Biocrust-linked changes in soil aggregate stability along a climatic gradient in the Chilean Coastal Range

Abstract

Abstract. Biological soil crusts (biocrusts) composed of cyanobacteria, bacteria, algae, fungi, lichens, and bryophytes stabilize the soil surface. This effect has mainly been studied in arid climates, where biocrusts constitute the main biological agent to stabilize and connect soil aggregates. Besides, biocrusts are an integral part of the soil surface under mediterranean and humid climate conditions, mainly covering open spaces in forests and on denudated lands. They often develop after vegetation disturbances, when their ability to compete with vascular plants increases, acting as pioneer communities and affecting the stability of soil aggregates. To better understand how biocrusts mediate changes in soil aggregate stability under different climate conditions, we analyzed soil aggregate samples taken under biocrust communities from four national parks in Chile along a large climatic gradient ranging from (north to south) arid (Pan de Azúcar), semi-arid (Santa Gracia), mediterranean (La Campana) to humid (Nahuelbuta). Biocrust communities showed a stabilizing effect on the soil aggregates in dry fractions for the three northern and the wet aggregates for the southernmost sites. Here, permanent vascular plants and higher contents of organic carbon and nitrogen in the soil control aggregate stability more than biocrusts, which are in intense competition to higher plant communities. Moreover, we found an increase in stability for edge aggregate size classes (< 2.0 mm and 9.5–30.0 mm). The geometric mean diameter of the soil aggregates showed a clear effect due to the climatic gradient, indicating that the aggregate stability presents a log-normal instead of a normal distribution, with a trend of low change between aggregate size fractions. Based on our results, we assume that biocrusts affect the soil structure in all climates. Their role for aggregate stability is masked under humid conditions by higher vegetation and organic matter contents in the topsoil.

Biocrusts: Overlooked hotspots of managed soils in mesic environments

“…Third, biocrusts can increase soil organic matter (Gao et al, 2017) and improve aggregate stability by bacterial metabolites such as exo-and lipopolysaccharides (Cania et al, 2020). However, these effects depend on climatic conditions (Kidron, Lichner, et al, 2022;Riveras-Muñoz et al, 2022) and species composition (Gypser et al, 2016) and have been poorly studied in mesic environments. As shown in Kidron, Lichner, et al (2022), biocrust-related mechanisms of runoff generation are very complex, with significant variability documented in arid environments.…”

“…Typical biocrust biota include algae, cyanobacteria, fungi, bacteria, archaea, protists, lichens, bryophytes, and microarthropods (Belnap et al., 2001; Khanipour Roshan et al., 2021; Weber et al., 2016, 2022). Biocrusts play an important ecological role in the creation and maintenance of healthy soils, and can (1) improve nutrient availability and fertility (Evans & Ehleringer, 1993; Gao et al., 2010; Li et al., 2012), (2) influence plant germination (Godínez‐Alvarez et al., 2012; Havrilla et al., 2019; Zhang & Belnap, 2015), (3) increase biogeochemical cycling (Miralles et al., 2012; Wang et al., 2017; Xu et al., 2013), (4) keep and enhance water availability at the soil surface (George et al., 2003; Li et al., 2022), (5) increase soil aggregate stability (Cania et al., 2020; Riveras‐Muñoz et al., 2022; Zhang et al., 2006), and (6) protect the soil surface by counteracting soil erosion from water (Chamizo et al., 2017; Seitz et al., 2017) or wind (Bullard et al., 2022; Zhang et al., 2006). However, thus far, biocrusts have primarily been studied in arid and semiarid regions (Weber et al., 2016).…”