You Are Studying Two Closely Related Tree Species, One Growing

You are studying two closely related tree species, one growing in a well-watered environment and one in a drier environment. You find that both species have similar photosynthetic rates and keep their stomata open for the same amount of time over the growing season, yet the species from the drier environment does not grow in height as quickly. A reasonable hypothesis for its slower growth might be that in the drier environment:

A) roots have to respire more to pull water from the soil, reducing the carbohydrate available for growth.
B) it takes more energy to generate enough osmotic pressure to open the guard cells in dry environments.
C) a plant has to invest more in leaf area to generate sufficient evaporative forces to pull water from drier soil.
D) stems and leaves have to invest in stiffer and denser xylem to support the tensions required to pull water from drier soil.