ORCID Profile
0000-0002-2500-6738
Current Organisation
Colorado State University
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Publisher: Elsevier BV
Date: 04-2010
Publisher: Wiley
Date: 11-04-2019
DOI: 10.1111/NPH.15805
Publisher: Oxford University Press (OUP)
Date: 2014
Publisher: Cold Spring Harbor Laboratory
Date: 18-07-2019
DOI: 10.1101/705400
Abstract: Two simplifying hypotheses have been proposed for whole-plant respiration. One links respiration to photosynthesis the other to biomass. Using a first-principles carbon balance model with a prescribed live woody biomass turnover, applied at a forest research site where multidecadal measurements are available for comparison, we show that if turnover is fast the accumulation of respiring biomass is low and respiration depends primarily on photosynthesis while if turnover is slow the accumulation of respiring biomass is high and respiration depends primarily on biomass. But the first scenario is inconsistent with evidence for substantial carryover of fixed carbon between years, while the second implies far too great an increase in respiration during stand development – leading to depleted carbohydrate reserves and an unrealistically high mortality risk. These two mutually incompatible hypotheses are thus both incorrect. Respiration is not linearly related either to photosynthesis or to biomass, but it is more strongly controlled by recent photosynthates (and reserve availability) than by total biomass.
Publisher: Wiley
Date: 18-09-2013
DOI: 10.1111/NPH.12502
Publisher: Elsevier BV
Date: 11-2011
Publisher: Wiley
Date: 26-10-2019
DOI: 10.1111/GCB.14857
Abstract: Two simplifying hypotheses have been proposed for whole‐plant respiration. One links respiration to photosynthesis the other to biomass. Using a first‐principles carbon balance model with a prescribed live woody biomass turnover, applied at a forest research site where multidecadal measurements are available for comparison, we show that if turnover is fast the accumulation of respiring biomass is low and respiration depends primarily on photosynthesis while if turnover is slow the accumulation of respiring biomass is high and respiration depends primarily on biomass. But the first scenario is inconsistent with evidence for substantial carry‐over of fixed carbon between years, while the second implies far too great an increase in respiration during stand development—leading to depleted carbohydrate reserves and an unrealistically high mortality risk. These two mutually incompatible hypotheses are thus both incorrect. Respiration is not linearly related either to photosynthesis or to biomass, but it is more strongly controlled by recent photosynthates (and reserve availability) than by total biomass.
Publisher: Wiley
Date: 11-03-2004
DOI: 10.1111/J.1469-8137.2004.01053.X
Abstract: Rising atmospheric CO 2 and temperatures are probably altering ecosystem carbon cycling, causing both positive and negative feedbacks to climate. Below‐ground processes play a key role in the global carbon (C) cycle because they regulate storage of large quantities of C, and are potentially very sensitive to direct and indirect effects of elevated CO 2 and temperature. Soil organic matter pools, roots and associated rhizosphere organisms all have distinct responses to environmental change drivers, although availability of C substrates will regulate all the responses. Elevated CO 2 increases C supply below‐ground, whereas warming is likely to increase respiration and decomposition rates, leading to speculation that these effects will moderate one another. However, indirect effects on soil moisture availability and nutrient supply may alter processes in unexpected directions. Detailed, mechanistic understanding and modelling of below‐ground flux components, pool sizes and turnover rates is needed to adequately predict long‐term, net C storage in ecosystems. In this synthesis, we discuss the current status of below‐ground responses to elevated CO 2 and temperature and potential feedback effects, methodological challenges, and approaches to integrating models and measurements.
Publisher: Springer Science and Business Media LLC
Date: 07-08-2017
DOI: 10.1038/S41559-017-0248-X
Abstract: Widespread tree mortality associated with drought has been observed on all forested continents and global change is expected to exacerbate vegetation vulnerability. Forest mortality has implications for future biosphere-atmosphere interactions of carbon, water and energy balance, and is poorly represented in dynamic vegetation models. Reducing uncertainty requires improved mortality projections founded on robust physiological processes. However, the proposed mechanisms of drought-induced mortality, including hydraulic failure and carbon starvation, are unresolved. A growing number of empirical studies have investigated these mechanisms, but data have not been consistently analysed across species and biomes using a standardized physiological framework. Here, we show that xylem hydraulic failure was ubiquitous across multiple tree taxa at drought-induced mortality. All species assessed had 60% or higher loss of xylem hydraulic conductivity, consistent with proposed theoretical and modelled survival thresholds. We found erse responses in non-structural carbohydrate reserves at mortality, indicating that evidence supporting carbon starvation was not universal. Reduced non-structural carbohydrates were more common for gymnosperms than angiosperms, associated with xylem hydraulic vulnerability, and may have a role in reducing hydraulic function. Our finding that hydraulic failure at drought-induced mortality was persistent across species indicates that substantial improvement in vegetation modelling can be achieved using thresholds in hydraulic function.
Location: United States of America
No related grants have been discovered for Michael Ryan.