The impact of phosphorous nutrition on plant growth, symbiotic N 2 fixation, ammonium assimilation, carbohydrate and aminoacid accumulation, as well as on nitrogen, phosphorus and ATP content in tissues in common bean (Phaseolus vulgaris) plants was investigated. Plants inoculated with Rhizobium tropici CIAT899 were grown in Leonard jars under controlled conditions, with P-deficient (0 and 0.1 mM), P-medium (0.5, 1 and 1.5 mM) and P-high (2mM) conditions in a N-free nutrient solution. The P application, increased leaf area, whole plant DW (67%), nodule biomass (4-fold), and shoot and root P content (4-and 6-fold, respectively) in plant harvested at the onset of flowering (28-days-old). However, P treatments decreased the total soluble sugar and amino acid content in vegetative organs (leaf, root and nodules). The root growth proved less sensitive to P deficiency than did shoot growth, and the leaf area was significantly reduced at low P-application. The absence of a relationship between shoot N content, and P levels in the growth medium could indicate that nitrogen fixation requires more P than does plant growth. The optimal amount for the P. vulgaris-R. tropici CIAT899 symbiosis was 1.5 mM P, this treatment augmented nodule-ARA 20-fold, and ARA per plant 70-fold compared with plants without P application.

Bacteria with the ability to grow on nitrogen-free media and with nitrogenase activity under aerobic or microaerobic conditions were isolated from sugarcane roots collected from four different agricultural locations in Granada (Spain). Isolates were Gram negative rods and were identified as Azotobacter chroococcum and Azospirillum brasilense. Our results suggest that Azotobacter isolates do not have a particular affinity for sugarcane rhizospheres and that, on the contrary, Azospirillum isolates show specific association and perhaps endophytic colonization of sugarcane. However, obligate endophytes (Gluconacetobacter diazotrophicus) were not found in the apoplastic fluid of the stems and macerates extracts of sugarcane tissues with the procedure applied. Population of this microorganism might be in low number in the Spanish sugarcane varieties studied which is also discussed.

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The distribution of neodymium, lead, thorium and uranium was investigated in about 100 samples of 12 different species of common, edible and non-edible mushrooms collected in unpolluted areas in the province of Ciudad Real, Central Spain. The quantitative analysis of heavy metals was performed by X-ray fluorescence spectrometry (a simple, accurate and non-destructive method). The concentration of these elements was related to three factors: mushroom specie, life style/substrate and study area. The results reveal considerable amounts of the four metals in all species analyzed as well as significant differences on the capability to accumulate these elements. The maximum absorption of Nd and Pb was found in the ectomycorrhizal Cantharellus cibarius, reaching values of 7.10 and 4.86 microg g(-1), respectively. Thorium and uranium were mainly accumulated (3.63 and 4.13 microg g(-1), respectively) in Hypholoma fasciculare although it is an epiphyte species, isolated from the mineral particles of soil. The distribution patterns of these metals in sporocarps of different habitats and locations showed no significant differences, except for thorium, mainly accumulated in mushrooms living on wood regarding these living on soil organic matter. The species-specific is therefore the determining factor for accumulation of Nd, Pb, Th and U, more than substrate, in this study.

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