Effects of sand burial on growth and photosynthesis and water metabolism of Pinus sylvestris var. mongolica saplings

In order to assess the effects of sand burial on growth properties and photosynthesis and water metabolism of Pinus sylvestris var. mongolica saplings,the survival rate,plant height,aboveground biomass,photosynthetic rate( Pn),transpiration rate( Tr) and water use efficiency( WUE) of 3-year-old P. sylvestris var. mongolica saplings with different sand burial depths were measured in the Horqin Sand Land of Inner Mongolia in the spring of 2013. The results showed that the maximum depth of the saplings to withstand sand burial should not exceed 2 cm above the plant height,and all saplings died when the sand burial depth was over 2 cm above the plant height. When the sand burial depth was below 2 cm above the plant height,sand burial promoted the height growth but did not benefit the biomass accumulation of the saplings,and significantly increased Pn,Tr,stomatal conductance( gs),and intercellular CO2concentration( Ci),with a maximum increase of Pn,Tr,gs,respectively when the sand burial depth was at 50% of the plant height. Ciwas the maximum when the sand burial depth was 2 cm above the plant height.Although the sand burial did not result in the decrease of water content in the saplings,WUE of the saplings tended to decline with increase of the sand burial depth,with the lowest WUE when the sand burial depth was 2 cm above the plant height. There was a significant and positive correlation between sapling height and Pn,Tr,between Pnand gsand Ci,and between WUE and plant water content and Tr. The correlation was not significant between the aboveground biomass and Pnand Tr.