Hey Ted, I agree with the previous two postings. Additionally, there is certainly value in measuring the wet weight of your rhizomes at the time of planting for potential use as a covariable. Try to plant as uniform rhizomes (number and size) as possible. Then run your stat model to test for any significant treatment effects on rhizome wet weight - hopefully there will be none (and therefore no need to use wet weight as a covariable on final biomass, which has its own limitations regarding non-linearity in response, etc.). Importantly, if you fail to detect a treatment effect on wet weight, you can be assured that you started out with similar amounts of biomass among treatments.
Best, Mark Mark W. Hester Coastal Plant Ecology Lab Biology Department University of Louisiana at Lafayette PO Box 42451 Lafayette, LA 70504-2451 Email: [email protected] Office: (337) 482-5246 Cell: (504) 237-1151 ---------- Original Message ----------- From: "Stephen R. Keller" <[email protected]> To: [email protected] Sent: Wed, 5 Aug 2009 11:40:13 -0400 Subject: Re: [ECOLOG-L] Measuring Growth rate in plants > Hi, > > I would worry about differences in the relative water content of > your starting tissue (rhizome) vs. your end tissue (whole plant). If > different tissue types have different WC, then growth rate estimates > based on fresh weights alone will be biased. If you measure the dry > weights for a subsample of your rhizomes (per treatment, as > suggested by an earlier post), and the regression is good, then you > could convert the rest of your rhizome wet weight measurements to > estimates of dry weight, and compare those to the dry weights at the > end of the experiment to get your RGR. > > Steve > > On Tue, 4 Aug 2009 19:11:03 -0400 > Ted Turluck <[email protected]> wrote: > > Hello, > > > > I've posted before with questions about other methods and got a lot of > > responses. Thank you to all who responded before. > > > > I'm going to be starting an experiment in which I plan to measure growth > > rates of two different haplotypes of Phragmites australis under varying > > water depths and salinities. I plan to use change in height and number of > > shoots over time as a measure of growth. I'm planting rhizome fragments. > > I'll measure length, diameter, number of nodes, and number of buds before > > planting. I'll try to make the fragments as similar in size as possible. > > > > I would like to measure biomass before and after as well (or maybe > > instead). But I don't know if measuring fresh biomass before planting and > > after harvest is a legitimate method. > > > > Would there be a chance that there would be a difference in moisture > > content between each rhizome fragment that could mess up my data? > > > > Is height change a good way of measuring growth in grasses? > > > > Is fresh biomass a good thing to measure before and after a growth > > experiment? > > > > Thanks for any advice. ------- End of Original Message -------
