Does mycorrhizal inoculation improve plant survival, aggregate stability, and fine root development on a coarse‐grained soil in an alpine eco‐engineering field experiment?

Abstract

Steep vegetation‐free talus slopes in high mountain environments are prone to superficial slope failures and surface erosion. Eco‐engineering measures can reduce slope instabilities and thus contribute to risk mitigation. In a field experiment, we established mycorrhizal and nonmycorrhizal research plots and determined their biophysical contribution to small‐scale soil fixation. Mycorrhizal inoculation impact on plant survival, aggregate stability, and fine root development was analyzed. Here we present plant survival (ntotal = 1248) and soil core (ntotal = 108) analyses of three consecutive years in the Swiss Alps. Soil cores were assayed for their aggregate stability coefficient (ASC), root length density (RLD), and mean root diameter (MRD). Inoculation improved plant survival significantly, but it delayed aggregate stabilization relative to the noninoculated site. Higher aggregate stability occurred only after three growing seasons. Then also RLD tended to be higher and MRD increased significantly at the mycorrhizal treated site. There was a positive correlation between RLD, ASC, and roots <0.5 mm, which had the strongest impact on soil aggregation. Our results revealed a temporal offset between inoculation effects tested in laboratory and field experiments. Consequently, we recommend to establish an intermediate to long‐term field experimental monitoring before transferring laboratory results to the field.

Root density drives aggregate stability of soils of different moraine ages in the Swiss Alps

“…As they are relatively easy to assess, Root Mass Density (RMD = root dry mass per soil volume) and Root Length Density (RLD = root length per soil volume) are normally used in studies dealing with hillslope stability (Pohl et al 2012;Erktan et al 2015;Hudek et al 2017b). However, in alpine habitats, there are only few studies dealing with roots, and even less is known about their role in maintaining ecosystem services above the timberline (Bast et al 2016;Hudek et al 2017a, b;Pohl et al 2009Pohl et al , 2011.…”

“…The most relevant previous studies dealing with the impact of vegetation dynamics on hillslope functioning above the timberline have mainly dealt with narrow environmental gradients (Bast et al 2014(Bast et al , 2016Martin et al 2010;Pohl et al 2009Pohl et al , 2012. Therefore, little is known about the long-term development of hillslope stability during landscape evolution.…”

Visualizing the dynamics of soil aggregation as affected by arbuscular mycorrhizal fungi

“…Biotic factors play a key role in soil stability, and fungal hyphae, especially those produced by arbuscular mycorrhizal fungi (AMF), are among the most important factors affecting long-term soil aggregation [5,[15][16][17][18][19][20][21][22]. Much of the aggregating capacity of fungi is attributed to their filamentous growth habit giving the ability to enmesh particles in soil [5,23].…”

Soil and water bioengineering: Practice and research needs for reconciling natural hazard control and ecological restoration

“…For the last 30 years, practitioners and scientists have been studying the installation phase, by e.g. examining the relationship between the richness of pioneer species and soil aggregate stability (Pohl et al, 2012), or the efficacy of using mycorrhizal inoculations to improve plant growth and soil structure on eroded soil (Powell, 1980;Yildiz et al, 2015;Bast et al, 2016;Demenois et al, 2017). These studies concluded that the key to fully understanding ecological processes at eroded sites requires similar long-term experiments in the field.…”