Jenny/Lee- Perhaps this optional symbiosis (optional in the sense that not all plants require it to compete successfully in an ecosytem) lends strong support to the theory of evolution? -Don
> Date: Thu, 12 Mar 2009 11:23:54 -0500 > From: [email protected] > To: [email protected] > Subject: [ENTS] Re: Roots? > > > Jenny: > > Regarding mycorrhizae, its one of those interesting questions where the > answer is yes and no. With very high soil fertility, trees can survive > and grow without them, and in isolation, they can often grow without > them. However, under most field conditions, and with the competition > from numerous other trees, they are necessary for an individual tree to > survive and grow, as well as for the function of the entire ecosystem. > > Regarding nitrogen fixation--its another case where both answers are > correct. Free living bacteria (Azotobacter and Clostridium, some > blue-green algae, and others) fix a small amount of nitrogen in the > soil. Rhizobium bacteria form a symbiotic relationship with roots, in a > nodule, which can easily be seen if you pull up a clover plant. This > occurs mainly in legumes (locust), but also in some other trees (via > other genera of microorganisms) such as alder, and shrubs such as Myrica > (sweet gale), and Shepherdia (buffaloberry). The presence of nitrogen > fixing plant species can fertilize the soils, thereby increasing the > growth of tree species that cannot form nitrogen fixing nodules. > > Whether the nodule forming microorganisms are considered part of the > tree depends on your point of view. They are halfway between ancient > microorganisms such as certain algae and bacteria that have become > chloroplasts in leaves, and mitochondria in cells of plants and animals > (which are clearly part of the organisms, and cannot live by > themselves), and microorganisms that cannot form a symbiotic > relationships with plants at all. Its a continuum, and where you make a > distincion along that continuum depends on the individual > > Lee > > JennyNYC wrote: > > Lee, et. al., > > > > I would love to see one of these "rhizotrons". Fascinating. > > > > I have questions if anyone can help me out: > > > > 1. Are mycorrizae absolutely essential for young tree roots to grow > > and do trees have mycorrizae associations throughout their lives? > > > > 2. I'm confused about the exact relationship between the bacteria in > > the soil that fix nitrogen and the tree root itself. I know this is > > a broad and vague question....just wondering it those bacteria are > > considered part of the tree organism? > > > > Thanks, > > > > Jenny > > > > On Mar 12, 8:54 am, Lee Frelich <[email protected]> wrote: > > > >> Ed et al.: > >> > >> We usually measure root biomass by taking soil cores (usually 2-4 inches > >> in dimeter, from 1-3 feet deep, depending on the purpose of the study), > >> and separating the roots so they can be dried and weighed. By taking a > >> number of such samples, we can estimate the biomass of roots per acre in > >> the forest. Roots are also studied in rhizotrons (underground rooms with > >> large windows all around). One can observe the root growth against the > >> windows, study how earthworms move, and how the soil zonation changes > >> over time, etc. The University of Michigan Biological Station and > >> Michigan Tech have rhizotrons that I have visited. There are also mini > >> rhizotrons that can be placed throughout the forest. > >> > >> Of course, these do not give you an estimate of the roots of one tree. > >> I have seen that done by blasting away the soil with high pressure > >> hoses, so that the root system can be mapped and measured. This is done > >> in a stand that is planned to be clearcut, or perhaps a few trees in an > >> experimental forest, and it only works in ecosystems with shallow soils > >> and/or rooting depths. > >> > >> Lee > >> > >> Edward Frank wrote: > >> > >>> Jenny > >>> > >>> I am sure if there was some practical and non-destructive method of > >>> measuring the roots underground, we would give it a try. Ground > >>> Penetrating > >>> Radar is still a little expensive at the moment. > >>> > >>> Ed > >>> ----- Original Message ----- > >>> From: "Jennynyc" <[email protected]> > >>> To: "ENTSTrees" <[email protected]> > >>> Sent: Wednesday, March 11, 2009 8:06 PM > >>> Subject: [ENTS] Re: Roots? > >>> > >>> Russ, > >>> > >>> Thanks for letting me know about this. > >>> > >>> Jenny > >>> > >>> On Mar 11, 2:27 pm, [email protected] wrote: > >>> > >>>> Jen: > >>>> > >>>> No. That type of work is usually done by researchers looking for a > >>>> specific > >>>> piece of information about a tree or group of trees. > >>>> > >>>> Russ > >>>> **************Need a job? Find employment help in your area. > >>>> (http://yellowpages.aol.com/search?query=employment_agencies&ncid=emlc...) > >>>> > > > > > > > > _________________________________________________________________ Windows Live™: Life without walls. http://windowslive.com/explore?ocid=TXT_TAGLM_WL_allup_1a_explore_032009 --~--~---------~--~----~------------~-------~--~----~ Eastern Native Tree Society http://www.nativetreesociety.org Send email to [email protected] Visit this group at http://groups.google.com/group/entstrees?hl=en To unsubscribe send email to [email protected] -~----------~----~----~----~------~----~------~--~---
