What was done
The authors measured a number of atmospheric gases and particles in a Eucalyptus forest in Portugal and analyzed their observations to see if there was any evidence of biologically-produced gases being converted to particles that could function as cloud condensation nuclei.

What was learned
The data and analyses demonstrated that certain hydrocarbons emitted by vegetation (isoprene and terpenes, in particular) do indeed experience gas-to-particle transformations.  In fact, aerosols produced from two of these organic acids (cis- and trans-pinonic acid) comprised as much as 40% of the fine particle atmospheric mass during daytime hours.

What it means
These findings clearly demonstrate that the biology of the earth can influence the climate of the earth.  Specifically, they reveal a direct connection between the metabolic activity of trees and the propensity for the atmosphere to produce clouds.  What is more, the relationship is one that is self-protecting of the biosphere: as the air's CO2 content rises, plant productivity rises, which leads to an enhanced evolution of biogenic gases, which leads to the production of more cloud condensation nuclei, which leads to the creation of more clouds that reflect more solar radiation back to space, which tends to counteract any increase in the strength of the atmosphere's natural greenhouse effect that may have been produced by the initial rise in the air's CO2 content.