How long do suberin and sporopollenin persist in farm soils?

Some plant materials are chemically tough, such as suberin, the waxy polymer in roots and bark, and sporopollenin, which coats pollen and spores. If they last for decades in soil, crops that make more of them could store carbon; but soil science has learned that chemical toughness alone rarely guarantees persistence.

Question

How long do "recalcitrant" forms of plant carbon, such as suberin and sporopollenin, persist in agricultural soils, and what controls their persistence: their chemistry, their location in roots and soil aggregates, or the soil environment? The relevant timescale for carbon storage is years to decades, at field scale.

Background

The question is in the theme "mitigating climate change through agriculture" of the 100 essential questions for the future of agriculture, compiled from 419 questions submitted worldwide in 2022, next to questions on using soil to generate long-term carbon storage credits and on whether soil carbon sequestration improves cultivated land [1]. Knowing how long specific plant compounds last would show whether breeding crops for them could store carbon durably.

What is known

• In a wheat–maize chronosequence, root-specific suberin markers were strongly incorporated into soil organic matter during the first six years of maize, whereas new shoot-derived cutin was mostly degraded within a year, suggesting selective preservation of root material, possibly through physical protection [2].
• Molecular structure alone does not control the stability of soil organic matter; environmental and biological controls predominate [3].
• Suberin's structure and biosynthesis are increasingly understood, but quantitative, high-throughput methods are still needed to measure it in crops and to represent its contribution to soil carbon [4].
• Sporopollenin is an extraordinarily stable polymer that has been found chemically intact in sedimentary rocks some 500 million years old [5].

What would count as progress

No single result settles a question like this; contributions like these would move it forward:

• Isotope-labelling field experiments that follow suberin- and sporopollenin-derived carbon in farm soils over several years, using compound-specific measurements.
• Comparisons of crop lines that differ in root suberin content, measuring how much extra carbon remains in the soil and for how long.
• Soil carbon models that represent these compounds explicitly and are tested against such data.

References

1. Hu, Y. et al. (2023). 100 essential questions for the future of agriculture. Modern Agriculture 1(1), 4–12.
2. Mendez-Millan, M. et al. (2010). Molecular dynamics of shoot vs. root biomarkers in an agricultural soil estimated by natural abundance ¹³C labelling. Soil Biology and Biochemistry 42(2), 169–177.
3. Schmidt, M. W. I. et al. (2011). Persistence of soil organic matter as an ecosystem property. Nature 478(7367), 49–56.
4. Harman-Ware, A. E. et al. (2021). Importance of suberin biopolymer in plant function, contributions to soil organic carbon and in the production of bio-derived energy and materials. Biotechnology for Biofuels 14, 75.
5. Mackenzie, G. et al. (2015). Sporopollenin, the least known yet toughest natural biopolymer. Frontiers in Materials 2, 66.

Source

Imported from 100 essential questions for the future of agriculture, question 15, curated by Hu et al. Listed as open in the source (2023) and still an active research question as of 2026-10-20. The statement above is written in our own words; see the source for the original wording, history and discussion.