不同光强下生长的两种榕树叶片光合能力与比叶重、氮含量及分配的关系

观测了不同光强下生长的两种榕树幼苗叶片的光合能力、比叶重(LMA)、氮含量及在光合机构中的分配.结果表明,两种榕树幼苗的最大净光合速率(Pmax)均随生长光强的升高而升高,这与LMA、单位面积氮含量(NA)和光合氮利用效率随生长光强的升高而升高有关.除36%光强下外,相同光强下生长的喜光的斜叶榕(Ficus tinctoria)的Pmax均显著高于耐荫的假斜叶榕(Ficus subulata),这与其叶片中氮在羧化组份和生物力能学组份中的分配系数、LMA和NA较高有关.

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 photo-synthetic rate (Pmax), 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 Pmax of the two Ficus species increased with an increase in light intensity during their growth, and Pmax was higher in F. tinctoria than that in F. subulata under most growth light intensities (Fig.l). LMA was positively correlated with nitrogen content per unit area (NA) and Pmax, and Pmax was positively correlated with NA (Fig.6). But LMA was negatively correlated with nitrogen content per unit mass (NM) (Fig.5). The results suggest that change in LMA was the main reason of the changes in Pmax and NA 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 sig- nificant interspecific difference in PNUE at the same growth light intensities (Fig.4), although NA was significantly higher in F. tinctoria than that in F. subulata (Fig. 2). PNUE was not the reason of Pmax interspecific difference, but is the reason of Pmax intraspecific difference grown under different growth light intensities. Nitrogen partitioning to carboxylation (PC) and bioen-ergetics (PB) were higher in F. tinctoria than those in F. subulata (Fig.3). This is one of the reasons that Pmax was higher in F. tinctoria than in F. subulata. Another reason is that LMA and NA were higher in F. tinctoria than in F. subulata (Figs.l and 2). Variations of the parameters presented above are consistent with distribution and ecophysiological characteristics of the two Fi-cus species.