Effects Of Soil Drought On Non-structural Carbon And Nitrogen Contents Of Different Organs And Long-distance Transportation In Three Species Woody Plants

Soil drought and nutrition deficiency are the main factors of restricting plant growth andecological restoration in arid and semiarid areas of China. In order to examine the internalavailability of carbohydrates and nitrogen nutrition and long-distance mass flow via thephloem and xylem, one-year-old R. pseudoacacia, H. rhamnoides and B. alternifolia wereplanted individually in pots and exposed to three soil water contents (suitable soil watercontent, medium drought, and severe drought, corresponding to soil water contents between70~75%,50~55%and30~35%of field water capacity, respectively) from mid-May to lateAugust. We compared the differences of different treatments in biomass, soluble sugarconcentration, soluble amino compounds and protein content in different organs, activities ofnitrate reductase and long-distance mass flow of carbon and nitrogen via the phloem andxylem. The results showed that:(1) The biomass of R. pseudoacacia seedings in different organs was significantlyreduced with soil water content decreased, but the coarse root biomass under severe waterstress increased slightly compared to medium stress; Biomass of different organs of H.rhamnoides was declined with the increase of water stress; B. alternifolia also present declinetrend in biomass under water stress, but there was no significant change in coarse root andstem biomass medium drought, but the fine root biomass under severe water stress increasedslightly compared to medium stress.(2) Under all three water conditions, the soluble sugar concentration in stem and coarseroots of R. pseudoacacia seedings was significantly higher than that in leaves and fine roots.With the soil moisture decreased, soluble sugar concentration of stem, coarse and fine rootsincreased significantly, but no obvious change was observed in leaves; In H. rhamnoides thesoluble sugar concentration in stem and coarse roots was significantly higher than that inleaves and fine roots. Soil moisture had no significant effects on the sugar concentrations ofleaf and stem, but under severe drought sugar concentration in the coarse roots and fine rootsincreased significantly; Unlike R. pseudoacacia and H. rhamnoides, B. alternifolia leaves soluble concentration was significantly higher than that of other organs. Medium soil waterstress made B. alternifolia sugar concentration significantly decreased in the leaves, but sugarconcentration of the coarse and fine root increased significantly. Severe soil water stress madeB. alternifolia leaf sugar concentration increased significantly, other organs also showedincreasing trend.(3) The changes on the concentration of soluble sugar of phloem exudates in the threespecies tree: in R. pseudoacacia and H. rhamnoides phloem exudates in soluble sugarconcentration did not change obviously under the suitable soil water content and mediumdrought; exposed to severe water stress shows a decrease trend; B. alternifolia soluble sugarcontent in phloem exudates under medium and severe stress presented increasing trend. Inaddition, the soluble sugar content in phloem exudates is significantly higher than that of R.pseudoacacia and H. rhamnoides.The changes on the concentration of soluble sugar of xylem sap in the three species tree:R. pseudoacacia and B. alternifolia under medium water stress in xylem sap of soluble sugarcontent decreased significantly, but under severe water stress the soluble sugar concentrationsignificantly increased compared to medium drought. But H. rhamnoides unchanged undermedium water stress, exposed to severe water stress the concentration of soluble sugar issignificantly reduced.(4) Under drought stress, R. pseudoacacia activities of nitrate reductase in fine roots andleaves presented increasing trend; H. rhamnoides nitrate reductase activity in different organshad no obvious effects; B. alternifolia nitrate reductase activities in leaves and fine roots withdecreased along with the decrease of soil moisture. Moreover the nitrate reductase activity ofR. pseudoacacia was significantly higher that of other organs, whereas the nitrate reductaseactivity in leaves of H. rhamnoides and B. alternifolia were significantly higher than that inthe root.(5) As the soil water content decreased, and R. pseudoacacia soluble amino compoundscontent in different organs had a tendency to increasing, which under the severe soil waterstress, showed a significant increasing trend; H. rhamnoides under medium water stress thestems and coarse roots amino compounds significantly reduced, amino compounds in leavesand fine roots under severe drought significantly increased; B. alternifolia amino compoundscontent in different organs increased along with the decline of soil water.As the soil water content decreased, soluble protein content in different organs of R.pseudoacacia increased. The content of soluble protein in fine roots is significantly higherthan that of other organs; H. rhamnoides exposed to severe water stress the soluble proteincontent increased in different organs. The soluble protein content in leaves and stems were significantly higher than that in roots; B. alternifolia under medium water stress proteincontent showed increasing trend, but only in leaves soluble protein content significantlyincreased under severe water stress and other parts were not significantly changed.(6) Drought stress had no significant influence on R. pseudoacacia total amino nitrogenin the long distance transportation, but the composition and content of individual aminocompounds changed significantly. Under medium drought, the Asn in the phloem and GABAin the xylem increased significantly, Ala in the phloem has dropped significantly, the Gln andSarc in xylem reduced, whereas the content of Pro significantly increased. Under severedrought stress, Arg increased significantly in the phloem, the content of Asn, Sarc, His andSarc decreased in xylem, Pro significantly increased. In all water conditions, NH4+maintainedrelatively high level in the phloem and xylem sap.H. rhamnoides seedlings under medium and severe water stress, the amount of aminonitrogen in the phloem declined slightly, whereas the total amino nitrogen of xylem displayedincrease along with decline of soil water content, showing significant under severe waterstress. Under medium drought, content of Ser, Asn, Gln, Met, ethylamine and His in thephloem dropped significantly. In xylem, Asp and Asn significantly increased. Severe droughtstress significantly reduced the content of Asn, Met, ethylamine and GABA in the phloem, atthe same time, improve Thr, Ser, Asn, α-aminodip andα-aminobs in the xylem.The total amino nitrogen content of B. alternifolia in the phloem and xylem under thecondition of medium water stress tends to decline, but increased under severe drought stress.Under medium water stress, Arg content in phloem and xylem declined significantly. Undersevere water stress, the Asn, Glu, Arg and NH4+in the phloem dropped significantly.