Abstract: A comparative study was made on the photosynthetic characteristics and photo-adaptability of four Melilotoides ruthenica ecotypes by using Li-64 00 p ortable photosynthesis system and attached chlorophyll fluorescence chamber. Amo ng the test ecotypes, ecotype 00-61 from Tumetezuoqi of Inner Mongolia and ecot ype 93-21 from Songneng grassland of Heilongjiang had higher maximum net photos ynthetic rate (Pmax), photochemical efficiency (ΦPSⅡ), pho tochemical quenching coefficient (qP) and dark respiration rate but lower non-photochemical quenching coefficient (qN), indicating their higher pot ential to produce more biomass. Ecotype 00-61 also had higher light saturation point, and thus, had higher photo-adaptability to strong light, being adaptable to plant in relatively high-light environment. Ecotype 90-36 from Hunshandake desert area in Zhenglanqi of Inner Mongolia belongs to Melilotoides ruthenica var. oblongifolia, which had lower qP and higher qN, and thus, had hi gher defensive capability to light-inhibition damage than other three ecotypes. Ecotype 00-81 from the typical grassland of Xilinghot in Xilinguole League of Inner Mongolia had lower light compensation point and light saturation point, ex hibiting stronger shade tolerance and higher adaptability to weak light, compari ng with the other three ecotypes.

Key words: Spectral indices method, Water content, Soil-adjusted water index