| 1. Responses and adaptations of Leymus chinensis to soil moistureLeaf relative water content (RWC) was increased subtly by light and moderate soil drought, but reduced significantly by severe drought. Soil drought reduced biomass of plant, especially at the later growth stage. It was suggested that the leaf water status may be regulated adaptively by soil drought, and the growth was limited by extreme soil drought. The sheath allocation decreased gradually with growth development, but did oppositely for rhizome, suggesting the translocation from the matter in stored sheath to rhizome. Soil drought increased the root allocation and ratio of shoot to root in the earlier period, but did oppositely in the later period, indicating that the higher capacity of plant drought resistance through increasing root distribution decreased gradually after enduring long period of soil drought. Light drought (LD), moderate drought (MD) did not significantly affect leaf RWC, stomatal density, photosynthetic parameters, fluorescence parameters and community CO2 daily net exchange rate, but severe soil drought (SD) significantly reduced them.The soluble protein of Leymus chinensis leaf at MD was the greatest, but those at SD, especially very soil drought (VD) significantly were reduced, and the trend of free amino acid (FAA) similar. The activity of nitrate reductase (NR) gradually decreased with decline of soil moisture, and the activity of glutamine synthetase (GS) was increased by 25.75% and 12.22% at LD and MD respectively, but reduced by 8.21% and 28.72% at SD and VD respectively, indicating that NR was the sensitive to soil drought and GS had an adaptive response to drought. LD did not increase the activities of asparagine enzyme (AE) and endopetidase (EP), but MD, SD and VD significantly increased their activities, indicating LD slightly affected the degradations of leaf soluble protein and amino acid, but greatly enhanced the degraded procedure with increasing soil drought. SD and VD significantly reduced the contents of total nucleic acid and RNA, implying the severe soil water stress restricted the synthetic metabolism of nuclei acid and provoked its degraded metabolism. Severe soil drought also increased the malondialdehyde (MDA) content, indicating thatcell membrane peroxidating was provoked.2. Responses and adaptations of Leymus chinensis to soil drought and rewateringThe growth of Leymus chinensis could enhance because of moderate term drought acclimation, but rewatering offseted the loses of biomass and leaf area due to long term soil drought. The leaf stomatal density of moderate term soil drought (Mtd) was the largest followed by the short term soil drought (Std), those of Mtd and Std were 14.90% and 3.61% greater than that of the Control, and stomatal index was the similar trend. Rewatering stimulated leaf net photosynthetic rate (A), stomatal conductance (gs) and transpiration rate (E), and the recently rewatering could increase their kind of effect. Rewatering did not significantly affect leaf respiration at night. The diurnal fluctuation water use efficiency (WUE) showed the "M" curve pattern, which Mtd had the greatest peak, and which cubic function could be simulated by the curve in 24 h of day and night. Leaf chlorophyll fluorescence kinetic analysis showed that rewatering, especially recently, could significantly enhance PS II capacity, chlorophyll a and b, and its ratio, strengthen carbonic anhydrase (CA) activity.Nitrogen content was the greatest in leaves (4.40%), the lowest (1.99%) in roots, ranged from 2.26% to 4.40% in litter leaves, stems and sheaths, and rhizomes. That of control was the lowest and that of Std greatest in all Leymus chinensis organs. The ratio of carbon and nitrogen was the greatest at control, but other soil water treatments had no effects, implying that Leymus chinensis could acquire the nitrogen metabolism capacity when subjected to water stress in moderate term. The plant total nitrogen amount at Std was the greatest, compared to control, the nitrogen amount was increased by 35.58 , 2...
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