Small-Scale Vertical Distribution of Algae and Structure of Lichen Soil Crusts

Abstract

Although many studies have been conducted on the ecological functions and ecophysiological characteristics of lichen soil crusts (LSCs), no explanation of these results has been provided based on crust structures. Using algae soil crusts (ASCs) as comparison, this work studied the small-scale vertical distribution of algal biomass and stratification in two types of LSCs, by combining the binocular stereomicroscope observations, microscope observations, plate cultures, chlorophyll analysis, and polysaccharides analysis. The results showed an obvious difference in the proportion but not the composition of the algae species between the ASCs and the two LSCs. Approximately 60% and 80% of the total algal biomass were concentrated in the top 1 mm of the soil profile and thalli in the ASCs and LSCs, respectively. This implies that symbiotic algae are the dominant species and primary organic carbon producers in LSCs, and the algal biomass decreased with the depth in both the ASCs and LSCs. The small-scale vertical distributions of the crustal algal biomass and polysaccharides were characterized by obvious successional stage, whereas these were unrelated to the crust type within the successional stage. Additionally, a large amount of fungi, which were always piercing the entire crusts, were observed in the LSCs, but only occasionally in the ASCs. These special structures are purported to cause the LSCs to achieve specific ecological functions, such as higher carbon fixation and greater compressive strength. High biomass, large living space, and advantageous resource utilization privilege suggest that the lichen association is mutualistic and the direction from ASCs to LSCs is developmental.

Analysis of environmental factors determining development and succession in biological soil crusts

“…Chl-a content of the two subsamples respectively represented the free-living cyanobacterial and algal biomass and total photosynthetic biomass. In addition, the relative coverages of lichens and mosses were visually estimated on the sampled crust surface, as described by Wu et al (2011).…”

“…Collectively BSCs perform significant ecosystem services, however, the different crust developmental levels or successional stages still affect those services. At present, based on the difference of dominant organisms, BSCs are generally categorized into three different successional stages along with the developmental sequence, including: cyanobacterial, lichen and moss crusts (Housman et al, 2006;Su et al, 2009;Wu et al, 2011;Lan et al, 2012a).…”

Assessing Level of Development and Successional Stages in Biological Soil Crusts with Biological Indicators

“…The BSCs in this region formed slowly after the enclosure at different times; therefore, the ages of the BSCs were calculated according to the enclosure time. After half a century elapsed since the first enclosure, the environment of this region has improved, and substantial BSCs have been established including cyanobacterial crusts, lichen crusts, moss crusts, and some combination or transition types [6,16].…”

“…The sampling was conducted in June 2010, and the experimental region had not received any rainfall in the past 72 h. Intact samples including a series of different developmental and successional BSCs were randomly collected from the interspaces between shrubs (0.2 m away from the shrubs) according to Wu et al [16] and Lan et al [6]. Then the collected samples were enclosed in sterilized paper bags and transported back to the laboratory as quickly as possible, air dried in shade condition, and kept in desiccators for subsequent analysis.…”

“…Limited availability of resources, such as water, time, and space, also would stop the successional stage at a certain state [19,34]. Previously, some researchers differentiated BSCs into cyanobacterial crusts, lichen crusts, and moss crusts according to different dominant communities at different developmental stages [10,16]. Some other researchers differentiated BSCs into light and dark crusts based on different crust colors [12].…”