It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Sunday, June 02, 2024
Tropical forest resilience to seasonal drought linked to nutrient availability
International research team carry out Africa’s first large-scale nutrient addition experiment with nitrogen, phosphorus and potassium
Tropical forests are highly productive ecosystems accounting for nearly half of the global forest carbon sink. If tropical forests can no longer remove carbon dioxide from the atmosphere, the effects of climate change may become even more severe. In recent times, these forests have been found to be increasingly limited in nutrients, which may affect their resilience to seasonal droughts and the rate at which they can remove carbon dioxide from the atmosphere. To investigate this, an international research team led by the University of Göttingen established Africa’s first largescale nitrogen-phosphorus-potassium addition experiment in the Budongo Forest of Uganda. Their research showed that increasing the availability of certain nutrients can potentially sustain the productivity of these forests even under intense drought conditions – conditions already prevalent in most parts of the world. The results were published in the journal Nature Geoscience.
The researchers investigated how nutrients control the production of leaf litter onto the forest floor. Plant leaves actively remove human-produced carbon dioxide from the atmosphere when they photosynthesise to make their own food. This process leads to carbon accumulation in the plant’s wood or in the leaves themselves. However, under drought conditions most trees respond by shedding their leaves, which reduces the rate of carbon removal from the atmosphere. Eventually, the whole plant dies if the drought persists for a prolonged period. However, the researchers found in particular that for trees which were deficient in potassium, increasing the availability of this nutrient during the drier period delays the timing when most leaves are lost by four weeks. To overcome the low potassium levels, the trees had reallocated the potassium from their dying leaves to the rest of the plant before shedding them. Lead author Dr Raphael Manu from the University of Göttingen explains “that low potassium and phosphorus availability can make this vital tropical forest ecosystem more vulnerable to drought and a less effective carbon sink”.
In dry conditions, potassium helps plants to effectively regulate the minute pores in their epidermis, and phosphorus plays an important role in conserving water within the plant. This explains why these two nutrients are so important when conditions become drier in the future. Professor Edzo Veldkamp from the University of Göttingen adds, “This is the first time that we have experimentally linked soil nutrient availability to the seasonal drought response of tropical forests.”
The research was part of the project “Nutrient limitation in a Ugandan tropical forest (RELIANCE)”, funded by the German Research Foundation (DFG).
Original publication: Raphael Manu et al. Response of tropical forest productivity to seasonal drought mediated by potassium and phosphorus availability. Nature Geoscience 2024. Doi: 10.1038/s41561-024-01448-8
Litter collectors for monitoring litterfall in the Budongo Forest Experiment
Tropical forests are highly productive ecosystems accounting for nearly half of the global forest carbon sink. If tropical forests can no longer remove carbon dioxide from the atmosphere, the effects of climate change may become even more severe. In recent times, these forests have been found to be increasingly limited in nutrients, which may affect their resilience to seasonal droughts and the rate at which they can remove carbon dioxide from the atmosphere. To investigate this, an international research team led by the University of Göttingen established Africa’s first largescale nitrogen-phosphorus-potassium addition experiment in the Budongo Forest of Uganda. Their research showed that increasing the availability of certain nutrients can potentially sustain the productivity of these forests even under intense drought conditions – conditions already prevalent in most parts of the world. The results were published in the journal Nature Geoscience.
The researchers investigated how nutrients control the production of leaf litter onto the forest floor. Plant leaves actively remove human-produced carbon dioxide from the atmosphere when they photosynthesise to make their own food. This process leads to carbon accumulation in the plant’s wood or in the leaves themselves. However, under drought conditions most trees respond by shedding their leaves, which reduces the rate of carbon removal from the atmosphere. Eventually, the whole plant dies if the drought persists for a prolonged period. However, the researchers found in particular that for trees which were deficient in potassium, increasing the availability of this nutrient during the drier period delays the timing when most leaves are lost by four weeks. To overcome the low potassium levels, the trees had reallocated the potassium from their dying leaves to the rest of the plant before shedding them. Lead author Dr Raphael Manu from the University of Göttingen explains “that low potassium and phosphorus availability can make this vital tropical forest ecosystem more vulnerable to drought and a less effective carbon sink”.
In dry conditions, potassium helps plants to effectively regulate the minute pores in their epidermis, and phosphorus plays an important role in conserving water within the plant. This explains why these two nutrients are so important when conditions become drier in the future. Professor Edzo Veldkamp from the University of Göttingen adds, “This is the first time that we have experimentally linked soil nutrient availability to the seasonal drought response of tropical forests.”
The research was part of the project “Nutrient limitation in a Ugandan tropical forest (RELIANCE)”, funded by the German Research Foundation (DFG).
Original publication: Raphael Manu et al. Response of tropical forest productivity to seasonal drought mediated by potassium and phosphorus availability. Nature Geoscience 2024. Doi: 10.1038/s41561-024-01448-8
As our planet warms, many species are shifting to different locations as their historical habitats become inhospitable. Trees are no exception – many species’ normal ranges are no longer conducive to their health, but their shift to new areas that could better sustain them has been lagging behind those of other plants and animals. Now, scientists show that the reason for this lag might be found belowground. A study published in PNAS on May X, shows that trees, especially those in the far north, may be relocating to soils that don’t have the fungal life to support them.
Most plants form belowground partnerships with mycorrhizal fungi, microscopic, filamentous fungi that grow in the soil and connect with plant roots to supply plants with critical nutrients in exchange for carbon. Most large coniferous trees in northern latitudes form relationships with a kind of mycorrhizal fungi called ectomycorrhizal fungi.
“As we examined the future for these symbiotic relationships, we found that 35% of partnerships between trees and fungi that interact with the tree roots would be negatively impacted by climate change,” says lead author Michael Van Nuland, a fungal ecologist at the Society for the Protection of Underground Networks (SPUN).
The trees most at risk of this climate mismatch in North America are those in the pine family, find the authors. Areas of particular concern are the edges of species ranges where trees often face the harshest conditions. Here, the authors discovered that trees with higher survival rate in these locations have more diverse mycorrhizal fungi, a sign that these symbioses may be critical for helping trees withstand the effects of climate change.
“Ectomycorrhizal fungi have a different relationship to climate than ectomycorrhizal trees do,” says co-author Clara Qin, a data scientist at SPUN. “We are finding evidence that the trees have to answer for these differences.”
The study sheds light on how climate change might be affecting symbioses. “While we expect climate-driven migrations to be limited by abiotic factors like the availability of space at higher latitudes and elevations, we don't usually account for biotic limitations like the availability of symbiotic partners,” says Qin.
“It’s absolutely vital that we continue to work to understand how climate change is affecting mycorrhizal symbioses,” says Van Nuland. “These relationships underpin all life on Earth – it’s critical that we understand and protect them.”
A giant pine tree growing on Corsica, where climate change effects are extreme
CREDIT
SPUN/Quentin van den Bossche
Cortinarius spp., a mycorrhizal mushroom.
CREDIT
SPUN/Mateo Barrenengoa
A forest with ectomycorrhizal trees in the Apennine Mountains, Italy
This research was funded by a National Science Foundation grant awarded to Kai Zhu and Kabir Peay (NSF Awards 1926438, 2244711)
PNAS, Van Nuland et al., “Climate mismatches with ectomycorrhizal fungi contribute to migration lag in North American tree range shifts”
The Society for the Protection of Underground Networks (SPUN) is a scientific research organization with a mission to map and preserve Earth’s fungal networks. In collaboration with researchers and local communities, SPUN is accelerating efforts to protect the underground ecosystems largely absent from conservation and climate agendas. To learn more about SPUN, visit:https://spun.earth/.
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