Marcelo Fabián Arturi

Influence of weather variables and plant communities on grasshopper density in the Southern Pampas, Argentina.

Abstract A study was conducted to evaluate the influence of weather (precipitation and temperature) and plant communities on grasshopper density over a 14-year period (1996–2009) in Benito Juárez County, Southern Pampas, Argentina. Total density strongly varied among plant communities. Highest values were registered in 2001 and 2003 in highly disturbed pastures and in 2002 and 2009 in halophilous grasslands. Native grasslands had the lowest density values. Seasonal precipitation and temperature had no significant effect on total grasshopper density. Dichroplus elongatus (Giglio-Tos) (Orthoptera: Acridoidea), Covasacris pallidinota (Bruner), Dichroplus pratensis Bruner, Scotussa lemniscata Stål, Borellia bruneri (Rehn) and Dichroplus maculipennis (Blanchard) comprised, on average, 64% of the grasshopper assemblages during low density years and 79% during high density years. Dichroplus elongatus, S. lemniscata and C. pallidinota were the most abundant species in 2001, 2002 and 2003, while D. elongatus, B. brunneri and C. pallidinota in 2009. Dichroplus elongatus and D. pratensis, mixed feeders species, were positively affected by summer rainfall. This suggests that the increase in summer precipitation had a positive effect on the quantity and quality forage production, affecting these grasshopper populations. Scotussa lemniscata and C. pallidinota were negatively affected by winter and fall temperature, possibly affecting the embryonic development before diapause and hatching. Dichroplus elongatus and D. pratensis were associated with highly disturbed pastures, S. lemniscata with pastures and B. bruneri and D. maculipennis with halophilous grasslands. Covasacris pallidinota was closely associated with halophilous grasslands and moderately disturbed pastures. Weather conditions changed over the years, with 2001, 2002 and 2003 having excessive rainfall while 2008 and 2009 were the driest years since the study started. We suggest that although seasonal precipitation and temperature had no significant effect on total grasshopper density, these weather variables and plant communities had differential influence on the dominant grasshopper species.

Fertilization in a Fourth Rotation Eucalyptus grandis Plantation with Minimal Management

ABSTRACT Successive rotation and wood harvest of fast growing trees, like Eucalyptus grandis, can deplete soil nutrient pools. In these intensively used soils, productivity can decrease, and fertilization can be necessary to recover soil fertility. The aim of this work is to evaluate if fertilization with N and P increases tree growth and foliar nutrients in an Eucalyptus grandis plantation growing over a soil used for three rotations of this species. In the same experiment, both fertilization on seedlings and coppiced trees were evaluated. One and two years after planting, any fertilization treatment increased tree growth, even though coppiced trees had higher total height and DBH than replanted trees. Coppiced trees had lower specific leaf area, as well as lower N and P leaf concentration. The lack of promotion in growth due to fertilization can be explained by the inputs of nutrients from the harvest residues of the previous rotation. As residues were never burned in this site, its decomposition released a high part of nutrients necessary to sustain growth during the first two years. We conclude that in sites where residues were left on site and were not burned, nutrient availability is enough and so fertilization at establishment is not necessary. It remains to be determined if fertilization is necessary at mid or end rotation, in order to balance nutrients export with harvest wood.

Contenido de nutrientes en las raíces finas y el mantillo de rodales de Eucalyptus grandis de diferente edad en la Mesopotamia Argentina

La provincia de Entre Rios es un nucleo importante de plantaciones de Eucalyptus spp. en Argentina. Se planteo como hipotesis que con el aumento en la edad de las plantaciones aumenta la biomasa de raices finas y la masa del mantillo. Se muestrearon rodales de cinco, siete y diecisiete anos de edad de Eucalyptus grandis, de primera rotacion. Se estimaron las masas del mantillo y de las raices finas (< 5 mm) en los primeros 30 cm de profundidad. Se analizaron quimicamente: carbono, nitrogeno, fosforo, potasio, calcio y magnesio en raices finas vivas y en el mantillo. Se calcularon sus contenidos minerales. Se empleo ANDEVA para las comparaciones entre rodales. A 30 cm de profundidad las raices finas vivas de los rodales de siete y diecisiete anos presentaron similares biomasas y contenidos de nutrientes, pero mayores que a los cinco anos. A 10 cm de profundidad, el rodal de diecisiete anos presento la mayor biomasa y contenido de nutrientes de raices que aquellos de menor edad. Antes de los siete anos se estabilizaron la biomasa y contenido de nutrientes de raices finas. Con la edad aumento la masa y contenido mineral del mantillo. La redistribucion de raices en el perfil del suelo con la edad de los rodales se relaciono con el incremento del mantillo y su influencia sobre la dinamica del agua y los nutrientes del suelo.

Dissolved organic carbon in water fluxes of Eucalyptus grandis plantations in northeastern Entre Ríos Province, Argentina

Water fluxes in tree plantations and other ecosystems carry dissolved organic carbon (DOC) provided by atmospheric inputs, autotrophic and heterotrophic metabolisms and from the lysis of dead material. These compounds may be colorless or provide a yellow-to-brown color to water and may also absorb visible light due to the presence of chromophores in the chemical structure. Concentration and composition of DOC and DOC annual flux in water pathways of a Eucalyptus grandis plantation were studied in Entre Rios, Argentina. Samples of bulk precipitation, throughfall, stemflow, litter lixiviation, surface runoff and water table were analyzed for DOC concentration and color (optical density). Regression analyses for DOC concentration vs water fluxes intensity and for DOC concentration vs color were done. A DOC circulation model was calculated using available information on water budgets fluxes. Results showed that molecular features, values and range of DOC concentrations varied among fluxes, which may be explained by factors and processes influencing water gains and losses and by composition and availability of organic matter that may be dissolved in water in contact with biomass, necromass, soil and subsoil. Regression parameters from DOC concentration vs optical density were useful for DOC chemical composition analyses and interpretation of DOC changes. Annual circulation of DOC (in kg ha-1 year-1) showed that atmospheric contribution is low (ca. 30), aboveground biomass lixiviation is about 3-4 times the atmospheric input (126.7 to 101.4), and inputs to mineral soil (374.4 to 348.0) came mainly (74 to 78 %) from litter lixiviation.

Communities of anamorphic fungi on green leaves and leaf litter of native forests of Scutia buxifolia and Celtis tala: Composition, diversity, seasonality and substrate specificity

BACKGROUND Xeric forests dominated by two tree species, Scutia buxifolia (Rhamnaceae) and Celtis tala (Ulmacea), are temperate, semi-deciduous wooded communities that represent the most abundant woodlands on the eastern plains of Buenos Aires Province, Argentina. The district of Magdalena has one of the most well-preserved native-forest areas, with an environmental heterogeneity that gives rise to the wide variability in the vegetation present. AIMS The aim of this study was to analyze the species composition, diversity, seasonal variations, and substrate specificity of anamorphic fungi (Ascomycota) on the green leaves and in the leaf litter of native forests dominated by Scutia buxifolia and Celtis tala from Magdalena, Buenos Aires, Argentina. METHODS In order to obtain the mycobiota of decomposition, seasonal samples of green leaves and leaf litter from both types of trees were collected over a two-year period. In the laboratory, the leaves were placed in a moist chamber and incubated at room temperature. RESULTS A total of 100 species of anamorphic Ascomycota were identified in both forests. No significant variations were observed in the richness, diversity, or evenness of the fungal communities of the green leaves and leaf litter of both forests between seasons. CONCLUSIONS The species that characterized the fungal communities in the leaves of each of the trees were found to be different. The type of substrate had a stronger influence in determining the composition of the fungal community in both types of forests.

Evaluación del muestreo por recuento angular de Bitterlich en distintas distribuciones espaciales y diamétricas generadas por simulación

The precision and accuracy of Bitterlich angular count (BAC) for the estimation of basal area density could depend on diametric distribution since the inclusion probability of the trees increases with their basal area. Trees spatial pattern can also influences since point-tree distances determine their inclusion in the sample. In this study, the precision and bias of BAC under different diametric distribution and spatial patterns were evaluated by the means of simulations. Normal and lognormal diametric distributions were simulated with basal area density ranging between 30-33 m2 ha-1. These diametric distributions were simulated in three spatial patterns: regular, random and clumped yielding six combinations. A seventh class was simulated with bimodal diametric distribution and a mixed spatial pattern: clumped for small trees and random for large trees. Bias was less than 0.10 m2 ha-1 except for clumped pattern with lognormal diametric distribution and mixed pattern. In these cases bias tended to be negative (-0.15 a -0.25 m2 ha-1). The lowest mean absolute deviation (MAD) was observed for the regular pattern 3-7 %. In the clumped pattern it ranged 7-10 % and 8-11 % in the mixed. MAD tended to be slightly lower in the normal distribution than in lognormal in the regular spatial pattern but the reverse trend was observed in the clumped pattern. In practical terms BAC yields null bias and low MAD with a low intensity sampling for a wide variety of stand structures.

Modelo empírico integral de una plantación de Eucalyptus granáis en Concordia, Entre Ríos

La Mesopotamia argentina es la zona nucleo de especies forestales de rapido crecimiento del pais. Las plantaciones de Eucalyptus grandis constituyen el 90 % de la superficie forestada con eucaliptos del noreste de Entre Rios. A partir de estudios previos sobre sus aspectos estructurales y funcionales se propone elaborar un modelo integral del que emerjan nuevas propiedades vinculadas con los almacenajes de la materia y procesos ecosistemicos. Se utilizaron datos de plantaciones al turno, de: biomasa, productividad primaria neta, flujos hidricos, flujos de nutrientes, contenido de nutrientes en la biomasa, necromasa y en el suelo. Se destaca la contribucion de la parte aerea de la plantacion en la distribucion de la biomasa, asignacion de la productividad y requerimiento de nutrientes. Los requerimientos de nutrientes, excepto fosforo, fueron provistos mayormente por absorcion que por distribucion, contrario a lo que ocurrio con el fosforo. La caida al mantillo y mortalidad de raices fueron las vias principales de retorno de nutrientes, excepto el potasio, el cual retorno principalmente por los flujos hidricos. La elevada productividad de la plantacion fue sostenida por una alta eficiencia en el uso del agua y nutrientes. Se destaca la importancia del adecuado manejo de los residuos de la cosecha, ya que la exportacion de la biomasa aerea completa y los nutrientes que contiene implican una extraccion elevada, comparada con los almacenajes subterraneos. Comparada con el nitrogeno, la elevada eficiencia de redistribucion del fosforo permitiria a la plantacion mayor independencia de los procesos de mineralizacion e inmovilizacion edaficos.

Relationship Between Height Growth and Foliar Nutrient N and P Concentration in a Eucalyptus grandis Plantation in Northeastern Argentina

The relationship between the height growth, foliar concentrations of nitrogen (N) and phosphorus (P), and the N:P ratio was analyzed in a fourth rotation plantation that did not respond to fertilization with these nutrients. Spearmans nonparametric correlation analysis was used to evaluate the association between growth in height—calculated as the difference between heights measured at 1 yr and 2 yr after planting—and foliar N and P concentrations, as well as N:P ratio, determined in the 1-yr-old plantation. Only a weak positive correlation between height growth and foliar P concentration in planted seedlings was found. A significant negative relation was observed between the growth and N:P ratio in seedlings. Foliar concentrations suggest that there were neither P nor N limitations for growth in the analyzed period. This may be due to the management of harvest residues, which were abandoned on-site without burning.