Andersen Christian P, Rygiewicz Paul T
U.S. Environmental Protection Agency, Corvallis Environmental Research Laboratory, 200 SW 35th Street, Corvallis, Oregon 97333 USA.
New Phytol. 1995 Dec;131(4):471-480. doi: 10.1111/j.1469-8137.1995.tb03084.x.
The effect of ozone on tree growth and metabolism has been studied widely. Despite the research emphasis, relatively little is known about how the below-ground component responds when shoots are exposed to ozone, even though evidence suggests that ozone can affect roots more than shoots. Undemanding how ozone affects carbohydrate allocation throughout the plant is essential to understanding the mechanisms of response to ozone. The purpose of this study was to follow the allocation and metabolism of carbon in a Pinus Ponderosa Laws.-Hebeloma crustuliniforme (Bull.: St. Amans) Quel seedling system under ozone stress. The hypothesis that ozone affects carbon transport below ground and overall sink strength of roots. similarly in mycorrhizal and non-mycorrhizal seedlings was tested. To test the hypothesis, a unique culturing system was used to quantify carbon movement to all components of the symbiosis and to construct an overall budget for carbon for both mycorrhizal and non-mycorrhizal seedlings. Fluxes of CO and carbon allocation were followed by measuring instantaneous CO flux and by C labelling. Two experiments were conducted that differed in their total ozone exposure (39.3 ppm h in expt 1, and 58.1 ppm h in expt 2). Mycorrhizal inoculation significantly increased CO., assimilation rates (A) and A/R (R = shoot respiration) ratios in both experiments compared with non-mycorrhizal seedlings. Ozone exposure in expt 2 significantly decreased the A/R ratio (P < 0.003) in both mycorrhizal treatments. Below-ground respiration was significantly greater in mycorrhizal than in non-mycorrhizal seedlings in both experiments, and was not affected by ozone exposure, Intact, extramatrical hyphal respiration was lower by 33% in seedlings exposed to ozone, but differences were not statistically significant (P ≤ (0.167). Mycorrhizal seedling roots reached maximum respiratory CO release rates c. 5 h and < 20 h earlier than non-mycorrhizal seedlings in expts 1 and 2, respectively, suggesting accelerated transport of C below ground in mycorrhizal seedlings. Mycorrhizal seedlings also exhibited greater rates of C release below ground than non-mycorrhizal controls. The maximum rate of respiratory release of CO below ground was significantly reduced by exposure to ozone in both mycorrhizal and non-mycorrhizal treatments. Ozone significantly reduced C activity in the fungus of mycorrhizal plants. This constitutes the first report of an ozone-induced reduction in carbon allocation to the fungal symbiont in a mycorrhizal association. The results suggest a substantial impact of ozone on the carbon balance of the mycorrhiza: however, there was no evidence to suggest that mycorrhizal and non-mycorrhizal ponderosa pine seedlings responded differently to ozone stress.
臭氧对树木生长和新陈代谢的影响已得到广泛研究。尽管研究重点在此，但对于当嫩枝暴露于臭氧时地下部分如何响应，我们了解得相对较少，即便有证据表明臭氧对根系的影响大于对嫩枝的影响。了解臭氧如何影响碳水化合物在整个植株中的分配对于理解对臭氧的响应机制至关重要。本研究的目的是追踪在臭氧胁迫下黄松-皮壳状丝膜菌幼苗系统中碳的分配和代谢。检验了以下假设：臭氧对地下碳运输和根系的整体库强有影响，在菌根和非菌根幼苗中情况类似。为验证该假设，使用了一种独特的培养系统来量化碳向共生关系所有组分的移动，并构建菌根和非菌根幼苗的整体碳预算。通过测量瞬时二氧化碳通量和进行碳标记来追踪二氧化碳通量和碳分配。进行了两个实验，它们的总臭氧暴露量不同（实验1中为39.3 ppm·h，实验2中为58.1 ppm·h）。与非菌根幼苗相比，在两个实验中菌根接种均显著提高了二氧化碳同化率（A）和A/R（R = 嫩枝呼吸）比值。实验2中的臭氧暴露显著降低了两种菌根处理中的A/R比值（P < 0.003）。在两个实验中，菌根幼苗的地下呼吸均显著高于非菌根幼苗，且不受臭氧暴露的影响。完整的、根外菌丝呼吸在暴露于臭氧的幼苗中降低了33%，但差异无统计学意义（P ≤ 0.167）。在实验1和实验2中，菌根幼苗根部分别比非菌根幼苗早约5小时和不到20小时达到最大呼吸二氧化碳释放速率，这表明菌根幼苗中碳向地下的运输加速。菌根幼苗在地下的碳释放速率也高于非菌根对照。在菌根和非菌根处理中，臭氧暴露均显著降低了地下呼吸释放二氧化碳的最大速率。臭氧显著降低了菌根植物真菌中的碳活性。这是关于臭氧诱导菌根共生关系中向真菌共生体的碳分配减少的首次报道。结果表明臭氧对菌根的碳平衡有重大影响；然而，没有证据表明菌根和非菌根黄松幼苗对臭氧胁迫的响应不同。
