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

Abstract

Biological soil crusts (BSCs) perform vital ecosystem services, but the difference in biological components or developmental level still affects the rate and type of these services. In order to differentiate crust successional stages in quantity and analyze the relationship between crust developmental level and successional stages, this work determined several biological indicators in a series of different developmental BSCs in the Shapotou region of China. The results showed that crust developmental level (level of development index) can be well indicated by crust biological indicators. Photosynthetic biomass was the most appropriate to differentiate crust successional stages, although both photosynthetic biomass and respiration intensity increased with the development and succession of BSCs. Based on of the different biological compositions, BSCs were quantificationally categorized into different successional stages including cyanobacterial crusts (lichen and moss coverages <20 %), lichen crusts (lichen coverage >20 % but moss coverage <20 %), semi-moss crusts (moss coverage >20 % but <75 %), and moss crusts (moss coverage >75 %). In addition, it was found that cyanobacterial and microalgal biomass first increased as cyanobacterial crusts formed, then decreased when lots of mosses emerged on the crust surface; however nitrogen-fixing cyanobacteria and heterotrophic microbes increased in the later developmental BSCs. The structural adjustment of biological components in the different developmental BSCs may reflect the requirement of crust survival and material transition.

Artificially Accelerating the Reversal of Desertification: Cyanobacterial Inoculation Facilitates the Succession of Vegetation Communities

“…In our other experiments, it was also found that bacteria, fungi, and actinomycetes increased similarly, along with the development of BSCs. 7,26 Among these crust organisms, those photosynthetic species such as cyanobacteria, algae, and mosses resulted in substantial inputs of carbon (C) into the soil layer, increasing the soil organic matter, and those nitrogen-fixing species such as Scytonema and Nostoc fixed nitrogen (N), providing the necessary soil N nutrition. Crust organisms also promoted the conversion of sand into soil by increasing soil nutrients and improving topsoil texture.…”

“…6,7 On the basis of the different dominant species and developmental levels, BSCs are categorized into different successional stages, in sequence including cyanobacterial crusts, lichen crusts, and moss crusts. 6−8 Cyanobacterial crusts normally represent the primary successional stage, light, flat, and brittle.…”

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

“…Based on our previous observations, in Shapotou region (at the southeast edge of Tengger Desert) BSCs generally succeed from cyanobacterial crusts to lichen and moss crusts along a pathway of "cyanobacterial crusts, cyanobacteriallichen crusts, lichen crusts, lichen-moss crusts and moss crusts" (Lan et al, 2012a(Lan et al, , 2013. However in Dalate Banner region (mainly in Jiefangtan; at the eastern edge of Qubqi Desert), BSCs directly succeed from cyanobacterial crusts to moss crusts (Lan et al, 2012b(Lan et al, , 2014.…”

“…Then bacterial and fungal inoculations were placed at 37°C and 28°C (±2°C) respectively. Three to 5 days later, the microbial colonies were counted and expressed as CFU g −1 crusts (Lan et al, 2013).…”

“…Crust total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) were also measured with the standard soil analysis methods described by Namjing Institute of Soil Research, Chinese Academy of Sciences (1980) Crust pH and electrical conductivity (EC) were measured in 1:5 soil-water aqueous extract using calibrated YSI instruments (Abed et al, 2010). Crust available K, Na, Ca, Mg and Mn contents were measured in M3 soil extract using atomic absorption spectrophotometer (Lan et al, 2013).…”