bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interactions between drought and elevated CO2 on growth and gas exchange of seedlings of three deciduous tree species
Authors: TSCHAPLINSKI T. J. , STEWART D. B. , HANSON P. J. , NORBY R. J. 
Published: April 2006

summaryInteractions between elevated atmospheric CO2 and drought on growth and gas exchange of American sycamore (Platanus occidentalis L.), sweetgum (Liquidambar styraciflua L.) and sugar maple (Acer saccharum Marsh.) were investigated using 1‐yr‐old seedlings, planted in 8 1 pots and grown in four open‐top chambers, containing either ambient air or ambient air enriched with 300 μmol mol−1CO2. Two soil moisture regimes were included within each chamber: a ‘well‐watered’ treatment with plants watered daily and a ‘drought’ treatment in which plants were subjected to a series of drought cycles. Duration and depth of the drought cycles were determined by soil matric potential. Mean soil water potential at rewatering for the water‐stressed seedlings under ambient CO2 for sugar maple, sweetgum and sycamore was −0.5, −0.7 and −1.8 MPa, respectively, compared with > −0.1 MPa for all well–watered plants.Elevated CO2 increased relative growth rate of well‐watered sugar maple by 181%, resulting in a 4.3‐fold increase in total plant dry weight after 81 d, compared with 1.4 and 1.6‐fold increases for sweetgum and sycamore, respectively, after 69 d. Although elevated CO2 increased net CO2 assimilation rate of sugar maple by 115%, there was a 10‐fold increase in leaf area which contributed to the growth response. Although drought did not eliminate a growth response of sugar maple to elevated CO2 it greatly reduced the elevated CO2‐induced enhancement of relative growth rate. In contrast, relative growth rates of sweetgum and sycamore were not significantly increased by elevated CO2. Drought, under elevated CO2, reduced leaf area of all three species to a greater extent than it reduced net CO2 assimilation rate. The response ranged from no effect in sugar maple to a 40 % reduction in sycamore, with sweetgum exhibiting an intermediate response. Results indicate that drought may alter the growth response, gas exchange and water relations of tree species growing in an elevated CO2 atmosphere. Under high nutrient and water availability, sugar maple may benefit the most (of the three species studied) from a CO2‐ enriched atmosphere, but productivity gains will be limited if frequent drought is prevalent.
Effects of high nitrogen concentrations on ectomycorrhizal structure and growth of seedlings of Picea abies (L.) Karst.
Authors: BRUNNER IVANO , SCHEIDEGGER CHRISTOPH 
Published: April 2006

summaryHigh nitrogen concentrations are known to affect ectomycorrhizal and ectomycorrhizal fungi in field and laboratory experiments. Using NH/ as a nitrogen source in the growth pouch system, a variety of structural modifications were documented on first order lateral roots of Picea abies (L.) Karst. seedlings. Root cells increased in size and number at high levels of NH4+resulting in a hypertrophic appearance of roots in both uncolonized seedlings and in those inoculated with mycelia of the ectomycorrhizal fungus Hebeloma crustuliniforme (Bull, ex St. Amans) Quel. A fungal mantle surrounded short roots of inoculated seedlings, and the outer walls of epidermal and cortical cells were often thickened when in contact with fungal hyphae. No Hartig net developed, although intracellular penetration of fungal hyphae into epidermal and cortical cells frequently occurred. At moderate NH4+concentrations, Hartig net development was incomplete, but occasional intracellular penetration of Hartig net hyphae into epidermal and cortical cells occurred. The addition of high levels of NH4+after ectomycorrhizal development resulted in ectomycorrhizas with distinctly altered apical structures. None of the various NH4+concentrations resulted in significantly different plant dry weights after two months of exposure, either with or without fungal inoculation. After four months, dry weight, root length and branching indices were higher in both inoculated plants and those exposed to high nitrogen. The root/shoot ratio and number of short roots per seedling were high with fungal inoculation. Shoot nitrogen levels after two and four months and the Ca levels after 4 months were higher with increasing NH4+in the nutrient solution. Other mineral elements were not influenced by nitrogen concentrations and fungal inoculation.
Variations in habitat, season, flower traits and pollinators in dimorphic Narcissus tazetta L. (Amaryllidaceae) in Israel
Authors: ARROYO JUAN , DAFNI AMOTS 
Published: April 2006

summary Narcissus tazetta shows a genetically‐based discrete polymorphism for style length similar to that well known in heterostylous plants. Plants are either short‐ (S) or long‐styled (1). In Israel, marsh populations are dominated by S plants and hill populations by L plants. Populations differ in size, flowering time and duration, flower orientation, inflorescence display, vegetative reproduction, and pollinators. The main visitors to flowers in marshes are hawkmoths, whereas in the hills they are visited by short‐tongued insects: solitary bees and hoverflies. The pollination efficiency of these insects was investigated by studying foraging behaviour, visit rate, and pollen deposition on stigmas. Our findings are consistent with the hypothesis of lower efficiency of pollination of S flowers by short‐tongued insects, resulting in the exclusion of this morph from the hills. Additionally, we considered the possibility that there might be pollination ecotypes corresponding to the two habitats (marsh and hill) and examined variation in a set of continuous flower traits related to pollination biology. Flower tube length was the only trait showing a distinct difference between the two habitat types. Although the concentration of nectar was not different between habitats, L flowers presented more concentrated nectar than S flowers. Such a difference in nectar concentration may he of adaptive value for the pollination of the L flowers by short‐tongued pollinators in the hills.
Low genetic diversity in the Scottish endemicPrimula scoticaHook.
Authors: GLOVER BEVERLEY J. , ABBOTT RICHARD J. 
Published: April 2006

summaryPrimula scoticaHook., a rare Scottish endemic, is threatened with extinction due to habitat destruction. A survey of genetic variability within the species was conducted on five populations from the Orkney islands and nine from the Scottish mainland. Isozyme analysis revealed variation between individuals at only one of 15 enzyme encoding loci examined, while a survey of DNA sequence variation via RAPD analysis revealed no genetic diversity either within or between a subsample of four populations surveyed. Individuals exhibited a ‘fixed’ heterozygous genotype at seven of the enzyme encoding loci, indicating thatP. scoticais of allopolyploid origin. Despite the high level of heterozygosity per individual and the biochemical diversity that may stem from it, the species remains restricted to a very specific habitat. Implications for the conservation of the species are considered, including the need for habitat protection.
Pollination ecology and patch‐dependent reproductive success of the rare perennialGentiana pneumonantheL.
Authors: PETANIDOU T. , DEN NIJS J. C. M. , OOSTERMEIJER J. G. B. , ELLIS‐ADAM A. C. 
Published: April 2006

summaryThe reproductive behaviour ofGentiana pneumonantheL., a rare plant species in The Netherlands, was studied in a relatively large wet heathland population during summer 1989. The species co‐occurred with the grassMolinia caeruleaand co‐flowered withErica tetralixandCalluna vulgaris.The flowering period lasted from July to October, peaking in late August to late September. Flowers are protandrous. The species appeared to be self‐compatible, but spontaneous self‐pollination was strongly limited. Hand‐crossing and hand‐selfing resulted in the same amount of seed set as in natural pollination. Reproductive success was dramatically reduced late in the season. Pollination was achieved sternotribically by the speciesBombus pascuorum, which visited the flowers for nectar. In the study area, three patch types were distinguished: co‐dominated byErica, byCallunaandErica, and byMolinia, respectively. Frequency of visits toGentianawas highest in theErica‐patch. However, this did not result in a higher seed set. In theMolinia‐patch seed set was reduced. However, in theMolinia‐patch the mean number of ovules was greater than in the others (as high as in plants raised indoors and in cross‐pollinated plants). Fruits from theCalluna‐patch had less ovules than those from theErica‐patch. We conclude that, in this remnant population,Gentianais not pollination‐limited. However, it is likely that in theMolinia‐patch geitonogamy is frequent, which may lead to inbreeding depression. The greater number of ovules observed inMolinia‐patches may reflect an excess of nutrients available there, relative to theCalluna‐patch where there may be reduced water availability.
Enzyme activities in isolated root plasma membranes from a stand of Norway spruce in relation to nutrient status and ammonium sulphate application
Authors: ROSENGREN‐BRINCK ULRIKA , MAJDI HOOSHANG , ASP HAKAN , WIDELL SUSANNE 
Published: April 2006

summaryThe effect of ammonium sulphate application (100 kg N ha −1y −1) on the chemistry of the rhizosphere, fine roots and needles was studied using a Norway spruce stand. Data were also collected on enzyme activities in isolated root plasma membranes as well as on Ca and K uptake in fine roots. Application of ammonium sulphate decreased both pH and Al concentration whereas Ca/Al molar ratio as well as Ca and SO4 concentrations in the soil: water extracts increased. By contrast, no treatment effect was found either for the plasma membrane‐bound ATPase activity or the glucan synthase II (GS II) activity, or for the uptake of Ca or K. Independently of treatment, increased activity of the H‐+ ATPase in fine roots was correlated with a higher Ca/Al molar ratio of the rhizosphere soil and increased root length density. Increased root length density was also linked to lower Al concentration of both rhizosphere soil and fine roots. The stress‐related enzyme GS II in fine roots showed increased activity as the P concentration in the roots decreased and was positively linked to increased K uptake. Thus, plasma membranes could be isolated from forest roots and reliably used in enzyme activity assays. Furthermore, the relations between different parameters could be determined, although data were collected only from selected parts of the intact forest ecosystem.
Response of red alder seedlings to CO enrichment and water stress
Authors: HIBBS DAVID E. , CHAN SAMUEL S. , CASTELLANO MICHAEL , NIU CHIH‐HAO 
Published: April 2006

summaryRed alder (Alnus rubra Bong.) is a nitrogen‐fixing pioneer tree species of the Pacific Northwest of North America. We investigated the response of different seed sources of red alder to elevated atmospheric CO2 and to varied levels of water stress. Seeds were stratified, germinated and grown for up to 147 d under ambient (350 //.I I−1) or elevated (700 ftl I−1) CO2.There were no significant interactions of seed source latitude with either treatment, although seedlings from more northerly sources were larger. Elevated CO2 and low moisture stress resulted in larger plants with more leaf area; effects of the two factors appeared additive. Effects of both factors on biomass allocation, including root: shoot ratios, were small or nonsignificant. Elevated CO2 decreased specific nitrogenase activity and generally increased photosynthesis (A) and stomatal conductance (g). The ratio A: g, potential water use efficiency, also increased when plants were under water stress. Elevated CO2 appears to improve drought tolerance in red alder.Overall, these results indicate that red alder would benefit in total plant growth from increased ambient CO2 and could tolerate changes in precipitation.
Atmospheric CO2, soil nitrogen and turnover of fine roots
Authors: PREGITZER KURT S. , ZAK DONALD R. , CURTIS PETER S. , KUBISKE MARK E. , TEERI JAMES A. , VOGEL CHRISTOPH S. 
Published: April 2006

summaryIn most natural ecosystems a significant portion of carbon fixed through photosynthesis is allocated to the production and maintenance of fine roots, the ephemeral portion of the root system that absorbs growth‐limiting moisture and nutrients. In turn, senescence of fine roots can be the greatest source of C input to forest soils. Consequently, important questions in ecology entail the extent to which increasing atmospheric CO2may alter the allocation of carbon to, and demography of, fine roots. Using microvideo and image analysis technology, we demonstrate that elevated atmospheric CO2increases the rates of both fine root production and mortality. Rates of root mortality also increased substantially as soil nitrogen availability increased, regardless of CO2concentration. Nitrogen greatly influenced the proportional allocation of carbon to leaves vs. fine roots. The amount of available nitrogen in the soil appears to be the most important factor regulating fine root demography inPopulustrees.
Effects of ozone on stomatal conductance and photosynthesis in populations of Plantago major L.
Authors: REILING K. , DAVISON A. W. 
Published: April 2006

summaryBritish populations of Plantago major L. differ in ozone resistance. As stomata regulate ozone uptake it is possible that some of this variation in ozone resistance is the result of differences in stomatal behaviour. This paper reports a comparative study of the effects of ozone exposure on the stomatal conductance (gs), net CO2 uptake (A) and intercellular CO2 concentration (C1) of 28 populations over a 5 d period under controlled conditions. The ozone exposure was 70 ml 70 nl1−1 for 7 h d−1 while controls in charcoal filtered air received < 5 ml 1−2. There was no relationship between mean or maximum stomatal conductance in charcoal filtered air and ozone resistance. Ozone reduced gs in all populations within hours of the start of fumigation, but particularly so in the more sensitive ones, then over the next 4 d the pattern changed as the effect on the sensitive populations decreased. The effect on the resistant populations remained more constant. Conductance measurements made in the dark period showed that the stomata did not close completely, and that in ozone fumigated plants gs was on average 75% of that in control plants. Although the resistant populations showed a large reduction in gs, ozone had no effect on A or C, indicating that closure was not caused by reduced photosynthesis and higher C. It is argued that closure was probably caused by direct effects on the guard cells. In sensitive populations ozone reduced A to around 50–60% of the controls on day 1 but only to 70–80% of the controls on day 5. The recovery might have been caused by the decreasing effect on gs but as the uptake of ozone would have increased at the same time it might have been related to acclimation.
Influence of nitrogen supply on the response of clones of birch (Betula pendula Roth.) to ozone
Authors: PÄÄKKÖNEN E. , HOLOPAINEN T. 
Published: April 2006

summaryClonal birch (Betula pendula Roth.) seedlings were exposed to slightly higher than ambient levels of ozone and different levels of nitrogen supply under open‐field conditions in three experiments: (1) three 2‐year‐old clones exposed to ozone and 74/150 kg N ha−1 y−1 for two growing seasons, (2) three 2‐year‐old clones under a corresponding exposure regime for one growing season and (3) one 2‐year‐old clone exposed to ozone and 37/74/150 kg N ha−1 y−1 for one growing season. The cumulative ozone exposures were 1–5 x (1992) and 1–7 x (1993) higher than ambient levels. In these experiments no significant differences between the clones were found in their response to each treatment. Ozone exposure reduced the mean leaf size and the leaf area, accelerated autumn yellowing and loss of leaves, and increased the palisade layer thickness. High nitrogen availability increased the height growth, the mean leaf size, the leaf area, the shoot/root ratio, the leaf water content and the stem dry weight, but decreased the number of leaves and the leaf dry mass per area, and retarded autumn senescence of leaves. It also reduced the leaf and palisade layer thickness and increased the intercellular space of the palisade layer. Significant interactions between ozone and nitrogen supply were found as an increase in leaf biomass production, root dry weight and spongy intercellular space, and as a decrease in leaf loss, yellowing of leaves and palisade layer thickness. The results suggest that sufficient nitrogen supply can confer the birch with greater resistance to ozone.
The effect of repeated nitrogen fertilization on mycorrhizal infection in heather [Calluna vulgaris (L.) Hull]
Authors: CAPORN S. J. M. , SONG W. , READ D. J. , LEE J. A. 
Published: April 2006

summaryThe effects of repeated nitrogen fertilization over three years (1989–92) on mycorrhizal infection of Calluna vulgaris (L.) Hull growing in peat soils in north Wales are described. Solutions of NH4NO3 were added at regular intervals (10 to 20 times annually) to provide 0, 40, 80 or 120kg N ha−1 a−1 above background deposition. An estimate of mycorrhizal biomass in washed roots from soil cores sampled in May and July 1992 was gained by determining the concentration of ergosterol, a fungal metabolite, in ethanol extracts. The concentrations of ergosterol (per mg fresh weight) were significantly greater in fine hair roots than in thicker roots and also higher in surface horizons than deeper in the soil core. In May, the only significant effect of nitrogen application was found in the fine roots in the surface (0–15 mm) soil. In this fraction, ergosterol was significantly higher in the plots which received 80 kg N ha−1 a−1 plots than in all the other treatments. However, in July the ergosterol concentration in the fine, surface root fraction were not changed by the nitrogen additions. No changes were observed in the soil nutrients (total N and P, extractable base cations) or surface pH, but nitrogen fertilization did stimulate shoot growth, flowering and litter production. Nitrogen concentrations in living shoots and litter were raised as a result of the N inputs while the levels of other main nutrients P and K were not altered. Given the relatively small changes measured in the amount of mycorrhizal infection in the recent experiment, this measurement may be a poor indicator of excess atmospheric nitrogen deposition to heathlands soils.
Functional compatibility in arbuscular mycorrhizas measured as hyphal P transport to the plant
Authors: RAVNSKOV S. , JAKOBSEN I. 
Published: April 2006

summaryThe functional compatibility of symbioses between host plants and arbuscular mycorrhizal fungi was measured as hyphal P transport to plants. Cucumber (Cucumis sativus L.), wheat (Triticum aestivum L.) and flax (Linum usitatissimum L.) were inoculated with Glomus caledonium (Nicol. & Gerd.) Trappe & Gerdemann (isolate RIS42, BEG 15) and Glomus invermaium Hall (isolate WUM10) or left uninoculated and grown for 28 days in soil divided into three compartments. One side compartment was separated from the main compartment by a 20 um nylon mesh, and radioactive labelling with 32P was used to determine hyphal P uptake. The other side compartment was separated from the main compartment by a 700 um nylon mesh and 33P was used to determine the combined P‘uptake by roots and hyphae.All plant‐fungus combinations were compatible with respect to mycorrhiza formation, measured both as root colonization and growth of external hyphae. In contrast, the symbioses differed markedly with respect to functional compatibility as phosphorus uptake by each fungus depended on the species of host plant. The hyphal transport of 32P was high in G. caledonium in symbioses with all three plant species, whereas G. invermaium transported significant amounts of 32P only when associated with flax. Consequently, to determine the P‐transport effectiveness of a mycorrhizal fungus is meaningful only in the context of its associated host plant species.
Arbuscular mycorrhiza and phosphorus as controlling factors in the life history of Hyacinthoides non‐scripta (L.) Chouard ex Rothm.
Authors: MERRYWEATHER JAMES , FITTER ALASTAIR 
Published: April 2006

summaryThis investigation aimed to assess the degree of dependence of young plants of Hyacinthoides non‐scripta (L.) Chouard ex Rothm. on the formation of arbuscular mycorrhiza (AM) at different stages of its life cycle. H. non‐scripta is a bulbous perennial with a restricted root system of coarse, unbranched elements which are plainly inadequate for the acquisition of phosphate (P) from soil. In a glasshouse experiment non‐mycorrhizal H. non‐scripta were unable to take up sufficient P to maintain a positive P budget, confirming that the species is obligately mycorrhizal when adult.We needed to be able to assess the ages of field‐collected plants. The bulb of H. non‐scripta, which is totally rebuilt annually, provides no indicator of age other than size. The development of individual bulbs was monitored in reconstructed soil profiles for several years and the relationship of size and age calculated in order to determine the age structure of a population in the field and to quantify the mycorrhizal colonization of their roots according to age and depth in the soil.Seedlings of H. non‐scripta are supplied with a P‐rich endosperm and initially inhabit upper soil horizons where P is plentiful. However, they are at risk from winter frosts, summer drought and, possibly, predators. During their first four to five seasons they descend in the soil to a depth of approximately 20 cm, down a gradient of decreasing soil phosphorus concentration; simultaneously, their roots become increasingly colonized by arbuscular mycorrhizal fungi. Because of the change in environment, they appear to become increasingly dependent on the symbiosis, suggesting that the association changes from facultative to obligate during the plant's life history.
Leaf development in Lolium temulentum L.: photosynthesis in relation to growth and senescence
Authors: GAY ALAN P. , THOMAS HOWARD 
Published: April 2006

summaryLength, area, weight and concentrations of pigment were measured from just after emergence until senescence of the fourth leaf of Lolium temulentum L. seedlings grown in nutrient solution in a controlled environment. At the same time the progress of photosynthesis, respiration and carbon contents of the leaf were recorded. A new approach to calculating photosynthesis indices for grasses was developed, based on logistic curves fitted to leaf lengths. Dry weight and photosynthetic rates per unit area were greatest in young leaves. Subsequently photosynthetic capacity at light saturation declined, as did photosynthetic rates at the light incident on the leaf, although the decrease was less pronounced in the latter case. Dry weight per leaf remained fairly constant once full expansion was reached, with perhaps a slight rise in the oldest leaves. The photosynthesis and carbon content data were combined to calculate the carbon balance of leaf 4, with respect both to the atmosphere and to the rest of the plant. Net gas exchange became positive about 7 d before full leaf expansion. Leaf weight continued to increase so that the carbon balance with the rest of the plant did not become positive until just after final leaf size had been attained. These results are discussed in relation to the likely contribution of the various components of the balance to plant productivity.