[Effect of flooding time length on mycorrhizal colonization of three AM fungi in two wetland plants].

In order to provide information for elucidating effect of flooding on the formation and function of AM in wetland plants, three AM fungi (Glomus intraradices, Glomus versiforme, Glomus etunicatum) were used to investigate the effects of flooding time length on their colonization in cattail (Typha orientalis) and rice (Oryza sativa L. ). The results showed that the mycorrhizal colonization rate (MCR) presented downtrend with increasing flooding time length. In cattail, MCR of the fungus F3 was higher than those of fungi F1 and F2, but no significant difference in MCR was found between fungi F1 and F2. In rice, the MCRs of fungi F2 and F3 were higher than that of E1. In both plants, the proportional frequency of hyphae was the highest while the proportional frequency of arbuscules and vesicles was very low in all treatments, indicating that hyphal colonization was the main route for AM formation. The proportional frequency of hyphae in cattail increased with the flooding time length, but no significant trend was observed in rice plant. The proportional frequency of arhuscules decreased with the increase of flooding time, and was the highest in the treatment without flooding (treatment IV). The number of spores produced by AM fungi increased with increasing flooding time, and reached the highest in the treatment of long time flooding (treatment I). In the same treatment, the fungus F3 produced more spores than fungi F1 and F2. Changes in wet weight of the two plants showed that AM could increase cattail growth under flooding, hut little effect on rice growth was found. It is concluded that flooding time length significantly affected the mycorrhizal colonization rate and the proportional frequency of colonization. AM could enhance the growth of wetland plant, but this depends on the mycorrhizal dependence of host plant on AM fungi. Therefore, flooding time length should be considered in the inoculation of wetland plants with AM fungi.

[Strategies of nutrients control in lakes based on ecoregions of lakes in China].

In order to better reduce lake eutrophication, based on five ecoregions of lakes, the relationships of total nitrogen (TN), total phosphorus (TP), and TN/TP ratio with chlorophyll-a (Chl-a) in 100 lakes were discussed, furthermore, strategies of nutrient control were proposed respectively. Results showed that among the five ecoregions, the lake eutrophication level was the lowest in Dongbei ecoregion and the highest in Huabei ecoregion, but the eutrophication level in lakes of all the five ecoregions is increasing in recent years. Algal growth in lakes of Dongbei and Huabei ecoregions was limited by phosphorus, while it was simultaneously limited by nitogen and phosphorus in lakes of other three ecoregions (Zhongdongbu, Yungui and Mengxin). In lakes with TN/TP < 10, significant correlation between Chl-a concentration and TN was found in lakes of the five ecoregions except for Huabei ecoregion, and significant correlation between Chl-a concentration and TP was found in lakes of Dongbei and Mengxin ecoregions. In lakes with TN/TP > 17, significant correlation between Chl-a concentration and TP was found in lakes of the five ecoregions except for Mengxin ecoregion, and significant correlation between Chl-a concentration and TN was found in lakes of Zhongdongbu, Yungui and Mengxin ecoregions. In lakes with 10 < TN/TP < 17, no significant correlation between Chl-a and TN (or TP) was found in lakes of all ecoregions except for Zhongdongbu ecoregion where Chl-a concentration was significantly affected by TN. As for strategies of nutrient control and reduction in the five ecoregions, lakes of Huabei ecoregion should adopt TP control in priority, and in Dongbei ecoregion, TP and TN should be controlled simultaneously in lakes with TN/TP < 10, while other lakes should focus on TP control. Lakes in other three ecoregions (Zhongdongbu, Mengxin and Yungui) should control TP and TN simultaneously.

[Effect of elevated O3 on the arbuscular mycorrhizal (AM) structure and glomalin production in two genotypes of snap bean].

In an environment with simulated elevated atmospheric ozone, two genotypes of snap bean (Phaseolus vulgaris L.) that differed in O3 sensitivity (O3-sensitive: S156; O3-tolerant: R123) were selected as host plants for arbuscular mycorrhizal (AM) fungi. The objective was to investigate the effect of elevated O3 on the AM structure and glomalin production in two genotypes, and to understand the effect of elevated O3 the growth of AM fungi and formation of AM structure. The results showed that in comparison with ambient O3 (20 nL x L(-1)), elevated O3 (70 nL x L(-1)) significantly decreased the mycorrhizal colonization rate in both genotypes, particularly the S156 plant (decreased by 43.6%). Elevated O3 exposed a great negative effect on the AM structure in both genotypes. For example, the arbuscule number per unit root, and the length of external hyphae in root compartment and hyphal compartment were significantly decreased, especially in S156 plant. However, the effect of elevated atmospheric O3 was not significant on the vesicule number per unit root in both genotypes. Total glomalin production in mycorrhizosphere and hyphosphere of both genotypes was only slightly affected by elevated O3, however, the production of easily extractable glomalin was significantly increased. In addition, no evident difference in glomalin concentration was observed between two genotypes at either ambient O3 or elevated O3. This study showed that the mycorrhizal colonization rate, AM structure and production of easily extractable glomalin gave great response to elevated O3 especially in the O3-sensitive plant.

[Effect of CO2 fertilization on residual concentration of cypermethrin in rhizosphere of C3 and C4 plant].

In order to achieve sustainable economic and environmental development in China, CO2-emission reduction and phytoremediation of polluted soil must be resolved. According to the effect of biological carbon sequestration on rhizosphere microenvironment, we propose that phytoremediation of polluted soil can be enhanced by CO2 fertilization, and hope to provide information for resolving dilemma of CO2-emission reduction and phytoremediation technology. In this study, effects of CO2 fertilization on cypermethrin reduction in rhizosphere of C3-plant (bush bean) and C4-plant (maize) were investigated. Results showed that dry weight of shoot and root of bush bean (C3 plant) was increased by CO2 fertilization. Relative to ambient CO2, dry weight of root was increased by 54.3%, 31.9% and 30.0% in soil added with 0, 20 and 40 mg x kg(-1) cypermethrin respectively. Microbial biomass was increased by CO2 fertilization in rhizosphere soil added with 0 mg x kg(-1) cypermethrin, but negative effect was found in rhizosphere soil added with 20 and 40 mg x kg(-1) cypermethrin. CO2 fertilization slightly affected residual concentration of cypermethrin in rhizosphere soil added with 0 mg x kg(-1) cypermethrin, but significantly decreased residual concentration of cypermethrin as 24.0% and 16.9% in soil added with 20 and 40 mg x kg(-1) relative to ambient CO2. In maize plant, however, plant growth, microbial biomass and residual cypermethrin concentration in rhizosphere was slightly affected by CO2 fertilization, and even negative effect was observed. This study indicated that CO2 fertilization decreases the residual concentration of cypermethrin in rhizosphere of C3-plant, and it is possible to enhance phytoremediation of organic-polluted soil by C3-plant through CO2 fertilization. However, further study is needed for C4-plant.