Although mineral nitrogen generally has negative effects on nodulation in legume-rhizobia symbioses, low concentrations of ammonium stimulate nodulation in some legumes. In this study, the effects of ammonium and nitrate on growth, nodulation and expression of 2 nitrogen transport and 12 putative nodulation-related genes of the model symbiosis of Medicago truncatula - Sinorhizobium meliloti are investigated. After 3 weeks of hydroponic growth, whole-plant nodulation was enhanced in all the ammonium treatments and up to three-fold in the 0.5 mM treatment compared with the zero-nitrogen control. Specific nodulation (nodules g(-1) root dry weight) was greatly stimulated in the 0.1 and 0.5 mM NH4+ treatments, to a lower extent in the 0.1 mM NO3- treatment, and inhibited in all other treatments. Expression of the 14 selected genes was observed at 0, 6, 12 and 24 h after exposure to rhizobia and nitrogen. Expression of nitrogen transporter genes increased significantly, but responses of the three genes putatively associated with symbiosis signaling/nodule initiation were mixed. There were infrequent responses of genes coding for an ABA-activated protein kinase or a gibberellin-regulated protein, but an ethylene-responsive element-binding factor showed increased expression in various treatments and sampling times. Three auxin-responsive genes and three cytokinin-responsive genes showed varied responses to ammonium and nitrate. This study indicates that low concentrations of ammonium stimulate nodulation in M. truncatula, but the data were inconclusive in verifying the hypothesis that a relatively high ratio of cytokinin to auxin in roots may be an underlying mechanism in this stimulation of nodulation.

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Sustainable production of biomass crops is important in the development of feedstocks for the production of biofuels and other bioproducts. This study investigates the use of nine beneficial soil microbes and a plant biostimulant (i.e., Ascophyllum nodosum seaweed extract) to increase the growth of two giant Miscanthus (Miscanthus × giganteus) cultivars, ‘Amuri’ and ‘Nagara’, under greenhouse conditions and in the field on poor-quality, marginal land. Greenhouse trials indicated increases in shoot dry weight (DW) in ‘Amuri’ in treatments with Gluconacetobacter diazotrophicus PAL5T LsdB++, Gluconacetobacter johannae UAP-Cf-76, and Variovorax paradoxus JM67 by 15%–24% compared with untreated controls. In ‘Nagara’, shoot DW was increased in the treatments with Penicillium bilaiae by 11% and the seaweed extract by 10%. The nutrient content of shoot tissues increased in the same treatments in which biomass was increased. Despite a lack of treatment effects on shoot DW in ‘Amuri’ in the field, several treatments increased Fe and Zn content in shoots by up to 1.9×. In ‘Nagara’ in the field, treatment with G. johannae UAP-Cf-76 and the seaweed extract resulted in increases in shoot DW by 16% and 23%, respectively, and several treatments resulted in increases in shoot Fe and Zn concentrations. The productivity enhancements in giant Miscanthus by beneficial soil microbes and the seaweed extract may be associated with increasing access to limited soil nutrients. These findings suggest that the use of beneficial soil microbes and plant biostimulants may aid in the sustainable production of giant Miscanthus on marginal lands.

The sustainability of purpose-grown biomass production on marginal lands in Canada is uncertain. In this study, an assessment of biomass yield and sustainability was performed for two poplar clones (Poplus deltoides × P. nigra, DN-34-PDN, and P. nigra × P. maximowiczii, NM-6-PNM) and two switchgrass cultivars (Panicum virgatum 'Cave-in-Rock'-SGC, and P. virgatum 'Nebraska'-SGN) on three marginal lands in Guelph (ON), Kemptville (ON), and Nappan (NS) in Canada. The differences in stem biomass across sites were not significant; however, differences in stem biomass among plants were statistically significant between poplar and switchgrass (p < 0.0001) and between poplar clones (p < 0.0001). The 2-yr stem biomass yield in PNM (15.27 ± 1.28 t ha −1 ) was significantly higher than those in PDN (7.02 ± 0.54 t ha −1 ), SGC (2.57 ± 0.28 t ha −1 ), and SGN (1.45 ± 0.22 t ha −1 ). Two sustainability indices based on macronutrients (MBSI) and nitrogen (NBSI), were developed to assess sustainability. Both indices show that the biomass production system of high-yielding poplar clone PNM depicts nutrient loss and may require external nutrient inputs via fertilization during the establishment phase. Higher index values for switchgrass SGC (1.47 ± 0.22, 1.11 ± 0.15) and SGN (1.37 ± 0.16, 1.17 ± 0.12) for MBSI and NBSI, respectively, indicate that despite low stem biomass yields, switchgrass biomass production is sustainable. These findings suggest that, from a nutrient perspective, sustainable biomass production systems can be established on marginal lands in Canada; however, there is a trade-off between high yield and long-term sustainability in purpose-grown biomass production systems.Key words: marginal lands, nutrient, poplar, sustainability, switchgrass.Résumé : On ignore dans quelle mesure la production de biomasse sur les terres marginales du Canada serait une activité durable. La présente étude évalue le rendement de la biomasse et la pérennité de deux clones de peuplier (Poplus deltoides × P. nigra, DN-34 -PDN, et P. nigra × P. maximowiczii, NM-6 -PNM) ainsi que de deux cultivars de panic raide (Panicum virgatum cv. Cave-in-Rock -SGC et Panicum virgatum cv. Nebraska -SGN) sur trois terres peu productives situées à Guelph (ON), à Kemptville (ON) et à Nappan (NS), au Canada. La biomasse des tiges n'a pas varié de façon significative aux trois endroits, cependant, l'écart entre la biomasse des peupliers et celle du panic raide est statistiquement significatif (p < 0,0001), de même que l'écart entre la biomasse des deux clones de peuplier (p < 0,0001). Le rendement en biomasse de PNM au cours des deux années de l'étude (15,27 ± 1,28 t par hectare) était sensiblement plus important que celui de PDN (7,02 ± 0,54 t par hectare), de SGC (2,57 ± 0,28 t par hectare) et de SGN (1,45 ± 0,22 t par hectare). Les auteurs ont élaboré deux indices pour évaluer la pérennité d'après la concentration de macronutriments (MBSI) et celle d'azote (NBSI). Les deux indices révèlent que la production de For personal use only.biomasse ...

N partitioning among shoots, roots, and soil in Brassica napus genotypes varying in seed oil content potential, Biocatalysis and Agricultural Biotechnology, http://dx.doi.org/ 10. 1016/j.bcab.2013.02.001 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractFour genotypes of B. napus (cultivars Topas, Sentry and Polo, and the experimental line 04C204) varying in seed oil content (SOC) potential (from 42.2% to 50.0% seed DW) were used to study C and N partitioning among shoots, roots and soil, as well as nitrogen use efficiency (NUE). Topas, with lowest SOC potential, had higher biomass accumulation in shoots and roots and higher NUE than 04C204 with the highest SOC potential. Although the absolute amounts of biomass and N accumulated in Topas were greater than in 04C204, the percentage of 13 C partitioned to shoots was lower, and the percentage of 15 N partitioned to roots was higher. These results imply that SOC may be more associated with the proportions of C and N partitioned between shoots and roots, than with absolute amounts accumulated in these organs. This study also indicates that while Topas fixed the most CO 2 , it also had the greatest nitrogen fertilizer demand, while 04C204, with the highest SOC potential, had the greatest proportion of whole plant C retained within shoots of all the genotypes. These results suggest that a breeding strategy to optimize B. napus as a biodiesel feedstock may well be selection for maximum SOC at a minimal investment in vegetative biomass (and hence a lower N fertilizer requirement).

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