Climate and landform favoring early rice agriculture and human impact in eastern China

The outset of agriculture, a profound economic transition in Neolithic history is regarded as an adaption of human to the changing environment in Holocene and accelerates anthropogenic modification of Earth surface. For rice agriculture prevailing in East and South Asia, however, environmental preconditions of its origin are still controversial. Excavations of rice relic indicate low Yangtze region as one of the cradles of rice cultivation, where we select Kuahuqiao site regarded as the foremost pioneer of rice agriculture. Here we report total organic carbon (TOC), black carbon (BC), 13CTOC, 13CBC, carbon-nitrogen ration (C/N) (fig. a) in Kuahuqiao from 11,860 to 5,820 aBP. Plotted 13CTOC and C/N in 25.80~8.40 m (9,200~7,950 aBP) (red arrow in fig. b) show a transition of sedimentary organic resources from terrestrial plants to algae, confirming the wetland formed due to sea-level rising prior to the Kuahuqiao culture (7,950~7,600 aBP), which offered a favorable landscape for rice paddy. Meanwhile, the positive trends of 13CTOC and 13CBC (yellow arrows in fig. a) attribute to improved water-use efficiency of plants driven by the hotter but drier climate, which is confirmed by increased BC representative for more aridity-caused fires. This climatic condition benefitted rice agriculture by augmenting the growth of wild rice and C4 herbs, as proven by pollen records. Human occupation impressed 13CTOC record by a sharp positive trend i.e. decreased C3/C4 ratio (green arrow in fig. a) by manipulating forest for hunting-gathering or/and by clearing forests for agriculture. As culture developing, rice agriculture advanced but fire never played a vital role in agriculture since our BC and 13CBC remain stable (cyan area in fig. c). Hence, we suggest the origin of rice-agriculture in eastern China different from the burning and slashing due to the absence of fire use. Dramatic peaks of TOC, BC and plummets of 13CTOC, 13CBC (purple area in fig. c) resulted from the catastrophic flood events, which ruined Kuahuqiao culture, revealing a fragile balance between fertility of estuarine wetland and its vulnerability to hydrological disasters. Our work generalized environmental features of incipient rice agriculture, shedding light on the discussion of Neolithic human-nature interaction.