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Effects of Soil Water Stress on Photosynthetic Physiological and Biochemical Characteristics of Hippophae Rhamnoides Linn

Author: PeiBin
Tutor: ZhangGuangCan
School: Shandong Agricultural University
Course: Soil and Water Conservation and Desertification Combating
Keywords: Hippophae rhamnoides Linn. Drought Stress Gas Exchange ChlorophyllFluorescence Antioxidant Enzyme Activity
CLC: S793.6
Type: Master's thesis
Year: 2013
Downloads: 34
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In the Loess Plateau, drought and water shortage is the key ecological problems affectingthe physiological processes of trees and tree growth. Hippophae rhamnoides Linn. is one ofthe widely planted common species in this region. While, so far, the quantitative relationshipbetween the physiological process and growth conditions in Hippophae rhamnoides Linn. andthe soil moisture has not been very clear. Experimental field was located in Shanxi Provincefangshan county valley mouth town TuQiao groove valley. Test material was used by3-year-old Hippophae rhamnoides Linn.. In this study, multilevel soil water contents wereobtained by water supply control and natural water consumption, measurement techniquesand principles of chlorophyll fluorescence and leaf gas exchange were used. The responseprocess and characteristics of net photosynthetic rate (Pn), transpiration rate (Tr), water useefficiency (WUE) and other gas exchange parameters to soil moisture of Hippophaerhamnoides Linn. were studied, the restriction degree and influence mechanism of soilmoisture stress on photosynthesis were revealed, including stomatal limitation mechanism,fluorescence kinetics mechanism and biochemical mechanism, the quantitative relation ofdifferent photosynthesis efficiency parameters and soil moisture was cleared, and the soilmoisture environment suitable for growth and high efficiency water was cleared. Thesefindings are of great theoretical value to study deeply photosynthetic characteristics andphysiological mechanisms of drought and have practical value in tree species siteconfiguration and Soil moisture management in the Loess hilly region. The results showedthat:1. The response process and mechanism of photosynthesis to soil moisture(1) When relative soil water content (RWC) was70.5%, the net photosynthetic rate (Pn)was maximal. When RWC was between38.9%and70.5%, Pn, stomatal conductance (Gs) andintercellular CO2concentration (Ci) significantly decreased with increasing drought stress,meanwhile, stomatal limitation (Ls) significantly increased, indicating that stomatal limitationwas responsible for reduction in Pn. When RWC was lower than38.9%, Pnand Lsdecreasedand Ciincreased with increasing drought stress, showing that the main reason for restrictingPnhad turn into non-stomatal limitation. Turning point of RWC from stomatal to non-stomatallimitation was38.9%for leaf photosynthesis.(2) The maximal fluorescence (Fm), maximal photochemical efficiency(Fv/Fm) of PSII, actual photochemical efficiency (ΦPSⅡ) and photochemical quenching (qP) all showeddeclining trends under continuous drought stress, while minimal fluorescence (Fo) increasedsignificantly, non photochemical quenching (NPQ) increased and then decreased. When RWCwas between38.9%and70.5%, thermal energy dissipation was the significantphotoprotective mechanism. And RWC lower than38.9%caused the inhibition ofphotosynthetic electron transport and damage of PSII.(3) Chlorophyll content and leaf relative water content (LRWC) decreased and proline(Pro) and soluble sugar (Ss) increased with the increasing drought stress. The activities ofsuperoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) increased and thendecreased with the deepening of drought stress, while malondialdehyde (MDA) contentsincreased continuously. These showed that the activities of the antioxidant enzyme wereactivated in the region where SWC were from48.3%to70.5%. Under severe water stress(RWC<38.9%), the antioxidant enzyme system was damaged, the activities of the antioxidantenzymes declined and cell membrane was destroyed.(4) The function of photosynthetic apparatus in Hippophae rhamnoides Linn. seedlingleaves was maintained by a synergistic effect of thermal energy dissipation and regulating theantioxidant enzymatic activity jointly in the region where SWC were from48.3%to70.5%,and the decreased Pnwere mainly due to stomatal limitations through stomatal regulation.Major non-stomatal limitation responsible for reduction in Pnwas associated with theimpairment of PSⅡ and antioxidant enzyme system under severe water stress (RWC<38.9%).2. The threshold response of photosynthetic physiological parameters on soil moistureand the classification of soil water photosynthetic productivity(1) Pn, Trand WUE of Hippophae rhamnoides Linn. showed obvious threshold responseto soil moisture, they first increased and then decreased with the increasing drought stress.When RWC was60.1%, water use efficiency was the highest. When RWC was71.2%,photosynthetic efficiency was the highest. When RWC was79.5%, transpiration efficiencywas the highest. When RWC was less than18.9%, photosynthetic efficiency was invalid.When RWC was less than38.7%, photosynthetic limiting factor was from stomatal limitationto non-stomatal limitation. RWC=38.9%was the soil water maximum deficit level allowed inthe semiarid loess hilly region for Hippophae rhamnoides Linn.(2) The light response curves of Hippophae rhamnoides Linn. in different droughtstresses were fittrd by rectangular hyperbola model, non–rectangular hyperbola model,exponential model and modified rectangular hyperbola model, and the results showed modified rectangular hyperbola model best fitted. The apparent quantum yield (AQY), lightcompensation point (LCP), light saturation point (LSP), dark respiration rate (Rd) andmaximum net photosynthetic rate (Pnmax) of Hippophae rhamnoides Linn. had obviousthreshold response to soil moisture. AQY, LSP, Rdand Pnmaxfirst increased and then decreasedwith the aggravation of drought stress, while LCP first decreased and then increased. WhenRWC was71%, light response characteristic parameters reached extreme, the ability ofabsorbing and using light intensity was the highest, photosynthesis potential was maximum,dark respiration activity was the highest, and photosynthetic physiological activity was thehighest. So, RWC=71%was the optimum soil moisture threshold for photosyntheticphysiological activity of leaves in Hippophae rhamnoides Linn..(3) In the Loess Plateau, the range of RWC less than18.9%was non productivity andnon WUE, the range of RWC more than79.5%and18.938.7%were low productivity andlow WUE,38.7%60.1%was middle productivity and high WUE,60.1%71.2%was highproductivity and middle WUE, and71.12%79.5%was middle productivity and low WUE.In order to improve the water use efficiency as the core of the soil moisture managementthoughts, the range of RWC suitable for growth of Hippophae rhamnoides Linn. was38.7%60.1%, in this range, the more soil moisture was, the higher Pnand WUE were, when WUEreached60.1%, Pnand WUE reached the highest, this critical threshold was called as highproductivity and high WUE.

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CLC: > Agricultural Sciences > Forestry > Forest tree species > Broad-leaved shrubs > Seabuckthorn
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