Soil resources and element stocks in drylands to face global issues

César Plaza,Fernando T Maestre,Ana Tarquis,Claudio Zaccone,Edward A G Schuur,Kasia Sawicka,Ana M Méndez,Gerard B M Heuvelink,Gabriel Gascó

doi:10.1038/s41598-018-32229-0

Abstract

Drylands (hyperarid, arid, semiarid, and dry subhumid ecosystems) cover almost half of Earth’s land surface and are highly vulnerable to environmental pressures. Here we provide an inventory of soil properties including carbon (C), nitrogen (N), and phosphorus (P) stocks within the current boundaries of drylands, aimed at serving as a benchmark in the face of future challenges including increased population, food security, desertification, and climate change. Aridity limits plant production and results in poorly developed soils, with coarse texture, low C:N and C:P, scarce organic matter, and high vulnerability to erosion. Dryland soils store 646 Pg of organic C to 2 m, the equivalent of 32% of the global soil organic C pool. The magnitude of the historic loss of C from dryland soils due to human land use and cover change and their typically low C:N and C:P suggest high potential to build up soil organic matter, but coarse soil textures may limit protection and stabilization processes. Restoring, preserving, and increasing soil organic matter in drylands may help slow down rising levels of atmospheric carbon dioxide by sequestering C, and is strongly needed to enhance food security and reduce the risk of land degradation and desertification.

Highlights

Drylands are regions of the Earth characterized by a water deficit in average climatic conditions, having a ratio of precipitation to potential evaporation, or aridity index (AI), less than 0.651–3
Soil organic matter, are key components of drylands, as of any terrestrial ecosystem, and provide a range of functions and services that have a broad impact on major global issues, such as food security and climate change[10,11,12]
Decreasing precipitation and increasing evapotranspiration reduce the loss of salts by leaching, leading to the accumulation of calcium carbonate and gypsum, high base saturation, and relatively high pH typical of dryland soils[27]

Summary

Introduction

Drylands are regions of the Earth characterized by a water deficit in average climatic conditions, having a ratio of precipitation to potential evaporation, or aridity index (AI), less than 0.651–3. The most commonly used compendia of dryland soil information, including soil C stock, available at this time date back several decades[1,16,17,18] This information lacks uncertainty estimates and is fundamentally based on the delineation of dryland boundaries reported in the second edition of the World Atlas of Desertification, which relied on climatic data collected from 1951 to 19803. We use the most recent and detailed climatic and soil global geo-databases to provide an updated description of drylands soils and major element stocks, with a focus on C, aimed at serving as a benchmark in the face of future challenges, including population and food security, land degradation, especially erosion and desertification, biodiversity loss, and climate change. For P stocks, we use the most recently released and detailed maps of the global distribution of different forms of soil P23

Methods

Results

Conclusion