Abstract: 【Objective】Plant stems function as supporting organs among many other functions, however, information on their load-bearing capacity has seldom been reported. The objectivs of this study were to: (1) define some stem functional traits; (2) examine effects of abiotic and biotic factors on these traits; (3) feature plasticities of these traits; and (4) explore their potential implications. 【Method】Three stem functional traits, namely, linear mass density (MD), ratio of load to self-weight (RLSW), and ratio of load to linear density (RLMD), were proposed and examined in 6 field experiments with maize (Zea Mays) as a model plant. MD = internode weight / its length, RLSW = internode mass load / its weight, RLMD = internode mass load / MD, where the mass load of an internode is the sum of the weights of all organs and tissues above the internode. The plasticity of a trait was represented as plasticity coefficients, which were computed after the manner of variation coefficients, and where variance components were estimated from the component models of expected mean squares for the experiment’s data. The 6 field experiments were conducted in Taigu, Shanxi. The treatments of these experiments are as follows: (1) the combinations of 5 sites by 2 cultivars; (2) the combinations of 11 sampling timings by 2 cultivars; (3) the combinations of 4 plant densities by 3 sampling timings; (4) 4 plant densities from 2.4 to 6.0 plants per square meter; (5) the combinations of 3 nitrogen fertilizer rates by 2 fertilization timings; and (6) high plant density without fertilization versus low plant density with fertilization. All 3 traits were subject to ANOVA, and means were separated by means of Least Significant Difference. The profile of MD along node ranks was fitted with a negative logarithm equation. 【Result】MDs of internodes varied from 0.052 to 0.72 g DW·cm^-1 and followed a straight line equation of a negative logarithm of node ranks. RLSWs of internodes ranged from 7 to 51, and RLMDs of internodes from 122 to 260 cm. If including load of ear weights, these ratios for the first node below the ear jumped to 246 and 3225 cm at their maximum values, respectively. These 3 stem functional traits showed statistically significant differences among genotypes and geographical sites. In the late duration of the kernel filling stage, MDs generally went down. MDs decreased with plant density, but RLSWs remained stable within a large range of plant densities. Higher nitrogen fertilizer rates increased MDs, but did not affect RLMDs, compared with lower ones. The plasticity of stem functional traits ranked as: MD＞RLSW＞RLMD, and the biomass investments for supporting were modulated by the optimization strategy. 【Conclusion】These findings showed that the stem functional traits proposed were able to feature the load-bearing of stems, and could delineate the biomass investments in the stem structure of plants and the investment efficiency, and may improve the understanding of biomass partitioning within whole plants.

Key words: Zea mays, stems, functional traits, trait plasticity, genotype, sites and agronomic measures, linear mass density, ratio of load to self-weight, ratio of load to linear density