中国亚热带灌丛植物生活型组成及其与水热因子的相关性

Composition of plant life forms of subtropical shrubland in China and its correlation with temperature and precipitation

灌丛是亚热带一种重要的自然植被类型,有关其植物生活型方面的研究资料较少。该文采用分层随机抽样方法布设688个样点,系统调查了亚热带常绿阔叶林区域内灌丛维管植物生活型组成,分析其生活型谱特征、地理格局及其与水热因子间的关系。研究发现:(1)亚热带灌丛中,木本植物种数占总种数的56.37%,其中落叶和常绿木本植物种数各占33.88%和22.49%;草本植物占43.63%,以多年生草本为主,占35.15%;生活型组成以高位芽植物为主,其次为地面芽植物,生活型谱表现为高位芽植物>地面芽植物>一年生草本>隐芽植物>地上芽植物。(2)植物生活型主要表现为经度和海拔格局;高位芽植物随经度增加逐渐增多,地面芽植物、隐芽植物和一年生植物随经度增加而减少;地面芽植物和隐芽植物随海拔升高而逐渐增加,高位芽植物、地上芽植物和一年生植物随海拔升高而逐渐减少。(3)气候因子中,最热月平均气温和最冷月降水量与高位芽植物、地面芽植物、隐芽植物和一年生植物的相关性最大;随着最热月平均气温的升高和最冷月降水量增多,高位芽植物比例增加,地面芽植物、隐芽植物和一年生植物减少;最热月平均气温和最冷月降水量可解释亚热带灌丛生活型谱地理格局变异的41.97%,其中28.35%由两者共同贡献。研究结果表明:高位芽植物和地面芽植物受温度和降水共同影响,隐芽植物对温度梯度的反应更加灵敏,一年生植物对降水的响应更加强烈,地上芽植物不随水热梯度发生大的波动;最热月平均气温和最冷月降水量是影响灌丛植物生活型谱地理格局最重要的水热因子。

Aims Shrubland is one of the most important vegetation types in subtropical region, but studies on its life-form composition and geographic patterns are scarce. In this paper, we addressed the following questions： what are the characteristics of the composition of plant life forms of subtropical shrublands in China？ And what are the relationships between the life form compositions, geographic patterns of subtropical shrublands and hydrothermal factors？ Methods A total of 688 plots, designed with the stratified random sampling method, were systematically set and investigated in subtropical shrublands in China. Life forms were identified based on Raunkiaer’s （1934） life form systems. Life form spectrums were compiled at each sampling site and within the whole shrubland, respectively. Partial correlation analysis was applied to reveal the latitudinal, longitudinal and altitudinal patterns of each life form. Pearson’s correlation analysis was adopted to evaluate the relationships between each life form and hydrothermal factors. Further, redundancy analysis （RDA） was used to distinguish the effect of temperature and precipitation on geographical variations of life forms. Important findings （1） In subtropical shrublands in China, 56.37% of the total species were woody species, among which 33.88% were deciduous species and 22.49% were evergreen species. The remaining 43.63% of the total species were herbaceous species, dominated by 35.15% perennials. Generally, phaenerophytes （Ph） was the most dominant component, while the second dominant one was hemicryptophytes （H）. The life form spectrum showed a pattern of Ph （55.74%） 〉 H （31.03%） 〉 T （therophytes 8.80%） 〉 Cr （cryptophytes 4.08%） 〉 Ch （chamaephytes 1.34%）. （2） Plant life forms mainly exhibited longitudinal and altitudinal patterns. With the increase of longitude, the percentage of Ph tended to increase while H, Cr and T tended to decrease. Furthermore, an increase in altitude would lead to an increase in H and Cr but a decrease in Ph, Ch and T. （3） Among all the investigated climatic factors, the mean temperature of the warmest month （MWT） and the mean precipitation of the coldest month （MCP） had the greatest impact on Ph, H, Cr and T. With an increase of MWT and MCP, Ph would increase while H, Cr and T would decrease. Taken together, MWT and MCP could explain 41.97% of the variation of life form spectrum, among which 28.35% was attributed to their joint-effect. The results suggested that Ph and H were mainly influenced by both temperature and precipitation, and that Cr was more sensitive to temperature gradients. Besides, T was more sensitive to precipitation, and Ch showed little fluctuation along hydrothermal gradients. In conclusion, MWT and MCP are the most important hydrothermic factors that determine the geographic patterns of life forms in subtropical shrublands in China.