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 days of growth under semi controlled condition. The Soil organic carbon (SOC) content, δ13C and F14C of soil samples were measured, and the plant-derived C amount and Clost / Cnew ratio in 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 to the soil at early stage of pearl millet growth. The concentration of plant-derived C in 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 was more important for the low-aggregation lines than for the high-aggregation ones indicating a better C sequestration potential of these latter.
Highlights
The results showed a significant increase in δ13C in the root-adhering soil (RAS) of the four pearl millet lines compared to the control soil, suggesting that this approach was able to detect plant C input to the soil at early stage of pearl millet growth
Soil organic carbon (SOC) content was not significantly different between RAS, bulk soil and unplanted control fractions in 140 any of the pearl millet lines, which was expected given the method of measuring C and the short duration of the experiment (28 days) (Fig. 1A)
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
Summary
25 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 SOC content would have beneficial effects on agriculture by increasing soil fertility, and improving food security (Lal et al, 2015). Following rainfall decline in recent decades, farmers have privileged short-cycle varieties that give optimal yield to cope with the short rainy season (Vigouroux et al, 2011). Despite this adaptation, pearl millet yields remain very low (less than 1 ton/hectare)
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