynthetic system was seriously damaged, and the growth of V. tricolor was severely affected. According to a comprehensive ranking of results, the degree of NaCl stress on V. tricolor was lower than that from NaHCO3 when the treatment concentration was lower than 50 mmol·L−1, but higher than that from NaHCO3 when it exceeded 50 mmol·L−1.