Legume cover crops as a nitrogen source for pecan

Crimson clover (Trifolium incarnatum L.) plus hairy vetch ( Vicia villosa Roth), red clover (Trifolium pratense L.), white clover (Trifolium repens L.), red clover plus white clover, and bermudagrass (Cynodon dactylon [L.] Pers.) were evaluated as cover crops for pecans. Crimson clover plus hairy vetch supplied the equivalent of 101 to 159 kg nitrogen (N)/ha. Red clover plus white clover supplied up to 132 kg N/ha. Either white clover or red clover alone were less effective in supplying N than when grown together. Soil Kjeldahl‐N was usually not affected or increased using the legumes compared to fertilized bermudagrass sod. Soil nitrate (NO₃) concentrations during October were occasionally higher in unfertilized legume plots than in bermudagrass plots with March‐applied N.     

Effect of salicylic acid and salt on wheat seed germination

Abstract

The effects of pretreatment with salicylic acid on wheat seed germination (Triticum aestivum L. cv. Roshan), lipid peroxidation, and superoxide dismutase, catalase, polyphenol oxidase, and peroxidase activity were studied under conditions of salt stress. Seeds treated with different concentrations of salicylic acid were used for measuring germination traits. Salt stress was induced by sodium chloride solution. Seeds were soaked in salicylic acid solution for 24 h, dried with sterile paper, transferred to sterile Petri dishes, and treated with 10 ml NaCl solution at different concentrations. After 1 week, the number of germinated seeds, root length, seedling length, and dry weight were recorded. Antioxidant enzyme activity and lipid peroxidation were also assayed. Salinity decreased seed germination. Thus, a high concentration of NaCl (200 mM) decreased germination by 17.6% compared with control treatment. Salicylic acid significantly increased germination in stressed and control seeds. Salicylic acid increased the level of cell division of seedlings and roots, which increased plant growth. Salt stress significantly increased the activity of the antioxidative enzymes catalase, superoxide dismutase, peroxidase, and polyphenol oxidase in wheat seedlings, and salicylic acid reduced the activity of antioxidant enzymes as stress signal molecules. Our results indicated that scavenging of reactive oxygen species was effective, especially by salicylic acid, and that membrane damage was limited. The aim of the present work was to study the character of changes in enzymatic systems induced by NaCl and salicylic acid in wheat seedlings under conditions of salt stress. In brief, salicylic acid treatment reduced the damaging action of salinity on embryo growth and accelerated a restoration of growth processes; thereupon it may be effective for the improvement of seed germination in arid and semi-arid regions.     

Competition for nodule occupancy between introduced and native strains of Rhizobium leguminosarum biovar trifolii

The aim of this work was to evaluate the competitive ability between Rhizobium leguminosarum bv trifolii strain U204 used as commercial inoculants in Uruguay for Trifolium repens L. and Trifolium pratense L. and two native strains isolated from inoculated pastures of T. pratense. T126 is an efficient nitrogen fixer and a melanin producer strain; T70 is inefficient and a melanin non-producer strain; and U204 is very efficient in both hosts but is a melanin non-producer strain. Competitiveness between the strains was determined in experiments in pots and in growth pouches under controlled conditions. In the last experiment, we evaluated pH of plant nutrient solution and inoculum ratios. Plant dry weight was determined, and the identification of nodule bacteria was done using melanin production and DNA fingerprinting (GTG₅-PCR). The U204 symbiotic efficiency was not affected by the co-inoculation with the others two native strains. The T70 strain was a poor competitor when was co-inoculated with one of the effective strains in both experiments. Our results confirmed a “selective nodulation” because an effective symbiosis occurred preferentially over an ineffective one in Trifolium species. The native effective strain competed with U204 for nodule formation in both clovers species, but the nodule occupancy depended on the inoculum ratio. The pH of nutritive solution did not affect competition ability of the studied strains. It may be possible to isolate efficient, competitive, and genetically different native rhizobial strains to be used as inoculant strains for clover pastures in Uruguay. Both (GTG)₅-PCR and melanin production were useful methods to identify nodulating bacteria in competition studies.     

Water‐stress mitigation by selenium in Trifolium repens L.

This study was designed to examine whether external selenium (Se) may improve the tolerance of Trifolium repens L. to polyethylene glycol (PEG)–induced water deficit, and to determine the physiological mechanisms of the possibly enhanced tolerance. Trifolium repens seedlings were subjected to PEG‐induced water deficit alone or combined with 5 μM Na₂SeO₄ for 24, 48, and 72 h. During the experimental period, the fresh weight (FW) of T. repens seedlings and the relative water content (RWC) of the leaves decreased gradually, and the chlorophyll concentration increased after 24 and 48 h, but decreased after 72 h. The PEG+Se‐treated plants had higher FW, RWC, and chlorophyll concentration than the PEG‐treated plants. Smaller amounts of thiobarbituric acid‐reactive substances (TBARS) and H₂O₂ accumulated in PEG+Se‐treated plants than in plants treated only with PEG. The activity of superoxide dismutase (SOD) increased gradually during the water‐deficit period, and Se application promoted SOD activity further. Catalase (CAT) activity remained unchanged after 24 and 48 h and insignificantly increased after 72 h of water deficit, whereas ascorbate peroxidase (APOX) activity increased linearly and glutathione reductase (GR) activity increased slightly over the course of treatment. Whereas the Se application exhibited no effect on the CAT activity, seedlings treated with PEG+Se had higher APOX activity during the whole experimental period and a higher GR activity after 48 and 72 h than PEG‐treated plants. These results suggest that exogenous Se treatment enhanced T. repens tolerance to PEG‐induced water deficit, and this enhancement was related to alleviation of lipid peroxidation and activation of antioxidant enzymes such as SOD, APOX, and GR.     

EXOGENOUS CALCIUM ALTERS ACTIVITIES OF ANTIOXIDANT ENZYMES IN TRIFOLIUM REPENS L. LEAVES UNDER PEG-INDUCED WATER DEFICIT

This study was designed to examine whether external calcium (Ca²⁺) would improve the tolerance of Trifolium repens L to polyethylene glycol (PEG)-induced water deficit, and to determine the physiological mechanisms of Ca²⁺ effect on plant tolerance to water deficit. T. repens seedlings were subjected to PEG-induced water deficit alone or combined with 5 mM calcium chloride (CaCl₂) for 72 h. During PEG-induced water deficit period, leaf relative water content (RWC) decreased gradually, and chlorophyll content increased after 24 and 48 h of water deficit but decreased below the control level after 72 h. The Ca²⁺-treated plants had higher RWC and chlorophyll content than untreated plants. Smaller amounts of thiobarbituric acid reactive substances (TBARS) and hydrogen peroxide (H₂O₂) accumulated in Ca²⁺-treated plants than in untreated plants during the period of water deficit. The activity of superoxide dismutase (SOD) increased gradually during the experimental period, and external Ca²⁺ treatment further promoted SOD activity under water deficit. The activity of the catalase (CAT) was not influenced after 24 and 48 h of water deficit and insignificantly increased after 72 h, whereas the activity of ascorbate peroxidase (APOX) increased linearly and glutathione reductase (GR) activity slightly increased over the course of treatment. Seedlings treated with Ca²⁺ had higher CAT, GR, and APOX activities than untreated plants under water deficit. These results suggested that exogenous Ca²⁺ application enhanced T. repens tolerance to PEG-induced water deficit, and this enhancement was related to alleviation of lipid peroxidation and maintenance of antioxidant activities.     

Inoculation responses of perennial forage legumes grown in fresh hill‐land ultisols as affected by soil acidity‐related factors

A growth chamber experiment was initiated with two field moist, marginal and acidic (pH 5.1–5.2) soils of the Lily series (Typic Hapludults) in order to determine the need for improved legume‐rhizobia symbioses for forage species of current, or potential, use in the renovation of Appalachian hill‐land pastures. One soil was from an abandoned pasture having broomsedge (Andropogon virginicus L.) as the predominant vegetation, whereas the other was from a minimally‐managed pasture dominated by orchardgrass (Dactylis glomerata L.). Treatments included inoculation (or no inoculation) and the addition of aluminum, nil, or lime to provide a range of soil acidities. Both soils contained effective populations of naturalized rhizobia for white clover (Trifolium repens L.) and red clover (Trifolium pratense L.), but low and/or ineffective naturalized populations of rhizobia for alfalfa (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.), bigflower vetch (Vicia grandiflora Scop.), and flatpea (Lathyrus sylvestris L.). Seed inoculation, by lime‐pelleting, was highly beneficial in establishing effective symbioses for all these latter species. The addition of low levels of aluminum or lime (1.5 and 2.0 cmol/kg soil, respectively) had little effect on any of the symbioses, with the exception of those for alfalfa. Thus, an improved legume rhizobia symbiosis would not seem to be a prerequisite for renovating pastures established on chemically similar ultisols with the forage legume species examined in this study, especially if the pasture has at least some history of management.     

Physiological and biochemical effects of boron toxicity in mustard during the seedling stage

A study was conducted to determine the physiological and biochemical effects of boron in seedlings of mustard (Brassica juncea L. var Varuna). For this seeds were sown in petridishes with varying concentrations of boron (0, 0.33, 3.3, 33, 330 mM) in seed germinator. Seed germination and vigor index was found to be decreased and percentage phytotoxicity was increased in seeds with increase in the concentration of boron in germinating solution. There was accumulation of sugars and decreased starch concentration in cotyledons and embryonic axes of growing seedling with increasing boron stress. For the estimation of oxidative damage in cotyledons and embryonic axes of mustard seedlings, hydrogen peroxide (H₂O₂), thiobarbituric acid reactive substances (TBARS), phenols and activities of antioxidative enzymes- polyphenoloxydase (PPO), superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) were determined. Boron toxicity caused accumulation of H₂O₂, TBARS and phenols and affected the antioxidative enzyme activity in growing seedling components.     

SODIUM CHLORIDE PRIMING IMPROVES SALINITY RESPONSE OF TOMATO AT SEEDLING STAGE

We aimed to investigate whether sodium chloride seed priming and irrigation at seedling stage enhance response of 5-leaf stage tomato plants (Lycopersium esculentum Mill.) to high salt stress. Three experimental groups were as; non-primed seeds, seeds primed with 0.05M sodium chloride (NaCl), and seeds primed and irrigated with 0.05M NaCl starting from sowing to salt stress application. Sodium chloride solutions (0.1M, 0.2M, 0.4M, and 0.6M) were added to cups under pots in every 2 days for 10 days to treatment groups. Control groups were irrigated with distilled water at the same time intervals. At least two experimental setups contained at least four plants, and two samplings of leaf and root tissues were performed for analysis of each plant to evaluate changes in pigment and proline contents, lipid peroxidation and electrolyte leakage levels, and ascorbate peroxidase and catalase activity. Priming reduced mean germination time, and increased final germination percentage together with energy of germination. Increased root and hypocotyl lengths as well as increases in fresh weights supported enhanced seedling vigor. Considering growth and stress parameters such as chlorophyll content, chlorophyll to carotenoid ratios, and lipid peroxidation and electrolyte leakage were less affected in primed plants. Moreover, improvement of the accumulation of osmoregulating defense molecules, such as proline and anthocyanin, and of the inductions of the antioxidative enzyme system points out to higher adaptive response of these plants against deleterious effects of salt.     

Effects of CaCN2 treatment of seeds of Inubie (Echinochloa oryzicola) on synthesis of protein and RNA during germination

Protein and RNA induction during the germination of Inubie (Echinochloa oryzicola) seeds pretreated with CaCN₂ was studied. It was observed that the germination of Echinochloa oryzicola seeds was delayed after pretreatment with a high concentration of CaCN₂ for 18 h. A considerable difference in the protein patterns was detected in the SDS-PAGE gel between the control (H₂O) and CaCN₂ treatment, particularly a 48 kilodalton (kD) protein band disappeared in CaCN₂ treatment. At the tested three levels of CaCN₂, the induction of this 48 kD protein was apparently inhibited during the germination process even when the duration of the pretreatment was as short as 2 h. When imbibed with water, the amount of the 48 kD protein increased rapidly within 1 h from the trace level in the dry seeds, and reached the maximum level after about 1–2 d. The results showed that the CaCN₂ treatment also decreased the total RNA level in the germinating seeds. The relation of this protein induction and RNA decline with the beginning of Echinochloa oryzicola germination was discussed.     

Different leguminous pre-crops increased yield of succeeding cereals in two consecutive years

Leguminous pre-crops are an important source of green manure in organic crop rotations for improving soil fertility and achieving high yields of cereals. We aimed to study the potential of various leguminous species, other than the traditionally cultivated red clover (Trifolium pratense L.), as green manure pre-crops for subsequent cereals. The use of different legume species enables to exploit advantages of specific legumes in organic cereal production. In order to test the legumes as pre-crops for cereals, we carried out trials located in the temperate climate zone of northeast Europe (58°44′59.41″ N, 26°24′54.02″ E). We sowed the following perennial legumes as pre-crops: red clover, alsike clover (Trifolium hybridum L.) and Washington lupine (Lupinus polyphyllus Lindl.), biennial white sweet clover (Melilotus albus Medik.) and annual Alexandria clover (Trifolium alexandrinum L.), and crimson clover (Trifolium incarnatum L.). Timothy (Phleum pratense L.) was used as a control. The leguminous pre-crops were followed by three spring cereals (barley, oat and spring wheat) and two winter cereals (rye and winter wheat). We tested the first-year after-effect (all cereals) and second-year after-effect (only barley and oat) of pre-crops on the grain yield of cereals. Perennial and biennial legume species produced the highest dry matter yield and contained the highest amount of nutrients, especially nitrogen, compared to annual species. All subsequent cereals produced significant extra yields after each leguminous pre-crop in the following two years, although the effect was smaller in the second year. The most suitable pre-crops for spring cereals were red and alsike clover followed by lupine, whereas the best pre-crops for winter cereals were sweet clover and annual clovers. Our results show the potential of various leguminous pre-crop species as valuable sources of green manure in organic crop rotation.     

Effects of Multiple Reference Plants,Season, and Irrigation on Biological Nitrogen Fixation by Pasture Legumes using the Isotope Dilution Method

Abstract

The popular and widely used ¹⁵nitrogen (N)–isotope dilution method for estimating biological N fixation (BNF) of pasture and tree legumes relies largely on the ability to overcome the principal source of error due to the problem of selecting appropriate reference plants. A field experiment was conducted to evaluate the suitability of 12 non‐N₂‐fixing plants (i.e., nonlegumes) as reference plants for estimating the BNF of three pasture legumes (white clover, Trifolium repens L.; lucerne, Medicago sativa; and red clover, Trifolium pratense L.) in standard ryegrass–white clover (RWC) and multispecies pastures (MSP) under dry‐land and irrigation systems, over four seasons in Canterbury, New Zealand. The ¹⁵N‐isotope dilution method involving field ¹⁵N‐microplots was used to estimate BNF. Non‐N₂‐fixing plants were used either singly or in combination as reference plants to estimate the BNF of the three legumes. Results obtained showed that, on the whole, ¹⁵N‐enrichment values of legumes and nonlegumes varied significantly according to plant species, season, and irrigation. Grasses and herb species showed higher ¹⁵N‐enrichment than those of legumes. Highest ¹⁵N‐enrichment values of all plants occurred during late summer under dry‐land and irrigation conditions. Based on single or combined non‐N₂‐fixing plants as reference plants, the proportion of N derived from the atmosphere (% Ndfa) values were high (50 to 90%) and differed between most reference plants in the MSP pastures, especially chicory (Cichorium intybus), probably because it is different in phenology, rooting depth, and N‐uptake patterns compared to those of legumes. The percent Ndfa values of all plants studied also varied according to plant species, season, and irrigation in the MSP pastures. Estimated daily amounts of BNF varied according to pasture type, time of plant harvest, and irrigation, similar to those shown by percent Ndfa results as expected. Irrigation increased daily BNF more than 10‐fold, probably due to increased dry‐matter yield of pasture under irrigation compared to dry‐land conditions. Seasonal and irrigation effects were more important in affecting estimates of legume BNF than those due to the appropriate matching of N₂‐fixing and non‐N₂‐fixing reference plants.     

Excess nickel–induced changes in antioxidative processes in maize leaves

Maize (Zea mays L. cv. 777) plants grown in hydroponic culture were treated with 100 µM NiSO₄ (moderate nickel (Ni) excess). In addition to growth parameters, metabolic parameters representative of antioxidant responses in leaves were assessed 24 h and 3, 7, and 14 d after initiating the Ni treatment. Extent of oxidative damage was measured as accumulation of malondialdehyde and hydrogen peroxide in leaves 7 and 14 d after treatment initiation. Apart from increasing membrane‐lipid peroxidation and H₂O₂ accumulation, excess supply of Ni suppressed plant growth and dry mass of shoots but increased dry mass of roots and decreased the concentrations of chloroplastic pigments. Excess supply of Ni, though inhibited the catalase (EC 1.11.1.6) activity, increased peroxidase (EC 1.11.1.7), ascorbate peroxidase (EC 1.11.1.11), and superoxide dismutase (EC 1.15.1.1) activities. Localization of isoforms of these enzymes (peroxidase, ascorbate peroxidase, and superoxide dismutase) on native gels also revealed increases in the intensities of pre‐existing bands. Enhanced activities of peroxidase, ascorbate peroxidase, and superoxide dismutase, however, did not appear to be sufficient to ameliorate the effects of excessively generated reactive oxygen species due to excess supply of Ni.     

Agronomic evaluations of grass and legume forage species collected in the Xinjiang Autonomous Region of the People's Republic of China and Mongolia

Because rangelands in the Xinjiang Autonomous Region of thePeople's Republic of China (PRC) and Mongolia are typicallyseverely overgrazed, bilateral (U.S./ PRC, U.S./Mongolia)efforts have been initiated to expedite capture of the remaining geneticdiversity. The current study was designed to evaluate selected germplasm of thefollowing forage species collected in these threatened areas: Bromusinermis Leyss., Dactylis glomerata L.,Festuca arundinacea Schreb., Festucaovina L., Festuca rubra L., Phleumphleoides (L.) Karsten, Phleumpratense L., Poa palustris L., Poapratensis ssp. angustifolia (L.) H.Lindb., Medicago sativa ssp. falcataArcengeli, Medicago sativa L. ssp. sativa, Medicago lupulina L.,Medicago ruthenica (L.) Ledebour,Trifolium fragiferum L., Trifoliumlupinaster L., Trifolium pratense L., andTrifolium repens L. Accessions were evaluated in the fieldat Beltsville MD (USA) on an Iuka sandy loam(coarse-loamy, siliceous, acid, thermic, Aquic Udigluvent; pH6.5) in a two-year study. Comparative check cultivars were included.There was significant variation in days to 50% heading (grassspecies) or flowering (legume species), leaf texture (grassspecies), growth habit, spring vigor, and dry matter yield among accessionsof at least some genera. Accessions did not demonstrate higher diseasesusceptibility relative to check cultivars, except in the case of severalF. arundinacea and oneM. sativa ssp.falcata entries. There was no significant variation in leafshape among the legume accessions, nor were leaf shapes significantly differentfrom those of the check cultivars. Several F.ovina, F. rubra,and Poa pratensis accessions may have potential in turfgrass breeding programs. There were apparent positive relationships amongupright growth habit, spring vigor, late development, and yield.     

Beneficial effects of silicon nutrition in alleviating salinity stress in hydroponically grown canola,Brassica napus L., plants

Abstract

Silicon (Si) is the second most abundant element in soil and effectively counteracts the effects of various abiotic stresses, such as drought, heavy metal toxicity and salinity, on plants. In the present study the ameliorating effects of Si nutrition supplied as 2?mmol?L^?1 sodium silicate were investigated on hydroponically grown canola (Brassica napus L.) plants under salinity stress (i.e. 150?mmol?L^?1 sodium chloride). Salinity decreased plant growth parameters such as tissue fresh and dry weights. These decreases were accompanied by increased lignin contents, Na⁺ ion accumulation, increased lipid peroxidation and decreased chlorophyll contents in plants. Silicon nutrition, however, enhanced plant growth parameters and led to the prevention of lignin and the Na⁺ accumulation in shoots, reduced levels of lipid peroxidation in the roots and higher levels of chlorophyll. As a result of salinity, catalase activity in the whole plant and both soluble and cell wall peroxidase activities in the shoots decreased. Silicon nutrition, however, increased the reactive oxygen species scavenging capacity of salt-stressed plants through increased catalase and cell wall peroxidase activities. Thus, silicon nutrition ameliorated the deleterious effects of salinity on the growth of canola plants through lower tissue Na⁺ contents, maintaining the membrane integrity of root cells as evidenced by reduced lipid peroxidation, increased reactive oxygen species scavenging capacity and reduced lignification.     

Evenness and plant species identity affect earthworm diversity and community structure in grassland soils

Diversity of plant species and the species composition (identity) are known to influence below-ground diversity. In this paper we examine the effects of plant species diversity (richness and evenness), rates of nitrogen application and planting density, on earthworm community structure in grassland. The study was carried out at three sites in Ireland using a Simplex experimental design to define the compositions of the experimental plant communities used.A negative relationship was detected between diversity (evenness) of plant species and diversity of earthworms in the soils. However, plant species identity also affected the structure of the earthworm assemblage. In particular, the legume, Trifolium repens had a strong effect but this was conditional on the rate of nitrogen application. No earthworm species favoured communities dominated by slow growing grasses (Phleum pratense and Dactylis glomerata) (P = 0.02).Higher N inputs reduced earthworm abundance and biomass under T. repens. Earthworm richness, was negatively influenced by elevated amounts of N inputs. No effect of planting density was detected but this factor also did not affect plant biomass production.     

Effect of chemical composition on the release of nitrogen from agricultural plant materials decomposing in soil under field conditions

Summary In two field experiments, plant materials labelled with ¹⁵N were buried separately within mesh bags in soil, which was subsequently sown with barley. In the first experiment, different parts of white clover (Trifolium repens), red clover (T. pratense), subterranean clover (T. subterraneum), field bean (Vicia faba), and timothy (Phleum pratense) were used, and in the second, parts of subterranean clover of different maturity. The plant materials were analysed for their initial concentrations of total N, ¹⁵N, C, ethanol-soluble compounds, starch, hemicellulose, cellulose, lignin, and ash. After the barley had been harvested, the bags were collected and analysed for their total N and ¹⁵N. In the first experiment the release of N was highest from white clover stems + petioles (86%) and lowest from field bean roots (20%). In stepwise regression analysis, the release of N was explained best by the initial concentrations of lignin, cellulose, hemicellulose, and N (listed according to decreasing partial correlations). Although the C/N ratio of the plant materials varied widely (11–46), statistically the release of N was not significantly correlated with this variable. The results of the second experiment using subterranean clover of different maturity confirmed those of the first experiment.     

Effects of Ozone on Growth of Seven Grass and One Clover Species

Abstract

Seven species of grass and one of red clover were grown at different ozone (O₃) concentrations for about five weeks in growth chambers located in a greenhouse. At an O₃ concentration of 55 compared with 10 nmol mol^?1 during 7 h day^?1 the shoot dry weight decreased by 45% in Phleum pratense, 28% in Dactylis glomerata and Poa pratensis, 23% in Festuca rubra and 16% in Festuca pratensis, while the effects on Agrostis tenuis were not significant. No effect was found at 25 compared with 10 nmol mol^?1O₃. Visible O₃ injury was observed in all six species at 55 nmol mol^?1 and this effect was generally well correlated with the effect on the dry weights. In another experiment no effect was found with O₃ concentrations of up to 62 nmol mol_?1 on Lolium perénne, while the dry weight in Trifolium pratense decreased by 30% at 59 compared with that at 6 nmol mol^?1.     

Elevated CO2 and plant species diversity interact to slow root decomposition

Changes in plant species diversity can result in synergistic increases in decomposition rates, while elevated atmospheric CO₂ can slow the decomposition rates; yet it remains unclear how diversity and changes in atmospheric CO₂ may interact to alter root decomposition. To investigate how elevated CO₂ interacts with changes in root-litter diversity to alter decomposition rates, we conducted a 120-day laboratory incubation. Roots from three species (Trifolium repens, Lespedeza cuneata, and Festuca pratense) grown under ambient or elevated CO₂ were incubated individually or in combination in soils that were exposed to ambient or elevated CO₂ for five years. Our experiment resulted in two main findings: (1) Roots from T. repens and L. cuneata, both nitrogen (N) fixers, grown under elevated CO₂ treatments had significantly slower decomposition rates than similar roots grown under ambient CO₂ treatments; but the decomposition rate of F. pratense roots (a non-N-fixing species) was similar regardless of CO₂ treatment. (2) Roots of the three species grown under ambient CO₂ and decomposed in combination with each other had faster decomposition rates than when they were decomposed as single species. However, roots of the three species grown under elevated CO₂ had similar decomposition rates when they were incubated alone or in combination with other species. These data suggest that if elevated CO₂ reduces the root decomposition rate of even a few species in the community, it may slow root decomposition of the entire plant community.     

Plant root morphology and soil biological indicators under primary development of various swards

Plant nutrition conditions are limited in naturally acidic soil due to harmful hydrogen and aluminium ions. More favourable conditions for plant nutrition (soil liming) will affect root qualitative and quantitative parameters and influence ecosystem stability. Four legume–grass swards were cultivated. The swards were a combination of one species of legume and two species of grasses: Trifolium pratense L., Trifolium repens L., Trifolium hybridum L., Medicago sativa L. (each of 50%) with Phleum pratense L. (35%) and Poa pratensis L. (15%). The aim of this study is to evaluate the root morphological and soil biological indicators of legume–grass swards under the first two years of development in soils with different pH levels.

Sward ecosystem development depends on the pH of the soil, sward species composition and soil biota. During the first year of sward development, soil pH had a significant influence on the morphology of root system. Sward‘s root mass and total root length was 2.4 and 2.2 times bigger in naturally acidic soil. This resulted in a change of biological parameters.

In the second year of sward development, soil pH had no significant influence on sward‘s root mass. However, under the impact of different soil pH, various sward‘s root systems were formed and the root C:N ratio had changed. It is observed that, regardless of the sward species composition and the year of development, at higher root C:N ratio soil microbial biomass was higher and CO₂ emissions were lower in swards in naturally acidic soils.

Regardless of soil pH, different types of clover–grass swards promoted organic carbon immobilization in microbial biomass and, at the same time, stabilized the sward ecosystem in the top soil layer (soil respiration in 0–10 and 10–20?cm layers was lower) more effectively than the alfalfa–grass sward.     

Improved growth and Cu tolerance of Cu excess-stressed white clover after inoculation with arbuscular mycorrhizal fungi

The effects of arbuscular mycorrhizal (AM) fungus, Glomus intraradices, on growth and copper (Cu) tolerance of white clover (Trifolium repens) were investigated in soils with different Cu amounts. The AM inoculation increased plant biomass and the total or bound Cu concentrations in shoots and roots but decreased the total Cu in soils and the exchangeable Cu in shoots, roots and soils at all Cu levels. Mycorrhizal plants had higher levels of root phosphorus and shoot zinc (Zn) at lower Cu levels and more nitrogen and Zn in roots and potassium, calcium and magnesium in shoots and roots at all Cu addition levels. Additionally, AM inoculation enhanced urease, acid phosphatase and catalase activities in rhizosphere soils and mycorrhizal roots showed higher levels of peroxidase, catalase, proline and soluble sugar at all Cu addition levels. These results indicate that mycorrhizal white clover is potentially suitable for Cu phytoremediation based on greenhouse studies.