Study On Ecological Adaptation Of Saxicolous Mosses To Drought Environment Of The Karst Rock Desertification In Guizhou

Guizhou Province is located in the center of the karst area in East Asia. The total karst area accounts for73.8%of the province, hence there are large areas of karst in China. Karst rocky desertification is one major type in desertification, which is under irrational human impact on the vulnerable eco-geo-environment. In this process, the vulnerable eco-geo-environment serves as its base, violent human impaction as its driving force, devolution of bearing capability of the land is the essence, and the appearing of landscape similar to desert is the sign. Rocky desertification has threatened seriously the ecological safety of the Yangtze River, Pearl River Basin. However, it is very difficult to handle the environmental problems in karst regions and hard to recover and governance if once deteriorated. Therefore, rock desertification has been severely restricted the sustained development in southwest China. Meanwhile, theoretical researches of Rocky Desertification has lagged far behind comprehensive improvement of karst areas in China. This leads to the blindness of controlling rocky desertification and the uncertainty to local ecological environment. It is very important for the recovery of the degradation of the karst ecosystem and reconstruction for the in-depth study about moss community succession law and adaptability. Lack of such researches is extremely detrimental to reveal mechanism of community succession and development of specific ecological management measures. In this study, Barbula fallax Hedw. and Erythrodontium julaceum (Schwaegr.) Par. the saxicolous mosses grow in the regions of rock desertification in Guizhou were determined via a combination of field investigation and laboratory experiments. Furthermore, of Bryum argenteum Hedw., a widely distributed to soil mosses, as the reference was also investigated, especially in the physiological ecology of rocky desertification in drought environments adaptive mechanisms. These results provide the theoretical proofs for the study of karst plant on adapt mechanisms and rocky desertification environment governance. These results in detail were shown as follows:(1) Sampling methods are adopted to investigate30sample plot150small quadrat in the aquatic environment of intense rocky desertification area and record saxicolous mosses9families and25genera and55species. Dominant families are Pottiaceae and Bryaceae, a total of17genera,41species. Dominant generas are Campyulopus, Gymnostomum, Barbula, Weisia, Entodon, a total of6families and30kinds. The flora of saxicolous mosses have10ingredients are mainly distributed in tropical Asia, and unique to China and East Asian. Life forms are chiefly Turfs and Wefts, the total number of species in96.4%, less Mats. Because Karst rocky desertification area rocks are mostly carbonate rocks, barren environment of the drought and soil nutrition results in an absolute advantage of Bryo-xero-petrophytia. The saxicolous mosses drought tolerance in the region, therefore, is of good growth and reproduction, and there gradually accumulates in the rock surface with a thin layer. Thus, it improves the local rock surface temperature and humidity environment, and ranks to create, a certain extent, the conditions for the colonization of other plants.(2)Through paraffin wax section and microscopic observation, the study of comparative anatomy and morphology are as for12saxicolous mosses stems and leaves in different environments of karst rock desertification. The results showed that:1) There is a significant difference among different types of saxicolous mosses such as the absence or presence of hydrome cells, the numbers of cell layer and the density of the costae, leaf cell layers and cell density, the numbers of laminal cell layer, and some of them have attachment on surface, etc. The saxicolous mosses under dry conditions often have thickened laminal cell-walls on the surfaces, Erythrodontium julaceum (Schwaegr) Par has no costa structure, while the remaining11kinds have obvious costa structure. As for all types of Bryaceae have different hair points of prominent forms. The absence of costa reflects on the different water absorption and modes of transport; except the Bryum knowltonii Barnes and Bryum argenteum Hedw, there is no apparent Hydrome chief cell. The Hydrome chief cell with saxicolous mosses of the costa structure is more developed; different saxicolous mosses class in the costa thickness and cell density between leaf thickness and cell density exists a significant correlation, but the costa is not significantly related to the thickness of layers; attachment on surface have varied kinds of different shape and number of papillae. Atrichum undulatum (Hedw.) P. Beauv. has lamellae structure and the existence of these attachment on surface has positive adaptation to the dry conditions.2) The stems of12saxicolous mosses species were of different types among stem shape, cell shape, the layers numbers of epidermisand the thickness, the differentiation and layers of cortex, the existence or inexistence and the scale of the mainaxis of stems varied highly. The tightly arrayed epidermis in their stem, the distinctly thickened cellwalls in epidermis were found in xeric saxicolous mosses, the majority of one cell-layer. More types are outward protruding extension and form cells glands; only Anoectangium thomsonii Mitt. and Barbula fallax has inner cortex or external cortex as well as the thickened cell walls of external cortex. The remaining10species of mosses have no differentiation of the inner and external cortex. The Bryum argenteum, Atrichum undulatum and Barbula fallax with the mainaxis of differentiation, the differentiation of the remaining8species saxicolous mosses is not very obvious. However, the mainaxis of Weisin semipallida C. Muell. has not differentiation, which indicates that the Karst Areas of saxicolous mosses on water uptake and conduction are the ectohydric based and mixohydric supplemented. Therefore, the anatomical structure of the saxicolous mosses leaves and stems in the xerophytic environment has important ecological significance of adaptation.(3) In this study, a theoretical foundation for the interest of recovering and administering the environments of rock-desertification ecology was provided by compared with the adaptability to habitat heterogeneity in rocky desertification environments among Eiythrodontium julaceum, Barbula fallax and Bryum argenteum. The results show that, firstly, E. julaceum and B. fallax are more than B. argenteum in the capacity of holding maximal water and also in the rate of preserving natural water. Secondly, the water-uptaking processes of the three mosses are outer water uptake and inner water uptake. Although the three species had the same dynamic curve of the S type saturated water content, they had considerably different dynamic properties. Little difference was found in the amount of water saturated by E. julaceum and B. fallax. However, the amount of saturated water in E. julaceum and B. fallax were about2.5times of that in the silver B. Argenteum. The amount of saturated water and the maximal rates of water uptake, inner as well as outer water uptake in E. julaceum were3.41,2.52and3.02times than those of B. argenteum, respectively. Similar results were also found in B. fallax. Furthermore, the stem cross-section structure of three mosses showed that B. argenteum and B. fallax had the obvious conducting strand and belonged to endohydric mosses. In contrast, E. julaceum owned no conducting strand and belonged to the part of the ectohydric. Strictly, the structure of endohydric and ectohydric in mosses is not the decisive factor of water absorption capability, which has close relationship with many aspects including growth form, type of capillary system and microstructure of stem and leaf positive correlations.(4)-2Mpa PEG-6000is adopted to simulate drought treatment on typical karst rocky desertification Erythrodontium julaceum and Barbula fallax of saxicolous mosses, and native Bryum argenteum, and the study touches on changes of four kinds of osmolytes in different time to deal with the same intensity material. With the increase of the stress time, the soluble sugar, reducing sugar and free proline is rising, but the accumulation of free proline is weaker; after rewatering three kinds of substances decreased in varying degrees, but it is higher than the control. Soluble protein shows a first decreased and then increased, and then a downward trend. In addition to the Erythrodontium julaceum is slightly higher than the control Barbula fallax, Bryum argenteum content is lower than the control; after rewatering, the content of the three kinds of mosses in the control decreased in varying degrees. Based on the four indicators to evaluate the drought tolerance of the three kinds of mosses, osmotic adjustment ability on the type of ear branches is like: Erythrodontium julaceum> Barbula fallax> Bryum argenteum, while the contribution rate of different osmolytes is soluble sugar> soluble protein> reducing sugar> proline.(5) The research focuses on the antioxidant protection mechanism of three species of saxicolous mosses by PEG-6000simulated drought stress and rewatering conditions. In the early period, the contents of three kinds of mosses superoxide dismutase dismutase (SOD), catalase (CAT), peroxidase (POD) activity and carotenoids (Car) content increased, and at late declined. This shows that the mosses have an adaptation-injury process. The increasing stress in the initial period reacts to resist drought, but later to reduce self-inflicted injury. When osmotic stress intensifies, Biyum argenteum and Barbula fallax superoxide anion (O2-), malondialdehyde (MDA) show the increase-lower-slightly increasing trend. However, the Erythrodontium julaceum performs increase-reduce trend. As for the relative permeability of membrane, three kinds of mosses were shown a trend of the S-curve and increased in varying degrees. There is a slight decline after24hours. Therefore, the increases in drought stress early O2-and other reactive oxygen species (ROS) induce enzymatic and non-enzymatic scavenging system to start to clear ROS. With the aggravation of stress, ROS exceeds the scavenging capacity of the antioxidant enzyme system so as to injury plant. The rewatering of three kinds of moss can restore physical vitality, and it instructs that physiological dormancy in later period can help to escape the very intensity of the response from drought stress because of the reaction phenomenon adapted to drought stress phase.(6) The study of drought and rewatering on the Barbula fallax, Erythrodontium julaceum, Bryum argenteum chlorophyll content and fluorescence characteristics. The results showed that under the increase of drought stress, total chlorophyll content was the first rose and then dropped, and then the tendency to increase. F0and qN of three kinds of mosses was increased while the Fm, Fv/Fm, Yield, ETR and qP are decline with drought stress. Fluorescence parameters after rewatering can be restored to normal levels in mild to moderate stress, and severe stress is more difficult to return to the control level. Analysis of the relationship among O2-and membrane permeability fluorescence quenching shows that O2-and membrane permeability with stress increased accompany by qP coefficient lower and qN increased in the coefficient. It confirms that the activity of enzymes of antioxidant defense system in the stress process relates to the changes of anti-oxidation material content. The production of ROS is beyond the plant clearance resulting in the vivo metabolic disorder. Water use efficiency (WUE) decreased continuously with the increased stress in WUE. The most drought tolerance is the Barbula fallax>Erythrodontium julaceum>Bryum argenteum.In summary, the saxicolous mosses grown in the karst dry enviroment have not only certain features and morphology of adaptations from the distribution of moss species, but also adapt to changes of the physiological and ecological mechanisms in karst environments by adjusting osmotic and improving the ability of the antioxidant enzyme system to maintain the stability of photosynthetic apparatus.