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

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 (> 250 µm) (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 extra-radical 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.

Expanding the toolbox of nutrient limitation studies: A novel method of soil microbial in‐growth bags to evaluate nutrient demands in tropical forests

“…Set in relation to the large‐scale field nutrient manipulation experiment conducted at these sites, the novel experimental approach contributes to distinguish among responses caused by primary microbial/fungal nutrient limitations versus secondary consequences of shifts in other ecosystem processes. Soil hyphal extractions from the field experiment similarly revealed increasing abundance following P (NaH 2 PO 4 ) additions at the 1,000‐m site (Camenzind, Papathanasiou et al., ), whereas, as reported here at 2,000 m, P caused no significant effects (unpublished data). Hamer et al.…”

Long‐term influence of phosphorus fertilization on organic carbon and nitrogen in soil aggregates under no‐till corn–wheat–soybean rotations

“…Ghosh et al (2018) reported that 120:26 kg N/P application showed 12% higher macroaggregates than plots receiving only 120 kg N in 0 to15 cm, however microaggregates and silt-and-clay-sized fraction did not differ significantly. Camenzind et al (2016) observed 4.1% increase in water stable aggregates with P application rate of 10 kg ha −1 yr −1 than control in tropical ecosystem. Soil aggregation tends to increase SOC by influencing soil fertility and crop productivity by reducing erosion and controlling air permeability, water infiltration, and nutrient cycling (Singh et al, 2019b;Zhang et al, 2012).…”

“…Camenzind et al. (2016) observed 4.1% increase in water stable aggregates with P application rate of 10 kg ha −1 yr −1 than control in tropical ecosystem. Soil aggregation tends to increase SOC by influencing soil fertility and crop productivity by reducing erosion and controlling air permeability, water infiltration, and nutrient cycling (Singh et al., 2019b; Zhang et al., 2012).…”

Soil Fungal Community Characteristics and Mycelial Production Across a Disturbance Gradient in Lowland Dipterocarp Rainforest in Borneo

“…Mycelial productivity was significantly positively related to soil inorganic P (Figure 6), although mycelial biomass has previously been shown to be greater in more P-deficient forests (Potila et al, 2009). However, in some cases the proliferation of mycorrhizal hyphae into nutrient 'hotspots' has been observed both in laboratory experiments and natural systems (Ekblad et al, 2013), whilst the role of inorganic P in controlling rates of mycelial production has been demonstrated in forests using hyphal in-growth bags augmented with mineral P, and field manipulations using fertilizer applications (Hagerberg et al, 2003;Potila et al, 2009;Ekblad et al, 2013;Camenzind et al, 2016). In the current study, the tenuous nature of this relationship (being mainly driven by one sampling point in SL; Figure 6) limits interpretation of underlying mechanisms, and should be approached with caution.…”