Stocks declined sharply on Wednesday morning with yesterday's rebound proving short-lived as fears about the impact of a slowdown in China came back to haunt markets.Following a three-day weekend for the UK and US, indices surged on Tuesday on renewed hopes of continued monetary easing in Europe and Japan. Meanwhile, US consumer confidence came in at a five-year high and American home prices registered their biggest annual jump since 2006.The news prompted a triple-digit gain on the FTSE 100 in London and pushed the Dow Jones index on Wall Street to another record close, as traders began to focus more on the upbeat outlook for the US economy, rather than the concerns about the Federal Reserve scaling back stimulus which hit markets hard last week.However, the bullish mood has now been dampened after the International Monetary Fund (IMF) slashed its 2013 economic growth forecasts for Asian powerhouse China from 8.0% to 7.75%, citing weak global demand.The IMF's Deputy Managing Director David Lipton said that the Chinese economy "need[s] continued liberalisation and reduced government involvement, allowing a greater role for market forces". He said that the country needs to make a "decisive push" to launch new market-orientated reforms.Ex-div stocks and miners weigh on marketsA number of heavyweight stocks went ex-dividend this morning, meaning that new investors won't have the chance to tap into their latest payouts. These included Amec, Marks & Spencer, Cable & Wireless Communications and Premier Farnell.Mining stocks were also in the red early on as concerns over Chinese demand weighed on the sector. Antofagasta, Randgold, EVRAZ and Polymetal were among the worst performers.Smiths Group, the global technology firm, was another heavy faller after Deutsche Bank downgraded the stock to 'hold', while retailer Halfords was hit by a ratings cut by Espirito Santo to 'neutral'.Defence and security group Cobham was lower despite winning a AUD$85m five-year contract extension in Papua New Guinea for its Fly-in Fly-out (FIFO) aviation services to transport workers to remote mines.De La Rue, which makes banknotes, was also down after seeing sales fall 8.0% to £484m in the year to March 30th, worse than the £509m forecast.Elsewhere, software group Idox was a big mover on AIM, dropping over 20% after its bottom-line guidance for the full year came in below analysts' expectations. The company expects EBITDA to be around £18m after a slower-than-expected first half, worse than the current consensus forecast for £21m.FTSE 100 - RisersAdmiral Group (ADM) 1,316.00p +0.30%Standard Chartered (STAN) 1,554.50p +0.29%FTSE 100 - FallersPolymetal International (POLY) 646.00p -2.93%Marks & Spencer Group (MKS) 471.00p -2.89%Antofagasta (ANTO) 937.00p -2.85%Amec (AMEC) 1,033.00p -2.46%National Grid (NG.) 819.00p -2.44%ARM Holdings (ARM) 986.50p -2.33%Experian (EXPN) 1,253.00p -2.26%Evraz (EVR) 140.80p -2.15%CRH (CRH) 1,410.00p -2.08%Babcock International Group (BAB) 1,181.00p -1.99%FTSE 250 - RisersRathbone Brothers (RAT) 1,556.00p +1.70%Paragon Group Of Companies (PAG) 306.00p +0.96%Bank of Georgia Holdings (BGEO) 1,845.00p +0.82%RPC Group (RPC) 414.30p +0.80%LondonMetric Property (LMP) 115.80p +0.70%Petra Diamonds Ltd.(DI) (PDL) 107.10p +0.66%COLT Group SA (COLT) 112.00p +0.63%Computacenter (CCC) 455.50p +0.49%Dexion Absolute Ltd. GBP Shares (DAB) 150.00p +0.33%International Public Partnerships Ltd. (INPP) 129.80p +0.31%FTSE 250 - FallersSpectris (SXS) 2,040.00p -3.41%Cable & Wireless Communications (CWC) 44.86p -3.09%Kazakhmys (KAZ) 324.90p -3.04%Marston's (MARS) 148.10p -2.95%Ferrexpo (FXPO) 169.60p -2.92%Great Portland Estates (GPOR) 558.00p -2.79%Premier Farnell (PFL) 218.80p -2.71%International Personal Finance (IPF) 540.00p -2.70%KCOM Group (KCOM) 84.50p -2.54%Fenner (FENR) 341.20p -2.49%