深圳湾红树木榄根系生物量及空间分布格局

Root biomass and its spatial distribution of Bruguiera gymnorrhiza in the mangrove of Shenzhen Bay, South China

关键词:  地下生物量, 空间分布格局, 木榄, 福田红树林, 植物生态

Key words:  root biomass, spatial distribution, Bruguiera gymnorrhiza, Futian Mangrove, plant ecology

摘要:

采用分层挖掘法,对深圳湾乡土种红树植物木榄不同活力和径级根系生物量及相关底泥性质的空间分布格局进行了研究。结果表明:木榄人工林平均总根系生物量为61.23 t·hm^-2,其中活根生物量占86.42%,死根占13.58%。在活根中,粗根(直径>10 mm)所占比例最高(84.57%),其次为细根(2～5 mm,5.84%)、极细根(<2 mm,4.94%)和中根(5～10 mm,4.66%)。木榄总根系生物量从基部到树冠落水线处递减,生物量分别为77.54 t·hm^-2(基部)、22.88 t·hm^-2(中部)和16.15 t·hm^-2(边缘); 基部直径>10 mm的活根生物量为中部和边缘活根生物量的5倍以上; 随着水平距离的增加,<2 mm根系生物量占相应距离处活根生物量的比例增加。垂直分布以中下层(20～60 cm)居多,分别占相应水平距离处总根系生物量的80.89%(基部)、73.41%(中部)和71.76%(边缘); 总根系生物量分布主要受水平距离的影响(P<0.05)。底泥含水量、容重、pH和电导率的变化范围分别为30.66%～35.86%、1.23～1.40 g·cm^-3、5.75～7.01 S·m^-1和0.22～0.37 S·m^-1,其中底泥容重与不同活力根系生物量呈显著负相关(P<0.05),是影响木榄根系生物量及其空间分布的主要环境因子。该研究结果为福田红树林地下碳分配、储量及周转速率等进一步研究提供了科学依据。

Abstract:

The native species Bruguiera gymnorrhiza in the Futian Mangrove of Shenzhen Bay, was selected to study the spatial distribution of root biomass. The hierarchical sampling method is adopted. The results showed that root biomass of the B. gymnorrhiza was about 61.23 t·hm^-2; among which, living root biomass accounted for 86.42%, dead root biomass accounted for 13.58%. For the living root biomass, the thick root(>10 mm in diameter)had the highest proportion(84.57%), followed by fine root(2-5 mm, 5.84%), very fine root(<2 mm, 4.94%), and the medium root(5-10 mm, 4.66%). From the tree base to the edge of the canopy, the horizontal distribution of root biomass presented decreasing trend, and the decrement was slowing down, with the root biomass of 77.54 t·hm^-2 (the base), 22.88 t·hm^-2(the middle)and 16.15 t·hm^-2 (the edge), respectively. In the tree base, > 10 mm in diameter of living root biomass was more than 4 times higher than living root biomass in the middle and the edge. The proportions of < 2 mm living root biomass to the living root biomass increased from the tree base to the canopy edge. Vertical distribution of root biomass was mainly in the lower layer(20-60 cm), with root biomass accounted for 80.89%(the base), 73.41%(the middle)and 71.76%(the edge)for the total root biomass, respectively. The spatial distribution of total root biomass was mainly influenced by the horizontal distance from the tree base(P<0.01), with no significant impact from sediment depth(P > 0.05). In sediments, the value of water content, bulk density, pH and electrical conductivity was(30.66±0.88)%-(35.86±7.59)%,(1.23±0.07)-(1.40±0.00)g·cm^-3,(5.75±1.49)-(7.01±0.50)S·m^-1 and(0.22±0.02)-(0.37±0.12)S·m^-1, respectively. There was no significant relationships between root biomass and sediment properties, such as pH, water content and electrical conductivity(P>0.05). While, significant negative correlations were detected between bulk density and different levels of root biomass, including total root, total live root, total dead root, >10 mm live root and ≥10 mm dead root. It showed that bulk density was one of mean environmental factors influencing the root biomass and its spatial distribution. Biomass is an important basis to evaluate the capacity of carbon sink, this research can provide a basic reference for the further study of underground carbon distribution, reserves and turnover rate in the Futian Mangrove.