海南岛三种人工林土壤化学计量特征研究

Research on soil stoichiometry of the three types of plantations in Hainan island

为更好地经营管理海南岛内的人工林,在五指山市、昌江县、三亚市三地,分别取桉树林、橡胶林、相思树林这三种岛内最主要的人工林林下土壤进行了化学计量学分析。结果表明,在不同调查地,同一人工林林下土壤有机碳(SOC)、总氮(TN)、总磷(TP)的含量存在差异,而在同一调查地内,人工林下土壤SOC与TN的含量比率关系相近。就各元素的垂直分布而论,SOC和TN含量在各区域各样地均以0~20cm土层较高,总体来看自上而下呈递减趋势;TP含量则表现为分层不明显(昌江和三亚)或于60~80cm土层达到最高(五指山)。在所有区域各类人工林中,五指山桉树林的SOC和TN含量最高,昌江相思树林的TP含量最高,三亚桉树林的SOC和TN含量最低,五指山橡胶林的TP含量最低。研究还发现,三个地区所有样地的林下土壤C/N和N/P比值均可分为两组,组间存在显著差异,其中N/P普遍偏低,存在明显的氮限制。根据调查结果推测,影响林下土壤化学计量学特征的因素包括水热条件、地表凋落物积累、土壤淋溶强度及元素的周转率等,前二者有利于土壤养分的输入和聚集,而淋溶过强则易造成土壤养分的流失,但较快的元素周转可以抵消淋溶的负面效应。综上所述,各类人工林林下土壤的化学计量学特征总体上因地而异,建议对于岛内人工林的C、N、P管理应充分考虑区域性差异。

For the purpose of managing plantations in Hainan island more effectively, the study, conducted in Wuzhishan city, Changjiang county, Sanya city, performed an eco-stoichiometric analysis here of on Eucalyp- tus plantations （Eucalytus spp.）, rubber plantations （Hevea brasiliensis） and Acacia plantations （Acacia spp.）, all of which are the main types of plantations in Hainan province. As found by the study,the content of SOC （ Soil organic carbon）, TN （Total nitrogen ） and TP （Total nitrogen）within understory soil in certain plan- tation differed among study areas, and the ratio of SOC contents in certain plantations to each other was similar to that of TN in the same study areas. With respect to the vertical distributions of individual nutrients in the soils, the contents of SOC and TN were respectively high within 0 - 20cm layers in all plots, and, as a whole, showed a decline from top to down, but the contents of TP showed more even distributions among layers in Changjiang and Sanya, or showed a peak at 60 - 80cm layer in Wuzhishan instead. Then all element contents withtin understory soils in all plots among study areas are compared, the results showed that the content of SOC and TN was highest in Wuzhishan Eucalyptus plantation, the TP content was highest in changjiang Acacia plantation, and the SOC and TN content and the TP content was lowest in Sanya Eucalyptus plantation and Wuzhishang plantation respectively. It is also found that both C/N and N/P ratio can be divided into two groups, which are statistically different from each other, and indicated a possible N limitation since N/P were generally lower in all plots. In light of our investigation, it can be inferred that stiochiometric characteristics ofunderstory soils likely vary with factors including thermal and water conditions,litter accumulation, leaching level and geochemistry cycle rates of elements etc. The former two factors promote input and gathering of soil nutrients, but leaching can result in loss of nutrients while faster cycle rates of elements can compensate this negative effect. Finally, It is, in conclusion, suggested that the C, N, P within plantation understory soil should be managed differently by region in view- of their stiochiometry change from one place to another.