The Penalty of a Long, Hot Summer. Photosynthetic Acclimation to High CO2 and Continuous Light in “Living Fossil” Conifers

Deciduous forests covered the ice-free polar regions 280 to 40 million years ago under warm “greenhouse” climates and high atmospheric pCO2. Their deciduous habit is frequently interpreted as an adaptation for minimizing carbon losses during winter, but experiments with “living fossils” in a simulated warm polar environment refute this explanation. Measured carbon losses through leaf abscission of deciduous trees are significantly greater than losses through winter respiration in evergreens, yet annual rates of primary productivity are similar in all species. Here, we investigate mechanisms underlying this apparent paradox by measuring the seasonal patterns of leaf photosynthesis (A) under pCO2 enrichment in the same trees. During spring, A increased significantly in coastal redwood (Sequoia sempervirens), dawn redwood (Metasequoia glyptostroboides), and swamp cypress (Taxodium distichum) at an elevated pCO2 of 80 Pa compared with controls at 40 Pa. However, strong acclimation in Rubisco carboxylation capacity (Vc,max) completely offset the CO2 response of A in all species by the end of 6 weeks of continuous illumination in the simulated polar summer. Further measurements demonstrated the temporary nature of acclimation, with increases in Vc,max during autumn restoring the CO2 sensitivity of A. Contrary to expectations, the acclimation of Vc,max was not always accompanied by accumulation of leaf carbohydrates, but was associated with a decline in leaf nitrogen in summer, suggesting an alteration of the balance in plant sources and sinks for carbon and nitrogen. Preliminary calculations using A indicated that winter carbon losses through deciduous leaf abscission and respiration were recovered by 10 to 25 d of canopy carbon fixation during summer, thereby explaining the productivity paradox

Enrichment of the hot intracluster medium: observations

Four decades ago, the firm detection of an Fe-K emission feature in the X-ray spectrum of the Perseus cluster revealed the presence of iron in its hot intracluster medium (ICM). With more advanced missions successfully launched over the last 20 years, this discovery has been extended to many other metals and to the hot atmospheres of many other galaxy clusters, groups, and giant elliptical galaxies, as evidence that the elemental bricks of life - synthesized by stars and supernovae - are also found at the largest scales of the Universe. Because the ICM, emitting in X-rays, is in collisional ionisation equilibrium, its elemental abundances can in principle be accurately measured. These abundance measurements, in turn, are valuable to constrain the physics and environmental conditions of the Type Ia and core-collapse supernovae that exploded and enriched the ICM over the entire cluster volume. On the other hand, the spatial distribution of metals across the ICM constitutes a remarkable signature of the chemical history and evolution of clusters, groups, and ellipticals. Here, we summarise the most significant achievements in measuring elemental abundances in the ICM, from the very first attempts up to the era of XMM-Newton, Chandra, and Suzaku and the unprecedented results obtained by Hitomi. We also discuss the current systematic limitations of these measurements and how the future missions XRISM and Athena will further improve our current knowledge of the ICM enrichment.Comment: 49 pages. Review paper. Accepted for publication on Space Science Reviews. This is the companion review of "Enrichment of the hot intracluster medium: numerical simulations

Revisiting the stability of spatially heterogeneous predator-prey systems under eutrophication

We employ partial integro-differential equations to model trophic interaction in a spatially extended heterogeneous environment. Compared to classical reaction-diffusion models, this framework allows us to more realistically describe the situation where movement of individuals occurs on a faster time scale than the demographic (population) time scale, and we cannot determine population growth based on local density. However, most of the results reported so far for such systems have only been verified numerically and for a particular choice of model functions, which obviously casts doubts about these findings. In this paper, we analyse a class of integro-differential predator-prey models with a highly mobile predator in a heterogeneous environment, and we reveal the main factors stabilizing such systems. In particular, we explore an ecologically relevant case of interactions in a highly eutrophic environment, where the prey carrying capacity can be formally set to 'infinity'. We investigate two main scenarios: (i) the spatial gradient of the growth rate is due to abiotic factors only, and (ii) the local growth rate depends on the global density distribution across the environment (e.g. due to non-local self-shading). For an arbitrary spatial gradient of the prey growth rate, we analytically investigate the possibility of the predator-prey equilibrium in such systems and we explore the conditions of stability of this equilibrium. In particular, we demonstrate that for a Holling type I (linear) functional response, the predator can stabilize the system at low prey density even for an 'unlimited' carrying capacity. We conclude that the interplay between spatial heterogeneity in the prey growth and fast displacement of the predator across the habitat works as an efficient stabilizing mechanism.Comment: 2 figures; appendices available on request. To appear in the Bulletin of Mathematical Biolog

Perspectives on Intracluster Enrichment and the Stellar Initial Mass Function in Elliptical Galaxies

Stars formed in galaxy cluster potential wells must be responsible for the high level of enrichment measured in the intracluster medium (ICM); however, there is increasing tension between this truism and the parsimonious assumption that the stars in the generally old population studied optically in cluster galaxies emerged from the same formation sites at the same epochs. We construct a phenomenological cluster enrichment model to demonstrate that ICM elemental abundances are underestimated by a factor >2 for standard assumptions about the stellar population -- a discrepancy we term the "cluster elemental abundance paradox". Recent evidence of an elliptical galaxy IMF skewed to low masses deepens the paradox. We quantify the adjustments to the star formation efficiency and initial mass function (IMF), and SNIa production efficiency, required to resolve this while being consistent with the observed ICM abundance pattern. The necessary enhancement in metal enrichment may, in principle, originate in the observed stellar population if a larger fraction of stars in the supernova-progenitor mass range form from an initial mass function (IMF) that is either bottom-light or top-heavy, with the latter in some conflict with observed ICM abundance ratios. Other alternatives that imply more modest revisions to the IMF, mass return and remnant fractions, and primordial fraction, posit an increase in the fraction of 3-8 solar mass stars that explode as SNIa or assume that there are more stars than conventionally thought -- although the latter implies a high star formation efficiency. We discuss the feasibility of these various solutions and the implications for the diversity of star formation in the universe, the process of elliptical galaxy formation, and the origin of this "hidden" source of ICM metal enrichment.Comment: 22 pages, 24 figures; uses emulateapj.cls; moderate revisions following referee feedback (now includes author's name!); now ApJ in pres

A phylogeny of birds based on over 1,500 loci collected by target enrichment and high-throughput sequencing

Evolutionary relationships among birds in Neoaves, the clade comprising the vast majority of avian diversity, have vexed systematists due to the ancient, rapid radiation of numerous lineages. We applied a new phylogenomic approach to resolve relationships in Neoaves using target enrichment (sequence capture) and high-throughput sequencing of ultraconserved elements (UCEs) in avian genomes. We collected sequence data from UCE loci for 32 members of Neoaves and one outgroup (chicken) and analyzed data sets that differed in their amount of missing data. An alignment of 1,541 loci that allowed missing data was 87% complete and resulted in a highly resolved phylogeny with broad agreement between the Bayesian and maximum-likelihood (ML) trees. Although results from the 100% complete matrix of 416 UCE loci were similar, the Bayesian and ML trees differed to a greater extent in this analysis, suggesting that increasing from 416 to 1,541 loci led to increased stability and resolution of the tree. Novel results of our study include surprisingly close relationships between phenotypically divergent bird families, such as tropicbirds (Phaethontidae) and the sunbittern (Eurypygidae) as well as between bustards (Otididae) and turacos (Musophagidae). This phylogeny bolsters support for monophyletic waterbird and landbird clades and also strongly supports controversial results from previous studies, including the sister relationship between passerines and parrots and the non-monophyly of raptorial birds in the hawk and falcon families. Although significant challenges remain to fully resolving some of the deep relationships in Neoaves, especially among lineages outside the waterbirds and landbirds, this study suggests that increased data will yield an increasingly resolved avian phylogeny.Comment: 30 pages, 1 table, 4 figures, 1 supplementary table, 3 supplementary figure

Paradox as invitation to act in problematic change situations

It has been argued that organizational life typically contains paradoxical situations such as efforts to manage change which nonetheless seem to reinforce inertia. Four logical options for coping with paradox have been explicated, three of which seek resolution and one of which ‘keeps the paradox open’. The purpose of this article is to explore the potential for managerial action where the paradox is held open through the use of theory on ‘serious playfulness’. Our argument is that paradoxes, as intrinsic features in organizational life, cannot always be resolved through cognitive processes. What may be possible, however, is that such paradoxes are transformed, or ‘moved on’ through action and as a result the overall change effort need not be stalled by the existence of embedded paradoxes