Plants release oxygen during the day, if enough oxygen is released the water becomes saturated and therefore unable to hold any more oxygen. At this stage, the oxygen produced by the plants is no longer dissolved into the water and forms bubbles on the leaves where the oxygen is being released from. You may see streams of bubbles going to the surface or they may collect into a larger bubble until it's big enough to float to the surface.
Higher light and Co2 are the leading, biggest cause of pearling..That being said your plants need the correct levels of all other nutrients to grow well for long evn if they are pearling. One thing to remember is that pearing is mearly a sign of fast growth. Even plants that are difficient in some, or several, nutrients will pearl as long as they have high light and CO2.
Remember that pearling is the plant producing O2 through photosynthesis. Photosynthesis is cloroplasts (the green and red pigments in plants) using light to breakdown CO2 into a carbon source (remember highschool science. Carbon is the "life blood" of every living thing on earth) and releasing the O2 from the Co2, which the plant does not need (well actually it does need Oxygen but in much lower quantities than is normally avaliable to it) That freed carbon is combined with hydrogen and oxyger to produce various sugars which the plants use as energy and food. The food is used for growth, the production of cells and all parts of the cells.
This is where the other nutrients we want in our tanks come in. N(nitrogen), P (phosphorus), K (potassium), Fe (iron), Mg (magnessuim) Mn(manganese) Ca(calcium) and many other nitrients are all used to produce various parts of the cell. K is very important for cell walls as well as the stomtas(I think), the guard cells that allow nutrients to enter the plant. Fe and Mg are both very important in the production of hte cloraplasts as well as necessary components of the nucleui's devolpment.
Many of these nutrients are supplied either by us, through fertalization or by decaying plant food, wish waste, etc. This is where good nutrient levels really come into play. The increased growthfrom the highr light and Co2 cause the plants to use a lot more nutrients because of hte increased growth. The sources I just mentioned for hte nutrients in the tank can easily be depleated due to the better growth. Soon, if we don't add more, the plants become defficient of what ever nutrients are in lowest supply. The ghealth of hte plant then decreases and growth slows down. This is when we start to get algae blooms. Algae, basically a very simple plant wiht much simplier needs, can use the nutrients that the the plants are not able to use anymore because of their decreased growth.
This sounds much more dramatic than it really is. The best thing you can do is make sure your nutrients are balanced wiht you tank conditions. Higher light requires CO2 addition, and lower light anks also benifit greatly from it aswell, and well balanced nutrient levels. Lower light tanks generally are able to supply more of its own nutrients(through the nitrogen cycle and decaying material in the tank) although often some addition of fertalizer is needed.
What are your tank conditions? Please, tell us about your entire setup. That will help us be more helpful. The important tests results needed are NO3, P, Kh and pH(used to determine co2 levels when injecting co2). Gh would be nice to know initally because it will tell whether or not extra additions of elements like Ca and Mg are needed.
Also, do some searches and read mant of the posts here. The stickies at hte top of the forums are a good place to start.