Decomposition increases amount of organic matter in soil.
Fungi are involved in decomposition, as well.
Fungi are involved in increasing the amount of organic matter in soil.
What can help increase the amount of organic matter in soil? 
(a) Fungi
(b) mussels
(c) pine
(d) worms
(e) animals
(f) Enzymes
(g) solutes
(h) trees