The widely observed carbon fertilization effects on plant photosynthesis worldwide are declining, researchers report in a new study. Its results suggest that the positive effects that the carbon dioxide (CO2) fertilization effect (CFE) has on mitigating atmospheric carbon may have limits. Climate models that rely on this important carbon sink may underestimate projections for future warming, the authors say. The phenomenon known as CFE is driven by the acceleration of photosynthesis in response to an increased supply of CO2, which has the overall effect of enhancing plant productivity. In addition to making the planet "greener," the resulting enhanced growth has an overall effect of increasing the amount of CO2 that is pulled from the atmosphere and stored as organic matter on the land. Because of this, it's widely thought that CFE plays an important role in the global carbon sink and mitigating climate change. However, measuring CFE is difficult. Just how enhanced plant productivity contributes to the mitigation of climate warming is not well understood and represents a source of uncertainty in projections of future climate warming. Songhan Wang and colleagues combined multiple long-term satellite- and ground-based datasets and found that CFE has declined across much of the globe from 1982 to 2015 - a trend that correlates well with observed changes in nutrient concentrations and available soil water. According to Wang et al., the findings indicate a substantial reduction of the positive effects of increasing atmospheric CO2 on terrestrial carbon sinks, which is not adequately considered in the current carbon cycle models used to predict future climate change.
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Journal
Science