Chin J Plan Ecolo ›› 2012, Vol. 36 ›› Issue (1): 72-80.DOI: 10.3724/SP.J.1258.2012.00072

• Research Articles • Previous Articles     Next Articles

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

SUN Dong-Bao and WANG Qing-Suo*   

  1. Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences/Key Laboratory of Dry Land Agriculture of Ministry of Agriculture, Beijing 100081, China
  • Received:2011-04-18 Revised:2011-10-06 Online:2012-01-01 Published:2012-01-05
  • Contact: WANG Qing-Suo

Abstract:

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 (Gs), transpiration rate (Tr), and net photosynthetic rate (Pn).
Important findings The original light conversion efficiency (Fv/Fm), Gs, Tr, and Pn of alfalfa were significantly improved by increasing irrigation. Moreover, correlation analysis showed that the mean value of the day of Fv/Fm, Gs, Tr, and Pn had significantly positive relationships with the average soil water content of 0–280 cm depth. Pn had a significantly positive relationship with Fv/Fm × PAR (photosynthetically active radiation). Additional irrigation also changed the diurnal courses of leaf Pn. 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. Pn 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.