The Soil Seed Bank: Plant Communities’ Secret Weapon

Source Article: Ren, A., Hu, D.-Y., Qi, P.-X., Zhang, S.-C., Gao, H.-M., Mickan, B. S., Xiong, Y.-C., & Yuan, L.-Y. (2023). Buffering effects of the soil seed bank on annual plant community composition after wetland drying. Land Degradation & Development, 34(6), 1601–1611. 

Featured Image Caption: Bidens pilosa is a common find in drier areas of the Dajiuhu wetland in Hubei Province, China. Image Source: Alpsdake, CC BY-SA 3.0, via Wikimedia Commons          

Plants’ Buried Secrets

Plant communities have a secret survival tool buried underground: the soil seed bank. The soil seed bank is made up of all the seeds of any plant species buried in the soil in an area. They build up over the years as plants drop seeds which lie dormant, sometimes for many years, until they germinate and grow up into a new plant. When the environment changes, the seed bank helps buffer the plant community against those changes. In other words, the seed bank maintains a stable plant community in stressful conditions. It works because even if many plants die to temporary harsh conditions, new plants can still grow up again from the seed bank. This buffering effect that protects plant communities is extremely important because plants play a foundational role in how ecosystems function, from providing habitat and food for animals to affecting the flow of water, nutrients, and pollution on the landscape.

The seed bank also allows plant communities to regenerate after fires, as pictured here in a boreal forest in Estonia. Image Source: Hannu, Public domain, via Wikimedia Commons

But there are two big aspects of the seed bank and its role in ecosystems that we don’t fully understand. First, does the seed bank buffer plant communities against all environmental changes or just certain kinds? The seed bank might be better at buffering some kinds of environmental changes but not others. For example, if none of the species present in the seed bank can survive in the new conditions. Second, can environmental conditions affect the seed bank itself? This could reduce the beneficial impact of seed bank buffering in some environments.

Welcome To The Wetland

Researchers used a wetland in the mountains of Hubei Province, China to test the seed bank’s ability to buffer changes in water availability and how water availability affects the seed bank. A wetland is a convenient place to study these questions because different areas within a wetland naturally have different amounts of water. The researchers collected samples of soil from sites with three different water levels and observed the plant species present at these sites. To figure out which seeds were present in the seed bank at each site, the scientists gave the seeds ideal conditions to germinate, and identified each plant as it grew up. Soil was also collected for chemical analysis.

The Dajiuhu wetland in Hubei Province, China. Image Source: (Open Access Article) Li, Y., Ma, C., Zhou, B., Cui, A., Zhu, C., Huang, R. & Zheng, C. 2016: Environmental processes derived from peatland geochemistry since the last deglaciation in Dajiuhu, Shennongjia, central China. Boreas, Vol. 45, pp. 423–438. 10.1111/bor.12168. ISSN 0300-9483.
A Long-Lasting Seed Bank Buffer
Sphagnum moss was common in the wettest site. Image Source: Bernd Haynold, CC BY-SA 3.0, via Wikimedia Commons

While the plants they found in each level of water availability were different, the plant species present in the seed bank were very consistent among the sites. This meant that there were large differences between which species were growing at a site and which seeds were in the soil. The researchers also found that the density and diversity of seeds in the soil changed slightly with water availability mainly because of changes in pH and the plant species growing at a site, not because of the moisture itself. The seeds were also able to germinate even after, presumably, a long time buried in the soil.

Based on this information, the researchers inferred that the soil seed bank likely can buffer against changes in water availability. If the wetland became suddenly drier or wetter and the plants at the surface died, there would still be seeds in every part of the wetland that could grow in the new drier or wetter conditions. However, the driest environment did have a slightly more dense and diverse soil seed bank, suggesting that seed banks might be slightly more effective buffers of environmental conditions in drier soils.

Seeds Could Help Save the Day

Climate change is causing more and more dramatic variation in environmental conditions, for example, more intense droughts, floods, cold spells, and heat waves. These extreme conditions don’t always last very long, so even if some species of plants at the surface die, the seed bank can rescue these species once the extreme event is over. Also, because seeds can sometimes wait in the soil and sprout during a wide range of environmental conditions, plant communities may regenerate with different species when there are stressful changes. This is good news for the Dajiuhu wetland, but more research will be needed in other ecosystems to figure out when the seed bank will or won’t be helpful for plant communities in a changing world.

Sanguisorba officinalis was commonly found in steppe meadow ecosystems at Dajiuhu wetland, the driest sites observed. Image Source: Florian Grossir, CC BY-SA 3.0, via Wikimedia Commons

Aside from water availability, other environmental changes may have their own effects on the seed bank that affect the ability of the seed bank to buffer these changes. Future seed bank research also must investigate how invasive species benefit from their seed banks. Evidence suggests that invasive plant species are successful because their seed banks can survive more stressful environmental conditions than most plants’ seeds. Given these complexities, further research on the seed bank may greatly improve our understanding of the effects of climate change on plant communities around the world.

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Julia Bebout

Julia Bebout

I am a PhD student at the University of California San Diego studying how the timing of germination and flowering shapes plant communities. I'm fascinated by how past environments can affect present and future ecosystems, especially faced with climate change. My favorite things to write about are community ecology, wetland and alpine ecosystems, and regenerative agriculture. I also love hiking, climbing, baking, and dancing! Twitter: @BeboutJulia

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