水分对苜蓿叶片光合特性的影响

采用田间试验, 对每茬灌水3次(W₃)、2次(W₂)、1次(W₁)和不灌水(W₀)四种条件下的土壤水分, 苜蓿(Medicago sativa)叶片的叶绿素荧光参数、气孔导度(G_s)、净光合速率(P_n)和蒸腾速率(T_r)进行测定。结果表明, 灌水提高了苜蓿叶片的原初光能转换效率(F_v/F_m)、P_n和T_r, 并随着灌水量的增加而增加。苜蓿叶片的F_v/F_m、P_n和T_r的日均值与土壤含水量均呈极显著正相关关系。苜蓿叶片的P_n与F_v/F_m和光合有效辐射(PAR)的乘积呈正相关关系。灌水还改变了苜蓿叶片P_n的日变化格局。灌水较多的处理(W₃和W₂), 苜蓿叶片没有出现光合“午休”现象,P_n的日变化趋势呈现“单峰”型。而灌水较少和不灌水的处理(W₁和W₀), 苜蓿叶片出现了明显的光合“午休”现象, 其P_n的日变化进程呈现“双峰”型。在相同的水分条件下, 初花期苜蓿叶片的P_n高于再生期的, T_r则相反。

Effects of water on the photosynthetic characteristics of alfalfa (Medicago sativa)

Aims Alfalfa (Medicago sativa) is the most extensive perennial leguminous forage. In the semi-arid region, water is the most important limiting factor for alfalfa growth. Our objective was to study the effect of soil water content on physiological properties of alfalfa.
Methods Our field experiment consisted of four treatments: non-irrigation (W₀) and irrigated (75 mm each) once (W₁), twice (W₂) and three times (W₃) for each crop. We evaluated soil moisture, leaf chlorophyll fluorescence parameters, stomatal conductance (G_s), transpiration rate (T_r), and net photosynthetic rate (P_n).
Important findings The original light conversion efficiency (F_v/F_m), G_s, T_r, and P_n of alfalfa were significantly improved by increasing irrigation. Moreover, correlation analysis showed that the mean value of the day of F_v/F_m, G_s, T_r, and P_n had significantly positive relationships with the average soil water content of 0–280 cm depth. P_n had a significantly positive relationship with F_v/F_m × PAR (photosynthetically active radiation). Additional irrigation also changed the diurnal courses of leaf P_n. Photosynthesis of alfalfa under W₂ and W₃ treatments did not present the “midday depression”, and the diurnal courses were unimodal. Nevertheless, treatments W₁ and W₀ exhibited an apparent “midday depression” phenomenon, and the diurnal variation was bimodal. There were different physiologically activities at different growth stages of alfalfa. P_n of alfalfa in the early flowering stage was obviously higher than in the regeneration stage, in contrast Tr was lower at the early flowering stage.