岷江干旱河谷25种植物一年生植株根系功能性状及相互关系

相同条件下相同生长期的植物根系生长与适应策略及其差异性还不清楚。因此,采集岷江干旱河谷地区25种乡土植物(木本15/草本10种)的种子于2009年3月播种在同一干旱环境中,9月测定了1年生植株的最大根深(RDmax)、根幅(RW)与根生物量(RB),计算了总根长(TRL)、比根长(SRL)及细/粗根生物量比(RBf/c),分析了它们之间的关系,进行了根系功能组划分。结果表明:1)25种植物1年生植株RDmax与RW变异较小,总变异率为14.9%和20.7%;TRL和SRL变异相对较大,分别为28.5%和34.7%,草本植物SRL明显大于木本植物;RB和RBf/c种间变异较大,总变异率分别为50.1%和70.5%;2)25种植物的RDmax、RW、RB和TRL间呈显著正相关关系,表明根系较深的物种RW较大,TRL和RB也较高;SRL与RDmax呈极显著负相关关系,与RBf/c呈极显著正相关关系,表明根系垂直分布较浅的物种细根发达,SRL较大;3)主成分分析显示,25种植物可分为3个功能组:第1组具有较大RDmax、RW和RB,资源利用持续时间较长;第2组具有较大TRL、SRL和RBf/c,资源利用效率较高;第3组根系功能性状没有一致的突出特点,可能通过降低自身生理机能适应生存条件。综合分析表明,岷江干旱河谷区25种植物1年生植株根系的功能性状变异明显,可塑性大,历经长期自然选择压力而形成了不同的环境适应策略,但生长型并不必然表达出1年生植株根系功能性状的差异性。

Root functional traits and trade-offs in one-year-old plants of 25 species from the arid valley of Minjiang River

The functional traits and distribution patterns of roots affect the amount of soil resources used by the plant. These functional traits can mirror plant ecological resource utilization strategies for capturing soil water and nutrients. Changes in root functional traits can affect important plant processes, including water- and nutrient-use efficiencies and the ability to compete for belowground resources. In this study, root functional traits and correlations among them were investigated in one-year-old plants of 25 species from the arid valley of Minjiang River. The specific objectives were to compare plants of the same age growing in the same conditions to assess the trade-offs among root functions based on correlations among different functional traits, and to define plant functional types and their adaptation strategies. Seeds of vascular plant species were pretreated and sown in March 2009 in a field at the Maoxian Station for Ecosystem Research, Chinese Academy of Science. Complete root systems were sampled by excavating the entire individual in September, 2009, when plants were one year old. We measured six root functional traits; root depthmax, root width, total root length, specific root length, total root biomass, and ratio of fine/coarse root biomass. We examined the specific ecological strategies of the 25 species in adapting to the same habitat by comparing and contrasting the individual trait range and testing relationships among root functional traits. There was relatively low variability among the 25 species in terms of root depthmax (14.9%) and root width (20.7%), but higher variability in total root length (28.5%) and specific root length (34.7%). The specific root length of herbaceous plants was markedly greater than that of woody plants. Among the 25 species, there were significant differences in root biomass (total variance ratio, 50.1%) and the ratio of fine/coarse root biomass (total variance ratio, 70.5%). At the species level, there were significant positive correlations among root depthmax, root width, total root length, and root biomass, indicating that plants with deeper roots generated greater root width, longer total root length, and greater root biomass. In addition, specific root length was significantly positively correlated with the ratio of fine/coarse root biomass but negatively correlated with root depthmax. These results indicated that plants with higher specific root length tended to generate more fine roots but a relatively shallow root system. The principal component analysis showed that the 25 species could be divided into three functional groups, explaining nearly 80% of the total variation. The first group had larger root depthmax, greater root width, and greater root biomass; the second group had greater total root length, greater specific root length, and larger ratio of fine/coarse root biomass; the third group did not show uniform patterns for any of the six functional traits. This comprehensive analysis revealed that there was variability in the individual root functional traits among 25 different species from the arid valley of Minjiang River, and that different functional types showed various environmental adaptation strategies. Species adapt to local water and nutrient conditions either by improving water- and nutrient-use efficiencies or by decreasing root performance functions. The life-form of a given species could not predict differences in functional root traits at the one-year-old growth stage.