Search

Soil fungi have pivotal ecological roles as decomposers, pathogens and symbionts. Alterations to their diversity arising from climate change could have substantial effects on ecosystems, particularly those undergoing rapid warming that contain few species. Here, we report a study using pyrosequencing to assess fungal diversity in 29 soils sampled from a 1,650 km climatic gradient through the maritime Antarctic, the most rapidly warming region in the Southern Hemisphere. Using a ‘space-for-time’ substitution approach, we show that soil fungal diversity is higher in warmer habitats, with increases of 4.7 (observed) and 11.3 (predicted) fungal taxa per degree Celsius rise in surface temperature along the transect. Among 22 predictor variables, air temperature was the strongest and most consistent predictor of diversity. We propose that the current rapid warming in the maritime Antarctic (0.34 °C per decade) will facilitate the colonization of soil by a wider diversity of fungi than at present, with data from regression models suggesting 20–27% increases in fungal species richness in the southernmost soils by 2100. Such increases in diversity, which provide a sentinel for changes at lower latitudes, are likely to have substantial effects on nutrient cycling and, ultimately, productivity in the species-poor soils of maritime Antarctica.

Rapid warming is expected to increase plant growth in the Arctic, and result in trees gradually colonizing tundra. Models predict that enhanced carbon (C) storage in plant biomass may help offset atmospheric CO2increases and reduce rates of climate change. However, in some Arctic ecosystems, high plant productivity is associated with rapid cycling and low storage of soil C (refs , , ); thus, as plant growth increases, soil C may be lost through enhanced decomposition. Here we show that, in northern Sweden, total ecosystem C storage is greater in tundra heath (owing to greater soil C stocks) than in more productive mountain-birch forest. Furthermore, we demonstrate that in the forest, high plant activity during the middle of the growing season stimulates the decomposition of older soil organic matter. Such a response, referred to as positive priming, helps explain the low soil C storage in the forest when compared with the tundra. We suggest that, as more productive forest communities colonize tundra, the decomposition of the large C stocks in tundra soils could be stimulated. Thus, counter-intuitively, increased plant growth in the European Arctic could result in C being released to the atmosphere, accelerating climate change.

Interactance spectra (700–1100 nm) of intact fruit possess features interpreted as being due to the dilution and perturbation of water OH stretching and combination bands (with the second and third overtones of OH stretching at 960 nm and 740 nm, respectively), while the contribution from citric acid CH_2 and OH stretching and combination bands are not obvious. A model developed using interactance spectra collected from the cut surfaces of lime fruit (mean ± SD of 7.3 ± 0.51 g citric acid equivalents 100 mL^−1, units subsequently presented as% w/v) achieved prediction results of RMSEP=0.16%, r_p^2 = 0.79, bias = −0.03%. However, for intact lime fruit, model calibration results (RMSECV=0.16, r_cv^2 = 0.85) were markedly better than prediction results (RMSEP=0.30, r_p^2 = 0.49). For a low total titratable acidity (TTA) product, peach (with spectra collected across fruit maturity stages; mean ± SD of 0.88 ± 0.17%), calibration results were relatively poor (RMSECV=0.09%, r_cv^2 = 0.79) and the model failed in prediction (RMSEP=0.10%, r_p^2 = 0.00, bias = 0.02%). It is concluded that interactance geometry shortwave (700–1100 nm) near infrared spectroscopy using diode array instrumentation and an interactance optical geometry suited to on-line or field-portable instrumentation used for Brix and DM assessment is not appropriate for assessment of the acidity of intact low TTA fruit and has limited use for high TTA fruit.

Spectra (700–2500 nm) of citric acid dissolved in water possess features interpreted as being due to the dilution and perturbation of water OH stretching and combination bands (with the second and first overtones of OH stretching at 960 nm and 1420 nm, respectively, and a combination band of OH vibration at 2132 nm) and also to citric acid OH stretching and combination bands and citric acid CH_2 bands (first overtone of CH_2 stretching at 1680 nm and a combination band of CH_2 at 2284 nm). A searching window method was used to optimise the wavelength region for a partial least squares (PLS) regression model development (around 743–904 nm for the region below 1100 nm). Despite the apparent lack of information below 1100 nm, a PLS regression model based on transmission spectra (743–904 nm) of pure citric acid—water mixtures (standard deviation = 6.65g citric acid 100 mL^−1) yielded a root mean square error of cross-validation (RMSECV) of 0.34% and correlation coefficient of determination (R_cv^2) = 0.998. However, if the matrix was varied with 0, 10 and 13% sucrose or fruit juice, RMSECV increased to 0.79%. This RMSECV value is proposed as a benchmark for attempts to assess titratable acidity of juice based on shortwave (700–1100 nm) near infrared spectra of intact fruit collected using silicon diode array instrumentation.

For the past 50 years there has been rapid warming in the maritime Antarctic, with concurrent, and probably temperature-mediated, proliferation of the two native plants, Antarctic pearlwort (Colobanthus quitensis) and especially Antarctic hair grass (Deschampsia antarctica). In many terrestrial ecosystems at high latitudes, nitrogen (N) supply regulates primary productivity. Although the predominant view is that only inorganic and amino acid N are important sources of N for angiosperms, most N enters soil as protein. Maritime Antarctic soils have large stocks of proteinaceous N, which is released slowly as decomposition is limited by low temperatures. Consequently, an ability to acquire N at an early stage of availability is key to the success of photosynthetic organisms. Here we show that D. antarctica can acquire N through its roots as short peptides, produced at an early stage of protein decomposition, acquiring N over three times faster than as amino acid, nitrate or ammonium, and more than 160 times faster than the mosses with which it competes. Efficient acquisition of the N released in faster decomposition of soil organic matter as temperatures rise may give D. antarctica an advantage over competing mosses that has facilitated its recent proliferation in the maritime Antarctic.