Contribution of subsurface peat to CO2 and CH4 fluxes in a neotropical peatland

Tropical peatlands play an important role in the global carbon cycling but little is known about factors regulating carbon dioxide (CO₂) and methane (CH₄) fluxes from these ecosystems. Here, we test the hypotheses that (i) CO₂ and CH₄ are produced mainly from surface peat and (ii) that the contribution of subsurface peat to net C emissions is governed by substrate availability. To achieve this, in situ and ex situ CO₂ and CH₄ fluxes were determined throughout the peat profiles under three vegetation types along a nutrient gradient in a tropical ombrotrophic peatland in Panama. The peat was also characterized with respect to its organic composition using ¹³C solid state cross‐polarization magic‐angle spinning nuclear magnetic resonance spectroscopy. Deep peat contributed substantially to CO₂ effluxes both with respect to actual in situ and potential ex situ fluxes. CH₄ was produced throughout the peat profile with distinct subsurface peaks, but net emission was limited by oxidation in the surface layers. CO₂ and CH₄ production were strongly substrate‐limited and a large proportion of the variance in their production (30% and 63%, respectively) was related to the quantity of carbohydrates in the peat. Furthermore, CO₂ and CH₄ production differed between vegetation types, suggesting that the quality of plant‐derived carbon inputs is an important driver of trace gas production throughout the peat profile. We conclude that the production of both CO₂ and CH₄ from subsurface peat is a substantial component of the net efflux of these gases, but that gas production through the peat profile is regulated in part by the degree of decomposition of the peat.     

Towards an understanding of how phloem amino acid composition shapes elevated CO2‐induced changes in aphid population dynamics

1. The performance of foliage feeders tends to decrease under elevated CO₂, but the responses of phloem‐feeding insects have been much more equivocal. As phloem tissues are less accessible than whole‐plant tissues, much less is known about how phloem composition is altered under elevated CO₂ and the mechanisms driving changes in aphid performance. 2. In this study, the plant mechanisms underlying the performance of Rhopalosiphum padi aphids on Hordeum vulgare (barley) grown under ambient (390 ppm) and elevated (700 ppm) CO₂ were examined. We used aphid stylectomy to sample pure phloem from plants in CO₂‐controlled conditions and high‐performance liquid chromatography to analyse phloem samples for amino acid concentrations. 3. Aphid abundance significantly increased by 127% under elevated CO₂. Consequently, plant biomass decreased under elevated CO₂ in trials with herbivores present, possibly due to the increased herbivore load, but increased when aphids were absent. The intrinsic rate of population increase (r_m) was significantly higher under elevated CO₂; however, there were no statistically significant effects on aphid fecundity or development time. The concentration of individual amino acids tended to increase, although these increases were statistically significant in only a few cases. A principal components analysis revealed that the relative abundance (mol %) of those amino acids considered essential for aphids tended to increase under elevated CO₂. 4. These results indicate that CO₂ may affect nutrient translocation in plants in ways that are contrary to predictions about nitrogen metabolite responses to CO₂. Such plant biochemical responses may underlie observations of improved phloem feeder performance under elevated CO₂.     

A cost‐effective method of assessing thermal habitat quality for endotherms

The conservation of many endothermic species depends critically on the availability of suitable retreat sites, yet we know little about the variation in thermal quality of such microhabitats. Studies of thermal habitat suitability for birds and mammals must account for the effect of endothermic heat production on their microclimates. For example, endotherms may significantly raise the air temperature in their retreat sites and this effect must be considered when assessing retreat site quality. We devised an inexpensive means by which to construct pseudo‐endothermic ‘environmental temperature’ models with the use of disposable heat pads. We applied this technique to investigate thermal aspects of nest box design, illustrating the potential positive and negative effects of nest box insulation depending on the environmental context. We suggest that, from a thermal perspective, the avoidance of heat stress is an important and underappreciated issue in the retreat site selection of endotherms.     

From climate change to population change: the need to consider annual life cycles

Detailed studies of organisms' life cycles are important for understanding population response to climate change. However, in general one cannot make strong inference about the overall population response from such studies, unless the full annual cycle of the species in question is covered. Here, we present a theoretical framework for the understanding of population response to climate change. Owing to the combined effects of demography, intraspecific feedback, and a possible use of environmental cues, environmentally induced changes in survival and/or reproduction do not necessarily lead to a straightforward change in population size. This framework can guide our thinking about how abiotic conditions work their way to the population level. More specifically, it can help us to identify mechanisms that need to be examined when predicting population change in response to expected climate change.     

Leaf‐cutting ants as ecosystem engineers: topsoil and litter perturbations around Atta cephalotes nests reduce nutrient availability

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Morphometric correlates of karyotype and host plant in genus Euceraphis (Hemiptera: Aphididae)

Abstract Samples of birch- and alder-feeding aphids of genus Euceraphis were measured and analysed using multiple discriminant analysis (canonical variates) to find out if morphological variation correlated with previously reported differences of karyotype and host association. The dataset comprised groups of specimens defined solely by locality and collection date. Mean scores on the first two canonical variates clustered the samples fully in accordance with their karyotypes and host plants, confirming the existence of a number of morphologically similar but distinct host-specific taxa within the E. betulae group. Three new species are described: Euceraphis borealis Blackman, sp.n. on Betula glandulosa and B. nana , Euceraphis papyrifericola Blackman, sp.n. on B. papyrifera , and Euceraphis quednaui Blackman, sp.n. on B. occidentalis . A key is provided to alate viviparae of the genus.