Carbon isotope ratios of plants and occurrences of C₄ species under different soil moisture regimes in arid region of Northwest China

Abstract

Carbon isotope ratio of leaf dry matter, δ 13 C, was measured on species occurring within Baiyin desert community, consisting of valley, slope and ridge microhabitats, and within Shandan desert community, consisting of Gobi desert and seasonal flooded creek microhabitats, in Northwest China. δ 13 C of C 3 species increased with a decrease in soil water availability, suggesting that water‐use efficiency (WUE) increased with decreasing soil moisture, whereas for all C 4 species, δ 13 C tended to decrease with decreasing soil water availability, suggesting that WUE also increased with decreasing soil moisture. Above results indicated that water‐use pattern was conservative under drought for C 4 and C 3 plants. In this present study, C 4 species' occurrences within different microhabitats were investigated and C 4 plants were observed to be absent and/or scarce within relatively lower soil moisture microhabitats, whereas they occurred and/or even had a high abundance within relatively higher soil moisture microhabitats, suggesting limited moisture available was a key factor of limiting C 4 distribution in arid region of Northwest China.