bluuebunny/crossref_metadata_2025_split huggingface dataset:
EFFECTS OF A SIMULATED ACID RAIN EPISODE ON PHOTOSYNTHESIS AND RECOVERY IN THE CARIBOU‐FORAGE LICHENS, CLADINA STELLARIS (OPIZ.) BRODO AND CLADINA RANGIFERINA (L.) WIGG.
Authors: SCOTT MARTHA G. , HUTCHINSON THOMAS C. 
Published: April 2006

SummaryThe effect of simulated acid rain on net photosynthesis of two common boreal forest lichens, Cladina stellaris and Cladina rangiferina, was investigated. Repeated measurements of net photosynthetic rate (NPR) were conducted on podetial tips over a week‐long period to assess both immediate response to an acid spray treatment (2:1 H2SO4:HNO3; pH range 2.5 to 3.5) and subsequent photosynthetic recovery after the solution of artificial rain had been rinsed out of the cells. A control group, which was treated with pH 5.6 episodes, was used to monitor natural fluctuations in NPR over time in a laboratory environment. Although lowered photosynthetic rates were observed for both species immediately following a low pH treatment, differences between groups were not significant. Three days following treatment, however, significant decreases in photosynthesis of up to 40% of pretreatment values were found for pH 2.5 and 3.0‐sprayed C. stellaris, and a decline in NPR of 25% was recorded for pH 3.0‐treated C. rangiferina. Six days after the simulated rain episode, a 20% recovery of photosynthesis had occurred in pH 2.5‐treated C. stellaris, while pH 3‐0‐sprayed C. rangiferina underwent a 20% stimulation of NPR compared to the pretreatment value. In spite of the demonstrated ability to recover partially following a single low pH event, it is hypothesized that even temporary declines in NPR could restrict growth potential and biomass accumulation of boreal cyptogamic species which have a short growing season and photosynthesize only when moisture is available. Results of the study indicate that C. stellaris is more sensitive to single low pH events than is C. rangiferina.
EFFECTS OF SIMULATED ACID RAIN ON PRODUCTION, MORPHOLOGY AND COMPOSITION OF EPICUTICULAR WAX AND ON CUTICULAR MEMBRANE DEVELOPMENT
Authors: PERCY K. E. , BAKER E. A. 
Published: April 2006

SummaryLeaves of Phaseolus vulgaris L., Vicia faba L., Pisum sativum L. and Brassica napus L. were exposed to simulated rain from emergence to full expansion at seven pHs between 5.6 and 2.6, applied at 2 mm h−1 in amounts and at intervals representative of ambient rain in southwestern England. Leaf expansion was unaffected by rain pH greater than 30 in V. faba, and pH 2–6 in the other species. Macroscopic foliar injury was induced at pH 3.4 in non‐wettable leaves of P. sativum and B. napus which had relatively large deposits of crystalline epicuticular wax, and at pH 3.0 in wettable leaves of P. vulgaris and V. faba which had small deposits of amorphous wax. Foliar injury was greatest in species with crystalline wax. Wax production was affected by simulated acid rain in all species and was often accompanied by changes in wax composition. Wax quantity was reduced on leaves of P. vulgaris exposed to rain at pH 4.6, while wax on leaves of P. sativum and B. napus had increased numbers of smaller plates and tubes, respectively, per unit area at pH 4.6. Leaves of B. napus, stripped of crystalline epicuticular wax at about 20% full expansion, regenerated less wax at pH 3.4 than at pH 5.6. The thickness of the cuticular membranes in leaves of P. vulgaris, V faba and P. sativum exposed to simulated acid rain at pH 4.2 decreased by 28 to 35 % compared with those exposed to pH 5.6 rain. Membrane ultrastructure was also altered in leaves of P. vulgaris. Taken together, these changes could have important consequences for leaf wettability, rainfall retention, foliar uptake of chemicals and host‐parasite interactions.
SOME PHYSIOLOGICAL RESPONSES OF THEOBROMA CACAO VAR. CATONGO SEEDLINGS TO AIR HUMIDITY
Authors: GOMES A. R. SENA , KOZLOWSKI T. T. , REICH P. B. 
Published: April 2006

SummaryThe stomata of three‐month‐old seedlings of Theobroma cacao L. var. Catongo were more open in high relative humidity (RH) (76 to 89%) than in low relative humidity (39 to 62 %). In both regimes, stomata closed gradually during the day, with the rate of closure accelerating in the late afternoon. Transpiration rate (TR) was correspondingly high early in the day and low late in the day. Average leaf diffusive resistance (r1) was 26% lower at the high RH. Nonetheless, TR was generally higher for plants in the low RH, because of the much greater vapour pressure gradient between the leaf and air. Abruptly lowering the RH at noon rapidly increased (r1) and increasing RH decreased r1, In another experiment conducted in constant high or low RH regimes, r1 was lower, the rate of net photosynthesis (Pn) was higher, leaf water potential (Φ) was lower (more negative), and TR was lower in the high RH regime. Water‐use efficiency (WUE) was higher in high than in low RH. The relationships between Pn and r1 were identical at high and low RH. Thus, differences in TR and WUE at high vs low RH were a direct result of variations in vapour pressure deficit (VPD) between the two humidity regimes. Stomatal opening and closing reflected direct effects of humidity on guard cells rather than responses to changes in bulk leaf Φ. In addition, root to leaf hydraulic conductivity apparently was greater at low than at high RH.
EFFECTS OF EXPERIMENTAL DEFOLIATION ON A POPULATION OF PEDUNCULATE OAK (QUERCUS ROBUR L.)
Authors: HILTON G. M. , PACKHAM J. R. , WILLIS A. J. 
Published: April 2006

SummaryAn experiment simulating defoliation at three levels of severity was conducted on 196 young oaks in a plot at Wolverhampton.In comparison with control plants, defoliation caused (1) earlier production of growth spurts (which are normal in undefoliated trees) and formation of more lateral branches, which were susceptible to winter frost damage; (2) production of more abundant, smaller leaves; (3) reduced diameters of main stems, from which can be calculated growth rates, varying with both defoliation treatment and growing conditions over the year, and returning to normal values as soon as defoliation ceased; (4) formation throughout the season of xylem of early wood type having a lower proportion of xylem fibres.With light defoliation, most of these responses were scarcely apparent, but with more severe defoliation, morphological effects dominated. The most noticeable effects of total defoliation were low growth rates and effects on wood anatomy.The results suggest that substantial natural defoliation could cause failure of regeneration, although in un shaded plots of young trees leaf loss results in retarded growth rather than death.
THE EFFECTS OF PLANT DENSITY AND SNAIL GRAZING ON FEMALE AND MALE SPINACH PLANTS
Authors: MILLER JOY , DOUST JON LOVETT 
Published: April 2006

SummaryMale and female plants of the dioecious herb, Spinacia oleracea L. cv. Viking were grown in pots of five, 10 and 20 plants. Pots at each density were also exposed to grazing by the landsnail, Helix aspersa Muller (Helicidae; Gastropoda). Leaf longevity and rates of production for each of 13 leaf cohorts were determined for grazed and ungrazed female and male plants at each density. Dates of initiation of seed set and anthesis were recorded. At harvest, plant height, total dry weight and dry weights of leaves and stem, and of fruits and male reproductive organs were recorded. There were significant differences between females and males in time to anthesis, number of leaves per plant, leaf birth rate and reproductive effort. Females flowered and senesced later than males. Density had a significant effect on total number of leaves, leaf birth rate and leaf longevity. The only significant effect of snail grazing was a reduction in leaf longevity, particularly at the highest density. This corroborates recent suggestions that grazing has more effect on plants already exposed to relatively high levels of other pressures.
GENETIC DIFFERENTIATION IN TEMPERATURE‐ENFORCED SEED DORMANCY AMONG GOLF COURSE POPULATIONS OF POA ANNUA L.
Authors: WU LIN , TILL‐BOTTRAUD IRENE , TORRES ARMANDO 
Published: April 2006

SummarySeed germinability at high temperature (25 °C) was found to differ among golf course populations of Poa annua L. located along a gradient of different intensities of turf irrigation and mowing practices. A seed germination index was calculated to express the effect of temperature on seed germination. The seed germination indices of the less managed populations from the golf roughs were uniformly low and less than 30%, with a mean index of 5%. Conversely, the germination indices of the golf green populations were high. Most seed families of the golf green populations had a germination index higher than 60%. A wide range of seed germination indices was found in seed families of the fairway populations, ranging from 10 to 90% with a mean index of 49%, and with a bimodal distribution. The results of this study indicate that rapid genetic differentiation in temperature‐enforced seed dormancy among populations of Poa annua had taken place at the micro‐ecological level.
REGULATION OF RESERVE CARBOHYDRATE METABOLISM IN MESEMBRYANTHEMUM CRYSTALLINUM EXHIBITING C3 AND CAM PHOTOSYNTHESIS
Authors: KEILLER D. R. , PAUL M. J. , COCKBURN W. 
Published: April 2006

SummaryDifferences in carbohydrate metabolism between the C3 and CAM forms of Mesembryanthemum crystallinum L. were demonstrated and studied. The CAM form accumulated less starch (defined as boiling water‐insoluble polyglucan) than the C3 form at high irradiances, but at limiting light diverted a greater proportion of photosynthate to starch. Starch accumulation was more sensitive to the effects of exogenous inorganic phosphate in the C3 form than in the CAM form.Following induction of CAM by salt treatment, the CAM form ceased to accumulate glucose and fructose and commenced accumulating pinitol. Pinitol is not involved directly in CAM but may act as a compatible osmoregulatory solute.Concentrations of fructose 2,6‐bisphosphate in the C3 and CAM forms were similar, but the cytosolic fructose 1,6‐bisphophatase extracted from the two forms was markedly different in sensitivity to this effector. The two enzymes also differed both in their sensitivity to inorganic phosphate and in their affinity for fructose 1,6‐bisphosphate.The concentrations of key intermediates of carbohydrate metabolism, fructose and glucose 6‐phosphate and fructose 1,6‐bisphosphate were measured in the C3 and CAM forms. Concentrations of fructose 1,6‐bisphosphate were higher in the CAM form, whereas those of glucose and fructose 6‐phosphate were higher in the C3 form.The differences observed are discussed in relation to the regulation of storage carbohydrate metabolism in the two forms. A partial explanation is offered for the differences in the characteristics of starch accumulation between the C3 and CAM forms through the influence of the effector fructose 2,6‐bisphosphate on the enzyme fructose 1,6‐bisphosphatase.
SEASONAL AND DIURNAL CHANGES IN ABSCISIC ACID AND WATER RELATIONS OF APRICOT LEAVES (PRUNUS ARMENIACA L.)
Authors: LOVEYS B. R. , ROBINSON S. P. , DOWNTON W. J. S. 
Published: April 2006

SummarySeasonal and diurnal changes in leaf water relations, stomatal behaviour and abscisic acid were studied in apricot (Prunus armeniaca L.) trees growing in Adelaide, Australia. Diurnal changes in stomatal conductance and foliar abscisic acid (ABA) were small and the ABA content of expressed xylem sap was low (0·3 to 0·9 × 10−4 mol m−3). This concentration of ABA was too low to influence stomatal conductance, although diurnal changes and some seasonal changes in leaf ABA could be accounted for by uptake from the xylem. Water potential fell throughout the growing season but high values of turgor were maintained by a corresponding fall in leaf osmotic potential. The fall in leaf osmotic potential was partly accounted for by a decrease in relative water content but measurements of osmotic potential at full turgor showed that there was a net accumulation of solute between December and March. Sorbitol was the solute chiefly responsible for this increase.The ability of apricot leaves to synthesize ABA in response to zero turgor was greatly reduced between November and March, although this ability was partly regained in April. ABA appears to be relatively unimportant in the control of stomatal conductance in apricot.
WATER RELATIONS OF SOME NATIVE AND EXOTIC SHRUBS OF NEW ZEALAND
Authors: KISSEL RUTH M. , BASTOW WILSON J. , BANNISTER PETER , MARK ALAN F. 
Published: April 2006

SummaryThe water relations of three native and four exotic shrub species occurring in semi‐arid Central Otago, New Zealand were examined. Water potentials at midday were low in the native Kunzea ericoides, while those in the exotic Lupinus arboreus remained high, but there were no other obvious distinctions between the field water potentials of the native and exotic species. An examination of the relation between water potential and water content, however, showed a low potential at full turgor in the native Coprosma propinqua, while the exotic species Rosa rubiginosa and L. arboreus both showed large changes in water potential for relatively small changes in water content after turgor had been lost. The exotics R. rubiginosa and Thymus vulgaris showed a rapid loss of water content in drying conditions; the exotic ‘broom’Cytisus scoparius and the native ‘broom’Carmichaelia compacta showed the lowest rates. It is concluded that there is no overall difference between the mechanism of adaptation of the native and exotic species; the exotic species that invaded are those that were pre‐adapted to the conditions.
THE EFFECT OF LIGHT ON THE RELATIONSHIP BETWEEN APHIS FABAE SCOP. AND ITS HOST PLANT, VICIA FABA L.
Authors: GARSED S. G. , GALLEY D. J. , MUELLER P. W. 
Published: April 2006

SummaryPlants of Vicia faba were grown in pots at photosynthetic photon flux densities (PPFD) of 143, 315 or 906 μmol m−1 for 8, 13 or 18 d. The effects of the dry matter loss caused by the feeding of Aphis fabae, or by removal of the cotyledons, were measured. Differences in dry weight between infested and control plants were positively correlated with the dry matter ingested, and increased with PPFD and time. Dry weights of aphid colonies increased non‐linearly, but the honeydew produced per unit weight of aphid linearly, with PPFD. Aphid production/ consumption (P/C) ratios had a significant inverse linear relationship to log PPFD (r= 098). Net assimilation rates (NAR) calculated from the dry weights of the infested plants alone were significantly lower than in controls, but when calculated with the ingested dry matter added to the plant weight were little different from controls. No stimulations of NAR were found. Dry weights of all plant components, leaf area and specific leaf area were reduced by low light, removal of the cotyledons and by infestation. The last increased leaf area ratio (LAR) at the two later harvests but, otherwise, the treatments had only minor effects on the partitioning of dry matter in the plants.
DEVELOPMENT OF SYMPTOMS OF BROWN RUST OF BARLEY IN RELATION TO THE DISTRIBUTION OF FUNGAL MYCELIUM, STARCH ACCUMULATION AND LOCALIZED CHANGES IN THE CONCENTRATION OF CHLOROPHYLL
Authors: SCHOLES J. D. , FARRAR J. F. 
Published: April 2006

SummaryThe development of symptoms of brown rust (Puccinia hordei Otth.) of barley was examined in relation to the distribution of fungal mycelium within the leaf, the accumulation of chloroplastic starch and localized changes in the concentration of chlorophyll. Symptom development correlated exactly with the growth and distribution of mycelium within the leaf. Starch accumulated in cells associated with or directly surrounded by fungal mycelium, but rarely in cells beyond the leading edge of the colony. A photographic study of the development of a group of brown rust pustules from the flecking stage to the formation of green islands, using incident light and light transmitted through the leaf, suggested that the yellow colour of the flecks was not caused by chlorophyll breakdown, but that the major loss of chlorophyll occurred from regions between fungal pustules. This conclusion was supported by a study of the density of chlorophyll within different regions of the leaf (using the absorption of red light as a measure of chlorophyll density) and by extraction of chlorophyll from different regions of the leaf. These results are discussed in relation to the controversy surrounding the mode of formation of green islands.
FUNGAL COMMUNITIES IN ATTACHED ASH BRANCHES
Authors: BODDY LYNNE , BARDSLEY D. W. , GIBBON O. M. 
Published: April 2006

SummaryAttached dead and partly living ash branches of (Fraxinus excelsior) were cut from mature trees and the three‐dimensional structure of their decay communities analyzed. The communities were characterized by three Ascomycotina, seven Basidiomycotina and two Deuteromycotina, which varied in their ecological roles. The Ascomycotina Daldinia concentrica (Bolt: Fr.) Ces. & DeNot. and Hypoxylon rubiginosum Pers.: Fr. were pioneers growing in partly living or recently dead wood but causing only slow decay. D. concentrica is very combative and was apparently often able to persist until the wood was well decayed. Peniophora limitata (Fr.) Cooke was also probably a pioneer but tended to be found mainly in middle or terminal regions, as did Peniophora quercina (Fr.) Cooke on the few occasions that the latter was found. Both P. limitata and P. quercina caused extensive white rot. Exidia thuretiana was found fruiting on the bark but was not isolated from wood and appeared to cause cambial death. An unidentified ascomycete was also found in small superficial regions associated with bark death or wounds. Peniophora lycii (Pers.) Höhn & Litsch and Peniophora violaceolivida were secondary invaders usually found in distal regions which were subject to desiccation. Radulomyces confluens (Fr.) M. P. Christ was found in two branches in similar positions to P. limitata and P. quercina; its role was not completely clear but it was probably acting as a secondary colonizer. Mycoacia uda (Fr.) Donk was isolated once from terminal regions where it was replacing other species. In addition two Deuteromycotina, Phomopsis platanoidis Died, and a sterile unidentified sp., were isolated on a number of occasions, the former apparently resulted in little decay, although the latter was often found in decayed wood.
SURVIVAL AND GROWTH OF MICROCOLONIAL ROCK FUNGI AS AFFECTED BY TEMPERATURE AND HUMIDITY
Authors: PALMER F. E. , EMERY D. R. , STEMMLER J. , STALEY J. T. 
Published: April 2006

SummaryMicrocolonial rock fungi occur most typically in conditions of high temperature, sparse water, and low nutrients. This study was designed to assess their growth and survival under various conditions of temperature and relative humidity. In one set of experiments, rocks containing microcolonial fungi (MCF) from Arizona and Oregon deserts were exposed in the laboratory to different temperatures and humidities, and the survival of MCF was tested by transferring them to growth medium. The survival of MCF from Oregon and Arizona rocks was similar: many survived at 70 and 80°C even after 21 d of exposure. Those from the Sonoran Desert in Arizona which were exposed to 100°C were dead after 4 d. Low humidity favoured tolerance to high temperatures. Pure cultures of MCF from these locales in the USA as well as from Australia and Egypt were tested for growth at various temperatures and relative humidities. No isolates were able to grow at water activities below 0–95. Some strains grew at temperatures as low as 4°C, but none grew at 50°C or higher. These results indicate that these MCF are not able to grow during the hot periods encountered on desert rock surfaces regardless of the humidity, but they are able to survive for extended periods under these conditions.
PHOSPHATASE ACTIVITY ASSOCIATED WITH THE ROOTS AND THE RHIZOSPHERE OF PLANTS INFECTED WITH VESICULAR‐ARBUSCULAR MYCORRHIZAL FUNGI
Authors: DODD J. C. , BURTON C. C. , BURNS R. G. , JEFFRIES P. 
Published: April 2006

SummaryAcid phosphatase activity associated with the root and in the rhizosphere of rape (Brassica napus) L., wheat (Triticum aestivum L.) and onion (Alliutn cepa L.) plants was investigated in the presence or absence of vesicular‐arbuscular mycorrhizal fungi. The plants were inoculated singly with three different species of Glomus, or were left uninfected, and were grown in sand with little available phosphorus. Root and rhizosphere levels of phosphatase activity were higher for plants infected with G. geosporum (Nicol. & Gerd.) Gerd. & Trappe and G. mosseae (Nicol & Gerd.) Gerd. & Trappe compared with control plants. Infection with G. monosporum Gerd. & Trappe did not result in a similar increase in phosphatase activity but significant increases in plant growth nevertheless occurred. Further experiments, using wheat only, showed that increases in phosphatase activity induced by infection by G. geosporum or G. mosseae became apparent between 25 and 51 d after sowing.
SPATIAL VARIATION IN INOCULUM POTENTIAL OF VESICULAR‐ARBUSCULAR MYCORRHIZAL FUNGI CAUSED BY FORMATION OF GOPHER MOUNDS
Authors: KOIDE R. T. , MOONEY H. A. 
Published: April 2006

SummaryTwo sites in California, on serpentine soil bearing annual grassland, were studied. Spatial (horizontal and vertical) variation in inoculum potential of vesicular‐arbuscular mycorrhizal fungi in soils was measured by a bioassay. Unvegetated gopher mounds had significantly lower inoculum potentials than did undisturbed soils. The decreased inoculum potential in gopher mounds is attributed to the reduced amount of inoculum in subsurface soil brought to the surface during formation of mounds. A difference in inoculum potential between two distinct types of vegetation (grass‐or forb‐dominated) was also found.
EFFECTS OF ARTIFICIAL ACID PRECIPITATION ON THE MYCORRHIZAS OF SCOTS PINE SEEDLINGS
Authors: DIGHTON J. , SKEFFINGTON R. A. 
Published: April 2006

SummaryRoots were examined from three‐year‐old Scots pine seedlings (Pinus sylvestris L.) growing on a humo‐ferric podzol in monolith soil lysimeters which had received simulated acid rain at pH 3 or non‐acidified rain. This is about 30 times the rate of wet H+ deposition at the site from which the lysimeters were taken. Root biomass was similar between treatments, but acid‐treated root systems showed significantly reduced fine root branching compared to the controls. The reduced branching of acid‐treated root systems was attributed to a significant reduction in the occurrence of two corralloid mycorrhizal morphs. The coralloid mycorrhizas were characterized by profuse extramatrical hyphal development, the growth of which was retarded by soil conditions in the acid‐treated lysimeters. Soil solution measurements showed the major effects of the acid treatment to be increases in concentrations of H+, Ca2+, A1 and SO42−. It seems likely that an increase in Al and reduction of pH had affected the growth of these mycorrhizas. This may have nutritional consequences for trees on acidic soil.
A MINI‐MONOLITH CUTTER FOR ABSOLUTE POLLEN ANALYSIS AND FINE SECTIONING OF PEATS AND SEDIMENTS
Authors: CLOUTMAN E.W. 
Published: April 2006

SummaryThe construction and operation of a mini‐monolith cutter is presented. The apparatus will allow the extraction of accurate volumes of peats and sediments for absolute pollen techniques, or cut thin sections for fine resolution analysis. The design ensures a minimum amount of compression or contamination. The overall error of the machine is 4·6%.