林隙与林下环境对锐齿槲栎和米心水青冈种群更新的影响

EFFECTS OF GAP AND UNDERSTORY EVIRONMENTS ON THE REGENERATION OF QUERCUS ALIENA VAR. ACUTESERRATA AND FAGUS ENGLERIANA

锐齿槲栎(Quercusalienavar.acuteserrata )和米心水青冈(Fagusengleriana)是广泛分布在我国暖温带和亚热带山地中海拔地段的主要建群种,对水土保持和维持生态系统稳定具重要意义。该文通过在神农架地区的典型样地调查,分析了这2个种群在林隙和林下不同光环境中的更新状况和径级结构;利用便携式Licor_6 4 0 0光合仪测量了2种苗木的光饱和及光诱导曲线,探讨了光对这2个树种更新的影响机理。实验结果表明,在所调查的林地中,锐齿槲栎和米心水青冈种群都有充足的幼苗库,锐齿槲栎幼苗以实生为主,米心水青冈幼苗以萌生为主;从幼苗到幼树的转化过程中,锐齿槲栎的成活率几乎为零,而米心水青冈的成活率约为6 %～8% ;在两者的混交林中,米心水青冈种群呈稳定的金字塔形年龄结构,而锐齿槲栎则是某一生长阶段的种群占据主导地位。光饱和曲线显示,对2年生同生群苗木,在林窗下,锐齿槲栎的最大净光合速率(4.6 1μmol·m-2 ·s-1)比米心水青冈的(4.16 μmol·m-2 ·s-1)要高;而在林冠下,米心水青冈的最大净光合速率(Pn=3.89μmol·m-2 ·s-1)比锐齿槲栎的最大净光合速率(Pn=3.6 8μmol·m-2 ·s-1)要高。无论在林窗下或林冠下,米心水青冈幼苗的光饱和点比锐齿槲栎的要低。两者混交林下的光诱导曲线显示,与米心水青冈幼苗?

Quercus aliena var. acuteserrata and Fagus engleriana are important species in the temperate and subtropical middle-elevation mountainous areas of China. In this study, we investigated the regeneration dynamics, diameter size class distributions, and the light response curve of these two species to better understand the effects of light availability on the regeneration of Q. aliena var. acuteserrata and F. engleriana. The results showed that both species had a high abundance of seedlings in the field, but the survival rate from seedling to sapling stage was nearly zero for Q. aliena var. acuteserrata and only 6%-8% for F. engleriana. In the mixed-forest that contained both species, the population of F. engleriana showed a stable pyramidal age structure, but the size structure of Q. aliena var. acuteserrata was dominated by a few cohorts of trees that were able to establish within a short time period. From the light saturation response curve of the two-year old cohort, Q. aliena var. acuteserrata seedlings in gaps had a higher maximum photosynthetic rate (4.61 μmol·m -2 ·s -1 ) than F. engleriana (4.16 μmol·m -2 ·s -1 ) and, for the seedlings under canopy, F. engleriana had higher maximum photosynthetic rate (3.89 μmol·m -2 ·s -1 ) than Q. aliena var. acuteserrata ( 3.68 μmol·m -2 ·s -1 ). Moreover, seedlings of F. engleriana reached maximum photosynthetic rates with lower photosynthetic photon flux density than Q. aliena var. acuteserrata. The light induction curve indicated that both the response speed and the maximum photosynthetic rate of Q. aliena var. acuteserrata understorey seedlings were lower than that of F. engleriana, which demonstrated different competitive abilities and shade-tolerance characteristics of the two species. Resource allocation experiments showed that Q. aliena var. acuteserrata seedlings allocated more biomass to above-ground growth whereas F. engleriana seedlings allocated more biomass to under-ground growth. These results are consistent with the different light use strategies of the two species.