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Sphagnum physiology in the context of changing climate: emergent influences of genomics, modelling and host-microbiome interactions on understanding ecosystem function.
Peatlands harbour more than one-third of terrestrial carbon leading to the argument that the bryophytes, as major components of peatland ecosystems, store more organic carbon in soils than any other collective plant taxa. Plants of the genus Sphagnum are important components of peatland ecosystems and are potentially vulnerable to changing climatic conditions. However, the response of Sphagnum to rising temperatures, elevated CO2 and shifts in local hydrology have yet to be fully characterized. In this review, we examine Sphagnum biology and ecology and explore the role of this group of keystone species and its associated microbiome in carbon and nitrogen cycling using literature review and model simulations. Several issues are highlighted including the consequences of a variable environment on plant-microbiome interactions, uncertainty associated with CO2 diffusion resistances and the relationship between fixed N and that partitioned to the photosynthetic apparatus. We note that the Sphagnum fallax genome is currently being sequenced and outline potential applications of population-level genomics and corresponding plant photosynthesis and microbial metabolic modelling techniques. We highlight Sphagnum as a model organism to explore ecosystem response to a changing climate and to define the role that Sphagnum can play at the intersection of physiology, genetics and functional genomics
Evaluation of mTOR-regulated mRNA translation.
mTOR, the mammalian target of rapamycin, regulates protein synthesis (mRNA translation) by affecting the phosphorylation or activity of several translation factors. Here, we describe methods for studying the impact of mTOR signalling on protein synthesis, using inhibitors of mTOR such as rapamycin (which impairs some of its functions) or mTOR kinase inhibitors (which probably block all functions).To assess effects of mTOR inhibition on general protein synthesis in cells, the incorporation of radiolabelled amino acids into protein is measured. This does not yield information on the effects of mTOR on the synthesis of specific proteins. To do this, two methods are described. In one, stable-isotope labelled amino acids are used, and their incorporation into new proteins is determined using mass spectrometric methods. The proportions of labelled vs. unlabeled versions of each peptide from a given protein provide quantitative information about the rate of that protein's synthesis under different conditions. Actively translated mRNAs are associated with ribosomes in polyribosomes (polysomes); thus, examining which mRNAs are found in polysomes under different conditions provides information on the translation of specific mRNAs under different conditions. A method for the separation of polysomes from non-polysomal mRNAs is describe
Local randomness in Hardy's correlations: Implications from information causality principle
Study of nonlocal correlations in term of Hardy's argument has been quite
popular in quantum mechanics. Recently Hardy's argument of non-locality has
been studied in the context of generalized non-signaling theory as well as
theory respecting information causality. Information causality condition
significantly reduces the success probability for Hardy's argument when
compared to the result based on non-signaling condition. Here motivated by the
fact that maximally entangled state in quantum mechanics does not exhibit
Hardy's non-local correlation, we do a qualitative study of the property of
local randomness of measured observable on each side reproducing Hardy's
non-locality correlation,in the context of information causality condition. On
applying the necessary condition for respecting the principle of information
causality, we find that there are severe restrictions on the local randomness
of measured observable in contrast to results obtained from no-signaling
condition.Still, there are some restrictions imposed by quantum mechanics that
are not obtained from information causality condition.Comment: 6 pages, 2 tables, new references adde
An Improved Approach for Mapping Quantitative Trait Loci in a Pseudo-Testcross: Revisiting a Poplar Mapping Study
A pseudo-testcross pedigree is widely used for mapping quantitative trait loci (QTL) in outcrossing species, but the model for analyzing pseudo-testcross data borrowed from the inbred backcross design can only detect those QTLs that are heterozygous only in one parent. In this study, an intercross model that incorporates the high heterozygosity and phase uncertainty of outcrossing species was used to reanalyze a published data set on QTL mapping in poplar trees. Several intercross QTLs that are heterozygous in both parents were detected, which are responsible not only for biomass traits, but also for their genetic correlations. This study provides a more complete identification of QTLs responsible for economically important biomass traits in poplars
A lower bound on the dimension of a quantum system given measured data
We imagine an experiment on an unknown quantum mechanical system in which the
system is prepared in various ways and a range of measurements are performed.
For each measurement M and preparation rho the experimenter can determine,
given enough time, the probability of a given outcome a: p(a|M,rho). How large
does the Hilbert space of the quantum system have to be in order to allow us to
find density matrices and measurement operators that will reproduce the given
probability distribution? In this note, we prove a simple lower bound for the
dimension of the Hilbert space. The main insight is to relate this problem to
the construction of quantum random access codes, for which interesting bounds
on Hilbert space dimension already exist. We discuss several applications of
our result to hidden variable, or ontological models, to Bell inequalities and
to properties of the smooth min-entropy.Comment: 8 pages, revtex, v2: improved presentation. To appear in Phys. Rev.
Oak forest carbon and water simulations:Model intercomparisons and evaluations against independent data
Models represent our primary method for integration of small-scale, process-level phenomena into a comprehensive description of forest-stand or ecosystem function. They also represent a key method for testing hypotheses about the response of forest ecosystems to multiple changing environmental conditions. This paper describes the evaluation of 13 stand-level models varying in their spatial, mechanistic, and temporal complexity for their ability to capture intra- and interannual components of the water and carbon cycle for an upland, oak-dominated forest of eastern Tennessee. Comparisons between model simulations and observations were conducted for hourly, daily, and annual time steps. Data for the comparisons were obtained from a wide range of methods including: eddy covariance, sapflow, chamber-based soil respiration, biometric estimates of stand-level net primary production and growth, and soil water content by time or frequency domain reflectometry. Response surfaces of carbon and water flux as a function of environmental drivers, and a variety of goodness-of-fit statistics (bias, absolute bias, and model efficiency) were used to judge model performance.
A single model did not consistently perform the best at all time steps or for all variables considered. Intermodel comparisons showed good agreement for water cycle fluxes, but considerable disagreement among models for predicted carbon fluxes. The mean of all model outputs, however, was nearly always the best fit to the observations. Not surprisingly, models missing key forest components or processes, such as roots or modeled soil water content, were unable to provide accurate predictions of ecosystem responses to short-term drought phenomenon. Nevertheless, an inability to correctly capture short-term physiological processes under drought was not necessarily an indicator of poor annual water and carbon budget simulations. This is possible because droughts in the subject ecosystem were of short duration and therefore had a small cumulative impact. Models using hourly time steps and detailed mechanistic processes, and having a realistic spatial representation of the forest ecosystem provided the best predictions of observed data. Predictive ability of all models deteriorated under drought conditions, suggesting that further work is needed to evaluate and improve ecosystem model performance under unusual conditions, such as drought, that are a common focus of environmental change discussions
Bispecific PD1-IL2v and anti-PD-L1 break tumor immunity resistance by enhancing stem-like tumor-reactive CD8<sup>+</sup> T cells and reprogramming macrophages.
Immunotherapies have shown remarkable, albeit tumor-selective, therapeutic benefits in the clinic. Most patients respond transiently at best, highlighting the importance of understanding mechanisms underlying resistance. Herein, we evaluated the effects of the engineered immunocytokine PD1-IL2v in a mouse model of de novo pancreatic neuroendocrine cancer that is resistant to checkpoint and other immunotherapies. PD1-IL2v utilizes anti-PD-1 as a targeting moiety fused to an immuno-stimulatory IL-2 cytokine variant (IL2v) to precisely deliver IL2v to PD-1 <sup>+</sup> T cells in the tumor microenvironment. PD1-IL2v elicited substantial infiltration by stem-like CD8 <sup>+</sup> T cells, resulting in tumor regression and enhanced survival in mice. Combining anti-PD-L1 with PD1-IL2v sustained the response phase, improving therapeutic efficacy both by reprogramming immunosuppressive tumor-associated macrophages and enhancing T cell receptor (TCR) immune repertoire diversity. These data provide a rationale for clinical trials to evaluate the combination therapy of PD1-IL2v and anti-PD-L1, particularly in immunotherapy-resistant tumors infiltrated with PD-1 <sup>+</sup> stem-like T cells
Iron (Oxyhydr)Oxides Serve as Phosphate Traps in Tundra and Boreal Peat Soils
Arctic and boreal ecosystems are experiencing pronounced warming that is accelerating decomposition of soil organic matter and releasing greenhouse gases to the atmosphere. Future carbon storage in these ecosystems depends on the balance between microbial decomposition and primary production, both of which can be regulated by nutrients such as phosphorus. Phosphorus cycling in tundra and boreal regions is often assumed to occur through biological pathways with little interaction with soil minerals; that is, phosphate released from organic molecules is rapidly assimilated by plants or microorganisms. In contrast to this prevailing conceptual model, we use sequential extractions and spectroscopic techniques to demonstrate that iron (oxyhydr)oxides sequester approximately half of soil phosphate in organic soils from four arctic and boreal sites. Iron (III) (oxyhydr)oxides accumulated in shallow soils of low‐lying, saturated areas where circumneutral pH and the presence of a redox interface promoted iron oxidation and hydrolysis. Soils enriched in short‐range ordered iron oxyhydroxides, which are susceptible to dissolution under anoxic conditions, had high phosphate sorption capacities and maintained low concentrations of soluble phosphate relative to soils containing mostly organic‐bound iron or crystalline iron oxides. Thus, substantial quantities of phosphorus in these organic soils were associated with minerals that could reduce bioavailability but potentially also serve as phosphorus sources under anoxic conditions. The implication of this finding is that mineral surfaces effectively compete with biological processes for phosphate and must be considered as a nutrient regulator in these sensitive ecosystems
Decoupling with unitary approximate two-designs
Consider a bipartite system, of which one subsystem, A, undergoes a physical
evolution separated from the other subsystem, R. One may ask under which
conditions this evolution destroys all initial correlations between the
subsystems A and R, i.e. decouples the subsystems. A quantitative answer to
this question is provided by decoupling theorems, which have been developed
recently in the area of quantum information theory. This paper builds on
preceding work, which shows that decoupling is achieved if the evolution on A
consists of a typical unitary, chosen with respect to the Haar measure,
followed by a process that adds sufficient decoherence. Here, we prove a
generalized decoupling theorem for the case where the unitary is chosen from an
approximate two-design. A main implication of this result is that decoupling is
physical, in the sense that it occurs already for short sequences of random
two-body interactions, which can be modeled as efficient circuits. Our
decoupling result is independent of the dimension of the R system, which shows
that approximate 2-designs are appropriate for decoupling even if the dimension
of this system is large.Comment: Published versio
The impacts of recent permafrost thaw on land–atmosphere greenhouse gas exchange
© The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Environmental Research Letters 9 (2014): 045005, doi:10.1088/1748-9326/9/4/045005.Permafrost thaw and the subsequent mobilization of carbon (C) stored in previously frozen soil organic matter (SOM) have the potential to be a strong positive feedback to climate. As the northern permafrost region experiences as much as a doubling of the rate of warming as the rest of the Earth, the vast amount of C in permafrost soils is vulnerable to thaw, decomposition and release as atmospheric greenhouse gases. Diagnostic and predictive estimates of high-latitude terrestrial C fluxes vary widely among different models depending on how dynamics in permafrost, and the seasonally thawed 'active layer' above it, are represented. Here, we employ a process-based model simulation experiment to assess the net effect of active layer dynamics on this 'permafrost carbon feedback' in recent decades, from 1970 to 2006, over the circumpolar domain of continuous and discontinuous permafrost. Over this time period, the model estimates a mean increase of 6.8 cm in active layer thickness across the domain, which exposes a total of 11.6 Pg C of thawed SOM to decomposition. According to our simulation experiment, mobilization of this previously frozen C results in an estimated cumulative net source of 3.7 Pg C to the atmosphere since 1970 directly tied to active layer dynamics. Enhanced decomposition from the newly exposed SOM accounts for the release of both CO2 (4.0 Pg C) and CH4 (0.03 Pg C), but is partially compensated by CO2 uptake (0.3 Pg C) associated with enhanced net primary production of vegetation. This estimated net C transfer to the atmosphere from permafrost thaw represents a significant factor in the overall ecosystem carbon budget of the Pan-Arctic, and a non-trivial additional contribution on top of the combined fossil fuel emissions from the eight Arctic nations over this time period.This study was supported through
grants provided as part of the National Science Foundation’s
Arctic System Science Program (NSF OPP0531047),
a Department of Energy (DOE) Early Career Award (DOEBER
#3ERKP818), the National Aeronautics and Space
Administration’s New Investigator Program (NNX10AT66G)
and the NextGeneration
Ecosystem Experiments (NGEE
Arctic) project supported by the Office of Biological and
Environmental Research in the DOE Office of Science
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