Guo, Qinfeng; Taper, Mark; Schoeneberger, Michele M.; and Brandle, James R., "Spatial-temporal population dynamics across species range: from centre to margin" (2005). USDA Forest Service / UNL Faculty Publications. 15.

No abstract

No abstract

No abstract

Pisum sativum L. was exposed to ultraviolet-B (UV-B) radiation (280-315 nm) in greenhouse and controOled environment chambers to examine the effect of this radiation on photosynthetic processes. Net photosynthetic rates of intact leaves were reduced by UV-B irradiation. Stable leaf diffusion resistances indicated that the impairment of photosynthesis did not involve the simple limitation of CO2 diffusion into the leaf. Dark respiration rates were increased by previous exposure to this radiation. Electron transport capacity as indicated by methylviologen reduction was also sensitive to UV-B irradiation. The ability of ascorbate-reduced 2,6-dichlorophenolindophenol to restore much of the electron transport capacity of the UV-B-irradiated plant material suggested that inhibition by this radiation was more closely associated with photosystem II than with photosystem I. Electron micrographs indicated structural damage to chloroplasts as well as other organelles. Plant tissue irradiated for only 15 minutes exhibited dilation of thylakoid membranes of the chloroplast in some cells. Some reduction in Hill reaction activity was also evidenced in these plant materials which had been irradiated for periods as short as 15 minutes.Ultraviolet radiation in the 280 to 315 nm waveband, usually denoted as UV-B radiation, is readily absorbed by nucleic acid and protein chromophores (8) and effectively inhibits many plant processes (5), including photosynthesis (2, 22). Ultraviolet radiation of this waveband is of particular interest to photobiologists because this radiation occurs in normal sunlight and would be intensified if the atmospheric ozone layer were reduced (3,10). Although the action of intense 254 nm UV radiation on photosynthetic processes has been well studied (7), this radiation would not reach the Earth's surface even in the event of severe ozone radiation.The present study was initiated to evaluate effects of UV-B radiation on photosynthesis and aspects of the electron transport system, and to define morphological changes of chloroplasts in Pisum sativum L. plants exposed to Results of this study tend to support the hypothesis that photosynthetic processes primarily associated with PSII are affected by the levels of UV-B radiation tested in this study. MATERIALS AND METHODSP. sativum L. cv. Early Alaska plants were grown under greenhouse conditions with an approximate 14-hr photoperiod and PAR4 of about 400 ,ueinsteins m-2 sec-'. Studies of the effects of plant biomass were initiated when the seedlings were 7 days old. In all other experiments, the seedlings were 14 days old upon initiation of treatment.Spectral irradiance for the controlled environment studies was provided by the lamp filter system previously described (21). The PAR was 800 ,ueinsteins -m-2 -sec-1 with a 16-hr photoperiod. Temperatures were programmed to simulate a July day in northern Utah (13 to 37 C). Spectral irradiance for both the control and UV radiation treatments are illustrated in Figure 1.The biomass study was carried out i...