角倍蚜虫瘿对盐肤木光合特性和总氮含量的影响

通过温室栽培和接种实验,以接种角倍蚜形成虫瘿的盐肤木和未接种角倍蚜的盐肤木为实验材料,测定和分析虫瘿对盐肤木光合特性和不同组织氮含量的影响。结果表明虫瘿对盐肤木的光合作用形成扰动,与对照植株相比较：(1)有虫瘿复叶的最大净光合速率升高,其中虫瘿初期、中期和后期分别升高14.49%、32.17%和42.01%;虫瘿还引起无虫瘿复叶最大净光合速率升高,但中期以后下降到正常水平;(2)虫瘿中期有虫瘿复叶的光饱和点升高、无虫瘿复叶光饱合点下降;虫瘿初期和中期有虫瘿复叶的光补偿点升高、无虫瘿复叶光补偿点下降;(3)虫瘿初期引起有虫瘿复叶及邻近无虫瘿复叶暗呼吸速率升高,但中期和后期影响不显著。虫瘿对盐肤木光合作用的扰动程度与小叶的位置和虫瘿生长时期密切相关。同时,虫瘿改变了盐肤木叶片氮含量分布,其中虫瘿外壁、有虫瘿复叶和无虫瘿复叶的氮含量分别为1.13%、1.98%和2.14%,这可能是营养物质从无虫瘿复叶流向有虫瘿复叶,并最终流向虫瘿,满足虫瘿和瘿内蚜虫生长需求的原因。     

Diversity and ubiquity of xylariaceous endophytes in live and dead leaves of temperate forest trees

To test the hypothesis that xylariaceous endophytes were ubiquitous on live and dead leaves of various tree species in the field, xylariaceous fungi were isolated from live leaves and bleached and nonbleached portions of dead leaves of a total of 94 tree species in a cool temperate forest in Japan. The biodiversity of xylariaceous endophytes was evaluated as the richness of operational taxonomic units (OTUs) determined by phylogenetic analysis of the nucleotide sequence of the D1/D2 region of the LSU rDNA of fungal isolates. A total of 326 isolates of xylariaceous fungi were isolated from live and dead leaves and classified into 15 OTUs. The three major OTUs, Xylaria sp.1, Nemania sp., and Biscogniauxia sp., accounted for 94% (308 isolates) of the total number of isolates, and were isolated from various live and dead leaves. Xylaria sp.1 was frequently encountered on bleached portions (which were produced due to the selective decomposition of lignin) of dead leaves of broad-leaved deciduous tree species. The results suggest that xylariaceous endophytes did not show host specificity and had a saprobic phase on dead leaves in their life cycles and that Xylaria sp.1 was capable of decomposing lignin in the field conditions.     

Chemotype variation of the weed Melaleuca quinquenervia influences the biomass and fecundity of the biological control agent Oxyops vitiosa

Host plant nutritional and non-nutritional variability can have a significant effect on herbivore populations by influencing survival, larval performance, and fecundity. The effect of chemical and physical variation of the leaves of two chemotypes of the weed Melaleuca quinquenervia was determined on the biomass and fecundity of the biological control agent Oxyops vitiosa (Coleoptera: Curculionidae). M. quinquenervia chemotypes were distinguished by the principal terpenoids E-nerolidol and viridiflorol using gas chromatography and mass spectroscopy. Not only were the terpenoid profiles of the two chemotypes different but the viridiflorol leaves had greater toughness (1.2-fold) and reduced nitrogen (0.7-fold). When the larvae and adults were fed leaves of the E-nerolidol chemotype increased adult biomass (1.1-fold) and fecundity were found (2.6- to 4.5-fold) compared with those fed leaves of the viridiflorol chemotype. Regardless of the larval diet, when adults were fed the E-nerolidol chemotype leaves they had greater egg production compared with those adults fed the viridiflorol leaves. Moreover, adult pre-oviposition period was extended (1.5-fold) when individuals were fed the viridiflorol leaves compared with those fed the E-nerolidol leaves. By rearing the O. vitiosa weevil on the more nutritious chemotype plants these results assisted in the mass production and establishment of the M. quinquenervia biological control agent.     

Rapid and Pervasive Occupation of Fallen Mangrove Leaves by a Marine Zoosporic Fungus

Samples of leaves of red mangrove (Rhizophora mangle) were incubated on an agar medium selective for pythiaceous oomycetes. Leaves on trees above the water did not contain oomycetes. Marine oomycetes, principally Phytophthora vesicula, had colonized leaves within 2 h of leaf submergence, probably finding them by chemotaxis. The frequency of occurrence of P. vesicula in submerged leaves reached 100% within 30 h of submergence. By 43 h most, if not all, parts of leaves were occupied, and surface treatment with a biocide indicated that leaves were occupied internally. Frequencies of P. vesicula remained near 100% through about 2 weeks of submergence and then declined to about 60% in older (≥4 weeks) leaves. Leaves of white mangrove (Laguncularia racemosa) were also extensively occupied by P. vesicula after falling into the water column, but decaying leaves of turtlegrass (Thalassia testudinum) were not colonized by oomycetes. Ergosterol analysis indicated that the standing crop of living, non-oomycete (ergosterol-containing) fungal mass in submerged red-mangrove leaves did not rise above that which had been present in senescent leaves on the tree; decaying turtlegrass leaves had an ergosterol content that was only about 2% of the maximum concentration detected for red-mangrove leaves. These results suggest that oomycetes are the predominant mycelial eucaryotic saprotrophs of mangrove leaves that fall into the water column and that for turtlegrass leaves which live, die, and decompose under submerged conditions, mycelial eucaryotes make no substantial contribution to decomposition.     

A Cost-Benefit Analysis of Leaves of Eight Australian Savanna Tree Species of Differing Leaf Life-Span

Cost-benefit analysis of foliar construction and maintenance costs and of carbon assimilation of leaves of differing life-span were conducted using two evergreen, three semi-deciduous, and three deciduous tree species of savannas of north Australia. Rates of radiant-energy-saturated CO₂ assimilation (P _max) and dark respiration were measured and leaves were analysed for total nitrogen, fat, and ash concentrations, and for heat of combustion. Specific leaf area, and leaf N and ash contents were significantly lower in longer-lived leaves (evergreen) than shorter-lived leaves (deciduous) species. Leaves of evergreen species also had significantly higher heat of combustion and lower crude fat content than leaves of deciduous species. On a leaf area basis, P _max was highest in leaves of evergreen species, but on a leaf dry mass basis it was highest in leaves of deciduous species. P _max and total Kieldahl N content were linearly correlated across all eight species, and foliar N content was higher in leaves of deciduous than evergreen species. Leaf construction cost was significantly higher and maintenance costs were lower for leaves of evergreen than deciduous species. Maintenance and construction costs were linearly related to each other across all species. Leaves of evergreen species had a higher cost-benefit ratio compared to leaves of deciduous species but with longer lived leaves, the payback interval was longer in evergreen than deciduous species. These results support the hypotheses that longer lived leaves are more expensive to construct than short-lived leaves, and that a higher investment of N into short-lived leaves occurs which supports a higher P _max over a shorter payback interval.     

Comparative protective strategies of Cistus albidus and Quercus ilex facing photoinhibitory winter conditions

The role of structural photoprotection under photoinhibitory winter conditions was evaluated in two Mediterranean woody species: Cistus albidus (semideciduous) and Quercus ilex (evergreen). Shoots were manipulated in order to modify the light load naturally received by the leaves throughout the cold season, and monitored for changes in maximum photochemical efficiency of PSII, phenology, and leaf morphology. Naturally steep leaves of C. albidus were restrained to a horizontal position, and compared with control leaves (naturally horizontal, or steeply inclined). Fully exposed leaves of Q. ilex were artificially protected through partial shading, and compared with control leaves (not shaded). During the cold season, the most exposed (either naturally or artificially) leaves were always more photoinhibited (had lower maximal photochemical efficiency of PSII) than the photoprotected ones. The differences disappeared at the beginning of spring. Winter photoinhibition was not more pronounced in older than in younger leaves of C. albidus, indicating that inclination rather than age affected their photochemical efficiency. Leaf chlorophyll contents were not significantly affected by the manipulations. Leaf thickness decreased slightly in the least exposed shoots of the evergreen species, but no changes were detected in leaf morphological traits of the semideciduous one. The increased photoinhibitory pressure led only to slight and non-significant changes in phenology and growth.     

Changes in cotton leaf chemistry induced by volatile elicitors

Cotton (Gossypium hirsutum) leaves were exposed for 7 days to volatile chemicals originating from Aspergillus flavus-infected cotton leaves, A. flavus cultures or mechanically damaged cotton leaves. Volatiles from A. flavus-infected leaves triggered significant increases of 52 and 34% in phloroglucinol-reactive compounds in wounded or undamaged cotton leaves, respectively. Increased production of heliocides (C₂₅ terpenoid aldehydes) were found in the volatile recepient wounded or undamaged cotton leaves. The heliocides are natural insecticides presumed localized in the subepidermal pigment glands in leaves. Myrcene, a volatile precursor of heliocide H₂, also caused significant increases in heliocide production when leaves were exposed to the volatilized chemical.     

The synthesis and defluorination of monofluoroacetate in some Dichapetalum species

Leaves from Dichapetalum toxicarium (G. Don) Baill. (Dichapetalaceae) removed from the plant and aqueous extracts prepared from the leaves of D. heudelotii (Planch. ex Oliv.) Baill. were able to synthesize monofluoroacetate from NaF. D. pallidum (Oliv.) Engl. leaves were not able to synthesize monofluoroacetate from NaF. Aqueous extracts from both D. toxicarium and D. heudelotii containing monofluoroacetate and possibly other organo-fluorine compounds were defluorinated by a micro-organism from the air. This organism was able to defluorinate fluorocitrate but not difluoroacetate or trifluoroacetate. In D. toxicarium monofluoroacetate is present in a form which is easily leached from the leaves, and which is defluorinated if the leaves are kept under herbarium conditions. The monofluoroacetate in this species is not defluorinated if the leaves are dried at 100° and stored in sealed polythene bags.     

CO2 assimilation,photosystem II photochemistry,carbohydrate metabolism and antioxidant system of citrus leaves in response to boron stress

Seedlings of Citrus grandis were fertilized every other days for 15 weeks with nutrient solution containing 0 (deficiency), 10 μM (control) or 500 μM (excess) H₃BO₃. CO₂ assimilation and chlorophyll (Chl) content decreased to a greater degree in B-deficient than in B-excess leaves, but photosynthetic enzyme activities were similarly decreased. Starch accumulated in B-deficient leaves, but not in B-excess ones. Chlorophyll a fluorescence transient showed that the positive L- and K-steps were more pronounced in B-excess than in B-deficient leaves. Maximum quantum yield of primary photochemistry (F_v/F_m), maximum variable fluorescence (F_v), oxygen-evolving complex (OEC) were less decreased in B-deficient than in B-excess leaves, whereas minimum fluorescence (F₀) was less increased in B-deficient leaves. Boron-deficient leaves displayed higher or similar antioxidant enzyme activities and higher ascorbate (AsA) and reduced glutathione (GSH) contents compared to B-excess leaves. Content of thiobarbituric acid (TBA) reactive compounds was less increased by B-deficiency than by B-excess. We conclude that B-deficient leaves are less damaged by oxidative stress than B-excess leaves due to their higher ability to scavenge reactive oxygen species. Both the donor (i.e. the OEC) and the acceptor sides of photosystem II were less photoinhibited by B-deficiency than by B-excess. The greater decrease in CO₂ assimilation and Chl content in B-deficient leaves may be caused by the excessive accumulation of starch. The reduction of CO₂ assimilation by B-excess is probably caused by a combination of factors such as oxidative damage, reduced photosynthetic enzyme activities and impaired electron transport capacity.     

Genotoxicity of Nicotiana tabacum leaves on Helix aspersa

Tobacco farmers are routinely exposed to complex mixtures of inorganic and organic chemicals present in tobacco leaves. In this study, we examined the genotoxicity of tobacco leaves in the snail Helix aspersa as a measure of the risk to human health. DNA damage was evaluated using the micronucleus test and the Comet assay and the concentration of cytochrome P450 enzymes was estimated. Two groups of snails were studied: one fed on tobacco leaves and one fed on lettuce (Lactuca sativa L) leaves (control group). All of the snails received leaves (tobacco and lettuce leaves were the only food provided) and water ad libitum. Hemolymph cells were collected after 0, 24, 48 and 72 h. The Comet assay and micronucleus test showed that exposure to tobacco leaves for different periods of time caused significant DNA damage. Inhibition of cytochrome P450 enzymes occurred only in the tobacco group. Chemical analysis indicated the presence of the alkaloid nicotine, coumarins, saponins, flavonoids and various metals. These results show that tobacco leaves are genotoxic in H. aspersa and inhibit cytochrome P450 activity, probably through the action of the complex chemical mixture present in the plant.     

Effect of RotyIenchulus reniformis on Reflectance of Cotton Plant Leaves

Differences between light reflectance from leaves of cotton (Gossypiurn hirsutum) plants grown with a low- or no-nematode (Rotylenchulus reniformis) population (nonstressed), and from leaves grown with a high nematode population (stressed) were measured in field and greenhouse experiments. Reflectance was measured spectrophotometrically in the laboratory on single leaves and spectroradiometrically in the field on plant canopies. Nematode-stressed cotton plants were stunted with fewer, smaller, and darker-green leaves than nonstressed plants. Over the 0.5- to 2.5-/μm waveband, stressed leaves had lower reflectance than nonstressed leaves of the same chronological age for both field- and greenhouse-grown plants. Reflectance differences between stressed and nonstressed leaves in the visible (0.5 to 0.75 μm), near-infrared (0.75 to 1.35 μm) and infrared water absorption (1.35 to 2.5 μm) regions were primarily caused by differences in leaf chlorophyll concentration, mesophyll structure, and water content, respectively. Results indicate the potential for remotely sensing nematode-infested plants to distinguish them from normal plants.     

A comparison of the volatile oils of mature versus young leaves of Juniperus scopulorum: Chemosystematic significance

The volatile oils of leaves of clonal, greenhouse grown trees of J. scopulorum cv. platinum were examined from young (juvenile or whip leaves) and mature (adult or scale leaves) foliage. Of 36 compounds subjected to analysis of variance, 19 showed significant differences between young and old leaves. In general, the hydrocarbon terpenoids were higher in concentration in new leaves while the oxygenated compounds were higher in the older leaves. This same pattern has been reported in several other gymnosperms. Numerical taxonomy using data on the volatile oils from young and mature leaves yielded the same relative similarities among the five trees examined. Surprisingly, the plants were more similar in the volatile oil from the young leaves than from the mature leaves. The mixing of different ages of leaves in samples for chemosystematic studies is, however, to be discouraged     

Comparative analysis of volatiles from Drimys brasiliensis Miers and D. angustifolia Miers (Winteraceae) from Southern Brazil

The essential oils obtained from Southern Brazilian native Drimys brasiliensis Miers and Drimys angustifolia Miers were analyzed by GC and GC/MS. The oils from leaves of both species showed predominance of monoterpenoids, while the oils from stem barks were characterized by sesquiterpenoids. Bicyclogermacrene (20.0% in leaves and 25.4% in stem bark) and drimenol (1.4% in leaves and 26.2% in stem bark) were the most abundant in D. angustifolia, and cyclocolorenone (from 16.0% to 32.3% in fresh and dried leaves and almost 50% in stem bark) in D. brasiliensis. The oil from fruits of D. brasiliensis was also analyzed and presented 31.0% of cyclocolorenone. The predominance of this unusual aromadendrane-type sesquiterpene in D. brasiliensis essential oils could be used as a chemosystematic marker.     

Changes in the chlorophylls and carotenoids of leaves of Nicotiana tabacum during senescence

In addition to chlorophylls a and b, β-carotene, lutein, violaxanthin and neoxanthin, leaves of tobacco (Nicotiana tabacum L. cv. Virginia Gold) contain antheraxanthin in some harvests. In lower leaves, chlorophylls decreased more rapidly than carotenoids during senescence, but both types of pigment decreased at equal rates in upper leaves. The chlorophyll a:b ratio decreased only in post-mature leaves. Total carotenoid decreased with age, with the relative proportion of β-carotene increasing in lower leaves. Seasonal influences rather than age of leaf determines whether antheraxanthin is present. No esterified xanthophylls were found in senescent leaves.     

Seasonal variation in leaf characteristics and food selectionby larval noctuids on an evergreen Mediterranean shrub

Despite year round availability of foliage, abundance of generalist noctuid larvae (Lepidoptera: Noctuidae) in evergreen-dominated Mediterranean forests has a narrow, distinct spring peak. This restricted larval period has been suggested to result in part from avoidance of the nutritionally poor mature foliage, and preference for nutritionally superior spring-produced young leaves. This study examines this hypothesis by (i) documenting differences in nutritional characteristics between expanding (April) and mature (June) young leaves of the evergreen Mediterranean shrub Daphne laureola L. (Thymelaeaceae), and (ii) experimentally studying the feeding preferences of noctuid larvae for young leaves, old leaves (≥ 1 yr old), and developing fruits of this species in one south-eastern Spanish locality. Young leaves of D. laureola declined in nutrient concentration and specific dry mass from April to June. The responses of noctuid larvae, in terms of both relative preference and total consumption, to this seasonal variation in chemical and physical features of young leaves were also investigated. When noctuid larvae were simultaneously offered young leaves, old leaves and developing fruits, they exhibited similar preferences for young leaves and developing fruits, and rejected old leaves developed during the previous year. Noctuid larvae did not modify their consumption of young leaves relative to old leaves and developing fruits in response to seasonal changes. Food selection patterns exhibited by D. laureola noctuid herbivores, notably the rejection of old leaves in favour of young ones, are consistent with the hypothesis relating restricted larval periods of these generalist consumers with the low food value of the previous season leaves of evergreen Mediterranean plants.     

Does leaf ontogeny lead to changes in defensive strategies against insect herbivores?

Plants use different defense strategies throughout their ontogenetic development. In this study, three questions were proposed: (1) Is there a greater abundance of ants on young leaves, which possess active extrafloral nectaries, than on mature leaves? (2) Do ants exert an indirect defense that is effective against the attack of herbivorous insects? (3) Do mature leaves have a greater concentration of physical and chemical defense than young leaves? These questions were addressed through an ant-exclusion experiment in which two branches of Copaifera langsdorffii (n = 25) were marked and monitored throughout the entire foliar expansion and development period. A reduction in the abundance of ants throughout foliar development was observed. The ants exerted an effective defense against herbivores on C. langsdorffii: the branches where ants were excluded had a greater number of herbivores. The mature leaves possessed a greater index of leaf sclerophylly than young leaves, but the leaves did not differ in the concentration of tannins. The foliar ontogeny of C. langsdorffii promoted an inversion in the defense strategy against herbivores, and despite showing an opportunistic relationship, the interaction between ants and extrafloral nectaries appears to play an important role in structuring the interactions between herbivorous insects and their host plants.     

Correlation between the activity of membrane-bound ATPase and the decay rate of flash-induced 515-nm absorbance change in chloroplasts in intact leaves,assayed by means of rapid isolation of chloroplasts

(1) The relationship between activation of the membrane-bound ATPase and the stimulation of dissipation of the flash-induced membrane potential by preillumination was studied in intact spinach leaves by measuring the ATPase activity of rapidly isolated chloroplasts and the decay of the flash-induced 515-nm absorbance change (ΔA₅₁₅) in intact leaves. (2) The decay of ΔA₅₁₅ was accelerated by preillumination. The ΔA₅₁₅ decay in leaves treated with N,N′-dicyclohexylcarbodiimide (DCCD) became slower and was not accelerated by preillumination. However, treatment with DCCD did not lower the intensity of delayed fluorescence. (3) Membrane-bound ATPase of chloroplasts which were rapidly isolated from the preilluminated leaves (90 s preparation time) showed a higher activity (over 200 μmol P_i/mg chlorophyll per h in the case of 2-min preillumination) than that of chloroplasts isolated from dark-adapted leaves. (4) The acceleration of ΔA₅₁₅ decay and the activation of ATPase showed similar dependences on illumination time in intact leaves. 3-(3′,4′-Dichlorophenyl)-1,1-dimethylurea, carbonyl cyanide p-chlorophenylhydrazone and DCCD inhibited the activation of ATPase and the acceleration of the ΔA₅₁₅ decay by preillumination. (5) The ATPase activity of chloroplasts isolated from illuminated leaves showed a single exponential decay (‘dark inactivation in vitro’). The ATPase activity induced by illuminating the leaves became lower as the dark interval between illumination and the isolation of chloroplasts was increased (‘dark inactivation in vivo’). The time course of the decay of activity had a lag and showed a sigmoidal curve when plotted semilogarithmically. The decay had an apparent half-time of 25 min. (6) The recovery of the accelerated ΔA₅₁₅ decay in preilluminated leaves to the original slow rate showed a sigmoidal decay similar to that of the activity of ATPase in intact leaves with a half-time of about 23 min in the dark. (7) It was concluded that the decay rate of ΔA₅₁₅ reflected the chloroplast ATPase activity in intact leaves and that the ion conductance of thylakoid membrane was mainly determined by the H⁺ flux through the ATPase, the activity of which was increased after the formation of the high-energy state.     

Development and Leaf Consumption by Spodoptera cosmioides (Walker) (Lepidoptera: Noctuidae) Reared on Leaves of Agroenergy Crops

Spodoptera cosmioides (Walker) (Lepidoptera: Noctuidae) is a polyphagous pest that threatens more than 24 species of crop plants including those used for biodiesel production such as Ricinus communis (castor bean), Jatropha curcas (Barbados nut), and Aleurites fordii (tung oil tree). The development and leaf consumption by S. cosmioides reared on leaves of these three species were studied under controlled laboratory conditions. The egg-to-adult development time of S. cosmioides was shortest when reared on castor bean leaves and longest when reared on tung oil tree leaves. Larvae reared on castor bean and Barbados nut leaves had seven instars, whereas those reared on tung oil tree leaves had eight. Females originating from larvae reared on castor bean and Barbados nut leaves showed greater fecundity than did females originating from larvae reared on tung oil tree leaves. Insects fed on castor bean leaves had shorter life spans than those fed on tung oil tree and Barbados nut leaves although the oviposition period did not differ significantly. The intrinsic and finite rates of increase were highest for females reared on castor bean leaves. Total leaf consumption was highest for larvae reared on tung oil tree leaves and lowest for those reared on Barbados nut leaves. We conclude that castor bean is a more appropriate host plant for the development of S. cosmioides than are Barbados nut and tung oil tree.     

模拟酸雨对西洋杜鹃生理生态特性的影响

采用盆栽方法,研究了不同pH值条件下的模拟酸雨对西洋杜鹃生长及其叶片主要生理生化特征的影响。结果表明:在酸雨胁迫下,随着酸雨胁迫的增强,西洋杜鹃叶片受害程度逐渐加重;叶片丙二醛含量逐渐升高;可溶性蛋白含量先升后降;过氧化氢酶(CAT)、过氧化物酶(POD)和超氧化物歧化酶(SOD)活性均呈先升后降的单峰曲线变化,其中pH值为4.3的处理下西洋杜鹃叶片CAT和SOD活性最高,pH值为3.0的处理下其POD活性最高;其叶绿素含量逐渐下降;叶片净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)及水分利用率(WUE)均呈先升后降的趋势,而胞间CO2浓度(Ci)则持续下降,pH值为4.3的处理下其Pn、Tr、Gs和WUE均达到最高。研究表明,大致可以认为pH值≤3.0是酸雨对西洋杜鹃造成隐形伤害的阀值,而酸雨灾害严重地区的降水pH值为2.0—4.0左右,说明西洋杜鹃可以在酸雨灾害较重的地区生长,可作为酸雨灾害严重地区园林绿化及植被构建的物种之一。