SUSSEX University scientists are putting trees to the ultimate test in a bid to discover whether they can offer a solution to global warming. Working with six other institutions from Europe, the Sussex scientists are growing six small groups of poplars through which different concentrations of carbon dioxide will be pumped. Trees normally absorb carbon dioxide through photosynthesis. In the short term, plants can absorb excess carbon dioxide which boosts their growth, but little is known about whether long-term growth is limited. If it is not, scientists say plantations could provide a perfect sink for the gas.