Agenda - Planning Commission - 03/02/1999

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bacteria inside the eight-micron tunnels. · A common treatment for compaction is to fracture th6 S°il. The fracturing allows air to penetrate the soil, but does not provide any.eight-micron tunnels for the bacteria, The only way to bring back the tunnels is to bring back the fungi in well- eomposted wood and leaf mulch, as Nature does, or by inoculating the mulch with mycorrhizhl fungi. ' Who was First?. .. I do not know if the ftmgi were the first to grow into the root to get at exudates or whether it was the bacteria. Regardless~ bacteria and their close relatives, the actin0mycetes, also infect non-woody roots to form organs that serve for the fixation of atmospheric nitrogen, Fixation means that the nitrogen that makes up almost 80% of our air is converted to a soldble ionic form by the action of the bacteria and actinomycetes within the.: nodules 6n the roots. (Some free-living soil bacteria can also fix' nitrogen.) An enzyme called nitrogenase is the catalyst for the reaction, which will take place only under very exacting conditions. There must be, soluble molybdenum and iron and no free oxygen availablei'Theso conditions are present within the '~' ' nodules. Here again, the microorganigtus benefit the tree by of elemgnts, and the nodules provide a nitrogen source. Many species of trees have actinorhizae, which are the nodules formed by the root infections bY actinomycetes. Species of Alnus have very large nodules. The actinorhizae are common on tropical and · subtropical trees, and especially on tre6s that have adapted to soils low in available nutrients. On some subtropical and tropical trees, such as the macadamia, multi-branched clusters of non-woody roots called proteoid roots form. The proteoid roots alter the rhizosphere by acidification processes that facilitate the absorption of phosphorus-containing ions. When I examined the roots of dying macadamia trees in an orchard in Hawaii, I could not find proteoid roots; yet only a few days earlier I had found them'on macadamia trees growing in the wild. I learned later that the ' orchard where trees were dying was heavily and regularly fertilized with phosphorus. · - · Another type of nOdule forms on species of eycads. These nodules harbor blue green algae, or cyanohacteria, that have the ability, to fix atmospheric nitrogen. My 'point is that many different synergistic associations have developed in, on, and about non-woody roots that provide elements, not an energy These associations are of extreme benefit'to all connected -.. members. At the same time, the conditions that support the associations are very delicate and exacting. It does not take much to disrupt them. It Does Not Take Much to Disrupt Them This statement deserves ~ting and repeating. The delicate ' "threads" that hold these powerful associations ~0gether needtoobe recognized and respected. Trees in cities grow only so long as ibese "thr~ls' remain connected. · · · · . -: -Trees grow as large oscillating pumps, with the tOP trapping energy and pumping it downward. The bottom absorbs water and elements and pumps them upward. The pumps have developed over time to work on the basis of many syn~gistic associations that maximize'benefits for all connected members and to. x. ','- "Many of life's eSSentials fo~ the bottom aSsociates c{~m~ from · ' the Wp of the tree. And the top works only .because the bottom .... works. Energy is required to move things, and elements and ' >::: water are required to build things. "... Tree Treatments and the Rhlzosphere When trees are over-pruned, the top will be injured first. When it is injured, it will not serve the energy requirements of -. the bottom. Soon root'diseases start and are blamed for the . - decline Or death of the. tree. Where over-pruning is common, so ' ' Compacted soil blocks air and water tO the bottom and : crushes'all the microcavifies where the microorganisms live. In . nature, decomposing wood and leaves keep conditions optimal .for the rhizosphere inhabitants2' ~' .'- Over-watering stalls'the respiration processes in the roots. When respiration stops, carbonic acid is not formed. When carbonic'acid is not formed, ions necessary for tim absorption process do not form..When absorption is down, the tree system is in trouble. Fertilizers can be of great benefit to trees growing in soils low in or lacking elements essential for growth. Elements or molecules made up of a few to many different atoms enter the roots as ions. An ion is a charged atom or molecule. Ions with a positive charge are cations, and those with a negative charge are anions. Each particle or granule of fertilizer. providing a some of soluble nitrogen, and, in turn, the bacteria and actinomycetes get first chance at exudates. Even more importantly, the nodules protect them from foraging protozoa.. Infections that result in benefits to both parties are 6ailed mutualistic. When the benefits are greater thaB the sum Of the. parts, the association is called synergistic. Species of legumes commonly have bacterial nitrogen-fixing nodules and mycorrhiz-ae. The mycorrhiz~e facilitate absorption NEW FORESTRY · DECEMBER 1998 27