Climate change doesn’t just make plants warmer. Flobert Ndah and colleagues in Denmark and Finland note that rising temperatures can also increase nutrients in the soil, and reduce sunlight due to increased cloud cover. In a study published in Annals of Botany, the team examined how these changes could affect subarctic vegetation by altering the emissions of biogenic volatile organic compounds (BVOCs) and leaf anatomy. They find that increased nutrient availability could help plants improve their protection against stresses, especially heat and drought.
While the planet is getting hotter, the increase in heat varies. The temperature rise has been particularly dramatic in the arctic and subarctic regions. While rising air temperatures cause changes in plant growth and shifts in range, changing ground temperatures can cause changes to the soil. Warmer soil can have increased nutrient availability, thanks to increased soil organic matter mineralisation rates caused by the heat. The warmth can expose more soil too, as ice retreats, leading to increasing cloud cover from aerosol particles released from the now ice-free surface.
These changes in conditions will lead to increased stresses for plants, partly due to abiotic factors as they adapt to a changing growing season and differing rainfall, and with biotic stresses, for example, increased herbivore activity. Plants can cope with some of these stresses by making biogenic volatile organic compounds, BVOCs. There have been plenty of experiments showing that, as temperature rises, BVOC emissions will rise. But Ndah and colleagues haven’t seen so much on how increased nutrient availability will affect BVOC emissions. What results have been published are contradictory, so the botanists set out to discover how BVOC emissions from arctic and subarctic plants respond to increased soil nutrient availability.
They also looked at leaf anatomy. This is because plants can change their leaf anatomy to cope with new conditions. However, if the leaves change, then so will the BVOC emissions they release.
The team used the subarctic tundra heath in Abisko, Northern Sweden. This is a site that has been running climate experiments for thirty years. Here, they examined three subarctic dwarf shrub species, Empetrum hermaphroditum, Cassiope tetragona and Betula nana. The team set up six treatments: control, warming, shading, fertilization (increased nutrient availability), fertilization + warming and fertilization + shading. The team replicated each of these treatments six times, resulting in thirty-six 120 × 120 cm plots.
The warmer plots were under open-top polyethylene film tents, which increased the air temperature by 3–4 °C. They used hessian cloth tents to simulate increased cloud cover for shading, which cut the sunlight by around 50%.
In August, two-thirds of the way through the growing, the scientists isolated the plants in bags to sample the air around them for BVOCs without getting rogue compounds from elsewhere in the sample. A little after that, they collected fully developed leaves for light microscopy and scanning electron microscopy.
The results were a surprise, write Ndah and colleagues in their article.
“Contrary to our expectations, increased nutrient availability did not decrease BVOC emissions but increased monoterpene emissions of B. nana and tended to increase oxygenated monoterpene and sesquiterpene emissions of C. tetragona. In a sampling conducted at the same site 5 years earlier, 18 years from the beginning of the experiment, Rinnan et al. (2011) found that fertilization caused no statistically significant change in BVOC emissions from the same shrubs. Valolahti et al. (2015) reported that ecosystem-level terpenoid emissions from dwarf-shrub-dominated subarctic tundra were not affected by litter addition increasing nutrient availability after 11 and 13 years of experimental manipulation, but litter addition enhanced the BVOC emissions from warming treatment. The responses observed in this study suggest that more than two decades of increased nutrient availability starts to affect BVOC emissions of individual dwarf shrub species, which highlights the importance of long-term experiments.”
The team’s findings show that increased nutrient availability could help subarctic shrubs develop increased resistance to biotic and abiotic stresses. However, to do so, they’ll need to be able to photosynthesise to build these compounds. Increased cloudiness negatively affects the plants by cutting the opportunity for photosynthesis. So the future of the artic will be shaped by interactions between warmth, nutrients, and cloud cover.
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Ndah, F., Valolahti, H., Schollert, M., Michelsen, A., Rinnan, R. and Kivimäenpää, M. (2022) “Influence of increased nutrient availability on biogenic volatile organic compound (BVOC) emissions and leaf anatomy of subarctic dwarf shrubs under climate warming and increased cloudiness,” Annals of Botany, 129(4), https://doi.org/10.1093/aob/mcac004