Abstract:

【Objective】The objective of this study is to investigate the nitrogen (N) and phosphorus (P) allocation patterns in the above- and below-ground organs of three different tree species in northeast China, namely Populus davidiana, Fraxinus mandshurica and Taxus cuspidata, and to provide theoretical insights into the trade-offs and allocation strategies of nutrient distribution among tree species.【Method】Mature individuals of P. davidiana, F. mandshurica and T. cuspidata were selected as research subjects. The N and P contents in aboveground organs, i.e., leaves, twigs and belowground organs, i.e., coarse roots, fine roots, were analyzed and the allocation ratios of N and P contents in the leaves, twigs and roots were calculated. Standardized major axis regressions were employed to examine the relationships of N and P elements between aboveground (belowground) organs of three tree species and the bidirectional nutrient transport of the same elements between aboveground and belowground organs.【Result】(1)The N and P contents in the leaves of P. davidiana and F. mandshurica were similar. However, the N and P contents in the leaves of these two species were significantly higher and lower, respectively, compared to T. cuspidata (P<0.05). The twigs of T. cuspidata exhibited the highest N and P contents, while F. mandshurica had the highest P content in coarse roots and N and P contents in fine roots. The N content in coarse roots was similar among the three species. (2)The ratios of N and P contents in leaves to twigs and leaves to coarse roots were the highest in F. mandshurica and P. davidiana, respectively, while the ratios of leaves to fine roots were the lowest in F. mandshurica. (3)For P. davidiana and T. cuspidata, the aboveground and belowground organs showed an allometric and isometric relationship respectively between N and P contents, with the scaling exponent in belowground being approximately half of that in aboveground. In contrast, F. mandshurica exhibited similar scaling exponents aboveground and belowground, both exhibiting significantly greater than 1 allometric relationship. For P. davidiana, the slopes of both aboveground and belowground P in both directions are half of the corresponding N values. For T. cuspidata, the slopes of P content in the upward direction were also half of the corresponding N values, and the downward N and P relationships were not significant. For F. mandshurica, the slopes of N and P content in the upward direction were similar, whereas in the downward direction, the P content slope was approximately 2/3 of N.【Conclusion】In contrast to P. davidiana and T. cuspidata, F. mandshurica tended to allocate N and P to metabolically active organs such as leaves and fine roots. The relationships between N and P in aboveground (or belowground) organs and N and P between above- and below-ground showed distinct coordinations for F. mandshurica compared to P. davidiana and T. cuspidata.

Key words: nitrogen and phosphorus stoichiometry, nutrient allocation, inter-specific variation, Populus davidiana, Fraxinus mandshurica, Taxus cuspidate