Associated growth of C3 and C4 desert plants helps the C3 species at the cost of the C4 species

C-3 desert plant Reaumuria soongorica (RS-C-3) and C-4 desert plant Salsola passerina (SP-C-4) may exist either in individual or in associated communities. Carbon isotope composition, leaf water potential, gas exchange and chlorophyll fluorescence characteristics of the individual and associated communities were compared with reveal, whether the associated growth represent an advantage under harsh habitat. The results showed that the delta C-13 values of leaves of RS-C-3 and SP-C-4 across different habitats fluctuated, respectively, from -24 to -27 aEuro degrees and from -14 to -16 aEuro degrees. Leaf water potential of RS-C-3 was lower than SP-C-4 all day long, growing either individually or associated with the C-3 plant. When associated with the C-4 plant, the net photosynthetic rate of the RS-C-3 increased, and the photosynthetic rate of the partner SP-C-4 decreased. The transpiration rates of the associated RS-C-3 and SP-C-4 were both lower than in their individual colonies. In associated communities, in RS-C-3, the maximal photochemical efficiency, the effective photochemical efficiency, the relative electron transport rate, the photochemical quenching of PS II increased, and the non-photochemical quenching of PS II decreased; all these parameters changed oppositely in the SP-C-4 plant. This shows that, in the associated community, the C-4 plants might facilitate adaptation of the RS-C-3, while SP-C-4 plant can adapt to the harsh environment through their own specialties. The association favored the expression of natural photosynthetic characteristics and survival of RS-C-3, while retarded the growth of SP-C-4. Associated growth decreases the transpiration rate of the whole community; it is conducive to improve its water use efficiency.