Which biological kingdom comprises the greatest biomass on Earth?
Probably Eukaryotes. Specifically, plants.

This is a very fundamental question of life that is often overlooked. It goes without saying that plants and animals are the strongest contenders. However bacteria may also rival them. Be aware though that this is a contentious claim given more thorough estimations that take into account fluctuations in bacterial presence. This EMBO Reports science and society article claims that plants account for 99% of Eukaryotic biomass.

For further reading the Wikipedia page on biomass doesn't seem too shabby for more details on tonnage and methods of calculation.



The most numerous organisms could possibly be viruses or bacteriophages depending on if you count viruses as "living".