| Explore three tree species photosynthesis and the suitable quantitative relationship of soilmoisture in loess hilly region, for plant introduction and screening of the reconstruction, andstanding a reasonable configuration to provide theoretical and technical reference fragileecological zones. The application of plant physiological ecology principles, leaf gas exchangeand chlorophyll fluorescence test technology, three species of Prunus sibirica L., Hippophaerhamnoides L., Pinus tabulaeformis Carr. and field seedlings as test material were measureddaily dynamic process in photosynthesis under different soil moisture, and chlorophyllfluorescence parameters of dynamic process. Exploring the three species of diurnal variationsof photosynthesis characteristics of stomatal regulation mechanism, proved the photosyntheticefficiency (photosynthetic rate, water use efficiency, etc.) and quantitative relationshipbetween soil moisture and its variation and mechanisms. Determine the three tree speciesphotosynthesis and efficient water and suitable soil moisture threshold. The study made thefollowing main results and conclusions:1. Revealing the diurnal variation and the physiological mechanisms of the three treespecies in photosynthetic efficiencyThree tree species photosynthesis process of change are different and affected significantlyby the influence of soil moisture changes; the non-stomatal limitation of photosynthesisappears under severe water stress.Three tree species photosynthesis process of change are different and affected significantlyby the influence of soil moisture changes. With water stress intensifies, the diurnal changetype of the three species by the obvious double-peak curve into a single peak curve, and thenby a single peak curve gradually transition to the double-peak curve. Its transition threshold ofsoil moisture are between40%-60%. the main reason for three species photosynthesis "lunchbreak" performances the change of stomatal limitation to non-stomatal with the intensificationof soil water stress, when the RWC>50%of the soil moisture range, the falling of all speciesphotosynthetic rate at noon due to stomatal limitation, but in RWC between30%-50%, themain reason for the photosynthesis "lunch break" shift to non-stomatal limitation gradually. 2. Three tree species had a stronger ability to drought and photosynthesis on soil moisture toadapt to a wide range of species, but its photosynthesis level and appropriate moisture scopehave certain differences.The photosynthesis level of three species were as follows: Prunus sibirica L. is49.3%-77.0%, Hippophae rhamnoides L. is54.2%-76.8%and Pinus tabulaeformis Carr. is54.1%-80.9%. The Pnand WUE of Prunus sibirica L., Hippophae rhamnoides L. and Pinustabulaeformis Carr. had the highest in56.1%,60.4%and65.8%,its not good for the plant touse water when the soil moisture too high or low.The average daily net photosynthetic rate ofthree species were: Prunus sibirica L.（3.22μmol·m-2·s-1）> Hippophae rhamnoides L.(2.88μmol·m-2·s-1)> Pinus tabulaeformis Carr.(2.87μmol·m-2·s-1). Prunus sibirica L. had ahigh photosynthetic productivity, and then Hippophae rhamnoides L., Pinus tabulaeformisCarr. was the lowest. Average daily water use efficiency were: Hippophae rhamnoides L.(1.6μmol·mmol-1)> Prunus sibirica L.(1.1μmol·mmol-1)> Pinus tabulaeformis Carr.(1.0μmol·mmol-1). In addition to the outside of Prunus sibirica L., Pinus tabulaeformis Carr. hadthe lowest water use efficiency of three species. When the relative soil water content（RWC）was respectively at the range of49.3%-77.0%、54.2%-76.8%、54.1%-80.9%, Prunus sibiricaL., Hippophae rhamnoides L., and Pinus tabulaeformis Carr. could keep the highphotosynthetic level.3. Soil water stress intensified to enhance the three tree species photosynthesis inphotoinhibition; increase in heat dissipation is the main mechanism of plants againstphotoinhibition.Three species of the Pn、Fm、Fv/Fmand ΦPSⅡhad a midday decline of the phenomenon,that is to say three species have the photosynthesis photoinhibition. Its NPQ has middaytended to increase heat dissipation increases, indicating that the photosynthetic apparatus isone of the main mechanism of the three species to resist light suppression and mitigation ofthe photosynthesis of the lunch break. when the RWC>50%, species did not occur thephotoinhibition, Pndecline were mainly caused by non-stomatal restrictions in the afternoon.when the RWC were30%-50%, three species were occured the photoinhibition, with thewater stress mitigation, the photoinhibition had a lower degree. After more than13:00, Pnwere from stomatal limitation to non-stomatal limitation. when the RWC <30%, the plantleaves had occur the photo-oxidation damage. Under different water conditions, the treesNPQ had a midday rise trends show that the heat dissipation increases, that is one of the mechanisms of the trees to resist photoinhibition and to ease the photosynthesis "lunchbreak". |
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