Reviewer 1 is right with his statement that myo-inositol has been found in soils (and .... matter in the first stages of a vegetation succession. Geoderma 100:1â24.
Plant and Soil Analysis of non-cellulosic polysaccharides helps to reveal the history of thick organic surface layers on calcareous Alpine soils --Manuscript Draft-Manuscript Number:
PLSO-D-12-00156R1
Full Title:
Analysis of non-cellulosic polysaccharides helps to reveal the history of thick organic surface layers on calcareous Alpine soils
Article Type:
Manuscript
Keywords:
biomarkers; carbohydrates; depth profile; GM/AX ratio; Folic Histosols; Tangelhumus
Corresponding Author:
Joerg Prietzel, Professor Chair of Soil Science, Technische Universität München Freising, GERMANY
Corresponding Author Secondary Information: Corresponding Author's Institution:
Chair of Soil Science, Technische Universität München
Corresponding Author's Secondary Institution: First Author:
Joerg Prietzel, Professor
First Author Secondary Information: Order of Authors:
Joerg Prietzel, Professor Nicolas Dechamps Sandra Spielvogel
Order of Authors Secondary Information: Manuscript Region of Origin: Abstract:
Background and aims: We investigated the potential of non-cellulosic polysaccharides (NCP)as biomarkers to identify the plant types that dominate present and past litter input into organic surface covers on calcareous Alpine soils and to reveal historic vegetation changes. Methods: At two sites in the Alps, NCP monomers were quantified in different organs of site-dominating plants, the Oa horizon of four Folic Leptosols, and different sections of thick organic surface layers of four Folic Histosols on calcareous bedrock. Results: The dominating plant types at our study sites differ markedly in their NCP composition and (galactose+mannose)/(arabinose+xylose) [GM/AX] ratio (grasses and sedges: 0.2; dicots Fagus and Vaccinium: 0.2-0.6; conifers Abies, Picea, Pinus: 0.72.4; mosses: 5). For all except one soil, the NCP signature of the uppermost Oa horizon reflects the present vegetation. For all Histosol O horizons, NCP signatures indicate a dominance of conifer litter throughout their development (up to 1500 years). Different NCP and GM/AX depth profiles reflect specific patterns of O layer genesis. Conclusions: NCP and GM/AX depth profiles in organic surface covers of soils provide important information about dominating litter sources in the past and can be valuable tools to reveal historic vegetation and/or land use changes.
Response to Reviewers:
Dear Editor, Dear Reviewers: Thank you very much for your constructive comments to the earlier version of the paper. In the revised version, we have addressed your comments and suggestions. Please find a detailed list of our responses to your comments and suggestion as attachment. Best regards, Joerg Prietzel, also in behalf of my co-authors.
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Response to Reviewers’ Comments Comments of Reviewer 1 General Comments 1)
In the revised version of the manuscript, the paragraph dealing with the description of the study sites has been rewritten to facilitate the reading. Additionally a figure has been added in which the studied soils are localized.
2)
Reviewer 1 is right with his statement that myo-inositol has been found in soils (and particularly in peats, where its microbial decomposition is probably impeded by phenolic compounds). However, the amount of natural myo-inositol in most soils usually is small (exception: some anaerobic organic wetland soils) compared to the amount added as internal standard. This is the reason why the use of myo-inositol as internal standard is common practice in many studies dealing with analysis of NCP in soils (e.g. Rumpel and Dignac (2006) and Eder et al. (2010). To test the potential confounding effect of soil-intrinsic myo-inositol in our study, we determined the content of soil-intrinsic myo-inositol in two randomly-selected samples (GC analysis without addition of any myo-inositol as internal standard). For the two soils, the amounts of intrinsic myo-inositol were negligible (always less than 0.5% the amount of myo-inositol which has been added as internal standard); this means that no confounding effect of soil-intrinsic myo-inositol is likely to affect the results of in our study. In the revised version of the manuscript, we made a statement about the potential interference of soil-intrinsic myo-inositol in our study. Reviewer 1 is also right with his statement that using GC-FID, each individual monomer has its own GC response factor. However, a preliminary study has shown that the differences among most sugars are small, ranging between 1.22 and 1.86 (Eder et al. 2010) and will thus affect our results only to a small extent. Especially the response factors of arabinose (1.48), xylose (1.58), mannose (1.22) and galactose (1.77) were rather similar. Only the response factors of rhamnose and glucose (2.44 and 2.09, respectively) were slightly higher, those sugars, however do not contribute to the GM/AX ratio. The response factors obtained in our preliminary study are in accordance with response factors reported elsewhere (Rumpel and Dignac, 2006; Zhang et al., 2007) Most important, the basic aim of our study, to attribute the NCP signature in the studied soils to specific plant sources, is not jeopardized at all, because any differences in GC response factors will affect the NCP signature of the plant materials and soil samples in exactly the same way, so that the comparison between soil and plant signatures is not affected at all by any differences in the GC response factors among the different sugar monomers.
3)
Reviewer 1 is right with his concern that replicates are lacking in our study. However, the analysis of NCP in plants and soils takes significant personnel and GC capacity, and particularly the 14C determination is very expensive. Therefore we had to restrict the amount of samples in our study, and 14C determinations were conducted on four (not three) samples only. With respect to the concern of Reviewer 1, the discussion part (particularly the genesis of organic tangelhumus) has been shortened considerably in the revised version of the manuscript, and the manuscript has been rearranged, following the suggestion of Reviewer 1.
Reviewer 1 is also right with his statement, that the word “significant” should not be used in a study without replicates. In the revised version of the manuscript, we replaced the words “significant” with “marked[ly]” or considerabl[e/y]” which have no statistical connotation. 4)
The conceptual model of GM/AX ratio depth profiles is based on the combination of three facts (i)
In a soil with a thick organic surface layer in which SOM is derived from one single litter source, with increasing humification status and progressive conversion of plant-derived SOM into microbial-derived SOM from younger, upper layers to older, lower layers, the GM/AX ratio increases systematically from the younger, upper layers to older, lower layers [supposed that confounding effects by root penetration, translocation of water-soluble NCP are small] (Bochter and Zech 1985; Rumpel and Dignac 2006; Spielvogel et al. 2007)
(ii)
Litter from different plant types has different GM/AX “starting levels”,e.g. the GM/AX ratio of grass litter is much smaller than that of conifer litter (see Section 3.1. of our study, and also LIT). Therefore the monotonic increase of the GM/AX ratio in a soil with a thick organic surface layer, in which SOM is derived from one single litter source, with increasing humification status and progressive conversion of plant-derived SOM into microbial-derived SOM from younger, upper layers to older, lower layers, starts at different values in the uppermost layer (e.g. lower starting value for grassland than for conifer forest)
(iii)
Changes in vegetation during the formation of a thick tangelhumus layer result in superimposition effects of (i) and (ii).
(iv)
Root penetration (injection of younger litter into older SOM) also results in superimposition effects of (i) and (ii) (Guggenberger and Zech (1994), Nierop et al. (2001)
In the revised version of the manuscript, these points were included in the presentation of the conceptual model of GM/AX ratio depth profiles.
5)
We appreciate the positive valuation of key parts of our paper by Reviewer 1. The discussion has been rewritten according to his/her suggestions.
References used in our reply to the General Comments of Reviewer 1 Bochter R, Zech W (1985) Organic compounds in Cryofolists developed on limestone under subalpine coniferous forest, Bavaria. Geoderma 36:145-157. Eder E, Spielvogel S, Kölbl A, Albert G, Kögel-Knabner I (2010) Analysis of hydrolysable neutral sugars in mineral soils: Improvement of alditol acetylation for gas chromatographic separation and measurement. Org Geochem 41:580-585.
Guggenberger G, Zech W (1994) Composition and dynamics of dissolved carbohydrates and lignin-degradation products in two coniferous forests, N.E. Bavaria, Germany. Soil Biol Biochem 26:19–27. Nierop KGJ, van Lagen B, Buurman P (2001) Composition of plant tissues and soil organic matter in the first stages of a vegetation succession. Geoderma 100:1–24. Oades JM (1984) Soil organic matter and structural stability: mechanisms and implications for management. Plant Soil 76:319-337. Rumpel C, Dignac MF (2006) Gas chromatographic analysis of monosaccharides in a forest soil profile: Analysis by gas chromatography after trifluoroacetic acid hydrolysis and reduction-acetylation. Soil Biol Biochem 38:1478-1481. Spielvogel S, Prietzel J, Kögel-Knabner I (2007) Changes of lignin phenol and neutral sugar pools in different soil types of a high-elevation forest ecosystem 25 years after forest dieback. Soil Biol Biochem 39:655-668. Zhang W, He H, Zhang X (2007) Determination of neutral sugars in soil by capillary gas chromatography after derivatization to aldononitrile acetates. Soil Biol Biochem 39:2665– 2669.
Specific Comments Introduction L45-110: Some more recent references have been added to the Introduction in the revised version of the manuscript. L-55
The term „humus morphology“ is used as expression for the visual appearance the humus-forming SOM and the layering pattern in the organic surface layer according to Zanella et al. (2011). This has been clarified in the revised version of the manuscript.
L-57
The pH of seepage water leaving tangelhumus covers is circumneutral, and often the concentrations of NO3 and Ca are elevated. This statement has been added in the revised version of the manuscript and a reference has been given.
L 64-66
The sentence has been shortened and clarified.
L 67-68
The sentence has been shortened and clarified.
L73/74
The sentence has been deleted in the revised version of the manuscript.
L74
Changed as suggested by Reviewer 1.
L86
In our opinion, “Associated” is correct.
L90
We have removed some of the Zöttl (1965) citations and added more recent ones in the Introduction.
Materials and Methods L137 In the revised version of the manuscript, a reference describing the site Wettersteinwald was added as requested by Reviewer 1. L154
In the revised version of the manuscript, the number of analyzed plant samples is reported as requested by Reviewer 1.
L156
In the revised version of the manuscript, the word “which contribute significantly to” was replaced by “which were relevant constituents of”
L184-187
Changed as suggested by Reviewer 1.
L236
In the revised version of the manuscript, the sentence has been shortened and clarified.
Discussion L397 Typo; changed as suggested by Reviewer 1. (should be 387) L410-411
In the revised version of the manuscript, the sentence has been clarified and corrected.
L451
Corrected as suggested by Reviewer 1.
L504
In fact four different ages have been measured for the four Histosols. Histosol 1 at WETT: 1500 years; Histosol 2 at WETT: 710 years; Histosol Top at GUG: 510 years: Histosol Slope at GUG 50% of NCPC). Foliage of Abies alba and
275
Picea abies has larger glucose contents (about 50% of NCPC) than that of Pinus (38%) and
276
Fagus (33%). All mosses are characterized by exceptionally large percentages of rhamnose
277
(“R”; 8–11% of NCPC) and galactose (“G”; 22–27% of NCPC) compared to the other plants
278
(0.6–3.0%) and small percentages of arabinose (“A”) and xylose (“X”) (4–6% each). The 11
279
opposite is the case for the grasses and sedges, which have exceptionally large arabinose
280
(20% of NCPC) and xylose contents (43–48% of NCPC), but small galactose (10%) and
281
particularly mannose (“M”) contents (2%). Small mannose contents ( conifers
1.5
2.5
3.5
3 Grasses,sedges -> conifers -> grasses,sedges
Oa1 1
Oa2 2
a
2
Oi 0.5
Oe
Oa2 2
3.5
1
Conifers -> shrubs -> conifers
c
4
GM/AX ratio 0
1
2
3
4
0.5
Oa Oa1 1
GUG Leptosols GUG Top
1.5
GUG Slope .
Oa2 2
WETT Leptosols WETT 1
2.5
WETT 2 (CWD)
Oa3 3
