岩溶生态系统中的植物

岩溶生态系统是受岩溶环境制约的生态系统，是脆弱的生态系统，缺水、少土、富钙是岩溶生态系统无机环境的基本特征，植物与岩溶环境长期的相互作用，演化出独特的岩溶植物。岩溶植物具有喜钙性、石生性、旱生性，其多样性表现为少属科、寡种属和特有种，更有岩溶生态系统中特有的洞穴弱光带、天坑植物群落。植物是生态系统的生产者，肩负着生态系统的生产力、生态服务功能的重任，退化岩溶生态系统的修复，需要根据中国岩溶生态系统发育特色，探索发展具有仿自然特色的生态产业，走出岩溶区“绿水青山就是金山银山”的道路，完善中国岩溶生态系统理论。 

Karst ecosystem and its plants

Karst ecosystem is a vulnerable ecosystem constrained by a karst environment that is characterized as being rich in calcium, short of soil resources and insufficient for water resources (less surface water and rich groundwater water). Compared with silicate rocks, carbonate rocks are soluble, rich in calcium and magnesium, but lacking silicon, iron and aluminum. Carbonate rocks averagely contain 27.30%-54.33% of CaO, 0.49%-19.66% of MgO, and 0.41%-10.53% of insoluble matter. Thus, the vulnerability of karst ecosystem is ascribed to these geological properties. With the long-term interaction between plants and karst environment, surviving plants finally evolve into unique karst plants, featuring xerophyte, calciphilia and chomophyte.CALCIPHILIA of karst plants is demonstrated by Calciphile plants only growing on substrates rich in calcium carbonate and limestone soils, and Calcicole plants growing very well in Calcareous soil, but worse in acidic soil. Tolerance, exclusion and blocking mainly contribute the adaptation of karst plants to rich calcium environment. As relatively high free carboxyl existing in the intercellular space of plants, tolerance has high cation exchange capacity. Karst plants can accommodate a high content of calcium. There are two approaches in terms of exclusion. One is to improve the calcium protease activity, such as the cytoplasm membrane Ca2+-ATPase (ATPase) activity. Exclusion can transport calcium from cytoplasm out of the cell, and then store calcuim in the cell-wall. By another approach, excess calcium is ejected out of the cell through calcium channels, calcium secretion glands and even stoma. Blocking refers to a phenomenon that karst plants immobilize excess calcium around the rhizosphere to form calcified roots and restrict the transport of excess calcium to the living bodies mentioned above.CHOMOPHYE of karst plants means there exists much more underground biomass in karst ecosystem. Results of underground biomass investigation of karst vegetation in Maolan Nature Reserve show that biomass of karst vegetation is lower than that of non-karst forest in the same latitude, and only equivalent to that of temperate forest. However, underground biomass, reaching 57.49-58.15 mg·hm-2, is not only higher than that of non-karst forests in the same latitude, but also higher than that of non-karst forests both in temperate and tropical regions, and the absolute amount is nearly twice as large as that of non-karst forests in temperate tropical regions. Limestone and dolomite are two major carbonate rocks. Limestone is more likely to dissolve to form karstic fissures and conduits which can provide greater physical space for the growth of woody plant roots. The low anti-solubility, the aptness to the well-distributed weathering, and the uniform surface soil covering of dolomite are conducive to the development of shallow root plants. Survey results of Puding county in Guizhou Province show the high woody plant coverage and strong vegetation activity, but low ecosystem productivity in the limestone-dominated area. However, herbaceous and bush vegetation coverage is high, and the vegetation activity is weak, but ecosystem productivity is high in the dolomite-dominated area. XEROSPHYTE is the property for karst plants to adapt themselves to karst drought, on account of the karst hydrogeological structure with double layers of the epikarst and underground river. Consequently, ecological water is insufficient to meet the needs of the karst plants in karst areas in the dry season. The adaptive mechanism of karst plants mainly includes ecological regulation and physiologic regulation. The regulation of ecological traits of karst plants primarily involves prolonging roots to absorb deep water from soil and rock fissure, even underground river; decreasing the diameter of ducts and enriching parenchyma in xylem to reduce moisture transpiration; decreasing stomatal index to shrink leaves, and thickening cuticles and waxy layers to lower water loss. The regulation of physiologic traits of karst plants mainly includes,(1) accumulating proline, soluble sugar and other organic osmotic regulators to regulate the osmotic potential of plasma membrane and maintain cell membrane stability. The more contents of superoxide dismutase (SOD) peroxidase (POD) and catalase (CAT) are, the more reactive oxyradicals are produced, and the lower degree of membrane lipid peroxidation is. (2) Improving the activity of carbonic anhydrase in leaves, converting intracellular bicarbonate ions into water and CO₂, supplementing water shortage in leaves and reducing intercellular CO₂ during the dry season. These methods of regulation can improve the adaptability of karst plants to drought and avoid harzards. The diversity of karst plants presents minor genera families and a small number of species genera and endemic species. For example, in Xishuangbanna, Yunnan Province, the karst terrain covers an area of 3,600 km2, accounting for 19% of the total land area. Results of the forest survey show that karst vegetation includes 153 families, 640 genera and 1,394 species of vascular plants, accounting for 77.7% of the total family, 56.1% of the genera and 37.9 of the species, respectively. In Guangxi, the karst terrain covers an area of 82,100 km2, accounting for 34.8% of the total land area. The forest survey reveals that karst vegetation includes 175 families, 662 genera and 1,500 species of vascular plants, accounting for 76.75% of the total family, 59.11% of the genera and 50.28% of the species, respectively. Karst plants growing in cave twilight zone give their increasingly weak luminous intensity. Preliminary results show their species composition of herbs (88%), shrubs (8%) and vines (4%). The most abundant families include Urticaria (73 species), Gesneriaceae (37 species), Begoniaceae (22 species), Pterophoraceae (20 species) and Pterophoraceae (20 species). The most abundant genera include Stairweeds (42 species), Begonias (22 species), Auricerns (19 species), Primula Nerneris (19 species) and Coldwater flowers (13 species). Karst plants growing in Tiankeng (big collapse doline) provide possible access to the understanding of a succession of regional plant communities. In Leye Tiankeng, 863 species of seed plants belonging to 445 genera and 137 families are found. Ratios of temperate to tropical components are 1:2.31 in families and 1:1.5 in genera inside Tiankeng. Ratios of temperate components inside to outside Tiankeng are 1:2.79 and 1:2.18 respectively, showing higer proportion temperate components inside Tiankeng. The results suggest that with global warming, tropical components of a vegetation community outside Tiankeng increase continuously, while those inside Tiankeng develop slowly. Plants are producers of ecosystem, and their importance lies in their productivity and ecological service function. In order to restore the degraded karst ecosystem, we should find a proper approach to develop eco-industries with a win-win strategy for both environment and economy, based on natural karst. We should practice the principle of "lucid waters and lush mountains are invaluable assets" in the karst area, and improve and solidify the theory of karst ecosystem in China.