Achieving a fast initial growth is crucial for legumes because grasses grow more rapidly and compete much better with forbs. In a pot experiment with a nutrient-deficient soil, we added nitrogen (N), phosphorus (P) and N + P to pure and mixed stands of Lotus tenuis and Festuca arundinacea and investigated the effects of on plant growth, nutrient uptake and symbiotic associations with arbuscular mycorrhizae and rhizobia. Plant yield, N and P acquisition, mycorrhizal colonisation, rhizobial nodulation and root length were measured and root diameter and root surface area were calculated after two harvests. Species responded differently to specific nutrients when grown pure or mixed. Comparing pure with mixed stands in soils fertilised with P and N + P, L. tenuis showed decreased shoot and particularly root biomass, whereas F. arundinacea showed increases in both biomasses. This suggests that the competitiveness of the grass with the legume increased upon P and N + P addition. In mixed stands, F. arundinacea produced 51–64% of the total shoot biomass and 69–74% of the total root biomass with P and N + P, respectively. Root length and root surface area were greater and the roots thinner in F. arundinacea than in L. tenuis. Addition of P and N + P increased rhizobial nodulation in legume roots but decreased mycorrhizal colonisation in both plants. Supply of N does not necessarily favour grasses, whereas P supply favours legumes. Optimisation of P nutrition might help to maximise N inputs into grasslands by symbiotic N-fixation and decrease inputs of inorganic N by fertilisation.

Seasonal micronutrients concentration in leaves of four forest species from Parque Chaqueño, Argentina. Nutrients cycling is a fundamental component in the functioning of forest ecosystems. Leaves of different forest species observe specific chemical composition, and some seasonal differences in biomass production, may be related to climate fluctuations and/or changes in plant phenology and the variation on nutrient contents. The objective of this study was to analyze the seasonal variability of Fe, Mn, Cu and Zn concentrations in leaves of Gleditsia amorphoides (Ga); Patagonula americana (Pa); Maclura tinctoria (Mt) and Astronium balansae (Ab) from Colonia Benítez Strict Nature Reserve (Chaco, Argentina). The leaves of each forest species were collected monthly, dried at 70ºC and their weight by tree species were recorded. Samples for analytical determinations were prepared by humid oxidation of organic substances from vegetal nets, using oxidant acids such as ternary mixture of HNO 3 -H 2 SO 4 -HClO 4 . After digestion, total micronutrients leaves concentrations were determined by atomic absortion spectrophotometry. Leaves Fe highest values were detected during fall in Mt (76.1mg/kg), Pa (75.2mg/kg), Ab (59.5mg/kg) and Ga (45.3mg/kg). Highest foliar concentrations of Mn were detected in Pa (54.0mg/kg), Ga (50.0mg/kg), Mt (48.0mg/kg), and Ab with the lower Mn concentration (39.7mg/ kg). No significant differences were found for Cu between the different forest species, standing for Pa (11.3mg/ kg), Ga and Mt (11.0mg/kg) and Ab (10.4mg/kg). With regard to leaves Zn, highest concentrations were found in Mt (347.4mg/kg), Ga (319.9mg/kg), Pa (280.2mg/kg) and Ab (255.7mg/kg). Generally, a marked seasonal variation was observed for Mn and Cu concentrations (except in Ga) and Zn (except in Pa), with no statistical differences for Fe. in the species studied, the concentration of micronutrients analyzed showed a marked and erratic seasonal variation, attributed to the relationship established between the native species, and the strong influence of the environment over a long period of time, especially temperature and rainfall. Rev. Biol. Trop. 60 (3): 1109-1116. Epub 2012 September 01.

<p>El objetivo del trabajo fue estudiar: i) el aporte al suelo de la hojarasca proveniente de árboles de <em>Schinopsis balansae </em>Engler, ii) la tasa de descomposición de sus hojas en un bosque primario y con manejo silvopastoril y iii) la relación entre la composición de N, P y K en hojas verdes y secas de esta especie forestal en ambos ecosistemas forestales. Se seleccionaron dos sitios, uno en un monte nativo de 5. <em>balan.me </em>Engler sin intervención humana (MN); y el otro sitio, en un bosque similar sujeto a un manejo silvopastoril (SP). Las hojas senescentes se recolectaron mensualmente en canastos y simultáneamente se muestreaban las hojas verdes de cada árbol. Posteriormente se lavaban, secaban a 70 ºC y se realizaron los análisis de N, P y K foliares. Se detectó que los diferentes tratamientos no impactaron negativamente en el aporte de hojarasca al suelo. Las constantes de descomposición <em>(k) </em>fueron 0, 10 año 1 en MN y 0,12 año· 1 en SP, no detectándose diferencias entre los sitios. Se obtuvieron menores concentraciones de N, P, y K en las hojas senescentes con respecto a las hojas verdes, indicando una re-absorción de los mismos. Las mayores concentraciones foliares registrada5, siguen el orden P &gt; N &gt; K.</p>

We have studied the uptake and distribution of arsenic (As) and phosphorus (P) in roots, shoots and berries of tomato plants, grown on uncontaminated soil, irrigated with As-contaminated solutions at four concentrations (0, 0.5, 2 and 4 mg L -1 ), in presence or absence of P fertilization.The biomass of tomato plants decreased with increasing As concentration in irrigation water, especially tomato berries. In addition, the reduction of biomasses was significantly greater in plants non-fertilized with P. The beneficial effect generated with the P addition indicated that this nutrient played an important role in alleviating As toxicity in tomato plants. The higher the As concentration in irrigation water the higher the As concentration in plant tissues; most of the As absorbed by plants was accumulated in their roots. Phosphorus application has allowed to reduce As translocation toward tomato berries, enhancing plant P status. These observations may be useful for certain areas of the World, in which As-contaminated waters are used for agricultural purposes.

El objetivo del trabajo fue caracterizar el grado de halomorfismo del suelo y correlacionarlo con las medidas dasométricas en forestaciones con <i>Schinopsis balansae</i> Engler (Quebracho Colorado Chaqueño) de la Ecorregión del Chaco Húmedo. Se seleccionaron tres forestaciones, cada una formada por 12 parcelas y cada parcela, constituida por un árbol dominante. Se midió el diámetro a la altura del pecho (DAP) y la altura de fuste. Se muestreó el suelo a 0-7; 7-30; 30-60; 60-90; 90-120 y>120 cm de profundidad. Se realizaron análisis de pH en agua y en KCl, conductividad eléctrica (CE); Ca²⁺, Mg²⁺ y Na⁺ solubles; y se calculó la Relación de Absorción de Sodio (RAS). Las concentraciones elevadas de la CE se observaron en el horizonte superficial con valores promedios de 1,61 dS m^-1, disminuyendo con la profundidad y la RAS en superficie arrojó valores promedios de 5, 92 aumentando en profundidad de 30. Se correlacionaron las variables de las plantaciones y las del suelo. Se concluye que el mayor desarrollo del Quebracho Colorado Chaqueño está directamente relacionado con los bajos valores de CE y RAS en los horizontes superficiales de 0 a 60 cm. de profundidad.