| 英文摘要: | Soil fungi have pivotal ecological roles as decomposers, pathogens and symbionts1, 2. Alterations to their diversity arising from climate change could have substantial effects on ecosystems, particularly those undergoing rapid warming that contain few species3, 4. 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 Hemisphere5, 6. 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 decade6) 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. The maritime Antarctic is undergoing rapid climate change. Surface air temperatures in the region, which broadly encompasses the Antarctic Peninsula and islands of the Scotia Arc, have risen by up to 2.8 °C over the past 50 years, at rates several times that of the global mean5, 6. Rising temperatures in the region have led to changes to the physical environment, including ice shelf collapses and glacial retreats5. However, in recent years, biological responses to warming have also become apparent across the region7. These include order of magnitude increases in the population sizes of the two native angiosperms, increased moss growth rates, and the establishment of non-native plant species8, 9, 10. The range expansions of native plant populations and the establishment of non-native species in the typically unvegetated soils of the region are thought to be associated with new areas of land becoming exposed following glacial retreat, enhanced plant growth and reproduction, and accelerated soil nutrient cycling7, 10, 11. Although climate change effects on the maritime Antarctic flora have recently become apparent, far less is known of soil microbial responses to warming in the region. Artificial warming experiments in the natural environment have shown relatively minor changes to the composition of bacterial communities in response to increased soil temperatures (0.5–2 °C annual means), which is not surprising, as the experiments have only lasted for one to three years12, 13. However, the responses of soil fungi to climate warming in the maritime Antarctic have yet to receive attention. Despite their pivotal importance in terrestrial ecosystems as decomposers, pathogens and symbionts1, 2, the majority of fungi are filamentous in form and—especially for the lichens—grow slowly in the natural environment14, hampering assessments of their responses to warming treatments. For instance, in the low Arctic, substantial changes to root symbiotic fungal communities in response to warming only become apparent after 17 years of treatment15. Here, to circumvent the problem of detecting the responses of these slow-growing microbes to warming manipulations, we studied fungi in soil sampled from along a natural climatic gradient through the maritime Antarctic. Using a similar approach to previous ‘space-for-time’ substitution studies16, 17, we employ the gradient as a proxy to predict changes to soil fungal communities arising from climate warming in the region. We show that surface air temperature is a significant factor shaping the diversity and composition of soil fungal communities. On the basis of our observations, we predict that future warming in the region will lead to 20–27% increases in the numbers of fungal species present in the southernmost soils of the region by the end of the century, and that this will have consequent effects on biological productivity. We studied 29 soils sampled during the 2007–2008 austral spring and summer from along a 1,650 km gradient between 72° S and 60° S (Fig. 1 and Supplementary Table 1). The soils were free of vegetation (Supplementary Fig. 1), and were hence representative of the barren soils that are frequent in maritime Antarctic terrestrial ecosystems. Data from the Regional Atmospheric Climate Model18 indicated a significant increase in mean annual surface air temperature (MASAT) between south-eastern Alexander Island (72° S; MASAT −11 °C) and Signy Island in the South Orkney Islands (60° S; MASAT −4 °C), with a 0.62 °C increase in air temperature for each degree decrease in latitude (Fig. 1, upper inset; Supplementary Table 2). To determine whether other abiotic parameters varied along the transect, we analysed soils for a suite of 20 physicochemical parameters (including pH, electrical conductivity and the concentrations of 11 elements and five dissolved ions). Soil C:N ratio declined significantly at lower latitudes (R2 = 33%, P = 0.001; Fig. 1, lower inset; Supplementary Table 2) and was negatively associated with MASAT (R2 = 31%, P = 0.002). This is consistent with previous observations that soils in cold ecosystems have higher C:N ratios than those in warmer ecosystems19, most likely because of slow organic matter decay1. The strong influence of latitude on MASAT, and its weaker effect on soil C:N ratio, were also confirmed by structural equation modelling (Supplementary Fig. 2). None of the other parameters that we measured, including the altitude from which the samples were taken, varied significantly with latitude (Supplementary Table 2).
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