Why would dormancy be necessary outside of suboptimal conditions?

[RiverbankMudlark]

I'm planning on getting a Sedirea japonica Minmaru and Minmaru-shima. In preparation for it, I've been doing a bit of a deep-dive into Sedirea japonica care/culture and... I'm not gonna lie, some of what I've found confuses me.

A lot of people say that Sedirea japonica needs a dormancy to stay healthy. Supposedly, if it is kept at intermediate temperatures consistently, and the plant doesn't experience any sort of dormancy, it only lives about 5-10 years before "slowing" and dying of "exhaustion".

To be honest, the claim seems a little bit anecdotal to me. Like, I wouldn't be surprised if people's Sedirea japonicas are just starving for nutrients for one reason or another (e.g. nutrient lockout, the particular watering method flushes the nutrients before they can be absorbed much — maybe it's just a heavy-feeding species and wants more than it's given usually), and they are living longer when they have Winter dormancy, because during those times the orchid's metabolism is slowed and it isn't using those resources as fast (i.e. the plant is still slowly dying of nutrient deficiency, but it's "living longer" because of the added time where its growth is halted, during which it isn't using those resources as much).

To me, it doesn't make much sense biologically for Sedirea japonica (or really any other plant) to require a dormancy outside of the conditions where it protects the plant. Plants produce their own energy via photosynthesis (and they shouldn't have any reason to die of exhaustion unless there's some growth abnormality that takes all the energy e.g. some unstable hybrids grow so quickly and flower so much they die).

Though we call it 'Winter rest', dormancy in plants is a survival mechanism for suboptimal conditions (too cold, too dry, too dark). Since photosynthesis itself is reduced from less water and less sun (as well as the cold slowing down metabolic functions), a plant in dormancy wouldn't be 'recovering' or 'resting' — if anything it would be just surviving on what little energy it can generate, holding out until ideal conditions return and it can grow properly.

Having said all of that, I'm not a botanist. This is all based on my own understand of how plants work. My reason for this post is to try and figure out if I'm wrong. Have there been any studies or research into why (or how) dormancy would be more than just a way to adapt to harsh conditions?

P.S.
Just to be clear, I'm not asking specifically for Sedirea japonica, but really all plants in general. I think there's similar claims about "dormancy is a must" with some carnivorous plants? Like I say, it doesn't make a ton of sense to me why an adaptation to survive harsh environmental conditions would be needed when those conditions aren't around.

[Roberta]

I just grow these outside on my patio...so they do experience seasonal change (like winter chill by southern California standards). I don't change my treatment over the year, though. I just generally water a little less in winter because things don't dry out as fast, but this species gets watered with everybody else. (But then I don't dry out Dendrobiums either... the chill seems to be all the trigger they need)

[estación seca]

I don't know about Sedirea japonica, but there are thousands of plants that die quickly when they don't get their expected cool dormancy. For example, tulips, most narcissus, hyacinth, many maples, and hundreds more temperate climate, winter-dormant plants.

[RiverbankMudlark]

Really? I haven't grown any of those before.

Do you know what the biological reason for that is?

[Roberta]

Indeed, there are orchids that also need a truly cold winter, such as Cypripedium. (I can't grow them where I live) Organisms evolve to their specific habitats. They can do OK a bit outside the usual range, but there are limits. A polar bear could not survive in the tropics, for instance.

Sedirea japonica comes from a range of elevations in Japan, Korea and China. Some habitats may experience significant frost, but probably not hard freeze. So it can tolerate low temperatures, but would be forgiving if it it didn't experience the extremes.

[RiverbankMudlark]

I mean, a polar bear can't live in the tropics because it would overheat, since its body is adapted to conserve heat. The polar bears body would not change to handle a different environment.

Where there is no change in the polar bear, there is a change in plants. Dormancy is a change in how the plant functions according to the conditions around it.

What confuses me about the whole dormancy thing is that it is a state that occurs in the event that conditions become bad for the plant. If conditions don't go bad for the plant, why should that be a bad thing?

I get the argument that "if a plant evolved to particular conditions, it thrives in those conditions," however, I don't think that implies that those conditions are all ideal to the plant.

Toxin resistance can occur where animals can benefit by eating food that would otherwise poison them. That doesn't make those toxins good for the animal though. It just means they can handle them.

Winter is bad for plants in terms of photosynthetic production of energy, and in extremes, ice crystals forming inside cells can result in serious damage. That's why deciduous plants drop their leaves (also, they do that to conserve water lost through transpiration).

If a plant has no environmental reason for entering dormancy, and it can continue on the way it normally does, why would that be harmful?

[estación seca]

Plants requiring dormancy have evolved that way. It must increase their environmental fitness or they would not have survived.

[Ray]

Though we call it 'Winter rest', dormancy in plants is a survival mechanism for suboptimal conditions (too cold, too dry, too dark). Since photosynthesis itself is reduced from less water and less sun (as well as the cold slowing down metabolic functions), a plant in dormancy wouldn't be 'recovering' or 'resting' — if anything it would be just surviving on what little energy it can generate, holding out until ideal conditions return and it can grow properly.

It’s all about the accumulation and storage of phytochemical resources.

For some plants, winter is accompanied by more light. Yes, there may be a more reduced solar flux, but the reduced canopy density of deciduous host trees means a net increase.

The chemical processes within plants are varied and pretty complex, with some occurring in daylight, while others are done in the dark. Some are accelerated by temperature while others by light intensity - and very likely - some by both. Generalizing doesn’t fit.

I think, however, that this is “putting the cart before the horse”, and that the seasonal weather changes are “triggers” to blooming and the plants have evolved resource accumulation strategies to take advantage of that - i.e., there will be more pollinators around when it warms and rains more, so let's “sock ‘em away” while we can.

Dendrobium kingianum is a good example. Withhold fertilizer and keep it cool and very bright over the winter and it’ll put on a great show of blossoms when spring returns. Keep feeding it, grow it too warm or with too little light and you’ll turn it into a non-blooming “keiki factory”.

[Pegleg]

“I get the argument that "if a plant evolved to particular conditions, it thrives in those conditions," however, I don't think that implies that those conditions are all ideal to the plant.”

But, they are ideal to the plant because the plant has adapted to just those conditions.

Think of a standard set of processes every plant has to perform to thrive. A plant in the tropics with little seasonal variation may be able to do all of those things all the time. A plant in a location with wide seasonal variation has to prioritize certain functions in certain seasons. If the plant doesn’t get the right trigger to switch gears, functions that are supposed to happen during dormancy don’t start at the right time and/or won’t have enough time dormant to be ready for the next season. A dormant plant is still doing things we can’t see. So, bud development, for example, doesn’t happen, fewer happen or, what forms is weaker.

Also, going into, or coming out of, dormancy is triggered by various factors leading up to the conditions that require it. That’s the adaptation. Plants that don’t start preparations in due time will die or fail to reproduce. Think of seeds that won’t germinate without cold and then warming.

[RiverbankMudlark]

You know, you make some really good points.

I was thinking about it some more this morning, and I suppose it wouldn't be outside of the realm of possibility that the dormancy might also help regulate hormones. Like it might clear the plant of excess growth hormones present in the active growth stage — if dormancy helps prevent build-ups of cytokinins (basically keiki paste), that might explain why the Dendrobium kingianum produces a lot of keikis.

This does raise some questions though. If dormancy is an important part of hormone regulation, how do plants that do not experience dormancy manage to avoid these hormonal issues, despite growing continuously?

Also, why are there some orchids that undergo dormancy that can go without it? For example, I've read that in Japan, as Dendrobium moniliforme is typically grown for its foliage ore than its leaves, people keep it at constant temperatures to avoid it dropping its leaves. How could they sustain that?