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16 WINTER 2015 ARBOR AGE www.arborage.com PLANT HEALTH CARE "stuff " inside the cell begins to build pressure that increases its likelihood to rupture. Other plants take it one step further and undergo a process referred to as "deep supercooling." Deep supercooling is a way to keep a liquid in a liquid state well below its freezing point. To do this, these plants produce a special protein to prevent freezing. These are conveniently known as "antifreeze proteins" or AFPs, and they are pumped into the spaces between the cells during the fall acclimation period. AFPs work not by lowering the freezing point, but by inhibiting the re-formation of ice crystals. They also function at very low concentrations, which means they do not have the same issues related to increasing the osmotic pressure as other methods. Deep supercooling also has its range limits, but will allow trees such as oak, elm, maple, beech, ash, walnut, hickory, rose, rhododendron, apple, pear and stone fruits to survive temps down around negative 40 degrees Fahrenheit. Although that number seems ridiculously cold to our tropical-loving bodies, that is still only about half as cold as the Dahurian larch can endure. Trees such as paper birch, redtwig dogwood, willow, quaking aspen, and, of course, the Duhurian larch survive the damaging crystallization effects of freezing water by trying to rid themselves of as much water as possible. Rather than pumping more items into their cells, these plants spend the approaches for surviving winter. Annuals survive winter by not surviving at all. They have developed a way to complete their lifecycle in a single season, leaving only their more storage- friendly seeds to endure the off-season. Herbaceous perennials often have specialized belowground structures that can store water and carbohydrates for the winter, and can reactivate them in the spring. This includes familiar structures like the bulbs of a tulip, the tubers of a potato, and the taproot of a carrot. Hardy woody plants, such as trees and shrubs, do not have the luxury of moving all their tissues into the soil, so they have developed a few different strategies for subzero temperature endurance, and it all starts with water management. Although trees appear solid to us, their cells are comprised primarily of water, and what they do with that water in the winter determines their survival. One mechanism involves pumping sucrose and the amino acid proline into the cell. This acts essentially like salting your sidewalks in winter by lowering the freezing point of the solution inside the cell to remain liquid. Just like salting the sidewalk, however, this is only effective for combating "warmer" freezing temps of about 20 to 32 degrees Fahrenheit. This is due partly to the effects of osmotic pressure; you could keep increasing the quantity of dissolved solutes to continually lower a cell's potential freezing point, but at a certain concentration the increased volume of Larix gmelinii larch Hardy trees withstand freezing temps for months. ALL PHOTOS PROVIDED BY RAINBOW TREECARE SCIENTIFIC ADVANCEMENTS