ORCID Profile
0000-0002-3128-3002
Current Organisation
Singapore-MIT Alliance for Research and Technology
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Publisher: Wiley
Date: 10-01-2017
DOI: 10.1111/GCB.13516
Publisher: Wiley
Date: 04-2007
DOI: 10.3732/AJB.94.4.640
Abstract: Freeze-thaw cycles pose a major physiological challenge for all temperate perennial plants, but monocotyledonous vines face a still greater risk because their few large vessels are especially susceptible to embolism and are not replaced by secondary growth. The genus Smilax is particularly remarkable because it is widespread in the tropics but includes species that survive the hard frosts of New England winters. Smilax rotundifolia was monitored for a year for evidence of stem xylem freeze-thaw cavitation and refilling. Embolism of metaxylem was complete by late November and was completely reversed by late April, when root pressures rose as high as 100 kPa. Protoxylem remained full of sap throughout the year in cryogenic scanning electron micrographs. Three methods were used to quantify embolism: percent loss conductivity (PLC), gravimetric air fraction (GAF: mass of water in stem xylem relative to capacity), and cryogenic scanning electron microscopy (cryo-SEM). The three methods corroborated one another well and gave quantitatively similar results. Osmolality of xylem sap extracted from exuding stems was 64 mol/kg (±7.0, N = 8), consistent with the root pressures observed. Strong root pressure can account for Smilax's survival in temperate regions with severe frosts, where few monocots with persistent aboveground organs are found.
Publisher: Wiley
Date: 13-12-2007
DOI: 10.1111/J.1469-8137.2007.02317.X
Abstract: Bordered pits are cavities in the lignified cell walls of xylem conduits (vessels and tracheids) that are essential components in the water‐transport system of higher plants. The pit membrane, which lies in the center of each pit, allows water to pass between xylem conduits but limits the spread of embolism and vascular pathogens in the xylem. Averaged across a wide range of species, pits account for 50% of total xylem hydraulic resistance, indicating that they are an important factor in the overall hydraulic efficiency of plants. The structure of pits varies dramatically across species, with large differences evident in the porosity and thickness of pit membranes. Because greater porosity reduces hydraulic resistance but increases vulnerability to embolism, differences in pit structure are expected to correlate with trade‐offs between efficiency and safety of water transport. However, trade‐offs in hydraulic function are influenced both by pit‐level differences in structure (e.g. average porosity of pit membranes) and by tissue‐level changes in conduit allometry (average length, diameter) and the total surface area of pit membranes that connects vessels. In this review we address the impact of variation in pit structure on water transport in plants from the level of in idual pits to the whole plant. Contents Summary 1 I. Introduction 2 II. The basic structures 2 III. Safety of transport ‐ pits as safety valves 5 IV. Hydraulic resistance of pits and pit membranes ‐ the cost of safety 9 V. Impacts of pit function on whole‐plant hydraulics 14 VI. Future directions 15 Acknowledgements 15 References 15
Publisher: American Geophysical Union (AGU)
Date: 02-2022
DOI: 10.1029/2021GB007057
Abstract: Peatlands contain a significant fraction of global soil carbon, but how these reservoirs will respond to the changing climate is still relatively unknown. A global picture of the variations in peat organic matter chemistry will aid our ability to gauge peatland soil response to climate. The goal of this research is to test the hypotheses that (a) peat carbohydrate content, an indicator of soil organic matter reactivity, will increase with latitude and decrease with mean annual temperatures, (b) while peat aromatic content, an indicator of recalcitrance, will vary inversely, and (c) elevation will have a similar effect to latitude. We used Fourier Transform Infrared Spectroscopy to examine variations in the organic matter functional groups of 1034 peat s les collected from 10 to 20, 30–40, and 60–70 cm depths at 165 in idual sites across a latitudinal gradient of 79°N–65°S and from elevations of 0–4,773 m. Carbohydrate contents of high latitude peat were significantly greater than peat originating near the equator, while aromatic content showed the opposite trend. For peat from similar latitudes but different elevations, the carbohydrate content was greater and aromatic content was lower at higher elevations. Higher carbohydrate content at higher latitudes indicates a greater potential for mineralization, whereas the chemical composition of low latitude peat is consistent with their apparent relative stability in the face of warmer temperatures. The combination of low carbohydrates and high aromatics at warmer locations near the equator suggests the mineralization of high latitude peat until reaching recalcitrance under a new temperature regime.
Publisher: Elsevier BV
Date: 10-2018
DOI: 10.1016/J.JTBI.2018.07.036
Abstract: Vessel length is an important functional trait for plant hydraulics, because it determines the ratio of flow resistances posed by lumen and pit membranes and hence controls xylem hydraulic efficiency. The most commonly applied methods to estimate vessel lengths are based on the injection of silicon or paint into cut-off stem segments. The number of stained vessels in a series of cross-sections in increasing distance from the injection point is then counted. The resulting infusion profiles are used to estimate the vessel length distribution using one of several statistical algorithms. However, the basis of these algorithms has not been systematically analysed using probability theory. We derive a general mathematical expression for the expected shape of the infusion profile for a given vessel length distribution, provide analytic solutions for five candidate distributions (exponential, Erlang(2), gamma, Weibull, and log-normal), and present maximum likelihood estimators for the parameters of these distributions including implementations in R based on two potential s ling schemes (counting all injected vessels or counting the injected and empty vessels in a random subset of each cross-section). We then explore the performance of these estimators relative to other methods with Monte Carlo experiments. Our analysis demonstrates that most published methods estimate the conditional length distribution of vessels that cross an injection point, which is a size-biased version of the overall length distribution in the stem. We show the mathematical relationship between these distributions and provide methods to estimate either of them. According to our simulation experiments, vessel length distribution was best described by the more flexible models, especially the Weibull distribution. In simulations, the estimators were able to recover the parameters of the vessel length distribution if its functional form was known, achieving an overlap of 90% or more between the true and predicted length distribution when counting no more than 500 injected vessels in 10 cross-sections. This s le size nowadays can easily be reached with the help of automated image analysis.
Publisher: Wiley
Date: 25-04-2012
Publisher: Public Library of Science (PLoS)
Date: 23-11-2022
DOI: 10.1371/JOURNAL.PONE.0275149
Abstract: Peatlands account for 15 to 30% of the world’s soil carbon (C) stock and are important controls over global nitrogen (N) cycles. However, C and N concentrations are known to vary among peatlands contributing to the uncertainty of global C inventories, but there are few global studies that relate peatland classification to peat chemistry. We analyzed 436 peat cores s led in 24 countries across six continents and measured C, N, and organic matter (OM) content at three depths down to 70 cm. Sites were distinguished between northern (387) and tropical (49) peatlands and assigned to one of six distinct broadly recognized peatland categories that vary primarily along a pH gradient. Peat C and N concentrations, OM content, and C:N ratios differed significantly among peatland categories, but few differences in chemistry with depth were found within each category. Across all peatlands C and N concentrations in the 10–20 cm layer, were 440 ± 85.1 g kg -1 and 13.9 ± 7.4 g kg -1 , with an average C:N ratio of 30.1 ± 20.8. Among peatland categories, median C concentrations were highest in bogs, poor fens and tropical sw s (446–532 g kg -1 ) and lowest in intermediate and extremely rich fens (375–414 g kg -1 ). The C:OM ratio in peat was similar across most peatland categories, except in deeper s les from ombrotrophic tropical peat sw s that were higher than other peatlands categories. Peat N concentrations and C:N ratios varied approximately two-fold among peatland categories and N concentrations tended to be higher (and C:N lower) in intermediate fens compared with other peatland types. This study reports on a unique data set and demonstrates that differences in peat C and OM concentrations among broadly classified peatland categories are predictable, which can aid future studies that use land cover assessments to refine global peatland C and N stocks.
Publisher: Proceedings of the National Academy of Sciences
Date: 07-2010
Abstract: Cellulose synthase-interactive protein 1 (CSI1) was identified in a two-hybrid screen for proteins that interact with cellulose synthase (CESA) isoforms involved in primary plant cell wall synthesis. CSI1 encodes a 2,150-amino acid protein that contains 10 predicted Armadillo repeats and a C2 domain. Mutations in CSI1 cause defective cell elongation in hypocotyls and roots and reduce cellulose content. CSI1 is associated with CESA complexes, and csi1 mutants affect the distribution and movement of CESA complexes in the plasma membrane.
Publisher: Wiley
Date: 07-2006
DOI: 10.3732/AJB.93.7.993
Abstract: The hydraulic resistance of pit membranes was measured directly in earlywood vessels of Fraxinus americana and Ulmus americana. The area-specific resistance of pit membranes (r(mem)) was higher than modeled or measured values obtained previously for hardwood species, with r(mem) of 5.24 × 10(3) MPa·s·m(-1) for Fraxinus and 2.56 × 10(3) MPa·s·m(-1) for Ulmus. The calculated resistance of pit canals was three orders of magnitude below total pit resistance indicating that pit membranes contributed the majority of resistance. Scanning electron microscopy indicated that pit membranes of Ulmus were thinner and more porous than those of Fraxinus, consistent with the difference in r(mem) between the species. Measurements of average vessel diameter and length and area of wall overlap with neighboring vessels were used to partition the vascular resistance between vessel lumen and pit membrane components. Pit membrane resistance accounted for 80% of the total resistance in Fraxinus and 87% in Ulmus in 2-yr-old branch sections. However, measurements of vessel dimensions in the trunk suggest that the ision of resistance between pit membrane and lumen components would be closer to co-limiting in older regions of the tree. Thus, pit membrane resistance may be of greater relative importance in small branches than in older regions of mature trees.
Location: Singapore
No related grants have been discovered for Alex Cobb.