Allocation of nitrogen and phosphorus within and between the needles, stems, and roots of Picea seedlings

The allocation of nutrients links ecosystem supply services to the functional traits and development of plants. This is particularly true for nitrogen (N) and phosphorus (P), which are important limiting resources in natural systems and are related to many aspects of plant biology. We investigated the scaling relationships associated with the N and P contents within specific organ types (needles, stems, and roots) and the same nutrients in the different organs of Picea seedlings from nine taxa grown under greenhouse conditions. Our results showed that the N and P contents were highly correlated within and between plant organs. A common isometric scaling relationship (scaling exponent ≈ 1) between N and P was observed in spruce needles, stems, and roots. The N and P contents had different scaling exponents in different plant organs. The scaling relationships of the N content across different organ types tended to be allometric (scaling exponent < 1) between stems and non-stem organs, and isometric between needles and roots. For P contents, similar scaling relationships were also found in the three organs. These results may further advance our understanding of plant nutrient allocation strategies within and between major organs.