Effects Of Root Exudates Of The Same Or Opposite Sex On The Growth Of Populus Cathayana Seedlings

Plants have evolved the elaborate mechanisms to specifically detect and respond to their neighbors through roots, which is significant for the maintenance of population and community composition. However, the research about the sex recognition in dioecious plant is still very rare. In our study, male and female P.cathayana seedlings were chosen as experimental material, and the seedlings were watered with the root exudates of the same or opposite sex in order to explore the impacts on the morphological characteristics and biomass, photosynthetic traits and water use efficiency, root physiology and nutrient content of the seedlings. The results can reveal the response difference of the seedlings to root exudates of the same or opposite sex, and provide reference for the mechanism of sex recognition. The main results are as follows:1. The impact of root exudates on the morphological characteristics and biomass of male and female P. cathayana seedlings.Compared with control, the root exudates of the same sex significantly inhibited the height, leaf biomass, above-ground biomass, root biomass in females and the diameter, leaf biomass, stem biomass, root biomass, total biomass in males. On the other hand, in treatment with the root exudates of the opposite sex, the diameter in females was significantly higher than that of the control, and the specific leaf area in males was significantly decreased, while other traits have no significant difference with the control group. The results suggest that the growth and development of the seedlings was obviously inhibited by the root exudates of the same sex, however, the root exudates of the opposite sex promoted the growth of females and inhibited the growth of males, and the effects were lesser. Moreover, the specific root length and specific surface area in females and the specific root length in males significantly increased under the treatment of the root exudates of the same sex.2. The impact of root exudates on the photosynthetic traits and water use efficiency of male and female P. cathayana seedlings.The root exudates of the same or opposite sex had no significant effects on the photosynthetic pigments, photochemical efficiency of photosystem II, gas exchange and water use efficiency in male and female seedlings, except that the Pn and δ13C were significantly reduced in treatment with the root exudates of the same sex.However, the photosynthetic pigments and water use efficiency displayed somechanges. In treatment with root exudates, the chlorophyll and carotenoid in females were higher than those in the control, and the photosynthetic pigments in males were decreased. In addition, the WUEi in females was increased, while the δ13C was decreased with the treatment of root exudates, and the δ13C, WUEi in males were also decreased. On the whole, in respect of photosynthetic traits and water use efficiency,only the male plant was sensitive to the root exudates of the same sex.3. The impact of root exudates on the root physiology of male and female P.cathayana seedlings.The starch content in the roots of male and female plants was significantly increased in the treatment of the root exudates of the opposite sex, and the soluble sugar content in the roots of males was inhibited by the root exudates of the same sex.Besides, the root exudates of the same sex inhibited males and females in the root activity. Whereas, the root activity was enhanced in females, and it was decreased in males in treatment with the root exudates of the opposite sex. But no significant difference was observed. In addition, under the treatment of root exudates, the ABA content in females was significantly decreased, while the ABA content in males showed no significant difference with that of the control. On the whole, effects of the root exudates of the same or opposite sex on the non-structural carbohydrates were different, and the root activity was less affected by root exudates. Furthermore, only the ABA in female’s roots was affected by root exudates.4. The impact of root exudates on the nutrient content of male and female P.cathayana seedlings.In treatment with the root exudates of the same sex, the C, N concentration in roots, and the N, P, K concentration in stem, and the C, K concentration in leaves of females were significantly higher than that of the control. The C, N, K concentration in stem, and the C, K concentration in leaves of males were also significantly increased. Moreover, the C/N in stem of male and female seedlings and the C/N in roots of females were significantly decreased. The results suggest that the root exudates of the same sex may inhibit the utilization of nutrient. On the other hand, the C, N concentration in leaves and roots of females were significantly higher than that of the control under the treatment of the root exudates of the opposite sex, which was in favor of the growth and development of the seedlings. As to the males, the C, N concentration in stem significantly increased, while the N concentration in leaves was significantly decreased. In addition, the C/N in stem was significantly decreased. It issuggest that the root exudates of the opposite sex made the nitrogen transfered to stem,which lead to the lower use efficiency. Furthermore, The study also showed that the N,P, K accumulation in males were significantly decreased with the treatment of the root exudates of the same sex, and the N accumulation in females was significantly increased with the treatment of the root exudates of the opposite sex.In a word, the response of male and female seedlings to the root exudates of the same or opposite sex was different, which suggest that root exudates can impart gender-related information, and play a role in the detection and response to the gender of their neighbors.