Which is often a limiting a limiting factor on terrestrial ecosystems? 

A)  dissolved oxygen 
B)  dissolved hydrogen 
C)  precipitation 
D)  salinity

Precipitation is often a limiting factor on terrestrial ecosystems because it directly affects the availability of water for plants and animals. In areas with low rainfall, plant growth may be limited, leading to fewer herbivores and thus fewer predators in the food chain. This can have a cascading effect on the entire ecosystem. However, the other options - dissolved oxygen, dissolved hydrogen, and salinity - are more relevant to aquatic ecosystems.