Showing papers in "New Phytologist in 1980"

An evaluation of techniques for measuring vesicular arbuscular mycorrhizal infection in roots

Abstract: Summary Assessment of infection is an essential part of many studies involving VA mycorrhiza. A summary is given of the range of techniques that have been used. We calculated the standard error of four methods of assessment based on observations of stained root samples either randomly arranged in a petri dish or mounted on microscope slides. The methods are based on presence or absence of infection at root/grid intersect points, on a visual estimate of percentage cortex occupied by fungus or on estimates of length, or presence or absence of infection in root pieces mounted on slides. The number of replicate observations required for a given standard error % infection can be read from the curves provided. The advantages of the different methods of assessment are discussed and reasons given why they all probably overestimate the true values.

Sexual strategies in plants

Abstract: Summary It is postulated that in one reproductive session the level of maternal expenditure of an angiosperm plant is determined by a temporal series of controls on the number of potential fruit in which an investment is made. The serial adjustment hypothesis has three parts: A. The amount of maternal expenditure is regulated at many developmental units, particularly single flowers and fruit, at three principal sequential stages – the determination of flowers, the development of ovaries and the maturation of fruit. B. At each stage, the initiation or continuation of an investment requires an amount of available resources above a certain threshold. Hence maternal expenditure is continually adjusted to the resources available at each developmental site. C. The pattern of controls that maximizes the maternal fitness of a plant is selected. Many factors affect the relative advantages of regulation at the three stages, therefore species and sexual morphs appear to vary widely in their proportional use of the three stages. Regulation of flower determination has the general advantages of offering bidirectional adjustment of maternal investment, maintaining a constant ratio of maternal to paternal investment, and reducing wasted expenditure. The later stages, ovary and fruit regulation, allow secondary adjustments of maternal investment in unpredictable circumstances and permit adjustment of the relative numbers of polliniferous and seminiferous flowers. The relative advantages of restricting the numbers of developing ovaries, or of maturing fruit, depend principally on the extent to which differences in the capacity of flowers to mature fruit are evident before anthesis.

Regulation of photosynthesis by sink activity–the missing link

Abstract: Abbreviations: ADP, adenosine diphosphate; ATP, adenosine triphosphate; FBP, fructose 1,6bisphosphate; F6P, fructose 6-phosphate; GlP, glucose 1-phosphate; G6P, glucose 6-phosphate; P, phosphorus; PGA, 3-phosphoglycerate; Pi, inorganic orthophosphate; PPi, pyrophosphate; RPPP, reductive pentose phosphate pathway; RuBP, ribulose 1,5-bisphosphate; S, sucrose; SP, sucrose-P, sucrose phosphate; TP, triose phosphate; UDP, uridine diphosphate; UTP, uridine triphosphate; UDPG, uridine diphosphate glucose.

Photosynthesis by aquatic plants: effects of unstirred layers in relation to assimilation of co2 and hco3−and to carbon isotopic discrimination

Abstract: Summary We review and reassess experimental evidence which indicates that the unstirred layers of solution bathing aquatic plant cells or organs represent a major factor limiting their rate of photosynthesis under natural conditions. Unstirred layers may also limit membrane transport of HCO3− where this occurs. Some authors have suggested that aquatic plants carry out C4photosynthesis and cite in support measurements of discrimination between 13C and 12C. We propose that this discrimination can also be a manifestation of the presence of unstirred layers or membrane transport or both.

Short- and long-distance transport of boric acid in plants.

Abstract: SUMMARY The molecular weight and ether-water partition coefficient of boric acid are consistent with a PB(OH)3 in plant cell membranes of at least 10-6 cm s-1. This permeability coefficient is high enough to account for the measured magnitude of boric acid fluxes at many plant cell membranes. The use of active transport of boric acid to maintain B distribution across a membrane away from thermodynamic equilibrium is consequently likely to be energetically expensive. The content of m-diols (with which boric acid can form complexes) in cell walls and inside the cells varies widely between different plant species without any obvious correlation with either total B content or with the B content at which deficiency (in B-requirers) or toxicity symptoms are manifested. B distribution at the cell level depends on the relative extents of passive permeation, active transport and cisdiol formation; regulations may be in response to total intracellular B rather than free boric acid. The net uptake of boric acid by intact vascular land plants is influenced by the rate of transpiration; while transport of B within the xylem is probably directly proportional to the rate of transpiration, neither whole plant B uptake nor transfer from root tissue into the xylem exhibit such a simple relationship. Redistribution of B in the phloem from transpirational termini is very limited. This limitation could result from the toxicity of B (which requires a low B concentration in the translocation stream relative to other nutrients and to sink requirements) or to ‘counter-current distribution’ of B from the phloem to the adjacent xylem stream (low in B) through the B-permeable sieve-tube plasmalemma. The transport of B is discussed in relation to the evolution of multi-cellular algae and of vascular land plants.

Leaf-canopy-induced seed dormancy in a grassland flora

Abstract: SUMMARY The germination of 27 species from calcareous grassland was tested in three light treatments in the laboratory: in darkness, under tungsten lamps and under a leaf-canopy. Germination was significantly lower under a leaf-canopy than in the dark in 17 species. The phenomena of leaf-canopy induced dormancy was not associated with the life-span of species, though there was a weak, negative relationship with seed weight amongst 20 perennials in the sample. It is suggested that the co-existence of species at high density in calcareous grasslands may, in part, be explained by differences in germination response to fine-grained variations in the light environment at the soil surface.

Pleistocene forest history in east anglia

Abstract: Summary The East Anglian Pleistocene succession records eight temperate stages with forest and also interstadials with forest in two of the intervening cold stages. The forest histories of these temperate stages and interstadials are described. The records through the Pleistocene of the tree genera involved are considered. The forest assemblages in each of four substages of the temperate stages (pre-temperate, early-temperate, late-temperate, post-temperate) are compared. The development of heath in the temperate stages is also examined. Floristic and phytogeographic changes indicated by the palaeobotanical evidence give information on Tertiary-relic genera and on extinctions, and have a bearing on the problem of the history of cold stage refugia. The success or failure of particular genera in response to the stress of climatic change is discussed. Finally, comparisons are made with Pleistocene forest history in north-west Europe.

Boron, lignification and the origin of vascular plants-a unified hypothesis

Abstract: SUMMARY It is proposed that the development of an essential role for boron was a prerequisite for the evolution of vascular from prevascular plants since there is a prima facie case that a primary role of boron concerns the biosynthesis of lignin and, in conjunction with auxin, differentiation of xylem. In particular, a potential role for borate in regulating the hydroxylase and oxidase activities of the phenolases involved in the biosynthesis of caffeic and hydroxyferulic acids is suggested. The origin of this role for boron depended on the selection of sucrose in the Chlorophyta as a mobile and storage carbohydrate since, compared with the acyclic sugar alcohols accumulated in other algal groups, sucrose forms only a very weak complex with borate. It is argued that only when borate was not sequestered by complexing with other carbohydrates did the way become clear for it to acquire an essential role. This acquisition catalysed the evolutionary dichotomy between non-lignified and lignified photosynthetic landplants, the bryophytes and tracheophytes. Boron subsequently became involved in two other requirements for success on land - the exploitation of soil for anchorage, water and minerals, and the emancipation of fertilization from external water-since this element is required for development of adventitious roots (again in conjunction with plant hormones) and, in angiosperms, for germination of pollen.

Pollen allelopathy—a new phenomenon

Abstract: SUMMARY White dust spread on the leaves and stigmatic surface of Crotalaria pellida L. and Desmodium heteracarpon (L.) DC var. strigosum Meeuwen growing in the midst of a Parthenium hysterophorus L. stand was found to be clusters of Parthenium pollen. The fruit set in those species was poor. It was found that Parthenium pollen grains contained growth inhibitors which inhibited fruit set in many test species when artificially dusted on the stigmatic surface. In culture conditions the germination and pollen tube growth of the test species were inhibited in the presence of Parthenium pollen or their extract. The plant produces on an average 3375 million pollen grains per square metre areas of the stand. The pollen grains disperse in dusters of 600 to 800 each and are carried great distances by wind. Pollen grains deposited on leaves in large quantity also reduce the chlorophyll content in these species.

Influence of plant interactions on vesicular-arbuscular mycorrhizal infections. i. host and non-host plants grown together

Abstract: Summary Mycorrhizal infections formed by different endophytes were examined in 10 crop species grown separately and in pairs in sterilized and unsterile soils. No infection was observed in cabbage, kale, rape or swede (in the supposedly non-mycorrhizal family Cruciferae) and only traces were seen in sugar beet (supposedly non-mycorrhizal Chenopodiaceae) when these plants were grown alone. However, slight (< 5 %) infection (cortical mycelium and vesicles, but no arbuscules) developed in some when a mycorrhizal host plant was present and there were many clumps of endophyte mycelium on their root surfaces, usually attached to entry points which had often aborted. Glomus fasciculatus‘E3’ was a more infective endophyte than Gigaspora margarita. Infection was usually well developed in the host plants barley, lettuce, maize, potato and onion. It was depressed only in a few pairs but no more by the presence of a ‘non-host’ plant than by a host plant. The results suggest that the barriers to mycorrhizal infection in ‘non-hosts’ are intrinsic and more probably related to characteristics of the root cortex or epidermis than to any infection-inhibiting factors that might be released in root exudates.

Relation of internal phosphorus concentration and plant weight in plants infected by vesicular‐arbuscular mycorrhizas

Abstract: Summary Our own results and a search of the literature have shown that shoots of plants infected with vesicular-arbuscular mycorrhiza normally contain higher internal concentrations of P than those of uninfected plants of equal size, over wide ranges of external P supply and of host plants. Increased demand for carbon by infected roots is a possible explanation for this, and simple graphical methods of estimating the resulting dry wt loss are suggested.

Effect of vesicular-arbuscular mycorrhiza on Citrus jambhiri water relations.

Abstract: SUMMARY Recovery from water stress was studied on similarly sized VA mycorrhizal and non-mycorrhizal rough lemon seedlings (Citrus jambhiri Lush). VA mycorrhiza affected stomatal conductance, photosynthesis and proline accumulation, but not leaf water potential, suggesting that most of the effect of the mycorrhizal association is on stomatal regulation rather than on root resistance.

Translocation and transfer of nutrients in vesicular-arbuscular mycorrhizas. III. Polyphosphate granules and phosphorus translocation

Abstract: Summary X-ray microanalysis has confirmed, and measured, the phosphorus content (0·03 g cm-3) of cytochemically-demonstrated polyphosphate granules in onion mycorrhizas. The volume occupied by the granules measured from stereoscopic high-voltage electron micrographs of thick sections was 0·8 % of the fungal volume, and cytoplasmic streaming rates of the extra-matrical mycelium in soil measured in the light microscope were around 12·6 cm h-1. From these data a flux rate of about 2·7 × 10-8 mol P cm-2 s-1 has been calculated, which fulfils the hypothesis that phosphorus is translocated in the fungus by means of the transport of polyphosphate granules by cytoplasmic streaming.

Multiple metal tolerances in the grass deschampsia cespitosa (l.) beauv. from the sudbury smelting area

Abstract: Summary An investigation was conducted into the multi-element tolerance of the grass Deschampsia cespitosa growing around a nickel/copper smelting complex at Coniston, near Sudbury, Ontario. Tolerances for nickel, copper, aluminium, zinc, lead and cadmium in this population were compared with those of control populations growing on uncontaminated pastures. Distinctive population differences were found in distributions of copper and nickel tolerances, indicating that elevated tolerance to these elements had evolved in the Coniston population. More subtle differences between the populations in aluminium, zinc and lead tolerance were also noted, with increased tolerances showing in the smelter area population, despite a lack of elevation in zinc and lead levels in the soils. Various individuals in the Coniston population demonstrated a positive response to nickel and copper at levels as high as 0.3 μg cm-3 in water culture. This ‘need’ for the metals was reflected in the seed population from Coniston which germinated and survived better in the copper/nickel-contaminated soils than in the control soil. In contrast, germination of the control seed population was uniformly good, but seedling survival was poor on the metal contaminated soils compared with that of the Coniston seedlings. The relevance of these findings to evolution of multi-metal tolerances and the possible uses of the species for reclamation are discussed. The occurrence of coincidental metal tolerances is considered.

The biology of mycorrhiza in the Ericaceae VII. The relationship between mycorrhizal infection and the capacity to utilize simple and complex organic nitrogen sources.

Abstract: Young mycorrhizal plants of Vaccinium macrocarpon could utilize amino acids as a nitrogen source as readily as ammonium whereas aseptically grown plants and plants inoculated with common soil saprophytic fungi were unable to utilize the organic nitrogen compounds. Seedlings of Festuca ovina grown as controls in the sterile condition and in the presence of the ericaceous endophyte also failed to utilize the amino compounds. The capacity of the ericaceous plant to exploit these compounds is therefore dependent upon mycorrhizal infection. In contrast to cultures of Marasmius oreades, the endophyte failed to grow on complex nitrogenous humic and fulvic acids extracted from soils under ericaceous plants. The capacity to utilize simple organic nitrogen compounds could be of importance for mycorrhizal ericaceous plants in mor-humus soils which are characterized by slow rates of nitrogen mineralization.

Effects of ammonium and nitrate ions on mycorrhizal infection, nodulation and growth of trifolium subterraneum

Abstract: SUMMARY Addition of combined nitrogen decreases vesicular-arbuscular mycorrhizal development in young T. subterraneum plants. Ammonium ions, added as (NH4)2SO4, are more effective than nitrate ions, added as NaNO3. Addition of Na2SO4 as a control treatment also decreases infection, suggesting a less specific ‘salt effect’ underlying the responses to combined nitrogen. Inhibition of nodulation and nitrogenase activity occurs (as is normal) in the presence of combined nitrogen. These effects have been studied as a function of time (10 to 30 days), using a range of external concentrations. Different methods of application (surface addition versus mixing throughout the soil) have been tested. Effects on the levels of N, K+ and Na+ in the plants have also been determined. The results are discussed in relation to the effects of ammonium nitrogen and nitrate nitrogen on the mineral nutrition of plants, especially within the context of the influence of vesicular-arbuscular mycorrhizas on plant growth.

Root size, root hairs and mycorrhizal infection: a re-examination of baylis's hypothesis with tropical trees

Abstract: Summary A series of 89 Brazilian forest species, for which root characteristics and VA mycorrhizal condition were known, was used to test an aspect of Baylis's magnolioid root hypothesis. A non-parametric statistical test showed a significant association between magnolioid root characteristics and VA infection.

Sexual strategies in plants. ii. data on the temporal regulation of maternal investment

Abstract: Seventeen angiosperm species were examined to determine the degree to which the plants of each sexual morph limit their maternal investment during one reproductive session at three successive floral stages (flower determination, pre-anthesis ovary development, and postanthesis fruit maturation) The results indicate that species and sexual morphs differ dramatically in the relative use they make of the three stages Both the flower number per inflorescence and the proportion of flowers with developed ovaries are generally less variable in species with inflorescences which have well defined sequences of flower development In most species, the variability among the plants of one morph is greater in the frequency of fruit maturation than in the frequency of ovary development Much of the intra-morph variation in both the frequency of ovary development and the frequency of fruit maturation appears to be non-genetic In most of the morphs examined, the frequencies of ovary development and fruit maturation are not correlated with the number of flowers per plant or with each other The results provide circumstantial evidence in support of the hypothesis of serial adjustment of maternal investment

Ectomycorrhizal associations of australian indigenous plants

Abstract: SUMMARY Besides species of Eucalyptus, Leptospermum, Casuarina and Pomaderris which are known to form ectomycorrhizas, many other Australian native plants may form ectomycorrhizal associations. The plants include many legumes, especially in the tribe Podalyrieae of the Fabaceae and Acacia in the Mimosaceae, all members of the Rhamnaceae examined, and species of such diverse genera as Opercularia, Poranthera, Platysace, Goodenia and Stylidium. Many, perhaps most, of these ectomycorrhizal plants may also form endomycorrhizas of the VA type. The ectomycorrhizal species range from large forest trees to small non-woody herbs. The associations vary from well-defined mycorrhizas of the beech type to looser ones of a continuous or partial sheath, with or without a Hartig net. In soil low in available phosphate both typical and looser ectomycorrhizal associations markedly increased plant growth compared with that of uninoculated plants.

The requirement of aquatic bryophytes for free co2 as an inorganic carbon source: some experimental evidence

Abstract: Summary Twenty bryophyte species were tested for photosynthetic uptake of bicarbonate by immersing plants in 2.0 mM and 0.2 mM NaHCO3 and monitoring rise in pH. Equilibrium values were clustered around pH 9.0 and pH 8.0 in the two solutions, indicating limitation by free CO2 and inability to use bicarbonate. Anthoceros husnotii reached a maximum pH value of 9.5 in 2.0 mM NaHCO3, suggesting possible, although inefficient, bicarbonate uptake. Four species of bicarbonate-using plants tested for comparison gave final pH values in the range of 10.1 to 10.9. Field measurements gave results consistent with the laboratory experiments. Availability of CO2 to bryophytes growing in different aquatic habitats is discussed and their ecology is considered in light of the results.

The reproductive biology of asclepias tuberosa: i. flower number, arrangement, and fruit‐set

Abstract: SUMMARY An analysis of the inflorescence of the herbaceous perennial milkweed Asclepias tuberosa was carried out by sampling populations in North Carolina and Virginia in 1975 and 1976. Reproductive characters are strongly associated within a given level of comparison (e.g. stems per plant with flowers per plant) but show relative independence between levels (e.g. stems per plant with umbels per branch). Plant size is negatively correlated with fruit production on a proportional basis (fruit-set) but positively related to the absolute numbers of fruits produced. The invocation of a ‘pollen donor strategy’ to explain the occurrence of large inflorescence displays in Asclepias is unnecessary, as these large plants have a larger female contribution to the next generation, irrespective of their male contribution. Self-pollination is proposed as a process determining the upper limit of inflorescence size in Asclepias. Experimental pollinations suggest that early competition among ovaries within umbels is very important in determining levels of fruit-set. Competition among ovaries in different umbels, time of pollination, and location of umbels also exert an effect. Inflorescence architecture likely represents a series of evolutionary compromises between maximization of pollinator attractiveness on the one hand and maximization of fruit maturation on the other.

Branching patterns in forest shrubs and understory trees in relation to habitat

Abstract: SUMMARY We investigated the branching and leaf display of dominant forest shrubs and understory trees in central New Jersey to determine (1) whether branching differentiation occurs in shrubs which reach optimum development in different successional environments, (2) the contrast in branching of small trees between field and forest and (3) the nature of within-crown branching plasticity in a mature canopy tree. We discovered that shrubs do not differ in gross branching structure (ratio of terminal to supporting branches) and propose that branch angle, length and alteration of leaf orientation may be significant display characters. Small trees exhibit markedly variable response to open v. closed habitats, confirming the expected increase in branching ratio in open environments. Within, but not outside, the forest, earlier successional species were more variable in branching. A single canopy tree crown also demonstrated alteration of leaf display components, including increased length and wider angle of branches, but not branch ratio in the shaded, lower crown. We suggest some of the fine-scale morphological traits of shrub branching which may be important in determining their leaf display. Finally, we discuss differences in shrub and tree habit, such as cloning and the presumably reduced costs of support in shrubs, which may explain the failure of shrubs to exploit the same component of branching strategy as trees.

The Rhizobium requirements of the non-legume Parasponia in relationship to the cross-inoculation group concept of legumes.

Abstract: Summary Parasponia andersonii was nodulated by thirty four of thirty nine slow-growing rhizobia isolated from tropical legumes and by R. japonicum and JR. lupini. The nitrogenase activity of nodulated plants within a rhizobial treatment varied widely. Effective associations were obtained with some but not all isolates from Cajanus cajan, Centrosema pubescens, Crotalaria anagyroides, Flemingia congesta, Inocarpus fragiferum, Macroptilium lathyroides, Phaseolus calcaratus, Stizolobium deeringianum and Stylosanthes gracilis. Little or no nitrogen was fixed with rhizobia from Albizia stipulata, Cassia mimosoides, Desmodium microphyllum, Pterocarpus indicus, Uraria lagopoides, and the wide-host range cowpea Rhizobium strain CB 756. Fast-growing rhizobia from Leucaena leucocephala, Mimosa invisa, M. pudica, Sesbania grandiflora and Lablab pur-pur eus nodulated Parasponia with a low level of nitrogen fixation. Isolates from Parasponia failed to nodulate most of the legumes usually nodulated by slow-growing rhizobia and when tropical legumes were nodulated, the association was either partially effective or ineffective; only isolate CP 283 was highly effective and promiscuous. Hosts normally nodulated with fast-growing rhizobia, including Leucaena and Mimosa were not nodulated with isolates from Parasponia. It was concluded that the Parasponia-Rhizobium symbiosis is best located in the ‘cowpea miscellany’.

The resource costs of gender and maternal support in an andromonoecious umbellifer, smyrnium olusatrum l.

Abstract: SUMMARY In hermaphrodite flowers the various organs are potentially in competition with each other for resources translocated via the peduncle. It is an interesting question to ask: in what proportions does a plant with hermaphrodite flowers allocate various potentially limiting resources between these potentially ‘competing’ organs – between sporophylls and organs of attraction (petals, nectaries) and between stamens and pistils? The question becomes even more interesting in an andromonoecious species in which the plant supplies resources to both male and hermaphrodite (perfect) flowers. In the biennial andromonoecious umbellifer Smyrnium olusatrum L. a constant ratio of one hermaphrodite flower to four staminate flowers was found to be maintained despite a fivefold range in both total flower number and total plant dry wt produced by surgery and nutrient depletion. The allocation of nitrogen, phosphorus and potassium in floral organs was studied in S. olusatrum that had received various experimental treatments. The ratio of resource allocated to sporophylls and to ancillary attractive organs was found to remain relatively constant whereas the allocation to the two types of attractive organs (petals and stylopodia) tended to vary with the experimental manipulations. The relative allocation of nutrient resources to male and female activities was scarcely altered by the treatments. Before fertilization plants distributed a greater (c. fivefold) proportion of phosphorus to male than to female organs. However, the cost of placental support of developing embryos reversed the ratio such that at seed maturity a greater proportion of phosphorus (c. × 2) had been allocated to seed than to stamens.

The location and size of the extension zone of emerging wheat leaves

Abstract: Summary The length of the extension zone (LEZ) of emerging wheat leaves varied with the stage of leaf development and between leaves with the length of the encircling sheath (LES). The ratio LEZ/LES varied from 0·60 when the leaf tip emerged from the encircling sheath to 0·35 when the ligule emerged. The relationship between LEZ/LES and an index of leaf development (DI), defined as the sheath length of the growing leaf relative to LES, was: LEZ/LES= 0·632 exp (-0.622.DI); (r= 0.91). 14C incorporation studies supported the measurement of extension zone location and length. There appeared to be a small zone of non-expanding tissue, within the extension zone, around the ligule, but it was not a major discontinuity within the whole extension zone. The relative extension rate of the extension zone declined by only 50 % from leaf tip to ligule emergence whereas the relative extension rate of the whole leaf declined by 90 % over the same interval. There was little variation in protein and carbohydrate concentrations around the upper limit of the extension zone in emerging leaves. For studies of leaf growth in wheat where it is not possible to measure LEZ, harvesting the lower 50 % of the enclosed part of an emerging leaf would adequately sample the extension zone.

Links between roots by hyphae of vesicular–arbuscular mycorrhizas

Abstract: SUMMARY Using a buried slide technique, hyphal connections are shown to exist between different roots on one plant, Lolium perenne L., and also between two roots of different species L. perenne and Plantago lanceolata L. These two species are commonly found together in permanent pasture.

The effectiveness of vesicular-arbuscular mycorrhizas in increasing growth and phosphorus uptake of subterranean clover from phosphorus sources of different solubilities

Abstract: SUMMARY The effect of inoculation, with a VA mycorrhizal fungus on growth and phosphorus uptake of subterranean clover was examined using three phosphorus sources with different solubilities. Mycorrhizas markedly increased growth and phosphorus content of tops at intermediate rates of phosphorus application for all sources. The effectiveness of phosphorus for plant growth for mycorrhizal plants relative to non-mycorrhizal plants was the same for a water soluble source (superphosphate) and two insoluble sources (C-grade Christmas Island rock phosphate and calcined Christmas Island rock phosphate). The effectiveness of phosphorus from each of the three sources for phosphorus uptake by mycorrhizal plants relative to non-mycorrhizal plants was also independent of the solubilities of the phosphorus sources applied. At a given phosphorus concentration in tops, non-mycorrhizal subterranean clover produced more dry matter than mycorrhizal clover supplied with superphosphate. Mycorrhizal and non-mycorrhizal subterranean clover supplied with C grade rock phosphate had the same dry weight at a given phosphorus concentration in their tops. VA mycorrhizas increased zinc but not calcium uptake by subterranean clover.

Mycorrhizae and nutrient cycling in natural forest ecosystems

Abstract: SUMMARY The widespread occurrence of mycorrhizae in nature and their importance in the mineral nutrition of almost all plants has been extensively documented but despite this mycorrhizae have not been included in nutrient cycling studies of forest ecosystems. This neglect may be due to a failure on the part of researchers to recognize the functional differences between mycorrhizae and roots and to the labour-intensive effort needed to study mycorrhizae. Biomass or surface area of mycorrhizae must be measured before information on ion absorption by mycorrhizae can be applied to forest ecosystems. A full assessment of the importance of mycorrhizae in nutrient cycling also requires data on mycorrhiza production, senescence, and decomposition. Few mycorrhiza studies have provided such data. Consequently, our information on nutrient cycling is derived from fine root (≥ 5 mm in diameter) data which may or may not include mycorrhizae. Recent studies have shown that most of the organic input to the decomposition process results from fine root production. Fine root mortality and decomposition is also more important than other mechanisms for returning nitrogen immobilized in vegetation to the soil in both deciduous and coniferous forests. A recently completed study indicates that mycorrhizae account for 50% of the annual throughput of biomass and for 43% of the nitrogen released annually in a Douglas fir ecosystem. These transfers are five times larger than the releases from litterfall or litter decomposition. Clearly, the study of mycorrhizal nutrient cycling is in an embryonic state and considerable additional research is needed.

Adaptation of vesicular‐arbuscular mycorrhizae to edaphic factors*

Abstract: Summary In three field soils, birdsfoot trefoil (Lotus corniculatus L.) transplants infected with mycorrhizal fungi from 42 soils showed no clear superiority of strains from these individual soils after a year's growth. Differences among strains decreased with time and were only significant for all three soils at the first cutting. There were low-level correlations between yield and various chemical properties of the soils from which the cultures were derived. In the greenhouse, with sterilized soils low in P, trefoil yield was always greatest when the inoculum used was indigenous to the soil in which the plants were grown as compared to inocula from five different soils. These results suggest that indigenous strains of mycorrhizal fungi may possess an adaptation to edaphic factors and that the performance and persistence of strains otherwise more efficient in nutrient uptake may be limited by their lack of adaptation.

A re‐investigation of character correlations among dicotyledons

Abstract: SUMMARY A computerized analysis of the occurrence among 291 dicotyledon families of 107 morphological or biochemical characters is described. The results confirm earlier work and increase the number of characters that are shown to be statistically associated from 26 to 39. Many of these occur more often in rain-forest floras than in the rest of the world. They also occur more often in families that are represented in the fossil record than they do in the present-day world flora, and aile therefore regarded as primitive. Using 30 of these correlated characters, the percentage advancement index of the various families is calculated. Among the most advanced families are Dipsacaceae, Valerianaceae and Hippuridaceae. The most primitive ones are Aextoxicaceae and Degeneriaceae, with Stachyuraceae and Magnoliaceae also very primitive.