The Responses Of Leymus Chinensis To Salt-alkali Stress And Clipping

Songnen plain is one of the main districts in which Chinese saline-alkali soil concentrates. Overgrazing often enhanced degradation processes and turned out to be an additional major threat for livestock farming. Leymus chinensis is dominant species in this grassland. It has been considered this species adapts grazing pressure under a certain salt stress. However, the adaptation mechanism is unclear. Field experiment was conducted with mixed salt-alkali solution (NaCl: NaHCO₃: Na₂CO₃ = 1:1:1) and clippings (removal 60% of aboveground green biomass) of L. chinensis. The regrowth biomass, plant density and photosynthesis were measured in the field.Our results indicated that individual plant biomass was increased under salt addition, while the tiller density was significant decreased. The net photosynthesis rate and water use efficiency were also higher under salt stress conditions. L. chinensis is rhizome grass and can produce lots of ramets along the rhizomes. The productivity improvement can by increasing the number of tillers, ramet biomass, or their combination. In our case they behaved as the total ramets decreased after salt addition, but the single ramet biomass increased to compensate the loss and finally increased biomass regrowth. On one hand, the reduction of density can not only decrease the material and energy consumption of the population, but also can take away part of salt ions to lower down the salt stress. One the other hand, the water resource can be used by per ramte increased since ramte number reduced. This is why the photosynthesis of L. chinensis was higher under salt addition conditions.The relative growth rate and photosynthesis were significant higher under clipping situation. Combined with the changes in soluble sugar content, we can speculate that the compensation capacity of L. chinensis was mainly due to stored carbohydrates hydrolyzed into soluble carbohydrate and then transferred to the aboveground. Besides, the new leaves contained more efficient light-harvesting pigment, thus photosynthesis was increased.