[The relationships between photosynthetic capacity and lamina mass per unit area, nitrogen content and partitioning in seedlings of two ficus species grown under different irradiance].

Acclimation of maximum net photosynthetic rate (P(max)), lamina mass per unit area (LMA), leaf nitrogen content and partitioning in different photosynthetic machinery to growth light intensity were studied in two Ficus species seedlings grown under four different light levels (4%, 12%, 36% and 100% daylight). Seedlings of F. tinctoria, a light-demanding species, are distributed mainly around and in rain forest gaps; seedlings of F. subulata, a shade-tolerant species, are distributed mainly in rain forest understory. The results demonstrated that P(max) of the two Ficus species increased with an increase in light intensity during their growth, and P(max) was higher in F. tinctoria than that in F. subulata under most growth light intensities. LMA was positively correlated with nitrogen content per unit area (N(A)) and P(max), and P(max) was positively correlated with N(A). But LMA was negatively correlated with nitrogen content per unit mass (N(M)). The results suggest that change in LMA was the main reason of the changes in P(max) and N(A) with growth light intensities. Photosynthetic nitrogen utilization efficiency (PNUE) of the two Ficus species increased with an increase of growth light intensity, but there was no significant interspecific difference in PNUE at the same growth light intensities, although N(A) was significantly higher in F. tinctoria than that in F. subulata. PNUE was not the reason of P(max) interspecific difference, but is the reason of P(max) intraspecific difference grown under different growth light intensities. Nitrogen partitioning to carboxylation (P(C)) and bioenergetics (P(B)) were higher in F. tinctoria than those in F. subulata. This is one of the reasons that P(max) was higher in F. tinctoria than in F. subulata. Another reason is that LMA and N(A)were higher in F. tinctoria than in F. subulata. Variations of the parameters presented above are consistent with distribution and ecophysiological characteristics of the two Ficus species.