This is something I have never really thought about.
Several things are required for a plant to live and grow:
Light, water, air, nutrients, good temperature, and physical
support.
Obviously if you take away either water or sunlight, the plant will
not
survive for long.
But which will survive longer? Let's look at what water and sunlight
do
for the plant.
Plants make carbohydrates from sunlight by a process called
photosynthesis. These carbohydrates can be stored in a plant until it
needs the energy it has stored. A carrot, for example, store this
extra
food in its large root so it has food to grow the next year.
Water is used in the plant during photosynthesis and respiration (the
process of turning the stored food into energy). So if there is no
water,
the plant can neither make food or use the food it has stored.
A couple of other factors will make a big difference for you run this
experiment. What type of plant are you growing? A big cactus will
have a
lot more stored water than a tomato. How big/old are the plants.
Seedlings that have just emerged from the soil use food stored in the
seed
until they are large enough to make all of their own food, so taking
away
light from these plants will not make a difference for several
days.
Normally, I would say that a plant without sunlight will last longer
than
a plant without water.
Thanks for the question!
Eric J. Biddinger
Grad Student - Department of Horticulture
Penn State University ejb190@psu.edu