Soil microbial abundance and activity across forefield glacier chronosequence in the Northern Patagonian Ice Field, Chile

Figures & data

Figure 1. Study site description: a) Satellite image illustrating the retreat of the Exploradores glacier in last 70 years. Color lines show the age-limit of the three stages of soil development. b) Photo showing a frontal view of Exploradores forefield glacier. c) A principal component analysis (PCA) of soil features during soil development. F and P-value correspond to PerManova test results. Open symbols: stage 1; light grey: stage 2; dark grey: stage 3

Table 1. Changes in soil biogeochemical features across three stages of soil development of the NPFI chronosequence

	Chronosequence stage
Parameters	Stage 1	Stage 2	Stage 3	p Value
Age (years)*	~17	~30	>70
TC (%)	0.09 (0.003)^a	0.51 (0.061)^b	1.06 (0.124)^c	<.001
TN (%)	0.02 (0.003)^a	0.06 (0.007)^b	0.08 (0.006)^b	<.001
TP (%)	0.09 (0.002)	0.09 (0.003)	0.08 (0.002)	<.135
pH	5.45 (0.083)^a	4.97 (0.041)^b	4.67 (0.065)^c	<.001
Chlorophyll a (μg/g dry soil)	0.12 (0.022)^a	0.88 (0.082)^a	2.26 (0.070)^b	<.001
Bulk density (g/cm^3)	1.71 (0.02)^a	1.40 (0.02)^a	1.50 (0.016)^b	<.001

Notes. Values are mean (±1 SE) of five samples taken at each stage. Letters on superscript indicate pairwise differences (Tukey Honestly Significant Difference test) at P < 0.05 among stages of soil development.

*Age was estimated from satellite imagery and aerial photography.

Table 2. Differences in the relative abundance of microbial groups, measured as ratios across the three stages of soil development of the NPFI glaciar retreat chronosequence

	Chronosequence stage
Ratios	Stage 1	Stage 2	Stage 3	p Value
Archaea:bacteria	0.39 (0.007)^a	0.53 (0.016)^b	0.56 (0.002)^b	<.001
Fungi:bacteria	0.74 (0.018)^a	0.77 (0.009)^a	0.88 (0.006)^b	<.001
nifH:bacteria	0.81 (0.013)^a	0.82 (0.007)^a	0.88 (0.002)^b	<.001

Note. Values are mean (±1 SE) of five samples taken at each stage. Letters on superscript indicate pairwise differences (Tukey Honestly Significant Difference test) at P < 0.05 among stages of soil development

Figure 2. Changes in microbial community abundance and the nifH gene (i.e. nitrogen cycle gene) across stages of soil development at the NPIF. In a) Archaeal, b) Bacterial, c) Fungal abundances, and in d) nifH gene-copy number. Bars represent mean values and ±1 SE of gene abundance from five samples. Different letters shows significant differences across stages of soil development for F and P-values of ANOVA given in right upper corner

Figure 3. Changes in the relative abundance of microbial groups as a function of changes in (a) soil C:N and (b) soil pH (i.e., soil variables with the highest relative contribution to change in microbial abundance). Circles: fungal-to-bacterial ratios; Triangles: archaeal-to-bacterial ratios across three stages of the NPFI. (c), (d) Changes in nifH gene copy number. For all panels, open symbols: stage 1; light grey: stage 2; dark grey: stage 3. Solid lines represent significant linear regression adjusted for variables

Figure 4. Differences in mass loss (buried) across stages of soil development in the NPIF chronosequence. (a) Mass loss of Whatman filter after nineteen months in three stages of soil development. T1: after seven months, T2: after 12 months; T3: after nineteen months. (b) Relationship between mass loss of Whatman filters as a function of higher fungal abundance across stages of the NPIF chronosequence. Open circle: stage 1; light grey: stage 2; dark grey: stage 3. Solid lines represent a significant linear relationship (all data included)