四川大头茶若干生态问题的研究

STUDIES ON SOME ECOLOGICAL QUESTIONS OF GORDONIA ACUMENATA

四川大头茶（Ｇｏｒｄｏｎｉａａｃｕｍｅｎａｔａ）是我国亚热带西南地区常绿阔叶林优势种之一，材质好，生长快而又未被人注意的一种优良树种。由于它是喜阳的常绿阔叶顶极先锋种（ｐｉｏ－ｎｅｅｒｃｌｉｍａｘｓｐｅｃｉｅｓ）其幼苗耐阴，所以在针阔叶混交林中排挤了先锋树种（ｐｉｏｎｅｅｒｓｑｅｃ－ｉｅｓ）马尾松，而本身又在常绿阔叶林演替阶段，被更耐阴的顶极种（ｃｌｉｍａｘｓｐｅｃｉｅｓ）所代替。这是由于顶极种有较高的生态位重叠（ｎｉｃｈｅｏｖｅｒｌａｐ）和最大的生态位宽度（ｎｉｃｈｅｂｒｅａｄ－ｔｈ）值。四川大头茶Ｐｎ日变化具有双峰曲线型和单峰曲线型两种模式，而年变化有明显的季节现象。光照强度和温度是决定Ｐｎ的两个主要生态因子，并具有较高的饱和净光合速率和降低暗呼吸能力使其成为喜阳速生的特性。由于速生，其生物量可达１７６．６２ｔ·ｈａ￣（－１）；生产量达１０．８６ｔ·ｈａ￣（－１）。四川大头茶幼苗的蒸腾强度与大气湿度、叶温、光强、相对湿度、叶含水量等参数的变化有密切关系。干旱胁迫使光合速率明显下降，从而影响地上部分的生物生产力，但根／冠比却增加１８．１８％，这可能是植株对于旱胁迫的一种生态适应对策。四川大头茶各器官的营养?

Gordonia acumenata is one of the species dominating tbe subtropical ever- green broad-leaved forests in the southwest China. It is a pioneer climax sp-ecies that has light-demanding adults and shade-tolerant seedlings.Its curves of diurnal variation of Pn in the sunny days of spring,sum- mer and autumn have two peaks,one in the morning and the other in theafternoon,while in the winter,only one peak occurs at about 14∶00 o’clock,Beijing time.Gordonia acumenata is characterized by high saturated net photosyntheticrate and low dark respiration,therefore,its adults are light-demanding,wh-1le its seedlings are shade-tolerant.The transplration rates of its seedlings are greatly influenced by air temperature,leaf temperature,light intensity,relative humidity and leaf water content.Its photosyntbetic rate can be signi-ficantly decreased by drought-stress,accompanied with this is an increased root/shoot ratio of the seedlings.This might be a strategy for Gordonia acu-menata to be adapted to drought-stress.The nutrient content in different organs of Gordonia acumcnata varies with season.