The Future Fund tipped another $3.5 billion into debt securities over the December 2008 quarter to take its holdings of this asset class to $9.0 billion, the quarterly investment update published on Friday by the fund shows.Debt securities now represent 17 per cent of the fund's "ex-Telstra" investment aggregate of $52 billion, up from 10 per cent at the end of September 2008.The fund invested another $1.6 billion in alternative assets over the quarter to take its holdings of that asset class to $1.9 billion.The fund experienced a decline in value of a little more than $3 billion over the quarter.