Foliar metabolic heat rate of seedlings and mature trees of Pinus ponderosa exposed to acid rain and ozone

We investigated the effects of acid rain and ozone on respiration rates of 1-year-old and current-year foliage of half-sib seedlings and mature clones of a ponderosa pine genotype by measurement of foliar metabolic heat rates. Two rain regimes (pH 5-1 and 3-0) were applied weekly to foliage only, from January to April 1992. Two ozone regimes (ambient and twice-ambient) were applied from September 1991 to November 1992. Metabolic heat rate was measured in April on 1-year-old foliage, in June on both 1-year-old and current-year foliage, and in November on current-year foliage in 1992. Except for current-year foliage in June, the metabolic heat rate was calculated per unit of both foliar dry mass and N mass. In seedlings, both measures of metabolic heat rate increased in late June for 1-year-old foliage exposed to twice-ambient ozone, and in November for current-year foliage exposed to the combination of twice-ambient ozone and pH 3-0 rain. In mature trees, metabolic heat rate was not affected significantly by ozone, rain acidity, or their interaction. In June, when both 1-year-old and current-year tissues were examined, the metabolic heat rate of expanding, current-year foliage was higher than that of fully expanded, 1-year-old foliage regardless of plant age or treatment combination.     

Ultrastructure and some plasma membrane characteristics of ozone-exposed loblolly pine needles

Tropospheric ozone is a widespread and phytotoxic air pollutant in the industrialized world and causes reduced growth in many tree species. It is therefore important that, for example, the responses of the economically important loblolly pine to ozone are determined thoroughly. The objective of the study was to determine changes in ultrastructure, the vanadate-sensitive ATPase activity of the plasma membrane, the fatty acids of plasma membrane phospholipids, visible injury, and growth in loblolly pine (Pinus taeda L.) needles exposed to different concentrations of ozone in open-top chambers. The treatments were charcoal filtered air (CF), nonfiltered air (NF), or NF-air with ozone added for 12 h daily at 1.5- or 2-fold ambient ozone concentrations from May to October, 1993. Visible injury was more severe in the high than in the low ozone treatments. Growth of needles of the first flush of 1993 was significantly reduced in the highest ozone treatment. Two types of ultrastructural injury, characterized as either acute or chronic, were observed in mesophyll cells under elevated ozone. The acute injury lead to cell collapse and death. The chronic injury, characterized by several symptoms, e.g. decreased chloroplast size and increased density of the stroma, was also found in the NF ozone treatment. Increased density of chloroplast stroma and swelling of thylakoids were transient symptoms, suggesting partial recovery as ozone concentrations decreased in fall. Ozone induced decreases in the specific activity of vanadate-sensitive ATPase of plasmalemma and in the degree of unsaturation in phospholipid fatty acids. The detected reduced needle growth, ultrastructural injury and perturbations in the function and composition of the plasma membrane indicate susceptibility of loblolly pine to ozone. Changes in the plasma membrane phospholipids may have contributed to the decrease in ATPase activity. Injury to the key enzyme of the plasma membrane can directly affect intracellular processes. In the long-term, decreased viability of needles can lead to reductions in loblolly pine productivity.     

The effects of UV-B radiation on loblolly pine. 3. Interaction with CO2 enhancement

Projected depletions in the stratospheric ozone layer will result in increases in solar ultraviolet-B radiation (290–320 nm) reaching the earth's surface, These increases will likely occur in concert with other environmental changes such as increases in atmospheric carbon dioxide concentrations. Currently very little information is available on the effectiveness of UV-B radiation within a CO₂-enriched atmosphere, and this is especially true for trees. Loblolly pine (Pinus taeda L.) seedlings were grown in a factorial experiment at the Duke University Phytotron with either 0, 8.8 or 13.8 kJ m⁻² of biologically effective UV-B radiation (UV-B_BE). The CO₂ concentrations used were 350 and 650 μmol mol⁻¹. Measurements of chlorophyll fluorescence were made at 5-week intervals and photosynthetic oxygen evolution and leaf pigments were measured after 22 weeks, prior to harvest. The results of this study demonstrated a clear growth response to CO₂ enrichment but neither photosynthetic capacity nor quantum efficiency were altered by CO₂. The higher UV-B irradiance reduced total biomass by about 12% at both CO₂ levels but biomass partitioning was altered by the interaction of CO₂ and UV-B radiation. Dry matter was preferentially allocated to shoot components by UV-B radiation at 350 μmol mol⁻¹ CO₂ and towards root components at 650 μmol mol⁻¹ CO₂. These subtle effects on biomass allocation could be important in the future to seedling establishment and competitive interactions in natural as well as agricultural communities.     

土壤重金属污染的微生物生态效应研究进展

对近年来土壤重金属污染微生物生态效应的研究进展进行了归纳总结,主要从微生物群落特性和微生物生理、生化参数等几个方面进行了阐述。重金属污染土壤后,尤其是高浓度的重金属污染对微生物生物量和群落结构都有破坏作用,但由于微生物群落结构的复杂性和研究方法的片面性,一直是研究的热点和难点,开发更加简便、直接的方法将是对这方面研究的突破。同时,微生物的生理、生化参数是从另一侧面反映重金属污染对微生物的影响,它是对微生物群落特性研究的有利补充,所以不同方法的合理选择和搭配是实验取得预期结果的关键因素之一。     

Seasonal development of loblolly pine lateral roots in response to stand density and fertilization

In 1989, two levels each of stand density and fertilization treatments were factorially established in a 9-year-old loblolly pine plantation on a P-deficient Gulf Coastal Plain site in Rapides Parish, Louisiana, USA. In 1995, a second thinning was conducted on the previously thinned plots and fertilizer was re-applied to the previously fertilized plots. The morphology of new long lateral roots was evaluated at 2-week intervals in five Plexiglas rhizotrons per plot of two replications. The overall objective of this study was to evaluate the seasonal initiation of six morphological categories of long lateral roots ( 2.5 cm in length) in response to stand density and fertilization. Lateral root development exhibited a seasonal pattern with the initiation of branched lateral roots predominantly occurring in spring and summer. The initiation of non-branched lateral roots occurred throughout the year regardless of season. Stand density did not affect lateral root morphological development. However, fertilization stimulated the initiation of branched lateral roots that were greater than 1 mm in diameter.     

接种彩色豆马勃对模拟酸沉降下马尾松幼苗生物量的影响

外生菌根能够提高宿主植物对外界环境胁迫的抵抗力,促进植物的生长,本文试图揭示外生菌根对酸雨胁迫下马尾松生长的保护作用。本研究采用盆栽试验,共设置四个处理：酸雨对照处理（Control check (CK), 约pH值5.5）不接种,酸雨对照处理接种,酸雨pH值3.5处理不接种,酸雨pH值3.5处理接种。pH值3.5的酸雨处理降低马尾松的生物量,在试验前期降低根冠比,试验中后期则提高根冠比,在试验初期增加了叶面积,但中后期显著降低了叶面积。接种外生菌根菌有利于马尾松幼苗的生长,pH值3.5处理下接种外生菌根菌能提高马尾松幼苗的生物量,外生菌根菌对生物量分配和叶面积的影响与酸雨胁迫的影响是相反的,即外生菌根菌抵消了酸雨胁迫对马尾松的影响。     

Net CO2 exchange of Pinus taeda shoots exposed to variable ozone levels and rain chemistries in field and laboratory settings

Net CO₂ exchange rates (CERs) were measured in seedlings of two loblotly pine ( Pinus taeda L.) families following 6- or 13-week exposures to ozone (charcoalfiltered or ambient air + O₃) and acid rain treatments (pH 3.3, 4.5 and 5.2). Ozone exposures (14 or 170 nl l⁻¹) were made in open-top chambers, and in continously stirred tank reactors (14, 160 or 320 nl l⁻¹) located in the field and laboratory, respectively. The CERs of whole shoots were measured in an open infrared gas analysis system at 6 levels of photosynthetic photon flux density (0, 33, 60, 410, 800 and 1660 μmol m⁻² s⁻¹). Treatment effects were not consistent between field- and laboratory-exposed seedlings. Ozone-treated field seedlings exhibited statistically significant reductions in light-saturated CER of 12.5 and 25% when measured at 6 and 13 weeks, respectively. Laboratory seedlings exhibited mixed responses to O₃, with one family showing reduced CER only after 6 weeks of O₃ exposure and the other only after 13 weeks (O₃ >160 nl l⁻¹ for both). After 13 weeks of exposure, pH 3.3, and 4.5 rain treatments enhanced light-saturated CER by an average of 52% over that observed in seedlings exposed to the pH 5.2 treatment. Enhanced CERs due to acid rain were of the same magnitude (3–5 μmol CO₂g⁻¹ s⁻¹) as ozone-induced CER reductions. No differences in dark respiration were detected between treatments. Although ozone and acid rain treatments altered seedling CER, the differences were not translated into altered final plant dry weights over the 13-week exposure period.     

Distribution of extractable heavy metals in different soil fractions

Abstract

Due to the difficulties of precisely characterizing environmentally contaminated soil, the effects of heavy metals on plants are studied using uncontaminated soil spiked with known quantities of heavy metals. One problem in using spiked soils is how accurately the distribution of metals mimics stabilized natural soils. We studied the distribution of cadmium, chromium, copper, lead, nickel, and zinc in soil fractions after application in soluble form. The soil samples included a control (an uncontaminated Typic Argiudoll) and two samples spiked with either a moderate or high heavy metal concentration). After application of the salts the soils were subjected to wet/dry cycles over the course of three months. The soils were fractionated using a sequential chemical extraction procedure employing: (1) CaCl₂,(2) NaOH, (3) Na₂EDTA and (4) HNO₃, HCl, and HF. Soil physical separation was carried out by ultrasonic dispersion. The heavy metal levels were determined using ICP-AES. Each heavy metal displayed a unique behavior when added to soil in the form of soluble salts. Cadmium and zinc remained in the soluble fraction, indicating that no equilibrium was attained, while nickel primarily appeared in the insoluble fraction. Chromium, copper and lead were distributed among various soil chemical fractions. The highest levels of all metals appeared in the clay fraction except lead which was mainly present in the silt fraction.     

High-efficiency Agrobacterium-mediated transformation of Norway spruce (Picea abies) and loblolly pine (Pinus taeda)

Agrobacterium-mediated gene transfer is the method of choice for many plant biotechnology laboratories; however, large- scale use of this organism in conifer transformation has been limited by difficult propagation of explant material, selection efficiencies and low transformation frequency. We have analyzed co-cultivation conditions and different disarmed strains of Agrobacterium to improve transformation. Additional copies of virulence genes were added to three common disarmed strains. These extra virulence genes included either a constitutively active virG or extra copies of virG and virB, both from pTiBo542. In experiments with Norway spruce, we increased transformation efficiencies 1000-fold from initial experiments where little or no transient expression was detected. Over 100 transformed lines expressing the marker gene -glucuronidase (GUS) were generated from rapidly dividing embryogenic suspension-cultured cells co- cultivated with Agrobacterium. GUS activity was used to monitor transient expression and to further test lines selected on kanamycin-containing medium. In loblolly pine, transient expression increased 10-fold utilizing modified Agrobacterium strains. Agrobacterium-mediated gene transfer is a useful technique for large-scale generation of transgenic Norway spruce and may prove useful for other conifer species.     

Ecophysiological responses of Japanese forest tree species to ozone, simulated acid rain and soil acidification

In this review, I summarized the results obtained from experimental studies on the ecophysiological responses of Japanese forest tree species to O₃, simulated acid rain and soil acidification. Based on the studies conducted in Japan, exposure to ambient levels of O₃ below 100 nl·l⁻¹ (ppb) for several months is sufficient to inhibit dry matter production and net photosynthesis of sensitive Japanese forest tree species such as Siebold's beech and Japanese zelkova. On the other hand, exposure to simulated acid rain with a pH of 4.0 or above for several months cannot induce any adverse effects on dry matter production and physiological functions of Japanese forest tree species. However, when the pH of simulated rain or fog is lowered below 4.0, negative effects appear on dry matter production and physiological functions such as transpiration in several sensitive Japanese forest tree species such as Japanese fir and Nikko fir. Based on limited information, it may be concluded that (1) Al dissolved into soil solution is the most important limiting factor for dry matter production, physiological functions and nutrient status of Japanese forest tree species grown in acidic soil, (2) the (Ca+Mg+K)/Al molar ratio in soil solution is a useful indicator to evaluate and predict the effects of soil acidification due to acid deposition on whole-plant dry matter production of Japanese forest tree species at the present time and in the future, and (3) Japanese coniferous tree species such as Japanese cedar and red pine are relatively sensitive to a reduction in (Ca+Mg+K)/Al molar ratio in soil solution compared with European forest tree species such as Norway spruce.     

Photosynthetic capacity of loblolly pine (Pinus taeda L.) trees during the first year of carbon dioxide enrichment in a forest ecosystem

Our objective was to assess the photosynthetic responses of loblolly pine trees (Pinus taeda L.) during the first full growth season (1997) at the Brookhaven National Lab/Duke University Free Air CO₂ Enrichment (FACE) experiment. Gas exchange, fluorescence characteristics, and leaf biochemistry of ambient CO₂ (control) needles and ambient + 20 Pa CO₂ (elevated) needles were examined five times during the year. The enhancement of photosynthesis by elevated CO₂ in mature loblolly pine trees varied across the season and was influenced by abiotic and biotic factors. Photosynthetic enhancement by elevated CO₂ was strongly correlated with leaf temperature. The magnitude of photosynthetic enhancement was zero in March but was as great as 52% later in the season. In March, reduced sink demand and lower temperatures resulted in lower net photosynthesis, lower carboxylation rates and higher excess energy dissipation from the elevated CO₂ needles than from control needles. The greatest photosynthetic enhancement by CO₂ enrichment was observed in July during a period of high temperature and low precipitation, and in September during recovery from this period of low precipitation. In July, loblolly pine trees in the control rings exhibited lower net photosynthetic rates, lower maximum rates of photosynthesis at saturating CO₂ and light, lower values of carboxylation and electron transport rates (modelled from A–C_i curves), lower total Rubisco activity, and lower photochemical quenching of fluorescence in comparison to other measurement periods. During this period of low precipitation trees in the elevated CO₂ rings exhibited reduced net photosynthesis and photochemical quenching of fluorescence, but there was little effect on light- and CO₂-saturated rates of photosynthesis, modelled rates of carboxylation or electron transport, or Rubisco activity. These first-year data will be used to compare with similar measurements from subsequent years of the FACE experiment in order to determine whether photosynthetic acclimation to CO₂ occurs in these canopy loblolly pine trees growing in a forest ecosystem.     

The effect of acid rain,soil temperature and humidity on C-mineralization rates in organic soil layers under spruce

The biological activity in organic soil layers under spruce was determined by measuring rates of carbon dioxide emission. Under laboratory conditions, biological activity was found to be optimal at temperatures ranging from 20°C to 35°C and at water contents ranging from 40% to 60%. Weakly acidic to neutral pH values of organic materials stimulated microbial CO₂ formation whereas high acidity (pH<2.4) inhibited it. Low CO₂ emission rates were observed at pH<2.4 and therefore populations of microorganisms highly resistant to acid must be present in the organic materials. The O_L horizon was found to contribute 50% of the total potential C-mineralization with the lower horizons O_F and O_H contributing 25% each. In simulating acid rain experiments, analysis of water percolating through the organic layers was shown to cause constant leaching of cations at the pH 3 to 6.5 range. In this respect, the O_L horizon exerts a buffering effect. It can be postulated that the acidification of soil organic material under spruce by acid rain inhibits C-mineralization and decreases the release of mineral nutrients. In the long run this can be expected to affect the turnover of mineral nutrients in forest ecosystems.     

Secondary xylem-specific expression of caffeoyl-coenzyme A 3-O-methyltransferase plays an important role in the methylation pathway associated with lignin biosynthesis in loblolly pine

Two types of structurally distinct O-methyltransferases mediate the methylation of hydroxylated monomeric lignin precursors in angiosperms. Caffeate 3-O-methyltransferase (COMT; EC 2.1.1.68) methylates the free acids and caffeoyl CoA 3-O-methyltransferase (CCoAOMT; EC 2.1.1.104) methylates coenzyme A esters. Recently, we reported a novel hydroxycinnamic acid/hydroxycinnamoyl CoA ester O-methyltransferase (AEOMT) from loblolly pine differentiating xylem that was capable of methylating both acid and ester precursors with similar efficiency. In order to determine the possible existence and role of CCoAOMT in lignin biosynthesis in gymnosperms, a 1.3 kb CCoAOMT cDNA was isolated from loblolly pine that showed 79–82% amino acid sequence identity with many angiosperm CCoAOMTs. The recombinant CCoAOMT expressed in Escherichia coli exhibited a significant methylating activity with hydroxycinnamoyl CoA esters whereas activity with hydroxycinnamic acids was insignificant. Moreover, 3.2 times higher catalytic efficiency for methylating caffeoyl CoA over 5-hydroxyferuloyl CoA was observed which could serve as a driving force towards synthesis of guaiacyl lignin. The secondary xylem-specific expression of CCoAOMT was demonstrated using RNA blot analysis, western blot analysis, and O-methyltransferase enzyme assays. In addition, Southern blot analysis indicated that CCoAOMT may exist as a single-copy gene in loblolly pine genome. The transgenic tobacco plants carrying loblolly pine CCoAOMT promoter-GUS fusion localized the site of GUS activity at the secondary xylem tissues. These data suggest that CCoAOMT, in addition to AEOMT, plays an important role in the methylation pathway associated with lignin biosynthesis in loblolly pine.     

土壤重金属生物毒性研究进展

世界范围内土壤重金属污染不断加重,由污染所带来的问题以及如何治理污染已经受到人们越来越多的关注.土壤重金属将对土壤生物产生影响,而土壤生物在重金属的胁迫下也会产生不同的响应.综述了国内外近年来土壤重金属生物毒性的研究进展,介绍了土壤重金属污染对陆地生态系统中植物、动物和微生物生长的影响;土壤重金属生物毒性的影响因素;土壤重金属生物毒性的研究方法;土壤重金属生物毒性的预测模型,最后提出了问题和展望.