Effects of soil warming on growth processes of unmanaged subarctic grasslands
Wandji, R. P. T . 2025.
Abstract
High-latitude plant growth processes involve a range of physiological and biochemical mechanisms that allow
plants to progress during relatively short growing seasons from unmature to fully developed organisms capable of
reproducing.
During the past decades, terrestrial ecosystems have experienced a lot of alterations from climate change, and high
latitude ecosystems are affected at a faster pace compared to other terrestrial ecosystems. Therefore, it is important
to study how further warming is likely to affect high-latitude plant communities, including Iceland.
There are now 18 whole-soil warming experiments ongoing worldwide to increase our understanding of how plant
and soil communities are likely to respond to further climate warming, and the ForHot research site is one of them.
It utilises warm bedrocks below the soil profiles of known age to study the impacts of soil warming.
The ForHot contains six ecosystem-level field experiments that involve different amounts of soil warming,
duration of warming and N-availability in different vegetation communities. Whereof I used two grassland
experiments. That is the medium-term warming (MTW) site that has been warm since 2008 and the long-term
warming (LTW) site with the same type of grassland, but where the warming has been ongoing for >60 years.
To understand how subarctic grassland growth processes respond to soil warming, I looked at the first step in the
plant growth processes, that is, the responses in the photosynthetic system. Secondly, I studied the duration of
vegetation activity (phenology) throughout the growing season with both traditional and remote-sensing methods.
Lastly, I investigated how soil warming and interannual variation affected the aboveground net primary productivity
(ANPP).
The main outcomes were that even if the photosynthetic capacity remained unaltered per unit leaf area under
warmer conditions, the amount of community leaf area over each m2 of surface (NDVI) increased and the
duration of growth lengthened with warming. Which likely resulted together in more seasonal carbon uptake
and the observed increases in ANPP under warming in both grasslands. Nevertheless, the increasing ANPP was
associated with a "down-regulation" at the higher warming levels, which was possibly linked to N losses from the
warmed soils. Duration of warming was generally not found to be important in plant aboveground responses.
Key Words
Iceland, photosynthesis, reproductive and growth phenology, NDVI, ANPP, remote sensing.
