Bacterial Gut Symbionts Contribute to Seed Digestion in an Omnivorous Beetle

Obligate bacterial symbionts alter the diets of host animals in numerous ways, but the ecological roles of facultative bacterial residents that colonize insect guts remain unclear. Carabid beetles are a common group of beneficial insects appreciated for their ability to consume insect prey and seeds, but the contributions of microbes to diet diversification in this and similar groups of facultative granivores are largely unknown.Using 16S rRNA gene clone libraries and terminal restriction fragment (tRF) length polymorphism analyses of these genes, we examined the bacterial communities within the guts of facultatively granivorous, adult Harpalus pensylvanicus (Carabidae), fed one of five dietary treatments: 1) an untreated Field population, 2) Seeds with antibiotics (seeds were from Chenopodium album), 3) Seeds without antibiotics, 4) Prey with antibiotics (prey were Acheta domesticus eggs), and 5) Prey without antibiotics. The number of seeds and prey consumed by each beetle were recorded following treatment. Harpalus pensylvanicus possessed a fairly simple gut community of approximately 3-4 bacterial operational taxonomic units (OTU) per beetle that were affiliated with the Gammaproteobacteria, Bacilli, Alphaproteobacteria, and Mollicutes. Bacterial communities of the host varied among the diet and antibiotic treatments. The field population and beetles fed seeds without antibiotics had the closest matching bacterial communities, and the communities in the beetles fed antibiotics were more closely related to each other than to those of the beetles that did not receive antibiotics. Antibiotics reduced and altered the bacterial communities found in the beetle guts. Moreover, beetles fed antibiotics ate fewer seeds, and those beetles that harbored the bacterium Enterococcus faecalis consumed more seeds on average than those lacking this symbiont.We conclude that the relationships between the bacterium E. faecalis and this factultative granivore's ability to consume seeds merit further investigation, and that facultative associations with symbiotic bacteria have important implications for the nutritional ecology of their hosts

Crown structure and biomass allocation strategies of three juvenile tropical tree species

We measured leaf distribution, crown shape, and biomass allocation patterns in open-grown saplings of three tree species (Cedrela odorata, Cordia alliodora, and Hyeronima alchorneoides) that differed in above-ground architecture and successional status. The objectives were to: (1) analyze the relationship between crown structure and biomass allocation in free-growing juveniles and (2) assess whether predictions that relate crown structure and biomass distribution of adult individuals can be applied to noncompeting saplings. Significant differences in crown structure and biomass allocation were found among the three species. Mean dry biomass was 990 g in Cedrela, 665 g, in Cordia, and 1281 g in Hyeronima. Cedrela allocated a greater proportion of biomass into roots than the other two species. We observed no distinct pattern of foliage angle, and no evidence of decrease in crown construction efficiency with tree size. Predictions stated by other authors for mature individuals partially explained the relationships between biomass allocation and morphological variables of non-competing saplings. We proposed two alternative biomass allocation patterns: (1) in open conditions saplings of early successional species exhibit structural characteristics more adapted for high light levels than gap-dependent species, and (2) early successional species have lower cost-benefit ratio for biomass construction and higher foliar efficiency than late successional ones. In general, crown morphometric characteristics and biomass distribution patterns of the three species studied corresponded with the two proposed patterns

Canopy development in tropical tree plantations: a comparison of species mixtures and monocultures

In this study, the early development of monocultures and mixtures of Cedrela odorata, Cordia alliodora, and Hyeronima alchorneoides was measured to determine what interspecific differences in structural characteristics lead to good ecological combining ability in fast-growing tropical tree species. Plantations were established at high density (2887 trees/ha) on fertile alluvial soil in the humid Atlantic lowlands of Costa Rica. The three species are native to the region and were selected to represent a range of crown structure, leaf morphology, and phenology. Height growth was rapid for all three species, with dominant heights (mean height of tallest 20% of trees) of monocultures reaching 7–8 m at age 2.0 yr, and 14–15 m at age 4.0 yr. At age 2.0 yr, monocultures had nearly reached their maximum leaf area index (LAI), with Hyeronima forming a denser canopy (LAI of 4.5) than the other two species (LAI's of 2.5). In mixtures, a partially stratified canopy developed with the tallest Cordia forming an upper canopy stratum above Cedrela and Hyeronima. Mixtures reached an LAI of 3.9 by age 3.0 yr, approaching the level of the Hyeronima monoculture. Compared to their growth in monoculture, Cordia was taller and Hyeronima was shorter in mixture, but both species developed larger mean crown size and breast-height diameters in mixture. In contrast, Cedrela was smaller in all dimensions in mixture than in monoculture. The poor growth of Cedrela in mixture likely resulted from the early onset of interspecific competition coupled with damage from attacks of the shootborer Hypsipyla grandella. Cedrela seedlings recovered their rapid growth in monoculture after early insect attacks, but were suppressed in mixtures by the competition from surrounding trees of Cordia and Hyeronima which are not susceptible to the shootborer. The compatibility of Cordia and Hyeronima was related to the formation of a stratified canopy in mixture. Cordia has more rapid seedling height growth than Hyeronima, but forms a more open canopy with low LAI and semi-deciduous foliage. This results in the interception of sufficient solar radiation in the upper canopy to allow high productivity of Cordia, and yet adequate transmission of radiation to the dense, evergreen crowns of Hyeronima for rapid growth of that species in the lower canopy. This combination of characteristics is likely to lead to compatibility in other sets of tree species.249-26

Nitrogen dynamics and red pine growth following application of pelletized biosolids in Massachusetts, USA

Pelletized biosolids from municipal wastewater treatment were applied to a thinned red pine plantation to determine if there were treatment levels that could produce a fertilization growth response without resulting in unacceptable nitrate leaching. The pellets (total nutrient concentrations of 4.4% N, 1.4% P, 0.2% K) were applied at four levels (0, 200, 400, 800 kg/ha total N). Only 26% of labile organic N in the pellets was mineralized in the first year after application. Foliar N increased with increasing application rate, but other nutrients were unchanged. Red pine basal area growth was unchanged with low and medium levels, but decreased to 50% of control plots with the highest level. A decrease in foliar K/N ratio resulting from high N uptake with little additional K is hypothesized as the cause for the growth decline. The highest treatment level resulted in lysimeter nitrate-N concentrations increasing to 2 mg/L in the first year and 9 mg/L in the second, returning to control levels in the third; no increase occurred in other treatments. These results contrast with those found with liquid sludge applications, in which nearly all N mineralization and the highest nitrate leaching rates occurred in the first year. The slower release of inorganic N from pellets over 2 years may allow higher total N application rates without causing high nitrate leaching.1477-148

Canopy development in tropical tree plantations: a comparison of species mixtures and monocultures

In this study, the early development of monocultures and mixtures of Cedrela odorata, Cordia alliodora, and Hyeronima alchorneoides was measured to determine what interspecific differences in structural characteristics lead to good ecological combining ability in fast-growing tropical tree species. Plantations were established at high density (2887 trees/ha) on fertile alluvial soil in the humid Atlantic lowlands of Costa Rica. The three species are native to the region and were selected to represent a range of crown structure, leaf morphology, and phenology. Height growth was rapid for all three species, with dominant heights (mean height of tallest 20% of trees) of monocultures reaching 7–8 m at age 2.0 yr, and 14–15 m at age 4.0 yr. At age 2.0 yr, monocultures had nearly reached their maximum leaf area index (LAI), with Hyeronima forming a denser canopy (LAI of 4.5) than the other two species (LAI's of 2.5). In mixtures, a partially stratified canopy developed with the tallest Cordia forming an upper canopy stratum above Cedrela and Hyeronima. Mixtures reached an LAI of 3.9 by age 3.0 yr, approaching the level of the Hyeronima monoculture. Compared to their growth in monoculture, Cordia was taller and Hyeronima was shorter in mixture, but both species developed larger mean crown size and breast-height diameters in mixture. In contrast, Cedrela was smaller in all dimensions in mixture than in monoculture. The poor growth of Cedrela in mixture likely resulted from the early onset of interspecific competition coupled with damage from attacks of the shootborer Hypsipyla grandella. Cedrela seedlings recovered their rapid growth in monoculture after early insect attacks, but were suppressed in mixtures by the competition from surrounding trees of Cordia and Hyeronima which are not susceptible to the shootborer. The compatibility of Cordia and Hyeronima was related to the formation of a stratified canopy in mixture. Cordia has more rapid seedling height growth than Hyeronima, but forms a more open canopy with low LAI and semi-deciduous foliage. This results in the interception of sufficient solar radiation in the upper canopy to allow high productivity of Cordia, and yet adequate transmission of radiation to the dense, evergreen crowns of Hyeronima for rapid growth of that species in the lower canopy. This combination of characteristics is likely to lead to compatibility in other sets of tree species.249-26

What is the available evidence concerning relative performance of different designs of mixed-species plantings for smallholder and community forestry in the tropics? A systematic map protocol

Background There has been growing interest in mixed species plantation systems because of their potential to provide a range of socio-economic and bio-physical benefits which can be matched to the diverse needs of smallholders and communities. Potential benefits include the production of a range of forest products for home and commercial use; improved soil fertility especially when nitrogen fixing species are included; improved survival rates and greater productivity of species; a reduction in the amount of damage from pests or disease; and improved biodiversity and wildlife habitats. Despite these documented services and growing interest in mixed species plantation systems, the actual planting areas in the tropics are low, and monocultures are still preferred for industrial plantings and many reforestation programs because of perceived higher economic returns and readily available information about the species and their silviculture. In contrast, there are few guidelines for the design and management of mixed-species systems, including the social and ecological factors of successful mixed species plantings. Methods This protocol explains the methodology used to investigate the following question: What is the available evidence for the relative performance of different designs of mixed-species plantings for smallholder and community forestry in the tropics? This study will systematically search, identify and describe studies related to mixed species plantings across tropical and temperate zones to identify the social and ecological factors that affect polyculture systems. The objectives of this study are first to identify the evidence of biophysical or socio-economic factors that have been considered when designing mixed species systems for community and smallholder forestry in the tropics; and second, to identify gaps in research of mixed species plantations. Results of the study will help create guidelines that can assist practitioners, scientists and farmers to better design mixed species plantation systems for smallholders in the tropics