北京市典型古树群落生长及土壤理化性质的空间分异特征

Spatial Differentiation of Tree Growths and Soil Physical-Chemical Properties in A Typical Ancient Tree Community in Beijing

古树群落是北京市古树的主体,对其进行系统研究可以为古树保护与管理提供科学依据。以北京市典型的古侧柏群落为研究对象,对1088株古树的生长指标进行每木调查,分析不同坡位和坡向古树叶片叶绿素含量(叶绿素a、叶绿素b、叶绿素a+b、叶绿素b/a)和树冠投影范围内土壤的理化性质差异,并进一步分析叶绿素含量、土壤理化性质与古树生长的关系。结果表明:(1)下坡古树的树高、胸径和冠幅均显著高于中、上坡,增幅都超过了5%;阴坡的树高和胸径比阳坡的显著增加了8%以上。(2)古树叶片叶绿素含量在下坡比中、上坡显著降低了15%~43%,阳坡比阴坡显著增加7%以上。(3)从下坡到上坡,土壤容重由1.30 g·cm^(-3)降低到1.12 g·cm^(-3),而含水率由18.00%增加到32.68%,土壤有机质、有效磷含量都是中坡最高,碱解氮、速效钾、含盐量和含水量都是上坡最高;土壤有机质、碱解氮、含盐量、含水量都是阳坡大于阴坡,而有效磷、速效钾和容重都是阴坡高于阳坡。(4)古树树高与叶绿素含量、土壤含水量极显著正相关,与土壤容重显著负相关。本研究表明,古树的生长、叶片光合特性、土壤理化性质随坡位、坡向呈现明显的空间分异特征,且不同坡位和坡向的土壤容重、含水量、有机质、碱解氮、有效磷、速效钾等土壤理化性质的差异对古树的生长产生了影响。今后应加强对古树群落土壤情况的连续监测,以制定更加科学的古树保护方案。

Ancient tree communities conserve the largest number of ancient trees in Beijing.The study of ancient tree communities can provide scientific basis for the protection and management of ancient trees.In this paper,1088 ancient trees in Beijing are individually investigated in terms of their growth indexes in a typical ancient Platycladus orientalis community,in order to analyze the chlorophyll content(chlorophyll a,chlorophyll b,chlorophyll a+b,and chlorophyll b/a)in the leaves of the ancient trees growing at different positions and aspects of slope and the physical and chemical properties of soil within the canopy projection range.The relationship among chlorophyll content,soil physical and chemical properties and the growth of ancient trees is then determined.The results show that:(1)The height,DBH and crown width of ancient trees on the lower slope are significantly higher than those on the middle and upper slopes by more than 5%;the height and DBH of the trees on the shady slope are higher by more than 8%than the trees on the sunny slope;(2)The chlorophyll content of ancient trees in the lower slope falls significantly by 15%-43%compared with those on the middle and upper slope,and the ancient trees in the sunny slope have their chlorophyll content increased by more than 7%compared with the trees on the shady slope;(3)From lower to upper slope,soil bulk density decreases from 1.30 g·cm^(-3)to 1.12 g·cm^(-3),and soil water content increases from 18.00%to 32.68%.The contents of soil organic matter and available phosphorus are the highest on the middle slope,and the contents of alkali-hydrolyzed nitrogen,available potassium,salt and water are the highest on the upper slope.Soil organic matter,alkali-hydrolyzed nitrogen,salt content and water content are higher on the sunny slope than on the shady slope,while available P,available K and bulk density are higher on the shady slope than on the sunny slope;and(4)The height of ancient trees is positively correlated with chlorophyll content and soil water content,and negatively correlated with soil bulk density.The results of this study show that the growth,photosynthetic characteristics of leaves and soil physical and chemical properties of ancient trees present obvious spatial differentiation with slope positions and slope aspects,and the differences in soil physical and chemical properties such as bulk density,water content,organic matter,alkali-hydrolyzed nitrogen,available phosphorus and available potassium in soil at different slope positions and slope aspects have an impact on the growth of ancient trees.Therefore,the continuous monitoring of soil conditions of ancient tree community should be strengthened in the future,so as to develop more scientific protection plan for ancient trees.