Elias de Melo Virginio Filho

Populações de minhocas em sistemas agroflorestais com café convencional e orgânico

Objetivou-se, neste estudo, determinar se as populacoes das minhocas sao alteradas em funcao do manejo do cafe (Coffea arabica) em Turrialba, CostaRica. Os seguintes sistemas de cultivo do cafe foram estudados: a pleno sol (PS) e sombreado com eritrina, Erythrina poeppigiana (E); terminalia, Terminalia amazonia (T) e casha, Chloroleucon eurycyclum (Ab). A hipotese foi de que o manejo orgânico do cafe e o fornecimento da serapilheira de melhor qualidade favoreceria a diversidade, a densidade e a biomassa das minhocas. As populacoes das minhocas foram alteradas, em funcao do manejo com insumos sinteticos ou orgânicos , sendo a densidade menor no cafe a pleno sol. Entre as especies utilizadas no sombreamento, a eritrina parece limitar a abundância das minhocas. Contudo, favorece a diversidade das mesmas, tendo sido registradas duas especies de minhocas com papeis ecologicos diferenciados, Pontoscolex corethrurus, endogeica e Metaphire californica, anecica; ao contrario dos demais tratamentos, onde somente foi encontrada a primeira especie, considerada cosmopolita com distribuicao pantropical.

Shade Effects on the Dispersal of Airborne Hemileia vastatrix Uredospores

Hemileia vastatrix caused a severe epidemic in Central America in 2012-13. The gradual development of that epidemic on nearly a continental scale suggests that dispersal at different scales played a significant role. Shade has been proposed as a way of reducing uredospore dispersal. The effect of shade (two strata: Erythrina poeppigiana below and Chloroleucon eurycyclum above) and full sun on H. vastatrix dispersal was studied with Burkard traps in relation to meteorological records. Annual and daily patterns of dispersal were observed, with peaks of uredospore capture obtained during wet seasons and in the early afternoon. A maximum of 464 uredospores in 1 day (in 14.4 m(3) of air) was recorded in October 2014. Interactions between shade/full sun and meteorological conditions were found. Rainfall, possibly intercepted by tree cover and redistributed by raindrops of higher kinetic energy, was the main driver of uredospore dispersal under shade. Wind gusts reversed this effect, probably by inhibiting water accumulation on leaves. Wind gusts also promoted dispersal under dry conditions in full sun, whereas they had no effect under shaded conditions, probably because the canopy blocked the wind. Our results indicate the importance of managing shade cover differentially in rainy versus dry periods to control the dispersal of airborne H. vastatrix uredospores.

Intraspecific trait variation and coordination: Root and leaf economics spectra in coffee across environmental gradients

Hypotheses on the existence of a universal “Root Economics Spectrum” (RES) have received arguably the least attention of all trait spectra, despite the key role root trait variation plays in resource acquisition potential. There is growing interest in quantifying intraspecific trait variation (ITV) in plants, but there are few studies evaluating (i) the existence of an intraspecific RES within a plant species, or (ii) how a RES may be coordinated with other trait spectra within species, such as a leaf economics spectrum (LES). Using Coffea arabica (Rubiaceae) as a model species, we measured seven morphological and chemical traits of intact lateral roots, which were paired with information on four key LES traits. Field collections were completed across four nested levels of biological organization. The intraspecific trait coefficient of variation (cv) ranged from 25 to 87% with root diameter and specific root tip density showing the lowest and highest cv, respectively. Between 27 and 68% of root ITV was explained by site identity alone for five of the seven traits measured. A single principal component explained 56.2% of root trait covariation, with plants falling along a RES from resource acquiring to conserving traits. Multiple factor analysis revealed significant orthogonal relationships between root and leaf spectra. RES traits were strongly orthogonal with respect to LES traits, suggesting these traits vary independently from one another in response to environmental cues. This study provides among the first evidence that plants from the same species differentiate from one another along an intraspecific RES. We find that in one of the world’s most widely cultivated crops, an intraspecific RES is orthogonal to an intraspecific LES, indicating that above and belowground responses of plants to managed (or natural) environmental gradients are likely to occur independently from one another.

Shade trees have higher impact on soil nutrient availability and food web in organic than conventional coffee agroforestry

Conventional, intensively managed coffee plantations are currently facing environmental challenges. The use of shade trees and the organic management of coffee crops are welcome alternatives, aiming to reduce synthetic inputs and restore soil biological balance. However, little is known about the impacts of the different types of shade tree species on soil functioning and fauna. In this paper, we assess soil nutrient availability and food web structure on a 17-year old experimental coffee plantation in Turrialba in Costa Rica. Three shade types (unshaded coffee, shaded with Terminalia amazonia, and shaded with Erythrina poepiggiana) combined with two management practices (organic and conventional) were evaluated. Total C and N, inorganic N and Olsen P content, soil pH, global soil fertility, and nematode and microarthropod communities were measured in the top 10 cm soil layer, with the objective of determining how shade tree species impact the soil food web and soil C, N and P cycling under different types of management. We noted a decrease in soil inorganic N content and nematode density under conventional management (respectively -47% and -91% compared to organic management), which suggested an important biological imbalance, possibly caused by the lack of organic amendment. Under conventional management, soil nutrient availability and fauna densities were higher under shade, regardless of the shade tree species. Under organic management, only soils under E. poeppigiana, a heavily pruned, N2-fixing species, had increased nutrient availability and fauna density, while T. amazonia shade had a null or negative impact. The effects of coffee management and shade type on soil nutrient availability were mirrored by changes in soil food web structure. Higher fertility was recorded in soil with balanced food webs. These results emphasize the importance of the choice of shade tree species for soil functions in low input systems, more so than in fertilized systems.