College of Science, Beijing Forestry University, Beijing, China.
Tree Physiol. 2012 Nov;32(11):1413-9. doi: 10.1093/treephys/tps089. Epub 2012 Oct 25.
There are different opinions of the dynamics of an air bubble entering a xylem conduit. In this paper, we present a thorough mechanical analysis and conclude that there are three types of cavitation caused by air seeding. After an air seed enters a conduit at high xylem pressure P'(1), along with the drop of the water potential, it will expand gradually to a long-shaped bubble and extend continually. This is the first type of air seeding, or the type of expanding gradually. When the xylem pressure is moderate, right after an air seed enters a conduit, it will expand first. Then, as soon as the pressure reaches a threshold the bubble will blow up to form a bubble in long shape, accompanied by acoustic (or ultra-acoustic) emission. It will extend further as xylem pressure decreases continually. This is the second type of air seeding, or the type of expanding-exploding, becoming a long-shaped bubble-lengthening by degrees. In the range of P'(1) ≤ - 3P(o) (P(o) is atmospheric pressure), soon after an air seed is sucked into a conduit it will explode immediately and the conduit will be full of the gas of the bubble instantly. This is the third type of air seeding, or the type of sudden exploding and filling conduit instantly. The third type is the frequent event in daily life of plant.
关于气泡进入木质部导管的动力学存在不同的观点。在本文中，我们进行了彻底的力学分析，得出由气穴引起的有三种类型的气穴现象。当一个气泡在高木质部压力 P'(1)下随水势下降进入导管时，它会逐渐膨胀成一个长形气泡并不断延伸。这是第一种气穴现象，即逐渐膨胀型。当木质部压力适中时，气泡进入导管后会先膨胀。然后，一旦压力达到一个阈值，气泡就会爆炸成一个长形气泡，并伴随着声（或超声）发射。随着木质部压力不断下降，它将进一步延伸。这是第二种气穴现象，即膨胀-爆炸型，气泡逐渐膨胀成一个长形气泡。在 P'(1)≤-3P(o)（P(o)为大气压力）的范围内，气泡一旦被吸入导管，就会立即爆炸，导管内会立即充满气泡的气体。这是第三种气穴现象，即瞬间爆炸并立即充满导管型。第三种类型是植物日常生活中常见的现象。
