The right answer is: Plant growth would decrease.
Decomposers are living beings directly involved in the decomposition of dead organic matter (necromass) or excrement or excreta of living beings. They play a major role, necessary for the recycling of the elements (minerals, trace elements ...) that make up the organic matter, in an inorganic matter which will subsequently be absorbed by the plants (which explains the decrease of the growth of the plants during the absence of decomposers).
