Study On Photosynthetic Pathway And Drought Resistance Ecophysiological Characteristics Of Seven Introduced Atriplex Species

Atriplex is a kind of typical plant species which grow in drought and semi-drought areasaround the world. In order to provide a theoretical basis of reference for its adaptability andphysio-ecological characteristics, a series of tests on 7 Atriplex species: Atriplex canescens(Pursch) Nutt.png, A. confertifolia (Torr & Frem)S.Wats.png, A. corrugate S.Wats.png,A. gardneri(Moq.) D. Dietr.png, A. lentiformis(Torr.) S. Wats.png, A. gardneri trident(Moq.)D. Dietr.png and A. obovata Moq.png which were introduced from North America have beencarried out in two testing bases (Minqin in Gansu Province and Yuanyan in Henan Province).The results showed:All of the 7 species have got Kranz anatomy fences-like Mesophyll cell which containsbundle sheath cell inside through leaf and stem anatomical structure observation. They cangrow in both drought sandy environment (Minqin in Gansu province) and relatively humidcondition (Yuanyang in Henan Province) with averageδ¹³C value from -13‰to -16‰andΔis between 3.514‰and 5.346‰(＜6‰). The light saturation points of the 7 species were from1 603μmol·m^-2·s^-1 to 2 185μmol·m^-2·s^-1 and the apparent quantum yields were from 0.049 5 to0.071 8 molCO₂·mol^-1photons during growing seasons. It was concluded that the 7 introducedAtriplex plant species are belonged to C₄ plant group and their photosynthetic pathway did notchange with places change. Theδ¹³C value of comparison species A. cana C. A.Mey.introduced from Xinjiang, China were -29.263±0.219, belonging to C₃ plant.Li-6400 portable photosynthesis system was used to determine the daily and monthlychanging characteristics of pure photosynthetic rate(Pn), evaporation(E) and water usageefficiency(WUE) of A.canescens and A.obovata growing well both in Minqin, GansuProvince and Yuanyang, Henan Province from May to October. The result showed: (1) Thedaily change graphs of Pn and E of the two species from June to Auguest presented single apexeach in Minqin, but in Yuanyang, only those of A.canescens presented single type whileA.obovata's presented double apices. The daily change graphs of WUE of the two species bothpresented "U" types. The average values of Pn, E and WUE of A.canescens in 6 periods of time in Minqin were 15.265μmol·m^-2·s^-1, 4.299 mmol·m^-2·s^-1 and 4.017μmolCO₂·mmol^-1H₂O, 25.81%, 13.31% and 13.48% higher than those of A.obovata; inYuanyang, the values of A. canescens in the same periods were 15.566μmol·m^-2·s^-1, 5.251mmol·m^-2·s^-1 and 3.443μmolCO₂·mmol^-1H₂O, 1.34% and 8.39% higher and 2.28% lowerthan those of A. obovata respectively, but the differences were not significant. The values ofthe three aspects of A.canescens showed 1.93% and 18.14% lower and 14.27% higher inMinqin than in Yuanyang while those of A.obovata showed 26.26%, 22.54% and 1.38%lower in Minqin than in Yuanyang. (2) The monthly change graphs of Pn, E and WUEpresented single apex each in Minqin, but presented double apices, single apex and near"W" respectively in Yuanyang. The average value of Pn, E and WUE of A.canescens ingrowing seasons in Minqin were 11.969μmol·m^-2·s^-1, 3.301 mmol·m^-2·s^-1 and 3.936μmolCO₂·mmol^-1H₂O, 23.29%, 8.18% and 13.51% higher than that of A.obovata; the valueof Pn, E and WUE of A. canescens in Yuanyang were 14.250μmol·m^-2·s^-1, 4.431mmol·m^-2·s^-1 and 3.792μmolCO₂·mmol^-1H₂O, 0.65%, 8.67% and 0.73% higher than that ofA. obovata, without significant difference. The three factors of A.canescens were 20.59%,32.67% lower and 10.02% higher in Minqin than in Yuanyan; that of A.obovata were38.32%, 29.58% and 8.56% lower in Minqin than in Yuanyang. (3) The different differencesand significant daily and monthly changes of Pn, E and WUE in different places showed thatthe two species mentioned above have strong adaptability to environment, and also can keepstronger abilities to accumulate dry materials and keep higher water usage efficiency withlower consume of water naturally in both dry and subhimid areas. Certain correlation amongδ¹³C,Δand WUE we got showed that when the value ofδ¹³C grows bigger, WUE ishigher. Therefore, plants have high WUE withδ¹³C value increases for the same plant underdifferent growing condition.δ¹³C of plant is higher in Minqin than in Yuanyang.Having studied the drought-resistance characteristics of 4 (A. canescens, A. obovata, A.lentiformis and A. gardneri)of the 7 species, the following results were got. (1) Due toeffects of soil drought stress, the leaf water and free water contents showed decrease whilewater saturation, bound water and bound water/free water value showed increase; waterpotential showed decrease in A. canescens, and showed increase at first and then decrease inA. obovata & A. lentiformis, showed decrease at first and then increase in A. gardneri. Time of leaf holding water ability for A. lentiformis was 87h, but it was 145 to 150h for the left 3species. All of the 4 Attriplex species could effectively keep and adjust their water balancewhich was important for Attriplex species to adapt to arid environment. (2) Under medium andserious water stress, the protective enzyme system of Attriplex could circulate effectivelyand keep usual physiological metabolize, avoiding the mass accumulation of active oxygen;under extreme drought stress, the continuous decrease of SOD, CAT and POD ofA. lentiformis caused the superoxide radical increase rapidly and accumulate thus made themetabolic function inside the plant disorder and unable to adapt to drought environment. SOD,CAT and POD activites of A. obovata showed a raising trend while the superoxide radicalincreased slowly; the SOD activities of A. canescens increased while those of CAT andPOD decreased a little and the superoxide kept in a low value; the POD activities ofA. gardneri increased while those of CAT and POD decreased a little with low superoxideradical in oder to adapt to the extreme drought environment. In the aspects of adaptabilities todrought environment and mechanism, there were differences among Attriplex species. Due tothe intercompensatories among the protective enzyme, the activities of SOD, CAT and PODshowed differences in different periods of drought stress. (3) Along with the increase ofdrought stress, the contents of MDA also increased and the rate even quickened when droughtdegree went from medium to serious (6.15times, 4.56times, 2.36times and 2.21times inA. obovata,A. canescens,A. gardneri and A. lentiformis respectively). The increase of MDAcontents became relaxed with increasing rate of 4.38%, 51.10%, 32.22% and 50.10% forA. canescens, A. obovata, A. gardneri and A. lentiformis respectively along with aggravationof drought stress. The contents of MDA reflected the degree of ceils' injury and membranesuperoxidation of of Attriplex species when suffered from drought stress.(4) The filter adjustmaterials proline and soluble sugar contents within the 4 Atriplex species increased undermedium and serious drought stress, but when the drought stress went from serious toextreme, the two filter adjust materials in A. lentiformis began to decrease and the filter adjustfunction disappeared, meanwhile proline and soluble sugar contents of the other 3 species stillincreasing. This showed that proline and soluble sugar are two important filter adjust materialswhich make Atriplex species adapt to the drought environment in a long period besides theimportance of keeping cell expand and compress, lowering filter force, securing usual metabolize and increasing drought resistance ability. (5) Drought resulted in reduce of totalchlorophyll contents in Atriplex. Along with the drought becoming more serious, the decreaserate of chlorophyll B content became quicker than chlorophyll A content. The total and Bchlorophyll content of A. lentiformis reduced greatly (39.2% and 57.95%) until the droughtstress became more serious. Those of A. obovata,A. canescens and A. gardneri showedplacidly decrease with drought stress increase. Drought stress suffocated the compound ofchlorophyl, together with the speedup of chlorophyllous decompound and content decrease,Atriplex species metabolic functions was affected.