Abstract
The present investigation was aimed to quantify the three principal components of the soil carbon (C) stock, namely inorganic, organic and permanganate oxidizable, in 0–5 cm and 5–30 cm soil layers, of the main Mediterranean agricultural land coverages: olive grove, olive forest, citrus grove, vineyard, arable irrigated, arable rainfed and natural soil covered by Mediterranean scrub and garrigue. We assessed the contribution of soil properties and climatic variables on soil TOC and POxC by Pearson’s correlations, multiple linear regressions, principal component analyses and variance partitioning. NAT and both olive cropping systems showed the highest TOC concentration while the other land covers showed values ranging between 8.0 and 26.6 g kg−1. Soil POxC represented between 0.5% and 2.2% of the total soil C. A large number of interrelated factors govern soil C accumulation in Mediterranean agroecosystems. Rainfall and temperature had a selective effect on soil C distribution between the sampling areas, while among soil properties, texture exerted a prominent effect, resulting in positive effects from clay and negative effects from sand. Soil POxC concentration showed a similar trend to soil TOC in all land uses although on each of them represent a different TOC portion.
Highlights
Soils contain the largest C stock on Earth, storing about 2500 Gt of C in the first meter of depth, greater than the atmospheric and vegetation pools [1], with a fundamental role on global C cycle being a determining factor of soil ecosystem services such as biological, physical and chemical functions [2].even minimal variation of this large reserve can cause massive consequences on the biosphere from the fertility of the soil up to the greenhouse gases concentration in the atmosphere [3]
The relationship between total organic C (TOC) and biotic and abiotic factors can strongly vary across environments and is affected by land use and vegetation types, making it possible to identify specific factors that govern soil C accumulation in the agroecosystems at a regional scale [5,6]
On the upper soil layer (0–5 cm), total nitrogen ranged from 1.0 g kg−1 to 2.5 g kg−1 with the lowest values observed in ACI and the highest in NAT soils (Table 1)
Summary
Soils contain the largest C stock on Earth, storing about 2500 Gt of C in the first meter of depth, greater than the atmospheric and vegetation pools [1], with a fundamental role on global C cycle being a determining factor of soil ecosystem services such as biological, physical and chemical functions [2].even minimal variation of this large reserve can cause massive consequences on the biosphere from the fertility of the soil up to the greenhouse gases concentration in the atmosphere [3]. Soil C stock is generally constituted by two components, both involved in the C exchanges between soil and atmosphere: an inorganic (TIC) and an organic (TOC) C pool. If the TIC pool strictly depends on the parent material and soil forming factors, representing the most stable component, on the other side, the TOC pool, which is more labile, is influenced by several biotic and abiotic factors. For its considerable importance, it is fundamental to understand the factors that can influence the C stock in the soil [4,5]. The relationship between TOC and biotic and abiotic factors can strongly vary across environments and is affected by land use and vegetation types, making it possible to identify specific factors that govern soil C accumulation in the agroecosystems at a regional scale (arable, natural and semi-natural) [5,6]. Among biotic factors there are vegetation type, crop residue deposition and the soil microbial community [7,8], while abiotic factors include topography, soil physicochemical
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