Pak S. Chow

Non-structural carbohydrates in woody plants compared among laboratories

Non-structural carbohydrates (NSC) in plant tissue are frequently quantified to make inferences about plant responses to environmental conditions. Laboratories publishing estimates of NSC of woody plants use many different methods to evaluate NSC. We asked whether NSC estimates in the recent literature could be quantitatively compared among studies. We also asked whether any differences among laboratories were related to the extraction and quantification methods used to determine starch and sugar concentrations. These questions were addressed by sending sub-samples collected from five woody plant tissues, which varied in NSC content and chemical composition, to 29 laboratories. Each laboratory analyzed the samples with their laboratory-specific protocols, based on recent publications, to determine concentrations of soluble sugars, starch and their sum, total NSC. Laboratory estimates differed substantially for all samples. For example, estimates for Eucalyptus globulus leaves (EGL) varied from 23 to 116 (mean = 56) mg g(-1) for soluble sugars, 6-533 (mean = 94) mg g(-1) for starch and 53-649 (mean = 153) mg g(-1) for total NSC. Mixed model analysis of variance showed that much of the variability among laboratories was unrelated to the categories we used for extraction and quantification methods (method category R(2) = 0.05-0.12 for soluble sugars, 0.10-0.33 for starch and 0.01-0.09 for total NSC). For EGL, the difference between the highest and lowest least squares means for categories in the mixed model analysis was 33 mg g(-1) for total NSC, compared with the range of laboratory estimates of 596 mg g(-1). Laboratories were reasonably consistent in their ranks of estimates among tissues for starch (r = 0.41-0.91), but less so for total NSC (r = 0.45-0.84) and soluble sugars (r = 0.11-0.83). Our results show that NSC estimates for woody plant tissues cannot be compared among laboratories. The relative changes in NSC between treatments measured within a laboratory may be comparable within and between laboratories, especially for starch. To obtain comparable NSC estimates, we suggest that users can either adopt the reference method given in this publication, or report estimates for a portion of samples using the reference method, and report estimates for a standard reference material. Researchers interested in NSC estimates should work to identify and adopt standard methods.

Effects of burial, stem portion and cultivar on the decomposition of canola straw

Buried canola straw underwent 1.6 to 2 times as much decomposition as straw on the soil surface. Decomposition of Brassica napus L. was slightly less than that of B. rapa L. and cultivar effects were small in one year and insignificant in the other. Because treatment effects varied between stems and roots, plant portion likely should be considered in decomposition studies. Key words: canola, straw decomposition, burial, cultivars

Impact of chipping residues and its leachate on the initiation and growth of aspen root suckers

Field chipping operations often disperse chipping residues of bark and branches in layers or piles in cut-overs. We tested the effects of these residues on the root sucker regeneration of aspen (Populus tremuloides Michx.), using root systems established in large pots. After decapitation of the stems, the root systems were covered with a 4 cm thick layer of chipping residues. Other root systems were treated with an extract of the water-soluble compounds leached from a similar amount of residues while others were left untreated as controls; all three treatments were left to sucker for 7 wk. There were no differences in the number of root suckers that were initiated on the aspen root system among the three treatments. There were, however, significantly lower numbers of suckers that emerged through the chipping residue and their emergence was delayed relative to the other treatments. The delay in emergence and the reduction in sucker numbers were likely a result of the residues acting as a physical barrier. ...

Nitrate stimulates root suckering in trembling aspen (Populus tremuloides).

In a greenhouse experiment, we tested whether the initiation, density, and growth of trembling aspen (Populus tremuloides Michx.) root suckers are related to postdisturbance soil nutrient availabil...

Evaluating fungi from wood and canola for their ability to decompose canola stubble

The survival and impact on canola of Leptosphaeria maculans, the causal agent of blackleg, might be reduced by agents that decompose canola stubble. Fifty-six fungal isolates from wood or canola were evaluated for their ability to overcome several biological and (or) physical constraints to their effectiveness in decomposing and (or) eliminating L. maculans from canola stubble. Relative to fungi from canola, wood decay fungi were more tolerant of reduced water potential but somewhat less tolerant of lower temperature. Wood decay fungi were no better than those isolated from canola at decomposing sterile canola stubble and less able than Coprinus spp. and Cyathus olla in colonizing and surviving in nonsterile stubble. None of the isolates were effective in eliminating L. maculans from stubble pieces or causing significant decomposition of nonsterile stubble either under laboratory conditions or in the field. These results suggest that considerable effort would be required to find isolates effective in managing blackleg disease through stubble decomposition. Wood decay fungi would seem to have little potential as biological control agents in this pathosystem because of their inability to colonize and decompose nonsterile canola stubble.

Inoculation of Populus tremuloides with Pollaccia americana

Disease resistance may represent the best approach for controlling shoot blight, caused by Pollaccia americana Ondrej, in aspen (Populus tremuloides Michx.) plantations. Experiments were conducted to develop methods for screening for resistance under greenhouse conditions. Chickpea agar supported abundant inoculum production. An inoculum concentration of 5 × 104 spores/mL and a seedling age of 5-9 weeks were appropriate for evaluating infection. Infection severity was not correlated with tree height or leaf number. Differences in infection among clones varied with fungal isolate. The number of isolates and replicates needed to detect resistance differences among clones was calculated using estimated values of experimental error and clone × isolate interactions.

Biases underlying species detection using fluorescent amplified -fragment length polymorphisms yielded from roots

BackgroundRoots of different plant species are typically morphologically indistinguishable. Of the DNA-based techniques, fluorescent amplified-fragment length polymorphisms (FAFLPs) are considered reliable, high throughput, inexpensive methods to identify roots from mixed species samples. False-negatives, however, are not uncommon and their underlying causes are poorly understood. We investigated several sources of potential biases originating in DNA extraction and amplification. Specifically, we examined the effects of sample storage, tissue, and species on DNA yield and purity, and the effects of DNA concentration and fragment size on amplification of three non-coding chloroplast regions (trnT-trnL intergenic spacer, trnL intron, and trnL-trnF intergenic spacer).ResultsWe found that sample condition, tissue and species all affected DNA yield. A single freeze–thaw reduces DNA yield, DNA yield is less for roots than shoots, and species vary in the amount of DNA yielded from extractions. The effects of template DNA concentration, species identity, and their interaction on amplicon yield differed across the three chloroplast regions tested. We found that the effect of species identity on amplicon production was generally more pronounced than that of DNA concentration. Though these factors influenced DNA yield, they likely do not have a pronounced effect on detection success of fragments and only underscore the restriction on the use of FAFLPs for measuring species presence rather than their abundance. However, for two of the regions tested—the trnT-trnL intergenic spacer and the trnL intron—size-based fragment competition occurred and the likelihood of detection was higher for smaller than larger fragments. This result reveals a methodological bias when using FAFLPs.ConclusionsTo avoid potential bias with the use of FAFLPs, we recommend users check for the disproportionate absence of species detected belowground versus aboveground as a function of fragment size, and explore other regions, aside from the trnT-trnL intergenic spacer and trnL intron, for amplification.