Flame curtain kilns produce biochar from dry biomass with minimal methane emissions.

Flame curtain kilns have emerged as the preferred biochar technology for smallholders but reported methane emissions (30 g kg-1 biochar) have impeded carbon certification. Here, for flame curtain kilns we show almost no methane (0-3.6 g kg-1 biochar) emissions for dry (<15 % moisture) feedstock consisting of twigs and leaves. Wet feedstock (>40 % moisture) however generated significant methane (>500 g kg-1 biochar), underscoring that feedstock preparation is decisive for the carbon balance. Even for dry feedstock, both aerosol and CO emissions were significant (21-82 and 40-118 g kg-1 biochar, respectively). The data demonstrate that certification of low-tech biochar made from dry twigs and leaves should not be objected to on the grounds of methane. Careful selection of feedstock and potential after-combustion of the syn-gases are probably needed to avoid CO and aerosol emissions. More data are needed on methane emissions of other dry feedstocks.

The distribution of cadmium in soil and cacao beans in Peru.

Peru is the eighth largest producer of cacao beans globally, but high cadmium contents are constraining access to international markets which have set upper thresholds for permitted concentrations in chocolate and derivatives. Preliminary data have suggested that high cadmium concentrations in cacao beans are restricted to specific regions in the country, but to date no reliable maps exist of expected cadmium concentrations in soils and cacao beans. Drawing on >2000 representative samples of cacao beans and soils we developed multiple national and regional random forest models to develop predictive maps of cadmium in soil and cacao beans across the area suitable for cacao cultivation. Our model projections show that elevated concentrations of cadmium in cacao soils and beans are largely restricted to the northern parts of the country in the departments of Tumbes, Piura, Amazonas and Loreto, as well as some very localized pockets in the central departments of Huánuco and San Martin. Unsurprisingly, soil cadmium was the by far most important predictor of bean cadmium. Aside from the south-eastern to north-western spatial trend of increasing cadmium values in soils and beans, the most important predictors of both variables in nation-wide models were geology, rainfall seasonality, soil pH and rainfall. At regional level, alluvial deposits and mining operations were also associated with higher cadmium levels in cacao beans. Based on our predictive map of cadmium in cacao beans we estimate that while at a national level <20 % of cacao farming households might be impacted by the cadmium regulations, in the most affected department of Piura this could be as high as 89 %.

Optimal allocation of resources in response to shading and neighbours in the heteroblastic species, Acacia implexa.

BACKGROUND AND AIMS: Heteroblasty is an encompassing term referring to ontogenetic changes in the plant shoot. A shaded environment is known to affect the process of heteroblastic development; however, it is not known whether crowded or high density growing conditions can also alter heteroblasty. Compound leaves of the shade-intolerant Acacia implexa allocate less biomass per unit photosynthetic area than transitional leaves or phyllodes and it is hypothesized that this trait will convey an advantage in a crowded environment. Compound leaves also have larger photosynthetic capture area - a trait known to be advantageous in shade. This studied tested the hypothesis that more compound leaves will be developed under shade and crowded environments. Furthermore, this species should undergo optimal allocation of biomass to shoots and roots given shaded and crowded environments. METHODS: A full factorial design of irradiance (high and low) and density levels (high, medium and low) on three populations sourced from varying rainfall regions (high, medium and low) was established under controlled glasshouse conditions. Traits measured include the number of nodes expressing a compound leaf, biomass allocation to shoots and roots, and growth traits. Key Results A higher number of nodes expressed a compound leaf under low irradiance and in high density treatments; however, there were no significant interactions across treatments. Phenotypes strongly associated with the shade avoidance syndrome were developed under low irradiance; however, this was not observed under high density. There was no significant difference in relative growth rates across light treatments, but growth was significantly slower in a crowded environment. Conclusions Heteroblastic development in Acacia can be altered by shade and crowded environments. In this experiment, light was clearly the most limiting factor to growth in a shaded environment; however, in a crowded environment there were additional limiting resources to growth.

Habitat Quality Differentiation and Consequences for Ecosystem Service Provision of an Amazonian Hyperdominant Tree Species.

Ecosystem services of Amazonian forests are disproportionally produced by a limited set of hyperdominant tree species. Yet the spatial variation in the delivery of ecosystem services by individual hyperdominant species across their distribution ranges and corresponding environmental gradients is poorly understood. Here, we use the concept of habitat quality to unravel the effect of environmental gradients on seed production and aboveground biomass (AGB) of the Brazil nut, one of Amazonia's largest and most long-lived hyperdominants. We find that a range of climate and soil gradients create trade-offs between density and fitness of Brazil nut trees. Density responses to environmental gradients were in line with predictions under the Janzen-Connell and Herms-Mattson hypotheses, whereas tree fitness responses were in line with resource requirements of trees over their life cycle. These trade-offs resulted in divergent responses in area-based seed production and AGB. While seed production and AGB of individual trees (i.e., fitness) responded similarly to most environmental gradients, they showed opposite tendencies to tree density for almost half of the gradients. However, for gradients creating opposite fitness-density responses, area-based seed production was invariable, while trends in area-based AGB tended to mirror the response of tree density. We conclude that while the relation between environmental gradients and tree density is generally indicative of the response of AGB accumulation in a given area of forest, this is not necessarily the case for fruit production.

The adaptive value of functional and life-history traits across fertility treatments in an annual plant.

BACKGROUND AND AIMS: Plant functional traits are assumed to be adaptive. As selection acts on individuals and not on traits, interpreting the adaptive value of a trait not may be straightforward. For example, productive leaves are associated with fertile environments. However, it is not clear if productive leaves confer an advantage in these habitats, or if they are an advantage as part of a suite of coordinated traits. METHODS: Genotypes of Arabidopsis thaliana were grown in high and low nutrient treatments and low, neutral and high pH treatments. Nutrient availability is reduced in acidic or basic soils relative to neutral pH soils. pH treatments were used to alter the availability of resources rather than the amount of resources. KEY RESULTS: Leaf function (specific leaf area, SLA) and life history (size at reproduction, age at reproduction) were variable across genotypes and were plastic. High nutrient availability induced higher SLA and larger size at reproduction. Genotypes that reproduced at large size in high nutrient conditions at neutral pH had the greatest fruit production. SLA was only indirectly related to fruit production through a causal relationship with rosette size; in high nutrient conditions, plants with high SLA were large at reproduction and had higher fruit production. In high nutrient and high pH treatments, plants were large at reproduction, but large size at reproduction was associated with low fecundity. This suggests that large size is adaptive under high nutrient availability. CONCLUSIONS: Interpreting the adaptive value of functional traits will sometimes only be possible when these traits are considered as a suite of correlated and coordinated traits. Leaf functional traits may be important in defining adaptive strategies in A. thaliana but only through how they affect plant life history. Finally, manipulating soil pH can be a valuable tool in assessing adaptive plasticity on nutrient gradients.

Soil carbon is a useful surrogate for conservation planning in developing nations.

Defining the optimal placement of areas for biodiversity conservation in developing nations remains a significant challenge. Our best methods for spatially targeting potential locations for biodiversity conservation rely heavily on extensive georeferenced species observation data which is often incomplete or lacking in developing nations. One possible solution is the use of surrogates that enable site assessments of potential biodiversity values which use either indicator taxa or abiotic variables, or both. Among the plethora of abiotic variables, soil carbon has previously been identified as a potentially powerful predictor for threatened biodiversity, but this has not yet been confirmed with direct observational data. Here we assess the potential value of soil carbon for spatial prediction of threatened species using direct measurements as well as a wide range of GIS derived abiotic values as surrogates for threatened plant species in the PEBANPA network of permanent plots in Southern Patagonia. We find that soil carbon significantly improves the performance of a biodiversity surrogate elaborated using abiotic variables to predict the presence of threatened species. Soil carbon could thus help to prioritize sites in conservation planning. Further, the results suggest that soil carbon on its own can be a much better surrogate than other abiotic variables when prioritization of sites for conservation are calibrated on increasingly small sets of observation plots. We call for the inclusion of soil carbon data in the elaboration of surrogates used to optimize conservation investments in the developing world.

Germination requirements and responses to leaf litter of four species of eucalypt.

We studied how the responses of four species of eucalypt to leaf litter related to their germination responses to light and water availability. Two of the species (Eucalyptus obliqua and E. baxteri) have a mesic distribution, while the other two (E. oleosa, and E. incrassata) are more xerophytic. We studied the effect of litter on emergence of the four species in a glasshouse experiment. Litter did not affect the emergence of E. incrassata and E. oleosa, but enhanced the emergence of E. obliqua and E. baxteri. Litter increased the seedling mortality of all four species. Germination responses to light and water availability were studied in growth cabinets under controlled conditions. The germination of E. obliqua and E. baxteri was substantially lower under fluorescent light than in darkness, but that of E. oleosa and E. incrassata was not affected by the light environment. The germination of E. obliqua and E. baxteri was significantly reduced by reduced water potential (ψa). Substantial germination of E. oleosa and E. incrassata occurred even at very low ψa (less than -1.05 MPa). We conclude that both the shade and the humid micro-environment provided by litter may have contributed to the emergence responses of the four species to litter, and these responses may correspond to ecological adaptations to the different environments in which they live.

Priority effects produced by plant litter result in non-additive competitive effects.

Litter may indirectly affect competitive interactions. It is not clear whether these changes are additive or non-additive indirect effects. Non-additivity could result from: (1) changes in biomass allocation patterns by competitors towards organs not directly involved in resource acquisition (e.g., longer hypocotyls); (2) changes in the proportion of different functional groups (e.g., grasses and forbs) that possess different competitive abilities; or (3) through priority effects caused by subtle changes in timing of emergence. We used a combination of field and glasshouse experiments in which Eucalyptus obliqua seedlings were grown either with or without leaf litter (grass litter/eucalypt litter), and with or without competitors. Eucalypt species growing in the field and in pots attained more biomass with litter than without when competitors were absent. Competition substantially decreased the biomass of eucalypt seedlings. Competitive intensity was heavily influenced by litter type and was most intense in the presence of grass litter. Litter produced a small change in patterns of biomass allocation in the competing herbaceous vegetation, and there was a slight (marginally non-significant) indication of a change in the proportion of grasses relative to forbs when litter was present. However, when the integral of competitor biomass over time was used to calculate competitive intensity, the combined effects of the experimental factors (litter and competition) became additive, suggesting that the effect of leaf litter on the timing of germination and establishment in the grasses and forbs, relative to that of Eucalyptus seedlings, was the principal mechanism by which leaf litter altered the interaction strength of the species studied.