Abstract:

Gas exchange, water relations and leaf chemical characteristics were examined of two dominant psammophytes: Artemisia frigida Willd and A. halodendron Turcz. ex Bess in Horqin sandy land, Nei Mongol, China under different water regimes. The measurements were conducted by submitting the plants to five different irrigation levels. A. frigida was characterized by lower photosynthetic rate (P_n), lower transpiration rate (TR) and lower shoot water potential (Y_w) relative to A. halodendron. Foliage of A. frigida had higher values of relative water deficit (RWD), bound water content (BWC), ratio of bound water content to free water content (BWC/FWC) and integrated drought-resistant index (DI) than that of A. halodendron. Water relations differed significantly between two species in response to soil water availability. Yw, BWC and BWC/FWC ratio of A. halodendron exhibited large variation with gradual decrease of soil moisture. However, in terms of these parameters, A. frigida was characterized by higher capacity of water holding and drought tolerance relative to A. halodendron. Proline and total soluble sugar contents of A. frigida and A. halodendron tended to increase with decrease of soil moisture and the former had a larger increase amplitude than the latter. This shows that A. frigida has a higher osmotic regulation ability than A. halodendron. Under the extreme drought conditions, Yw, RWD, BWC and BWC/FWC of two species were approximate, but soluble proteins degraded largely. A large amount of accumulation of organic matter, proline and total soluble sugars were observed in both A. halodendron and A. frigida. The increase in proline and total soluble sugar contents and soluble protein degradation of A. frigida far exceeded those of A. halodendron. We believe that the accumulated materials at this moment are mostly of nutrient substances available for the recovery of plants after the drought. This is one of the reasons why A. halodendron plants died while A. frigida plants survived under extremely drought condition. Our results suggest that these ecophysiological features of A. frigida are favorable to its growth in the fixed sandy land compared with A. halodendron, which often lost its dominance due to weak competition for water sources under lower soil water availability and are major factors resulting in replacement of A. halodendron by A. frigida in the later stage of sandy vegetation succession in Horqin.

Key words: Artemisia frigida, A.halodendron, water stress, gas exchange, plant water relations, leaf chemical characteristic, adaptive strategy