Application of nitrogen fertilizer is the main way to increase yield in forage production. However, excessive nitrogen application can increase nutrient leaching and cause environmental problems. In recent years, biochar has been used as a new soil amendment to slow and control the the release of nitrogen fertilizer which has achieved some initial effect. However, the application methods for biochar need to be optimized. The effects of biochar application at different depths on soil nitrogen and plant nitrogen distribution require further analysis. In this study, no biochar was used as the control, and 0－20 cm, 20－40 cm, and 40－60 cm deep treatments were set up to conduct field pot experiments. The results showed that compared with other treatments, surface application of biochar (0－20 cm) was more conducive to the increase of biomass, which could effectively increase the total biomass by 19.3%. The fruit biomass was 24.6% higher than that of the control treatment (P < 0.05). In terms of nitrogen accumulation, the nitrogen content of the aboveground component of maize (Zea mays) increased by 29.9%. The nitrogen content of the fruit and leaf sheath was significantly higher than that of the control treatment (P < 0.05), which was 29.7% and 42.3% higher than that of the control treatment, respectively. The nitrogen accumulation was consistent with the increase in biomass. In terms of soil nitrogen fixation, the soil nitrate nitrogen content at 0－20 cm in depth was higher than that of the other treatments. Meanwhile, a moderate increase in the application depth to 20－40 cm was more conducive to soil ammonium nitrogen fixation. All the biochar application depth treatments could promote root growth. The total root length at application at 20－40 cm in depth was significantly longer than that of the control treatment (P < 0.05). The total root surface area at an application depth of 0－20 cm was 49.1% higher than that of the control treatment. The total root volume was 215.1% higher than that of the control treatment (P < 0.05). Therefore, a biochar application depth of 0－20 cm could significantly improve root growth. This lead to an increase in nitrogen accumulation in the aboveground component, improving soil nitrate nitrogen retention capacity, and increasing forage maize yield. The results have provided a scientific basis for nutrient management of forage maize and strategic use of biochar.
Nitrogen mineralization in the soil of alpine grasslands on the Tibetan Plateau is a key process affecting the global carbon and nitrogen cycle, as well as the succession of grassland ecosystems. The aim of this study was to explore the effects of temperature and organic fertilizer additions on the nitrogen availability in the soil of these alpine grasslands. Through incubation experiments involving different temperatures (5, 15, and 25 ℃) and gradients of organic nitrogen addition (0, 15, 45, and 75 kg·hm−2), we analyzed changes in soil nitrogen mineralization rates, mineralization potential, and mineralization reaction rate. The results showed that soil nitrogen mineralization increased with rising temperature, with values significantly higher at 25 ℃ than at 15 ℃ and 5 ℃. Organic nitrogen addition (15-45 kg·hm−2) significantly increased the mineralization of ammoniacal nitrogen in the soil. However, further increasing the fertilization gradient to 75 kg·hm−2 reduced the nitrogen mineralization capacity. The soil nitrogen mineralization rate exhibited a single peak trend with increasing incubation time, and the addition of organic nitrogen could increase the nitrogen mineralization rate in alpine grassland soil, reaching its maximum under N45 treatment. Temperature determined the mineralization potential of nitrogen in alpine grassland soil, but did not significantly affect the mineralization rate, k. In summary, the addition of 15-45 kg·hm−2 of organic nitrogen and higher temperature conditions are beneficial for enhancing the mineralization capacity of rapidly available nitrogen in the soil of alpine grasslands on the Tibetan Plateau, providing a theoretical basis for grassland management and organic fertilizer application in alpine grassland regions.
With the continuous warming of the global climate, the ecological environment of the Qinghai–Tibet Plateau is highly fragile. Studying the effects of temperature and water conditions on the germination activities of wild herbage species in this region and selecting suitable grass species for ecological restoration based on these conditions is vital for stabilizing and restoring ecological barrier function. The PEG-6000 osmotic potential was used to simulate soil drought conditions, and the spring and summer temperature conditions were simulated at 10 ℃ and 20 ℃, respectively. The germination behavior of 14 native herbs on the Tibetan Plateau was studied under different temperature and water potentials. The results showed that the germination strategies of the plants tested were diversified. Most of the plants under different temperature and water potential showed that the germination rate increased or decreased along with the germination time and germination rate. 50% of the plants, comprising seven species, had significant germination time and weak responses in terms of their germination rate. 28.6% of the plants, comprising four species, showed considerable variation in the three. The germination rate and germination time of Anaphalis xylorhiza were significantly different in individual plants. Astragalus strictus showed a weak response and Silene moorcroftiana had an increased germination rate. Overall, the germination rate and germination rate of plant seeds increased significantly at 20 ℃, and increased with increasing water potential. The effect of temperature on germination rate was more significant than that of water potential. The germination time of 12 plant seeds at 20 ℃ was significantly shortened by 8–10 d. The plants of different families had different responses to the change in water and heat, and the plants from Compositae and Dianthus had a higher germination rate. Most of the plants could be used as established grasses for ecological restoration on the Qinghai–Tibet Plateau in summer when the moisture conditions are more suitable. Tibetan Artemisia wellbyi can also be established in summer, and Western Tibet Flysthopsis, Leontopodium nanum, and wood root sweet grass can be used as established grasses in spring.
To explore the effects of drought stress on the responses and adaptability of leaf photosynthesis and chlorophyll fluorescence in sainfoin (Onobrychis viciaefolia) seedlings, twenty different sainfoin seedling genotypes, derived from national and international strains, were used in this study. Water deficit stress was simulated with PEG-6000 at four osmotic potentials (−0.5, −1.0, −1.5 and −2.0 MPa, respectively), alongside a nil-PEG (CK) control treatment. Corresponding results demonstrated that drought stress inhibited the plant height of sainfoin seedlings. Additionally, with increasing drought stress, chlorophyll content, carotenoid content, transpiration rate, net photosynthetic rate, and stomatal conductance were reduced, while water use efficiency was improved. Initially, the stomatal limitation value increased with increasing drought stress, and then decreased, with a maximum value being observed at −1.0 MPa. Intercellular carbon dioxide concentration initially decreased and then increased, reaching a maximum value at −2.0 MPa; this indicated that non-stomatal factors limited photosynthesis. Although the non-photochemical quenching coefficient increased, the actual photochemical efficiency, maximum photochemical efficiency, electron transport rate, photochemical quenching coefficient, and photochemical quantum yield decreased with increasing drought stress. The comprehensive evaluation of the results based on the membership function value demonstrated that the novel P1, Onobrychis viciaefolia ‘Gansu’ sainfoin line and the 1626 genotype possessed the strongest drought tolerance, whereas genotypes 1668, 6, and 2049 possessed the weakest drought tolerance. Therefore, P1, Onobrychis viciaefolia ‘Gansu’ and 1626 sainfoin lines could be used for a variety of regional and production analyses in the future.
Elymus nutans is the first domesticated wild forage grass in Tibet. We selected three seed yield indices and seven agronomic traits in an effort to identify correlations between seed yield and agronomic traits of E. nutans‘Baqing’. We sought to identify correlations between seed yield and agronomic traits of E. nutans ‘Baqing’ by principal component analysis, typical correlation analysis, and a stepwise regression method. Correlation analysis revealed that the number of spikes per plant and yield per plant both correlated positively with plant height, number of tillers, and mean flag leaf length (P < 0. 01) with a high degree of significance. Typical correlation analysis revealed that the number of tillers and seed length structure coefficients increased with increases in the combined agronomic trait index variables V1 and V2, indicating that the number of tillers and plant height are the main factors determining seed yield from Plantago lanceolata pendants. Stepwise regression analysis gave highly significant (P < 0. 01) coefficients correlating single plant yield with number of single spikes and average number of grains per spike. The average number of grains per spike was significantly different from the partial correlations between number of single spikes, seed length, average number of nodules, plant height, and average flag leaf length (P < 0. 05). The partial correlation of the number of single spikes with seed length, awn length, and average number of nodules per spike was found to be significantly different (P < 0. 05).
