Growth And Physiological Response To Short-term Drought And Re-watering Of Bothriochloa Ischaemum Under Different Nitrogen Supply Conditions

There is little rainfall and the distribution of annual and seasonal rain is uneven in semiarid Loess Plateau hilly region. Water is a major limiting factor of vegetation restoration and ecological construction in the region where is lack of nitrogen. After long-term natural selection, native species have formed a series of adaptation mechanisms under the local natural environment. Therefore, the study of physiological adaptability of native dominant species under different water and nitrogen conditions can provide a theoretical basis for the rational use of this species in vegetation construction. The natural grassland dominant species B. ischaemum in loess hilly region was used under potted contidion. There were three nitrogen treatments(N0- no nitrogen, N1-0.1 g N Kg-1 and N2-0.2 g N Kg-1) and four water treatments(continuous drought stress and re-watering B. ischaemum to 80% field capacity(80% FC) when the soil water content fall to 60% FC, 40% FC and 20% FC, respectively). The study aimed to compare gas exchange parameters, chlorophyll fluorescence parameters, biomass allocation and water use efficiency of B. ischaemum in different water and nitrogen conditions in the jointing stage. The main results were as follows:(1) Continuous drought stress significantly reduced the net photosynthetic rate(Pn) of B. ischaemum, but maximum photochemical efficiency(Fv/Fm) had no significance. When soil water content was not less than 40% FC, Fv/Fm under sufficient water supply condition had no significant difference with that under continuous drought stress. B. ischaemum could rehydrated green quickly even soil water fall to 20% FC, Fv/Fm and Pn could recover to the level of sufficient water supply.(2) There were no significant differences of Fv/Fm between sufficient water supply and N1 treatment under 30% FC soil water content. Fv/Fm and Pn were significantly higher of N1 treatment after re-watering than N0 and N2 treatment. Fv/Fm and Pn were significantly lower of N2 treatment than N0 treatment after re-watering.(3) Nitrogen treatment significantly reduced root-shoot ratio of B. ischaemum(P<0.05). The total biomass was significantly higher with N1 treatment than other treatments(P<0.05), and the water use efficiency was significantly higher with N1 treatment than other treatments when rehydrated at 20% FC soil water content(P<0.05).In summary, B. ischaemum has desiccation tolerance. It can survive when the soil water content fall to 20% FC and recover to higher physiological activity after re-watering. It is advantageous to photosynthesis, biomass accumulation and water use of B. ischaemum when applying nitrogen fertilizer at 0.1 g N Kg-1.