Mobilization of minerals and moisture loss during senescence of the energy crops Miscanthus×giganteus,Arundo donax and Phalaris arundinacea in Wales,UK

Miscanthus×giganteus, Arundo donax and Phalaris arundinacea were planted at three sites in Wales, UK, to study the timing of mineral and moisture decline during autumn and winter. The mineral and moisture content at several harvest dates throughout the period were compared with power station threshold levels. All crops showed a highly significant decrease in moisture content in all years with the exception of Arundo which did not lose moisture in the final year. The Miscanthus and Arundo crops remained above the moisture content threshold in all years and would require further drying before combustion. The Phalaris fell below the moisture threshold in January. The Miscanthus leaves fell below the nitrogen threshold before leaf abscission at one site but not at another, although the cane remained mostly within the guideline range. Both its leaves and cane remained above the potassium threshold level. Its leaf sulphur fell within acceptable levels during November and its cane remained below the lowest threshold from November onwards. The Arundo leaves remained above the nitrogen, potassium and sulphur thresholds throughout the period and it did not lose its leaves. The cane nitrogen increased above the threshold during autumn whereas its potassium remained higher than its threshold, with the exception of one sampling date at one site. Its sulphur remained within the guidelines. The Phalaris crop fell to within nitrogen guidelines at one site but increased at the other. Its potassium decreased to below the threshold at both sites in January, and its sulphur content was consistently within the guidelines.     

Chromosome doubling of the bioenergy crop,Miscanthus×giganteus

The perennial grass, Miscanthus×giganteus is a sterile triploid, which due to its growth rate and biomass accumulation has significant economic potential as a new bioenergy crop. The sterility associated with the triploid genome of this accession requires labor‐intensive vegetative, instead of seed propagation for potential commercial production. Chromosome doubling was used to produce hexaploid plants in an effort to restore fertility to M×giganteus. Tissue culture derived calli from immature inflorescences were treated with the antimitotic agents, colchicine and oryzalin in liquid and solid media. Calli survival rate decreased with increasing concentrations and durations of colchicine or oryzalin treatments and ranged from 0% to 100%. Nuclear DNA content, as determined by flow cytometry, indicated that the frequency of chromosome‐doubled calli varied between compounds and concentrations with the greatest proportion of callus doubling observed using 2‐day treatments of 15 μm oryzalin (78%) or 939 μm colchicine (67%). Liquid media treatments were more effective than solid gels for chromosome doubling. Although oryzalin was effective at chromosome doubling, it inhibited callus growth and plant regeneration frequency. Seven hexaploid plants with doubled DNA content were generated, which displayed increased stomata size (30.0±0.2 μm) compared with regenerated triploid M. ×giganteus plants (24.3±1.0 μm). Following clonal replication these plants will be evaluated for growth rate, biomass accumulation, and pollen viability. Successful chromosome doubling and plant regeneration of M.×giganteus suggests that ploidy manipulation of this plant and its parental species (Miscanthus sinensis and Miscanthus sacchariflorus) could be a means to access genetic variability for the improvement of Miscanthus as a biofuel/bioenergy crop.     

Synthetic polyploid production of Miscanthus sacchariflorus,Miscanthus sinensis,and Miscanthus x giganteus

Plants from the genus Miscanthus are potential renewable sources of lignocellulosic biomass for energy production. A potential strategy for Miscanthus crop improvement involves interspecific manipulation of ploidy levels to generate superior germplasm and to circumvent reproductive barriers for the introduction of new genetic variation into core germplasm. Synthetic autotetraploid lines of Miscanthus sacchariflorus and Miscanthus sinensis, and autoallohexaploid Miscanthus x giganteus were produced in tissue culture from oryzalin treatments to seed‐ and immature inflorescence‐derived callus lines. This is the first report of the genome doubling of diploid M. sacchariflorus. Genome doubling of diploid M. sinensis, M. sacchariflorus, and triploid M. x giganteus to generate tetraploid and hexaploid lines was confirmed by stomata size, nuclear DNA content, and chromosome counts. A putative pentaploid line was also identified among the M. x giganteus synthetic polyploid lines by nuclear DNA content and chromosome counts. Comparisons of phenotypic performance of synthetic polyploid lines with their diploid and triploid progenitors in the greenhouse found species‐specific differences in plant tiller number, height, and flowering time among the doubled lines. Stem diameter tended to increase after polyploidization but there were no significant improvements in biomass traits. Under field conditions, M. x giganteus synthetic hexaploid lines showed greater phenotypic variation, in terms of plant height, stem diameter, and tiller number, than their progenitor lines. Production of synthetic autopolyploid lines displaying significant phenotypic variation suggests that ploidy manipulation can introduce useful genetic diversity in the limited Miscanthus germplasm currently available in the United States. The role of polyploidization in the evolution and breeding of the genus Miscanthus is discussed.     

Effects of an organic sediment on performance of young Phragmites australis clones at different water depth treatments

Performance of young Phragmites australis plants was examined after 7 weeks on an artificial nutrient-enriched inorganic substrate and on the same substrate to which an organic sediment from a eutrophic lake was added, at three different water depth treatments. Growth decreased, and proportional allocation of biomass to roots increased, with the addition of sediment. These differences were significant in shallow and deep water, but not at a medium depth. Concentrations of phosphorus and nitrogen in plant biomass decreased, and concentration of iron increased, with addition of sediment.The effects of sediment addition may have resulted from a decreased availability of nutrients in the substrate or from an impaired root functioning. Nutrient exhaustion in the substrate, due to a fast plant growth, can explain the relatively strong effects in shallow water. Deep water, on the other hand, probably restricted oxygen transport to the roots, resulting in an impaired root functioning in the low-redox sediment environment. The results show that, especially in relatively deep water, growth of undisturbed plants of P. australis may be inhibited by eutrophication of sediments, probably because of an impaired root functioning in sediments containing reduced toxic compounds (e.g. ferrous iron).     

Potassium phosphite affects growth,antioxidant enzymes activity and alleviates disease damage in cucumber plants inoculated with Pythium ultimum

In the present study, the impact of potassium phosphite on response of cucumber plants inoculated with Pythium ultimum var. ultimum was assessed. Variations in the accumulation of both antioxidant enzymes and growth parameters were investigated. The results revealed that fresh and dry weights of shoot and root exhibited up to 2 fold increase in potassium phosphite-treated plants. The concentrations of peroxidase, superoxide dismutase and catalase were significantly higher in the plants treated with 4 g L^?1 of potassium phosphite compared to other treatments, at 48 h after inoculation. It was demonstrated that both 2 and 4 g L^?1 treatments could alleviate the disease damage to a high extent, while control plants were severely damaged by the pathogen. The results of this study suggest that the increased induction of antioxidant enzymes (2.2, 2.8 and 4 fold increase for superoxide dismutase, catalase and peroxidase, respectively) might have alleviated damping-off symptoms leading to increased plant growth and yield.     

Contribution of nitrogen fixation to first year Miscanthus × giganteus

Many characteristics make Miscanthus × giganteus an appealing bioenergy feedstock in temperate North America, but the degree to which this plant species interacts with nitrogen‐fixing bacteria remains understudied. Demonstration of associative nitrogen fixation in Miscanthus would support management with minimal fertilizer inputs that is demanded of long‐term biofuel sustainability. As a first step, we investigate the role of biological nitrogen fixation in nutrition of immature Miscanthus and temporal dynamics of plant‐associated nitrogen fixers. The contribution of biological nitrogen fixation to plant nitrogen acquisition in first year Miscanthus × giganteus was estimated using a yield‐dependent ¹⁵N isotope dilution model. Temporal changes in plant‐associated diazotroph relative abundance and community composition were analyzed with quantitative PCR and terminal restriction fragment length polymorphism of the nifH gene in rhizome and rhizosphere DNA extracts. We estimate 16% of new plant nitrogen was derived by nitrogen fixation during the growing season, despite non‐limiting soil nitrogen. Diazotroph communities from rhizome and rhizosphere changed with plant development and endophytic nitrogen fixers had significantly higher relative abundance and altered community composition at sampling dates in July and August. This study provides evidence for a small, but measurable, benefit of associative nitrogen fixation to first year Miscanthus × giganteus that underscores the potential and need for selection of breeding lines that maximize this trait.     

Mutual shading as a factor limiting the yield response of rice to application of nitrogen,phosphorus and potassium fertilizers

Summary The differences in fertilizer responses between rice plants grown under pot and field conditions were discussed.Under pot conditions, the rice plant responded more strongly to nitrogen applications at high phosphorus and high potassium levels than at low levels of these elements. This suggests that the balance of nitrogen, phosphorus, and potassium is an important factor in fertilizer application.Under field population conditions, however, mutual shading among plants limits grain yield. A big leaf area above a certain limit is associated with decreased grain yield. The response to nitrogen may be negative, and may not be changed even with the application of potassium and phosphorus.     

Community-level consequences of invasion: impacts of exotic clonal plants on riparian vegetation

Biological invasions by exotic species are occurring at exceptional rates and spatial scales worldwide and are increasingly recognized as key forms of global environmental change. Despite this growing prominence, surprisingly few ecological studies have quantified the impacts of exotic taxa on the plant communities they invade, and this is especially evident in riparian ecosystems. Along the Russian River in northern California, we used both comparative and experimental studies to investigate the influence of two exotic clonal plant species—giant reed (Arundo donax) and blue periwinkle (Vinca major)—on the composition of riparian plant communities. Our results indicate that Arundo invasion was associated with significantly lower richness of native perennial plant species on stream banks and floodplains, whereas there was no relationship on gravel bars. Additional research showed that plots invaded by Arundo and Vinca, both individually and collectively, exhibited significantly lower native and exotic species richness and abundance of both established plants and seedlings than uninvaded plots. Finally, after 2 years, experimental reductions of Arundo biomass via cutting and herbicide resulted in significantly increased native plant species richness and abundances of both established plants and seedlings, while having no effects on other exotics. In summary, our results indicate that Arundo and Vinca have strongly negative effects on diverse components of a riparian plant community, which must be addressed via effective control and restoration efforts.     

INFLUENCE OF SUPPLEMENTAL INORGANIC NUTRIENTS ON GROWTH,SURVIVORSHIP, AND MYCORRHIZAL RELATIONSHIPS OF SCHIZACHYRIUM SCOPARIUM (POACEAE) GROWN IN FUMIGATED AND UNFUMIGATED SOIL

Little bluestem grass Schizachyrium scoparium ([Michx.] Nash) plants were grown under field conditions for 2 years in soils fumigated with methyl bromide and chloropicrin, or in unfumigated soil, and treated with supplemental inorganic nutrients (bases calcium and magnesium) phosphorus, nitrogen, and potassium. Most differences in measured plant responses were due to interactions between fumigation and nutrient treatments. These included biomass production, root mass per unit length (μg/cm), root lengths, flowering culm production, percent colonization, colonized root length, and spore production in rhizosphere soil. Plants generally responded to mycorrhizal fungal colonization by reducing total root length and producing thicker roots. Treatment of plants with bases appeared to profoundly affect the mycorrhizal association by reducing sporulation of vesicular-arbuscular mycorrhizal fungi and increasing colonization. When fumigated or unfumigated soils were considered separately, base-treated plants produced more biomass than other treatments. Base-treated plants grown on unfumigated soil had more flowering culms and longer colonized root lengths than all other plants. Percent colonization by mycorrhizal fungi and colonized root length were positively correlated with phosphorus/nitrogen ratios, but the ratio was not correlated with plant biomass production. This suggests that phosphorus is not a limiting nutrient in our soil and investment in a mycorrhizal association may not result in enhanced plant growth. The base-nutrient effects may indicate a need to reevaluate earlier studies of macro nutrient effects that did not take into account the role played by calcium and magnesium in assessing fungus-host plant interactions.     

Invasive riparian plant litter alters aquatic insect growth

In a laboratory study, we examined growth and survival of the caddisfly, Lepidostoma unicolor, feeding on two types of native leaf litter (Alnus rhombifolia [Alder] and a Salicaceae mix [Salix spp. and Populus fremontii]) and two invasive, non-native species (Tamarix ramosissima [saltcedar] and Arundo donax [giant reed]). Larval survival was high (>85%), and did not differ, among those fed Alnus, Salicaceae, or Tamarix litter, but was much lower (20%) for larvae fed Arundo litter. Mean dry biomass of larvae fed Tamarix was 45% greater than that of larvae fed Alnus, and both were significantly greater than the biomasses of insects fed Salicaceae or Arundo. Although both Alnus and Tamarix increased in percent nitrogen with conditioning, Alnus had a significantly higher nitrogen content (4.9 and 3.6%, respectively). Final C : N-values for Alnus and Tamarix were below 18, while C : N for Arundo and Salicaceae were 56 and 44, respectively. Greater growth of larvae fed Tamarix is likely due to the high nutritive value of the conditioned litter, whereas conditioning of Arundo litter did not result in improved nutritive values. Larvae in the Alnus and Salicaceae treatments fed on the entire surface of the leaves until only the skeletons remained. In contrast, larvae in the Arundo treatments focused feeding activity along the margins and the torn portions of the blades. The low nutritional quality of Arundo and the high quality, but ephemeral nature of Tamarix litter potentially have negative effects on stream invertebrate production owing to the quality and duration of availability of leaf litter, as compared with native riparian vegetation.     

Plant growth stage effects on the feeding and growth responses of the bertha armyworm,Mamestra configurata to canola and mustard foliage

Mamestra configurata (Walker) (Lep., Noctuidae) larvae were fed excisedBrassica juncea (commercial brown mustard) orB. rapa cv. Tobin (Canola) foliage of three plant growth stages-rosette (stage 2), stem elongation (stage 3) and flowering (stage 4). Relative consumption rates (RCRi) were not significantly different between the plant species. Within theB. juncea treatments, there were no significant growth stage differences in RCRi. However, withinB. rapa, RCRi increased with advancing plant growth stage. Larvae fedB. juncea foliage had significantly reduced relative growth rates (RGRi) compared to larvae fedB. rapa foliage. Within theB. juncea treatments, RGRi decreased with advancing plant growth stage. There were no significant growth stage differences in RGRi in theB. rapa treatments. RGRi was inversely proportional to the levels of isothiocyanate-releasing glucosinolates in theB. juncea treatments. RCRi was inversely proportional to the levels of indolyl glucosinolates in theB. rapa treatments. Levels of total phenols and catechols inB. juncea did not show any trend which could be related to growth stage effects in the insect nutritional indices. InB. rapa, levels of phenols and catechols in stage 3 and 4 foliage were lower than that of stage 2 foliage. Analyses of total nitrogen in field-grown plants showed reductions in percent nitrogen from rosette to flowering stage foliage. The response ofM. configurata to different growth stages of its host plants are discussed in relation to changing levels of allelochemicals and nitrogen.     

Partitioning of nitrogen from biological fixation and fertilizer in Phaseolus vulgaris

Nitrogen uptake, distribution and remobilization in the vegetative and reproductive parts of the plant were studied in bean (Phaseolus vulgaris L.) cultivars Negro Argel and Rio Tibagi inoculated with either Rhizobium strain C05 or 127 K-17. Greenhouse grown plants were supplied with 2.5 mg N (plant)⁻¹ day⁻¹ as KNO₃ or K¹⁵NO₃ and the relative contribution to total plant nitrogen of mineral and symbiotically fixed nitrogen was determined. Control plants included those entirely dependent on fixed nitrogen as well as uninoculated plants supplied with 10 mg N (plant)⁻¹ day⁻¹. No differences were observed between inoculated treatments in total nitrate reductase activity and in the amount of mineral nitrogen absorbed, but there were considerable differences in the contribution of fixed nitrogen. Nitrogen fixation supplied from 58 to 72% of the total nitrogen assimilated during the bean growth cycle and the symbiotic combinations fixed most of their nitrogen (66 to 78% of total nitrogen) after flowering. Maximum uptake of mineral nitrogen was in the 15-day-period between flowering and mid-podfill (47 to 58% of total mineral nitrogen). Nitrogen partitioning varied with Rhizobium strains, and inoculation with strain C05 increased the nitrogen harvest index of both cultivars. Applied mineral nitrogen had a variable effect and in cv. Negro Argel was more beneficial to vegetative growth, resulting in smaller nitrogen harvest indices. Seed yield was not increased by heavy nitrogen fertilization. In contrast, cv. Rio Tibagi always benefited from nitrogen applications. Among the various nitrogen sources supplying the grain, the most important one was the fixed nitrogen translocated directly from nodules or after a rapid transfer through leaves, representing from 60 to 64% of the total nitrogen incorporated into the seeds.     

Comparative Growth,Biomass Production and Fuel Properties Among Different Perennial Plants,Bamboo and <Emphasis Type="Italic">Miscanthus</Emphasis>

Bamboo and Miscanthus species are perennial low-input plants that are excellent candidates for bioenergy feedstock production. Biological characteristics, dry matter yields and fuel properties of the bamboo and Miscanthus have been studied. Genotype growth characteristics were determined by measurements of plant height, tillering, tuft diameter, and shoot diameter. To date, comparisons of biomass yields of bamboo and Miscanthus have not been previously reported in the literature. Bamboo and Miscanthus species were collected and previous articles describing the productivity of bamboo and Miscanthus were examined. Genotypes differed in plant height, tillering, tuft diameter, and shoot diameter. Nitrogen, temperature, water and plant density have effects on mature stands biomass production, which ranged from 5.9 to 49.5 tonnes/ha/yr for bamboo and 3.2 to 49.0 tonnes/ha/yr for Miscanthus. With such biomass yields, bamboo and Miscanthus should be considered as two very promising plants for biomass production in Zhejiang, China in the near future.     

水分对敦煌阳关湿地芦苇叶片与土壤C、N、P生态化学计量特征的影响

土壤水分是影响干旱区植物养分吸收和利用策略的关键因子之一。研究不同水分梯度叶片与土壤生态化学计量特征,有助于揭示植物对环境变化的响应特征及生态适应性。通过野外调查与实验分析,对敦煌阳关不同水分梯度芦苇叶片与土壤碳(C)、氮(N)、磷(P)生态化学计量特征及其关系进行了研究。结果表明:(1)随土壤含水率升高,叶片C、N、P含量降低,叶片C/N、C/P、N/P升高。(2)随土壤含水率升高,土壤有机碳(OC)、总氮(TN)、总磷(TP)含量及土壤N/P升高,土壤C/N降低,土壤C/P先升后降。(3)低水分梯度叶片N、C/N与土壤N、C/N显著负相关(P0.05),叶片C、P、C/P、N/P与土壤C、P、C/P、N/P无显著相关性(P0.05);高、中水分梯度叶片C、N、P与土壤C、N、P化学计量特征相关性均不显著(P0.05)。低水分梯度叶片受干旱胁迫和土壤养分制约,且能够保持较高的叶养分含量,体现了干旱区湿地植物异质生境下独特的养分调节机制。     

The Effect of Reduced Light Intensity and Sub-optimal Potassium Supply on N2 Fixation and N Turnover in Rhizobium Infected Lucerne

The effect of low light intensity and suboptimal potassium supply on the fixation of molecular nitrogen by root nodules and the nitrogen turnover in the host plant was studied in Medicago sativa using ¹⁵N labelled molecular nitrogen. For the application of ¹⁵N₂ labelled gas a special box was used. Both low light intensity and a low potassium supply resulted in a substantial growth depression. In particular the protein content of tops, roots and nodules was lower in the plants of the low light intensity treatment as compared with the control plants. Decreasing potassium supply had a similar but less-pronounced effect on protein content. The low protein content was not a consequence of a lack of soluble amino nitrogen or NH₃, since these fractions were influenced to a lesser degree by the reduced light intensity and by the low potassium supply. This observation is supported by the data obtained with ¹⁵N. N₂ fixation and NH₃ assimilation were affected by both low light intensity and low K application to the same degree as the overall metabolism, thus showing no particular response to the treatments applied.     

Effects of salinity and gibberellin on water content,growth and mineral composition of cowpea,calabrese and red radish plants

Salinity had generally little influence on the water content of different parts of cowpea(Vigna sinensis L.), calabrese(Brassica oleracea L. var.botrylis) and red radish(Raphanus salivus L.) plants. Salinity showed a promotive effect on the growth of cowpea, while in calabrese the effect was either promotive or depressive depending upon the concentration of the NaCl, and in red radish plants salinity progressively suppressed growth. Total nitrogen, phosphorus, potassium and sodium contents of cowpea leaves were not affected by salinity treatments, while in calabrese and red radish leaves the contents of N, P and K were generally decreased as the salinity level increased. Gibberellin (GA₃) applied to salt-treated plants had either a stimulatory or inhibitory effect on the growth, water content and contents of N, P, K and Na in the leaves depending upon the plant type, the concentration of GA₃ and level of salinity.     

Plant‐mediated effects of soil nitrogen enrichment on a chemically defended specialist herbivore,Calophasia lunula

1. Nitrogen enrichment is an important driver of environmental change. In the present study, plant‐mediated effects of increased nitrogen on a specialist herbivore, Calophasia lunula Hufnagel, which sequesters antirrhinoside, an iridoid glycoside produced by its host plants, were examined. 2. Caterpillars were reared on Linaria dalmatica plants grown under low or high N treatments, and C. lunula performance traits and antirrhinoside levels were measured. Additionally, a bioassay was conducted with predatory ants to examine their response to antirrhinoside. 3. Nitrogen enrichment increased larval biomass and decreased larval antirrhinoside concentrations, but had no effect on plant iridoid glycoside concentrations or larval antirrhinoside content. Thus, differences in larval antirrhinoside concentrations were evidently a consequence of increased larval biomass. Additionally, nitrogen treatment had no effects on pupal performance or defence traits. 4. Bioassay results demonstrated a deterrent effect of antirrhinoside, but additional tests are necessary to evaluate the defensive role of this compound in insects. 5. Surprisingly, this study demonstrated little effect of a six‐fold increase in nitrogen availability on L. dalmatica iridoid glycoside concentrations or sequestration by C. lunula. Moreover, the results suggested that changes in plant primary chemistry were more important than secondary chemistry for this specialist herbivore, and that some insects may be insensitive to N enrichment.     

The effect of potassium and nitrogen on ionic relations and organic acid accumulation inPanicum maximum var.trichoglume

Summary In studies on the effect of potassium and nitrogen fertilizers on ionic relations inPanicum maximum var.trichoglume cv. Petrie (green panic) most of the non-volatile organic acids that accumulate in this species have been identified and the effect that variations in inorganic nutrition have on the relative amounts of these acids accumulated ascertained.Increasing levels of nitrogen lowered the ratio of monovalent to divalent cations in the plants and increased their total cation concentrations. A deficit of inorganic anions (C-A) that ranged from 747 to 1010 meq/kg dry weight was found in the plant tops. Much of this deficit was balanced by accumulation of oxalate, aconitate, citrate, malate, quinate and an unknown organic anion. The relative contributions that these six organic anions made towards maintenance of ionic balance was altered by changing the levels of potassium and nitrogen supplied to the plants.     

Interactive regulation of grass yield and chemical properties by defoliation,a salivary chemical,and inorganic nutrition

Summary Clones of 2 C₄ grass species, Sprobolus ioclados and S. pyramidalis, were obtained from more and less heavily grazed grasslands, respectively, in Tanzania's Serengeti National Park. Plants were grown in a factorial experiment to determine the effects of severe defoliation, nutrient limitation, and a salivary chemical (thiamine) on plant growth, nitrogen content, and non-structural carbohydrate content. The experimental design included: (1) species; (2) clipping, with plants either unclipped or clipped weekly to a height of 5 cm; (3) 0.2 ml of distilled water of 0.2 ml of 10 ppb aqueous thiamine sprayed on plants from an atomizer after clipping and identical treatments at the same time to unclipped plants; (4) phosphorus (P) at 0.2 or 1 mM; (5) nitrogen (N) at 3 or 15 mM. Clipping was the major variable affecting plant growth. Total and litter yields were reduced to half and residual plant yield was reduced to 30% of the values for unclipped plants. Clipping interacted strongly with other variables since they commonly had minor effects on clipped plants and major effects on unclipped plants. Exceptions to this generalization were generally due to better performance by S. ioclados under clipping. Compared to lower treatment levels, higher treatment levels promoted total yield of unclipped plants by 52% for N, 43% for thiamine, and 33% for P. In general, thiamine had greater effects than P but lesser effects than N. Thiamine promoted yield and modified the chemical balance of plants by promoting carbohydrate (CHO) concentrations and reducing N concentrations. N and P deficiencies promoted CHO accumulation. Clipping promoted the N of leaves and crowns and reduced the N levels in roots. Leaf blade water and N contents were positively correlated with very little scatter. The slope of the line was different for S. ioclados and S. pyramidalis. Leaf blade water and CHO contents were negatively related but there was more scatter and the species could not be distinguished. The species from more heavily grazed grasslands was conspicuously more sensitive to thiamine application. The results indicated that leaf treatment with thiamine, the only likely source of which in natural grasslands is saliva deposited by feeding herbivores, can have major effects on plant yield and metabolic balances at very low application levels. But under defoliation levels as severe as those imposed in this experiment, which reduced above ground plant biomass to a fourth of the level produced by unclipped plants, growth was so strongly limited by defoliation that neither thiamine nor inorganic nutrients affected plant yield residual from clipping. Therefore, whether chemicals such as thiamine that may be introduced onto grass foliage by grazing ungulates and other herbivores will influence the growth of grazed plants will depend upon the grazing intensity associated with the transfer.     

Preincubation of B. japonicum cells with genistein reduces the inhibitory effects of mineral nitrogen on soybean nodulation and nitrogen fixation under field conditions

Genistein is the major root produced isoflavonoid inducer of nod genes in the symbiosis between B. japonicum and soybean plants. Reduction in the isoflavonoid content of the host plants has recently been suggested as a possible explanation for the inhibition of mineral nitrogen (N) on the establishment of the symbiosis. In order to determine whether genistein addition could overcome this inhibition, we incubated B. japonicum cells (strain 532C) with genistein. Mineral N (in the form of NH₄NO₃) was applied at 0, 20 and 100 kg ha^-1. The experiments were conducted on both a sandy-loam soil and a clay-loam soil. Preincubation of B. japonicum cells with genistein increased soybean nodule number and nodule weight, especially in the low-N-containing sandy-loam soil and the low N fertilizer treatment. Plant growth and yield were less affected by genistein preincubation treatments than nitrogen assimilation. Total plant nitrogen content was increased by the two genistein preincubation treatments at the early flowering stage. At maturity, shoot and total plant nitrogen contents were increased by the 40 μM genistein preincubation treatment at the sandy-loam soil site. Total nitrogen contents were increased by the 20 μM genistein preincubation treatment only at the 0 and 20 kg ha^-1 nitrate levels in clay-loam soil. Forty μM genistein preincubation treatment increased soybean yield on the sandy-loam soil. There was no difference among treatments for 100-seed weight. The results suggest that preincubation of B. japonicum cells with genistein could improve soybean nodulation and nitrogen fixation, and at least partially overcome the inhibition of mineral nitrogen on soybean nodulation and nitrogen fixation. This revised version was published online in June 2006 with corrections to the Cover Date.