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Journal of AridEnvironments

Journal of Arid Environments 67 (2006) 521–527

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Short Communication

Man-made desert algal crusts as affected byenvironmental factors in Inner Mongolia, China

L. Chena,b, Z. Xieb, C. Hub, D. Lib, G. Wangb, Y. Liub,�

aSchool of Resource & Environmental Science, Wuhan University, Wuhan 430072, PR ChinabState Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, The Chinese Academy

of Sciences, 7 Donghu Nan Lu, Luojiashan, Wuhan 430072, Hubei, PR China

Received 18 November 2004; received in revised form 12 December 2005; accepted 24 February 2006

Available online 17 April 2006

Abstract

Man-made desert algal crusts were constructed on a large scale (3000m2) in Inner Mongolia,

China. Microcoleus vaginatus was mass cultivated and inoculated directly onto unconsolidated sand

dune and irrigated by automatic sprinkling micro-irrigation facilities. The crusts were formed in a

short time and could resist the erosion of winds and rainfalls 22 days after inoculation. The

maximum biomass in the man-made algal crusts could also reach 35mgChl a/cm2 of soil. Effects of

environmental factors such as temperature, irrigation, rainfall and soil nutrients on algal biomass of

man-made algal crusts were also studied. It was found that rainfalls and lower light intensity had

significantly positive effects on the biomass of man-made algal crusts. The preliminary results

suggested that man-made algal crusts could be formed rapidly, and thus it might be a new feasible

alternative method for fixing unconsolidated sand.

r 2006 Elsevier Ltd. All rights reserved.

Keywords: Desertification; Man-made desert algal crusts; Desert cyanobacteria; Mass cultivation; Soil ecosystem

remediation

1. Introduction

The importance of microbiotic crusts for sand surface stabilization and in particular fordune stabilization has long been acknowledged (Belnap and Gillette, 1997; Bowker et al.,2002). Microbiotic crusts could strengthen soil stabilization and improve the hydrologicalproperties of crust-covered dunes (Mazor et al., 1996). For example, it can resist grade 11

see front matter r 2006 Elsevier Ltd. All rights reserved.

.jaridenv.2006.02.018

nding author. Tel./fax: +86 8764715.

dress: liuyd@ihb.ac.cn (Y. Liu).

ARTICLE IN PRESSL. Chen et al. / Journal of Arid Environments 67 (2006) 521–527522

winds and reduce water erosion in the field (Hu et al., 2002a). Primary succession on algalcommunity structures and the cementing mechanism of algal crusts indicate the potentialof desert algae for forming man-made desert algal crusts, but it only retained in academicstudy phase (Neuman et al., 1996; Hu and Liu, 2003).Based on the previous work in Shapotou, Ningxia, China (Hu et al., 2002a, b; Hu and

Liu, 2003), the aim of this research was to make use of M.vaginatus for large-scaleformation of microbiotic crust and to consider the impact factors of biomass, so as todevelop a new method for fixing unconsolidated sand in soil ecosystem remediation. SinceM.vaginatus is the pioneer organisms in microbiotic crusts in the most regions, we havechosen it for the present investigation (Belnap and Gardner, 1993).

2. Materials and methods

2.1. Mass cultivation

Microcoleus vaginatus Gom. was isolated from desert algal crusts of Shapotou,Zhongwei County, Ningxia Hui Autonomous Region, China (371270N, 1041570E). Masscultivation was conducted in a greenhouse. The inoculum was inoculated into four small(1m� 4m) raceway culture ponds, then transferred to a large raceway culture pond(6m� 40m) after 12 days. Inocula were grown in BG-11 medium (Rippka et al., 1979)without microelements (A5), at room temperature (10–35 1C), illuminated with sunlightand stirred with electromotors.

2.2. Study area

The experimental area is located in Dalateqi county, Inner Mongolia (401210N,1091510E). All the experiments were conducted in late autumn from August 29 toSeptember 20, 2003. The rainfalls occurred at day 2, 4, 7, 8, 9, 19, 20 and 22, and thehighest ground temperature was 47 1C and the lowest air temperature was 9 1C afterinoculation. Sites 1 and 2 (45m� 31m) were unconsolidated sand on a mobile dune. Site 3contained Agriphyllum squarrosum, an annual grass that colonized in the spring of 2003.Site 4 (15m� 7m) was located in the south-facing footslope of the shifting dune and wasplanted with Astragalus adsurgens. Site 5 was located in the south-facing footslope of themobile dune and colonized by Aneurolepidium chinensis in the spring of 2003. Site 6(5m� 7m) was unconsolidated sand and covered with a sunlight-shielding net. Site 7(13m� 7m) was growing Aneurolepidium chinensis and Salix psammophila, and thesamples were taken at open ground or underneath grasses and shrubs.

2.3. Man-made desert algal crust

Cultures were harvested by filtration through silk after growing for 18 days, and directlyinoculated onto unconsolidated sand with a sprayer as homogeneously as possible. Sites2–7 were inoculated with a biomass of 6 mgChl a/cm2 of soil (Table 1) and intermittentlyirrigated with 20mm of ground-water per day by automatic sprinkling micro-irrigationfacilities from 9:00 to 16:30. Site 1 was not inoculated or irrigated as control site.

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Table 1

Soil properties of different sampling sites

Sample site Sites 1, 2, 3, 6 Site 4 Site 5 Site 7

Total N (mg/g) 0.370.0 0.370.1 0.470.1 0.570.2

Total P (mg/g) 0.470.1 0.970.3 0.470.0 0.370.0

K+ (mg/g) 5.270.7 19.872.1 8.671.0 7.270.9

Ca2+ (mg/g) 41.4710.3 52.276.3 68.1715.4 46.776.5

Mg2+ (mg/g) 24.270.9 31.473.5 26.173.1 28.274.3

Biomass (mgChl a/cm2) 0.1270.01 1.0170.10 0.3170.07 0.4170.10

Organic compounds (mg/g) 0.370.1 10.370.9 14.571.2 19.371.6

Biomass after inoculation (mgChl a/cm2) 0a 6.0270.17 6.0470.05 6.0570.03

6.0770.11b

Mean7SD, n ¼ 3:aSite 1.bSites 2, 3 and 6.

L. Chen et al. / Journal of Arid Environments 67 (2006) 521–527 523

2.4. Soil properties

Organic C and total N were analysed by standard soil analysis methods; K, Ca, Mg andP were measured with an atomic absorption spectrophotometer (WFX-1B, Beijing SecondOptical Instrument Factory) as described by Hu et al. (2002b).

Soil temperatures were measured with geothermometers and air temperatures weremeasured with air thermometers. Light intensity was measured with a Li-Cor 190SBquantum sensor with a Li-Cor LI-185B photometer.

2.5. Chlorophyll a, microscopy and species composition

Soil samples were gathered by gently turning a glass tube into the desert soils to a depthof 7mm. The samples were air-dried and ground with 95% ethanol, then refrigerated in thedark at 4 1C for 24 h. Samples were centrifuged (7000 rpm, 10min) and the supernatantswere measured with spectrophotometer according to the method of Chen et al. (2002).

Species composition and identification were done by direct observation with lightmicroscopy (Nikon Y5 100). Species diversity was calculated by the dilution culturemethod as described by Tsujimura et al. (2000).

2.6. Data analysis

Data were analysed using a one-way analysis of variance (ANOVA) and the valuesshown are the average of 3–4 replicates.

3. Results

3.1. Soil properties

There were no significant differences in N, P, Ca2+ and Mg2+ contents in study sites,but significantly higher K+, biomass and organic C (po0:05) in sites 4, 5 and 7 (Table 1).

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Potassium and P contents of site 4 were significantly higher than those of other sites(po0:01).Compared with sites 1 and 2, sites 3–7 had lower light intensity and soil surface

temperature, but higher coverage; sites 3, 4 and 7 had a moderate light intensity between350 and 700 mE/m2 s(Table 2). Sand surface temperature was higher at sites 1 and 2, anddecreased rapidly at sites 2–7 after irrigation.

3.2. Growth curves under different conditions

As shown in Fig. 1A, chlorophyll a of site 4 was significantly higher than sites 3 or 5after a 10-day-inoculation (po0:05), but there was no significant difference between sites 3and 5. It was also shown that the biomass of site 6 increased steadily and reached 35 mgChla/cm2 of soil after inoculation. However, rainfalls and temperatures did not have asignificant effect on the growth of inocula at site 6 (Fig. 1A).Compared with un-inoculated area, chlorophyll a of inoculated areas at site 7 also

increased significantly and reached a maximum 10 days after inoculation (po0:01),and then gradually decreased, but a significantly higher peak appeared at 19 daysafter inoculation (po0:05; Fig. 1B). It showed that inocula grown under grass or shrubscontained more biomass than those grown on unconsolidated sand at site 7.The peak values that appeared at day 10 and 19 were just with the occurrence of rainfall

at day 7–9 and 19 (Fig. 1A and B). But there was no significant difference of chlorophyll a

between sites growing shrub and sites growing grass.

3.3. Algal community structure

Algal diversity had also changed 22 days after inoculation. At sites 2–6, the amount ofM. vaginatus accounted for more than 99%, and that of Scytonema javanicum and Nostoc

sp. was less than 1%; whereas at site 7, the amount of M. vaginatu accounted for only91%, and that of Nostoc sp., Phormidium tenue and S. javanicum were 9%.

4. Discussion

Desertification has occupied 29% landmass and expanded at a rate of 3100 km2/year inChina. Many dune-fixing methods, such as mechanical, chemical, physical and biologicalmethods have been adopted, though few are effective (Zhang et al., 2002). Our worksshowed that only 20 days were needed to form algal crust. During the process of algal

Table 2

The variations of sand surface temperature, light intensity and coverage at different sample sites

Study sites Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7

Coverage (%) 0 0 30–50 60 470 100 20–40

Light intensity (mE/m2 s) 1973 1978 392–627 380–472 425–685 436 762–985

Soil surface temperature (1C) 47.3 46.2 32.3 30.9 31.1 29.6 34.3

Soil surface temperature after

irrigation (1C)

— 24.9 22.4 21.7 22.6 21.3 23.7

Values are the average of three measurements at 13:00 on September 13. ‘‘—’’ Was shown for no irrigation.

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0 5 10 15 20

0

3

6

9

12

15

18

21

24

27

30

33

36

Chl

orop

hyll

a (u

g/cm

2 soil)

)C

hlor

ophy

ll a

(ug/

cm2 so

il))

Site 6

0 5 10 15 20 25

0

2

4

6

8

10

12

14

16

18

20

22

shrub grass sand CK

Site 5 Site 4

Site 3 Site 2 Site 1

25Inoculation days

Inoculation days

Site 7

(A)

(B)

Fig. 1. The growth curves of inocula in different sites and growth conditions. Bars indicated the standard

deviation (n ¼ 3).

L. Chen et al. / Journal of Arid Environments 67 (2006) 521–527 525

colonization, microbial diversity increased, the biomass reached 35 mgChl a/cm2 of soiland could resist the erosion of 19mm rainfall and grade 4.3 wind (data provided bythe weather bureau) 20 days after inoculation, which suggests that man-made algal crustcould accelerate the stabilization of mobile dunes and is a feasible method for fixingunconsolidated sand. Since the degree of wind erosion and cementing ability of microbioticcrusts are related to algal biomass (Hu and Liu, 2003), the factors affecting the algalgrowth were also considered.

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It was found that moderate light intensity and temperature for photosynthetic activity ofM. vaginatus were about 300–700 mE/m2 s and 20–30 1C (Chen et al., 2002). Higher lightintensity and temperature could inhibit photosynthetic activity of inocula and result in adecrease in biomass (Ong et al., 1992). Sites 3–6 contained more biomass than sites 1 or 2,which might be attributed to grass or shrubs in sites 3–6 limiting sunlight and sand surfacetemperature necessary for photosynthesis (Arino and Saiz-Jimenez, 1996). Rainfall andirrigation had a positive influence on the growth of M. vaginatus. Compared with un-irrigated sites, irrigation could decrease the sand surface temperature and provide watersource for restoring the photosynthetic activity of inoculums (Gao and Yu, 2000). Table 2and Fig. 1 showed that the algal biomass of algal crust increased significantly at day 10 and19 after inoculation. This coincided with the rainfall at day 7, 8, 9 and 19, so it was possiblethat rainfalls provided persistent cloud cover, which resulted in more favorable growthconditions: such as lower air and soil temperatures, moderate light intensity and a lowerwater evaporation rate. However, the higher biomass of site 4 might also be attributed tothe higher potassium contents for keeping their photosynthetic activity (Qiu and Gao,1999).In conclusion, man-made desert algal crust could be formed on a large scale in the field.

Rainfall and light intensity were the main impact factors in affecting the biomass of man-made algal crusts. Considering the affecting factors as above, the feasible methods foraccelerating algal crust formation are to combine cyanobacterial inoculation with theplanting of shrubs or grasses during the rainy season.

Acknowledgement

We thank Mr. Steven Gladding for the assistance with the resulting discussion. Thisresearch was supported by National Natural Science Foundation (No. 30500068 and30170112) and the foundation of the Chinese Academy of Sciences (KSCX2-SW-322).

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