Comparative Study Of Reproduction Growth And Physiological Characteristics Of Three Kinds Of Dominant Mosses On The Soil Microbiotic Crusts In The Sandy Land And The Loess Hilly Region

Bryum dichotomum Dicks., Bryum argenteum Hedw. and Didymodon vinealis (Brid.) Zander. are dominant species of mosses biotic crusts in the Sandy land and the loess hilly region. In the article, the reproduction, growth, photosynthesis and respiration on ecological adaptation are comparatively studied by the method of field investigations and laboratory test, all the results as followed:1. Through the field investigation, water conditions getting better are found according to the order of arrangement:artificial caragana intermedia, Popunus simonii, Platycladus orientalis, Pinus tabulaeformis. The relative cover of Bryum dichotomum and Bryum argenteum is gradually reducing, while Didymodon vinealis is opposite. Species composition of the thinnest crust changes from Bryum dichotomum and Bryum argenteum to Bryum dichotonum, Bryum argenteum and Didymodon vinealis to Didymodon vinealis and Bryum dichotomum.The whole height increased significantly on Didymodon vinealis and Bryum dichotomum. Under artificial Pinus tabulae-formis, reproduction of Bryum argenteum has been restricted. The thickness crusts of Bryum dichotomum and Didymodon vinealis appear in artificial Popunus simonii and artificial Platycladus orientalis. The largest density of Bryum dichotomum appears in artificial caragana intermedia with 356 per square centimetre. Bryum argenteum's largest density appears in artificial Platycladus orientalis with 400 per square centimetre. Didymodon vinealis' largest density appears in artificial Popunus simonii with 236 per square centimetre.Water condition and dustfall have played an important role in crust thickening and density of population increasing. Uunder artificial Platycladus orientalis and Pinus tabulaeformis individual elongation growth is more and population density is lower to some extent. Mosses can adapt to various vegetation micro-habitat and form different the thickness and development stages of moss crust. Algae supplys foundation for the settlement of mosses. There are significant correlation among height, relative coverage and density of every species. However, population characteristics are negative correlation between different populations. With increasing of various groups density, settlement evoluted from multipopulation of community to single population gradually which can adapt to micro-habitats comprehensive conditions.2. Laboratory propagation experiments show that time on Bryum dichoto-mum and Bryum argenteum are obveriously shortter than Didymodon vinealis on germination and achievement of initial seeding plants in most soils. That is a reason why Bryum dichotomum and Bryum argenteum can germinate and settle down in artificial caragana intermedia dry-habitat and become the dominant species. The time of mosses'germination and reaching the initial number plant is shorter on migratory dunes and the deep soil of loessial soils, wheras time is obviously prolonged on chernozem mosses. Population growth accorded with the Logistic equation on three mosses. There were significant correlation between K value of population saturation and sample density. Population density are significantly higher than other soils, such as:Bryum dichotomum on chestnut soil and chernozem soil, Bryum argenteum on artifical loessal soil, semi-fixed sandy soil and migratory dunes, Didymodon vinealis on chestnut soil, deep loessal soil and brown caliche soil. All the above shows that Bryum dichotomum can adapt to the soil which contains more clay particle, more organic matter and in well water retention. Bryum argenteum is more suitable for the soil which contents increasing coarse grained content and with strong permeability on the surface soil. Didymodon vinealis' reproductive requirements on soils is smilar to Bryum dichotomum, but high content of organic matter has serious effects on its propagtion process. Morphology difference are significant among three mosses.The individuals of Bryum dichotomum and Didymodon vinealis which grow on the soils with high population density own large plant height and leaf distance. The individuals of Bryum argenteum in the high population density on some soils shows clearly decreased on plant height and distance between neighboring leaves. 3. Diurnal changes on photosynthesis research presents double peak curve on net photosynthetic rate of three mosses. Net photosynthetic of Bryum dichotomum is seriously affected by photosynthetically active radiation, while Didymodon vinealis better. Non-photochemical quenching of chlorophyⅡfluorescence parameters coefficient value is rendered as"∧", the other para-merers are opposite. Parameters changes conclud that the bility on endurance light intensity of Bryum argenteum is strong, followed by Didymodon vinealis and Bryum dichotomum. In the process of natural lossing water, Didymodon vinealis' ability is strongger than Bryum argentum and Bryum dichotomum on keeping water content of cells.The most suitable photosynthetic water content in mosses are:Bryum dichotomum 82.14%-87.10%,Bryum argenteum 80.04%-83.19% and Didymodon vinealis 85.90%-89.19%. During the process of lossing water, changes on chlorophyⅡfluorescence parameters indicated that ability on drought resistance of Bryum dichotomum is relatively very poor, Bryum argenteum and Didymodon vinealis are strongger. Light compensation point of Bryum dichotomum is minimum,17.902μmol·m-2·s-1 and net photosy-nthetic rate is the largest,51.290 molCO2·kg-1s-1.That is probable an important reason of why Bryum dichotomum can grow in the dark forest land. Organic matter accumulated better and propagation growth faster on Bryum dichotomum. All this results to its natural distribution wider than Bryum argen-teum and Didymodon vinealis. Net photosynthetic rate of Bryum argenteum is minimum,20.930μmolCO2·kg-1s-1, so as to its plants are small. Light satu-ration point of Didymodon vinealis is the largest,436.364μmol·m-2·s-1 with highest individual under the same natural conditions. During a day, respiration rate of Bryum dichotomum is larger than the others over all. Effect of drsication and rehydration on Bryum dichotomum is the biggest (7.55μl O2·g-1·h-1) while Didymodon vinealis is the lowest (13.12μlO2·g-1·h-1)and the changes process keeps consistent with net photosynthetic rate change.These study has provided important evidences of reproduction, growth and physiology for revealing the mechanism of formation and maintenance of moss crust distributed in the sandy land and the loess hilly region.