不同演替阶段树种的光合和生长对增强UV-B辐射的响应

Growth and Photosynthetic Responses of Different Successional Tree Species in Low Subtropics to Enhanced UV-B Radiation in the Field

利用野外盆栽实验方法,模拟南亚热带地区地面增强UV-B辐射20%(L)和30%(H)的条件下(L和H分别为4.83和7.24 kJ.m-2.d-1),研究南亚热带植被恢复先锋树种马占相思(Acacia mangium)、演替前期树种荷木(Schima superba)、演替中后期树种华润楠(Machilus chinensis)和黄果厚壳桂(Cryptocarya concin-na)等4种乔木树种对增强UV-B辐射的响应。结果表明,增强UV-B辐射处理引起马占相思和荷木的最大光合速率(Pm ax)明显下降,高剂量(7.24 kJ.m-2.d-1)和延长处理时间(160 d)的效应更加明显;它们的光合速率下降幅度依次为:马占相思>荷木>华润楠>黄果厚壳桂,先锋树种光合作用对增强UV-B辐射的响应明显大于演替中后期树种。增强UV-B辐射处理,马占相思的株高生长和茎生物量以及荷木的株高有较明显减小,它们的地径、总生物量和冠根比有减小的趋势;同时马占相思的叶宽度明显地增大。结果表明,马占相思和荷木属UV-B辐射敏感种,而华润楠和黄果厚壳桂则属低敏感种。当前臭氧层的减薄趋势没有得到有效遏制的情况下,马占相思和荷木因个体生长发育过程中对增强UV-B辐射的敏感性,可能会导致南亚热带地区群落的先锋种和演替前期树种加速衰退,而演替中后期树种由于较能忍耐UV-B辐射而能竞争到更多的资源以利其在群落竞争中占优势,从而保持更稳定的状态。

Better understanding of successional tree species responses to enhanced UV-B radiation is an important requirement. A pot experiment was conducted in the field to investigate the responses of plant growth and physiological process of 4 successional tree species at enhanced UV-B irradiance via artificial simulation. The biomass, leaf characteristics and ecophysiological characteristics of four species, including the pioneer species Acacia mangium, early successional stage species Schima superba, and mesophilous tree species Machilus chinensis and Cryptocarya concinna in lower subtropical forest community, were investigated under the treatment of enhanced ultraviolet-B （UV-B） radiation 20% （L） and 30% （H） （L was 4.78 kJ m^-2 d^-1 of enhanced UV-B radiation and H was 7.24 kJ m^-2·d^-1 ） in low subtropics. The results showed that maximum photosynthesis rates （Pmax） of A. mangium and S. superba were significantly decreased by enhanced UV-B radiation, which were aggravated by high dose UVB radiation irradiating and extending treatment time. The responses of their photosynthetic parameters of four tree species to enhanced UV-B radiation had very different, and the order from large to small was A. mangium, S. superba, M. chinensis and C. concinna. The photosynthetic responses of pioneers to enhanced UV-B radiation were lager than those of species in late successional stage. Compared with CK, the height and branch biomass of A. mangium and the height of S. superba were reduced visibly by enhanced UV-B radiation, while their diameter, total biomass and shoot to root ratio had reduced tendency. The results show that pioneer species A. mangium and early successional stage species S. superba were sensitive to enhanced UV-B radiation, while M. chinensis and C. concinna were tolerant. If the tendency of 03 depletion were not reduced efficiently, that would lead to an increase in the level of solar UV-B radiation reaching the earth＇s surface. A. mangium and S. superba may decrease competition in plant community, because the depression of ecophysiological processes induced by UV-B radiation and their individual height growth was prohibited. Hence, it could be concluded that pioneer and early successional stage species may accelerate degradation by enhanced UV-B radiation; as a result, they have to exit ecosystem competition earlier due to the influence of enhanced UV-B radiation; the late successional stage species are more tolerant to UV-B radiation and, therefore, can compete more resource to keep dominance in ecosystem. Thus, the A. mangium and S. superba community may be replaced by late successional UV-B radiation tolerant species ahead of time.