Role In Agroecosystems Research Articles

Impact of species identity and phylogenetic relatedness on biologically-mediated plant-soil feedbacks in a low and a high intensity agroecosystem

Plant species-specific effects on soil biota and their impacts on subsequent plant growth, i.e. plant-soil feedbacks (PSFs, henceforth), are major drivers in natural systems but little is known about their role in agroecosystems. We investigated the presence and magnitude of PSFs in two contrasting agricultural settings and tested the importance of species identity and phylogenetic relationships in determining PSFs. We compared PSFs that developed from an intensified agricultural site and a nearby non-cultivated pasture. Four weed and seven crop species were grown in soil inoculated with either biologically active or sterilized soils from each system. Four crop response species were grown to estimate PSFs. PSFs were species-specific. The identity of currently- and previously-planted species and their interactions explained over 80 % of the variation in feedbacks. Biota from the intensified agricultural site produced negative feedbacks in three of the four response species. Phylogenetic relationships partially explained PSFs. PSFs can alter crop growth and may be altered by agricultural practices. The species-specific effect to soil biota should be taken into account when assessing the extent to which crop and weed species could influence subsequent plant growth.

Non-linear responses of functional diversity and redundancy to agricultural intensification at the field scale in Mediterranean arable plant communities

Despite their key roles in agroecosystems, species diversity of arable plants is being severely reduced by agricultural intensification, although it remains unclear whether functional diversity is affected in a similar way. We analyzed the response of four functional traits of arable plants (specific leaf area, canopy height, seed mass and flowering onset) to agricultural intensification in Mediterranean arable plant communities. Two intensification gradients were obtained by PCA analysis on variables related either to management practices at the individual field scale or to the surrounding landscape structure and composition. Shifts in the community weighted mean (CWM) and the functional diversity (FD) of each trait along these intensification gradients were explored. The relationship between species richness and the FD of each trait (i.e. functional redundancy) along the same gradients was also analyzed. The responses of species richness and the considered functional traits were driven by intensification at the individual field scale, but not by intensification at the scale of the surrounding landscape. Species richness and FD of all the studied traits decreased with intensification, which favoured tall, heavy-seeded and early flowering species. The decrease of FD was non-linear for specific leaf area and seed mass, with maximum reductions at intermediate levels of intensification. Species richness and FD responses were decoupled, indicating that the functional redundancy in the studied communities responds to agricultural intensification in a non-linear fashion. Along the first stages of intensification, there was an important reduction in species richness that was not accompanied by changes in FD. Further levels of intensification resulted in substantial reductions in FD without changes in species richness. These findings provide new insights on how agricultural management interacts with plant communities through its non-linear effects on functional diversity and functional redundancy.

Nanoscale Science and Engineering for Agriculture and Food Systems

Nanoscale Science and Engineering for Agriculture and Food Systems

STRUKTUR KOMUNITAS HYMENOPTERA PARASITOID PADA TUMBUHAN LIAR DI SEKITAR PERTANAMAN PADI DI DAERAH ALIRAN SUNGAI (DAS) CIANJUR, JAWA BARAT

Hymenoptera Parasitoid Community Structure on Non-crops Vegetation Around Rice fields in Cianjur Watershed, West Java. Hymenoptera parasitoids have an important role in agroecosystem because of their ability in suppressing pest population. Their presence in the field is seen as the key to agricultural ecosystem. Their presence can be influenced by the availability of non-crop vegetation. Some adult Hymenoptera parasitoids require food in the form of pollen and nectar of wild flowers to ensure effective reproduction and longevity. The objective of this research was to study Hymenoptera parasitoid communities in non-crop vegetation around rice fields at Cianjur Watershed. Samplings were conducted at three different landscape, i.e. Nyalindung, Gasol and Selajambe West Java. Insects were sampled by two trapping techniques (farmcop and sweep net) in two lines of transect for each landscape. A total of 257 species from 25 families of Hymenoptera parasitoids were collected in non-crop vegetation at Cianjur Watershed. Landscape structure, flowering vegetation, and pesticide application affected the species richness, diversity and evenness of Hymenoptera parasitoid in non-crop vegetation.

Addition of a new resource in agroecosystems: Do cover crops alter the trophic positions of generalist predators?

Generalist predators can play an important role in agroecosystems by controlling herbivores via top-down effects. As cover crops are increasingly used in agroecosystems, the effects of this resource on generalist predator diet need to be evaluated. We studied the effect of adding a cover crop, Brachiaria decumbens, on trophic niches of generalist predators in a banana agroecosystem by analysing stable isotope variation in C and N for Cosmopolites sordidus, a major banana pest, and its potential predators (spiders, ants, centipedes, and earwigs). While addition of the new resource did not change the trophic niche of the banana pest C. sordidus, the trophic position of the generalist predators was changed as indicated by δ 13C signature. Cover crop provided resources that are likely to support a community of insect herbivores, which are alternative preys for generalist predators. The failure of the cover crop to increase δ 15N signature is inconsistent with the hypothesis that the cover crop would increase intraguild predation. By providing alternative preys, the addition of a new resource in agroecosystems has the potential to increase populations of generalist predators and therefore pest control.

Phytoseiid mites on grasses in Brazil (Acari: Phytoseiidae)

Surveys were conduced in 16 sites in the State of São Paulo to evaluate the phytoseid mite fauna on some of the most common grass species in that State: Brachiaria decumbens Stapf., Brachiaria brizantha (Hochst. ex A. Rich.) Stapf, Brachiaria ruziziensis R. Germ & C.V. Evrard, Melinis minutiflora Beauv., Panicum maximum Jacq. and Pennisetum purpureum Schumach. Twenty known species and one new species (Proprioseiopsis biologicus Lofego, Demite & Moraes sp. nov.) were found. Two species are reported for the first time in the American continent: Neoseiulus benjamini Schicha and Typhlodromus (Anthoseius) neobakeri Prasad . Seven of the species collected have been reported in Brazil from different crops. The largest number of specimens and of species of phytoseiids was found on M. minutiflora. The results of this study indicate that grasses may play a role in agroecosystems and pasture lands, serving as reservoirs of phytoseiids that prey upon mite pests.

Are predatory arthropods useful indicators in Australian agroecosystems?

Information on the diversity and roles of two groups of arthropod predators (Neuroptera and Araneae) in Australian cropping systems is reviewed, as a foundation for discussing the properties of such predators that may render them useful bioindicators, and for discussing their ecological roles in agroecosystems. Predators are a prime target for conservation and augmentation, reflecting their perceived or actual positive roles in pest management, but most appear to have little value as true bioindicators in agricultural environments. In Australia, Neuroptera are represented by very few species in most agroecosystems, and all of these species are polyphagous generalists. Biological knowledge of Araneae, and of the factors that influence their species richness, is too scanty to enable sound understanding of changes in assemblage composition that might otherwise be regarded as ‘indication’. The current value of these groups as bioindicators is minimal.

The Use of Allelopathic Legume Cover and Mulch Species for Weed Control in Cropping Systems

Traditional weed control practices in Mexico use legumes as cover crops or manures. Legumes used in these practices play a dual role in agroecosystems by protecting the soil from erosion and by enriching it with organic matter and N through Rhizobium symbiosis. Farmers in the tropical regions of Mexico use Mucuna spp., Canavalia spp. and other legumes to control weeds in their fields. We conducted in vitro bioassays and greenhouse experiments to evaluate the toxic effect of four legumes velvetbean [Mucuna deeringiana (Bort) Merr.], jackbean [Canavalia ensiformis (L.) DC.], jumbiebean [Leucaena leucocephala (Lam.) de Wit], and wild tamarind [Lysiloma latisiliquum (L.) Benth.] on weed growth, and on the survival of insects and nematodes. The aqueous leachates (1%) of the four legumes were tested on three test plants by seed germination and radicle growth bioassays in petri dishes. The aqueous leachates of all four legumes exhibited strong phytotoxic effect on the radicle growth of the test plants. The effects of velvetbean and jackbean leachates were also evaluated on the survival of phytopathogenic nematodes. Both leachates had nematotoxic effects. Greenhouse experiments were conducted to evaluate the effect of the four legumes dried leaves incorporated as mulches to potting soil, on the number and biomass of weeds, and on the biomass of tomato (Lycopersicon esculentum L.) plants. The decomposition of velvetbean and jackbean leaves in potting soil significantly reduced (>50%) the development of phytopathogenic nematodes in the roots of tomato. A 5‐yr field experiment conducted at the University of Yucatan (UADY) evaluated the effect of velvetbean and jackbean used as living cover crops, and jumbiebean and wild tamarind used as dead mulches incorporated on soil surface, on weed growth, and corn (Zea mays L.) yield. The experimental field was treated with the traditional slash and burn system in February 1994. In July 1994 the experiment was performed using the local agricultural practices in a complete randomized block design with three repetitions. The treatments were: corn+velvetbean, corn+jackbean, corn+jumbiebean, corn+wild tamarind, corn+Paraquat (1,1′‐dimethyl‐4,4′‐bipyridinium ion) herbicide, corn weeded by hand, and plots without corn weeded by hand. The number, biomass, diversity, and relative importance of weeds, as well as corn yield, were evaluated. In addition, taxonomic composition of weeds was determined. All legumes reduced weed growth with velvetbean (as living cover crop) producing the largest weed biomass reduction (68%). These legumes also improved the yield of corn during the first 2 yr of the experiment. For better management of natural resources, the use of legumes as biological tools in agriculture to control weeds and improve soil conditions should be encouraged through coordinated efforts between farmers, academic, and governmental institutions.

THE POTENTIAL OF SPIDERS TO EXHIBIT STABLE EQUILIBRIUM POINT CONTROL OF PREY: TESTS OF TWO CRITERIA

The mechanisms by which spiders limit prey populations were investigated with specific reference to the criteria required for equilibrium point control, a predator–prey model in the food-web literature that explains top-down effects on lower trophic levels. In this paper we review results of previous studies that demonstrate that spiders meet two of the four criteria of equilibrium point control: (1) they are generalist feeders, and (2) they are self-damped. We further present experimental evidence for the other two criteria of equilibrium point control: (3) spiders respond to temporal and spatial patterns of prey availability, and (4) species assemblages of spiders better limit assemblages of associated prey species than do individual spider species. We propose that the exhibition of equilibrium point control of associated prey populations by spiders will limit their role in agroecosystems to one of buffers to exponential increases in prey population numbers.

The ecological role of ants in two Mexican agroecosystems.

The development of the ant communities and their foraging dynamics were studied in two annual agroecosystems of the Mexican tropical lowlands: a "forest milpa" of corn, beans, and squash made by cutting and buring 40-year-old forest, and a "field milpa" of corn, beans, and squash made by plowing 1-year-old second growth. The ant community was sampled using tuna fish baits 26, 52, 110 and 353 days after planting. Although immediately after planting the same number of ant species occurred in each milpa type, thereafter the ant faunas diverged. The field milpa became completely dominated by the native fire ant, Solenopsis geminata, while the number of ant species in the forest milpa gradually increased over time, reaching eight species 110 days after planting and 14 species by 353 days. Initially S. geminata dominated the ant fauna in the forest milpa (occurring on 90% of the baits), but by 353 days planting it was found on only 26% of the occupied baits. Ant foraging efficiency, as measured by proportion of tuna baits occupied and the removal rates of dead Drosophila fly baits, was much higher (by a factor of 2 to 3) in the field than the forest milpa. This was caused by the extremely high density of S. geminata colonies in the field milpa. The simple Solenopsis-dominated community of the field milpa may be much more effective in biological control than the more diverse community of the forest milpa. Although S. geminata has potential negative impacts in annual agroecosystems (it stings, eats corn seeds, and guards homopterams), its overall impact appears to be beneficial. As forested areas of the lowland wet tropics are increasingly cut and converted to annual agriculture, the primary ant inhabitant of these highly disturbed environments, S. geminata, will necessarily play a much more significant ecological role in agroecosystems.

Community structure of parasitoids Hymenoptera associated with Brassicaceae and non-crop vegetation

Abstract. Yaherwandi. 2012. Community structure of parasitoids Hymenoptera associated with Brassicaceae and non-crop vegetation. Nusantara Bioscience 4: 22-26. Parasitoids Hymenoptera has an important role in agroecosystem because of their ability in suppressing pest population. Their presence in the field is seen as the key to agricultural ecosystem. Their presence can be influenced by the availability of non-crop vegetation. Some adult parasitoids Hymenoptera require food in the form of pollen and nectar of wildflowers to ensure effective reproduction and longevity. The objective of this research was to study communities of parasitoid Hymenoptera in Brassicaceae field and non-crop vegetation around Brassicaceae fields. Samplings were conducted at two different landscape structures, i.e. Kayu Tanduak and Padang Laweh representing complex landscapes, whereas Alahan Panjang and Sungai Nanam representing simple landscapes. Insects were sampled by three trapping techniques (farm crop, sweep net, and yellow pan traps) in one line of transect for each landscape. A total of 84 species from 17 families of parasitoids Hymenoptera were collected in Brassicaceae field and in non-crop vegetation. Landscape structure, flowering vegetation, and pesticide application affected the species richness, diversity and evenness of parasitoids Hymenoptera in Brassicaceae fields and non-crop vegetation.