I am designing a terraformed Venus, where the planet has been given an Earth-like atmosphere but keeps it's original rotation rate. Colonists are importing Earth life to Venus to add a biosphere to the planet. My question is whether or not Earth life could survive the long day-night cycle of Venus? Research done into the atmosphere of a terraformed Venus says that the atmospheric circulation will be enough to keep the night side of the planet close to the temperature of the day side, so temperature is not a problem. If this Earth life can't survive a 100 day long night, what is the maximum period of time it could?
Well many plants and animals survive in places with little to no light, I would actually suggest choosing these varieties and then shading them during the sunny period. Actually many plants may need a rest period in darkness so their leaves don't burn.
Also, most trees could survive this period, as shone by the shedding of leaves in winter for about 3 months aka 90 days. However, you would need to cool them in order for this effect to happen, so I'm not sure that would help them survive, but most likely certain species could.
Plants such as grass go long periods without light if covered, and invasive species often have year long or more light deprivation protocols to kill roots.
So the answer is depending on species, yes. Anyways, I would plant crops slightly before daylight happens so they start to sprout about the time the sun arrives, and choose crops that will be ready to harvest before or soon after the sun disappears again.
An ecosystem could survive forever without sunlight, it just needs an energy source. For the sea creatures living in the very deep ocean, volcanoes are the source of energy, rather than sunlight. In addition, think about the poles of the earth, where there is no sunlight in the winter. The ecosystems there are able to survive perfectly well.
Your ecosystems could take on a 100 day hibernation period during the night phase, much like the winters of the earth.