Interactions between biogeochemical and management factors explain soil organic carbon in Pyrenean grasslands

Antonio Rodríguez,Rosa Maria Canals,Leticia San Emeterio,M.-Teresa Sebastià,Josefina Plaixats,Àngela Ribas,Haifa Debouk,Juan José Jimenez,Elena Albanell,Jordi Garcia-Pausas

doi:10.5194/bg-17-6033-2020

Abstract

Abstract. Grasslands are one of the major sinks of terrestrial soil organic carbon (SOC). Understanding how environmental and management factors drive SOC is challenging because they are scale-dependent, with large-scale drivers affecting SOC both directly and through drivers working at small scales. Here we addressed how regional, landscape and grazing management, soil properties and nutrients, and herbage quality factors affect 20 cm depth SOC stocks in mountain grasslands in the Pyrenees. Taking advantage of the high variety of environmental heterogeneity in the Pyrenees, we built a dataset (n=128) that comprises a wide range of environmental and management conditions. This was used to understand the relationship between SOC stocks and their drivers considering multiple environments. We found that temperature seasonality (difference between mean summer temperature and mean annual temperature; TSIS) was the most important geophysical driver of SOC in our study, depending on topography and management. TSIS effects on SOC increased in exposed hillsides, slopy areas, and relatively intensively grazed grasslands. Increased TSIS probably favours plant biomass production, particularly at high altitudes, but landscape and grazing management factors regulate the accumulation of this biomass into SOC. Concerning biochemical SOC drivers, we found unexpected interactive effects between grazer type, soil nutrients and herbage quality. Soil N was a crucial SOC driver as expected but modulated by livestock species and neutral detergent fibre contenting plant biomass; herbage recalcitrance effects varied depending on grazer species. These results highlight the gaps in knowledge about SOC drivers in grasslands under different environmental and management conditions. They may also serve to generate testable hypotheses in later/future studies directed to climate change mitigation policies.

Highlights

Soil organic carbon (SOC) is crucial for the functioning of terrestrial ecosystems (Lal, 2004a)
According to the combined linear model, soil nutrient and herbage variables were other important SOC stock drivers (Fig. S7), but many of these effects occurred in interaction with grazer type
While most of the previous studies addressing soil carbon did not include any temperature seasonality variable as a potential SOC predictor, usually focusing on mean temperature and precipitation as the most important climate drivers of SOC (Hobley et al, 2015; Manning et al, 2015; Wiesmeier et al, 2019), our models suggest that TSIS and other temperature seasonality indexes should be included in further studies to provide more evidence of the extent of the effects of temperature seasonality on SOC stocks

Summary

Introduction

Soil organic carbon (SOC) is crucial for the functioning of terrestrial ecosystems (Lal, 2004a). Grasslands have small aboveground biomass compared to other ecosystems, their SOC stocks can be comparable to those in forest ecosystems (Berninger et al, 2015) This is due to their high root biomass and residues, which are a substantial carbon source and can contribute to water retention in soil. This creates favourable conditions for the accumulation of organic matter (Von Haden and Dornbush, 2014; Yang et al, 2018). These attributes, together with the high extent of grassland global cover, make grasslands store around 34 % of the terrestrial carbon, mostly in their soils (White et al, 2000)

Objectives

Methods

Results

Discussion

Conclusion