Tropical forests have strategies to survive in nutrient-poor soils

Tropical forests, storing a third of the world’s carbon, face uncertain futures as carbon sinks due to nutrient-poor soils. However, a new study published in the journal the New Phytologist has found that these forests have flexible nutrient acquisition strategies that might allow them to thrive despite nutrient limitations.

“We may not have to worry about it so much,” said senior author Sarah Batterman, a tropical forest ecologist at the Cary Institute of Ecosystem Studies. “Because of these flexible strategies, trees may be able to support a carbon sink in the future, even with nutrient constraints.” 

“Our findings support the potential of tropical reforestation and conserving intact forests as a long-term climate solution.”

Nutrient acquisition strategies of tropical forests

The experts conducted an unprecedented experiment in the lowland tropical wet forest of Panama, covering 76 plots across 16 square kilometers. 

The team examined how forests of different ages adjust nutrient acquisition strategies to access phosphorus, using either an enzyme called phosphatase or mycorrhizal fungi. Both methods require significant carbon and nitrogen investment from the trees.

“While belowground processes are very important for ecosystem function, they are poorly understood compared to above-ground processes because they are more difficult to study,” said lead author Michelle Wong, an assistant professor at Yale University and former postdoctoral fellow at the Cary Institute. 

Strategies differ depending on the forest’s age

The research showed that forests of different ages respond differently to nutrient additions. Younger forests, often limited by nitrogen, showed increased phosphatase activity when nitrogen was added, enabling better phosphorus acquisition. 

In contrast, older forests displayed increased phosphatase activity when phosphorus was added, indicating a shift from nitrogen to phosphorus limitation as forests mature.

Flexibility of tropical forests

These findings highlight the flexibility of nutrient acquisition strategies in tropical forests, with phosphatase activity increasing by half in response to nitrogen and decreasing by half in response to phosphorus. However, mycorrhizal colonization responses were less predictable.

“We still don’t know whether the flexibility is enough to get all the nutrients forests need in the future,” Batterman said. Despite this, there is a buffering capacity that may alleviate nutrient limitations temporarily. 

According to the researchers, the ability to adjust strategies might provide forests with resilience to recover from land-use changes and maintain productivity in a carbon-rich world.

For forest managers and reforestation organizations, the study offers practical advice: consider nutrient limitations and use a diversity of trees with different phosphorus acquisition strategies. Ensuring trees are adapted to the phosphorus levels at each site is crucial. 

Tropical forests as a climate solution 

Currently, most reforestation efforts focus on quickly planting available seedlings, but Batterman is optimistic about forests as a climate solution if managed correctly.

“We can implement it immediately, it’s low cost, and it has so many co-benefits, like protecting watersheds, enhancing biodiversity, and protecting species that are important to Indigenous people. But it needs to be done correctly,” said Batterman.

“We’re at a point where science can guide the process and ensure the carbon is going to be there for a long time to come.”

More about tropical forests 

Tropical forests, also known as rainforests, are dense, warm, and wet woodlands located near the equator. These forests experience a hot climate and receive high annual rainfall, making them incredibly biodiverse, home to more than half of the world’s plant and animal species. 

Characteristics

They are characterized by multiple layers of vegetation including towering trees, shorter understory plants, and ground level flora, which create a complex ecosystem. The tall canopy of the forest supports a variety of animals and plants, while the lower parts of the forest provide shelter and food for countless species.

Tropical forests play a crucial role in regulating global climates by absorbing carbon dioxide, and they are vital in maintaining the Earth’s water cycle through their transpiration processes. 

Ongoing threats 

However, they are under threat from deforestation, which is driven by logging, agriculture, and urban expansion. This loss not only threatens the biodiversity within these forests but also has a significant impact on global climate patterns and carbon storage capabilities. 

Conservation efforts are ongoing, aiming to protect these valuable ecosystems by promoting sustainable practices and establishing protected areas.

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