会仙喀斯特湿地三种典型植物叶片碳同位素(δ13C)特征及其指示意义

Characteristics and significance of δ13C of three typical aquatic plants in the Huixian karst wetland, Guilin

关键词:  喀斯特湿地, 水生植物, 营养元素, 稳定碳同位素(δ¹³C), 碳汇

Key words:  karst wetland, aquatic macrophytes, nutrient elements, stable carbon isotopic δ¹³C, carbon sink

摘要:

为探讨会仙喀斯特湿地不同生长环境下植物叶片碳(C)、氮(N)、磷(P)、稳定碳同位素(δ¹³C)特征及其生态学指示意义,该文以挺水植物芦苇、浮水植物水葫芦和沉水植物金鱼藻为研究对象,分析了三种典型不同生活型植物叶片的δ¹³ C特征及种间和微生境的差异,并基于植物碳同位素与碳酸酐酶显著正相关的二端元模型,估算了植物利用光合作用固定的碳酸氢根离子(HCO^-₃)的碳量。结果表明:(1)三种植物叶片δ¹³C的变化范围为-28.47‰～-21.69‰,平均值为-24.83‰,不同生活型植物间δ¹³C存在差异,金鱼藻>水葫芦>芦苇。(2)植物δ¹³C值与叶片C、N和P元素含量间呈显著正相关,与C/N、C/P和N/P呈显著负相关关系,与底泥的有机质、速效氮、总氮、速效磷和总磷含量呈显著正相关。(3)会仙喀斯特湿地三种不同生活型植物叶片N/P 平均值为10.34,表现出植物受N、P共同影响的特征。(4)δ¹³C的变化特征,揭示了三种水生植物可能通过增加磷利用效率来促进低水分利用率环境下的碳的合成,通过提高植物水分利用效率的策略来代偿较低的氮素利用效率。(5)芦苇光合作用固定HCO^-₃碳量为159.60 t·a^-1·km^-2,水葫芦为10.80 t·a^-1·km^-2,金鱼藻为9.24 t·a^-1·km^-2,平均值为59.88 t·a^-1·km^-2。会仙喀斯特湿地植物的不同生活型、光合作用途径和生长微环境,是影响叶片δ¹³C变化的主要因素。

Abstract:

In order to understand characteristics and significance of carbon(C), nitrogen(N), phosphorus(P)and stable carbon isotope composition(δ¹³C)in plant leaves of three typical aquatic plants under different growth environments, three life forms of aquatic plants including emerging plant(Phragmites australis), emersion plant(Eichhornia crassipes) and submerged plant(Ceratophyllum demersumin) of the Huixian karst wetland were selected as study objects. The differences of carbon isotope compositions of interspecies and different habitat conditions were studied, and the percentage of HCO^-₃ uptaken from water by aquatic photosynthesis was also estimated using the double-meta model. The results were as follows:(1)The foliar δ¹³C of three diffirent plant life forms ranged from -28.47‰～-21.69‰ with an average of -24.83‰. There were significant differences among species, and the sequence of relative value was Ceratophyllum demersum>Eichhornia crassipes>Phragmites australis, and among the three types of plants,Phragmites australis and Ceratophyllum demersum show the lowest and highest δ¹³ C, respectively.(2)For three types of halophytes,δ¹³C showed significantly positive correlations with foliar C, N and P. The δ¹³C was also positively correlated with the contents of organic matter, available nitrogen, total nitrogen, available phosphorus and total phosphorus of sediment. All types of halophytes showed a negative correlation among δ¹³C, C/N, N/P and C/P.(3)The foliar N/P ratio of halophytes was 10.34, indicating a co-limitation by N and P for halophyte growth in the Huixian karst wetland.(4)These results suggested that three halophytes were adapted to environment through a high water use efficiency at the expense of decreased nitrogen use efficiency, and might improve C sequestration by increasing phosphorus use efficiency in the habitat of low water availability.(5)The value of HCO^-₃ carbon sequestration by photosynhesis was 159.60 t·a^-1·km^-2 for Phragmites australis, 10.80 t·a^-1·km^-2 for Eichhornia crassipes, 9.24 t·a^-1·km^-2 for Ceratophyllum demersum, with a mean value of 59.88 t·a^-1·km^-2. Different plant life forms, pathways of carbon fixation in photosynthesis and micro-environment were the important factors on affecting plant foliar δ¹³C in the Huixian karst wetland.