DOI: 10.5061/dryad.9ghx3ffv2
title: Active restoration of degraded alpine grassland weakens mineral-associated soil organic carbon retention

description: Active restoration is predominant to reverse grassland degradation and
 soil organic carbon (SOC) loss. However, early studies focused on the bulk
 soil carbon (C) dynamics upon grassland degradation and restoration, with
 limited evidence involving SOC fractions. Here, we explored how the
 particulate and mineral-associated OC (POC and MAOC), metal-bound OC, soil
 aggregate-associated OC, SOC molecular structure, and microbial-derived OC
 respond to grassland degradation and restoration on the Tibetan Plateau,
 and also studied the effects of active restoration on SOC fractions across
 grassland ecosystems through a global-scale meta-analysis. We found that
 POC and soil aggregate-associated OC contents substantially decreased,
 while MAOC content remained stable after grassland degradation. In
 contrast, short-term active restoration induced significant decrease in
 MAOC and metal-bound OC due to lower soil pH, but POC content remained
 stable, indicating that grassland restoration resulted in a decrease in
 the SOC stability. Moreover, soil aggregate structure and its stability
 recovered rapidly during short-term active restoration, but
 aggregate-associated OC did not recover or even declined, suggesting
 asynchrony between them. Nuclear magnetic resonance spectroscopy revealed
 no significant changes in the SOC molecular composition between intact,
 degraded, and restored grasslands, suggesting that molecular structure
 alone does not mirror SOC stability. Furthermore, the meta-analysis
 revealed that the response of bulk SOC, MAOC and POC in degraded grassland
 to active restoration occurred sequentially in three phases characterized
 by vulnerability, retention, and re-loss of SOC, respectively. Synthesis
 and applications Combining a field experiment with a global synthesis, we
 found that grassland restoration induces divergent shifts in SOC
 fractions, with threshold effects during grassland restoration
 chronosequence. Relying solely on overall changes in bulk SOC may
 misrepresent the true impact of grassland restoration on SOC retention.
 Therefore, it is essential to pay more attention to the response of the
 functionally distinct SOC fractions to grassland restoration, which could
 help us more accurately assess and predict the grassland soil C-climate
 feedback.
description: # Active restoration of degraded alpine grassland weakens
 mineral-associated soil organic carbon retention ## Data files include:
 **Supplementary_data_1.xlsx**: Experimental design parameters, edaphic
 properties, physico-chemical protection, and soil organic carbon (SOC)
 content (total and fractions) for paired grassland treatments (intact,
 degraded, restored) across three geographically distinct sites. All data
 were collected by the authors. Blank cells represent missing data. |
 variables | units | description | | :------------- | :-------------- |
 :----------------------------------------------------------------------- |
 | Land type | categorical | the paired treatments (i.e., intact, degraded
 and restored grassland)  | | Site | categorical | the paired treatments by
 three geographically spaced demonstration sites | | Sampling | categorical
 | five replicates measured 30 m × 30 m at different land types | | SOC |
 mg / g dry soil | soil organic carbon | | POC | mg / g dry soil |
 particulate organic carbon | | MAOC | mg / g dry soil | mineral-associated
 organic carbon | | Metal-OC | mg / g dry soil | metal-bound organic carbon
 | | Fe-OC  | mg / g dry soil | iron- bound organic carbon | | Ca-OC | mg /
 g dry soil | calcium-bound organic carbon | | GRSP | mg / g dry soil |
 glomalin-related soil protein. | | Macroaggregate | % |
 macroaggregate(2000-250 um) | | Microaggregate | % |
 microaggregate(250-53um) | | Clay+Silt | % | clay+silt fraction(&lt;53 um)
 | | MWD | | mean weight diameter | | Macro-OC | mg / g dry soil |
 macroaggregate-associated organic carbon | | Micro-OC | mg / g dry soil |
 microaggregate-associated organic carbo | | Clay+Silt-OC | mg / g dry soil
 | clay+silt-associated organic carbon | | Fed | mg / g dry soil |
 dithionite-extractable Fe oxides | | Caexe | mg / g dry soil |
 exchangeable calcium | | pH | | soil pH level | | SWC | % | soil water
 content | | TN | mg / g dry soil | total nitrogen | | C:N | | soil organic
 carbon/total nitrogen | | Clay | % | volume fraction of clay(0-2 μm) | |
 Silt | % | volume fraction of silt(2-50 μm) | | Sand | % | volume fraction
 of sand(50-2000 um) | | CS | % | the sum of clay and silt volume fractions
 | **Supplementary_data_2.xlsx**: Molecular composition of SOC derived from
 solid-state 13C NMR spectroscopy for paired grassland treatments (intact,
 degraded, restored). All data were collected by the authors. Blank cells
 represent missing data. | variables | units | description | |
 :--------------------- | :---------- |
 :--------------------------------------------------------------------- | |
 Land type | categorical | the paired treatments (i.e., intact, degraded
 and restored grassland)  | | Alkyl C | % | Alkyl carbon (0–45 ppm) | |
 N-alkyl and methoxyl C | % | N-alkyl and methoxyl carbon (45–60 ppm) | |
 O-alkyl C | % | O-alkyl carbon (60–95 ppm) | | Di-O-alkyl C | % |
 Di-O-alkyl carbon (95–110 ppm) | | Aromatic C | % | Aromatic carbon
 (110–145 ppm) | | Phenolic C | % | Phenolic carbon (145–165 ppm) | |
 Amide/carboxyl C | % | Amide/carboxyl carbon (165–210 ppm) | | A/A-O | |
 Alkyl C:O-alkyl C ratio (0–45/45–110 ppm) | | Aromaticity | | aromatic C
 peak area (110–160 ppm)/total peak area (0–160 ppm) |
 **Supplementary_data_meta_analysis.xlsx**: A global meta-analysis dataset
 evaluating the effects of grassland restoration on bulk SOC and its
 fractions (POC, MAOC). Includes study-level metadata, effect sizes, and
 statistical parameters. All data were collected by the authors. Blank
 cells represent missing data. | variables | units | description | |
 :--------------- | :-------------- |
 :---------------------------------------------------------------------- |
 | Study | number | study number | | Citations | | data source | |
 Longitude | degrees | longitude coordinate | | latitude | degrees |
 latitude coordinate | | MAT | ℃ | mean annual air temperature | | MAP | mm
 | mean annual precipitation | | Climatic zones | categorical | climate
 classification | | Restoration year | number | year of active restoration
 | | Cn | number | sample size of control groups | | Tn | number | sample
 size of treatment groups | | C\_M\_SOC | mg / g dry soil | mean soil
 organic carbon (SOC) content in control groups | | C\_SD\_SOC | mg / g dry
 soil | standard deviation of SOC in control groups  | | T\_M\_SOC | mg / g
 dry soil | mean SOC in treatment groups | | T\_SD\_SOC | mg / g dry soil |
 standard deviation of SOC in treatment groups  | | Vi\_SOC | | variance of
 the natural logarithm of response ratios for SOC | | RR\_SOC | | natural
 logarithm of response ratios  for SOC | | C\_M\_POC | mg / g dry soil |
 mean particulate organic carbon (POC) content in control groups | |
 C\_SD\_POC | mg / g dry soil | standard deviation of POC in control
 groups  | | T\_M\_POC | mg / g dry soil | mean POC in treatment groups | |
 T\_SD\_POC | mg / g dry soil | standard deviation of POC in treatment
 groups  | | Vi\_POC | | variance of the natural logarithm of response
 ratios for POC | | RR\_POC | | natural logarithm of response ratios  for
 POC | | C\_M\_MAOC | mg / g dry soil | mean mineral-associated organic
 carbon (MAOC) content in control groups | | C\_SD\_MAOC | mg / g dry soil
 | standard deviation of MAOC in control groups  | | T\_M\_MAOC | mg / g
 dry soil | mean MAOC in treatment groups | | T\_SD\_MAOC | mg / g dry soil
 | standard deviation of MAOC in treatment groups  | | Vi\_MAOC | |
 variance of the natural logarithm of response ratios for MAOC | | RR\_MAOC
 | | natural logarithm of response ratios  for MAOC |