Former agricultural fields are increasingly abandoned in several regions in Southern Europe. In many cases this leads to vegetation succession which may have a direct impact on soil quality, biodiversity and hydrological connectivity. The aim of this study is to provide insights on the role of vegetation succession in response to land abandonment on soil quality changes, while keeping aspect into consideration. Information on soil quality change is incomplete and highly scattered especially in the Mediterranean and deserves more attention. Four different stages of land use change and vegetation succession (i.e. agricultural field, abandoned field, young forest, semi-mature forest) were selected and sampled on both north-, and south-facing slopes. For each of the eight conditions six representative sites were sampled. During vegetation succession soil organic carbon (SOC) content and total nitrogen (TN) content, and aggregate stability significantly increased. With increasing SOC, TN and aggregate stability the bulk density and pH decreased. In addition, the parameters SOC, TN and water retention are impacted by aspect. SOC contents increased slower over time on north exposed slopes, but were higher after 50 years. Carbon stocks showed a similar trend but were not different after 50 years for both studied expositions, due to aspect related changes in dry bulk density over time. Soil water availability was 24% higher for north-facing slopes. Soil water availability however did not change over time. Largest increase in soil quality was observed in the first 30 years after abandonment.

Alpine grasslands of the Neotropical Andes have high soil organic carbon (SOC) stocks and provide crucial ecosystem services. However, stability of the SOC in these grasslands is not well-studied. Having insights into SOC stability contributes to a better understanding of ecosystem vulnerability and maintaining of ecosystem services. The objectives were to get a first insight into organic matter (OM) stabilization in soils from different bedrocks of Andean alpine grasslands near Cajamarca, Peru (7° 11″ S, 78° 35″ W) and how this controls SOC stocks. Samples were collected from soils formed on limestone and acid igneous rocks. Stabilization mechanisms of OM were investigated using selective extraction methods separating active Fe, Al and Ca fractions and determined SOC stocks. In both soil types, the results showed important contributions of complexation with and/or adsorption on Fe and Al (oxides) to OM stabilization. Exclusively in the limestone soils, Ca induced OM stabilization by promoting the formation of Ca 2+ bridges between OM and mineral surfaces. Furthermore, no evidence showed that OM stabilization was controlled by crystalline Fe oxides, clay contents, allophones, Al toxicity or aggregate stability. Limestone soils had significantly higher SOC stocks (405 ± 42 Mg ha −1) compared to the acid igneous rock soils (226 ± 6 Mg ha −1), which is likely explained by OM stabilization related to Ca 2+ bridges in addition to the stabilization related to Fe and Al (oxides) in the limestone soils. Our results suggest a shift from OM stabilization dominated by Fe and Al (oxides) to that with the presence of Ca-related cation bridges, with increasing pH values driven by lithology.

Recent studies indicate that climate change influences soil mineralogy by altering weathering processes and thus impacts soil aggregation and organic carbon (SOC) stability. Alpine ecosystems of the Neotropical Andes are characterized by high SOC stocks, which are important for sustaining ecosystem services. However, climate change in the form of altered precipitation patterns can potentially affect soil aggregation and SOC stability with potentially significant effects on the soil's ecosystem services. This study aimed to investigate the effects of precipitation and lithology on soil aggregation and SOC stability in the Peruvian Andean grasslands, and it assessed whether occlusion of organic matter (OM) in aggregates controls SOC stability. For this, samples were collected from soils on limestone and soils on acid igneous rocks from two sites with contrasting precipitation levels. We used a dry-sieving method to quantify aggregate-size distribution and applied a 76 d soil incubation with intact and crushed aggregates to investigate SOC stability's dependence on aggregation. SOC stocks ranged from 153 ± 27 to 405 ± 42 Mg ha −1 , and the highest stocks were found in the limestone soils of the wet site. We found lithology rather than precipitation to be the key factor regulating soil aggregate-size distribution, as indicated by coarse aggregates in the limestone soils and fine aggregates in the acid igneous rock soils. SOC stability estimated by specific SOC mineralization rates decreased with precipitation in the limestone soils, but only minor differences were found between wet and dry sites in the acid igneous rock soils. Aggregate destruction had a limited effect on SOC mineralization, which indicates that occlusion of OM in aggregates played a minor role in OM stabilization. This was further supported by the inconsistent patterns of aggregate-size distribution compared to the patterns of SOC stability. We propose that OM adsorption on mineral surfaces is the main OM stabilization mechanism controlling SOC stocks and stability. The results highlight the interactions between precipitation and lithology on SOC stability, which are likely controlled by soil mineralogy in relation to OM input.

No abstract

Abstract. Recent studies indicate that climate change influences soil mineralogy by altering weathering processes, and thus impacts soil aggregation and organic carbon (SOC) stability. Alpine ecosystems of the Neotropical Andes are characterized by high SOC stocks, which are important to sustain ecosystem services. However, climate change in the form of altered precipitation patterns can potentially affect soil aggregation and SOC stability with potentially significant effects on the soil’s ecosystem services. This study aimed to investigate the effects of precipitation and lithology on soil aggregation and SOC stability in the Peruvian Andean grasslands, and assessed whether occlusion of organic matter (OM) in aggregates controls SOC stability. For this, samples were collected from limestone soils (LSs) and acid igneous rock soils (ASs) from two sites with contrasting precipitation levels. We used a dry-sieving method to quantify aggregate size distribution, and applied a 76-day soil incubation with intact and crushed aggregates to investigate SOC stability in dependence on aggregation. SOC stocks ranged from 153±27 to 405 ± 42 Mg ha−1, and the highest stocks were found in the LSs of the wet site. We found lithology rather than precipitation to be the key factor regulating soil aggregate size distribution, as indicated by coarse aggregates in the LSs and fine aggregates in the ASs. SOC stability estimated by specific SOC mineralization rates decreased with precipitation in the LSs, but minor differences were found between wet and dry sites in the ASs. Aggregate destruction had a limited effect on SOC mineralization, which indicates that occlusion of OM in aggregates played a minor role in OM stabilization. This was further supported by inconsistent patterns of aggregate size distribution compared to the patterns of SOC stability. We propose that OM adsorption on mineral surfaces is the major OM stabilization mechanism controlling SOC stocks and stability. The results highlight the interactions between precipitation and lithology on SOC stability, which are likely controlled by soil mineralogy in relation to OM input.