Biomedical subjects

Sune Linder

Publications and source records attributed to Sune Linder.

7 recordsLinked to original sources

PubMed2007

Physiological girdling of pine trees via phloem chilling: proof of concept.

Quantifying below-ground carbon (C) allocation is particularly difficult as methods usually disturb the root-mycorrhizal-soil continuum. We reduced C allocation below ground of loblolly pine trees by: (1) physically girdling trees and (2) physiologically girdling pine trees by chilling the phloem. Chilling reduced cambium temperatures by approximately 18 degrees C. Both methods rapidly reduced soil CO2 efflux, and after approximately 10 days decreased net photosynthesis (P(n)), the latter indicating feedback inhibition. Chilling decreased soil-soluble C, indicating that decreased soil CO2 efflux may have been mediated by a decrease in root C exudation that was rapidly respired by microbes. These effects were only observed in late summer/early autumn when above-ground growth was minimal, and not in the spring when above-ground growth was rapid. All of the effects were rapidly reversed when chilling was ceased. In fertilized plots, both chilling and physical girdling methods reduced soil CO2 efflux by approximately 8%. Physical girdling reduced soil CO2 efflux by 26% in non-fertilized plots. This work demonstrates that phloem chilling provides a non-destructive alternative to reducing the movement of recent photosynthate below the point of chilling to estimate C allocation below ground on large trees.

Carbon Dioxide↗

PubMed2006

A whole-tree chamber system for examining tree-level physiological responses of field-grown trees to environmental variation and climate change.

A whole-tree chamber (WTC) system was installed at Flakaliden in northern Sweden to examine the long-term physiological responses of field-grown 40-year-old Norway spruce trees [Picea abies (L.) Karst.] to climate change. The WTCs were designed as large cuvettes to allow the net tree-level CO(2) and water fluxes to be measured on a continuous basis. A total of 12 WTCs were used to impose combinations of atmospheric carbon dioxide concentration, [CO(2)], and air temperature treatments. The air inside the ambient and elevated [CO(2)] WTCs was maintained at 365 and 700 micromol mol(-1), respectively. The air temperature inside the ambient temperature WTCs tracked air temperature outside the WTCs. Elevated temperatures were altered on a monthly time-step and ranged between +2.8 and +5.6 degrees C above ambient temperature. The system allowed continuous, long-term measurement of whole-tree photosynthesis, night-time respiration and transpiration. The performance of the WTCs was assessed using winter and spring data sets. The ability of the WTC system to measure tree-level physiological responses is demonstrated. All WTCs displayed a high level of control over tracking of air temperatures. The set target of 365 micromol mol(-1) in the ambient [CO(2)] chambers was too low to be maintained during winter because of tree dormancy and the high natural increase in [CO(2)] over winter at high latitudes such as the Flakaliden site. Accurate control over [CO(2)] in the ambient [CO(2)] chambers was restored during the spring and the system maintained the elevated [CO(2)] target of 700 micromol mol(-1) for both measurement periods. Air water vapour deficit (VPD) was accurately tracked in ambient temperature WTCs. However, as water vapour pressure in all 12 WTCs was maintained at the level of non-chambered (reference) air, VPD of elevated temperature WTCs was increased.

Carbon Dioxide↗

PubMed2004

Feedback interactions between needle litter decomposition and rhizosphere activity.

The aim of our study was to identify interactions between the decomposition of aboveground litter and rhizosphere activity. The experimental approach combined the placement of labelled litter (delta13C=-37.9 per thousand ) with forest girdling in a 35-year-old Norway spruce stand, resulting in four different treatment combinations: GL (girdled, litter), GNL (girdled, no litter), NGL (not girdled, litter), and NGNL (not girdled, no litter). Monthly sampling of soil CO2 efflux and delta13C of soil respired CO2 between May and October 2002 allowed the partitioning of the flux into that derived from the labelled litter, and that derived from native soil organic matter and roots. The effect of forest girdling on soil CO2 efflux was detectable from June (girdling took place in April), and resulted in GNL fluxes to be about 50% of NGNL fluxes by late August. The presence of litter resulted in significantly increased fluxes for the first 2 months of the experiment, with significantly greater litter derived fluxes from non-girdled plots and a significant interaction between girdling and litter treatments over the same period. For NGL collars, the additional efflux was found to originate only in part from litter decomposition, but also from the decay of native soil organic matter. In GL collars, this priming effect was not significant, indicating an active role of the rhizosphere in soil priming. The results therefore indicate mutual positive feedbacks between litter decomposition and rhizosphere activity. Soil biological analysis (microbial and fungal biomass) of the organic layers indicated greatest activity below NGL collars, and we suppose that this increase indicates the mechanism of mutual positive feedback between rhizosphere activity and litter decomposition. However, elimination of fresh C input from both above- and belowground (GNL) also resulted in greater fungal abundance than for the NGNL treatment, indicating likely changes in fungal community structure (i.e. a shift from symbiotic to saprotrophic species abundance).

Biomass↗

PubMed2004

Time series diagnosis of tree hydraulic characteristics.

An in vivo method for diagnosing hydraulic characteristics of branches and whole trees is described. The method imposes short-lived perturbations of transpiration and traces the propagation of the hydraulic response through trees. The water uptake response contains the integrated signature of hydraulic resistance and capacitance within trees. The method produces large signal to noise ratios for analysis, but does not cause damage or destruction to tree stems or branches. Based on results with two conifer tree species, we show that the method allows for the simple parameterization of bulk hydraulic resistance and capacitance of trees. Bulk tree parameterization of resistance and capacitance predicted the overall diel shape of water uptake, but did not predict the overshoot water uptake response in trees to shorter-term variations in transpiration, created by step changes in transpiration rate. Stomatal dynamics likely complicated the use of simple resistance-capacitance models of tree water transport on these short time scales. The results provide insight into dominant hydraulic and physiological factors controlling tree water flux on varying time scales, and allow for the practical assessment of necessary tree hydraulic model complexity in relation to the time step of soil- vegetation-atmosphere transport models.

Models, Biological↗

PubMed1998

Effect of nitrogen on the seasonal course of growth and maintenance respiration in stems of Norway spruce trees.

To determine effects of stem nitrogen concentration ([N]) on the seasonal course of respiration, rates of stem respiration of ten control and ten irrigated-fertilized (IL), 30-year-old Norway spruce trees (Picea abies (L.) Karst.), growing in northern Sweden, were measured on seven occasions from June 1993 to April 1994. To explore sources of seasonal variation and mechanisms of fertilization effects on respiration, we separated total respiration into growth and maintenance respiration for both xylem and phloem bark. Stem respiration increased in response to the IL treatment and was positively correlated with growth rate, volume of living cells and stem nitrogen content. However, no significant effect of IL treatment or [N] in the living cells was found for respiration per unit volume of live cells. Total stem respiration during the growing season (June to September) was estimated to be 16.7 and 29.7 mol CO(2) m(-2) for control and IL-treated trees, respectively. Respiration during the growing season accounted for approximately 64% of total annual respiration. Depending on the method, estimated growth respiration varied between 40 and 60% of total respiration during the growing season. Between 75 and 80% of the live cell volume in the stems was in the phloem, and phloem maintenance accounted for about 70% of maintenance respiration. Because most of the living cells were found in the phloem, and the living xylem cells were concentrated in the outer growth rings, we concluded that the best base for expressing rates of stem growth and maintenance respiration in young Norway spruce trees is stem surface area.

Journal Article↗

PubMedDate not supplied

Performance of the LAI-2000 plant canopy analyzer in estimating leaf area index of some Scots pine stands.

The LAI-2000 plant canopy analyzer (Li-Cor, Inc., Lincoln, NE) was tested at six experimental plots of Scots pine (Pinus sylvestris L.) in central Sweden at peak leaf area in August and after litterfall in October 1990. An independent estimate of leaf area index for August 1990 was obtained based on an empirically derived regression of needle area on stem sapwood area, and the decrease in leaf area between the two measurements was estimated from measurements of litterfall. A strong linear relationship was found between estimates by the LAI-2000 (L(Li-Cor)) and the indirect estimates of leaf area index (taken as half of total surface area) (L). The finding that L(Li-Cor) was considerably smaller than L was explained theoretically. It was shown that if shoots, instead of individual needles, are randomly distributed in the canopy, L(Li-Cor) corresponds to L multiplied by a factor (beta) characterizing the mutual shading of needles on the shoot. The shading factor, beta, was equal to the ratio of spherically projected shoot area to spherically projected needle area, where the spherically projected area is defined as the average projection (silhouette) area taken over all directions in space. The quantity betaL was defined as the shoot silhouette area index (SSAI), and an equation for the relationship between SSAI and the mean silhouette to total area ratio (mean STAR) of shoots was derived. Measured values of mean STAR for Scots pine indicated that L(Li-Cor) corresponds to SSAI rather than L. However, the decrease in leaf area index due to litterfall occurring between August and October was only partly detected by the LAI-2000, possibly because SSAI did not change to the same degree as L, i.e., there was an increase in the factor beta. This hypothesis is supported by data showing a large increase in mean STAR with shoot age.

Journal Article↗

PubMedDate not supplied

Tree physiology research in a changing world.

Changes in issues and advances in methodology have contributed to substantial progress in tree physiology research during the last several decades. Current research focuses on process interactions in complex systems and the integration of processes across multiple spatial and temporal scales. An increasingly important challenge for future research is assuring sustainability of production systems and forested ecosystems in the face of increased demands for natural resources and human disturbance of forests. Meeting this challenge requires significant shifts in research approach, including the study of limitations of productivity that may accompany achievement of system sustainability, and a focus on the biological capabilities of complex land bases altered by human activity.

Journal Article↗