华南热带沿海不同林龄木麻黄人工林养分利用特征

Nutrient utilization by Casuarina equisetifolia plantation of different ages in the tropical coastal area of South China

木麻黄(Casuarina equisetifolia)人工林是我国东南沿海最重要的防护林类型,但近年来出现明显的衰退现象.以广东省电白县沿海4种林龄(3、6、13、18年生)木麻黄人工林为研究对象,比较不同林龄木麻黄人工林系统养分利用特征.研究表明,木麻黄不同器官含碳量差别不大,枝与干含碳量(448-462 g kg-1)略高于叶与枯落叶含碳量(416-430g kg-1),细根含碳量最低(320-391 g kg-1),除细根外,不同器官含碳量也不随林龄的增加而变化.木麻黄细根生物量与沙地土壤有机碳积累没有统计上的相关性.木麻黄含氮水平(9.9-11.9 g kg-1)与本地区其它植物叶片含氮量相当,其生理活性最高的叶片与细根含氮量最高,两者具有相似的动态特征,生长旺盛的6年林含氮量最低.木麻黄叶片含磷量最高(0.66-0.89 g kg-1),其次是细根,枝干含磷量最低.木麻黄不同器官含磷量在旺盛生长期(6年)和衰老期(18年)最低.4个林龄土壤中,3年林土壤含磷量远高于其它林地,3年林较高的土壤磷导致了较高的土壤有机碳和氮含量,但所有林地土壤碳、氮含量总体水平极低,约为同地带正常土壤碳氮含量的1/10.土壤含氮量与植物叶片及细根含氮量有一定的相关性,但土壤磷与植物磷没有统计上的相关性.木麻黄不同器官碳氮比及碳磷比基本不随林龄而变化,只有叶片有激烈的动态特征,6年林叶片处于最高值.木麻黄对衰老叶中氮转移效率不高,约为18%-30%,磷转移率在43%-58%,木麻黄的氮磷转移率与土壤或体内养分水平没有统计上的相关性.因而,当地木麻黄氮磷养分水平低,幼龄快速生长阶段受氮磷养分限制,较老阶段受磷养分限制,沙地土壤养分水平极低,土壤碳汇功能差.

Casuarina equisetifolia plantation plays a key role in protecting coastal areas from hazardous climate.However,the plantations in the tropical coastal area of south China have degraded severely in recent years.This research aimed to investigate the nutrient status of the plantation ecosystem along a chronological sequence.The results showed that different parts of the Casuarina equisetifolia had very similar level of Carbon（C）,448-462 g kg^-1 in the branch and trunk,416-430 g kg^-1 in the leaf and shed leaf,320-391 g kg^-1 in the fine root.Carbon content did not vary with the plantation age.High fine root biomass did not definitely lead to high soil carbon stock.Casuarina equisetifolia had Nitrogen（N） content of 9.9-11.9 g kg^-1,with the highest N found in the leaf and fine root.The Phosphorus（P） content was in the order of leaf fine root trunk.The plantation in fast growth period of age 6 had the lowest N and P.The soil of 3-year plantation had the highest P content among the 4 age classes,which also resulted in the highest soil C and N content in plantation of 3 years among all.However,the C and N stock of the sandy soil was extremely low compared to normal soil of the region.Soil N was weakly correlated with leaf N,but soil P not correlated with leaf P.Except for the obvious dynamics of C/N and C/P ratios in the leaf,which showed a peak in 6-year plantations,the C/N and C/P ratios of different organs did not change with the plantation age.Casuarina equisetifolia retranslocated nutrients from aging leaf at a rate of 18-30% for N and 43-58% for P.The nutrient resorption efficiency was not correlated with nutrient level in either soil or plant.In summary,Casuarina equisetifolia has low level of nutrient status.The plantation growth is limited by N and P in young period,but by P in relatively older period.