凋落物对杉木幼苗存活及早期生长的机械效应

Mechanical effects of litter cover on seedling survival and early growth of Cunninghamia lanceolata

凋落物覆盖对种子萌发及幼苗生长作用机制的研究多集中在物理作用和化感作用方面,机械作用机制尚缺乏系统研究。本研究以杉木已萌发种子为对象,通过室内控制实验研究3种凋落物类型(杉木、木荷、杉木和木荷1∶1混合(简称混合凋落物,下同))和4个覆盖厚度(对照,0 g·m^(-2);浅层,200 g·m^(-2);中层,400 g·m^(-2);深层,800 g·m^(-2))模拟不同凋落物覆盖条件对杉木幼苗存活和早期生长的机械效应。结果表明:(1)凋落物覆盖对已萌发种子的出苗率具有抑制作用。幼苗30 d的存活率总体表现为浅层促进,深层抑制的规律。出苗90 d后,混合凋落物深层覆盖和木荷凋落物中层和深层覆盖下已无幼苗存活。杉木凋落物中层和深层覆盖下的90 d存活率显著小于对照。(2)地径生长在杉木和混合凋落物覆盖下表现为浅层促进,深层抑制规律。根长生长随凋落物覆盖厚度的增加而降低,茎长则随覆盖厚度的增加而增加。与对照相比,杉木凋落物覆盖对幼苗苗高有促进作用,木荷和混合凋落物覆盖对苗高无明显影响。(3)杉木凋落物对总生物量的覆盖作用表现为浅层促进,中层不影响,深层抑制;混合凋落物浅层覆盖对总生物量无显著影响,中层覆盖有抑制作用;木荷浅层凋落物覆盖对总生物量有显著抑制作用。(4)根生物量比和根冠比随着凋落物厚度的增长逐渐减低。与对照相比,3种类型凋落物覆盖后叶生物量比和光合与非光合组织生物量比都显著增加,但不同覆盖厚度之间无显著差异。与对照相比,杉木凋落物浅层覆盖对粗壮度无显著影响,但中层和深层覆盖有显著抑制作用;木荷凋落物浅层覆盖对粗壮度有抑制作用。总体来看,凋落物机械作用对杉木幼苗生长的影响大小表现为:木荷凋落物>混合凋落物>杉木凋落物,即阔叶凋落物对杉木幼苗生长的影响最大。

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.