尾叶桉林下5种植物的耐阴性、生物量及其个体消长

为了解尾叶桉林下不同植物种类的生理生态特性和生长适应性,在鹤山站尾叶桉林中选取分布较多且药用价值和经济价值较高的5种林下植物为研究对象,测定各植物的叶片特征、叶绿素含量和光合-光响应曲线,同时结合2006年和2011年尾叶桉林的样方调查数据分析了5种林下植物生物量的变化和个体数量的消长。结果表明:(1)野牡丹叶片的宽度、厚度、单片叶面积等指标最大,梅叶冬青最小,桃金娘、栀子和山苍子处于两者之间;桃金娘、野牡丹和山苍子的光合速率随光照的增强迅速增大,其光饱和点较高;梅叶冬青和栀子的光合速率也随光照的增强而增大,但其斜率比野牡丹和山苍子大,并很快就达到光饱和点。综合聚类分析植物的耐阴程度,5种植物可分为2类:第1类为耐阴性较强的梅叶冬青、栀子,第2类为耐阴性较弱的野牡丹、山苍子和桃金娘。(2)随着尾叶桉林的生长,5种林下植物的生物量都有不同程度的增加,其中增幅较大的是野牡丹和桃金娘分别增加74倍和18倍,增幅最小的是栀子仅1.3倍。野牡丹、桃金娘和山苍子这3个种生物量的增加主要是由个体高度和地径的增长引起,而栀子和梅叶冬青生物量的增加是其个体数量、株高和地径做出的贡献。(3)在尾叶桉林生长过程中,耐阴种类梅叶冬青随着个体密度、株高和地径的增长,其在林内发展成为主要优势灌木种类;栀子的密度虽然有一定的增大,但其株高和地径增加量小,生物量也小,发展为次要灌木种类。野牡丹、桃金娘和山苍子等3种的个体密度都在下降,虽然其地径、株高和生物量也有一定的增长,但其较强的阳生性不能适应林内的荫蔽环境,只适于林窗或林缘光照较强的地方生长。因此,在桉树林经营管理过程中应适当保护和种植梅叶冬青和栀子;在短轮伐期经营模式下,林窗和林缘也可适当保留野牡丹、桃金娘和山苍子。

Dynamics of shade tolerance, biomass, and individual growth of five understory plant species in Eucalyptus urophylla plantations

In order to investigate the ecophysiological characteristics and growth adaptability of different understory plants in Eucalyptus urophylla plantations, five understory species with high economic and medicinal values, including Ilex asprella, Gardenia jasminoides, Melastoma candidum, Rhodomyrtus tomentosa, and Litsea cubeba, were selected to measure leaf characteristics, chlorophyll content, and photosynthetic light response curves. In addition, the dynamics of biomass and individual number were analyzed based on field sampling survey data in 2006 and 2011. Comparative analysis and cluster analysis revealed that:(1) the leaf width, thickness and, area of M. candidum were the largest, whereas those of I. asprella were the smallest. Overall, the net photosynthetic rate of the selected understory plants increased with increasing light intensity. However, the net photosynthetic rate of I. asprella and G. jasminoides increased more rapidly than that of M. candidum and L. cubeba, and reached the light saturation point more quickly. R. tomentosa, M. candidum, and L. cubeba had higher light saturation points than that of I. asprella and G. jasminoides. The selected understory plants could be classified into two groups in terms of shade-tolerance ability, based on hierarchical cluster analysis. I. asprella and G. jasminoides were assigned to the strong shade-tolerant group, whereas M. candidum, L. cubeba, and R. tomentosa were assigned to the low shade-tolerant group. (2) Biomass of the five selected understory species increased with stand age, but the range of increment varied. The greatest increase was observed in M. candidum (74 fold), followed by R. tomentosa (18 fold), and the least was observed in L. cubeba (1.3 fold). The increase in biomass of M. candidum, R. tomentosa, and L. cubeba was mainly caused by the increase in individual height and basal diameter, whereas the increase in biomass of I. asprella and G. jasminoides was mainly attributed to the increase in individual number, height, and basal diameter. (3) I. asprella, a shade-tolerant understory species with high economic value, dominated the shrub community with increasing stand age of the Eucalyptus plantations, mainly owing to the increase in density, individual height, and basal diameter. G. jasminoides showed lower dominance over the shrub community owing to lesser increase in individual height and basal diameter than those of I. asprella. The density of L. cubeba, R. tomentosa, and M. candidum showed an overall decline with minor increase in individual height, basal diameter, and biomass. L. cubeba, R. tomentosa, and M. candidum can only survive in forest gap and edge owing to light limitation. In conclusion, we suggested that I. asprella and G. jasminoides should be protected and re-introduced during Eucalyptus plantation management for biodiversity conservation. Under the short-rotation management regime, M. candidum, L. cubeba, and R. tomentosa should be retained and re-introduced in the forest gap and edge.