Remote sensing: through a collaboration with Dr Shridhar Jawak at the Svalbard Integrated Arctic Earth Observing System, an expert in the remote sensing of polar vegetation, the student will analyse changes to plant cover in recent decades on the Brøgger Peninsula on Svalbard in the High Arctic (78° 55′ N, 11° 44′ E). The primary source of satellite imagery will be two 10 × 10 km very high resolution (31 cm per pixel) WorldView-2 (WV-2) panchromatic visible and near infrared (VNIR) images of the peninsula and its adjacent islands, taken as near as possible to August 2023 (Objective 1, Table 1). The student will compare these images with additional high-resolution (e.g., Quickbird or IKONOS) cloud-free archive images from 2000 and 2011. The bands available in WV-2 imagery will enable the calculation of a wide range of vegetation indices (VIs). Statistical models (based on linear regressions and generalised linear models) will be used to calculate which VIs have most explanatory power with regard to the expansion of deciduous shrubs and spatial vegetation dynamics (12).
Analyses of pre-existing plots: through a collaboration with Dr Clare Robinson, fractional vegetation cover in pre-existing plots established close to Ny-Ålesund on the Brøgger Peninsula in summers 1991 and 2000 (13,14) will be compared with that in summer 2023 using a digital adaptation of the field-based point frame technique (15). Either BAS staff or Norwegian Polar Institute (NPI) staff based permanently at Ny-Ålesund, with whom we have an ongoing collaboration, will take images of the plots. These analyses will determine if vegetation cover has changed over the last 23–32 years (Objective 2, Table 1), over which time mean annual air temperature on Svalbard has risen by 3–5 °C (5,8,9), and whether plant species symbiotic with ECMs (viz., Salix polaris and Bistorta vivipara) account for any increase in cover.
ECM analyses: in 2024, Salix polaris and Bistorta vivipara will be sampled by either BAS or NPI staff from each plot of an open top chamber warming experiment established at Kongsfjordneset on the Brøgger Peninsula in autumn 2014 (Fig. 1a; see also https://www.youtube.com/watch?v=lAQUWjAO5ZI). The experiment consists of 48 plots, 24 of which are warmed with open top chambers and 24 of which are bi-annually irrigated, simulating summertime rainfall. Analyses of images of plots indicate that OTCs increase the cover of both S. polaris and B. vivipara (Fig. 1b–d) (16). Leaves of both species will be analysed for N concentrations and natural abundance of 15N, which is depleted in ECM plants in the High Arctic owing to isotopic fractionation of organic N during uptake by fungi (17). Root tips colonised by ECM fungi (Fig. 1a, inset) will be counted, excised and surface sterilised, and, following protocols developed by our collaborator Dr Filipa Cox (18), DNA will be extracted from 576 individual tips using kits. Internal transcribed spacer (ITS) regions of fungal ribosomal DNA will be amplified using the ITS1F/ITS4 primer set and amplicons bidirectionally sequenced at a commercial facility. The sequences will be compared with those deposited in UNITE (https://unite.ut.ee/), a publicly-accessible database of fungal ITS sequences. Using generalised linear models and regression, the student will determine treatment effects on the abundance and identity of ECM fungi, and will compare the frequency of ECM taxa with leaf N concentrations and δ15N values, with the specific aim of determining if fungal symbionts that are efficient at soil N capture are more frequent on the roots of warmed and irrigated plants (Objective 3, Table 1).
Collectively, the analyses described above will break new ground in understanding the rate of shrubification in the High Arctic, and the role of ECMs in this process. We anticipate several peer-reviewed scientific papers from the project, written and led by the student, which will significantly advance current knowledge of shrubification.