Abstract: Compared with the physical and allelopathic mechanisms of litter mulching on seed germination and seedling growth, the mechanical mechanism remains relatively unknown. In this study, we examined the mechanical effects of litter on seedling survival and early growth of Cunninghamia lanceolata. Three litter types (C. lanceolata, Schima superba, mixture of C. lanceolata and S. superba with litter mass ratio of 1∶1 (Referred to as mixed litter hereafter)) and four litter amounts (control, 0 g·m^-2; shallow layer, 200 g·m^-2; moderate layer, 400 g·m^-2; deep layer, 800 g·m^-2) were simulated in an indoor control experiment. The results showed that: (1) Litter mulching had negative effects on the emergence rate of germinated seeds. The 30day survival rate showed a promotion response in the shallow layer but an inhibition in the deep layer. Ninety days after emergence, no seedlings survived under the deep mulching of mixed litter and the moderate and deep mulching of S. superba litter. The 90 day survival rates under moderate and deep cover of C. lanceolata litter was significantly lower than that under the control. (2) Ground diameter growth was promoted in shallow layer and inhibited in deep layer under C. lanceolata and mixed litter cover. Root growth decreased and stem length increased with increasing litter cover thickness. Compared with the control, C. lanceolata litter cover had a promoting effect on seedling height, while S. superba and mixed litter cover did not affect seedling height. (3) The effect of C. lanceolata litter on total biomass was positive under shallow layer, neutral under moderate layer, but negative under deep layer. The mixed litter had no significant effect on total biomass under shallow layer, negative effect under the moderate layer. The S. superba litter of shallow layer had significant negative effect on total biomass. (4) The root biomass proportion and root/shoot ratio decreased gradually with increasing litter layer thickness. Compared with the control, the proportions of leaf biomass, photosynthetic and non-photosynthetic tissue biomass increased significantly under the cover of the three types of litter, but without difference between different cover thicknesses. Compared with the control, the robustness (ratio of aboveground biomass to seedling height) of C. lanceolata seedlings was not significantly affected by shallow cover of C. lanceolata litter, but was significantly inhibited by moderate and deep cover. The robustness of C. lanceolata seedlings was inhibited by shallow mulching of S. superba litter. In general, the mechanical effect of litter on the growth of C. lanceolata seedlings was as follows: S. superba litter > mixed litter > C. lanceolata litter, indicating stronger impacts of broadleaf litter.

Key words: litter, mechanical action, biomass, early growth.