Biotic and Abiotic Drivers of Topsoil Organic Carbon Concentration in Drylands Have Similar Effects at Regional and Global Scales

Abstract

Drylands contain 25% of the world's soil organic carbon (SOC), which is controlled by many factors, both abiotic and biotic. Thus, understanding how these factors control SOC concentration can help to design more sustainable land-use practices in drylands aiming to foster and preserver SOC storage, something particularly important to fight ongoing global warming. We use two independent, large-scale databases with contrasting geographic coverage (236 sites in global drylands and 185 sites in Patagonia, Argentina) to evaluate the relative importance of abiotic (precipitation, temperature and soil texture) and biotic (primary productivity) factors as drivers of SOC concentration in drylands at global and regional scales. We found that biotic and abiotic factors had similar effects on SOC concentration across regional and global scales: maximum temperature and the sand content had negative effects, while precipitation and plant productivity exerted positive effects. Our findings provide empirical evidence that increases in temperature and reductions in rainfall, as forecasted by climatic models in many drylands worldwide, promote declines in SOC both directly and indirectly via the reduction of plant productivity. This has important implications for the conservation of drylands under climate change; land management should seek to enhance plant productivity as a tool to offset the negative impact of climate change on SOC storage and on associated ecosystem services.

Disentangling Drought and Grazing Effects on Soil Carbon Stocks and CO2 Fluxes in a Semi-Arid African Savanna

“…Despite their low productivity, dryland grasslands play an important role in global carbon sequestration as decomposition rates are generally low due to lack of water. It is estimated that about 32% of the world's soil organic carbon is stored in dryland soils (Plaza et al, 2018;Gaitán et al, 2019). In dryland grasslands, grazing and variable rainfall are among the major determinants of grassland productivity (Bat-Oyun et al, 2016;Guuroh et al, 2018).…”

“…Grazing and drought both have strong effects on soil carbon storage and GHG emission in dryland grasslands, mainly indirectly through their effect on biomass production (Jones et al, 2005;Ferner et al, 2018;Gaitán et al, 2019). Among these two drivers, drought has been reported to have a greater influence on biomass production than grazing (Bat-Oyun et al, 2016).…”

Niche dynamics in amphitropical desert disjunct plants: Seeking for ecological and species‐specific influences

“…The main advantage of SEM is that it is theory oriented, and allows comparisons among competing hypotheses about causal networks (‘models’; Eisenhauer et al., 2015). Thus, in contrast to commonly used bivariate relationships, SEM provides a structured framework for interpretation of a large number of predictors and responses with potentially complex connections (Gaitán et al., 2019; Grace et al., 2010, 2014). We used the mean net primary productivity of the sites inhabited by the species in North and South America (NPP_NA and NPP_SA, respectively), as a proxy for the influence of biotic interactions to which the species are subjected in each continent.…”

The MARAS dataset, vegetation and soil characteristics of dryland rangelands across Patagonia

“…Drylands, areas where the aridity index -the ratio between precipitation and potential evapotranspiration -is below 0.65, are distributed over 100 of the world's nations, comprise about 45% of the earth's land total area 1 , and are highly prone to land degradation and desertification 2 . In addition to expanding the global area covered by drylands, ongoing climate change and the increases in aridity associated with it 3 are expected to trigger large variations in vegetation cover, biodiversity and key soil properties such as soil carbon content 4 . These ecosystem features largely influence the functioning and capacity of drylands to provide essential ecosystem services, such as biomass production and the maintenance of soil fertility, that sustain the livelihoods of more than 2 billion people living mostly in developing countries 5 .…”

“…The MARAS data allow for evaluations of ecosystem change with a precision that has not been previously possible at the regional scale in South America. The MARAS monitoring plots are thus useful for a wide variety of floristic, ecological and biogeographic studies, and have been used to describe biodiversity patterns in Patagonia 41 , to quantify the relative importance of biotic and abiotic factors as drivers of regional variations in plant productivity 42 and soil organic carbon 4 , to validate information from satellite data on the ground 43 , to assess how biodiversity modulates ecosystem responses to drought 44 and to explore how aridity and overgrazing affect the structure and functioning of drylands 45 . From the land manager perspective, the MARAS system has been used to compare the effects of different grazing systems 46 , 47 and in certification schemes such as sustainable management of grasslands 48 , Responsible Wool 49 or Organic Production.…”