Volume 1 Number 2 2007

CONTENTS AND ABSTRACTS

Anne Kasurinen, Petri A. Peltonen, Jarmo K. Holopainen, Elina Vapaavuori, Toini Holopainen (Finland) Leaf Litter Under Changing Climate: Will Increasing Levels of CO₂ and O₃ Affect Decomposition and Nutrient Cycling Processes? (pp 58-67)

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Invited Review: In this manuscript we review existing information about CO₂ and O₃ effects on leaf litter as well as discuss the potential impacts of climate change on decomposition processes and tree nutrition. So far field studies show that the average response to elevated CO₂ is increased litter production and increased litter C:N-ratios, the latter response being more prominent in deciduous than in coniferous trees. The few O₃ studies indicate that O₃ stress may decrease some nutrient concentrations, but O₃ effects on carbon-based compounds are more ambiguous. In general, field incubation studies show only some small or inconsistent CO₂- and O₃-induced changes in litter mass loss rates. On the other hand, recent long-term studies indicate that there are some CO₂ and O₃ effects on microbial functioning in the soil (e.g. CO₂ stimulates and O₃ dampens it), although the onset of these microbial responses may take years. Nonetheless, at the moment there is no consistent evidence of CO₂-induced and microbe-mediated progressive nitrogen limitation in temperate forests. Elevated O₃ effects on nutrient cycling are far less studied, and also more information about long-term CO₂ and O₃ effects on decomposition and nutrient cycling in boreal forests is still needed. Furthermore, some results indicate that the combined effects cannot be predicted on the basis of single exposures and therefore, the effects of increasing CO₂ and O₃ on decomposition and nutrient cycling processes must be studied in combination.

Carlos A. Barassi, Rolando J. Sueldo, Cecilia M. Creus, Liliana E. Carrozzi, Elda M. Casanovas, María A. Pereyra (Argentina) Azospirillum spp., a Dynamic Soil Bacterium Favourable to Vegetable Crop Production (pp 68-82)

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Invited Review: The soil is not merely an inert support for anchoring the plant. Its complexity and dynamics determine the way plants will grow and develop. In these processes, the root and its interaction with the different abiotic and biotic soil components represent a key point in the acquisition of water and essential nutrients. However, anthropogenic effects on the environment - including soil and water deterioration and contamination - could alter these relationships. In addition to these, vegetable production presents diverse problems, which could be mitigated by the use of plant-growth promoting microorganisms (PGPMs). On the soil, PGPMs could contribute to solubilize and/or to acquire essential minerals, making scarce nutrients more available to the plant. On the host, they stimulate several physiological changes that could lead to a better growth and to a plant more tolerant to abiotic stresses. Amongst PGPMs, Azospirillum is one of the most studied genera. Even though it colonizes different plant species in an ample variety of soils, its favourable effects on vegetable germination, emergence and growth, have not been thoroughly studied. This review describes the beneficial effects PGPM inoculation could have on vegetables growing either under normal or stressful conditions, with an emphasis on the use of Azospirillum. It also focuses on the recent advances on Azospirillum-plant interactions and the bacterial mechanisms of plant growth promotion.

Pallavolu M. Reddy, Martha Rendón-Anaya, María de los Dolores Soto del Río, Sanghamitra Khandual (Mexico) Flavonoids as Signaling Molecules and Regulators of Root Nodule Development (pp 83-94)

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Invited Review: Flavonoids are a diverse class of secondary plant metabolites, synthesized from phenylpropanoid precursors, which play an array of important functions in plants, ranging from floral pigments for the attraction of insect pollinators to antioxidants and auxin transport inhibitors. Many plant species also use flavonoids as signal molecules for beneficial microorganisms in the root rhizosphere, and as antimicrobial defense compounds in their interactions with pathogenic microbes. In legumes, flavonoids also play a critical role in promoting nitrogen-fixing symbiosis with rhizobia. Legume root-exuded flavonoids act both as chemo-attractants for symbiotic rhizobia, and signaling molecules for the activation of the expression of rhizobial nod genes, which are responsible for the synthesis of Nod factors, the bacterial signals that are necessary for the initiation of a new plant organ, the nodule. In addition, flavonoids also play a key role in enabling the initiation of differentiation of nodule primordia by inhibiting auxin transport in roots in response to rhizobial Nod factors. This review reports our present level of understanding on the role of flavonoids in the establishment of legume-Rhizobium symbiosis. Also described are the limits of our knowledge in this area of research, and how functional genomic strategies will help in clarifying the regulatory roles of individual flavonoids in mediating nod gene induction in rhizobial cells and auxin transport inhibition in the legume roots during the course of the development of legume-Rhizobium symbiosis.

Ernest F. Bazen, James A. Larson, Roland K. Roberts (USA) Economics of Fertility Management in Cotton Production in the United States (pp 95-104)

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Invited Review: Cotton is a high-value crop that requires the extensive use of costly fertilizers and chemicals. This paper provides a synthesis of the literature on the economics of fertilizer management in U.S. cotton production. The review identifies several production factors and nutrient application strategies based on published research including: 1) economically optimal N, P, and K management as affected by cotton lint and input prices, tillage practices, row-spacing, winter cover crops, and production risk (yield variability); 2) the trends in the adoption of precision farming technology to improve the efficiency of fertilizer and lime application in cotton production; and 3) the profitability of using precision technology for N, P, and K nutrient management in cotton production. Studies from peer-reviewed journals, Proceedings of the Annual Beltwide Cotton Conferences, and university publications were used to summarize current knowledge and suggest future avenues of research.

Peter Wafula Masinde (Kenya), Christopher Ochieng Ojiewo (Japan), Kenji Murakami (Kenya), Stephen Gaya Agong (Japan) Scaling up Production of Traditional Green Leafy Vegetables in Kenya: Perspectives on Water and Nitrogen Management (pp 105-111)

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Mini-Review: Traditional green leafy vegetables are promising alternative vegetable crops consumed in Kenya and other African countries. The crops whose consumption is on the increase include vegetable amaranth (Amaranthus spp.), African nightshades (Solanum spp.) and spiderplant (Cleome/Gynandropsis gynandra). They are popular in the Kenyan retail markets and key supermarket chains as surveys have shown. This offers the urban dwellers access to these vegetables on one hand, while offering a reliable market for growers on the other hand. They are also potential export crops as the consumption continues to widen in most parts of Asia too. For a long time these crops have not been integrated into mainstream agriculture. Consequently, they have received little attention in terms of research and development, resulting in many gaps in information. Production continues to be on small-scales, with the farmers being the major custodians of the genetic materials and production technologies. With the current upsurge of interest in traditional vegetables, there is need to raise production to meet the increasing demand. Some agronomic studies aiming to develop optimal cultivation practices for improved yield and nutritive quality of these crops have been reported. More research work on these crops is necessary to facilitate increased production. In this paper, research into the water and nitrogen use in traditional leafy vegetables is reviewed. The paper aims to show the current status of research, major gaps in information in an effort to scale up production of these crops to meet the increasing demand.

P.W. Masinde (Kenya), C.O. Ojiewo (Japan), S.G. Agong (Kenya), M. Masuda (Japan) Plant Growth, Water Relations and Gas Exchange of Octoploid and Tetraploid Solanum villosum Mill. ssp. miniatum (Bernh. ex Wild.) Edmonds under Water Deficit Conditions (pp 112-121)

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