Nitrogen (N) and phosphorus (P) are essential nutrients that influence many plant functions, such as growth, reproduction and defence, and as a result the allocation of N and P has long been of interest to scientists studying the evolution of plant functional traits. Given that the functional requirements for N and P might be organ-specific, knowledge of nutrient partitioning among plant organs is critical to explain organ function, organ growth and plant growth form. The N and P content in the different organs of a plant reflect nutrient uptake and utilisation efficiency during plant growth, while the N–P relationship in tissues can aid in identifying flows of energy and element cycling. A general relationship between the N and P content of all plant organs is hypothesized to exist according to whole-plant economics spectrum (PES) theory, but the evidence supporting these expected patterns remains scarce.
In a new study published in AoBP, Chen et al. investigate whether a general relationship exists to describe N and P partitioning within and among the major plant organs of woody plants of the Wuyishan National Nature Reserve, south-eastern China. They found the scaling exponents of the N-P relationship were not significantly different from 1.0 in all organs, with a common slope of 1.08. The numerical values of these scaling slopes and the scaling constants were not found to vary with elevation. These results indicate that different organs of subtropical woody plants do share a similar isometric scaling relationship between their N and P content. They also highlight that the effects of N and P content on the N:P ratio differ between metabolic organs (leaves and fine roots) and structural organs (twigs). The authors suggest that future work in this field should consider N and P limitation in different organs in the subtropical region, which has long been considered “P-controlled”.