Drought differently affects growth properties, leaf ultrastructure, nitrogen absorption and metabolism of two dominant species of Hippophae in Tibet Plateau

Hippophae has been exploited as food, medicine as well as pioneer species for fixing nitrogen (N) and preventing desertification in Tibetan Plateau. In the paper, the eco-physiological responses and adaptive abilities of Hippophae rhamnoides and Hippophae thibetana seedlings under two levels of drought (50% and 30% field capacity) were investigated. The results indicated that two drought treatments differently affected biomass partition, water use efficiency, ammonia (NH4-N) and nitrate nitrogen (NO3-N) absorption, contents of hydrolysable amino acids (AA) and leaf ultrastructure of the two species of Hippophae. The two species had better resistance to moderate drought, while extreme drought showed more negative effects on biomass and ultrastructure of H. rhamnoides. Two drought treatments significantly increased water use efficiency of the two species. In H. rhamnoides, the two levels of drought stresses decreased the absorption of ammonia and nitrate nitrogen, whereas only inhibited NO3-N absorption of H. thibetana. The H. thibetana seedlings had more root nodules and higher R/S ratio than H. rhamnoides, while H. rhamnoides seedlings increased most individual and total AA in leaf and root organs under two drought treatments. The different growth, N-related absorption as well as metabolism responses of the two dominant species of Hippophae to drought stress may affect seedling colonization, the ecological function of N fixation and preventing desertification in Tibet Plateau in the future.