Increases in Soil Aggregation Following Phosphorus Additions in a Tropical Premontane Forest are Not Driven by Root and Arbuscular Mycorrhizal Fungal Abundances

Tessa Camenzind,Dietrich Hertel,Pål A Olsson,Matthias C Rillig,Juan P Suárez,Helena J Papathanasiou,Antje Förster,Jürgen Homeier,Yvonne Oelmann,Karla Dietrich

doi:10.3389/feart.2015.00089

Abstract

Tropical ecosystems have an important role in global change scenarios, in part because they serve as a large terrestrial carbon pool. Carbon protection is mediated by soil aggregation processes, whereby biotic and abiotic factors influence the formation and stability of aggregates. Nutrient additions may affect soil structure indirectly by simultaneous shifts in biotic factors, mainly roots and fungal hyphae, but also via impacts on abiotic soil properties. Here, we tested the hypothesis that soil aggregation will be affected by nutrient additions primarily via changes in arbuscular mycorrhizal fungal (AMF) hyphae and root length in a pristine tropical forest system. Therefore, the percentage of water-stable macroaggregates (> 250µm) (WSA) and the soil mean weight diameter (MWD) was analyzed, as well as nutrient contents, pH, root length and AMF abundance. Phosphorus additions significantly increased the amount of WSA, which was consistent across two different sampling times. Despite a positive effect of phosphorus additions on extraradical AMF biomass, no relationship between WSA and extra-radical AMF nor roots was revealed by regression analyses, contrary to the proposed hypothesis. These findings emphasize the importance of analyzing soil structure in understudied tropical systems, since it might be affected by increasing nutrient deposition expected in the future.

Highlights

Soils represent a complex system due to the interactions of roots, fungi, fauna, and bacteria embedded within the soil structural environment
In 2010 effects were strongest in the NP treatment, whereas in 2013 both, P and NP additions affected the amount of water-stable macroaggregates (WSA) (Figure 1)
The increase in WSA was not reflected in an increase in mean weight diameter (MWD), which potentially indicates that these changes do not solely affect the number of macroaggregates, but rather their stability

Summary

Introduction

Soils represent a complex system due to the interactions of roots, fungi, fauna, and bacteria embedded within the soil structural environment. Soils represent one of the largest terrestrial C pools, which is of particular interest in the light of future global change scenarios (Kimble et al, 1990; Batjes, 1996). In particular, play an important role as C sink, since tropical forests hold an estimated 20% of the world’s terrestrial vegetation and soil C pool (Jobbagy and Jackson, 2000; Jimenez and Lal, 2006). Tropical forests are highly endangered by deforestation, land use change, fertilization and increased nutrient deposition by anthropogenic activities (Gullison et al, 2007; Galloway et al, 2008; Mahowald et al, 2008). Increases in nutrient deposition have been shown to affect plant diversity, ecosystem productivity, soil community composition as well as nutrient cycling (Treseder, 2008; Bobbink et al, 2010; Isbell et al, 2013; Wilcke et al, 2013b; Camenzind et al, 2014), and directly or indirectly may have an impact on soil aggregation processes

Methods

Results

Conclusion