科研之友
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摘要
Through the systematic investigation of nitrogen isotope composition (delta N-15) in modern plants in Dongling Mountain in Beijing, the characteristics of delta N-15 in plants, the differences of delta N-15 among plants with different functional types, and the altitudinal trends of plant delta N-15 values revealed the environmental effects on delta N-15. Our results are: (1) the values of delta N-15 of plants in Dongling Mountain range between -8.0% and 14.0%, with an average value of -1.03%; (2) delta N-15 values are variant among different plant functional types. Generally, the delta N-15 of shrubs are smaller than that of trees, and larger than that of herbaceous plants. The main reason may be the selective absorption of variant nitrogen resource with different delta N-15 values in soil; (3) there is a second-order polynomials relationship between the altitudes and the average delta N-15 values of plants, which shows a negative and positive correlation below and above 1350 m a.s.l., respectively. This indicates that the precipitation is a main controlling factor of plant N-15 fractionation for the former, and the temperature for the latter; (4) three different, i.e., positive, negative, and no significant, correlations are performed between delta N-15 of individual species and altitudes. This may be related to different inherited characteristics and the process of nitrogen metabolize; and (5) variant altitudinal trends of plant delta N-15 are associated with different N-15 composition of soil at different altitude, for which the key influencing factors are the changing temperature and precipitation with altitude rather than nitrogen content in leaf.
