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In order to understand the dynamic variations of photosynthetic capacity of Rhododendron to adapt to environmental factors in different seasons. Rhododendron delavayi, widely introduced and cultivated, was planted in a 2-gallon plastic basin in the open field. The dynamic variations of photosynthetic characteristics and influencing factors in different growth phases were investigated by the technique of gas exchange and chlorophyll fluorescence. The results were as follows: The growth cycle of R. delavayi were almost overlaps with photosynthetic variation at Kunming area. The variations of photosynthetic characteristics reflected the variations of growth cycle. In the net early growth period from May to July, the photosynthetic rate(Pn)increased rapidly, the stomatal conductance(Gs)was the decisive factor affecting (Pn). The relative humidity of air(RH)had a significant indirect effect on (Pn) by affecting Gs and transpiration rate(Tr). The (Pn) and growth could be stimulated by increasing RH at this phase. In the peak growth period from July to October, the RH, (Pn) and Gs of R. delavayi were high and stable. However, lower air temperature(AT)in this phase was a unique climate character in Kunming area. Low AT became an important factor affecting photosynthetic capacity at this phase, and increasing AT could improve (Pn) and promote the growth of R. delavayi. In the late growth phase after October, AT and RH decreased rapidly, stomata closed gradually, the maximum quantum efficiency of photosynthetic system Ⅱ(Fv/Fm)and (Pn) were declined. Gs and Fv/Fm were the main factors affecting photosynthesis at this stage. Our results can provide important references for the scientific cultivation and popularization of R. delavayi. [ABSTRACT FROM AUTHOR]

In order to explore the effects of fertilization on the growth and photosynthesis in Heritiera littoralis seedlings, we used 2-year-old H. littoralis seedlings as plant material, and a pot experiment was set up with fertilization treatment of 6 levels, i.e., CK(0 g per plant), N1(10 g per plant), N2(15 g per plant), N3(20 g per plant), N4(25 g per plant)and N5(30 g per plant). This experiment lasted for 140 d, and the differences in growth, biomass, leaf chlorophyll content, photosynthetic parameters and chlorophyll fluorescence parameters were compared across different fertilization levels. The results were as follows:(1)The growth(seedling height and ground diameter), biomass(leaf, stem and root), leaf chlorophyll content [Chl a, Chl b and Chl(a+b)], leaf net photosynthetic rate(Pn), transpiration rate(Tr), stomatal conductance(Gs), water use efficiency(WUE), maximum photochemical efficiency(Fv/Fm), actual photosynthetic efficiency(ΦPS Ⅱ), apparent photosynthetic quantum transfer efficiency(ETR)and photochemical quenching coefficient(qP)all displayed a hump-shaped trend with increasing fertilization, while intercellular CO2 concentration(Ci)and non-photochemical quenching coefficient(NPQ)displayed a decreasing trend.(2)The growth, biomass, gas exchange parameters and chlorophyll fluorescence parameters of H. littoralis seedlings had different responses to fertilization. Specifically, seedling chlorophyll content, root mass and total biomass maximized at the fertilization level of 10 g per plant, seedling growth(height and ground diameter), leaf and stem mass maximized at 20 g per plant, and gas exchange parameters(Pn, Tr and Gs), chlorophyll fluorescence parameters(Fv/Fm, ΦPS Ⅱ, ETR and qP)maximized at 30 g per plant. In conclusion, our results suggested that an appropriate amount of fertilization can significantly enhance the leaf chlorophyll content, stomatal conductance, photochemical efficiency and electron transfer rate in H. littoralis seedlings, resulting in lower heat dissipation and thus higher photosynthetic capacity, while over-fertilization can induce photoinhibition in H. littoralis seedlings, which decreases photochemical efficiency and suppresses seedling growth. [ABSTRACT FROM AUTHOR]

Pot experiment was conducted to evaluate the effect of volatile oil from an invasive plant, Chenopodium ambrosioides and its two main components α-terpene and cymene on the photosynthetic characteristics of Vicia faba seedlinGs. The results showed that the volatile oil treatment significantly reduced the net photosynthetic rate(Pn), stomatal conductance(Gs), transpiration rate(Tr), maximum photochemical efficiency(Fv/Fm), actual photochemical efficiency(ΦPS II)and total chlorophyll content. However, it increased the concentration of intercellular CO2(Ci), which was the dual effect of dose and time, and the effect of high dosed volatile oil treatment was irreversible. Compared with the control group, α-terpene treatment reduced Pn, Fv/Fm and ΦPS II, increased Ci, Gs and Tr, and all the parameters were gradually approaching to the control level after stopping treatment. However, the effects of cymene on photosynthetic characteristics of Vicia faba seedlinGs were not significant. These results suggested that the volatile allelochemical stress from Chenopodium ambrosioides on photosynthesis of receptor plants was due to the the synergistic effect of many allelochemicals, instead of a single component. [ABSTRACT FROM AUTHOR]

Hybrid zone is a natural laboratory for studying speciation and evolution. In order to explore the ecophysio-logical adaptability of three species of seabuchthorn(Hippophae), we measured the relevant environmental factors and diurnal changes in photosynthetic characteristics of female and male plants of the three Hippophae species in Qilian County of Qinghai Province in July. The results were as follows:(1)The diurnal variation of photosynthesis between female and male plants of the same species was basically consistent, and there are differences in the diurnal variation of photosynthetic characteristics of the threeHippophae species. Diurnal changes of net photosynthetic rate(Pn)in H. rhamnoides ssp. sinensis showed a significant bimodal curve, with peak values at 10:00 and 14:00, and the highest value was(19.53±5.35)μmol·m-2·s-1 when photosynthetically active radiation(PAR)and air temperature(Ta). Although the diurnal changes of Pn in H. goniocarpa and H. neurocarpa ssp. neurocarpa were all nearly bimodal curve, the higher values at 8:00 and 16:00, and the highest values were(13.43±3.43)and(15.27±2.43)μmol·m-2·s-1, repectively when PAR and Ta were lower.(2)Water use efficiency(WUE)of the three species of Hippophae was consistent with the change of Pn, but H. rhamnoides ssp. sinensis had a higher WUE, which peaked at 10:00 and 14:00, and the highest value was(6.7±0.95)μmol·mmol-1. The peak values of H. goniocarpa and H. neurocarpa ssp. neurocarpa were 8:00 and 16:00, and the highest values were(4.03±1.08)and(4.93±0.86)μmol·mmol-1, respectively.(3)The diurnal changes of transpiration rate(Tr), stomatal conductance(Gs), intercellular CO2 concentration(Ci)and stomatal limiting value(Ls)of the three species of Hippophae were similar. Gs decreased uniformly after 10:00 among them, and there were different degrees of stomatal closure at around 12:00, which was one of the causes of leaf photosynthetic depression in midday. In diurnal changes of photosynthesis, H. rhamnoides ssp. sinensis was significantly different from others, H. goniocarpa showed similar change trend with H. neurocarpa ssp. neurocarpa, and its Pn and WUE may be affected by environmental factors such as Ta, PAR and air relative humidity(RH). [ABSTRACT FROM AUTHOR]

Mangrove associates are a category of plants that can grow and reproduce on both intertidal coastal zones and land. As subtropical coastal zones are characterized by high sun light and temperature, how mangrove associates adapt to such an environment is an important issue. Some researches show that mangrove associates are similar to land plant as well as thalassophyte in certain morphological structures and biochemical characteristics. However, there are few studies focusing on plant physiological characteristics of mangrove associates, especially in leaf gas exchange characteristics. Hibiscus tiliaceus(Malvaceae)is a pantropical mangrove associate that usually occurs in coastal zones. It is widely used for the conservation of sea banks, architecture and medicine. In order to disentangle the photosynthetic physiological mechanims underlying its habitat adaptation to high light and temperature under south subtropical climate, leaf gas exchange characteristics of H. tiliaceus were measured using LI-6400 portable photosynthesis system(Li-Cor Inc, USA)at Mangrove Natural Reserve of Qi'ao Island of Zhuhai City, Guangdong Province during July and August of 2013. The nature reserve(22°23'40'' N, 113°36'40'' E)is characterized by a typical south subtropical monsoon climate. The diurnal changes in photosynthetic rate(Pn), stomatal conductance(Gs), intercellular CO2 concentration(Ci)and transpiration rate(E)in H. tiliaceus all exhibited a mono-peak modal, and the peak value of Pn occurring at noon was around 26.8 μmol CO2 · m-2 · s-1 without obvious photoinhibition during the daytime. The high photosynthetic rate in H. tiliaceus was associated with high stomatal conductance, which was probably related to anatomical features of leaves, such as high stomatal density and dense trichomes in the lower leaf epidermis. Analysis of light response curves revealed that its light saturation point was 800 μmol photons·m-2 ·s-1 and its light compensation point was 26 μmol photons·m-2 ·s-1. The net photosynthesis at saturating irradiances was high at 27.8 μmol CO2 · m-2 · s-1. These photosynthesis parameters, along with high daily mean photosynthetic rate(19.6 μmol CO2 · m-2 · s-1)in H. tiliaceus suggested that this mangrove associate was characterized as a typical sun plant species. The results showed that the fast growth of H. tiliaceus might be attributed to its high and stable photosynthetic capacity, thus providing basic data for further revealing the eco-physiological mechanism underlying habitat adaptation of H. tiliaceus and other mangrove associates to coastal environment with high temperature and high light in summer. These results can also provide theoretical supports for its planting and reforestation practices. [ABSTRACT FROM AUTHOR]