Showing papers in "New Phytologist in 1982"

Life histories and demography of shade‐tolerant temperate forest herbs: a review

Abstract: Summary Information is reviewed on the life histories and demographic patterns of shade-tolerant herbs of temperate deciduous forest. Most of the species that have been studied are deciduous perennials. These species generally have a juvenile (non-flowering) period of several years followed by an extended period of flower and seed production. About half the species reviewed are self-incompatible, the others are at least partially self-compatible. Although vegetative reproduction is common, replacement does not always occur by vegetative spread; many species appear to be able to replace themselves by seed. Sexual reproductive effort ranges from 1–5 to 50 % among the species reviewed; seed weight averages 2–6 mg. Short dormancy periods (one season) are most common, with germination rates generally below 50%. Mortality rates of small plants are high, but decline as plant size increases. ‘Ageing’ does not appear to occur. No information exists on population growth rates of temperate deciduous forest herbs, or on the temporal stability of their population sizes or structures. The transition matrix model is suggested as a promising approach to future studies in plant demography.

Plant‐induced changes in the rhizosphere of rape (brassica napus var. emerald) seedlings

Abstract: Summary Additions of soluble phosphate to P-deficient Begbroke sandy loam delayed or completely prevented the fall in rhizosphere pH observed when rape was grown at high root densities in this soil (Parts I to III, this series). Whereas the pH of the unamended rhizosphere soil fell from 6–6.5 to 5.1–5.3 by day 41, the rhizosphere pH of soil with an extra 2 μmol P g−1 remained steady (6 to 6.5) until day 35, and that of soil with an extra 20 μmol P g−1 increased slightly from pH 6 to 6.4 during 41 days of growth. The increase in rhizosphere phosphatase activity with increasing severity of P deficiency appeared to be a response to increasing root density and decreasing concentration of soluble inorganic P in the soil. No significant change in levels of soil organic P was detected. Plants that acidified their rhizosphere (low P status) depleted acid-soluble forms of soil P and absorbed twice the amount of P which could be desorbed from the control soil in 10−2 M Ca(NO3)2at pH 6.1. Uptake of P by plants which did not acidify their rhizosphere (high P status) was never greater than the amount of P desorbable in 10−2m Ca(NO3)2 at pH 6.1, and was derived from alkali-soluble and resin-extractable forms of soil P. Cation uptake exceeded anion uptake in both low and high P plants, but the difference was greater in low P plants. These differences in cation and anion uptake (mEq) were approximately equal to the milliequivalents of H+ (OH−) required to produce the observed changes in rhizosphere pH. These results explain why models for P uptake based on in vitro measurements of physicochemical parameters governing phosphate diffusion in soil work well for P sufficient plants, but tend to underestimate P uptake by P deficient plants growing in soils in which soluble P levels are sensitive to pH change.

Vesicular‐arbuscular mycorrhiza in natural vegetation systems

Abstract: Summary The intensity of vesicular-arbuscular mycorrhizal infection was assessed in the major vegetation types of east-central England. All of the most important species of grassland, scrub and woodland were mycorrhizal and each individual of any species normally carried a heavy VA infection. Members of the Gramineae were particularly heavily infected. In limestone grassland, infection extended to members of the Cyperaceae and Juncaceae. Infection levels were high throughout the year, the highest levels occurring in the most nutrient-stressed situations. Mycorrhiza develops soon after germination, often while seedlings are still in the cotyledon stage. Since numbers of viable Glomus type spores are low, infection is thought to arise from root to root contact rather than from spores. The Ecological implications of the widespread infection are discussed.

A comparison of the toxicity of heavy metals, using root elongation of rye grass, lolium perenne

Abstract: SUMMARY The order of toxicity of different metals affecting root growth of seedlings of rye grass (Lolium perenne S24) was: copper > nickel > manganese > lead > cadmium > zinc > aluminium > mercury > chromium > iron. With the sole exception of manganese, these results confirm those of other studies and the order follows that of the stability of the metallic-organic complexes. The results are of value in predicting the toxicity of heavy metals in plant growth on contaminated soils.

Enzymatic studies on the metabolism of vesicular–arbuscular mycorrhizas

Abstract: Summary The ultrastructural localization of ATPase activities was identical in onion and sycamore mycorrhizas. DES-sensitive ATPase activity was associated with the fungal plasmalemma and paramural bodies whilst a DES-insensitive ATPase activity was detected within the fungal vacuole. The development of the mycorrhizal fungus within root cells modified the distribution of DES-sensitive plasmalemma-bound ATPase activity of the host. This became concentrated around the finer arbuscule branches and appeared to be a specialization of the invaginated host membrane which occurred when arbuscule structure was favourable for nutrient exchange. These observations strengthen the hypothesis that nutrient exchange in VA mycorrhizas must occur across the living host-fungus interface and that phosphate is transferred from fungus to host by an active transport mechanism in the finer branches of the arbuscule.

The distribution of carbon and the demand of the fungal symbiont in leek plants with vesicular-arbuscular mycorrhizas

Abstract: SUMMARY Leek plants (Allium porrum) were grown on partially sterilized soil either inoculated (M) or not (NM) with the vesicular-arbuscular mycorrhizal fungus, Glomus mosseae. They were pulse-fed with 14CO2 in an apparatus which allowed CO2 subsequently respired either by the shoots or by the roots plus soil to be separately monitored. There were three experiments. In two, plants were harvested 48 h after labelling and in the third after 214 h. At harvest, the distribution of 14C between shoot, root, soil organic matter and root washings was measured. Similar growth curves for M and NM plants were obtained by supplying extra phosphorus to the latter, so that C distributions for both treatments could be compared directly. In all three experiments, about 7 % more of the total fixed C was translocated from shoot to root in M plants compared to NM plants. In the third experiment, this extra translocate could be accounted for by increased root respiration plus increased loss of C to the soil but, despite this drain, M and NM plants had equal rates of C assimilation per unit of leaf area. However, shoots of M plants had a lower content of dry matter and hence higher assimilation rates expressed on a dry matter basis. Increased hydration is suggested as a mechanism whereby leaf area and hence C assimilation increases in mycorrhizal plants and which offsets the effects of the drain imposed by the mycorrhizas.

Plant induced changes in the rhizosphere of rape brassica napus cultivar emerald seedlings 1. ph change and the increase in phosphorus concentration in the soil solution

Abstract: Rape (Brassica napus, var. Emerald) plants were grown in thin layers of a phosphate-deficient soil supplied with a P-free nutrient solution containing N solely as NO3(3 5 x 10-3 M). Inter-root competition (excluding root hairs) for soil P began on the 14th day of growth, after which all soil in the thin layer was considered to be rhizosphere soil. During subsequent plant growth the pH in the rhizosphere decreased as much as 2-4 units (from pH 6&5 to 4-1) before rising slightly towards the end of the experiment (35th day). The pH decrease was associated with an increase in solution P concentration in the depleted rhizosphere soils, compared to the P concentration attained when similar amounts of P were desorbed from unplanted control soils by shaking them in 102 M Ca(N03)2 at the original soil pH of 6-1. P desorption in 10-2 M Ca(NO3)2 at pH values between 6&2 and 4-5 indicated that a decrease in the soil pH from 6-5 to 4-1 could result in at least a 10-fold increase in the P released into solution, which would be available for plant uptake. These results may explain reports in the literature that rape is efficient in absorbing P from P-deficient soils.

Influence of vesicular‐arbuscular mycorrhizae on water movement through bouteloua gracilis (h.b.k.) lag ex steud*

Abstract: SUMMARY Root growth characteristics and water transport were compared between non-mycorrhizal Bouteloua gracilis and vesicular–arbuscular mycorrhizal Bouteloua gracilis infected with Glomus fasciculatus. Mycorrhizal plants did not have significantly different leaf area or root length from non-mycorrhizal plants, but did have significantly fewer and shorter root hairs. Mycorrhizal plants had 50% lower leaf resistance with no change in leaf or root water potentials; thus transpiration was increased 100% with a 50% reduction in whole-plant, soil-to-root and root-to-leaf resistance. Assuming that the difference in water uptake was due to transport via the mycorrhizal hyphae, estimated fungus-to-root transport was 2.8 × 10−5 mg s−1 per hyphal entry point which compares favourably with evapotranspiration rates measured in other coenocytic fungi. Thus, one of the major factors causing increased water transport and reduced resistance to water through-flow with mycorrhizal infection may be the increased surface area provided by the hyphae.

Development of external hyphae by different isolates of mycorrhizal glomus spp. in relation to root colonization and growth of troyer citrange

Abstract: SUMMARY The hypothesis was tested that the amount of external hyphae of a vesicular-arbuscular mycorrhizal (VAM) fungus extending from roots out into soil is not always proportional to the extent of colonization of the root cortex. Growth enhancement and amount of external hyphae were compared for eight isolates of five Glomus spp. that differed in their geographic origin and capacity to enhance growth of Troyer citrange, but were similar in their capacity to extensively colonize Troyer citrange roots. In general, isolates from California increased growth in a P-deficient (9.8 mg kg−1) California soil more than did non-native isolates from Florida soils. The difference between the capacity of California and Florida isolates to enhance growth was not a function of the degree to which they colonized the roots since all had colonized over 95% of the root length by the time of harvest. Differences in growth enhancement did appear, however, to be a function of the amount of external hyphae that had developed as estimated by the weight of soil they had bound into aggregates. This study suggests that isolates of VA mycorrhizal fungi may differ in their capacity to develop an external hyphal system independent of their capacity to colonize the root cortex, and that we cannot assume that high levels of colonization will necessarily mean the fungus has also developed the mycelium in the soil necessary to transport nutrients responsible for plant growth enhancement.

The effects of salinity and waterlogging on the growth and cation uptake of salt marsh plants

Abstract: Summary Festuca rubra, Juncus gerardii, Armeria maritima, Plantago maritima, Aster tripolium, Triglochin maritima, Puccinellia maritima and Salicornia europaea from a salt marsh near Portaferry, County Down, were grown on drained and waterlogged salt marsh soils under saline and non-saline conditions. Shoot and root yields and the concentrations of sodium, potassium, calcium, magnesium, manganese and iron in the shoots were determined after a 2-month growing period. The tolerance of the plants to waterlogging and salinity differed in a way which was correlated with their position on the salt marsh ecotone. The growth of upper marsh species, but not that of lower marsh species, was strongly limited by both salinity and waterlogging. Only Salicornia europaea gave its maximum yield on the saline treatments and only Puccinellia maritima showed a preference for waterlogged soils. Reduced yields on the saline treatments were associated with large increases in shoot sodium concentrations but in general, salinity and waterlogging had little effect on shoot cation concentrations. It is suggested that factors other than the greater availibility of iron and manganese on araerobic salt marsh soils are involved in determining species distribution along the salt marsh ecotone.

Phytochrome control of seed germination in the tropical rain forest pioneer trees cecropia obtusifolia and piper auritum and its ecological significance

Abstract: SUMMARY The tropical forest pioneer trees Cecropia obtusifolia and Piper auritum germinate and become established in large light gaps of the forest canopy in the rain forest of south-eastern Mexico. Germination of the seeds of both species is under photocontrol and is triggered when the red: far-red ratio (R: FR) of the incident light increases due to a reduction of the green canopy density. Exposure to simulated light canopies retarded and reduced germination. The light environment inside the forest inhibits germination totally. Experiments with alternate R and FR light treatments indicate the need for long periods of exposure to R light for germination, and demonstrate a strong reversibility of the R light stimulation by FR light in both species. This property of the seeds may be related to the detection of light gap size and its differentiation from the normal sunflecks of the forest.

The influence of a springtail folsomia candida (insecta, collembola) on the mycorrhizal association of leek allium porrum and the vesicular-arbuscular mycorrhizal endophyte glomus fasciculatus

Abstract: Summary Seedlings of leek were grown in a factorial experiment to examine the interactions between mycorrhizal infection with Glomus fasciculatus, soil teachings and the Collembola, Folsomia Candida. The growth of leek was increased by mycorrhizal infection and leachings, the latter having a lesser effect, and reduced by F. Candida. There was a strong interaction between the effects of mycorrhizal infection and the presence of F. Candida since infected plants in pots with the Collembola grew little better than uninfected plants. Evidence from root weight ratios, phosphate inflows and the gut contents of the Collembola all suggest that this is due to grazing of the external hyphae of G. fasciculatus, so rendering the infection ineffective.

Interaction of light and mineral nutrient supply in the growth of impatiens parviflora

Abstract: Summary (1) Plants of Impatiens parviflora were grown on a boulder-clay woodland soil at four levels of irradiance with and without addition of ammonium nitrate and calcium phosphate. (2) Addition of nitrogen and phosphorus fertilizer increased dry wt yield and relative growth rate at all four levels of irradiance, and there was a true interaction between the level of irradiance and nutrient supply. (3) At the three higher levels of irradiance the increased growth resulted from an increase in unit leaf rate and leaf weight ratio, but at the lowest level an increase in leaf weight ratio alone was found. (4) Evidence was obtained for lower rates of respiration in the leaves of plants grown with fertilizer at high irradiance. Mycorrhizas were absent from all fertilized plants, but were well developed in the unfertilized plants at high irradiance and absent from unfertilized plants at the lowest irradiance. (5) Plants grown at high irradiance with additional phosphate alone responded initially exactly like plants with additional nitrogen and phosphorus but grew poorly later; plants with additional ammonium nitrate alone showed no response initially, but grew about as fast as plants with additional nitrogen and phosphorus later on. (6) Plants grown one per small pot responded only to additional phosphate in the short term, but plants grown 10 per small pot responded only to additional nitrogen. (7) Emphasis is placed on the important effects of the differential mobilities of nitrate and phosphate ions in experiments on the limiting mineral nutrients in soils. (8) The results are discussed in relation to earlier work, and the penetration of deeper shade by herbs on soils of higher pH is tentatively related to a superior supply of nitrate.

The effect of a foreign pollen on ovule development in diervilla lonicera (caprifoliaceae)

Abstract: Summary When pollen from Hieracium floribundum Wimmer and Grab. (Compositae) was applied to stigmas of Diervilla lonicera Mill. (Caprifoliaceae) in mixtures with Diervilla pollen, Diervilla fecundity was strongly depressed. While this phenomenon is unlikely to be of importance to Diervilla under field conditions, this property of Hieracium pollen may have stronger effects on other ecological associates. The only other reported instance of inhibitory pollen is from Parthenium hysterophorus L., which, like Hieracium, has allelopathic properties.

Lack of mycorrhizal specificity by the ericaceous hosts arbutus menziesii and arctostaphylos uv a‐ursi

Abstract: SUMMARY Twenty-eight cultures of ectomycorrhizal fungi isolated from diverse host and habitat associations were tested in pure culture syntheses with the ericaceous hosts Arbutus menziesii Pursh and Arctostaphylos uva-ursi (L.) Spreng. All but three of the fungi formed arbutoid mycorrhizas. Sheathing fungal mantles, Hartig net penetration and intracellular colonization were well developed on most mycorrhizas. These results confirm that ectomycorrhizal fungi form arbutoid mycorrhizas and that these particular hosts are broadly receptive towards fungal associates. The significance of these results with respect to ecological and practical implications and better understanding of ectomycorrhizal specificity is emphasized. Arbutoid mycorrhizas are most closely related to ectomycorrhizas than to ericoid mycorrhizas.

Accumulation of calcium oxalate in the mantle of ectomycorrhizal roots of pinus radiata and eucalyptus marginata

Abstract: SUMMARY Calcium oxalate crystals occur in the mantle of ectomycorrhizal roots of Firms radiata and Eucalyptus marginata. Dense concentrations of these crystals were observed in association with the fungal symbiont of both tree species. It is suggested that oxalate production may enhance nutrient uptake by ectomycorrhizal roots of forest species growing in nutrient impoverished soils. Concentrations of Ca, S, K and P were similar in mycorrhizal root masses of P. radiata and E. marginata.

Survival of mycorrhiza formed by cenococcum geophilum fr. in dry soils

Abstract: SUMMARY Seedlings and 2-year old saplings of Tilia cordata growing in the shade on sandy-textured soils can survive periods when the water potential of the soil decreases to −18 to −55 bars. Their mycorrhiza formed by Cenococcum geophilum is shown to remain alive. Measurement of rates of water-loss from seedlings in similar conditions decreases from 16.0 to 26.2 mg h−1 when the soil is wet, to 4.1 to 4.6 mg h−1 when the soil is dry. Calculation of the volume of the mycorrhiza shows that its water content would support transpiration for periods not exceeding 1 h. Survival of the mycorrhiza through long periods of drought is apparently related to the ability of the fungal partner to withstand desiccation.

Inflow of phosphate into mycorrhizal and non-mycorrhizal plants of trifolium subterraneum at different levels of soil phosphate

Abstract: Summary During early growth of mycorrhizal and non-mycorrhizal plants of Trifolium subterraneum fertilized with soluble (Na2HPO4) phosphate, inflow of phosphate (moles P absorbed per unit length root per unit time) into mycorrhizal roots from soil exceeded that into non-mycorrhizal roots over a range of levels of phosphate. High rates of uptake (up to 45 × 10−15 mol phosphate cm−1 s−1) were associated with reductions in root: shoot dry wt ratios. The length of mycorrhizal root per plant was little affected by fertilization with phosphate. However, rapid growth of roots at high levels of Na2HPO4 resulted in reductions in percentage root length infected by mycorrhizas. Results are discussed with respect to rates of uptake by whole plants and to differences in distribution of phosphate between roots and shoots in mycorrhizal and non-mycorrhizal plants.

Mycorrhizal associations in some woodland and forest trees and shrubs in tanzania

Abstract: SUMMARY The mycorrhizal associations in 47 indigenous Tanzanian trees and shrubs, mainly from less humid areas, were studied. Forty species were found to be endomycorrhizal. One, Uapaca kirkiana Mull. Arg. (Euphorbiaceae) was ectendomycorrhizal while six, four Brachystegia spp., Julbernardia globiflora (Benth.) Troup. (Caesalpiniaceae) and Monotes elegans Gilg. (Diptero-carpaceae), were ectomycorrhizal. The results demonstrated a dominance of endomycorrhizal species, which is typical for the tropics and is further reinforced by taxonomic considerations. However, in the Miombo (Brachystegia–Julbernardia) woodlands, a major ecosystem in East and South Central Africa, ectomycorrhizal trees predominate in volume. In three other ecosystems studied – a Combretum woodland, a groundwater forest and a semi-evergreen forest–ectomycorrhizal species were absent or almost absent. Nodulated leguminous species appeared to be more common in the fire-induced woodlands than in the closed forests.

Interaction of light intensity and soil temperature with phosphorus inhibition of vesicular-arbuscular mycorrhiza formation

Abstract: Summary The interaction between light intensity and soil temperature with phosphorus inhibition of vesicular-arbuscular mycorrhiza (VAM) formation in sudangrass (Sorghum vulgare, Pers.) was investigated in P-deficient (0.5 mg P kg−1) sandy soil amended with 0 (OP), 15 (15P) and 30 (30P) mg P kg−1 soil as superphosphate. For seedlings inoculated with Glomus fasciculatus and grown at 100, 75, and 50% of glasshouse light intensity, the reduction in VAM formation by added soil P (15 P and 30P) was greatest at the lower light levels, whereas in the OP treatment, VAM formation was unaffected by a decrease in light intensity. Increases in root P concentration resulted from both soil P amendment and, in the 15P treatment, from a decrease in light intensity, and were associated with decreases in root membrane permeability and corresponding decreases in root exudation of amino acids and sugars. The reduction in sugar exudation in the 15P treatment at lower light intensity was paralleled by a decrease in root extract levels of sugars, but decreases in amino acid exudation could not be explained by changes in amino acid levels in root extracts. These results suggest that P inhibition of VAM formation is more severe at lower light intensities because of a decrease in membrane-mediated exudation, although a reduction in sugar levels in root cells may also contribute to the observed decrease in exudation. When inoculated seedlings were grown at 25, 30, and 35°C soil temperatures, the reduction in VAM formation in the 15P and 30P treatments was overcome by increase in soil temperature. The increase in VAM formation by increased temperature in the 15P plants was associated with significant increases in root membrane permeability and exudation without a corresponding change in root P concentration. In the OP treatment, an increase in soil temperature increased VAM formation with little effect on root exudation, which suggested an effect of temperature on Glomus fasciculatus. Higher soil temperature may increase VAM formation through either a direct effect of temperature on the fungus or an indirect effect via an increase in leakage of root metabolites necessary for fungal activity, or both.

Responses of six species of vesicular‐arbuscular mycorrhizal fungi and their effects on soybean at four soil temperatures

Abstract: SUMMARY The effects of four soil temperatures on colonization of soybean roots, sporulation and enhancement of plant growth by six species of vesicular-arbuscular (VA) mycorrhizal fungi were tested. The mean values for all fungus and plant variates in three tests were generally greatest at 30 °C and lowest at 18 °C. Four fungus species, Glomus claroideum, Glomus clarum, Gigaspora pellucida, and Gigaspora gregaria, produced the greatest number of spores per gramme of colonized root at 24 °C, while Glomus mosseae and Acaulospora laevis reached their maximum at 30 °C. Gigaspora gregaria had its maximum percentage of root colonization at 36 °C, Glomus mosseae reached its maximum at 24 °C, while all other species had maximum root colonization at 30 °C. Glomus claroideum and Acaulospora laevis were the only species which had maximum root colonization and sporulation occurring at the same temperature, 30 °C. Spore diameter was generally less at 30 than 24 °C, but this varied with fungus species and test. Soybean flower numbers, pod set and seed yield varied considerably in the three tests, but plant height was little affected by soil temperature or by fungus species. Generally, plants colonized with Glomus mosseae had an increased plant response and those colonized with Acaulospora laevis had a depressed plant response. There was considerable variation in plant response to various combinations of temperature and fungus species, with both growth stimulatory and growth repressive effects occurring.

Light and self-thinning

Abstract: SUMMARY Monocultures of Lolium perenne were grown at high densities under various shade regimes to investigate the effects of shade on self-thinning. Unshaded populations conformed to the minus 3/2 power law when dead matter was taken into account in the calculation of mean weight per plant. In a plot of live weight per plant, populations reached a common minus 3/2 line but then deflected from it. Adherence to the minus 3/2 power law is a characteristic of shoots but not of whole plants of L. perenne. Populations increased in shoot:root ratio as they developed so that the thinning line for shoot plus root weight per plant was shallower than the thinning line for shoot weight per plant. Shoot: root ratios were generally higher in shaded than in unshaded populations. Tiller weights and numbers in experimental populations of L. perenne also conformed to the minus 3/2 power law. Populations grown in deep shade thinned along a line of slope minus 1 when sown at ‘low’ densities but those sown at very high densities underwent an initial period of thinning along a slope of minus 3/2, followed by a switch to a slope of minus 1. Populations at intermediate levels of shade showed a decrease in the intercept of the thinning line with increasing shade but no change in gradient. A schematic diagram is presented to help explain the effects of shade on self-thinning.

Regulation of plant cell growth: the changing perspective

Abstract: Summary This article outlines the main features of growth regulation by auxin and places them side-by-side with the physiological properties of fusicoccin The fundamental role of the plasma membrane located H+/K+ ATPase in growth responses is examined and the information about this enzyme briefly reviewed The effects of wounding on the activity of this enzyme are detailed and it is concluded that growth in excised tissue segments ceases not from lack of hormone but from impairment of ATPase function An additional conclusion of major importance for hormone studies is reached; that is, that the experimentally-realized reactivation of growth by auxin in excised tissues represents largely an accelerated recovery from injury Furthermore the calmodulin/Ca2+ system may be an essential intermediary in this recovery step Finally, the major area of ignorance, predisposition to growth, is considered

Structure and physiology of ectomycorrhizae

Abstract: SUMMARY The process of mycorrhiza formation in previously uninfected roots was studied in vitro, using the fungus Piloderma croceum Erikss. & Hjortst, and the Norway spruce, Picea abies (L.) Karst, as model organisms. The process could be divided into the following phases: fungal growth stimulation by root metabolites; formation of a hyphal envelope on the root; intercellular penetration by single hyphae, change in fungal morphology into labyrinthic tissue formation leading to Hartig net formation, and extension of labyrinthic tissue to form a mantle. P. croceum, growing in dead tissue, showed saprophytic growth in vitro, a capacity suppressed in living tissue. The way of fungal penetration appeared to be mechanical. A hypothetical model for host-fungus interactions regulating the mycorrhiza infection process is also discussed.

Oxygen exchange with the lacunae and across leaves and roots of the submerged vascular macrophyte, lobelia dortmanna l.*

Abstract: SUMMARY The oxygen dynamics of Lobelia dortmanna were examined by continuous oxygen measurements in the lacunae and in the water around leaves and roots during light/dark cycles. Lobelia exchanges about six times more oxygen over the root than the leaf surface. The exchange rates per unit of surface area are two or three times higher across roots than leaves in accordance with a similar difference in permeability constants. The delay in reaching constant rates of exchange across roots is about 45 min after switching to dark and about 25 min after switching to light. This delay corresponds to the time necessary to change the oxygen concentration in the lacunae to a new steady state gradient with the water around roots. The oxygen pools in lacunae and root-water change at the same rate at equilibrium. During incubation in a closed system it is necessary to correct for changes in the lacunal oxygen pool when it is significant relative to the oxygen pool in the external water. The lacunae of Lobelia are an effective pathway for gas movements between leaves and sediment. The extensive lacunae, and the diffusional barrier for gases in Lobelia, should facilitate recycling of oxygen, and probably carbon dioxide, within the plant-sediment system.

Influence of four vesicular‐arbuscular mycorrhizal fungi on nutrient uptake and growth in barley (hordeum vulgare)

Abstract: Summary Barley was inoculated with Glomus constrictus, G. fasciculatus isolate no. 185, G. fasciculatus isolate no. 0–1 and Gigaspora margarita in sterilized soil in pots. Plants inoculated with G. constrictus and with G. fasciculatus isolates showed an increased total uptake of P, Cu and Zn, an increased yield of grain and an increased yield of straw. Plants inoculated with G. margarita did not differ from control plants in growth or P, Cu and Zn uptake. Increase of growth was not correlated with intensity of infection.