Hydraulic Redistribution Of Nitraria Sphaerocarpa Between Root And Soil And Its Response To Drought Stress

The mechanism of desert plant adapting to drought stress is one of the hotspot in plant physiology. Hydraulic redistribution between root and soil and its mechanism were started to study from late 1980's. In China, the study especially on desert plants is inchoate. In this paper, we chose Nitraria sphaerocarpa from Alxa league, Inner-Mongolia autonomous region as the experimental material. Hydraulic lift of N. sphaerocarpa was identified by using a split-root apparatus, and changes of photosynthesis, root growth and soil available nutrients under hydraulic lifting conditions were studied. Mechanism of hydraulic lift was also discussed. Response of osmotic adjustment and growth to drought stressed condition was investigated by treatment of N. sphaerocarpa seedlings with different concentrations of iso-osmotic PEG6000 solutions. The main results were below:1. The phenomenon of hydraulic lift and inverse hydraulic lift of N. sphaerocarpa was identified. From 15:00 to 7:00, water potential of upper pots (hydraulic lift) or lower pots (inverse hydraulic lift) continuously increased. It was about 815±78g - 1695±45g/3plants for hydraulically-lifted water and 450±22g - 520±34g/3plants for inverse hydraulically-lifted water in average. Inverse hydraulic lift gives a chance to utilize the pulse water resources such as rainfall.2. Occurrence of hydraulic lift has something to do with the changes of water potential between soil and N. sphaerocarpa's roots. Hydraulic lift could be detected when the differences in water potential between roots and soil reached 0.54±0.018MPa, and it couldn't be detected when the differences increased to 0.97±0.026MPa.3. Hydraulic lift improved water content of shallow soil, so photosynthesis, transpiration and stomatal conductance of N. sphaerocarpa with hydraulic lift were significant higher than that without hydraulic lift, so were volume of taproot and lateral root, diameter of taproot. With higher photosynthesis, N. sphaerocarpa could synthesize and accumulate more substances to adapt stress. It could also absorb more water and nutrients with better root growth.4. Nutrients in the upper pots were activated by hydraulic lift, mineral nitrogen increased 32.65% to CK, and available phosphorus decreased 46.98% to CK. there was no significant difference of available potassium between HL and CK.5. N. sphaerocarpa seedlings grew well under light water stress condition. With increasing concentration of PEG, their dry weight would increase first, then decrease. At the PEG concentration of 15%, the seedlings could get the maximum dry weight. Change of MDA was opposite to change of dry weight, so the ability of anti-oxidation plays a more important role in N. sphaerocarpa's growth than osmotic adjustment.6. Strong adjustment ability of N. sphaerocarpa under PEG stress is mainly caused by organic solutes such as free proline and soluble sugar. With increasing water stress, the contents of free proline and soluble sugar would significantly increase, but content of K~+ decrease notably, and the content of Na~+ would first increase then decrease, but the total accumulated content of Na~+ changed little.