摘要
南非大阳光中的UV-B(28～315nm)曝射量在空间和时间上的变化是按2.5km^2的分辨率用臭氧、相对湿度、云量及海拔高度数据进行模拟并绘图的。计算机处理的结果显示,UV-B曝射量存在着很大的天然梯度,纬度跨越14度,变化幅度为34.2%,经度跨越16度,UV-B变化幅度为44.2%。对未来UV-B年曝射量情况的模拟显示出其小辐增长的趋势,2003年增加2.5%(臭氧耗减过程的最佳状况);2051年增加8.1%(臭氧耗减过程的最差状况)。值得注意的是,防臭氧耗减,UV-B的年内变率显著增加。2003年深秋(5月)曝射量增加12%,2051年同一季节增加35%。对代表103科468属的2146种受威胁(稀有、濒危、脆弱)生物分析其分类、生活型和机能特征,并将它们的分布与模拟得到的UV-B时空分布型式相比较。我们看到,在受威胁分类群中,常绿和内质的生活型及地下芽植物出现的比例很高,这说明,这些植物时太阳先中UV-B作用的增强有很高的生理修复能力,尽管有些生活型(如树木)的抵抗力显得相对差一些。有些植物机能类型(如一年生本本植物)显示出单位繁殖产出的降低及植物总体适应水平的下降,这些可能会导致物种共存型式、植物组成成分和多样性的改变。
Spatial and temporal changes in South African solar UV-B (280-315 nm) exposure were modeled and mapped at 2.5 km2 resolution using ozone, relative humidity, cloud amount and elevation data. Computations indicated large natural gradients in UV-B exposure ranging from a 34.2% change over 14° of latitude to a 44.2% change over 16° of longitude. Modelling of future scenarios in annual UV-B exposure indicated small increases ranging from 2.5% in the year 2003 (best-case ozone depletion scenario) to 8.1% in the year 2051 (worst-case ozone-depletion scenario). Notable were substantial increases in intra-annual variability in UV-B radiation with ozone depletion. Exposure exhibits a 12% increase during late autumn (May) in the year 2003 and a 35% increase during this season in the year 2051. Taxonomic, life form and functional attributes were analyzed in 2146 threatened (rare, endangered, vulnerable) species representing 468 genera and 103 families, and their distributions compared with modeled spatial and temporal UV-B distribution patterns. The high fractions of evergreen and succulent life forms and geophytes, present among threatened taxa, indicate a high degree of physiological resilience to increased solar UV-B stress, though some life forms, e.g. trees, appear relatively less resistant. Conceivable reductions in per capita reproductive output and overall plant fitness were indicated in some plant functional types, e.g. herbaceous annuals, which may lead to altered patterns of species coexistence, floristic composition and diversity.
