Zou Qiao Yun, Chen Hong Song, Ma Xing Yu, Nie Yun Peng
Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha 410125, China.
Huanjiang Observation and Research Station for Karst Ecosystems, Chinese Academy of Sciences, Huanjiang 547100, Guangxi, China.
Ying Yong Sheng Tai Xue Bao. 2019 Mar;30(3):759-767. doi: 10.13287/j.1001-9332.201903.012.
Although lack of soil coverage, rock outcrops with developed fractures in karst region can maintain water consumption of plants with different life forms. Water sources for plants on these habi-tats are unclear. Isolated rocky outcrop with relatively simple sources of water was selected for this study. We focused on typical plant species that still thrived after excluding rainfall (removing the water supply to the shallow water) over one year, compared with the same plant species living without rain shelter (always receiving rainfall supplies). Water sources of three representative tree species (Radermachera sinica, Celtis biondii, and Pittosporum tonkinense) were analyzed by using stable isotope techniques and combining with the measurement of plant water potential. The results showed that all the three species depended on deep water sources with similar isotopic values to spring water under rain-sheltered condition, during the rainy season, which explained why plants could still grow normally after rainfall-exclusion over one year. The predawn water potential of R. sinica and P. tonkinense under rain-sheltered condition was not significantly different from those living in natural conditions, which indicated both species were not under water stress. The predawn water potential of C. biondii under rain-sheltered condition was significantly lower than individuals living in natural conditions, which indicated it was under water stress. Under natural condition, water isotope values of stems of all the three species were significantly lower than that under rain-sheltered condition and were within the range of fluctuation of recent rainwater isotope values, indicating that these plants relied on shallow water sources that dominated by recent rainfall. Under both rain-sheltered and natural conditions, there was no obvious difference between the predawn water potential and the midday water potential of P. tonkinense, showing a conservative water use strategy. The midday water potential of other two species was significantly lower than the predawn water potential, showing a profligate/opportunistic water use strategy. Our results indicated that the ability to utilize shallow and deep water sources is key for the plants growing on the habitat of Karst rock outcrops where they could adapt different water environments and maintain diversified water use strategies under the condition with no soil coverage.
尽管岩溶地区缺乏土壤覆盖，但发育有裂隙的岩石露头能够维持不同生活型植物的水分消耗。这些生境中植物的水源尚不清楚。本研究选择了水源相对单一的孤立岩石露头。我们重点研究了在排除降雨（切断浅层水源供应）一年后仍能茁壮成长的典型植物物种，并与无遮雨设施（始终接受降雨供应）生长的同种植物进行比较。运用稳定同位素技术并结合植物水势测定，分析了三种代表性树种（菜豆树、毛叶朴和东京海桐）的水源。结果表明，在雨季有遮雨条件下，这三种树种均依赖与泉水同位素值相似的深层水源，这解释了为何在排除降雨一年后植物仍能正常生长。有遮雨条件下菜豆树和东京海桐的黎明前水势与自然条件下的差异不显著，这表明这两个物种均未受到水分胁迫。有遮雨条件下毛叶朴的黎明前水势显著低于自然条件下的个体，这表明其受到了水分胁迫。在自然条件下，这三种树种树干的水同位素值均显著低于有遮雨条件下的，且处于近期雨水同位素值的波动范围内，表明这些植物依赖以近期降雨为主的浅层水源。在有遮雨和自然条件下，东京海桐的黎明前水势和中午水势均无明显差异，表现出保守的水分利用策略。其他两个物种的中午水势显著低于黎明前水势，表现出奢侈/机会主义的水分利用策略。我们的结果表明，在岩溶岩石露头生境中生长的植物，其利用浅层和深层水源的能力是关键，在无土壤覆盖的条件下，它们能够适应不同的水环境并维持多样化的水分利用策略。
