Text by Lauri Laanisto
This Sino-Tibetian and Finno-Ugric collaboration in studying growth and stress of Chinese trees is continuing this year as well (see also this and this and that blog post). And the output of course is in Indo-European. So, this time Populus cathayana (the name is available only in another, already extinct Indo-European language) was studied. Well, Populus species are known for fast growth and big size, and the timber can be used in many ways, mainly as pulpwood in paper indusrty. Thus, it´s no wonder that lots of research is done with poplars, aspens and cottonwoods. For example, the black cottonwood, western balsam-poplar or California poplar (Populus trichocarpa) was the first tree species for which the full DNA genome was sequences (link to the paper).
The new study by Chen and others concentrates on how sexual competition, cadmium stress and their concurrence affect (the obviously dioecious) Populus cathayana. The reason to concentrate on cadmium is because this specific species is known to be able to grow on habitats degraded by heavy metals. However, it had not yet been studied how high heavy metal levels affect the growth and propagation of the species, and whether these potential effects are tolerated equally well with male and female individuals or not. And the gender differences in Populus cathayana growing in different soil conditions were detected in the previous study where the effect of nitrogen was studied (link to blog post).
Male and female plant cuttings from 15 populations were transplanted to pots where they experienced different levels of cadmium and competition. The authors studied many-many different traits – I´m not gonna list them all here, check the paper. Anyhow, the experimental treatments worked in the sense that significant differences were found on most of these traits. Like the Abstract says: “The results showed that competition significantly affects biomass partitioning, photosynthetic capacity, leaf and root ultrastructure, Cd accumulation, the contents of polyphenols, and structural and nonstructural carbohydrates.”
Citation: Chen, J., Duan, B., Xu, G., Korpelainen, H., Niinemets, Ü., & Li, C. (2016). Sexual competition affects biomass partitioning, carbon–nutrient balance, Cd allocation and ultrastructure of Populus cathayana females and males exposed to Cd stress. Tree Physiology, tpw054. (link to full text)
Although increasing attention has been paid to plant adaptation to soil heavy metal contamination, competition and neighbor effects have been largely overlooked, especially in dioecious plants. In this study, we investigated growth as well as biochemical and ultrastructural responses of Populus cathayana Rehder females and males to cadmium (Cd) stress under different sexual competition patterns. The results showed that competition significantly affects biomass partitioning, photosynthetic capacity, leaf and root ultrastructure, Cd accumulation, the contents of polyphenols, and structural and nonstructural carbohydrates. Compared with single-sex cultivation, plants of opposite sexes exposed to sexual competition accumulated more Cd in tissues and their growth was more strongly inhibited, indicating enhanced Cd toxicity under sexual competition. Under intrasexual competition, females showed greater Cd accumulation, more serious damage at the ultrastructural level and greater reduction in physiological activity than under intersexual competition, while males performed better under intrasexual competition than under intersexual competition. Males improved the female microenvironment by greater Cd uptake and lower resource consumption under intersexual competition. These results demonstrate that the sex of neighbor plants and competition affect sexual differences in growth and in key physiological processes under Cd stress. The asymmetry of sexual competition highlighted here might regulate population structure, and spatial segregation and phytoremediation potential of both sexes in P. cathayana growing in heavy metal-contaminated soils.