Things Donors Know: Can Trees Live Forever?

In honor of Tu Bashvet, the column will satisfy the curiosity of Corbus who asks if trees age or are they immortal

The question "why get old" sounds strange but at Animals aging and death are the result of a "decision" inherent in genes. In long-lived mammals (like us for example) the number of divisions that the body cells can go through is limited. The ends of the chromosomes called telomeres shorten with each cell division until the worn chromosome can no longer participate in another division and the cell dies. Telomerase, the enzyme that renews the telomere is active in the fetus, but evolution chose to silence it precisely in mammals that live longer to avoid the side effect of the accumulation of DNA damage - its film. In other animals, such as rodents, the telomeres do not wear out, but evolution, in an equally cruel decision, chose to invest everything in a high culture rate and not in repairing the environmental damage to the cells, thus condemning the creature to an even faster death. Planned death is no stranger to plants, shedding is not a casual death of leaves but their active and organized suicide. In response to changes in the environment, a chain of reactions is activated that begins with the cessation of photosynthesis and continues with the breakdown of proteins and nucleic acids associated with chlorophyll and the flow of the breakdown products through the sap tubes back to the plant. Similarly, the forehead prunes unhelpful root parts to free up resources for young roots.

In the course of evolution, plants, just like animals, needed to find the balance between investing resources in reproduction or longevity. Like the salmon that died after spawning, most plants chose not to extend their lives beyond the moment when the work of reproduction was completed. These plants that multiply once (monocarpic) are not necessarily annuals, the agave plants (from which they produce tequila) may live for about 20 years and bamboo even 100 years, but they are also programmed to bloom, spread the seeds and make way for the next generation.

In the biennial, like the single leaf before shedding, a chain of reactions is activated in the entire plant that ends as a mist. There are several good reasons for weeds to die: in order to sustain the sprout, a high concentration of protein and nucleic acids in the seed is required. Resources are limited and the best use of these materials from an evolutionary point of view is to break them down into their components and transfer them from the stem, root and leaf to the seed. There are plants such as members of the legume family where the seeds are heavy and fall close to the parents, it is better for the parent plant to die and leave virgin soil for them to germinate in. Like animals, most plants also have a good reason to die at the right time for their offspring. A poetic expression of this idea can be found in the description of the appropriate death that Eliphaz the Yemeni promises to Job "And you knew that your seed and your offspring are as numerous as the grass of the earth.    Come with haste to my grave, like a full moon in its time" (Job chapter XNUMX)

And now, Corbus, we have finally come to the trees. A tree is a plant that may belong to many families of plants and most trees have "relatives" who have chosen an herbaceous lifestyle. Trees are not a biological group with a common evolutionary past but rather a strategic choice made by plants from different families when they had to decide between rapid reproduction and longevity. A quick look at the butterfly flowers of the Hortem immediately betrays its familial relationship to the annual legumes. At some point in evolution, his ancestors chose a different strategy that gave him longevity. There are stable environmental conditions where there is an advantage to size and to grow you have to live a long time. A tall plant wins the competition for sunlight, stays away from the dangers swarming on the ground and spreads pollen and seeds over a long distance. The resources invested in growing to a height with a massive trunk and a root system that will sustain a large plant come at the expense of rapid seed formation but allow the plant to produce seeds for many years. At the decision point between the two strategies: the woody and the herbaceous, about 20% of the plants (about 80,000 species) "chose" to prolong life and grow taller, that is, to become trees. Unlike its lower relatives, the tree has no evolutionary interest in aging and death, and indeed a widespread opinion among botanists is that trees do not age: they take care to break down and die unnecessary parts such as leaves or unhelpful root branches, but the whole tree remains young forever. What makes the miracle possible is the ability of plant cells to undergo re-sorting, damaged plant parts can, therefore, be replaced by neighboring tissues. Gardeners are well aware of this phenomenon and use it to prepare cuttings: cells in a branch that has been pruned and placed in water become a living and functioning root. Throughout its life, the plant maintains an unsorted tissue (meristem) which is genetically equivalent to the embryonic stem cells and which allows it to grow new organs when necessary where they are needed. This ability allows the plant to reproduce asexually in addition to that through seeds. On the island of Tasmania south of Australia grows a rare plant called Lomatia tasmanica, the individuals sometimes flower but never fruits or seeds have been observed. Genetic research revealed that the entire population of plants are identical clones, if we consider all the clones as a single individual, we have before us a plant that is over 43,000 years old: the closest to "immortality" for a multicellular creature.  

In 1963 there was a tragic encounter between the infinity of trees' lives and the infinity of man's stupidity when the oldest tree: a 5000-year-old pine was cut down in California. Today, the oldest tree is "Methuselah" which is 4841 years old (almost 4000 years older than the biblical Methuselah). In fact, Methuselah is older than the human counting of years: when a 365-day calendar was put into use in Egypt in 2874 BC, Methuselah had already celebrated his sixth birthday. The length of the telomere, the pacemaker of our life, in the cells of 2000- and 3500-year-old pine trees is the same as in 30-year-old trees of the same species. How do we then explain the aging of the forests? Older trees grow more slowly, produce smaller leaves and are less efficient in the gas exchange required for respiration and photosynthesis. These changes may be interpreted as old age or simply as a side effect of the altitude: the higher the tree, the harder it is to bring water up to the top and the leaves on the higher branches live in desert conditions. In addition, a tall trunk and thick and heavy branches require a massive investment in stabilizing the structure which comes at the expense of the leaves and reproduction. To check whether old tree branches do indeed suffer from geriatric problems, the researcher Maurizio Mencuccini performed a long series of trains. For the agriculturally challenged, we will explain that compounding is planting a branch from one tree on the trunk of another (canna) tree. This is how, for example, oranges grow on a canna: a robust citrus tree whose fruits are inedible. This way you can test the performance of an old branch on a trunk and roots that provide growing conditions for a young tree. The results he received from Ancocin are unequivocal: the trees do not age. An old branch will function as a young one for everything as long as it is not required to support the cumbersome structure of an old tree. KKL-Junk's pine forests age and are replaced at about 50 years of age, but in assembly experiments, 270-year-old pine branches did not show any signs of aging. If we define old age as the wear and tear of the genetic material, then they maintain eternal youth. But there are other definitions for old age that refer to the whole organism and according to which the trees do age. When you check the chances of mortality in relation to age, it becomes clear that the life-extenders among the plants increase the chance of each plant dying from the age of 100 or so. Just as the chances of a 90-year-old man celebrating his 91st birthday are smaller than the chances of a Bar Mitzvah groom celebrating his 14th birthday, so are the chances of a 300-year-old tree reaching 400 years old compared to the chances of a 100-year-old tree celebrating 200 avivs. The reason for this is that the tree must grow: we can determine the age of a tree by the number of rings in the trunk because every year the tree has to grow a new network of tubes on the outside of the trunk. The tree is destined to continue and expand throughout its life. A tree that has reached an optimal size cannot stay there or even slow down its growth rate.  Surprisingly, the growth rate (in absolute values) of the tree actually increases with age. Old trees convert more carbon dioxide into cellulose than young trees simply because they have more leaves. This finding has an ecological implication: old trees have a significant contribution to fixing carbon dioxide and sometimes an old tree fixes a mass of carbon equal to the total mass of a young tree in the same forest. Thus the fate of each tree is determined to grow beyond its appropriate dimensions and become more vulnerable. Indeed, bonsai trees whose growth is artificially stunted outlive their counterparts in the open field. Preservation of embryonic cell tissue and a strategy of constant growth gave the trees extreme longevity, but in the end the trees too must die of the dignity of their years.

thanks to:

 Dr. Sergi Munne-Bosch, Dr. Maurizio Mencuccini

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More of the topic in Hayadan:

• Fungi capable of decomposing wood
• A volcano, an atomic bomb and an olive branch
• Everything is written in the rings on the tree trunks