Does climate change alter chemical composition of arctic tundra plants and soil?

The Arctic is experiencing pronounced changes in the climate. The temperature is projected to rise twice as much and at twice the rate of the global average. This temperature increase is accompanied with other environmental changes, such as increasing cloudiness in some areas. The aim of this study was to use near infrared reflectance (NIR) spectroscopy to assess whether increasing temperature and cloudiness affect the chemical quality of soil and plants in the arctic tundra. Samples of soil and dominant plant species were collected from a field experiment 20 km southeast of Nuuk, Greenland (64°07'N, 51°21'W). The experiment was complete randomized block design with six replicates of warming and reduced sunlight treatments of 1.2 x 1.2 m. Warming was accomplished with Plexiglas open top chambers, which increase air temperature by 2-3 °C and soil temperature by ~1 °C, and reduced sunlight with dome-shaped hessian tents, which decrease photosynthetically active radiation (PAR) by 65%. The treatments had been applied for six years prior to sampling. Samples of the surface soil, and the leaves of crowberry (Empetrum hermaphroditum) and willow (Salix glauca) were ovendried and finely ground prior to NIR analysis. Each sample was analyzed as four-five subsamples using Antaris II (Thermo Fisher) NIR spectrometer in the spectral range of 10000-4000 cm-1. We will use principal component analysis (PCA) to investigate treatment effects on the NIR spectra. We will also apply partial least squares (PLS) regression to test the correlation between the NIR data and reference measurements. For soil, these include inorganic and dissolved carbon, nitrogen, and phosphorus, plus bacterial and fungal abundance estimated by qPCR. For plant leaves, these include total carbon and nitrogen. Preliminary analyses show that the NIR spectra for the two plant species clearly differ. For the evergreen crowberry, the current year’s and the previous year’s leaves have different chemical composition. There appears to be differences between control, warming and reduced sunlight treatments, but these are shadowed by a strong block effect. Differences in chemical composition can influence the forage quality of the plants for herbivores. Further, alterations in plants and soil would impact microbial processes, such as decomposition, and thereby affect carbon storage capacity of the system.