I am really not sure about these translations, but I understand the source sentence that you need some sort of plastic foil to cover the plants, and "diffusant" and "climatique" seems to me a similar meaning, maybe these are two options of foil that can be taken for the same purpose?
http://www.greenhousegardeningtips.co.uk/building-a-greenhou...
Many new glazing materials have emerged since greenhouses hit the mainstream in the 70’s. Plastics now are the most popular type of covering since the weatherability has been enhanced in recent years with ultraviolet radiation degradation inhibitors, infrared radiation (IR) absorbency, anti-condensation drip surfaces and unique radiation transmission properties.
http://msucares.com/pubs/infosheets/is0941.htm
Three plastic film materials are in use as greenhouse covers. Polyyethylene (PE) film has been used in large quantities for several years. It has high light transmittance, except in the ultraviolet region of the spectrum, and is transparent to infrared or long-wave radiation. Its chief disadvantage is its lack of durability. There are ultraviolet-inhibited (UV or weatherable) PE's that will last longer.
Miranda Joubioux France Works in field Native speaker of: English PRO pts in category: 8
The translation workplace 
