Lotus Tenuis Research Articles

Root strength and trampling tolerance in the grass Paspalum dilatatum and the dicot Lotus glaber in flooded soil

Summary We studied the differences in root strength of species with contrasting root structural types (the grass Paspalum dilatatum and the dicot Lotus glaber), and their relationship with tolerance to simulated cattle trampling under flooding conditions. Root strength was analysed through measurement of the pressure required to cause root collapse. The responses of aerenchyma and plant mass to flooding and trampling were studied. Root aerenchyma increased from 28·0 to 40·2% in P. dilatatum and from 12·9 to 19·7% in L. glaber under flooding conditions. The increase in aerenchyma did not affect root strength in the relatively trampling‐resistant roots of P. dilatatum: roots cracked at >380 kPa in all treatments. In contrast, roots of L. glaber were weaker, cracking at 260 kPa; flooded roots with air spaces irregularly dispersed in the cortex cracked at 115 kPa. Trampling, flooding or their combination did not affect the biomass of P. dilatatum. Conversely, the isolated effects of either trampling or flooding both decreased biomass accumulation in L. glaber. The combination of both treatments killed all Lotus plants. In conclusion, root strength was positively associated with soil trampling tolerance. The effect of aerenchyma tissue generation on root strength varies among root structural types. Aerenchyma tissue increases root weakness in the less stable structural type of the dicot species, but had no effect on the strength of the grass.

Physiological and Anatomical Basis of Differential Tolerance to Soil Flooding of Lotus corniculatus L. and Lotus glaber Mill

Lotus corniculatus L. and Lotus glaber Mill. are warm-season legume species adapted to many kinds of environmental stress, including flooding conditions, whereas other popular forage legumes, like alfalfa or white clover, cannot thrive. This study evaluates the relationship between root aerenchyma, water relations and leaf gas exchange and the differential tolerance to soil flooding of L. corniculatus and L. glaber. Adult plants of these species, established independently in grasslands mesocosms, were subjected to 40 days of early spring flooding at a water depth of 6 cm. Both species presented constitutive aerenchyma tissue in the roots. Under flooding conditions, this parameter was 26.2% in L. glaber and 15.3% in L. corniculatus. In addition, flooded plants of L. glaber presented a leaf biomass 47.5% higher above water while L. corniculatus showed a leaf biomass 59.6% lower in the same layer, in comparison to control plants. Flooded plants of L. glaber maintained the stomatal conductance (gs) and transpiration rate (E) for 25 days, although these parameters reduce slightly to 40–60% in comparison to controls after 40 days of flooding. In this species, a reduction in photosynthesis (A) in flooding conditions was detected only on the last day of measurement. In L. corniculatus, the same parameters (gs, E and A) were affected by flooding since day 18 of treatment, and values reached 25–40% in comparison to control plants after 40 days of flooding. Flooding did not affect above-ground biomass in L. glaber; while in L. corniculatus, above-ground biomass was 35% lower than in control plants. Our results confirmed that L. glaber is more able to cope with flooding stress than L. corniculatus, even in the presence of natural competitors. On the whole, this experiment provides information that can aid in the identification of anatomical and physiological parameters associated with flood-tolerance in this forage legume species, with economic potential for the agricultural areas subject to periodic flooding.

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

Seedlings of Lotus glaber Mill., 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. Rhizobium nodules and mycorrhizal colonisation in L. glaber roots 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.

Nodule Development Induced by Mesorhizobium loti Mutant Strains Affected in Polysaccharide Synthesis

The role of Mesorhizobium loti surface polysaccharides on the nodulation process is not yet fully understood. In this article, we describe the nodulation phenotype of mutants affected in the synthesis of lipopolysaccharide (LPS) and beta(1,2) cyclic glucan. M. loti lpsbeta2 mutant produces LPS with reduced amount of O-antigen, whereas M. loti lpsbeta1 mutant produces LPS totally devoid of O-antigen. Both genes are clustered in the chromosome. Based on amino acid sequence homology, LPS sugar composition, and enzymatic activity, we concluded that lpsbeta2 codes for an enzyme involved in the transformation of dTDP-glucose into dTDP-rhamnose, the sugar donor of rhamnose for the synthesis of O-antigen. On the other hand, lpsbeta1 codes for a glucosyltransferase involved in the biosynthesis of the O-antigen. Although LPS mutants elicited normal nodules, both show reduced competitiveness compared with the wild type. M. loti beta(1-2) cyclic glucan synthase (cgs) mutant induces white, empty, ineffective pseudonodules in Lotus tenuis. Cgs mutant induces normal root hair curling but is unable to induce the formation of infection threads. M. loti cgs mutant was more sensitive to deoxycholate and displayed motility impairment compared with the wild-type strain. This pleiotropic effect depends on calcium concentration and temperature.

Seasonal variation of arbuscular mycorrhizal fungi in temperate grasslands along a wide hydrologic gradient

We studied seasonal variation in population attributes of arbuscular mycorrhizal (AM) fungi over 2 years in four sites of temperate grasslands of the Argentinean Flooding Pampas. The sites represent a wide range of soil conditions, hydrologic gradients, and floristic composition. Lotus glaber, a perennial herbaceous legume naturalised in the Flooding Pampas, was dominant at the four plant community sites. Its roots were highly colonised by AM fungi. Temporal variations in spore density, spore type, AM root colonisation, floristic composition and soil chemical characteristics occurred in each site and were different among sites. The duration of flooding had no effect on spore density but depressed AM root colonisation. Eleven different types of spores were recognized and four were identified. Two species dominated at the four sites: Glomus fasciculatum and Glomus intraradices. Spore density was highest in summer (dry season) and lowest in winter (wet season) with intermediate values in autumn and spring. Colonisation of L. glaber roots was highest in summer or spring and lowest in winter or autumn. The relative density of G. fasciculatum and G. intraradices versus Glomus sp. and Acaulospora sp. had distinctive seasonal peaks. These seasonal peaks occurred at all four sites, suggesting differences among AM fungus species with respect to the seasonality of sporulation. Spore density and AM root colonisation when measured at any one time were poorly related to each other. However, spore density was significantly correlated with root colonisation 3 months before, suggesting that high colonisation in one season precedes high sporulation in the next season.

Free spermidine and spermine content in Lotus glaber under long-term salt stress

Polyamine metabolism has long been involved in plant stress responses, although physiological roles of putrescine, spermidine and spermine are still under debate. Regarding long-term salinization, it have been suggested that high titers of spermidine and/or spermine, but not putrescine, are correlated with the response of plants to salinity. In this work, we use the moderately salt tolerant glycophyte Lotus glaber as a model to test the hypothesis that free spermidine and spermine are biochemical indicators of salt stress response. For such purpose, we evaluated polyamine content in three different long-term salt stress approaches: germinating and growing seedlings under salinity, salinization of growing plants and imposition of salt stress to clone stem cuttings obtained from plants recovered from saline lowlands. Proline was also tested to evaluate if polyamines levels correlate with this compatible solute response. Results from these experiments showed a similar trend concerning higher polyamines content i.e., a salt induced a decrease of free spermidine and an increase of free spermine, in line with the idea that polyamine are biochemical indicators of salt stress. However, polyamine levels not always paralleled the accumulation of proline. These observations are discussed with regard of the putative roles reported for polyamines in plant abiotic stresses.

Evaluation of salt-tolerant forages for sequential water reuse systemsII. Plant–ion relations

Abstract Implementation of the saline drainage water reuse system proposed for the westside of the San Joaquin Valley (SJV) of California requires development of sustainable cropping systems, which incorporate useful, salt-tolerant agronomic species. Ion composition in the saline drainage effluents present in the SJV is unique, with Na+, SO42−, Cl−, Mg2+ and Ca2+ predominating in that order. To identify potentially suitable crops for reuse systems, 10 forages were tested in greenhouse sand cultures located at USDA-ARS George E. Brown Jr. Salinity Laboratory, Riverside, California. Crops were: alfalfa (Medicago sativa L.) cvs. ‘Salado’ and ‘SW 9720’; narrowleaf trefoil (Lotus glaber Greene) cv. ‘PI 608022’; broadleaf trefoil (L. ulginosus Schk.) cv. ‘Big’; tall wheatgrass (Agropyron elongatum (Host) Beauv.) cv. ‘Jose’; alkali sacaton (Sporobolus airoides Torr.); kikuyugrass (Pennisetum clandestinum Hochst. Ex Chiov.) cv. ‘Whittet’; paspalum (Paspalum vaginatum Swartz) cvs. PI ‘299042’ and ‘Polo’; and bermudagrass (Cynodon dactylon L. Pers.) cv. ‘Tifton’. Two saline treatments, 15 and 25 dS m−1, were imposed. Shoots were sub-sampled for mineral ion analysis when the forages were harvested. Patterns of shoot ion concentrations were unique for each species and varied with salinity level, external ion ratios, harvest date and plant age. Plant preference for K+ over Na+ did not appear to be a reliable predictor of salt tolerance. Salt-tolerant crops, such as kikuyugrass and bermudagrass, were highly selective for K+ (SK,Na ∼ 200 to 400), whereas selectivity coefficients for the equally salt-tolerant grasses, alkali sacaton and tall wheatgrass, ranged from 20 to 40. The forages were highly selective for K+ over Mg2+ despite unusually low K+:Mg2+ ratios in the external solutions. Total-S in the herbage was high and generally increased as external SO42− increased. Based on sustained nutritional health and lack of visual signs of toxicity or deficiency symptoms, several of the forages tested show promise as suitable candidates for the saline–sodic water reuse systems.

Evaluation of salt-tolerant forages for sequential water reuse systems: II. Plant–ion relations

Implementation of the saline drainage water reuse system proposed for the westside of the San Joaquin Valley (SJV) of California requires development of sustainable cropping systems, which incorporate useful, salt-tolerant agronomic species. Ion composition in the saline drainage effluents present in the SJV is unique, with Na +, SO 4 2−, Cl −, Mg 2+ and Ca 2+ predominating in that order. To identify potentially suitable crops for reuse systems, 10 forages were tested in greenhouse sand cultures located at USDA-ARS George E. Brown Jr. Salinity Laboratory, Riverside, California. Crops were: alfalfa ( Medicago sativa L.) cvs. ‘Salado’ and ‘SW 9720’; narrowleaf trefoil ( Lotus glaber Greene) cv. ‘PI 608022’; broadleaf trefoil ( L. ulginosus Schk.) cv. ‘Big’; tall wheatgrass ( Agropyron elongatum (Host) Beauv.) cv. ‘Jose’; alkali sacaton ( Sporobolus airoides Torr.); kikuyugrass ( Pennisetum clandestinum Hochst. Ex Chiov.) cv. ‘Whittet’; paspalum ( Paspalum vaginatum Swartz) cvs. PI ‘299042’ and ‘Polo’; and bermudagrass ( Cynodon dactylon L. Pers.) cv. ‘Tifton’. Two saline treatments, 15 and 25 dS m −1, were imposed. Shoots were sub-sampled for mineral ion analysis when the forages were harvested. Patterns of shoot ion concentrations were unique for each species and varied with salinity level, external ion ratios, harvest date and plant age. Plant preference for K + over Na + did not appear to be a reliable predictor of salt tolerance. Salt-tolerant crops, such as kikuyugrass and bermudagrass, were highly selective for K + ( S K,Na ∼ 200 to 400), whereas selectivity coefficients for the equally salt-tolerant grasses, alkali sacaton and tall wheatgrass, ranged from 20 to 40. The forages were highly selective for K + over Mg 2+ despite unusually low K +:Mg 2+ ratios in the external solutions. Total-S in the herbage was high and generally increased as external SO 4 2− increased. Based on sustained nutritional health and lack of visual signs of toxicity or deficiency symptoms, several of the forages tested show promise as suitable candidates for the saline–sodic water reuse systems.

Symbiotic relationships and root nodule ultrastructure of the pasture legume Biserrula pelecinus L.—a new legume in agriculture

Biserrula pelecinus is a pasture legume species new to Australian agriculture. The potential N benefit from B. pelecinus pastures in agricultural systems may not be realised if its symbiotic interactions with Mesorhizobium spp. are not well understood. This study evaluated the symbiotic interactions of four strains of Biserrula root-nodule bacteria (WSM1271, WSM1283, WSM1284, WSM1497) with four genotypes of B. pelecinus (cv. Casbah, 93GRC4, 93ITA33, IFBI1) and with a range of related legumes, including species known to be nodulated by strains of Mesorhizobium loti and other Mesorhizobium spp. Structures of root nodules were studied using light and electron microscopy enabling the ultrastructure of effective and ineffective nodules to be compared. B. pelecinus always formed typical indeterminate, finger-like nodules. The number of bacteroids inside symbiosomes varied between host×strain combinations, however, nodules formed by ineffective associations had well developed peribacteroid membranes and abundant bacteroids. Considerable variation was found in N 2-fixing effectiveness of strains isolated from B. pelecinus on the four B. pelecinus genotypes. Strains WSM1271, WSM1284 and WSM1497 nodulated Astragalus membranaceus, only strains WSM1284 and WSM1497 nodulated Astragalus adsurgens. Strain WSM1284 also nodulated Dorycnium rectum, Dorycnium hirsutum, Glycyrrhiza uralensis, Leucaena leucocephala, Lotus edulis, Lotus glaber, Lotus maroccanus, Lotus ornithopodioides, Lotus pedunculatus, Lotus peregrinus, Lotus subbiflorus and Ornithopus sativus. The four strains from B. pelecinus did not nodulate Amorpha fruticosa, Astragalus sinicus, Cicer arietinum, Hedysarum spinosissimum, Lotus parviflorus, Macroptilium atropurpureum or Trifolium lupinaster. M. loti strain SU343 nodulated all four genotypes of B. pelecinus. However, M. loti strain CC829 only nodulated B. pelecinus genotypes 93ITA33 and IFBI1 and the nodules were ineffective. The root nodule isolates from H. spinosissimum (E13 and H4) nodulated B. pelecinus cv. Casbah whereas the commercial inoculant strain for Cicer (CC1192) could not nodulate any genotype of B. pelecinus. These results indicate that strains WSM1271, WSM1283 and WSM1497 isolated originally from B. pelecinus have a specific host range while strain WSM1284 is promiscuous in its capacity to nodulate with a broad range of related species. As B. pelecinus can be nodulated by Mesorhizobium spp. from other agricultural legumes, particularly Lotus, there is an opportunity to utilise this trait in cultivar development.

Symbiotic relationships and root nodule ultrastructure of the pasture legume Biserrula pelecinus L.?a new legume in agriculture

Biserrula pelecinus is a pasture legume species new to Australian agriculture. The potential N benefit from B. pelecinus pastures in agricultural systems may not be realised if its symbiotic interactions with Mesorhizobium spp. are not well understood. This study evaluated the symbiotic interactions of four strains of Biserrula root-nodule bacteria (WSM1271, WSM1283, WSM1284, WSM1497) with four genotypes of B. pelecinus (cv. Casbah, 93GRC4, 93ITA33, IFBI1) and with a range of related legumes, including species known to be nodulated by strains of Mesorhizobium loti and other Mesorhizobium spp. Structures of root nodules were studied using light and electron microscopy enabling the ultrastructure of effective and ineffective nodules to be compared. B. pelecinus always formed typical indeterminate, finger-like nodules. The number of bacteroids inside symbiosomes varied between host×strain combinations, however, nodules formed by ineffective associations had well developed peribacteroid membranes and abundant bacteroids. Considerable variation was found in N2-fixing effectiveness of strains isolated from B. pelecinus on the four B. pelecinus genotypes. Strains WSM1271, WSM1284 and WSM1497 nodulated Astragalus membranaceus, only strains WSM1284 and WSM1497 nodulated Astragalus adsurgens. Strain WSM1284 also nodulated Dorycnium rectum, Dorycnium hirsutum, Glycyrrhiza uralensis, Leucaena leucocephala, Lotus edulis, Lotus glaber, Lotus maroccanus, Lotus ornithopodioides, Lotus pedunculatus, Lotus peregrinus, Lotus subbiflorus and Ornithopus sativus. The four strains from B. pelecinus did not nodulate Amorpha fruticosa, Astragalus sinicus, Cicer arietinum, Hedysarum spinosissimum, Lotus parviflorus, Macroptilium atropurpureum or Trifolium lupinaster. M. loti strain SU343 nodulated all four genotypes of B. pelecinus. However, M. loti strain CC829 only nodulated B. pelecinus genotypes 93ITA33 and IFBI1 and the nodules were ineffective. The root nodule isolates from H. spinosissimum (E13 and H4) nodulated B. pelecinus cv. Casbah whereas the commercial inoculant strain for Cicer (CC1192) could not nodulate any genotype of B. pelecinus. These results indicate that strains WSM1271, WSM1283 and WSM1497 isolated originally from B. pelecinus have a specific host range while strain WSM1284 is promiscuous in its capacity to nodulate with a broad range of related species. As B. pelecinus can be nodulated by Mesorhizobium spp. from other agricultural legumes, particularly Lotus, there is an opportunity to utilise this trait in cultivar development.

Presence of different arbuscular mycorrhizal infection patterns in roots of Lotus glaber plants growing in the Salado River basin.

Morphological types of arbuscular mycorrhizal (AM) fungi associated with Lotus glaber in sodic soils of the Salado River basin were studied. At least eight colonization patterns (IP) of AM fungi in roots of L. glaber were observed after 30 plants were analyzed. Arum- and Paris-type infection were found in the same plant species. This result supports the idea that AM morphology is not solely under plant control, but is also influenced by fungal identity. One infection pattern, presumably corresponding to Glomus intraradices, and a second, possibly assignable to Glomus tenue, were the most commonly found. Our results reinforce previous suggestions that G. intraradices is well adapted to sodic-saline conditions and may play a role in the resistance of L. glaber to these soils.

Do polyamines modulate the Lotus glaber NADPH oxidation activity induced by the herbicide methyl viologen?

In recent years, there has been a growing interest in NADPH-oxidases which are involved in the active generation of reactive oxygen species (ROS), owing to their role in oxidative burst, signalling and oxidative damage derived from biotic and abiotic stresses. NADPH oxidase activity is enhanced by some environmental cues, such as zinc deficiency and chilling stress, where zinc and polyamines have been suggested to be involved in the modulation of ROS generation. In order to further characterise NADPH oxidation activity during oxidative stress we exposed Lotus glaber Mill. (narrow-leaf trefoil; syn. L. tenuis Waldst. et Kit. ex Wild var. Miller) plants to the herbicide methyl viologen (MV) and evaluated zinc and polyamines as oxidative stress regulatory compounds. For this purpose we conducted in vitro and in vivo experiments, observing that zinc and the higher polyamines spermidine and spermine inhibited the NADPH oxidation activity in vitro while preventing methyl viologen-induced superoxide production in vivo. It is suggested that these substances act through a direct effect on flavin oxidases. However, it was not possible to correlate free polyamine content of L. glaber with their hypothetical inhibitory role during oxidative stress, probably owing to the plant's natural tolerance to the herbicide tested. Therefore, tobacco, a more sensitive species, was tested for methyl viologen toxicity. High concentrations of methyl viologen induced free polyamine levels in crude extracts and intercellular fluids. However, only free polyamine content in the intercellular fluids was increased in plants treated with low methyl viologen concentrations. These results support the notion that polyamine metabolism in the apoplast is involved in the physiological response to oxidative stress.

Environmental factors during seed development of narrow‐leaved bird's‐foot‐trefoil (Lotus tenuis) influences subsequent dormancy and germination

AbstractNarrow‐leaved bird's‐foot‐trefoil (Lotus tenuis) is a perennial forage legume adapted to waterlogged and heavy and infertile soils and can replace alfalfa (Medicago sativa) in areas with these soils in Argentina. Its seeds are hard and water‐impermeable but the effects of environmental factors on seed dormancy and germination are not known. The objective was to evaluate the hypothesis that water availability during seed development and maturation affects the degree of hardseededness in L. tenuis by changing seed coat properties, conditioning water uptake through the seed coat; and subsequently affecting dormancy, germination and speed of germination. Seeds were harvested in December/January and in February in both 1993/1994 and 1994/1995 from a permanent pasture of L. tenuis growing in a Hapludol soil in San Miguel del Monte province of Buenos Aires. Environmental conditions of each anthesis‐harvest period were determined. Seeds of each harvest were subjected to chilling, washing and mechanical scarification. After 12 months seeds from each harvest were observed in a scanning electron microscope. The water deficit of the soil and relative humidity were greater in the second than the first anthesis‐harvest period in both seasons. In 1993/1994 the control treatment in December had a higher germination rate than the February control seeds (0·40 vs. 0·20) and a faster germination rate. Mechanical scarification and chilling significantly enhanced the germination rate (0·95) and its speed in seeds of both harvests. Low temperatures significantly enhanced germination rate, starting after 60 d for the seeds harvested in December, and 90 d for the seeds harvested in February. In 1994/1995 the results were similar but both the January and February control treatments had higher germination rates (0·60 vs. 0·40) than in the previous year. Seeds harvested in February were more dormant in both years. These differences could be explained by the conditions in February anthesis‐harvest period in both years that could have hastened the natural dehydration process of seed, changing integument structure and enhancing its impermeability.

Morphological Comparison of Progeny Derived from 4x‐2x and 4x‐4x Hybridizations of Lotus glaber Mill. and L. corniculatus L

Unreduced gametes (2n gametes) from Lotus glaber Mill. (2n = 2x = 12) may aid intercrossing with L. corniculatus L. (2n = 4x = 24) to produce progeny with a greater heterotic advantage than progeny derived from colchicine‐induced {7‐acetamido‐6,7‐dihydro‐1,2,3,10‐tetramethoxybenzo[a]heptalen‐9(5H)‐one} tetraploid (4x) L. glaber The objective of this research was to compare progeny produced from 4x with 2x (4x‐2x) and 4x with 4x (4x‐4x) crosses and determine if 2n gametes had a heterotic advantage over normal gametes derived from colchicine‐induced tetraploids. Vegetative cuttings of the 2n‐gamete‐producing L. glaber genotype 204882‐1 (2x 204882‐1) were treated with colchicine and successfully yielded an autotetraploid (2n = 4x = 24) of 204882‐1 (4x 204882‐1). Three randomly chosen genotypes from the L. corniculatus germplasm MU‐81 were used as maternal parents in crosses to 2x 204882‐1 and 4x 204882‐1. Progeny produced from 4x‐2x crosses were intermediate to or larger than their parents in their leaf and flower morphology. Progeny from 4x‐4x crosses were intermediate to or smaller than their parents in leaf and flower size. Size of leaves and flowers of progeny from 4x‐2x crosses were similar to or larger than 4x‐4x progeny. Morphological comparisons demonstrated that heterotic expression of progeny from 4x‐2x crosses was greater than progeny from 4x‐4x crosses. The results indicate that the generation of interspecific L. corniculatus × L. glaber hybrids via 2n pollen to be effective, but a means of exploiting any heterotic advantage in these cross‐pollinated species needs to be identified.

Biomass accumulation and potential nutritive value of some forages irrigated with saline-sodic drainage water

A controlled study using a sand-tank system was conducted to evaluate 10 forage species (bermudagrass, ‘Salado’ and ‘SW 9720’ alfalfa, ‘Duncan’ and ‘Polo’ Paspalum, ‘big’ and ‘narrow leaf’ trefoil, kikuyugrass, Jose tall wheatgrass, and alkali sacaton). Forages were irrigated with sodium-sulfate dominated synthetic drainage waters with an electrical conductivity of either 15 or 25 dS/m. Forage yield was significantly reduced by the higher (25 dS/m) salinity level of irrigation water compared to the lower (15 dS/m) level. There was wide variation in the sensitivity of forage species to levels of salinity in irrigation water as reflected by biomass accumulation. With the exception of bermudagrass, which increased accumulation at the higher level of salinity, and big trefoil, which failed to establish at the higher level of salinity, ranking of forages according to the percent reduction in biomass accumulation due to the higher level of salinity of irrigation water was: Salado alfalfa (54%) = SW 9720 alfalfa (52%) > Duncan Paspalum (41%) > narrow leaf trefoil (30%) > alkali sacaton (24%) > Polo Paspalum (16%) > Jose tall wheatgrass (11%) = kikuyugrass (11%). Bermudagrass and Duncan Paspalum were judged to be the best species in terms of forage yield and nutritive quality. Kikuyugrass, which had the third highest biomass accumulation, was judged to be unacceptable due to its poor nutritional quality. Although narrow leaf trefoil had a relatively high nutritional quality, its biomass accumulation potential was judged to be unacceptably low. Alfalfa cultivar’s biomass accumulations were the most sensitive to the higher level of salinity, among forages that survived at the higher salinity level, although actual accumulations at the higher salinity were high relative to other forages. Increased salinity influenced several forage quality parameters, including organic matter (OM), crude protein (CP), neutral detergent fibre (NDF), and in vitro gas production, generally leading to higher nutritional quality at the higher salinity level, although their significance varied amongst species and cuttings.

Phosphorus Utilization Efficiency in Populations of Narrow-Leaf Birdsfoot Trefoil

The widespread distribution of the pasture legume Lotus glaber Mill. throughout the Flooding Pampa in Argentina may be attributed to ecotypic differentiation among populations. In order to confirm such genetic variation, two morphologically distinct populations from contrasting soil types, particularly in the phosphorus (P) status, were compared in their response to a different P supply. Plants were cloned by stem cuttings and transplanted to a common soil fertilized with increasing amounts of P. Morphological characters including number of shoots, leaf length and width, as well as the leaf length/width ratio, remained different in spite of P supply. Biomass P content, tissue P concentration and the percentage of root length infected by mycorrhizae associated with P uptake, were similar between populations. However, both populations showed a different growth response to P fertilization in spite of being cultivated on the same soil. Consequently, they differed in the efficiency of P utilization (E), which is probably under genetic control. These results produce evidence in support of the existence of ecotypes for L. glaber adapted to local soil conditions.

Fire‐induced colonization of a Flooding Pampa grassland by thistles: Remnant litter and interference effects

Abstract. Winter and spring burnings constitute a traditional management practice of the Flooding Pampa grasslands which are dominated by the tussock grass Paspalum quadrifarium. In addition to increasing the primary productivity and the nutrient quality of the regrowth, this burning favours the establishment of opportunistic species, especially the legume Lotus glaber and the thistles Cirsium vulgare and Carduus acanthoides. The aims of the present study were to assess the effects of burning and those of the remnant litter on L. glaber and thistle recruitment, as well as the effects of L. glaber density on the emergence, survival and flowering of thistles. Two field experiments were carried out: 1. A completely randomized factorial design with occurrence of L. glaber and fire was applied in a mature Paspalum stand; 2. A completely randomized design with four L. glaber seed densities oversown on a burned Paspalum stand, as the treatments. Thistle and L. glaber recruitment within the Paspalum stand was dependent on fire, but their emergence in burnt plots was reduced by the presence of remnant litter. Remnant litter and interference from L. glaber provide complementary mechanisms to reduce fire‐cued colonization by thistles. While seedling emergence of thistles was mostly affected by the presence of remnant litter, seedling survival depended on local density of L. glaber. By the end of the first post‐fire growing season, the survivorship of established thistles was linearly reduced with increasing sowing density and above‐ground biomass of L. glaber. The maintenance of a significant litter coverage and a high density of L. glaber in the pre‐fire seed bank, as well as the oversowing of L. glaber after fire, may be useful tools in fire management of Paspalum stands aimed to improve their forage value with reduced dependence on chemical control of weeds.

Growth of Three Forage Species in Saline Conditions

Extensive areas of salt deposits are rendering agricultural soils in arid regions unsuitable for arable cropping. Identifying native plant species to grow in salt-affected soils or to grow with saline water may sustain productivity of salt affected lands. The objective of this greenhouse study was to compare biomass production and ion accumulation (i.e., Ca 2+ , Mg 2+ , Na + , and Cl m ) in potential salt tolerant forage species grown under simulated saline conditions found near La Junta region in southeast Colorado, USA. Seed-derived plants of tall fescue (Festucaarundinacea), narrowleafed birdsfoot trefoil (Lotus glaber), and broadleafed birdsfoot trefoil (Lotus corniculatus) were grown in pots filled with soil collected from nonsaline and saline areas near La Junta. Pots were irrigated with one of three qualities of water differing in EC: 0.13, 0.27, and 0.64 S m m 1 . For all treatments, F.arundinacea produced almost twice as much dry matter (DM) as L. glaber and L.corniculatus. Soil/water quality treatments appeared to have minimal effect on the DM yield of all species in 319 d, although DM yield appeared to be stimulated in L. glaber by either saline water or when grown in saline soil. Herbage Ca 2+ concentrations in all plants were higher when grown in nonsaline soil and decreased as water quality decreased. Herbage Mg 2+ concentrations were not affected by soil or water quality treatments. In contrast, herbage Na + and Cl m concentrations increased in all three species grown in either saline soils or irrigated with saline water. Soil EC increased at harvest for all plant species irrigated with saline water in both saline and nonsaline soils. Based on the growth responses observed for the three forage species under saline conditions, they all appear to be capable of growing in the salt-affected conditions of the La Junta region. Salt management practices will eventually be necessary to sustain productivity.

Fire-induced colonization of a Flooding Pampa grassland by thistles: Remnant litter and interference effects

Winter and spring burnings constitute a traditional management practice of the Flooding Pampa grasslands which are dominated by the tussock grass Paspalum quadrifarium. In addition to increasing the primary productivity and the nutrient quality of the regrowth, this burning favours the establishment of opportunistic species, especially the legume Lotus glaber and the thistles Cirsium vulgare and Carduus acanthoides. The aims of the present study were to assess the effects of burning and those of the remnant litter on L. glaber and thistle recruitment, as well as the effects of L. glaber density on the emergence, survival and flowering of thistles. Two field experiments were carried out: 1. A completely randomized factorial design with occurrence of L. glaber and fire was applied in a mature Paspalum stand; 2. A completely randomized design with four L. glaber seed densities oversown on a burned Paspalum stand, as the treatments. Thistle and L. glaber recruitment within the Paspalum stand was dependent on fire, but their emergence in burnt plots was reduced by the presence of remnant litter. Remnant litter and interference from L. glaber provide complementary mechanisms to reduce fire-cued colonization by thistles. While seedling emergence of thistles was mostly affected by the presence of remnant litter, seedling survival depended on local density of L. glaber. By the end of the first post-fire growing season, the survivorship of established thistles was linearly reduced with increasing sowing density and above-ground biomass of L. glaber. The maintenance of a significant litter coverage and a high density of L. glaber in the pre-fire seed bank, as well as the oversowing of L. glaber after fire, may be useful tools in fire management of Paspalum stands aimed to improve their forage value with reduced dependence on chemical control of weeds.

Seasonal Variations in Condensed Tannin Concentration of Three Lotus Species

Condensed tannins (CTs) are commonly found in herbage of Lotus spp. and can have beneficial or detrimental effects on feed value and animal performance. Our objectives were to (i) determine the level of CT concentration and its seasonal variations in three widely grown Lotus spp.; (ii) assess the distribution of CTs in leaves, stems, and flowers; and (iii) determine if herbage of greenhouse‐grown Lotus spp. contains CT concentrations with equivalent rank to field‐grown plants. Field herbage samples were taken in spring, summer, and fall and analyzed for CTs by near infrared reflectance spectroscopy (NIRS). Herbage of big trefoil (L. uliginosus Schkur.) germplasm ARS‐1221 and narrowleaf trefoil (L. glaber Mill.) germplasm ARS‐1207 had the greatest and lowest CT concentrations averaging 154 and 8 g catechin equivalent (CE) kg−1 dry matter (DM), respectively. The birdsfoot trefoil (L. corniculatus L.) cultivar ARS‐2620 had a greater CT concentration than ‘Norcen’, but both had moderate CT levels averaging 39 and 23 g CE kg−1 DM, respectively. Herbage CT concentration of Norcen, ARS‐2620, and ARS‐1221 was higher in spring and summer compared with fall while that of ARS‐1207 was low in spring, summer, and fall. Generally, stems had less CT than leaves and flowers, but there was no detectable CTs in stems of ARS‐1207. The rankings of the four entries for herbage CT concentration in the greenhouse and field were the same. This is the first report of CT concentrations for the germplasms ARS‐1221 and ARS‐1207, which are suitable candidates for genetic improvement to develop cultivars with desirable CT levels.