When and where does the energy act as limiting factor?

[dkniu]

I am not an ecologist. I have heard that nitrogen and phosphorus are the limiting factors of some plants. Now I want to know WHEN and WHERE does the energy act as limiting factor? That is, at which developmental stage, which stage of life cycle, or in which organ?

Potential answers on plants, animals and even on microorganisms would be greatly appreciated.

[mith]

energy or as building blocks?

[dkniu]

energy in narrow sense, like ATP. Not building blocks. For the carbohydrates, I concern the energy they carried, but not the materials that can be used in constructing the cells.

[mith]

I don't see where nitrogen or phosphorus comes in then...plants don't use them for energy.

[AstusAleator]

Well, in the case of ATP, all living things use them for energy.
http://upload.wikimedia.org/wikipedia/c ... ucture.png
Notice it contains both.
Phosphates are the active energy molecules carrying the charge that will be transferred.

To address the original question:
NPK aren't necessarily the issue here. The most crucial time in a plants life that I can think of, as far as energy is concerned, is germination. During this time, the germinating plant must rely on the endosperm until they can produce a photosynthetic shoot and sustain themselves from their own foliage. This is a critical point, at which if the plant does not recieve enough sunlight, it will die. Soon after, NPK also become a major concern, but it's my understanding that direct sunlight is the primary energy concern of a new shoot. the NPK can be supplied sufficiently by the endosperm until photosynthesis is established.

[dkniu]

Thanks to AstusAleator for kind reply.

I have further questions? Is it possible for seedlings and pollens? In seedlings, the stored energy has been exhausted and the photosynthesis just begin. In pollens, no photosynthesis occurs. In the process of pollen transfer, does the amount of stored energy determines the longevity of pollens?