Ecophysiological Characteristics Of Tsoongiodendron Odorum Under Different Light Regimes

The primary purpose of this study was to investigate the acclimation of Tsoongiodendron odorum saplings to different light regimes through measuring stem sap flux density (SFD), leaf-level net photosynthetic rate (Pn), transpiration rate(Tr),and stomatal conductance (Gs), and the biomass, stable carbon isotope composition (8I3C values) and C, N, P content of different organs of T. odorum under three different light levels (100%,40%and8%light intensity) in Wanmulin Nature Reserve in Fujian. The results showed that:(1) SFD of T. odorum increased as the imposed light intensity increased with the highest value under100%light intensity. Diurnal mean SFD varied significantly(p<0.05) or highly significantly (p<0.01) among different light regimes except in spring. Which showed that the water consumption decreased as shading increased. There was a significant correlation (P<0.05) between SFD, and Tr and Gs under different light levels in different seasons except that SFD and Gs showed no positive correlation under8%light intensity in summer and under100%light intensity in winter. SFD under different light intensity was deeply affected by environmental factors among which photosynthetically active radiation (PAR) exerted the greatest influences.(2) Diurnal mean Pn of T. odorum leaf increased as the imposed light intensity increased with the highest value under100%light intensity which indicated that the photosynthetic capacity of T. odorum decreased as shading increased. Under the same light regime, the diurnal mean and peak values of Pn both decreased in the following order:Summer> Spring>Autumn>Winter. There was a significantly positive (P<0.05) or highly significantly positive (P<0.01) correlation between Pn, and Tr and Gs under all three light intensity. The photosynthetically active radiation (PAR) highly significantly affected the variation of Pn (P<0.01).(3)The total biomass of T. odorum reduced significantly (P<0.05) as shading increased which showed that T. odorum accumulated more biomass under higher light intensity. The biomass allocation to different organs of T. odorum changed with light intensity that could be seen from the results that the shoot ratio was0.930under100%light intensity,0.695under40%light intensity and0.693under8%light intensity, which suggested that more biomass was invested in root under100%light intensity, but more was invested in leaf under40%and8%light intensity.(4) δ13C values (water use efficiency, WUE), and N, P content per unit mass of T. odorum leaf both decreased in the following order:100%light intensity>40%light intensity>8%light intensity, but the C/N (nitrogen use efficiency, NUE) and C/P (phosphorus use efficiency, PUE) of T. odorum leaf increased in the following order:100%light intensity<40%light intensity<8%light intensity. These results indicated that there existed a trade-off between WUE, and NUE and PUE under different light regimes, with a high WUE achieved with the cost of a low NUE and PUE.In summary, the SFD, biomass, leaf net photosynthetic rate, stable carbon isotope composition, and unit mass of N and P content of T. odorum saplings declined as the light intensity decreased. In the low-light conditions, T. odorum could improve the N and P use efficiency and lower WUE to get more limited light resources to meet the growth demand. It showed that T. odorum had a shade-tolerant characteristic.