Biomass allocation and growth rates in Pinus sylvestris are interactively modified by nitrogen and phosphorus availabilities and by tree size and age.

摘要

Biomass allocation and growth of Scots pine, Pinus sylvestris, of various sizes (height 0.03-20 m) and ages (1-151 years) were investigated in two infertile sites in Estonia between mid-July and early September 2000 to determine relative nitrogen and phosphorus limitations on productivity and their interactions and size-dependent controls. The first site was a raised bog at Mannikjarve in Endla State Nature Reserve and the second site was a sand-dune habitat in Kalevi-Liiva. Dry mass weighted average nitrogen (NW) and phosphorus (PW) contents were higher in P. sylvestris in sand dunes than in those in the raised bog, but PW:NW ratios overlapped between the sites. Leaf dry mass ratio (FL) and leaf-area ratio (LAR) increased with NW, and FL increased with PW. The relative growth rate (RG) was more strongly associated with PW than with NW. The net assimilation rate per leaf dry mass (NARM) scaled positively with PW but not with NW, demonstrating that the stronger effect of PW on growth was due to modified biomass allocation and physiology (RG=NARM x FL), while NW affected growth via biomass allocation. Partitioning and growth characteristics were poorly related to the PW:NW ratio. The overall decrease of growth in larger trees resulted from their lower LAR and FL. Increases in size further led to a lower NW but higher PW. We conclude that optimum productivity at a given NW requires a certain minimum PW, not a specific "non-limiting" PW:NW ratio. While nutrients affect growth by changing biomass allocation and physiological activity, size primarily modifies biomass allocation..