Font Size: a A A

Study On Acclimation Of Seeding And Sapling Foliage Of Japanese Yew(Taxus Cuspidata) To Different Light Intensity

Posted on:2013-01-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:W LiFull Text:PDF
GTID:1113330374471446Subject:Soil and Water Conservation and Desertification Control
Abstract/Summary:PDF Full Text Request
Sun light is one of the most important ecological factor for plant growth. Photosynthesis is plant basic life activity and the basis of all life. The low irradiance could decrease the photosynthetic rate of plant. However, the extremely high irradiance can lead to damage for the photosynthetic apparatus and even the death of plant. Japanese yew (Taxus cuspidata Sieb, et Zucc.) is a rare relic plant of the Tertiary Period, National Key I wild and endangered plant, which has a wide distribution in Northeast China. It grows in vegetated mixed forests in mountainous regions. The Japanese yew seeding can survive at the low irradiance under the field and artifical condition, and the high light can result in death. Howerver, in our study the Japanese yew sapling (minimum age15-year-old) can grow well under high irradiance (natural condition). It has become important aspect of studying the acclimation of seeding and sapling of leaves Japanese yew to different irradiance. In this paper, the photosynthetic characteristics of seeding and sapling of Japanese yew were studied, the differences between seeding leaves and sapling leaves in photoprotection were identified, and the effect of photorespiration and xanthophyll cycle on photoprotection were discussed. The results are as follows:The photosynthetic characteristics of seeding under the different irradiance condition were studied. The results showed that the seeding grown under one layer net shading and full sun light had the higher net photosynthetic rate (Pn) and light saturation point (LSP), and their LSP were ca.1000μmol·m-2s-1. The LSP of two and three layer net shading were ca.600μmol·m-2·s-1. The diurnal course of Pn in different irradiance presented "double peaks", and "midday depression" occurred significantly in seeding leaves under the full sun light and one layer net shading. The ratio of dry weight for sun light, two and three layer net shading leaves decreased.The efficiency of energy captured by open PSII reaction centers (Fv/Fm) for sun light Japanese yew decreased, suggesting that photoinhibition occurred under high irradiance. Sun light treatment had lower quantum yield of PSII electron transport (ΦPSⅡ) than the others. The sun light and one layer net shading had higher non-photochemical quenching (NPQ), indicating that high irradiance can increase dissipation of excess light energy as heat.Sun light and one layer net shading leaves of Japanese yew possessed lower levels in total chlorophylls content basis on weight, but had higher ratio of Chl a/b. The total antioxidant activity of on layer net shading leaves of Japanese yew was higher than the other treatments.The content of MDA, O2-produce rate and the content of H2O2for sun light seeding leaves were higher than other treatments, indicating that more excess excitation energy occurred under high irradiance and can not be dissipated. However, the capacity of photosynthesis for seeding leavs under low irrandiance decreased, and the dry weight can not accumulate due to the low irradiance.To further explain the acclimation of Taxus cuspidata to light intensity, the15-year old saplings of Taxus cuspidata were taken as test materials and the Photosynthetic Characteristics and chloropphyll Fluorescence were studied under different light intensities.Compared with salings of Taxus cuspidata grown in full light, lower photosynthetic rate and lower efficiency of primary enery conversion as well as lower electron transport were found in plant grown in weak light. The photosynthetic rate of leaves grown in weak light was60%the photosynthetic rate of leaves grown in full light, and the carboxylation efficiency was lower than the leaves grown in full light. When the irradiance was transferred from dark to high light, the photosynthetic quantum efficiency of sun leaves were higher than that of shade leaves, the fluorescence light responses curve of shade leaves' ΦPSⅡ deceased faster than sun leaves'and the sun leaves'ETR increased more quickly than the shade leaves'. Non-photochemical quenching (NPQ) of sun and shade leaves both increased, but the shde leaves reached its peak at low light intensity.The shade leaves possessed a higher chlorophylls, lower values for the ratio Chl a/Chl b, lower values for actual photochemical efficiency and lower values for electron transport rate, and showed low irradiance adaptation response to low light intensity. The shade leaves were more susceptible to photoinhibition due to low CO2assimilation and protection mechanisms.The differences in chloroplast pigments, gas exchange and photosystemⅡ (PSⅡ) photochemistry as well as xanthophyll in seeding and sapling leaves of Taxus cuspidata grown in full sunlight were examined. Compared with the sapling leaves, the chlorophyll content, photosynthetic capacity and light intensity for saturation of photosynthesis were lower in seeding leaves. The response curves of PSⅡ photochemistry demonstrated that both seeding and sapling leaves occurred a down-regulation of PSⅡ photochemistry at high irradiance, more serious down-regulation being examined in seeding leaves. And the down-regulation of PSⅡ photochemistry occurred significantly when measured at midday, indicating that photoinhibition occurred heavily in seeding leaves when exposed to high light. The actual PSⅡ efficiency(ΦPSⅡ) and the efficiency of excitation capture by open PSII centers drastically decreased with the increase of non-photochemical quenching(NPQ) at midday. The photorespiration rate in seeding leaves was lower than that in sapling leaves under high irradiance. The results indicated that the xanthophlly cycle was activated in both the seeding and sapling leaves at midday and a increase of de-epoxidation were observed, but a little higher level of de-epoxidation was measured in seeding leaves. The xanthophyll cycle may play an important role in the dissipation of excess light energy associated with NPQ to avoid photodamage. Our results suggested that photoinhibition occurred in seeding leaves significantly due to lower capacity of CO2assimilation, photorespiration and the light intensity for saturation of photosynthesis, as well as the lower PSII photochemistry at high irradiance; therefore the Taxus cuspidata seeding could not adapt to growing at high irradiance.
Keywords/Search Tags:Japanese yew(Taxus cuspidata), different light intensity, photosynthesis, antioxidants, photoprotection
PDF Full Text Request
Related items