| Since the implementation of Grain for Green ecological project, biological soil crusts(biocrusts) developed wildly in the revegetated grasslands in hilly Loess Plateau region. Moss-dominated crusts are the advanced stage of succession of biocrusts, and they play several important roles such as accelerating the formation of soils, improving soil physical and chemical properties, increasing the anti-erobility of soil and reducing the loss of soil and water. Ecological adaptability is the ability of organisms to adapt to the ecological environment, as well as the results of regulating of organisms under the condition of biological and environmental factors interact. Studies on the ecological adaptability and the influence of artificial cultivation on desiccation-tolerance moss may benefit the species selection according to the ecological environment condtion for moss culture. Four dominant moss species in the community of biocrusts in hilly Loess Plateau region were chosen as objects in this study. They were Didymodon vinealis(Brid.) Zand., Didymodon tectorum(C. Mull.) Saito, Barbula unguiculata Hedw. and Bryum argenteum Hedw. We have measured and observed the diversity and distribution characteristics of biocrustal moss species under different site conditions in field; analyzed the characteristics of mosses in different the spatial distribution conditions; measured the morphological and anatomical structure of the four moss species, objectives of the study was to analyze the relationship between environmental conditions and mosses phenotypic adaptability. Then, the cultured and wild growing Didymodon vinealis were sampled and treated with dehydration and rehydration, high temperature(35 oC) and high light intensity so as to explore the impact of cultivation on ecological adaptability of desiccation-tolerant mosses. Results of the study as bellow:(1) Moss species that investigated in the study showed obviouse difference in ecological adaptability. A distinct heterogenicity was detected in the spatial distribution pattern of biocrusts in the study region.In semi-sunny slope, the fragment index of biocrusts ranged from 0.22 to 0.34. The coverage of moss crusts was 20%, which was lower than that on the shady slopes. The plant density index on the shady slopes was bigger than that on the semi-sunny slope. The lower part of the shady slope was better for the developing of moss-dominant crusts. Moss crust coverage on shady slope was higher than that on the semi-sunny slope. The vegetation canopy cover has significantly influence on spatial niche, northwest direction of plants is more suitable for the development of moss crust which has better on the temperature and light conditions. The dominated species of moss crusts was Didymodon vinealisand Didymodon tectorum in semi-sunny slope, while in shady slope was Barbula unguiculata.(2) Didymodon vinealis 、 Didymodon tectorum 、 Barbula unguiculata and Bryum argenteum, the four dominated species of moss crusts showed significant difference in morphological and anatomical structure.The shoot height of D. vinealis was 6.1 mm, stem diameter was 298.6 μm, midribs width was 65.5 μm, leaf width was 590.9 μm and blade thickness was 14.8 μm which made it has a coarse stem and leaves, thus, desiccation tolerance of D. vinealis was stronger. Also, it was easy to adapt to environmental moisture variability. D. tectorum did not show significant advantages in its stem and leaves structure. The leaf length(3.2 mm) and basal leaf cells(191.2 μm2) of B. unguiculata were significantly strong and contain a much more chloroplasts, their midribs were showed in sharp “v” forms, this kind of morphological structures were closely related to their water harvesting. In B. argenteum, the cortex cell area was 987.8 μm2, and single cortex cell were accounts for approximately 3.1% of stem transverse-sectional area, which made it has strong water retention and carrying capacity, the leaf hair(274 μm) were long and the upper leaf cells and leaf hair of this species were transparent, which endows it to grow in the conditions with periodical drought stress and resist light radiation, had a fairly wide ecological adaptability.(3) Artificial cultivation significantly affected the ecological adaptability of desiccation-tolerance moss, compared with the wild moss, artificial moss has weak resistance to desiccation and rehydration, poor adaptability to high temperature and high light radiation. When the moss under stress treatments, their chlorophyll content was reduced and osmotic potential was imbalances, the weak self-protection and restoration ability cause damaged to the integrity and stability of the membrane system.With the extension of desiccation stress time, activities of protective enzymes, malondialdehyde content and osmoregulation substance content of artificial moss continuously increased. The chlorophyll content was declined by 36% at the end of drought stress period., The activities of malondialdehyde(MDA), superoxide dismutase(SOD), catalase(CAT) increased by 108.62%, 72%, 78%, respectively. After rehydration, relative conductivity, soluble sugar content, SOD and Peroxidase(POD) was 11 times, 6.9 times and 5 times as high as that wild gametophyte, respectively. The physiological activity of cultivate gametophyte under the high temperature stress were highly consistent with the desiccation and rehydration stress treatment. At the end of temperature stress period, compared with constant watering treatment, the chlorophyll content has the 12.7% decline, the activities of relative conductivity, MDA content and soluble sugar content increased by 26.9%, 32.1%, 18.2%, CAT and POD was 4.5times, 2.3 times as high as that 8 hours treatment period, respectively. With the extension of high temperature stress time, activities of chlorophyll content, protective enzymes, MDA content and osmoregulation substance content of wild gametophyte were maintained at a steady level. Under the treatments during light environment, with the extension of high lights radiation time, compared with treatment(CK),the activities of relative conductivity, MDA content and soluble sugar content was as high as 1.9 times, 2.4 times and 2.5 times, with the extension of light intensity, compared with control treatment(CK),the activities of relative conductivity, MDA content, soluble sugar content and POD was increased by 1.8 times, 2.1 times, 2.3 times and 1.7 times, respectively.(4) The ecological adaptability of desiccation-tolerance moss was degraded because artificial cultivation, which suggested that hardening-seedling to improve the ecological adaptability is necessary before the artificial moss-crusts to be grown in the field conditions. |
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