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Studies On Osmotic Adjustment And Photosynthetic Adaptations Of Iris Lactea Pall. Var Chinensis Koidz Grown In Salt And Alkali Soil

Posted on:2006-09-12Degree:DoctorType:Dissertation
Country:ChinaCandidate:G Y SunFull Text:PDF
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For several years, Iris lactea Pall, var chinensis(Fisch .) Koidz is bred a tolerant herbage to salt and alkali soil as virescence. In this paper, Ecophysiology of Iris lactea Pall, var chinensis(Fisch.) Koidz were studied to investigate growth, osmotic regulation, photosynthetic diurnal changes, photosynthetic apparatus characteristics grown in salt and alkali soil. The results were followings:1. A study was conducted to determine growth characteristics, capacity of osmotic adjustment of Iris Lactea Pall, var Chinensis Koidz grown in salt-alkali soil of Songnen plain in China. Iris Lactea Pall, var Chinensis Koidz grew more rapid on July and August, plant height is 5090cm, and has 5-8 branches. The biomass per plant is 47.2g/plant during growth and development period. The process of Iris growth is divided three stages: slow growth stage, rapid growth stage and stop growth stage. Substances of osmotic adjustment were analyzed to determine the capacity of osmotic adjustment and adaptation in Iris leaves. Accumulation of Na+ and K+, proline concentration and improvement of cell membrane penetration were conducted to adjusted very rapidly to salt and alkali content during each month. With the accumulation osmotic substances, water potentials and osmotic potentials in Iris leaves decreased, cell turgid pressure increased or maintained to preserve cell, leaf and then whole plant growth under salt and drought condition.2. The results showed that the ABA contents in leaves after salt and alkali treats increased markedly. The addition of exogenous ABA decreased the increment of MDA and H2O2 contents and retarded the attenuation of CAT activity, which were induced by salt and alkali treats, and enhanced the GR activity. The content of leaf ABA increased under long-term salt and alkali stress, but root ABA differed among plants. However, in corn roots which possess a well-developed exodermis, alkaline and saline conditions in the rhizosphere did not reduce the endogenous ABA concentration, because the leaching of ABA from corn roots into the rhizosphere was lower than that from Iris and soybean roots. ABA efflux from corn and Iris and soybeab roots into the soil solution was observed only during the first days of the experiments and thereafter became substantially decreased.3. The data acquired in this study showed that diurnal changes of Pn and Tr were two-peak-type-curve, and was marked midday depression of Pn, which could be fully accounted for Gs changes. Carboxylic efficiency(CE) photosynthetic rate at saturation for intercellular CO2 concentration(A350) apparent quantum yield(AQY) and photosynthetic rate at light saturation(Pmax) decreased in the midday. The result demonstrated that midday depression could be attributed to leaf temperature rising caused by the increasing of strong solar radiation (PAR).4. The results showed that Pn decreased with leaf ripping, and CO2 carboxylic efficiency (CE), apparent quantum yield(AQY) declined at same time, but maximum photochemical efficiency(Fv/Fm) had little changed during leaf senescence of Iris lactea Pall, var chinensis(Fisch.) Koidz. During senescence of Iris lactea Pall, var chinensis(Fisch.) Koidz, CE and A350 (net photosynthetic rate at light saturation) declined more rapid than AQY and Jmax (net photosynthetic rate at CO2 saturation (net photosynthetic rate at light saturation). This result showed that dark reaction or carbon cycle of photosynthesis declined more rapid than light reaction.5. The data acquired in this study showed that the diurnal changes of the maximum PS II photochemical efficiency (Fv/Fm) and actual photochemical efficiency of PS II (OPS II) were related to light intensity, the functional photosystem II reaction centers were decreased to cause significant photoinhibition. With the increasing of photosynthetic actual irradiation (PAR) to simulatePAR diurnal change, Fv/Fm and OPS II decreased, nonphotochemical quenching (NPQ) increased, and the fraction of excited energy allocated to PS II increased to enhance PS II burden carrying excited energy. These results indicated that photoinhibition in Iris leaves are caused primarily by increasing of excited energy allocated to PS II to enhance reversible inactivation of PS II centers except NPQ increasing. With the decreasing of PAR, Fv/Fm and OPS II increased, NPQ and unbalance index of excited energy allocated to PS II and PS I (p/a-1) declined respectively. This indicated that the recovery of PS II photochemical efficiency is caused primarily by renewing PS II activation owing to unloading the energy burden of PS II.6. Salt and alkali treatment (the content of salt 0.36%,pH 8.90) alone had no effect on the maximal photochemistry of PS II (Fv/Fm), but decreased apparent photosynthetic electron transport rate(ETR).However, the salt and alkali treatment accompanied with drought decreased Fv/Fm and the efficiency of excitation captured open PS II(Fv'/Fm'), and state transition (from II to I) caused 33.3% decrease in allocation of excited energy to PS I and 18.1% increase to PS II. At the same time, the salt and alkali treatment accompanied with drought resulted in serious imbalance of excited energy distributions between two photosystems, enhanced the pressure on PS II .It is suggested that Nonphotochemical quenching (NPQ) could play a key role in adaptation mechanism of plant to stress.7. NaCl treatment alone had no effect on the maximal photochemistry of PSII. However, the NaCl treatment modified pH stress on PSII photochemistry in Iris leaves, which was manifested by a lesser pH-induced decrease in photochemical quenching (qP), efficiency of excitation energy capture by open PSII reaction centers (Fv7Fm'), and quantum yield of PSII electron transport (OPSII). Additions of calcium and ABA could alleviate photoinhibition in Iris leaves treated by NaCl. But Additions of calcium has no effects on alleviating under alkaline stress, and ABA does.
Keywords/Search Tags:Iris Lactea Pall, var Chinensis Koidz, osmotic adjustment, diurnal changes of photosynthesis, chlorophyll fluorescence, state transition, ABA, salt and alkali soil
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