土壤水分胁迫对紫花苜蓿光合特性及其生物量的影响

紫花苜蓿是我国重要的豆科牧草，具有较强的抗旱能力，而水分亏缺是影响其产量的主要逆境因子之一。通过大田试验对不同水分胁迫下紫花苜蓿的光合特性及产量进行研究，结果表明：① 土壤水分胁迫对紫花苜蓿光响应参数影响显著(P＜0.05)，随着水分胁迫的加剧，最大净光合速率、表观量子效率、光饱和点逐渐降低，暗呼吸速率、光补偿点逐渐升高，从而直接影响紫花苜蓿光合作用对弱光的吸收和转化效率。② 随着水分胁迫的加剧紫花苜蓿叶片的净光合速率(Pn)和蒸腾速率(Tr)呈显著的下降趋势，气孔导度(Gs)呈先下降后上升的趋势，表明轻度水分胁迫下气孔因素是Pn下降的主要因素，中度和重度水分胁迫下非气孔因素是Pn降低的主要因素。③ 当光合有效辐射(PAR)为1 200 μmol·m^-2·s^-1时，轻度水分胁迫的水分利用效率(WUE)显著大于充分灌溉的WUE (P<0.05)，表明适度水分胁迫可提高紫花苜蓿叶片的水分利用效率。④ 轻度水分胁迫与充分灌溉干草产量之间无显著差异，表明轻度水分胁迫能达到高产节水的目的。

Effects of Soil Water Stress on Photosynthetic Characteristics and Biomass of Medicago sativa

Medicago sativa is an important legume forage in China, and it is strong in drought resistance. However, water deficit is still the main stress factor affecting its yield. The photosynthetic characteristics and yield of M. sativa under different water stress conditions were studied by carrying out the field experiments. The results showed that: ① Soil water stress affected significantly the photoresponse parameters of M. sativa. With the increase of soil water stress, the maximum net photosynthetic rate, apparent quantum yield and light saturation point were decreased gradually, but the dark respiration rate and light compensation point were gradually increased, thus the dyssophotic absorption and conversion efficiency of M. sativa in its photosynthesis were directly affected; ② With the increase of soil water stress, the net photosynthetic rate (P_n) and transpiration rate (T_r) of M. sativa leaves were reduced significantly, but the stomatal conductance (G_s) was decreased at first and then increased, which revealed that the stomatal factors under slight water stress were the main factors resulting in the P_n reduction, and the non-stomatal factors under moderate and severe water stress were the main factors resulting in the P_n reduction; ③ When the photosynthetically active radiation (PAR) value was 1 200 μmol·m^?2·s^-1, the water use efficiency (WUE) of slight water stress was significantly higher than that of full irrigation (P<0.05), indicating that moderate water stress could improve the water use efficiency of M. sativa;④ There was no significant difference of hay yield between slight water stress and fully irrigation, indicating that high forage yield and water-saving irrigation could be achieved under slight water stress.