Growth responses of African savanna trees implicate atmospheric [CO2] as a driver of past and current changes in savanna tree cover.

摘要: Atmospheric CO2 has more than doubled since the last glacial maximum (LGM) and could double again within this century, largely due to anthropogenic activity. It been suggested that low [CO2] contributed reduced tree cover in savanna grassland biomes at LGM, increasing over century promoted increases woody plants these ecosystems past few decades. Despite implications of idea for understanding global carbon cycle dynamics key role biome, there are still very experimental studies quantifying effects on growth demography savannas grasslands. In paper we present photosynthetic, allocation responses African trees (Acacia karroo Acacia nilotica) a C4 grass, Themeda triandra, exposed gradient concentrations from 180 (typical LGM) 1000 µmol mol−1 open-top chambers glasshouse as first empirical test idea. Photosynthesis, total stem length, diameter, shoot dry weight root acacias increased significantly across gradient, saturating higher concentrations. After clipping simulate fire, showed an even greater response diameter weight, signalling importance re-sprouting following disturbances such fire or herbivory systems. Root starch (per unit mass per plant) steeply along explaining response. contrast strong seedlings grass productivity little variation, These results suggest significant direct recruitment grassy ecosystems, influencing ability recover damage herbivory. Fire herbivore regimes were effective controlling thus be much less CO2-rich world, but field-based tests needed confirm suggestion.