Carlos Fragoso

Agricultural intensification, soil biodiversity and agroecosystem function in the tropics : the role of earthworms

Abstract Earthworm biodiversity is modified when forests and natural savannas are replaced by agroecosystems; these changes can be studied from the taxonomic and functional point of view. In the first case the number and origin (native or exotic) of species is important, as well as the geographic scale of the study (local or regional). The functional approach considers the ecological groups (epigeic, endogeic, anecic), which have different effects on soil function. Studies in Mexico, Peru and India reveal that agroecosystem earthworm communities (as compared with those in the undisturbed ecosystem) have lower species richness, lower number of native species, lower number of ecological groups and a predominance of endogeics. Therefore the role of endogeic species in intensifying agroecosystems is likely to be more important for soil function, especially because they act as ecosystem engineers and through their mutualistic interactions with microflora, selective ingestion of soil particles, high rates of ingestion and production of casts, galleries, burrows and chambers can affect nutrient and organic matter dynamics and other pedological processes. Epigeic and anecic species do not appear to be as widespread in agricultural systems and their dependence on a litter layer for survival implies that litter management practices must be implemented for their role in soil function to be of importance. The role of earthworms in enhancing primary production depends on the synlocalization (in the same place) and the synchronization (at the same time) of their activities with the period and the sphere of active root growth and nutrient demands. Several field studies have found significant yield increases with earthworm inoculation, though more research is needed. Incorporation of information on earthworm life histories, field population variations, ecological strategies and short and long term effects on soil properties, in addition to plant and environmental factors (climate, soil, cropping period and management of the agroecosystem), are essential to properly assess the potential role of a particular earthworm species on plant production. Future research must focus on describing the role of native species and their interaction with or replacement by exotic species (belonging to the same or to a different ecological group) in soil function and agroecosystem productivity.

Mycorrhizal colonization and nitrogen uptake by maize: combined effect of tropical earthworms and velvetbean mulch

Earthworms and mulch can have positive or negative effects on mycorrhizae (fungus-roots) and N uptake by plants. In the present experiment, maize plants were grown under greenhouse conditions with or without tropical earthworms (Balanteodrilus pearsei) and mulch of velvetbean (Mucuna pruriens var. utilis). The formation of vesicles and hyphae of arbuscular-mycorrhizal (AM) fungi in roots and N uptake by maize plants was measured at harvest. The addition of earthworms and velvetbean reduced AM root colonization. Earthworms had no effect on plant root or shoot biomass. In the absence of velvetbean, earthworms reduced AM colonization, but when velvetbean was present, this effect disappeared. The addition of velvetbean mulch, on the other hand, had an effect on plant biomass (above- and belowground) and a positive effect on AM fungal colonization of roots in presence of worms, but a negative effect when worms were absent. When both M. pruriens and B. pearsei were added, shoot and root biomass and N concentrations increased. Vesicle formation was related to velvetbean mulch decomposition as well as the higher N concentration in maize roots. Management of mulch–earthworm interactions may be of value, particularly in low-input and organic agricultural systems, and deserves further investigation.

Species-specific characteristics of trees can determine the litter macroinvertebrate community and decomposition process below their canopies

This paper tests whether individual trees in a mature forest stand influence the process of litter decomposition and the macroinvertebrate communities in the soil underneath their canopies, as a result of species-specific characteristics. A field decomposition experiment was performed in a mature forest stand of tropical montane cloud forest in Mexico. The areas under the canopies of Quercus laurina Humbl. & Bompl., Oreopanax xalapensis (Kunth) Decne. & Planchon and Beilschmedia ovalis (Blake) C. K. Allen trees were used as experimental units. The natural soil and litter macroinvertebrate communities were monitored and compared to the community that invaded decomposition boxes with reciprocally transplanted leaf litter. The abundances of four macroinvertebrate taxa in natural litter differed among tree species independently of season. No differences were found in the soil community. The response to experimental litter by macroinvertebrate taxa suggests that the production of a specific quality of litter is an important mechanism by which a tree influences the litter macroinvertebrate community that develops under its canopy. However, not all differences in community composition naturally found between tree species can be explained by differences in litter quality during the first year of decomposition. Differences in nutrient release that occur after the first year, and physical properties of litter also probably play an important role. Independently of the canopy tree, the initial chemical quality (N, P, Ca, Mg and lignin) of experimental litter largely determined the decomposition rate and nutrient dynamics of decomposing leaves. However, it was found that under O. xalapensis trees the breakdown of lignin from the litter produced by the same species of tree was particularly effective. This suggests that a feedback has developed between this tree species and the decomposer community prevailing under its canopy.

Growth, reproduction and activity of earthworms in degraded and amended tropical open mined soils: laboratory assays

Abstract The potential of four earthworm species to establish viable populations on soils degraded by the cement industry was tested in laboratory assays. We evaluated growth, reproduction, vertical distribution, and activity of endogeics Pontoscolex corethrurus and Octolasion cyaneum, and epigeics Amynthas corticis and A. gracilis, raised on artificial two layer soil profiles. Bottom layer consisted of mineral subsoil (MS) taken from a cement mine, whereas top layer was an organic substrate. A bifactorial experimental design with eight treatments per species was implemented. MS factor had two levels (pH 5.5 and 7.5), whereas organic substrate factor presented four levels of depth (0.0, 2.5, 5.0, and 13.0). The organic substrate layer varied between species: organic soil (OS) was used with P. corethrurus and O. cyaneum, OS mixed with composted coffee pulp was given to A. corticis, whereas vermicomposted coffee pulp was provided to A. gracilis. None earthworm species grew in the MS without an organic layer (OL). Growth and reproduction of P. corethrurus and A. corticis were positively affected by the organic treatments. A. gracilis survived in these treatments, but its growth was negligible. O. cyaneum proved to have little resistance to manipulation since high mortality rates were observed. P. corethrurus and A. corticis had the highest rates of cast deposition into the MS, but P. corethrurus was active even in the acid (pH 5.5). Based on vertical distribution and cast production patterns, P. corethrurus and, to a less extent, A. corticis proved to have the greatest potential for supporting pedogenic processes through bioturbation. Additional work is necessary to show the effect of species interactions over a range of MS properties.

Size shift in the Mexican earthworm species Balanteodrilus pearsei (Megascolecidae, Acanthodrilini): A possible case of character displacement

Abstract The earthworm genus Balanteodrilus includes three well-differentiated species. One of the species (B. pearsei) is common to eastern and south-eastern Mexico. All but one population of B. pearsei are medium-sized earthworms (6.4–11 cm in length). The smallest morph of B. pearsei was found sympatrically coexisting at La Mancha forest with another species of the genus. In this locality, resources are scarce, the two species present different vertical distributions and their abundances are relatively low. A change of size in this population was not the result of random variation. Three possible explanations are proposed: (1) character displacement resulting from past long-term competition; (2) response to poor soil nutrients; or (3) reproductive character displacement or reinforcement.

The influence of Gilberto Righi on tropical earthworm taxonomy: the value of a full-time taxonomist

During 40 years of active research, G. Righi published 85 papers on earthworm taxonomy, 5 on earthworm physiology, 5 on earthworm ecology and 3 on earthworm biogeography. In addition he published 16 papers on microdrile oligochaetes, and 17 on other groups (mainly crustaceans and molluscs). Most of his megadrile taxonomical papers related to Brazilian earthworms, although he also studied earthworms from other South and Central American countries (Colombia, Venezuela, Argentina, Ecuador, Peru, Bolivia, Mexico, Belize, Costa Rica,) and some Lower Antilles. G. Righi described one family, 25 genera and 224 species, mainly from Brazil (139 spp. in 16 genera), Colombia (36 spp., 5 genera) and Venezuela (24 spp., 2 genera). The majority of these new taxa belong to the Family Glossoscolecidae (161 spp, 14 genera). Analysis of the taxonomic production of G. Righi reveals a description rate of 6.4 species per year. This paper discusses the possibility of a complete worldwide species inventory, considering Righis rate of new species description.

Key attributes to the disturbance response of montane cloud forest trees: shade tolerance, dispersal mode and the capacity to form a seed bank

Abstract• ContextUnderstanding the biological mechanisms related to plant response to disturbance is essential for predicting the changes in the structure of plant communities resulting from disturbance.• AimsThe aims of this study are to identify the regeneration traits linked to the response to disturbance of tree species of a montane cloud forest in order to define regeneration types and to explore whether disturbance intensity acts to select specific regeneration types that can colonize disturbed plots.• MethodsA theoretical model was developed and evaluated using structural equation modeling to link two latent variables: regeneration type and vulnerability to disturbance. We studied two plots that were subjected to different intensities of disturbance and one plot of mature forest.• ResultsShade tolerance, dispersal mode, and the capacity to form a seed bank were the traits that determine regeneration type. There was a trend for re-sprouting capacity to be associated with the regeneration types dominant in disturbed plots. Regeneration types were differentially distributed among the sites.• ConclusionThere was evidence that disturbance intensity has a filtering effect on the colonization of disturbed plots. Species vulnerability to disturbance depends on specific combinations of regeneration traits. Structural equation modeling is useful for exploring plant response to disturbance using key parameters linked to plant persistence.

Protozapotecia acaxetlensis and Protozapotecia oyametlensis , two new earthworm species (Crassiclitellata: Acanthodrilidae) from Mexican central mountains

Two earthworm species from central Mexico are described: Protozapotecia acaxetlensis sp. nov. and Protozapotecia oya-metlensis sp. nov. Delimitation of species was supported by morphological and molecular evidence. The two new species differ from the other species of Protozapotecia by the position of the prostates in segments 18 and 20. This morphological characteristic relates them to the genus Diplocardia, from which they differ by the presence of two gizzards separated by a muscular septum (Protozapotecia), instead of two gizzards fused as one, separated by a thin membranous septum in intersegment 5/6 (Diplocardia).

New Diplotrema and Lavellodrilus earthworm species from southern Mexico (Annelida, Crassiclitellata, Acanthodrilidae)

Two acanthodriline new species from the states of Tabasco and Chiapas in southern Mexico are described, Diplotrema chajulensis sp. nov. and Lavellodrilus sheylae sp.nov. Diplotrema chajulensis sp. nov. has spermathecae where the ampulla inserts at a right angle from the duct and the diverticulum continues the main axis; it is distinguished from other neotropical Diplotrema species that share this character by the pattern of genital marks and the type of penial setae. Lavellodrilus sheylae sp. nov. is unique in the genus Lavellodrilus by the unpaired condition of the mesial spermathecae; variation in the number of spermathecal diverticula (one or two) was considered a polymorphism. Finally we discuss reasons to maintain one of the new species in an austral genus (Diplotrema) in spite of some morphological differences observed among the Mexican-Cuban-Central American (MX-CA) worms and the austral species. A short esophagus in all the holoic and meroic acanthodriline earthworms from MX-CA and a mid-ventral position of spermathecal pores in Lavellodrilus are interpreted as ancestral characters that evolved and were fixed in the worms that inhabited an ancient Laurasian block, probably in response to the semi-aquatic conditions that prevailed in this region during millions of years.

New species of the earthworm genus Zapatadrilus (Clitellata, Acanthodrilidae) from northern Mexico

Three new species of the earthworm genus Zapatadrilus are described from Tamaulipas, Mexico: Zapatadrilus aurelius sp. nov., Zapatadrilus huastecus sp. nov., and Zapatadrilus montezumensis sp. nov. Delimitation of the new species was supported by morphological and molecular (genetic distances) evidence. Diagnostic characters of the three new species include: tubulo-racemose prostates in segments 18 and 20, penial setae absent, typhlosole present and intestine beginning in 17/18. Z. montezumensis sp. nov. is separated by its metandric condition, Z. aurelius sp. nov. by the last hearts in 13 and Z. huastecus sp. nov. by the shape of the spermathecae and patterns of genital markings.