{"id":2772,"date":"2026-01-13T06:24:59","date_gmt":"2026-01-13T06:24:59","guid":{"rendered":"https:\/\/research.reading.ac.uk\/lemontree\/?p=2772"},"modified":"2026-01-13T06:43:51","modified_gmt":"2026-01-13T06:43:51","slug":"what-the-global-decline-in-c4-plants-means-for-the-carbon-cycle-and-why-it-doesnt-fully-explain-atmospheric-isotope-trends","status":"publish","type":"post","link":"https:\/\/research.reading.ac.uk\/lemontree\/what-the-global-decline-in-c4-plants-means-for-the-carbon-cycle-and-why-it-doesnt-fully-explain-atmospheric-isotope-trends\/","title":{"rendered":"What the global decline in C4 plants means for the carbon cycle and why it doesn\u2019t fully explain atmospheric isotope trends"},"content":{"rendered":"

As atmospheric CO\u2082 rises, ecosystems around the world respond in complex and sometimes surprising ways. One such response involves the balance between two major types of plants on Earth: C3 plants (left), which include trees and most temperate grasses, and C4 plants (right), which dominate many tropical grasslands and savannas and include important crops like maize and sugarcane.<\/p>\n

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Understanding how the global abundance of C3 and C4 vegetation is changing and what this means for the carbon cycle, is essential for interpreting long-term trends in the atmosphere, including the isotopic \u201csignature\u201d of CO\u2082.<\/p>\n

A new study led by Alienor Lavergne with LEMONTREE team members, published in Communications Earth & Environment<\/em><\/a>, uses a global optimality-based model of C3 and C4 plant distribution combined with a simple carbon-cycle model to investigate how the changing balance between these plant types has contributed to the observed trend in atmospheric carbon isotopes over the past four decades. The work builds on long-standing uncertainties around why atmospheric carbon isotopes (\u03b4\u00b9\u00b3CO\u2082) are declining more slowly than expected, a discrepancy linked to the well-known Suess effect.<\/p>\n

A global decline in C4 vegetation despite growing C4 croplands<\/h2>\n

Lavergne\u2019s model suggests that the fraction of C4 vegetation globally declined from about 16% to 12% between 1982 and 2016.<\/p>\n

This may seem counter-intuitive, given that C4 crops have expanded over the same period. But rising CO\u2082 gives a stronger competitive advantage to C3 plants, which benefit more from CO\u2082 fertilisation than C4 species. As a result, natural C4 grasslands and savannas appear to be losing relative ground.<\/p>\n

The new model shows strong agreement with observed soil carbon isotopes\u2014one of the best indicators of local C3\/C4 vegetation balance\u2014and performs better than previous global maps in key regions like Africa and Australia.<\/p>\n

What does this shift mean for global photosynthesis?<\/h2>\n

The reduced dominance of C4 plants, combined with rising CO\u2082, results in a substantial increase in global plant productivity.<\/p>\n

The study estimates:<\/p>\n