海南中部典型槟榔-象草复合系统中根系空间分布及地下竞争

Spatial Distribution and Underground Competition of Roots in Typical Areca Nut-elephant Grass Complex System in Central Hainan,China

农林复合系统中,各组分根系的空间分布决定了其对系统内资源的竞争能力,是复合系统设计的重要依据。本文采用带状分层挖掘法,对槟榔–象草复合系统中二者的根系密度和空间分布进行研究,并用Levins提出的生态位重叠公式计算槟榔与象草的地下竞争指数。结果显示,槟榔根系的生物量密度(1343.88 g/m3)是象草(558.53 g/m3)的2.41倍。在水平方向上,槟榔细根(0~2 mm)、中根(2~5 mm)和粗根(>5 mm)的生物量密度、根长密度及竞争指数随根系距槟榔树干基部距离的增加呈下降趋势;象草的根系生物量密度、根长密度及竞争指数则随距离的增加呈上升趋势,且分布相对均匀。水平方向上,在距槟榔树干80 cm内时槟榔的整体根系生物量密度显著大于象草,120~140 cm处时象草的根系生物量密度显著大于槟榔,其余距离内二者之间的差异不显著;20~40 cm处槟榔的根长密度大于象草,但差异不显著,其余水平距离内象草根系的根长密度均显著大于槟榔;除距离树干20~60 cm处,其余区域内象草的竞争指数均大于槟榔。垂直方向上,0~20 cm土层内槟榔细根、中根、粗根以及象草根系的生物量密度、根长密度及竞争指数均显著大于20~40 cm土层;在2个土层中,槟榔根系的根长密度均小于象草,而槟榔根系的生物量密度与竞争指数均大于象草。研究表明:槟榔和象草的根系分布在空间上虽然有重叠,但二者在一定区域内各有优势,均不能对另一方形成绝对竞争优势,从而二者均能够在竞争中健康生长。因此,为了能够有效降低槟榔和象草之间的竞争,同时充分发挥各自的优势,将二者产量效益最大化,应适当增加象草与槟榔树间的种植距离,并适当加强间作区域内上层土壤的水肥投入。

In the agroforestry system,the spatial distribution of the root system of each component determines its com-petitive ability to the resources in the system,which is an important basis for the design of an agroforestry system.In this paper,the root density and spatial distribution of Areca catechu and elephant grass in the compound system were studied by the zonal layered mining method,and the underground competition index of A.catechu and elephant grass was calculated by the niche overlap formula proposed by Levins.The biomass density of betel nut root(1343.88 g/m3)was 2.41 times that of elephant grass(558.53 g/m3).In the horizontal direction,the biomass density,root length density and competition index of fine roots(0–2 mm),middle roots(2–5 mm)and thick roots(>5mm)of A.catechu decreased with the increase of the distance between roots and the base of A.catechu trunk.The root biomass density,root length density and competition index of elephant grass increased with the increase of distance,and the distribution was relatively uniform.In the horizontal direction,the root biomass density of A.catechu in 80cm from the trunk of A.catechu was significantly higher than that of elephant grass,and the root biomass density of elephant grass in 120–140 cm was significantly higher than that of A.catechu,but there was no significant difference between them in other distances.The root length density of A.catechu in 20-40 cm was higher than that of elephant grass,but the difference is not significant.The root length density of elephant grass in other horizontal distances was significantly higher than that of A.catechu.Except 20-60 cm from the trunk,the competition index of elephant grass in other areas was higher than that of betel nut.In the vertical direction,the biomass density,root length density and competition index of fine root,middle root,thick root and elephant grass root in 0-20 cm soil layer were significantly higher than those in 20-40 cm soil layer.In the two soil layers,the root length density of A.catechu root system was smaller than that of elephant grass,while the biomass density and competition index of A.catechu root system were larger than that of elephant grass.The results show that although the root distribution of A.catechu and elephant grass overlaps in space,they have their own advantages in a certain area,and neither can form an absolute competitive advantage over the other,thus both can grow healthily in the competition.Therefore,in order to effectively reduce the competition between betel nut and elephant grass,give full play to their respective advantages,and maximize their yield and benefit,we should appropriately increase the planting distance between elephant grass and betel nut trees,and appropriately strengthen the water and fertilizer input in the upper soil in the intercropping area.