| Lead pollution in soils is one of increasingly serious environment problems with the development of industry in China, threatening the environmental safety and human health. Therefore, it's urgent to find a reasonable and effective method on reclamation of Pb-contaminated soil. Phytoremediation offers an easy handling, environmently friendly and cost-effctive technology. The method of combination of the microorganisms and plants is effctive to restoration of soil pollution, which can enhance phytoremediation efficiency and resistance of plants. In order to investgate effects of arbuscular mycorrhizal fungi on sex-specific responses of Populus cathayana in biomass accumulation and allocation, morphological characteristics, photosynthetic capacity, pigment content, antioxidant enzyme system, endogenous hormones and Pb accumulation and distribution under Pb pollution conditions, a controlled pot-experiment was taken. The major results and conclusions are as follows:(1) After four months of treatment, there was no significant gender difference of P. cathayana in biomass accumulation and morphological characteristics. The biomass indexes of females were higher than that of males, which is consistent to other researches on sexual dimorphism about P. cathayana. Under Pb pollution (100 mg Pb2+kg-1 dry soil) did not have a significant impact on biomass of both sexes, indicating that both sexes had a certain resistance to this Pb pollution level. The selected AMF showed a high infection rate to P. cathayana in this study, but symbiosis with exotic AMF did not significantly affect morphological characteristics of both sexes.(2) In terms of photosynthetic characteristics, when comes to photosynthetic parameters, Pb addition alone, the sxotic AMF alone and combined treatment did not induce a significant reduction in chlorophyll content in both sexes, when compared to the control. However, Fv/Fm and Yield decreased significantly under this Pb pollution level, both of which reflect damage of photosynthetic apparatus. Both of these two indicators had rebounded under the combination treatment. These results suggested that symbiosis with exotic AMF is helpful for mitigating negative impact of Pb on photosynthetic apparatus in both sexes.(3) Pb addition alone led to an increase of reactive oxygen species (ROS) in both sexes, induced the imbalance of the production and cleanup of ROS. In contrast, when compared with control, there was no significant difference in ROS of cuttings under the combination treatment. The results indicated that the inoculation of AMF has played a positive role in restoring balance of production and cleanup of ROS. On the other hand, Pb addition alone and especially the treatments pre-inoculated AMF significantly increased activities of antioxidant enzymes (SOD, CAT, APX and GR), and prompted accumulation of antioxidants (Gsh, ASC and dissociate proline) in the plant cell. The effective response of antioxidant system was beneficial to mitigate the negative effects of Pb stress, especially in males. It's worth noting that a further increase in antioxidant enzyme system occurred in both sexes under the combined treatment when pre-inoculated with AMF, especially in females. In addition, Pb pollution alone, the exotic AMF alone and combined treatment did not significantly affect the content of IAA and ABA in males. However, Pb addition alone induced a significant increase of ABA, but a significant decrease of IAA in females, when compared to the controls, the content of IAA and ABA in females did not change significantly under the combined treatment, indicating that AMF had a positive effect on maintaining the balance of endogenous hormones in females.(4) Pb addition alone did not have a significantly negative influence on absorption and assimilation of N, P of both sexes. Pre-inoculation with AMF did not significantly affect N absorption and assimilation in any organ of both sexes, whereas symbiosis with AMF had positive effect on the P absorption and assimilation, especially in root of both sexes. The promotion of P absorption and assimilation in males was more than that in females. In this study, culture matrix was supplied with nutrient-rich and adequate liquid nutrients weekly. Compared to the controls, contents of K, Ca and Mg in different organs did not changed significantly under Pb addition alone or exotic AMF inoculation alone. However, under combination treatment, formation of AM significantly increased contents of these elements in the organs of both sexes, especially in root. Meanwhile, promotion of K and Ca absorption and assimilation, when inoculated with extioc AMF, in males was more than that in females under Pb stress. It can be inferred that AM have a stronger promotion of various nutrient elements absorption and assimilation for plants on barren or polluted soils.(5) This study suggested that there is a significant difference between the sexes in Pb accumulation and distribution in poplars. The formation of AM significantly increased Pb absorption and accumulation in roots, and the increasing extent in female was more than that in males. The results showed that, under the low level of Pb pollution, as control conditions (20.5 mg Pb2+kg-1), absorption and accumulation of Pb in females was less than that in males to some extent, especially in the aerial part, while when exposed to high level of Pb pollution, there was much more Pb translocated and accumulated to females. From phytoremediation perspective, the adaptation strategies of Pb pollution in different sex were not identical. The high Pb accumulation features in females would result in higher Pb fixed by plant, and the AM significantly enhanced the properties, increasing the efficiency of phytoremediation of Pb, thus inevitably produced certain negative influence on the growth. In contrast, the males had adopted a strategy of exclusion in order to ensure its normal growth. |
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