Cyanogenesis of Wild Lima Bean (Phaseolus lunatus L.) Is an Efficient Direct Defence in Nature

In natural systems plants face a plethora of antagonists and thus have evolved multiple defence strategies. Lima bean (Phaseolus lunatus L.) is a model plant for studies of inducible indirect anti-herbivore defences including the production of volatile organic compounds (VOCs) and extrafloral nectar (EFN). In contrast, studies on direct chemical defence mechanisms as crucial components of lima beans' defence syndrome under natural conditions are nonexistent. In this study, we focus on the cyanogenic potential (HCNp; concentration of cyanogenic glycosides) as a crucial parameter determining lima beans' cyanogenesis, i.e. the release of toxic hydrogen cyanide from preformed precursors. Quantitative variability of cyanogenesis in a natural population of wild lima bean in Mexico was significantly correlated with missing leaf area. Since existing correlations do not by necessity mean causal associations, the function of cyanogenesis as efficient plant defence was subsequently analysed in feeding trials. We used natural chrysomelid herbivores and clonal lima beans with known cyanogenic features produced from field-grown mother plants. We show that in addition to extensively investigated indirect defences, cyanogenesis has to be considered as an important direct defensive trait affecting lima beans' overall defence in nature. Our results indicate the general importance of analysing ‘multiple defence syndromes’ rather than single defence mechanisms in future functional analyses of plant defences

High energy or protein concentrations in food as possible offsets for cyanide consumption by specialized bamboo lemurs in Madagascar

Plants producing toxic plant secondary metabolites (PSMs) deter folivores from feeding on them. Animals that can cope with noxious PSMs have a niche with a competitive advantage over other species. However, the ability to cope with toxic PSMs incurs the costs of detoxification. To assess possible compensations for the ingestion of toxic PSMs, we compare the chemical quality of plants consumed by bamboo lemurs (genera Hapalemur and Prolemur; strepsirrhine primates of Madagascar) in areas with and without bamboo. Some bamboo lemurs consume bamboo containing concentrations of cyanogenic substances 10–50 times above the average lethal dosage for mammals, and we postulate that animals consuming cyanogenic substances need supplementary protein or readily available energy for detoxification. We compared the chemical composition of food consumed by three species of bamboo lemurs that feed mainly (>80% of their time) on bamboo in the evergreen rainforest of Ranomafana (Madagascar) with published data of the diets of bamboo lemurs at two sites without highly cyanogenic plants (reed beds of Lac Alaotra and the evergreen littoral forest of Mandena) and with food of sympatric folivorous lemur species that do not feed on bamboo. Lemurs feeding on bamboo consumed up to twice as much protein as bamboo lemurs in areas without bamboo and sympatric lemur species that feed on leaves of trees. Concentrations of nonstructural carbohydrates (a source of energy) showed the opposite trend. This result supports the hypothesis that feeding on cyanogenic plants is linked to high protein intake, either as a source of protein or for sulfur-containing amino acids that can be used for detoxification. Owing to the high protein concentrations in bamboo, however, we cannot distinguish between the hypothesis that lemurs that eat bamboo target additional food items with higher protein from the hypothesis that lemurs feeding on bamboo unavoidably obtain higher concentrations of protein than animals feeding on leaves of trees, without an added nutritional benefit

Local Adaptation of Aboveground Herbivores towards Plant Phenotypes Induced by Soil Biota

Background: Soil biota may trigger strong physiological responses in plants and consequently induce distinct phenotypes. Plant phenotype, in turn, has a strong impact on herbivore performance. Here, we tested the hypothesis that aboveground herbivores are able to adapt to plant phenotypes induced by soil biota. Methodology and Principal Findings: We bred spider mites for 15 generations on snap beans with three different belowground biotic interactions: (i) no biota (to serve as control), (ii) arbuscular mycorrhizal fungi and (ii) root-feeding nematodes. Subsequently, we conducted a reciprocal selection experiment using these spider mites, which had been kept on the differently treated plants. Belowground treatments induced changes in plant biomass, nutrient composition and water content. No direct chemical defence through cyanogenesis was detected in any of the plant groups. Growth rates of spider mites were higher on the ecotypes on which they were bred for 15 generations, although the statistical significance disappeared for mites from the nematode treatment when corrected for all multiple comparisons. Conclusion/Significance: These results demonstrate that belowground biota may indeed impose selection on the aboveground insect herbivores mediated by the host plant. The observed adaptation was driven by variable quantitativ

In situ tropical peatland fire emission factors and their variability, as determined by field measurements in Peninsula Malaysia.

Fires in tropical peatlands account for >25% of estimated total greenhouse gas emissions from deforestation and degradation. Despite significant global and regional impacts, our understanding of specific gaseous fire emission factors (EFs) from tropical peat burning is limited to a handful of studies. Furthermore, there is substantial variability in EFs between sampled fires and/or studies. For example, methane EFs vary by 91% between studies. Here we present new fire EFs for the tropical peatland ecosystem; the first EFs measured for Malaysian peatlands, and only the second comprehensive study of EFs in this crucial environment. During August 2015 (under El Niño conditions) and July 2016, we embarked on field campaigns to measure gaseous emissions at multiple peatland fires burning on deforested land in Southeast Pahang (2015) and oil palm plantations in North Selangor (2016), Peninsula Malaysia. Gaseous emissions were measured using open-path Fourier transform infrared spectroscopy. The IR spectra were used to retrieve mole fractions of twelve different gases present within the smoke (including carbon dioxide and methane), and these measurements used to calculate EFs. Peat samples were taken at each burn site for physicochemical analysis and to explore possible relationships between specific physicochemical properties and fire EFs. Here we present the first evidence to indicate that substrate bulk density affects methane fire EFs reported here. This novel explanation of inter-plume, within-biome variability should be considered by those undertaking greenhouse gas accounting and haze forecasting in this region, and is of importance to peatland management, particularly with respect to artificial compaction

Testing the optimal defence hypothesis for two indirect defences: extrafloral nectar and volatile organic compounds

Many plants respond to herbivory with an increased production of extrafloral nectar (EFN) and/or volatile organic compounds (VOCs) to attract predatory arthropods as an indirect defensive strategy. In this study, we tested whether these two indirect defences fit the optimal defence hypothesis (ODH), which predicts the within-plant allocation of anti-herbivore defences according to trade-offs between growth and defence. Using jasmonic acid-induced plants of Phaseolus lunatus and Ricinus communis, we tested whether the within-plant distribution pattern of these two indirect defences reflects the fitness value of the respective plant parts. Furthermore, we quantified photosynthetic rates and followed the within-plant transport of assimilates with 13C labelling experiments. EFN secretion and VOC emission were highest in younger leaves. Moreover, the photosynthetic rate increased with leaf age, and pulse-labelling experiments suggested transport of carbon to younger leaves. Our results demonstrate that the ODH can explain the within-plant allocation pattern of both indirect defences studied

The use of Earth Observation for wetland inventory, assessment and monitoring

The use of Earth Observation (EO) provides Contracting Parties to the Ramsar Convention on Wetlands with new approaches to ensure the wise use and conservation of wetlands at the national and global levels. EO has many applications including the inventory, assessment and monitoring of wetlands. As technology advances, previous limitations of EO will be reduced, and it is anticipated that the use of EO in the management of wetlands will increase. This Ramsar Technical Report aims to provide practitioners with an overview and illustration, through case studies, on the use of EO for implementation of the Convention and the wise use of wetlands more broadly

Denial of long-term issues with agriculture on tropical peatlands will have devastating consequences

Non peer reviewe

The effects of ditch dams on water‐level dynamics in tropical peatlands

A significant proportion of tropical peatlands has been drained for agricultural purposes, resulting in severe degradation. Hydrological restoration, which usually involves blocking ditches, is therefore a priority. Nevertheless, the influence of ditch blocking on tropical peatland hydrological functioning is still poorly understood. We studied water-level dynamics using a combination of automated and manual dipwells, and also meteorological data during dry and wet seasons over 6 months at three locations in Sebangau National Park, Kalimantan, Indonesia. The locations were a forested peatland (Forested), a drained peatland with ditch dams (Blocked), and a drained peatland without ditch dams (Drained). In the dry season, water tables at all sites were deeper than the Indonesian regulatory requirement of 40 cm from the peat surface. In the dry season, the ditches were dry and water did not flow to them. The dry season water-table drawdown rates — solely due to evapotranspiration — were 9.3 mm day−1 at Forested, 9.6 mm day−1 at Blocked, but 12.7 mm day−1 at Drained. In the wet season, the proportion of time during which water tables in the wells were deeper than the 40 cm limit ranged between 16% and 87% at Forested, 0% at Blocked, and between 0% and 38% at Drained. In the wet season, water flowed from the peatland to ditches at Blocked and Drained. The interquartile range of hydraulic gradients between the lowest ditch outlet and the farthest well from ditches at Blocked was 3.7 × 10−4 to 7.8 × 10−4 m m−1, but 1.9 × 10−3 to 2.6 × 10−3 m m−1 at Drained. Given the results from Forested, a water-table depth limit policy based on field data may be required, to reflect natural seasonal dynamics in tropical peatlands. Revised spatial designs of dams or bunds are also required, to ensure effective water-table management as part of tropical peatland restoration

The distribution and amount of carbon in the largest peatland complex in Amazonia

Peatlands in Amazonian Peru are known to store large quantities of carbon, but there is high uncertainty in the spatial extent and total carbon stocks of these ecosystems. Here, we use a multi-sensor (Landsat, ALOS PALSAR and SRTM) remote sensing approach, together with field data including 24 forest census plots and 218 peat thickness measurements, to map the distribution of peatland vegetation types and calculate the combined above- and below-ground carbon stock of peatland ecosystems in the Pastaza-Marañon foreland basin in Peru. We find that peatlands cover 35 600 ± 2133 km2 and contain 3.14 (0.44–8.15) Pg C. Variation in peat thickness and bulk density are the most important sources of uncertainty in these values. One particular ecosystem type, peatland pole forest, is found to be the most carbon-dense ecosystem yet identified in Amazonia (1391 ± 710 Mg C ha−1). The novel approach of combining optical and radar remote sensing with above- and below-ground carbon inventories is recommended for developing regional carbon estimates for tropical peatlands globally. Finally, we suggest that Amazonian peatlands should be a priority for research and conservation before the developing regional infrastructure causes an acceleration in the exploitation and degradation of these ecosystems