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I have 2 dragon fruit (pitaya) growing under a large 30-year-old mesquite tree. The mesquite tree is dripping sap at the base of one of the dragon fruit plants. This plant is a deep green healthy color. The other plant (which does not have sap dripping at its base) is pale green and does not look as healthy.

Is it possible that the sap from the mesquite tree is providing nutrition to the dragon fruit and if so what is it in the sap that's doing this?

Not sure if this image of the two plants is sufficiently clear to show the distinction. The one on the left has the sap dripping to its base which you might be able to make out in the photo.

More info: They are two different types of Dragon Fruit. One is white and the other red although neither have produced fruit to date. I also don't know which one is which.

enter image description here

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    How long has the sap been dripping in that place?
    – J. Musser
    Feb 3 '15 at 23:08
  • The sap has probably been dripping in that place for years. The dragon fruit has been there for about a year.
    – Guy
    Feb 4 '15 at 4:04
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...maybe, it is possible that the sap is feeding mycorrhizal fungi, that are making more nutrients available, or there is some nutrient freely available in the sap, or maybe it is just shade... but most likely is that it is just a coincidence, and the other one is under some sort of stress, from heat, or dehydration, or disease, or injury...

if you think it is providing something, you could try a micronutrient fertilizer for the other one.

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I would agree with @Grady, but also add that mesquites are legumes.

My understanding is that fixed nitrogen in the root nodules will remain there until the tree dies, so it is unlikely to be that. But how much is transferred in the sap? Legume beans have high levels of nitrogen (in the protein), so some of it must be transferred in the sap. But is it enough to make a difference?

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  • yeah there could be some more nitrogen... good point, the nitrogen that is fixed in the root nodules could be available to other plants that are in the same root space... Feb 4 '15 at 14:17
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Your mesquite tree shouldn't really be constantly dripping sap - if the sap it is producing turns black or becomes smelly, it would indicate slime flux, a bacterial infection which sets in where sap is constantly running. These trees do bleed and produce sap when damage has taken place, or it has been pruned, particularly larger limbs, so it might be worth inspecting the tree to see if there is anything causing damage.

As for the nutrient value of the sap, mesquite contains calcium, magnesium, potassium, iron and zinc, probably with some fructose as well. The rich green might be to do with the iron content rather than anything else, since dragon fruit likes neutral to mildly acidic soil conditions. Or, in connection with your other question re dragon fruit, the pale one is actually sick, whereas the darker one isn't.

UPDATE: You've confirmed the pale one is the infected plant, so the colour difference might very much be to do with one plant being sick and the other not. Question is, why is the dark green one healthy - calcium from the sap, possibly? No way of proving it though, just a theory.

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