Air Quality Research Unit, U.S.D.A./A.R.S., 1509 Varsity Drive, 27606, Raleigh, NC, USA.
Photosynth Res. 1995 Feb;43(2):81-92. doi: 10.1007/BF00042965.
It has been suggested that increases in ground-level UV-B, as a result of stratospheric ozone depletion, may have major deleterious effects on crop photosynthesis and productivity. The direct consequences of such effects have been projected by some as a world-wide decrease in crop yields of 20-25%. Further losses, or unrealized gains, have also been suggested as a result of increased UV-B counteracting the beneficial effects of elevated atmospheric CO2. Deleterious UV-B effects may be largely partitioned between damage to the plant genome and damage to the photosynthetic machinery. Direct damage to DNA is a common result of absorption of high energy UV-B photons. However, most plants possess repair mechanisms adequate to deal with the levels of damage expected from projected increases in ground-level UV-B. In addition, most plants have the ability to increase production of UV-absorbing compounds in their leaves as a result of exposure to UV-B, UV-A and visible radiation. These compounds contribute substantially to reducing UV-B damage in situ. It has also been shown that in some plants, under the proper conditions, almost every facet of the photosynthetic machinery can be damaged directly by very high UV-B exposures. However, electron transport, mediated by Photosystem II (PS II) appears to be the most sensitive part of the system. Various laboratories have reported damage to virtually all parts of the PS II complex from the Mn binding site to the plastoquinone acceptor sites on the opposite surface of the thylakoid membrane. However, a critical review of the literature with emphasis on exposure protocols and characterization of the radiation environment, revealed that most growth chamber and greenhouse experiments and very many field experiments have been conducted at unrealistic or indeterminate UV-B exposure levels, especially with regard to the spectral balance of their normal radiation environment. Thus, these experiments have led directly to large overestimates of the potential for damage to crop photosynthesis and yield within the context of 100 year projections for stratospheric ozone depletion. Indeed, given the massive UV-B exposures necessary to produce many of these effects, we suggest it is unlikely that they would occur in a natural setting and urge reconsideration of the purported impacts of projected increases of UV-B on crop productivity.
有人认为，平流层臭氧消耗导致地面紫外线-B 增加，可能对作物光合作用和生产力造成重大有害影响。一些人预测，这种影响的直接后果将导致全球作物产量减少 20-25%。由于紫外线-B 抵消了大气 CO2 升高的有益影响，因此还可能导致进一步的损失或未实现的收益。有害的紫外线-B 影响可能主要分为对植物基因组的损害和对光合作用机制的损害。吸收高能紫外线-B 光子是 DNA 直接受损的常见结果。然而，大多数植物拥有足够的修复机制来应对预计地面紫外线-B 增加所带来的损害水平。此外，大多数植物有能力在暴露于紫外线-B、紫外线-A 和可见光辐射时，增加叶片中吸收紫外线的化合物的产量。这些化合物在现场大大减少了紫外线-B 的损害。研究还表明，在某些植物中，在适当的条件下，光合作用机制的几乎每个方面都可以直接被非常高的紫外线-B 暴露所损害。然而，电子传递，由光系统 II（PS II）介导，似乎是系统中最敏感的部分。各个实验室报告称，从锰结合位点到类囊体膜对面的质体醌受体位点，PS II 复合物的几乎所有部分都受到损害。然而，对文献的批判性回顾，重点是暴露方案和辐射环境的特征，表明大多数生长室和温室实验以及非常多的田间实验都是在不现实或不确定的紫外线-B 暴露水平下进行的，尤其是在它们的正常辐射环境的光谱平衡方面。因此，这些实验直接导致了对作物光合作用和产量潜在破坏的巨大高估，这在平流层臭氧消耗 100 年预测的背景下是如此。事实上，考虑到产生许多这些影响所需的大量紫外线-B 暴露，我们认为它们不太可能在自然环境中发生，并敦促重新考虑预测的紫外线-B 增加对作物生产力的所谓影响。
