Decreasing efficiency and slowdown of the increase in terrestrial carbon-sink activity

Anthropogenic fertilization of the Earth with increasing concentrations of atmospheric CO2 and nitrogen in-puts has enhanced plant photosynthesis and carbon sinks of terrestrial ecosystems. Several signals now suggest, however, that this carbon-sink activity is slowing its rate of increase because of limitations of nutrients, water, and heat, among other factors. Image: Pixabay.

Current anthropogenic warming, as a result of greenhouse had emission, particularly carbon dioxide (CO2), poses a very high risk to nature and human well-being. Up to now, this risk has been buffered by a key group of other species on the planet, terrestrial plants, which have assimilated almost a third of emissions, helping us avoid a much stronger and faster degree of warming.

In a new paper published in One Earth journal, author raises the question of how long will plants continue to rescue us. According to Prof Josep Penuelas from CSIC-CREAF, several signals suggest that this carbon-sink activity might be decreasing its efficiency and slowing its rate of increase because of limitations of nutrients, water, heat, fires, pollution, and reduced vegetation carbon residence time.

Author highlights that plant production requires many more nutrients than just C and N. Bio-elements such as phosphorus (P), potassium, calcium, magnesium, molybdenum, manganese, and zinc are needed for information and energy production and storage, functional control, catalytic power, physiological processes, and cell homeostasis, i.e., for cell structure and function, and therefore for plant growth. The availability of carbon from rising atmospheric carbon dioxide levels, and of nitrogen from various human-induced inputs to ecosystems, is continuously increasing. However, these increases are not paralleled by a similar increase in all these other bio-elements.

According to the study the limitations for increasing carbon sinks do not end with nutrients; many other limitations are linked to climate change itself, which raises temperatures above the optimum and drives aridification of many regions. With all these conspiring factors, we can thus expect the pace of current carbon sinks to slow because of decreased efficiency.

This scenario calls for a reconsideration of IPCC climate projections toward a possible reduction in the mitigation capacity of the terrestrial biosphere even warmer conditions than currently projected and stronger impacts. “If current models continue to ignore it, they may overestimate carbon sinks, and therefore underestimate climate warming and overestimate mitigation potential”, noted Prof. Penuelas.

Climate change is unfortunately already here and may become stronger if mitigation actions do not fully succeed, so countries should also aim to develop better adaptation strategies. Currently, adaptation strategies are largely fragmented, local, and incremental, with limited evidence of transformational adaptation and negligible evidence of risk reduction outcomes. “As we shift from a fertilization-dominated to a warming-dominated biosphere, we need to diversify our approaches and take action to healing harms already inflicted and avoid worse future ones”, concludes Prof. Penuelas.

Penuelas, J. 2023. Decreasing efficiency and slowdown of the increase in terrestrial carbon-sink activity. One Earth, Vol. 6, Issue 6p591–594 Published in issue: June 16, 2023