Evidence of shift in C 4 species range in central Argentina during the late Holocene
Aim Millennial-scale biogeographic changes are well understood in many parts of the world, but little is known about long-term vegetation dynamics in subtropical regions. Here we investigate shifts in C 3 /C 4 plant abundance occurred in central Argentina during the past few millennia Methods We determined present day soil organic matter δ 13 C signatures of grasslands, shrublands and woodlands, containing different mixtures of C 3 and C 4 plants. We measured past changes in the relative cover of C 3 /C 4 plants by comparing δ 13 C values in soil profiles with present day δ 13 C signatures. We analyzed 14 C activity in soil depths that showed major changes in vegetation. Results Present day relative cover of C 3 /C 4 plants determines whole ecosystem δ 13 C signatures integrated as litter and superficial soil organic matter (R 2 = 0.78; p < 0.01). Deeper soils show a consistent shift in δ 13 C, indicating a continuous replacement of C 4 by C 3 plants since 3,870 (±210) YBP. During this period, the relative abundance of C 3 plants increased 32% (average across sites) with significant changes being observed in all studied ecosystems. Conclusions Our results show that C 4 species were more abundant in the past, but C 3 species became dominant during the late Holocene. We identified increases in the relative C 3 /C 4 cover in grasslands, shrublands and woodlands, suggesting a physiological basis for changes in vegetation. The replacement of C 4 by C 3 plants coincided with changes in climate towards colder and wetter conditions and could represent a climatically driven shift in the C 4 species optimum range.