Abstract
Abstract. Rhizosheath size varies significantly with crop genotype, and root exudation is one among its driving factors. Unravelling the relationships between rhizosheath formation, root exudation and soil carbon dynamics may bring interesting perspectives in terms of crop breeding towards sustainable agriculture. Here we grew four pearl millet (C4 plant type: δ13C of −12.8 ‰, F14C = 1.012) inbred lines showing contrasting rhizosheath sizes in a C3 soil type (organic matter with δ13C of −22.3 ‰, F14C = 1.045). We sampled the root-adhering soil (RAS) and bulk soil after 28 d of growth under a semi-controlled condition. The soil organic carbon (SOC) content and δ13C and F14C of soil samples were measured and the plant-derived C amount and Clost / Cnew ratio in the RAS were calculated. The results showed a significant increase in δ13C in the RAS of the four pearl millet lines compared to the control soil, suggesting that this approach was able to detect plant C input into the soil at an early stage of pearl millet growth. The concentration of plant-derived C in the RAS did not vary significantly between pearl millet lines, but the absolute amount of plant-derived C varied significantly when we considered the RAS mass of these different lines. Using a conceptual model and data from the two carbon isotopes' measurements, we evidenced a priming effect for all pearl millet lines. Importantly, the priming effect amplitude (Clost / Cnew ratio) was higher for the small rhizosheath (low-aggregation) line than for the large rhizosheath (high-aggregation) ones, indicating a better C sequestration potential of the latter.
Highlights
In the context of climate change, a new challenge for agriculture is to sequester more carbon in the soil to mitigate CO2 increase in the atmosphere (Lal et al, 2015)
Using natural 13C abundances (δ13C), significant increases were noticed in the root-adhering soil fraction (δ13CRAS) of all four pearl millet lines compared to the unplanted control soil (p
There is no significant difference in δ13C between all four bulk soils and the control soil, showing that there is no significant input of fresh C4-derived carbon outside the rhizosheath
Summary
In the context of climate change, a new challenge for agriculture is to sequester more carbon in the soil to mitigate CO2 increase in the atmosphere (Lal et al, 2015) This will be important as increasing soil organic carbon (SOC) content would enhance soil fertility through improving physical and biological properties of the soil and would have beneficial effects on agriculture and improve food security (Lal et al, 2015). This strategy could be relevant in the Sahel region of Africa, where very little above-ground cover remains after harvest, leading to soil carbon depletion (Baudron et al, 2014). It is naturally adapted to drought conditions of these semiarid and arid regions and is a staple food for nearly 100 million people around the world
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