Spontaneously I´d say the overall development of the plant. Is it still forming leaves or does it in invest in reproduction already? Salt can delay the development of plants and reduce biomass.

What is the contribution of root-shoot ratios in stresses?

This ratio is quite important particularly in salt tolerant grasses

and for cold stress?

I work in a system which usually has warmer temperature and high soil salinity. Therefore i do not have any personal experience. However, it will be interesting to look using this angle.