Amazing Root System

Bristlecone Pines, have adapted the best root system for the environment they have to survive in. In order to maximize water uptake, the trees have a very branched shallow root system, usually only 2-7 inches below the soil's surface. The shallow root system allows for the tree to survive in the very rocky soil. The average precipitation per year in the White Mountains is less than 12 inches, and most of that is from snowfall, so the trees must be able to get as much water from the snow as soon as it starts to melt, and they do this by having a shallow branchy root system. The soil is derived from dolomite or limestone that is light in color, more than 50% rock, and allows for a large amount of water storage.(http://eol.org/pages/1034948/details)
The incredibly extreme environment that these trees live in makes it very difficult for disease or rot causing fungi to live, this is good for the bristlecones, but it also means that they don't have any symbionce with michorizzae or nitrogen fixing bacteria, because it cannot survive in the harsh conditions of the White Mountains. This also means that there is no competition for the Bristlecones to get water or nutrients from the soil, so it is able to obtain them that way, just very very slowly. Which is why the Bristlecone Pines can grow so old. (http://www.pbs.org/wgbh/nova/methuselah/long2.html)

Dry climate and water adaptations

Bristlecone Pines are very slow growing and long lived trees, that grow in a very dry and tough climate. The White Mountains are well known for their extreme climate. (http://articles.latimes.com/2011/jul/10/travel/la-tr-bristleconepine-20110710) Says that wind speeds often reach up to 100 mph, and temperatures are ever changing and can often drop below zero. 10,000 ft up in the mountains usually doesn't even get a ft of rain each year. According to (http://www.fs.fed.us/database/feis/plants/tree/pinlon/all.html) the trees are incredibly drought tolerant and can survive in poor rocky soil and extreme conditions because of their thick bundles of waxy, thick modified leaves (needles), which are good for avoiding water loss, can photosynthesize effectively for over 35 years. They also have a very shallow root system in order to maximize their water uptake. Since their needles are able to maintain a low leaf water potential, the trees internal water stress also remains low. This is how the Bristlecone Pine is able to survive for thousands of years in one of the most harsh climates for trees.