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Plant Answer Line questions and answers.

Salmon DNA in trees

Does salmon DNA end up in trees?

I saw a show about decomposing salmon being great for riparian ecosystems and that DNA from salmon could be found in the trees. Well, I shared this information with kids and a smart teacher fact- checked it with a scientist who said, no way! Nitrogen and carbon can be found, but not DNA.

It would certainly be cool if there were salmon DNA in trees, but is this true?

It seems obvious that decomposing salmon left by bears around forest trees would leave detectable traces of salmon DNA. Perhaps, along with the nutrients that are being added to the soil and taken up by the trees, there might be a detectable amount of salmon DNA in the trees, too. Certainly there is salmon DNA in salmon carcasses, the carcasses provide nutrients taken up by the tree, but does a test of the tree show traces of salmon DNA?

Let’s see what scientists in the field have to say. T.E. Reimchen is in charge of the lab at University of Victoria and is in charge of the Salmon Forest project there.

Here is a brief excerpt from their research:
“Conifer trees adjacent to salmon rivers on the west coast of North America incorporate marine-derived nitrogen from the carcasses of salmon carried into the forest by bears and other scavengers. We demonstrated (Reimchen et al. 2003) that small samples of wood (30 mg) extracted from cores of ancient trees contain detectable levels of 15N [nitrogen]. Comparisons among watersheds differing in number of salmon show that 15N levels in wood of trees are directly proportional to the present numbers of salmon entering the streams.”

When asked directly about the DNA question, Reimchen said, “I presume that the nitrogen that the tree is sequestering has come from the breakdown of the nucleic acids in the salmon. Have not heard about the incorporation of salmon DNA or RNA into the roots.”

Ray Hilborn, Professor of Aquatic and Fishery Sciences at the University of Washington, said, “I don’t know anything about the DNA — I doubt that very much. However what you do find in trees near salmon rivers is what are called ‘marine derived nutrients,’ that is, nitrogen isotopes that the salmon brought in their bodies back to freshwater.”

It certainly sounds catchy to say there’s salmon DNA in the trees, but it is probably just shorthand for a more complex concept.

Meyer lemon plant dropping its tiny lemons

I purchased a small Meyer lemon plant from a nursery in Florence, OR, and it grew, and blossomed very well, and even produced many tiny lemons – all of which have now, at this point, dropped off. The leaves are yellowing, too. It is in a good size container, in full sun. The container sits in a large saucer which does fill with rainwater. This I empty, but the plant remains wet. New blooms are coming on some of the branches, old blooms are shrivelling. No more lemons coming as yet.

My question is, why did the tiny lemons drop off? And, should the plant get overly wet? My nursery person has no information. I would appreciate any information you have.

 

The following information comes from Citrus (by Lance Walheim, Ironwood Press, 1996).

It sounds as if your container has good drainage, but maybe the plant is getting too much rainwater. That might be causing the leaves to turn yellow. Another cause could be a nitrogen deficiency, which would be most visible in older leaves, which would yellow from the tip to the base.

As far as the plant’s water needs, it will need water when the top two to three inches of soil become dry. Frequent watering (or excess rainwater) can leach nutrients from the soil, so the plant will need to be fertilized regularly — once or twice a month using a liquid, high-nitrogen fertilizer that includes the micronutrients zinc, iron, and manganese.

The small lemons which drop off may not be anything to worry about, as fruit drop occurs normally as the tree varies its fruit load with its carrying capacity. Pea-sized fruit usually drop about one month after bloom. A more noticeable drop occurs in late spring to early summer, when golfball-sized fruit may drop. Other reasons for fruit drop could be conditions which limit tree growth, such as excess heat, lack of soil moisture (not relevant in your case), and fluctuating weather conditions. It is also possible that the fruit drop is due to lack of nitrogen.