In high altitudes and high latitudes climate change manifests in upward and northward shifting treelines. This entails changes to the carbon (C) and nitrogen (N) composition of organic inputs to soils and can increase or decrease microbial mineralisation of native soil organic matter (positive or negative priming effect). It is currently unknown whether the observed treeline shifts will lead to carbon loss or storage in the soils of these ecosystems. We therefore investigated priming effects in treeline soils from high altitudes (Peruvian Andes) and high latitudes (subarctic Sweden). In a laboratory soil incubation, we added realistic amounts of organic carbon at a constant ratio of 30% substrate-C to each soils’ microbial biomass C. Substrate additions were neutral in pH and covered different C:N ratios, representing naturally occurring substances of the studied ecosystems. We observed a clear pattern linking the direction of priming (positive or negative) to land cover (boreal or tropical forest, tundra heath, Puna grassland) and soil horizon (organic or mineral). Mechanistically, no support was found for N-mining to induce positive priming, indeed half of all priming effects were negative. Whenever negative priming prevailed, the decrease in SOM-mineralisation was consistently linked to increased microbial substrate utilisation. In line with other recent studies, our results suggest preferential substrate use is pervasive, linked to negative priming and a promising tool to increase soil carbon storage. Yet, the positive priming observed alerts climate change-induced upwards shifts in high altitudes and deeper rooting plants in high latitudes may cause C-loss via positive priming.
Research Article
Preferential substrate use decreases priming effects in contrasting treeline soils
https://doi.org/10.21203/rs.3.rs-1518696/v1
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treeline
soil carbon
priming effect
C:N
preferential substrate use
Table 1 Properties of the eight soil types studied Values are mean ± SE for n = 6 for each soil type: AFO: Andean Forest Organic, AFM: Andean Forest Mineral, APO: Andean Puna Organic, APM: Andean Puna Mineral, BFO: Boreal Forest Organic, BFM: Boreal Forest Mineral, BTO: Boreal Tundra Organic, BTM: Boreal Tundra Mineral. Abbreviations: C: carbon, N: nitrogen, mb: microbial biomass, max AWC: maximum available water capacity, BD: bulk density, dwt: dry weight, OM: organic matter
|
AFO |
AFM |
APO |
APM |
BFO |
BFM |
BTO |
BTM |
|
|
C (g g-1 dwt) |
0.404 ± 0.105 |
0.24 ± 0.07 |
0.27 ± 0.04 |
0.18 ± 0.04 |
0.56 ± 0.07 |
0.08 ± 0.02 |
0.52 ± 0.2 |
0.19 ± 0.21 |
|
N (g g-1 dwt) |
0.026 ± 0.006 |
0.015 ±0.004 |
0.021 ±0.002 |
0.015 ±0.003 |
0.022 ±0.005 |
0.003 ±0.002 |
0.015 ±0.004 |
0.006 ± 0.009 |
|
soil C:N |
15.5 |
15.3 |
12.9 |
12.3 |
25.5 |
26.7 |
34.7 |
31.7 |
|
mb C (µg g-1 dwt) |
152.01 ± 55.1 |
48.91 ±28.26 |
152.4 ±30.86 |
66.36 ±33.54 |
328.9 ±84.95 |
20.96 ±11.13 |
492.1 ±75.82 |
28.74 ± 14.75 |
|
mb N (µg g-1 dwt) |
36.06 ± 14.59 |
16.9 ± 4.26 |
24.48 ± 3.2 |
18.47 ± 7.36 |
30.1 ±18.74 |
3.52 ± 1.43 |
30.74 ± 10.4 |
3.49 ± 2.2 |
|
mb C:N |
4.2 |
2.9 |
6.2 |
3.6 |
10.9 |
5.9 |
16.0 |
8.2 |
|
NO3- (µg g-1 dwt) |
4.94 ± 0.14 |
4.82 ± 0.07 |
4.82 ± 0.04 |
4.91 ± 0.18 |
7.94 ± 1.34 |
6.3 ± 0.33 |
7.13 ± 1.18 |
5.86 ± 1.32 |
|
NH4+ (µg g-1 dwt) |
1.12 ± 0.22 |
1.36 ± 1.14 |
1.48 ± 0.22 |
1.74 ± 2.08 |
1.79 ± 0.54 |
0.83 ± 0.14 |
1.58 ± 0.35 |
2.05 ± 2.13 |
|
pH |
4.2 ± 0.36 |
4.5 ± 0.36 |
4.6 ± 0.18 |
4.7 ± 0.33 |
5.1 ± 0.63 |
5.7 ± 0.78 |
4.8 ± 0.91 |
5.4 ± 0.8 |
|
Horizon depth (cm) |
15 ± 3.89 |
48 ±20.62 |
10 ± 4.51 |
34 ± 7.86 |
4.8 ± 2.18 |
35 ± 6.96 |
7.5 ± 2.34 |
28 ± 5.77 |
|
max WHC (%) |
294.7 ± 72.78 |
184.3 ±29.29 |
236.5 ±38.08 |
160.9 ±32.13 |
463.2 ±84.52 |
50.3 ±10.83 |
615 ±58.25 |
78.2 ± 65.71 |
|
BD (g cm-3) |
0.10 ± 0.02 |
0.57 ±0.2 |
0.19 ±0.13 |
0.73 ±0.15 |
0.23 ±0.07 |
0.25 ±0.13 |
0.59 ±0.16 |
0.93 ±0.45 |
|
Soil texture |
OM (+silty clay) |
(Silty) Clay loam |
OM (+silty clay (loam)) |
(Silty) Clay loam |
OM (+silt) |
Sand |
OM (+silt) |
(Loamy) Sand |
Table 2: Composition of the substrate treatments: C additions corresponded to 30 % microbial biomass for each soil horizon in each biogeographic region, added in form of 13C-labelled glucose. Treatments 2 to 4 additionally included a nutrient solution, with the nitrogen (N) content adjusted to provide solutions of C:N ratios mimicking biological counterparts with the C:N ratios 71:1, 17:1 and 7:1. LMW: low molecular weight, soil types: AFO: Andean Forest Organic, AFM: Andean Forest Mineral, APO: Andean Puna Organic, APM: Andean Puna Mineral, BFO: Boreal Forest Organic, BFM: Boreal Forest Mineral, BTO: Boreal Tundra Organic, BTM:
|
Soil type |
Microbial biomass C |
Substrate addition (µg g-1 dwt) (C and N contents from glucose and Hoagland’s) |
|||
|
|
|||||
|
Andean organic (AFO/APO) |
152.18 ± 39.9 |
45.654 |
0.643 |
2.686 |
6.522 |
|
Andean mineral (AFM/ATM) |
65.03 ± 25.8 |
19.509 |
0.275 |
1.147 |
2.787 |
|
Boreal organic (BFO/BTO) |
410.53 ± 114.78 |
123.159 |
1.735 |
7.245 |
17.594 |
|
Boreal mineral (BFM/BTM) |
27.85 ± 11.21 |
8.255 |
0.118 |
0.486 |
1.179 |
|
Treatment |
|
glu |
glu+N |
glu+NN |
glu+NNN |
|
C:N of added solution |
1:0 |
71:1 |
17:1 |
7:1 |
|
|
Representing |
LMW-sugar (exudate) |
leaf litter |
SOM |
microbial biomass |
|
Table 3 Effect of soil, substrate and microbial biomass C:N ratios on priming Significant results of three-way ANCOVA for all soil types testing for similarities of sample means of observed priming effects under four different substrate treatments in soils with different soil and microbial C and N characteristics. p-values provided with asterisk to significance levels < 0.001 ‘***’ ≤ 0.01 ‘**’ ≤ 0.05 ‘*’, where no numbers are given, variables were non-significant (ns) with p > 0.05
|
AFO |
APO |
BFO |
BTO |
AFM |
APM |
BFM |
BTM |
|
|
subCN |
0.026 * |
|
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|
|
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|
soilCN |
0.045 * |
0.021 * |
0.001 ** |
7.63e-5 *** |
0.005** |
0.028 * |
0.003 ** |
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|
mbCN |
|
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|
subCN:soilCN |
|
|
0.014 * |
|
0.042 * |
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subCN:mbCN |
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|
soilCN:mbCN |
|
|
0.0006 *** |
|
0.005 ** |
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subCN:soilCN:mbCN |
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