Traits and economic spectrum of different-aged leaf of <i>Kandelia obovata</i> in Minjiang River estuary, China.

To elucidate the adaptive mechanisms and strategies of different-aged leaves of <i>Kandelia obovata</i> in response to resource limitations in the Minjiang River Estuary Wetland Nature Reserve, we measured 21 leaf functional traits from current-year and previous-year leaves, and compared the traits between the two leaf types to construct leaf economic spectrum. The results showed that the fresh and dry weight of <i>K. obovata</i> in the previous-year leaves was 2.3 times of current-year leaves. There was a significant difference in nitrogen (N) content, with values of 20.59 mg·g^-1 for current-year leaves and 15.88 mg·g^-1 for previous-year leaves, as well as in phosphorus (P) content, with values of 1.40 and 1.06 mg·g^-1, respectively. There was a significant positive correlation between N and P content. The net photosynthetic rate differed significantly, with values of 7.53 and 4.68 μmol·m^-2·s^-1 for current-year and previous-year leaves, respectively. There was a significant difference in stomatal conductance (0.16 vs. 0.15 mol·m^-2·s^-1). The economic spectrum indicated that current-year leaves possessed traits such as thin structure, rapid extension, high photosynthetic efficiency, low leaf tissue density, and higher N and P content, reflecting a strategy of rapid investment and return. In contrast, previous-year leaves exhibited thicker structure, slower extension, lower photosynthetic efficiency, higher leaf tissue density, and lower N and P content, adopting a more conservative and slow-investment growth strategy. These findings suggested that <i>K. obovata</i> employed two distinct growth strategies, adjusting leaf structure and physiological properties to enhance its survival in stressed environments.