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July 2018 WINES&VINES 53 BOOK EXCERPT matter back down to soluble nu- trients that plants can suck up through their roots. Yet roots are not simply straws. They are two-way streets through which carefully negotiated and orchestrated exchanges occur. Plants release into the soil a vari- ety of carbon-rich molecules they make, and which can account for more than a third of their photo- synthetic output. For the most part, these exudates consist of proteins and carbohydrates (sug- ars) that provide an attractive food source for soil microbes. In this manner, plant roots feed the fungi and bacteria that pull nutri- ents from the soil — from the crystalline structure of rock frag- ments and organic matter. When enough microorganisms are present, root exudates do not last long. Microbes chow down on and assimilate most within hours, modifying and re-releasing them in other forms. In addition, with the help of soil-dwelling bacteria certain mycorrihizal fungi use their thread-thin, root-like hyphae to seek out and scavenge particu- lar biologically valuable elements, like phosphorus, from rocks or decaying organic matter. Then they trade the scavenged ele- ments, now in plant-available form, for root exudates. This sets up an exchange through which both sides benefit from the com- merce of the original underground economy. Likewise, the dead cells that roots slough off last for only a few days before microbes consume and reprocess them. The resulting microbial metabolites include plant-growth-promoting hor- mones and compounds that bol- ster plant health or aid in plant defense. Some form stable car- bon-rich deposits that, in turn, help structure communities of beneficial bacteria in the rhizo- sphere, a biologically rich zone around plant roots. Curiously, rhizosphere-dwell- ing bacteria are more effective at promoting plant growth once a critical microbial density is reached, triggering a process known as quorum sensing. When enough individual bacteria of the right kind are present, they coor- dinate the release of compounds that aid in promoting plant growth. But, if the population of soil microbes drops too low, they turn off the tap. In other words, they only work if there are enough of them to make a difference to the plant, which in turn produces a healthy exudate return for the microbes. By pushing enough exu- dates out into the soil, the plant can cultivate microbial popula- tions that produce compounds useful to the plant. The complex- ity and adaptation belowground, mirrors that aboveground, as plants recruit and feed specialized communities of bacteria and fungi in relationships every bit as spe- cialized as those between flowers and pollinators. Where do you think you would find the most bacteria in soils? Where the food is, of course — around plant roots. And where are the most bacteria-eating protists and nematodes? Also around the roots, where the bacteria are. This is another link in the soil food chain — after saprophytic fungi and bacteria consume organic matter, they become enriched with nutrients. Predatory arthro- pods, nematodes, and protozoa feast on them, then release those nutrients back into the soil in plant-available forms. Because the excrement of these microscopic predators is rich in nitrogen, phos- phorus, and micronutrients, it makes excellent micro-manure. In these ways, soil life makes soil fertile. Major elements like calcium, magnesium, phosphorus, potassium, sodium, and sulfur that plants need to make their bodies, and we need to make ours, ultimately come from rocks via the soil. So do essential trace ele- ments like copper, iodine, manga- nese, molybdenum and zinc. At every step along the way microbes are intimately involved in making most mineral-derived elements available to plants. And the more of these microbes that are on the job, the more nutrients that are available to plants. Most (though not all) soils have enough of most elements to grow healthy plants — as long as those elements are unbound from min- eral grains and organic matter and in forms that plants can take up. This is the microbes' job. Microbes 145 Jordan Street, San Rafael, CA 94901 415-457-3955 • www.boswellcompany.com he Premier Silicone Rubber Bung T The FAT-Lip Silicone Rubber Bung 145 Jordan Street, San Rafael, CA 94901 415-457-3955 • www.boswellcompany.com First in Value & Service Since 1981 707-765-6666 • www.scottlab.com A simple solution to inoculate your barrels Selected Wine Bacteria in Tablet Form Tested and approved for its efficiency, Malotabs™ is available for white and red wines and complements fresh and fruit driven wines with balanced mouthfeel. + 1 tablet 1 barrel Easy to add for complete dispersion of bacteria throughout the barrel A simple solution to inoculate your barrels