Abstract: To understand effects of stand density on the allocation of non-structural carbohydrates (NSC) in Pinus sylvestris var. mongolica, we analyzed concentrations of NSC and its components (soluble sugars and starch) in different organs of 39-year-old P. sylvestris var. mongolica monoculture with different stand densities (490, 750, 1110, 1550, 1800, 1930, 2560 and 3520 trees·hm^-2). The results showed that NSC concentrations in needles, branches and roots ranged from 50.51 to 82.12 mg·g^-1, from 58.24 to 76.28 mg·g^-1, and from 13.90 to 56.82 mg·g^-1, respectively. When stand density increased from 490 to 1550 trees·hm^-2, soluble sugars concentration of young needles decreased, starch concentration increased, and NSC concentration remained stable. When stand density increased from 1550 to 3520 trees·hm^-2, concentrations of soluble sugars, starch and NSC in young needles showed downward trends. With the increases of stand density, concentrations of soluble sugars, starch and NSC in old needles first increased and then decreased, and concentrations of soluble sugars and NSC in young and old branches exhibited trends of increasing-decreasing-increasing, while concentrations of soluble sugars, starch and NSC in the roots first reduced and then rose. The optimal management density for mature P. sylvestris var. mongolica plantation should be 1110 trees·hm^-2, in which concentrations of soluble sugars and NSC in young needles and branches were high and reached the maximum in old needles and branches, indicating more carbohydrate production and branch growth promotion.

Key words: soluble sugar, starch, density control, carbon allocation, Horqin Sandy Land