Abstract:

In order to find out the effects of root-root interactions on their production in the mixed stand,root growth and distribution studies were carried out both in the field and greenhouse.In the field studies,root density was studied on pure Fraxinus mandshurica,Larix gmelinii,and the zonal mixed plantations,all 10 years after planting,using a soil corer technique.Samples were taken along transects at the middle of plantation rows.Each sample was divided into three depth classes (0～10 cm,10～20 cm and 20～30 cm).In greenhouse,ash pure,larch pure and the mixed were planted both at pots and seedbed.4 seedlings were planted in one pot and 12 in one seedbed. The results from field experiments showed:horizontal distribution of root was different between ash and larch.Root density of ash was 3237.2g\5m^-3 and 3130.2g\5m^-3 between two species rows and between row 1 and 2 in the ash belt (including 3 rows,row 1 is on the side of other species),respectively.But the differences were not significant.However,root density of larch is only 939.4g\5m^-3 between two species rows,much lower than 2745.3g\5m^-3 between row 1 and 2 in the larch belt (including 5 rows).This result demonstrated that ash root had the tendency to invade to larch,and root distribution of larch was inhibited by ash.The vertical distribution of roots along the soil profile was more even in mixed plantations compared to pure plantations.Between two species rows,the proportion of root biomass within 0～10 cm, 10～20 cm and 20～30 cm depth soil layers was 41.9 %,28.7 % and 29.4 % of the total root biomass respectively, but 61.0 %,31.6% and 7.4 % in ash pure stand,55.6 %,27.9 % and 16.5 % in larch pure stand. Root density of ash is 3718.0g\5m^-3,higher than that of larch of which was 3040.7g\5m^-3. Greenhouse plantation results showed that the below-and above-ground biomass of ash was higher in mixed plantation than in pure planted both for potted or seedbed seedlings,particularly of that fine-root biomass (≤2 mm in diameter).Fine-root mass of potted and seedbed seedlings were increased about 28.8 % and 36.5 % respectively.In contrast,below-and above-ground biomass of larch was lower in mixed than in pure planted.Root/shoot ratio of ash was 0.78～0.81 for potted seedlings and 0.52～0.55 for seedbed seedlings,2 times higher than that of larch.The total root mass of ash was 4～6 times higher than that of larch. With relatively larger root mass and root/shoot ratio,ash is a superior competitor.Root system of ash developed rapidly and distributed widely,but slowly and straitly for larch under the condition of the mixed.It was this competition differences that had resulted in the significant increase of ash production in the mixed plantations.

Key words: Mixed stand, Root system, Fraxinus mandshurica, Larix gmelinii, Competition among trees