Soil organic carbon stock assessment in forest ecosystems through pedogenic horizons and fixed depth layers sampling: What's the best one?

Abstract

In soil organic carbon (SOC) survey, the role of sampling approach is crucial and should not be underestimated. In this sense, the appropriateness of soil sampling by pedogenic horizons (PGH) and fixed depth layers (FDL) in forest is still a field of debate. The present work aimed to: (a) study the spatial variability of SOC concentrations and C stocks through PGH and FDL samplings in uneven-aged sweet chestnut, European beech and Norway spruce forests of the Apennine chain (Italy); (b) clarify the major advantages and drawbacks of sampling by PGH and FDL. In a representative area (18 Â 18 m) of each forest, a soil profile was investigated and eight additional sampling points were selected. The sampling was performed both by PGH and FDL (0-15 and 15-30 cm). For each forest, no SOC content and C stock differences in 0-30 cm soil depth were found between PGH (58.8 ± 5.3 g kg À1 and 103 ± 7 g ha À1 , respectively) and FDL (52.7 ± 4.3 g kg À1 and 117 ± 9 Mg ha À1 , respectively) sampling. However, under Norway spruce, PGH sampling pointed-out that C was mainly stored in Oe and Oa horizons (51.1 vs. 146 Mg ha À1 in the 0-30 cm layer). The higher coefficient of variation obtained when soil horizons were considered (from 19.2% to 72.8% for PGH and from 16.5% to 25.7% for FDL) suggested that PGH sampling preserved the information about the spatial variability within an ecosystem. The information loss about SOC vertical and spatial distribution would indicate the inability of FDL sampling to support decision-making plans addressed for sustainable use of soil resource.

Pedodiversity and Organic Matter Stock of Soils Developed on Sandstone Formations in the Northern Apennines (Italy)

“…According to previous studies [22,123], within the study area, greater SOC and TN stocks were found at >1000 m a.s.l. compared to ≤1000 (Table 7).…”

“…Specifically, sandstone weathering processes generate soils with low clay and base contents and a weak soil structure [61,67,89], making them vulnerable to erosion. With organic matter serving as the major actor for the formation and stabilization of soil aggregates [90,91], such vulnerability was further boosted by low clay content, which likely limited organic carbon retention within the mineral horizons [22,92,93] and led to thin A horizons (5.5 cm, on average). However, the incorporation of organic matter within the mineral horizons was likely further prevented by acidic conditions resulting in the accumulation of organic matter on the soil surface as organic horizons [94].…”

“…Here, suitable soils for chestnut stands are present and are formed on sedimentary or siliceous soils [105] where acidic conditions predominate [106]. Acidic soils are, in fact, favorable for the growth of such plant species [22,107,108], with chestnut being susceptible to the presence of the carbonates that typically come from limestone and marl [109]. The investigated CHE soils were sampled from a mountain farm and had suitable physicochemical characteristics to produce chestnut plants with a good vegetative and adaptive state [110].…”

“…In addition, SOC stock is affected by soil development according to the different weight of each pedogenesis factor [20,21]. In this regard, recent papers highlighted the importance of soil type knowledge in terms of lithology, the physicochemical characterization of organic debris, and pedogenetic horizons to determine soil forming processes, in order to understand the distribution and quality of SOC stock [17,22].…”

“…Organic C content is particularly important for soil fertility and the efficient functioning of such ecosystems [34,35]. Although mountain soils store relevant amounts of organic C [22,26,36], the effect of the simultaneous impact of environmental factors on the amount and spatial dynamics of SOC in mountain areas is still underestimated. This knowledge gap is mainly related to the complexity of mountain ecosystems due to the climate conditioning of geobotanic zonality [37] and the vertical diversity of soil profiles and their biological activity [38][39][40][41].…”