Bertin N, Staudt M
Host Institute Joint Research Centre, Environment Institute, TP051, 21020, Ispra (VA), USA.
Oecologia. 1996 Sep;107(4):456-462. doi: 10.1007/BF00333935.
We investigated the effects of a short period of water stress on monoterpene emissions from Quercus ilex, a common oak species of the Mediterranean vegetation and a strong emitter of monoterpenes. The experiment was carried out on two young saplings with a branch enclosure system under semi-controlled conditions. Under unstressed conditions, small qualitative (cis-β-ocimene, trans-β-ocimene, β-caryophyllene and 1,8-cineol) and large quantitative (as much as 40% for the main compounds emitted) differences were observed between the two apparently similar trees. Nevertheless these differences did not affect the short-and long-term responses to temperature and water stress. Daily courses of emissions and gas exchanges were similar before and after the stress. During the most severe stress, emissions were reduced by a factor of two orders of magnitude and the log-linear relationship between emissions and temperature no longer existed. Photosynthesis and transpiration rates decreased as soon as the soil started to dry, whereas monoterpene emissions slightly increased for few days and then dropped when the daily CO balance approached zero. We concluded that under water stress monoterpene emissions were highly limited by monoterpene synthesis resulting from a lack of carbon substrate and/or ATP. After rewatering, both emissions and gas exchanges recovered immediately, but to a level lower than the pre-stress level. These results have many implications for monoterpene emission modelling in the Mediterranean area, since the dry period generally extends from May to August. If our results are confirmed by field experiments, water stress could lead to a large overestimation of the emissions under summer conditions, when the algorithms based on light and temperature would give high emission rates.
我们研究了短期水分胁迫对冬青栎单萜排放的影响，冬青栎是地中海植被中常见的一种栎树，也是单萜的强排放者。实验在半控制条件下，使用分支封闭系统对两棵幼树进行。在非胁迫条件下，在这两棵看似相似的树之间观察到了小的定性差异（顺式-β-罗勒烯、反式-β-罗勒烯、β-石竹烯和1,8-桉叶素）和大的定量差异（主要排放化合物高达40%）。然而，这些差异并未影响对温度和水分胁迫的短期和长期响应。胁迫前后排放和气体交换的日变化过程相似。在最严重的胁迫期间，排放减少了两个数量级，排放与温度之间的对数线性关系不再存在。一旦土壤开始变干，光合作用和蒸腾速率就会下降，而单萜排放在几天内略有增加，然后在每日二氧化碳平衡接近零时下降。我们得出结论，在水分胁迫下，单萜排放受到单萜合成的高度限制，这是由于缺乏碳底物和/或ATP所致。重新浇水后，排放和气体交换立即恢复，但恢复到低于胁迫前的水平。这些结果对地中海地区单萜排放建模有许多影响，因为干旱期通常从5月持续到8月。如果我们的结果得到实地实验的证实，那么在夏季条件下，当基于光照和温度的算法给出高排放率时，水分胁迫可能会导致对排放的大幅高估。
