[Photosynthetic characteristics of Leymus chinensis and Medicago sativa in artificial grassland]. / ç¾Šè‰å’Œç´«èŠ±è‹œè“¿äººå·¥è‰åœ°å ‰åˆç‰¹æ€§.

To explore the effect of monoculture and mixture sowing artificial grassland on the photosynthetic characteristics of Leymus chinensis and Medicago sativa, we determined the diurnal variation of photosynthetic properties of L. chinensis and M. sativa under different treatments. The results showed that the diurnal changes of net photosynthetic rate, blade temperature and transpiration rate of L. chinensis and M. sativa showed 'unimodal type' in monoculture, the stomatal conductance of M. sativa showed 'unimodal type', and the stomatal conductance and water use efficiency of L. chinensis showed 'bimodal type'. Under the mixed sowing treatment, the diurnal changes of net photosynthetic rate, blade temperature and transpiration rate of L. chinensis and M. sativa showed 'unimodal type', the stomatal conductance and water use efficiency of L. chinensis showed 'unimodal type', and the stomatal conductance of M. sativa showed 'bimodal type'. The peak photosynthetic rate of L. chinensis under mixture was signi-ficantly higher than that under monoculture, being 17.72 and 13.65 µmol CO2·m-2·s-1, respectively. Under monoculture and mixture sowing treatments, the chlorophyll content of L. chinensis was higher than that of M. sativa, nitrogen content of the leaves of L. chinensis was lower than that of M. sativa, and the nitrogen content in the leaves of mixture sowing L. chinensis was significantly higher than that of monoculture sowing L. chinensis, which were 27.60 and 22.55 g·kg-1, respectively. Net photosynthetic rates of L. chinensis and M. sativa were significantly positively correlated with stomatal conductance and transpiration rate, and significantly negatively correlated with intercellular CO2 concentration under different planting methods. Net photosynthetic rate of M. sativa was significantly positively correlated with blade temperature and water use efficiency. In summary, mixed sowing was beneficial to enhance nitrogen content of L. chinensis. Our results provided a theoretical basis for the response of the photosynthetic characteristics of forage to planting mode of artificial grassland.

[Effects of drought stress on C, N and P stoichiometry of Ulmus pumila seedlings in Horqin sandy land, China.] / å¹²æ—±èƒè¿«å¯¹ç§‘å°”æ²æ²™åœ°æ¦†æ ‘å¹¼è‹—C、N、P化学计量特征的影响.

To understand the effects of drought stress on C, N and P stoichiometry in different organs of Ulmus pumila, U. pumila seedlings were grown under suitable water level, mild, moderate and serious water stress treatment, i.e., 80%, 65%, 50% and 35% of field water holding capacity. The results showed that drought stress increased C content in leaves, stems, coarse and fine roots, N content in leaves, stems and coarse roots, and P content in fine roots, but decreased P content in leaves, stems and coarse roots. Moreover, C:N in leaves and stems decreased, while C:P and N:P in leaves, stems and coarse roots increased and in fine roots reduced in response to drought stresses. There were significant correlations of C content among different organs, while N content was not correlated with P content in all organs. Soil water content was negatively related to C content in all organs, N content in leaves, P content and C:N in fine roots, C:P and N:P in leaves, stems and coarse roots. There were positive relationships between the soil water content and N content in fine roots, P content in leaves, stems and coarse roots, C:P and N:P in fine roots. These findings indicated that the absorption and upward translocation of N and P of U. pumila seedlings were influe-nced by drought stress. Nitrogen limitation for the growth of U. pumila seedlings was found. With the increases of drought stress, however, P limitation was gradually enhanced.