Acta Geographica Sinica ›› 1993, Vol. 48 ›› Issue (5): 437-446.doi: 10.11821/xb199305007

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ON LICHEN KARST EROSION—A MICROMORPHOLOGICAL APPROACH

Zhang Jie   

  1. Department of Geo and Ocean Sciences, Nanjing University, Nanjing 210008
  • Online:1993-09-15 Published:1993-09-15

Abstract: Calcarous lichen is a very common biokarst erosional agent. Lichens on limestone sculpture relicts may be the significant destroyers. Although there are some papers on lichen erosion of calcarous rocks,it seems that there is still a lack of work on the relation between erosional forms and lichen tissues. The forms of Lichen erosion on karst rocks are mainly at micro scale. 1n order to collect sam-ples,I did field work on the limestone-built Rome arena in Pula,the limestone bedrock in the karst valley in Plitvice and the limestone karren in Postojna Pojie,former Yugoslavia in 1989. I also did some field work in China ,included Nanjing and Yixing in Jiangsu Province,the Stone Forest of Yongan in Fulian Province.Jiuzhaigou District in Sichuan Province and the limestone hillside in Tibet. From these areas,I collected the lichen erosion samples of limestone under various climatic conditions, including Medeteranean , Northern and Mid-humid Subtropic, and high-altitu- de and semi-arid climatic environments. According to the geometric feature of lichen erosional re- lieves found in research areas,I classified them into dotted,linear,and patched types. There are four basic lichen karst erosional forms named as pinprick , microgroove , ultra borehole and patched etosional nit and related micro-terrace. Pin-prick is a kind of very common microrelieves on the lichen covered limestone. It is a pin- head hole in a scale of 10-4一10-3m,which is bored by lichen fruiting body. There are two types of substrate surface among pinpricks. One is smooth surface which lacks organistns,and another is greyish in colour because of the covering of chasmolithic algae. Section observation under SEM shows that the wall of pinprick is bored by mycobiont hyphae,especial at the bottom of pinprick. In the substrate beneath lichen thallus,it is easy to find some embryonic fruiting bodies,which are composed of weaved micoboint hyphea. They were formed as the result of the gethering of boring hyphea. It showed the genetic roles played by mycobiont boring in the formation of pinprick. Lichen erosional microgrooves are zigzag linear erosional relieves with a width of about 0. 2mm. They are normally ocupied by dark oranic matter and micobiont hyphae. With SEM ob- servation,it shows that the prothallus or hypothalus may be the genetic agent for their formation. As we know ,there are dark edges around lichen thallus named as prothallus or hypothallus. They are composed of densely gethered mycobiont hyphae on which crustose lichen thallus develop. While two or more communities of lichen thallus gethered,the mycobiont hyphae will be strengt- hened. Under SEM observation,Some ultral erosional relieves on the substrate beneath lichen thallus can be observed,including ultra borehole and solutionsal concaved pits. Mycobiont borehole is a kind of ultral endolithic erosional relieves of lichen. Mycobiont hyphea can penetrate calcite crystals. The walls of boreholes can be both smooth and rough,de- pending on the kinds of substrates. Patched erosional pits on the lichen covered limestone surface are also common. Their forma- tion is due to the lichen thallus even effect on the limestone substrate. The edge of patched pits of- ten resembles relict microterrace. Patched erosional pits are greyish with hand specimen. Mechanisms of lichen karst erosion can basically be classified into three groups,i. e. chemi- cal,physical and biological ones. The chemical processe is the essential one. A compound biological process is composed of one or both of the former two processes. Chemical erosion,i. e. ,lichen affected solution on limestone substrate can be observed under SEM. There are both epilithic and endolithic micro solutional features,including at least three types:1)Boreholes formed by fungal hyphae and algal cells;2)Micro etched pyramids on the surf- ace of substrate which is directly touched by lichen thallus;3)Concaved solutional pits on calcite spar of limestone surface beneath lichen thallus. There are two possible chemical processes related to lichen secreted substance (lichenic acids and j or other organic acids ). Mechanical processes of lichen erosion can cause the calcite spar coming off. Micro-fissues and boreholes formed by lichen may benifit the mechanical weathering of limestone substrate. Crustosae endolithic lichen is the one that part of it may grow in the substrate. While the endolith- is part of crustose lichen thallus grows,it may cause the top layer of substrate limestone peeled off. Biological process is a synthetic process influenced by the lichen physiological processes. Pinpricks and micro-grooves are related to certain lichen tissues. They were formed during the processes of lichen growth or reproduction. Respiration of lichen thallus during the night may produce CO2 which is a significant erosional agent. The CO2 exchange of lichen thallus is related to the water content of lichen thallus so it seems that the water content of lichen thallus may further effect on the solution process. To conclude ,lichen karst erosion is a significant biokarst process which exist under various climatic conditions. There are epi-and endolithic lichen karst erosional relieves in micro scale in-eluding pinpricks,microgroovs,ultral boreholes and the patched pits and the related micro-terrace. Lichen karst erosional relieves may related to certain special tissues of lichen. There are three kinds of mechanisms of lichen karst erosion,i. e.,chemical,physical and biological ones. The chemical processes is the basic process. Micromorphology of lichen karst erosion may indicate the special genetic process of itself.

Key words: Lichen, Biokarst, Katst erosion, Micromorphology