C : N : P stoichiometry in six distinct habitats of a glacier terminus in the 1 Yangtze River Source Area 2

1 Advanced Institute of Natural Sciences, Beijing Normal University, Zhuhai, 519087, China 4 2 School of Environment, Beijing Normal University, Beijing, 100875, China 5 3 Key Laboratory of Geographic Information Science (Ministry of Education), East China Normal University, 6 Shanghai, 200241, China 7 4 School of Geographic Sciences, East China Normal University, Shanghai, 200241, China 8 5 Polar Research Institute of China, Ministry of Natural Resources, Shanghai 200136, China 9 6 Flathead Lake Biological Station, University of Montana, Polson, 59860, USA 10 *Corresponding Author: 11

and forefront soil with well-developed vegetation (VS). The results showed that SI had 23 significantly higher DOC and N concentrations as well as higher C:P and N:P ratios than 24 BI. However, BI had significantly higher SRP than SI. In addition, both SI and BI had very 25 high C:P and N:P ratios, suggesting P-limitation. For sediment/soil in glacier terminus, 26 nitrogen and organic carbon concentrations were significantly lower in BaS, TS, and DS 27 than in VS. Moreover, TP and SRP concentrations were significantly higher in BaS and 28 VS than in TS and DS. These nutrient patterns could be explained by differences in biotic 29 influence in soil development or by changes in soil physical properties. With regard to 30 nutrient limitation, VS had a significantly higher C:N, C:P, and N:P ratios than BaS, TS, 31 and DS, supporting a long-held biogeochemical and ecological paradigm that ecosystem 32 processes during early successional stages are primarily organic C and N limited but are P-

Chemical analyses 139
For ice samples (SI and BI), nutrient concentrations were tested after the ice melted at room 140 temperature. Total nitrogen (TN) was measured by ion chromatography after persulfate 141 oxidation (EPA 300.0). Total phosphorus (TP) was measured using the ascorbic acid 142 colorimetric method after persulfate oxidation (EPA 365.3). The meltwater samples used 143 for analyzing nitrate (NO3 --N), ammonium (NH4 + -N), and soluble reactive phosphorus 144 (SRP) were filtered using glass fiber filters (GF/F, Whatman). After filtration, NO3 --N was 145 determined by ion chromatography (EPA 300.0). NH4 + -N was determined using the 146 indophenol colorimetric method (EPA 350.1). Soluble reactive phosphorus (SRP) was 147 quantified using the ascorbic acid colorimetric method (EPA 365.3). pH and conductivity 148 in meltwater were also measured using a multiparameter instrument (YSI ProPlus, Yellow 149 Springs, Ohio) ( Figure S1). 150 Sediment and soil samples (BaS, TS, DS, and VS) were naturally dried and sieved through 151 100-mesh size to remove all visible roots, residues, and stones. Soil/sediment organic 152 carbon (SOC) was measured by oxidizing with potassium dichromate (HJ615-2011). Total 153 nitrogen (TN) was measured using the modified Kjeldahl Method (HJ717-2014). Total 154 phosphorus (TP) was measured using the ascorbic acid colorimetric method. Nitrate (NO3 -155 -N) and ammonium (NH4 + -N) were extracted using 2 M potassium chloride and percolated 156 through filters and measured by a spectrophotometer (HJ634-2012). Soluble reactive 157 phosphorus (SRP) were extracted using 0.5 M sodium bicarbonate and percolated through 158 filters and then measured using the ascorbic acid colorimetric method. pH was measured 159 in 1:2.5 soil to distilled water ratio using a pH and conductivity was measured in 1:5 soil 160 to distilled water ratio using a conductivity meter ( Figure S2). 161

Analyses 162
The statistical significance of differences of C, N, and P concentrations as well as their 163 stoichiometric ratios for different habitats were analyzed using ANOVA in R 3.4.4 (R Core 164 Team, 2017). All stoichiometric ratios are given as molar ratios. We plot the data using 165 ggplot2 package (Wickham, 2011) in R 3.4.4 (R Core Team, 2017).

C, N, and P concentrations and stoichiometry ratios in ice 168
At the glacier terminus, surface ice had a significantly higher DOC, TN, NO3 --N, and NH4 + -169 N concentrations than basal ice ( Figure 2). However, basal ice had a significantly higher 170 SRP than surface ice (Figure 2). TP was not significantly different between surface ice and 171 basal ice. In both surface ice and basal ice, NH4 + -N was 4.6 and 6.9 times higher than NO3 -172 -N in surface and basal ice, respectively ( (BI). The differences were tested using ANOVA. 183

C, N, and P concentrations and stoichiometry ratios in sediment and soil 184
Basal sediment had significantly higher TN, NH4 + -N, and SRP concentrations than the 185 newly exposed forefront soil close to glacial terminus (BaS vs. TS, Figure 3). The newly 186 exposed forefront soil close to glacial terminus had organic carbon and nutrient 187 concentrations similar to the soil distant from the glacier (TS vs. DS, Figure  Basal sediment had significantly lower DIN:SRP ratio than newly exposed forefront soil 198 close to glacial terminus (BaS vs. TS, Figure 3). Newly exposed forefront soil close to BaS (basal sediment), TS (newly exposed forefront soil close to glacial terminus), DS (soil 208 at increasing distances from the glacier), and VS (soil with well-developed vegetation). 209 Different lowercase letters indicate a significant difference between habitats while the same 210 lowercase letter indicates a non-significant difference from ANOVA. 211

Nutrient concentrations and stoichiometry ratios in ice 213
At the Dongkemadi Glacier, surface ice had significantly higher DOC and N concentrations 214 as well as higher C:P and N:P ratios than basal ice. However, basal ice had significantly 215 higher SRP concentrations than surface ice. In addition, both surface and basal ice had very

Nutrient concentrations and stoichiometry ratios in sediment and soil 272
At a glacier's terminus, basal sediments are exposed when the ice melts, forming barren 273 soil habitats. These newly exposed landscapes of glacier forefields are unique and sensitive 274 environments for studying ecosystem succession (Pessi et al, 2019). In our study, we 275 documented the nutrient concentrations and ratios in sediments/soils along successional 276 gradients, including BaS (basal sediment), TS (newly exposed forefront soil close to glacial 277 terminus), DS (soil with distances to glacier), and VS (soil with well-developed vegetation). 278 In our study, nitrogen and organic carbon concentrations were significantly lower in BaS, TS, and DS than in VS. Moreover, TP and SRP concentrations were significantly higher in 280 BaS and VS than in TS and DS (Figure 3). These nutrient patterns could be explained by 281 the influence of organisms in soil development and by changes in soil physical properties. 282 Proglacial soils close to the glacier terminus usually have low nutrient content but high 283 levels of disturbance (Matthews, 1992

Conclusions 329
Glaciers provide diverse and unique habitats, harboring extensive biological diversity and 330 playing important roles in global biogeochemical cycles. However, accelerating global 331 climate change places glaciers at risk of a permanent disappearance. Our study focused on 332 six distinct habitats in one glacier terminus in the Yangtze River Source area. This study 333 provided a comprehensive assessment of nutrient concentrations and stoichiometry in 334 distinct habitats in a glacier terminus. Our data showed that surface ice had significantly 335 higher DOC and N concentrations as well as higher C:P and N:P ratios than basal ice. 336 Moreover, both surface ice and basal ice had very high C:P and N:P ratios, suggesting the 337 possibility of strong P-limitation, especially for surface ice. For sediment/soil in glacier 338 terminus, the change patterns of nutrient concentrations and stoichiometric ratios support 339 that early successional stage is primarily nitrogen limited, while later successional stages 340 are primarily phosphorus limited. The results provide integrated understanding of the 341 ecological and biogeochemical differences and relationships between these dynamically 342 linked habitats, adding to our knowledge of the consequences of ongoing global change for 343 glacier ecosystems. 344 Figure S1 pH and conductivity of surface ice (IS) and basal ice (IB). The differences were 582 tested using ANOVA. 583 584 Figure S2 pH and conductivity of sediment and soil, including BaS (basal sediment), TS 585 (newly exposed forefront soil close to glacial terminus), DS (soil at increasing distances 586 from the glacier), and VS (soil with well-developed vegetation). The different lowercase 587 letter indicates a significant difference between habitats and the same lowercase letter 588 indicates a non-significant difference tested using ANOVA. 589 590