This study investigates the effects of the spatial arrangement of aerial stems and current-year shoots on patterns of herbivory, competition and on the requirements for mechanical support in Hydrangea hirta Sieb. et Zucc. growing in a light-limited environment. Stem demography was followed for three consecutive growing seasons. Stem mortality rates decreased with increasing stem age. Age-specific mortality rate was highest for new stems owing to the high incidence of herbivory. Mortality due to herbivory was low in older stems and was attributed to the dispersion of the risk of herbivore attack as a result of the increase in number of current-year shoots per stem. Clumping of stems led to intense intra-clonal competition as inferred from size-dependent mortality and density-dependent turnover of stems, and higher maximum stem length in clumps with higher stem density. Analysis of the spatial distribution of current-year shoots within the stem crown revealed a uniform, mono-layered crown architecture. The horizontal distribution of buds within the mono-layer was aggregated as a result of their opposite position, but as current-year shoots grew, their apices became uniformly distributed, resulting in efficient leaf display for light capture and shading out competing stems. However, limits on stem growth were observed in crown expansion, shoot production rate and current-year shoot size. Crown width increased with increasing basal diameter to reach a maximum. Both shoot production rate and current-year shoot size decreased with stem growth and a minimum current-year shoot size was defined. These limits on stem growth were attributed to suppression from intra-clonal competition and to the requirements for mechanical support of the mono-layered crown.

Hakea psilorrhyncha R. M. Barker seedlings were subjected to a two-way interaction experiment with two levels of water availability and two levels of light. Physiological drought was imposed by adding 6000 MW polyethylene glycol (PEG), at an osmotic potential of −0·56 MPa, in a continuous-flow drip irrigation system. Unstressed plants (-PEG) were watered with distilled water (osmotic potential of −0·01 MPa). Seedlings were grown under natural light (120–500 μmol m−2 s−1 sunlight at midday +L) or shaded (<150 μmol m−2 s−1 sunlight at midday; −L. Plant morphology tissue water relations and carbon isotope composition (δ13C) were measured after 12 wk growth. The smallest leaves had the highest mass per unit area (LMA, an index of sclerophylly) and were present in the +PEG+L treatment, whereas the largest, thickest leaves had the lowest density and were produced in the −PEG+L treatment. Plants in shade were smaller and less sclerophyllous. There was a linear decrease in osmotic potential at full turgor and turgor loss point, and an increase in elastic modulus and δ13C, as level of sclerophylly increased, with −PEG−L leaves at one extreme and +PEG+L at the other. We conclude that high levels of sclerophylly induced by low water availability and high light intensity are associated with substantial drought tolerance in H. psilorrhyncha.

The effects of prolonged simulated acid rain on percentage cover of ground vegetation, and on growth and reproduction of two dominating dwarf shrubs (Empetrum nigrum and Vaccinium vitis-idaea) were examined in a field experiment in the Finnish Subarctic, in an area with low ambient levels of sulphur and nitrogen deposition. Acid rain treatments included moderate (pH 3·8) and high (pH 2·9) concentrations of either H2SO4, or HNO3, or a mixture of them, and were compared with irrigated (pH 6) and dry control plots.

Long-term application of acid rain caused significant alteration in the cover and composition of ground vegetation. Effects of acid rain depended on the accompanying anion and on pH. Sub-plots under different canopy tree species differed in responses indicating that spatial heterogeneity is important in predicting the effect of acidifying pollution on this plant community.

In the bottom layer, acid rain caused significant reduction in cover of the cyanobacterial lichens Nephroma arcticum and Peltigera spp. Decrease in cover of fruticose lichens, mainly composed of Cladina spp., more likely resulted from additional watering.

In the field layer, acid rain containing moderate concentrations of NO3− caused an increase in cover of graminoid species. There were only slight alterations in growth and cover of the two dominant evergreen dwarf shrubs, E. nigrum and V. vitis-idaea, indicating that these species are tolerant to acid rain of as low as pH 3. Even some positive responses of dwarf shrubs were observed, depending on canopy tree. Application of acid rain of pH 3 to plots under pine trees caused an increase in cover of V. vitis-idaea and, when the nitric acid only was applied, a short-term increase in the number of new shoots of E. nigrum.

In contrast to vegetative growth, reproduction of the dwarf shrubs was more strongly affected by acid rain, but this also depended on local conditions and anion composition of acid rain. On ‘pine’ plots, rain of pH 3 reduced the number of berries and flower buds on terminal current shoot of E. nigrum, however, this was partially compensated by an increase in berry production at the ramet level. Simulated acid rain had mainly negative effects on berry production by V. vitis-idaea.

Tuberous roots of Viguiera discolor accumulate up to 80% of their dry mass as fructans. The distribution pattern of oligomers suggests the predominance of anabolic reactions at the beginning of dormancy, when a continuous series of fructans between sucrose and higher polymers is present. This paper describes the synthesis in vitro of fructans of high molecular mass by enzyme extracts prepared from growing tuberous roots of V. discolor at the beginning of dormancy. Sucrose[ratio ]sucrose fructosyl transferase activity was characterized by the synthesis of 1-kestose from sucrose and fructan[ratio ]fructan fructosyl transferase activity by the production of nystose from 1-kestose. The optimal temperature for both activities was 30°C and the optimal pH range was between 5·5 and 6·0. The apparent Km for sucrose with respect to 1-kestose synthesis was 173 mol m−3, whereas the Km for nystose synthesis from 1-kestose was much higher (592 mol m−3). Long incubation periods (up to 264 h) with sucrose, 1-kestose or nystose produced fructans of high molecular mass in vitro that resembled those found in vivo. Our data show that the higher the molecular mass of the substrate, the higher the average molecular mass of the product that was formed.

Twelve-day-old soybean plants were exposed to atmospheric NO2 (0·3 μl l−1) and simultaneously supplied, via the roots, with 5 mM or 1 mM of NaNO3 or NH4Cl. After exposure for 7 d, the amount of NO2 absorbed per plant was greater in plants supplied with nitrate than in plants supplied with the same concentration of ammonium. The NO2 AR (absorption rate) decreased with increasing exposure time. At the beginning of exposure, the NO2 AR for all plants was c. 12 mg NO2 h−1 m−2 μl−1 l. On the day 7 of exposure, the NO2 AR declined to 8·46, 8·97, 8·27, and 9·04 mg NO2 h−1 m−2 μl−1 l for plants receiving 1 mM ammonium, 1 mM nitrate, 5 mM ammonium, and 5 mM nitrate respectively. The plants supplied with nitrate had a higher concentration of leaf nitrate and a higher pH than those supplied with the equivalent concentration of ammonium. These results suggest that the NO2 absorption rate might be attenuated by the accumulation of H+ produced from N uptake and assimilation.

A partially purified enzyme preparation from leaves of Lolium temulentum L. was previously shown to catalyse the net synthesis of oligofructans and polyfructans from sucrose. Here the same preparation is shown to catalyse the hydrolysis of both sucrose and oligofructans. The magnitude and properties of these hydrolytic activities have been determined. The significance of these catabolic activities for studies of fructan polymerization both in vitro and in tissues in a physiologically anabolic state are discussed.

The preparation hydrolysed 1-kestose, 6-kestose, neokestose, inulin oligosaccharides of low degree of polymerization (DP 4 and 5) and endogenous oligofructans from L. temulentum, with the concomitant release of monosaccharide. The preparation also released reducing sugar at low rates from high molecular weight inulin but had no detectable activity against bacterial levan. Simultaneous incubation of sucrose and Neosugar (a commercially available mixture of predominantly β-2, 1 linked tri-, tetra- and penta-saccharides) showed that sucrose was preferentially hydrolysed by the preparation, with Neosugar fructans being protected from hydrolysis at sucrose concentrations >30 mol m−3. The kinetic properties for hydrolysis of both sucrose and Neosugar were determined. For sucrose and Neosugar respectively, Michaelis constants at 30°C and pH 6·0 were 7·7±0·5 and 14·1±1·1 mol m−3 (as terminal fructose) and maximum velocities were 6·5±0·1 and 2·7±0·1 mg g−1 fr. wt h−1 (equivalent to 10·0 and 4·2 nkat g−1 as reducing sugar release). Maximal temperatures for activity were 45 and 44°C, and Arrhenius activation energies were 39·9 and 46·9 kJ mol−1. Preincubations for 1 h at 49 and 48°C caused 50% loss of activity in subsequent assays at 30°C. The pHs for maximal activity for the two substrates were 5·2±0·1 and 5·5±0·1.

Using size exclusion chromatography (SEC), an activity catalysing the formation of fructan oligosaccharides and another catalysing sucrose hydrolysis, were not fully resolved, but exhibited distinct profiles of elution indicating Mr of 57 and 133 kD respectively. When assayed for the hydrolysis of Neosugar, the SEC eluate exhibited two peaks of activity indicative of Mr values of 57 and 133 kD.

Exposure to ozone (O3) has been shown to decrease the allocation of carbon to tree roots. Decreased allocation of carbon to roots might disrupt root metabolism and rhizosphere organisms. The effects of soil type and shoot O3 exposure on below-ground respiration and soil microbial populations were investigated using container-grown ponderosa pine (Pinus ponderosa Laws.) growing in a low-nutrient soil, or a fertilizer-amended organic potting media, and exposed to one of three levels of O3 for two growing seasons in open-top exposure chambers. A closed system, designed to measure below-ground respiratory activity (CO2 production, O2 consumption and RQ-Respiration Quotient; (CO2[ratio ]O2) of plants growing in pots, was used monthly to monitor below-ground respiration of 3-yr-old ponderosa pine.

Although seasonal differences were detected, CO2 production (μmol h−1 g−1 total root d. wt), O2 consumption (μmol h−1 g−1 total root d. wt) and RQ (CO2[ratio ]O2) increased with increasing O3 exposure level. Seasonal patterns showed increased respiration rates during periods of rapid root growth in spring and early fall. Respiration quotient tended to decrease during known periods of active root growth in control seedlings, but a similar response was not observed in O3-treated seedlings. Responses to O3 were greatest in the soil-grown plants, which had a lower fertility level than media-grown plants. Although root d. wt was decreased, root[ratio ]shoot ratios did not change in response to O3. Soil-grown plants had higher root-shoot ratios than media-grown plants, reflecting the lower fertility of the soil.

Plant exposure to O3 was found to affect both active and total populations of soil organisms. In both organic potting media and in soil, biomass of active soil fungi, and the ratio of active-fungal to active-bacterial biomass increased with increasing plant exposure to O3. The effect of O3 on total fungal and bacterial biomass was not linear: at low O3 levels, total fungal and bacterial biomass increased; at the high O3 level, total fungal and bacterial biomass decreased compared with those of controls.

Our results show that O3 exposure to shoots significantly disrupts CO2 production and O2 consumption of soil and roots of ponderosa pine seedlings. Below-ground respiratory differences were thought to be a result of changes in respiratory substrates, carbon refixation within the plant and soil microbial activity. Ozone also changes below-ground RQ, suggesting that O3 substantially disrupts root metabolism and interactions with rhizosphere organisms. Ozone exposure of ponderosa pine grown in different soil types can disrupt below-ground respiration and influence populations of soil organisms without alteration of biomass partitioning between above- and below-ground plant components. Collectively, the effect of O3 on the below-ground system is of concern since it is likely that these changes are accompanied by a change in the ability of root systems to acquire nutrient and water resources and possibly to synthesize amino acids and proteins necessary for normal plant function.

If metal tolerant plants, by virtue of their tolerance mechanism, are less efficient at the uptake, distribution or utilization of metals then essential micronutrient deficiency may occur at the low levels of metal supply found on non-mine soils. This argument forms the basis of the metal requirement hypothesis put forward to explain the lower fitness of tolerant individuals on uncontaminated soil, the so called ‘cost of tolerance’. In this paper, copper balance was investigated in Mimulus guttatus Fischer ex. DC (the yellow monkey flower) for plants with or without the major tolerance gene which confers primary tolerance, and plants with few or many modifier genes which control degree of tolerance. No conclusive evidence to support an increased copper requirement in plants with the major tolerance gene, and/or many modifier genes was shown. Any differences in copper requirement found during vegetative growth were small, and were deemed insufficient to explain the apparent cost of tolerance.

Five clonal plants of three genotypes of Lotus corniculatus were grown in each of eight controlled environments under combinations of two temperature regimes (18/10°C and 25/15°C), two CO2 concentrations (ambient and 700 ppmv) and two water applications (ad libitum or 60% droughted). Plants were harvested at full flower and measurements made of plant growth and development. Of the three environmental variables studied, higher growth temperatures resulted in the largest number of significant changes to the measured variables. Reproductive capacity, growth rate, shoot biomass, water use efficiency and chlorophyll content were all enhanced by raising the growth temperature from 18 to 25°C. Doubling the CO2 concentration enhanced the growth rate, shoot biomass and water use efficiency and ameliorated some of the effects of drought, including reproductive capacity, and biomass production, but reduced flowering time, specific leaf area, and chlorophyll content of both droughted and undroughted plants. Drought alone reduced reproductive capacity, growth rate and above ground biomass but significantly increased root biomass in all environments. The agronomic effects resulting from a combined increase in growth temperature, doubled CO2 concentration and mild drought in this experiment were a shorter vegetative period and an increase in biomass, but a fall in reproductive capacity.

Spring wheat (Triticum aestivum cv. Nandu) cultivated under glasshouse conditions was exposed to ozone in large fumigation chambers for 2 wk. Different exposure regimes were applied as constant concentrations as well as with ozone peaks, partly under equal dose-conditions, in times of high solar radiation during different stages of development (seedling, late tillering, anthesis). Chlorophyll fluorescence was monitored and amounts of carbohydrates (hexoses, sucrose, starch) and chlorophyll were measured in young leaves (seedling) and flag leaves (late tillering, anthesis) during and after ozone exposure. Although seedlings showed no significant response in photosynthesis, strong effects on photosynthesis and carbohydrate accumulation were measured when plants were fumigated during anthesis, especially after a heat stress period preceding ozone treatments. Under equal dose conditions chlorophyll fluorescence parameters (Fv[ratio ]Fm) and electron transport rate decreased and sucrose content of flag leaves increased significantly if ozone at a concentration of 220 μg m−3 was supplied for 4 h, indicating that peak concentrations show stronger effects than constant concentrations. The reaction of wheat plants is dependent on environmental conditions such as preceding heat stress and on the developmental stage during exposure. The results favour the hypothesis that photoinhibition and disturbance of photosynthesis are only secondary effects as a consequence of retarded sucrose export from the leaf, because of damage at the plasma membrane.

Zinc, lead and cadmium tolerance in four populations of Typha latifolia raised from seed collected from metal-contaminated and uncontaminated sites were investigated. Metal concentrations in natural plant populations showed that Zn, Pb and Cd in the leaves were maintained at low levels (Zn: 22–122, Pb: 4·7–40 and Cd: 0·2–0·8 μg g−1 d. wt), although concentrations of these metals in the associated soil-sediments (total concentrations of Zn: 86–3009, Pb: 26–18894 and Cd: 1·4–26 μg g−1 d. wt) and in the roots (Zn: 46–946, Pb: 25–3628 and Cd: 1·0–17 μg g−1 d. wt) varied widely. Some differences were found between metal-contaminated and uncontaminated populations in terms of metal uptake under controlled conditions. Seedlings from metal-contaminated populations accumulated considerably more metals (up to nearly twice as much Zn and Pb and three times as much Cd) in roots than the uncontaminated population in a pot trial. In general, however, different populations of T. latifolia showed similar growth responses (the longest leaf elongation, the longest root elongation, shoot and root d. wt), metal uptake and indices of metal tolerance when seedlings were grown in the same metal treatment solutions or in the same metal-contaminated media under laboratory conditions. The data do not support the hypothesis that populations from metal-contaminated sites have evolved tolerance to Zn, Pb and Cd, but rather that T. latifolia shows constitutional tolerance.

To study the role of fructan in leaf development of barley seedlings, fructan contents and the activities of enzymes involved in fructan metabolism were measured in segments of the third leaf at the stage of maximal growth. Fructans amounted to more than 10% of the d. wt in the growth zone at the base of the developing leaf and decreased sharply in the zone above. The specific activities of sucrose[ratio ]sucrose 1-fructosyltransferase (1-SST) and sucrose[ratio ]fructan 6-fructosyltransferase (6-SFT), two key enzymes in fructan synthesis, also peaked in the growth zone but decreased more slowly in the zone above. By contrast, the specific activities of invertase and fructan exohydrolase (FEH) were low in the growth zone at the leaf base and had their peak just above it. The specific activity of fructan[ratio ]fructan 1-fructosyltransferase (1-FFT) was approx. constant over the whole leaf. These results indicate that transitory accumulation of fructans in the growth zone plays a key role in the development of barley leaves.

The objectives of this study were (i) to evaluate the relative involvement of fructans from leaf sheaths and from elongating leaf bases to regrowth after defoliation of Lolium perenne L. by following fructan exohydrolase (FEH), sucrose-sucrose fructosyl transferase (SST) and invertase (INV) activities and (ii) to examine whether gibberellins could be implicated in regulation of FEH activity. In stubble, 36% of fructans are located in leaf bases and 64% in leaf sheaths. During the first phase of regrowth, the depletion of carbohydrates was mainly due to the decline of fructans, which represented 76% and 50% of the carbohydrates mobilized from leaf sheaths and elongating leaf bases respectively. Despite a decrease in protein content, FEH activity increased 2·5-fold in leaf sheaths and six-fold in elongating leaf bases, so that the fructan-hydrolysing activity was four times higher in growing leaves than in leaf sheaths, 2 d after defoliation. INV activity also increased, whereas the pattern of SST activity was inversely related to the variations of both hydrolysing activities. SST activity, which is highest in growing leaves, declined approximately threefold in leaf sheaths and elongating leaf bases at the beginning of regrowth.

The increase in activity of FEH in stubble was strongly inhibited by an inhibitor of the biosynthesis of gibberellin, uniconazole. FEH activity was decreased to c. 67%, 45% and 33% of the level in nontreated plants 24, 48 and 72 h following defoliation, respectively. The inhibition could be overcome by a subsequent treatment with gibberellic acids (GAs). For the first time, data are provided to support the view that GAs might play a role in the regulation of FEH activity, and the implication of this result is discussed.

Information on ozone uptake by various tree species has been derived mainly from controlled-exposure studies of seedlings. Parallel measurements of foliar physiological processes in large trees are rare, as are measurements of local ozone concentrations within forest environments. Thus, our objectives were to characterize foliar ozone uptake in forest trees of different size and to identify a mechanistic linkage between small and large trees. Light-saturated net photosynthesis (Pn), stomatal conductance (gH2O), and ozone uptake (gO3) in seedling (<2 m), sapling (2–5 m) and mature (9–21 m) black cherry (Prunus serotina Ehrh.), northern red oak (Quercus rubra L.) and red maple (Acer rubrum L.) trees were measured monthly over two growing seasons at sites at high (1240 m) and low (600 m) elevation in the Great Smoky Mountains National Park. Seasonal ozone dose to northern red oak and red maple in the upper crown of mature trees was approx. double that of respective understorey seedlings and saplings. Seasonal ozone dose to black cherry was up to six times greater in mature trees than in seedlings and saplings. The lower ozone dose to understorey trees was mainly a function of lower gH2O, although canopy gradients in ozone concentration were indicated. Differences in Pn and gH2O between small and large deciduous forest trees were linked to variation in nitrogen concentration expressed on a leaf area basis.

The effects of iron plaque on the growth of Typha latifolia L. and accumulation of copper and nickel in T. latifolia were investigated under laboratory conditions in nutrient solution cultures. Seedlings with and without iron plaque on their roots were exposed to 0·05 μg ml−1 Cu and 0·10 μg ml−1 Ni solutions for 72 d. The results showed no differences in root and shoot d. wt and leaf elongation when Cu or Ni were added to the solution and in the presence or absence of plaque. However, root length was reduced by Cu and Ni, and the reduction in root length was greater in the presence of plaque. Some Cu and Ni was adsorbed on root surfaces; roots with plaque took up more Cu, but less Ni than those without. The presence of plaque did not alter Cu uptake and translocation but increased Ni uptake and translocation. Most of the Cu and Ni taken up was retained in the roots, suggesting that the root tissue rather than the root surface or plaque is the main barrier for Cu and Ni transport. The results differ from those reported for other species.

Development of mycelial cord systems of Phanerochaete velutina (DC.: Pers.) Parmasto from 4-cm3 inocula on a nutrient-depleted non-sterile soil was studied in laboratory microcosms using image analysis techniques. Cord systems were ‘baited’ after 13 d growth with either fresh, non-sterile 4-cm3 wood baits or control Perspex® blocks of the same contact area placed behind the foraging mycelial front. After 26 d growth, mycelial ‘patches’ arose by dedifferentiation of consolidated mycelial cords in both wood- and Perspex-baited cord systems. ‘Patches’ comprised fine, highly branched separate hyphae extending radially from points of aggregated hyphae in cords. ‘Patches’ and cords could be readily distinguished by image analysis and the areas covered by patches and cords could be measured and compared. Whilst the total hyphal cover of Perspex- and wood-baited systems did not differ significantly (P>0·05), patch cover in wood-baited systems was up to 10 times greater than in Perspex-baited systems. Patches were temporary structures, regressing more rapidly with age than mycelial cords. Patch development ceased after application of a nutrient solution which replenished phosphate levels in the soil. Wood-baited mycelial systems displayed significant developmental polarity (P[les ]0·05) of both total hyphal cover (patches plus cords) and hyphae in patches towards the ‘baited’ sector of cord systems after 42 d, which corresponded with peak patch development. However, significant (P[les ]0·05) developmental polarity of the mycelial systems along the bait-inoculum line could be detected 8 d before patch formation when assessed by fractal geometry. Radiotracer studies showed that mycelial patches were not sinks for supplied 32P, but that they were sites of increased nutrient uptake capacity compared with that of mycelial cords. We discuss the need for mycelial cord systems to balance allocation of mycelial biomass between the two essential processes of colonizing wood resource units, and the acquisition of soluble inorganic nutrients from soil.

Plants from metalliferous soils often exhibit combined tolerance to different heavy metals. Such tolerance could rely either on the possession of a combination of different metal-specific tolerance mechanisms (‘multiple tolerance’), or on less specific mechanisms that pleiotropically confer tolerance to different metals (‘co-tolerance’). In this study, we examined the co-segregation of tolerances to Cu, Zn, Ni, Co and Cd in crosses between distinctly tolerant ecotypes of Silene vulgaris (Moench) Garcke. The results demonstrate non-pleiotropic genetic control of tolerance to Cu, Zn and Cd. Tolerance to Ni and Co, on the other hand, seems to represent the pleiotropic by-product of the tolerance allele of one particular locus for zinc tolerance.

A novel extracellular fructanhydrolase was isolated from the culture filtrate of Lactobacillus paracasei ssp. paracasei P 4134 grown on a mineral medium supplemented with fructan extracted from Timothy (Phleum pratense L.) as the only carbon source. The enzyme was purified by a combination of ammonium sulphate precipitation, affinity chromatography, preparative isoelectric focusing and anion-exchange chromatography. As a result of these procedures, the specific enzyme activity increased 93-fold, with a final yield of 28·4%. The substrate-specific activities against different fructan types were determined by incubating the enzyme fractions with fructan extracted from Timothy (predominantly β-2,6 fructosyl-fructose linkages), inulin from Dahlia tubers (mostly β-2,1 fructosyl-fructose linkages) and sucrose. The purified enzyme catalysed the hydrolysis of β-2,6-linked fructan more rapidly than the β-2,1 linkages of inulin. Additionally, the enzyme showed low ability to hydrolyse sucrose. Fructose was the main product of the degradation of Timothy fructan and inulin, indicating a high exohydrolytic activity of the enzyme. It is proposed that the fructan-degrading enzyme from L. paracasei ssp. paracasei P 4134 is a β-D-fructan-fructohydrolase (EC 3.2.1.80). The enzyme preparation showed a single protein band in sodium dodecyl sulphate-polyacrylamide gel electrophoresis with a mobility corresponding to molecular weight of c. 42 kDa. It was concluded that only one molecular weight of fructan-degrading enzyme exists in L. paracasei ssp. paracasei P 4134.

Cuttings of two clones of Norway spruce, Picea abies (L.) Karst., were exposed to three different ozone concentrations in open-top chambers during four months in the summer of 1990. The treatments were charcoal-filtered air, non-filtered air and non-filtered air with extra ozone (c. 30 ppb) added daily between 1100–1800 local time. During the last 4 wk of the exposure period, half the seedlings were drought-stressed, while the remainder were well watered. Biomass, gas exchange and water potential were measured during the drought stress period.

The ozone treatments affected the two clones very differently. High ozone reduced the rate of biomass increase in the faster-growing clone (clone M) whereas ozone generally stimulated the rate of biomass increase in the slower-growing clone (clone L). At the end of the measuring period, the high-ozone treatments reduced the rate of root biomass increase of the well watered seedlings of the M-clone, but it had no effect on the drought-stressed seedlings of the same clone, probably because the root growth was already to a large extent inhibited by the drought stress.

The treatment with the highest concentration of ozone partly protected the seedlings of the M clone against the drought stress, presumably by delaying shoot growth and thus delaying the increase in the total transpiring needle area. As a result, stomata tended to close less during the drought period in this treatment.

The results are discussed in relation to the suggested critical level for ozone effects on trees.

Arbuscular mycorrhizal (AM) fungi, Rhizobium bacteria and plant-growth-promoting rhizobacteria (PGPR) were isolated from a representative area of a desertified semi-arid ecosystem in the south-east of Spain. Microbial isolates were characterized and screened for effectiveness by a single-inoculation trial in soil microcosms. Anthyllis cytisoides L., a mycotrophic pioneer legume, dominant in the target mediterranean ecosystem, was the test plant. Several microbial cultures from existing collections were also included in the screening process. Two AM fungi (Glomus coronatum, native, and Glomus intraradices, exotic), two Rhizobium bacteria (NR4 and NR9, both native) and two PGPR (A2, native, and E, exotic) were selected. A further screening for the appropriate double and triple combinations of microbial inoculants was then performed. The parameters evaluated were biomass accumulation and allocation, N and P uptake, N2-fixation (15N) and specific root length. Overall, G. coronatum, native in the field site was more effective than the exotic G. intraradices in co-inoculation treatments. In general, our results support the importance of physiological and genetic adaptation of microbes to the whole environment, thus local isolates must be involved. Many microbial combinations were effective in improving either plant development, nutrient uptake, N2-fixation or root system quality. Selective and specific functional compatibility relationships in plant response between the microbial inoculants, were observed. Despite the difficulty of selecting a multifunctional microbial inoculum, appropriate microbial combinations can be recommended for a given biotechnological input related to improvement of plant performance. This could be exploited in nursery production of target plant species endowed with optimized rhizosphere/mycorrhizosphere systems that can be tailored to help plants to establish and survive in nutrient-deficient, degraded habitats. The relevance of this microbial-based approach in the context of a reclamation strategy addressed to environmental sustainability purposes is discussed.