Ileana García

Plant growth, nutrient acquisition and mycorrhizal symbioses of a waterlogging tolerant legume (Lotus glaber Mill.) in a saline-sodic soil

Seedlings of Lotus glaberMill., were grown in a native saline-sodic soil in a greenhouse for 50 days and then subjected to waterlogging for an additional period of 40 days. The effect of soil waterlogging was evaluated by measuring plant growth allocation, mineral nutrition and soil chemical properties. Rhizobiumnodules and mycorrhizal colonisation in L. glaberroots were measured before and after waterlogging. Compared to control plants, waterlogged plants had decreased root/shoot ratio, lower number of stems per plant, lower specific root length and less allocation of P and N to roots. Waterlogged plants showed increased N and P concentrations in plant tissues, larger root crown diameter and longer internodes. Available N and P and organic P, pH and amorphous iron increased in waterlogged soil, but total N, EC and exchangeable sodium were not changed. Soil waterlogging decreased root length colonised by arbuscular mycorrhizal (AM) fungi, arbuscular colonisation and number of entry points per unit of root length colonised. Waterlogging also increased vesicle colonisation and Rhizobium nodules on roots. AM fungal spore density was lower at the end of the experiment in non-waterlogged soil but was not reduced under waterlogging. The results indicate that L. glaber can grow, become nodulated by Rhizobium and colonised by mycorrhizas under waterlogged condition. The responses of L. glaber may be related its ability to form aerenchyma.

Deficit and excess of soil water impact on plant growth of Lotus tenuis by affecting nutrient uptake and arbuscular mycorrhizal symbiosis

The impact of deficit and excess of soil water on plant growth, morphological plant features, N and P plant nutrition, soil properties, Rhizobium nodulation and the symbiosis between arbuscular mycorrhizal (AM) fungi and Lotus tenuis Waldst. & Kit. were studied in a saline-sodic soil. Water excess treatment decreased root growth by 36% and increased shoot growth by 13% whereas water deficit treatment decreased both root and shoot growth (26 and 32%, respectively). Differences between stress conditions on shoot growth were due to the ability of L. tenuis to tolerate low oxygen concentration in the soil and the sufficiency of nutrients in soil to sustain shoot growth demands. Water excess treatment decreased pH, and increased available P and labile C in soil. Water deficit treatment decreased available P and also increased labile C. In general, N and P acquisition were affected more by water excess than water deficit. The number of nodules per gram of fresh roots only increased in water excess roots (97%). Under both stress conditions there was a significant proportion of roots colonized by AM fungi. Compared to control treatment, arbuscule formation decreased by 55 and 14% under water excess and water deficit, respectively. Vesicle formation increased 256% in water excess treatment and did not change under water deficit treatment. L. tenuis plants subjected to water deficit or excess treatments could grow, nodulated and maintained a symbiotic association with AM fungi by different strategies. Under water excess, L. tenuis plants decreased root growth and increased shoot growth to facilitate water elimination by transpiration. Under water deficit, L. tenuis plants decreased root growth but also shoot growth which in turn significant decreased the shoot/root ratio. In the present study, under water excess conditions AM fungi reduced nutrient transfer structures (arbuscules), the number of entry points and spore, and hyphal densities in soil, but increased resistance structures (vesicles). At water deficit, however, AM fungi reduced external hyphae and arbuscules to some extent, investing more in maintaining a similar proportion of vesicles in roots and spores in soil compared to control treatment.

Arbuscular mycorrhizal fungi and plant symbiosis in a saline-sodic soil

The seasonality of arbuscular mycorrhizal (AM) fungi–plant symbiosis in Lotus glaber Mill. and Stenotaphrum secundatum (Walt.) O.K. and the association with phosphorus (P) plant nutrition were studied in a saline-sodic soil at the four seasons during a year. Plant roots of both species were densely colonized by AM fungi (90 and 73%, respectively in L. glaber and S. secundatum) at high values of soil pH (9.2) and exchangeable sodium percentage (65%). The percentage of colonized root length differed between species and showed seasonality. The morphology of root colonization had a similar pattern in both species. The arbuscular colonization fraction increased at the beginning of the growing season and was positively associated with increased P concentration in both shoot and root tissue. The vesicular colonization fraction was high in summer when plants suffer from stress imposed by high temperatures and drought periods, and negatively associated with P in plant tissue. Spore and hyphal densities in soil were not associated with AM root colonization and did not show seasonality. Our results suggest that AM fungi can survive and colonize L. glaber and S. secundatum roots adapted to extreme saline-sodic soil condition. The symbiosis responds to seasonality and P uptake by the host altering the morphology of root colonization.

Relationships among soil properties, plant nutrition and arbuscular mycorrhizal fungi–plant symbioses in a temperate grassland along hydrologic, saline and sodic gradients

Temporal variations in the relationships among plant nutrient concentrations, soil properties and arbuscular-mycorrhizal (AM) fungal dynamics were studied along a topographic and saline gradient in a temperate grassland soil. Soil and plant (Lotus tenuis, Paspalum vaginatum, Stenotaphrum secundatum) samples were collected on four seasonally based occasions. The morphology of AM root colonization had a similar pattern in the plants studied. Maximum arbuscular colonization occurred at the beginning of the growing season in late winter and was minimal in late summer, but maximal vesicular colonization occurred in summer and was minimal in winter, suggesting a preferential production of these morphological phases by the fungus with respect to season. The greatest arbuscular colonization was associated with the highest N and P concentrations in plant tissue, suggesting a correspondence with increases in the rate of nutrient transfer between the symbiotic partners. Water content, salinity and sodicity in soil were positively associated with AM root colonization and arbuscule colonization in L. tenuis, but negatively so in the grasses. There were distinct seasonally related effects with respect to both spore density and AM colonization, which were independent of particular combinations of plant species and soil sites.

The interaction of heavy metals and nutrients present in soil and native plants with arbuscular mycorrhizae on the riverside in the Matanza-Riachuelo River Basin (Argentina).

This study assessed the contamination by heavy metals (Cr, Cu, Pb, Zn), and nutrients (N, P) in soils and native plants, and the effect of the concentration of those elements with the density of arbuscular-mycorrhizal (AM) spores in soil and colonization in roots from the riverside of the Matanza-Riachuelo River Basin (MRRB). The concentration of metals and nutrients in soils and plants (Eleocharis montana, Cyperus eragrostis, Hydrocotyle bonariensis) increased from the upper sites (8 km from headwaters) to the lower sites (6 km from the mouth of the Riachuelo River) of the basin. AM-colonization on the roots of H. bonariensis and spore density in soil decreased as the concentrations of metals in soil and plant tissues increased from the upper to lower sites of the basin within a consistent gradient of contamination associated with land use, soil disturbance, population, and chemicals discharged into the streams and rivers along the MRRB. The general trends for all metals in plant tissue were to have highest concentrations in roots, then in rhizomes and lowest in aerial biomass. The translocation (TF) and bioconcentration (BCF) factors decreased in plants which grow from the upper sites to the lower sites of the basin. The plants tolerated a wide range in type and quantity of contamination along the basin by concentrating more metals and nutrients in roots than in aboveground tissue. The AM spore density in soil and colonization in roots of H. bonariensis decreased with the increase of the degree of contamination (Dc) in soil.

Growth, nutrient uptake and symbiosis with rhizobia and arbuscular mycorrhizal fungi in Lotus tenuis plants fertilized with different phosphate sources and inoculated with the phosphate-solubilizing bacterium Pantoea eucalypti M91

Background and aimsThe aim of this work was to evaluate the ability of P fertilization and phosphate-solubilizing bacteria (PSB) inoculation to promote the growth of L. tenuis in typical soils of the Salado River Basin (Argentina) with low P availability.MethodsAboveground biomass and P and N levels were evaluated in field-grown L. tenuis plants inoculated with Pantoea eucalypti M91, either without fertilization or in combination with phosphate rock and triple superphosphate (TSP). The impact of P fertilization and inoculation on the symbiotic interactions between L. tenuis and native rhizobia bacteria and arbuscular mycorrhizal fungi was also evaluated.ResultsInoculation with M91 increased the L. tenuis biomass production and P concentration in shoots, at an early stage of plant growth. The combined treatment of inoculation with M91 and TSP significantly increased the P and N content in shoots compared to non-inoculated plants, fertilized or not. P. eucalypti M91 was found to endophytically colonize roots and leaves of L. tenuis plants grown in vitro and also under field conditions.ConclusionsThe results suggesting that inoculation of L. tenuis with the PSB such as P. eucalypti M91 strain might allow more efficient use of N and P and a more sustainable option for grasslands producers from the Salado River Basin, in order to reduce costs and avoid increased levels of P insoluble in soils.

Flavonoids of Lotus tenuis (Waldst. & Kit.) as markers of populations growing in soils of different saline and hydrologic conditions

Lotus tenuis Waldst. et Kit. (=Lotus glaber Mill.) e uma planta leguminosa muito difundida que cresce naturalmente em pastagens da Flooding Pampas, na Argentina. Uma das hipoteses para explicar a disseminacao de L. tenuis nessa area, e a diferenciacao de ecotipos. O objetivo deste trabalho foi investigar os compostos flavonoides presentes em populacoes de L. tenuis que crescem em uma grande variedade de solos. Amostras de cinco populacoes que crescem em solos com diferentes caracteristicas foram coletados, cultivados em estufas e comparados de acordo com seu perfil de flavonoides. Glicosideos dos seguintes flavonoides foram detectados: quercetina, 7-metoxi-quercetina eter, kaempferol, 7-metoxi-kaempferol eter e isorhamnetina. Somente as mostras de solos salino-sodicos mostraram agliconas metiladas: 7-metoxi-kaempferol eter e 7-metoxi-quercetina eter. Os ultimos compostos poderiam, portanto, ser considerados como a expressao de uma adaptacao bioquimica e sugerem uma diferenciacao em ecotipo. Lotus tenuis Waldst. et Kit. (=Lotus glaber Mill.) is a widely spread leguminous plant which grows naturally in low grasslands of the Flooding Pampas of Argentina. One of the hypothesis to explain the succesful spread of L. tenuis in this area, is the ecotypes differentiation. The aim of this work was to investigate the flavonoid compounds present in L. tenuis plant populations which grow in a variety of soils. Individuals from five populations growing in soils having different characterisctics were collected, cultivated in a glasshouse and compared according to their flavonoid profile. Glycosides of the following flavonoids were detected: quercetin, quercetin 7-methyl ether, kaempferol, kaempferol 7-methyl ether and isorhamnetin. Only those samples from a saline-sodic lowland, showed methylated aglycones: kaempferol 7-methyl ether and quercetin 7- methyl ether. The latter compounds could therefore be considered the expression of a biochemical adaptation and suggest an ecotype differentiation.

How do soil P tests, plant yield and P acquisition by Lotus tenuis plants reflect the availability of added P from different phosphate sources

The relative effectiveness (RE) of each one of three different sources of P—P in solution (Psol), triple superphosphate (TSP) and phosphate rock (PR)—for reflecting the availability of P in a P-deficient soil were assessed by measuring in Lotus tenuis variables associated with growth, organ morphology, and plant tissue P-content together with the amounts of P extracts from soil by two of the currently used soil-P tests—Bray I and Olsen. A hyperbolic equation was used to fit the response curves of each one of those plant variables to added-P. The ratio between the shapes of paired response curves of any P-sources was used to compute the RE and substitution rate (K) of one source relative to the other. More P was needed from TSP and PR compared to Psol-100% soluble P-source. On the average P applications as TSP relative to Psol and PR relative to TSP were only 68 and 63% effective respectively for plant growth. Plant roots were more sensitive than soil-P tests to detect shifts in P-availability from different P-sources. Because soil tests are commonly used to estimate the current P status in soil in order to calculate the optimum application levels of fertilizer P for a crop or pasture, these results would have practical agronomical consequences if reproduced in other cultivated species because they show that the response curve of a plant species as a function of added P and soil test might differ among fertilizer types, measured plant variables, and the test used to measure P availability in the soil.

Phosphorus fertilization of a grass-legume mixture: Effect on plant growth, nutrients acquisition and symbiotic associations with soil microorganisms

ABSTRACT Adding P on Lotus tenuis and Festuca arundinacea, pure or mixed, on growth, nitrogen (N) and phosphorus (P) acquisition and associations with soil microorganisms was studied to investigate the establishment of Lotus for competing with Festuca. Triple-superphosphate was applied on a Typic Natraquoll where Lotus grows spontaneously. Biomass, N-P uptake, arbuscular mycorrhizal colonization and rhizobia nodulation were measured. Lotus achieved the highest biomass, N-P uptake in fertilized stands and Festuca the lowest in fertilized and non-fertilized stands. Mycorrhizal colonization decreased with P-fertilization in both plants. Rhizobia nodules in Lotus showed little changes with P-fertilization. In mixed fertilized-stands, Lotus promoted the growth, N-P uptake of Festuca. P-fertilization increases the ability of Festuca to compete with Lotus for available-P in soil. Lotus improves nutrient cycling, maintains high level of rhizobia nodules and arbuscular mycorrhizal colonization in roots. Adding P to limited N-P environments depress grasses growth to compete with legumes for resources.

Competition and growth of a grass–legume mixture fertilised with nitrogen and phosphorus: effect on nutrient acquisition, root morphology and symbiosis with soil microorganisms

Abstract. Achieving a fast initial growth is crucial for legumes because grasses grow more rapidly and compete much better with forbs. In a pot experiment with a nutrient-deficient soil, we added nitrogen (N), phosphorus (P) and N + P to pure and mixed stands of Lotus tenuis and Festuca arundinacea and investigated the effects of on plant growth, nutrient uptake and symbiotic associations with arbuscular mycorrhizae and rhizobia. Plant yield, N and P acquisition, mycorrhizal colonisation, rhizobial nodulation and root length were measured and root diameter and root surface area were calculated after two harvests. Species responded differently to specific nutrients when grown pure or mixed. Comparing pure with mixed stands in soils fertilised with P and N + P, L. tenuis showed decreased shoot and particularly root biomass, whereas F. arundinacea showed increases in both biomasses. This suggests that the competitiveness of the grass with the legume increased upon P and N + P addition. In mixed stands, F. arundinacea produced 51–64% of the total shoot biomass and 69–74% of the total root biomass with P and N + P, respectively. Root length and root surface area were greater and the roots thinner in F. arundinacea than in L. tenuis. Addition of P and N + P increased rhizobial nodulation in legume roots but decreased mycorrhizal colonisation in both plants. Supply of N does not necessarily favour grasses, whereas P supply favours legumes. Optimisation of P nutrition might help to maximise N inputs into grasslands by symbiotic N-fixation and decrease inputs of inorganic N by fertilisation.