Carbon atoms in alkynes are sp hybridized
Alkenes sp2
Alkanes sp3
Hence %s character -50,33,25 resp.
An electron in p orbital is at a larger distance from the nucleus and is relatively loosely held,whereas an electron in s orbital is closer to the nucleus and is held more tightly.
Thus in hybridized state,electronegativity of carbon increases with increase in s character.
Hence alkynes can loose a proton relatively easily.

+I effect comes in picture when u r comparing two alkynes.