Growth and heavy metal accumulation of Koelreuteria paniculata seedlings and their potential for restoring manganese mine wastelands in Hunan, China.

The planting of trees on mine wastelands is an effective, long-term technique for phytoremediation of heavy metal-contaminated wastes. In this study, a pot experiment with seedlings of Koelreuteria paniculata under six treatments of local mine wastes was designed to determine the major constraints on tree establishment and to evaluate the feasibility of planting K. paniculata on manganese mine wastelands. Results showed that K. paniculata grew well in mine tailings, and also under a regime of equal amounts of mine tailings and soil provided in adjacent halves of pots. In contrast, mine sludge did not favor survival and growth because its clay texture limited fine root development. The bio-concentration factor and the translocation factor were mostly less than 1, indicating a low phytoextraction potential for K. paniculata. K. paniculata is suited to restore manganese mine sludge by mixing the mine sludge with local mine tailings or soil.

Effects of increased nitrogen deposition and rotation length on long-term productivity of Cunninghamia lanceolata plantation in southern China.

Cunninghamia lanceolata (Lamb.) Hook. has been widely planted in subtropical China to meet increasing timber demands, leading to short-rotation practices that deplete soil nutrients. However, increased nitrogen (N) deposition offsets soil N depletion. While long-term experimental data investigating the coupled effects related to short rotation practices and increasing N deposition are scarce, applying model simulations may yield insights. In this study, the CenW3.1 model was validated and parameterized using data from pure C. lanceolata plantations. The model was then used to simulate various changes in long-term productivity. Results indicated that responses of productivity of C. lanceolata plantation to increased N deposition were more related to stand age than N addition, depending on the proportion and age of growing forests. Our results have also shown a rapid peak in growth and N dynamics. The peak is reached sooner and is higher under higher level of N deposition. Short rotation lengths had a greater effect on productivity and N dynamics than high N deposition levels. Productivity and N dynamics decreased as the rotation length decreased. Total productivity levels suggest that a 30-year rotation length maximizes productivity at the 4.9 kg N ha(-1) year(-1) deposition level. For a specific rotation length, higher N deposition levels resulted in greater overall ecosystem C and N storage, but this positive correlation tendency gradually slowed down with increasing N deposition levels. More pronounced differences in N deposition levels occurred as rotation length decreased. To sustain C. lanceolata plantation productivity without offsite detrimental N effects, the appropriate rotation length is about 20-30 years for N deposition levels below 50 kg N ha(-1) year(-1) and about 15-20 years for N deposition levels above 50 kg N ha(-1) year(-1). These results highlight the importance of assessing N effects on carbon management and the long-term productivity of forest ecosystems.

Heavy metal accumulation by panicled goldenrain tree (Koelreuteria paniculata) and common elaeocarpus (Elaeocarpus decipens) in abandoned mine soils in southern China.

Phytoremediation can be used as a sustainable technology for mine spoil remediation to remove heavy metals. This study investigated the concentration of 7 heavy metal contamination in soil and plant samples at an abandoned mine site. We found that, after vegetation remediation at the abandoned mine site, the reduction rates for 7 heavy metals were in the range of 4.2%-86%, where reduction rates over 50% were achieved for four heavy metals (Zn, Mn, Cd, Ni). Transfer coefficients of the panicled goldenrain tree (Koelreuteria paniculata Laxm) and the common elaeocarpus (Elaeocarpus decipens) for Zn, Mn, Ni, and Co were more than 1. Enrichment coefficients of both trees for Mn were higher than 1. Our results suggest that the panicled goldenrain tree and the common elaeocarpus tree may act as accumulators in remediation. Moreover, the woody vegetation remediation in abandoned mining areas play an important role in improving scenery besides removing heavy metal from contaminated soil.

[CO2 exchanges between mangrove- and shoal wetland ecosystems and atmosphere in Guangzhou].

Based on the investigation of biomass and the measurement of CO2 and CH4 fluxes, the CO2 exchanges between mangrove- and shoal wetland ecosystems and atmosphere in Guangzhou were studied, and the CO2 absorption capability of the wetlands vegetation net productivity as well as the carbon sink function of the wetlands under different waterlogged conditions (perennial, intermittent, and no water-logging) was analyzed. As for mangrove wetland ecosystem, its vegetation net productivity absorbed 33.74 t x hm(-2) x a(-1) of CO2, and soil emitted 12.26 t x hm(-2) x a(-1) of CO2 (including the greenhouse effect amount of CH4 converted into that of CO2,) illustrating that mangrove wetland had a 21.48 t x hm(-2) x a(-1) net absorption of CO2, being a strong carbon sink. For shoal wetland ecosystem, its vegetation net productivity absorbed 8.54 t x hm(-2) x a(-1) of CO2, and soil emitted 5.88 t x hm(-2) x a(-1) of CO2 and 0.19 t x hm(-2) x a(-1) of CH4. If converting into carbon, the wetland absorbed 2.33 t C x hm(-2) x a(-1), and soil emitted 1.74 t C x hm(-2) x a(-1) (including the carbon in CH4), illustrating that shoal wetland fixed 0.59 t C x hm(-2) x a(-1), being a weak carbon sink. If the greenhouse effect amount of CH4 was converted into that of CO2, the soil emitted 9.78 t x hm(-2) x a(-1) of CO2, which was 1.24 t x hm(-2) x a(-1) more than the absorption. As a result, shoal wetland was a weak carbon source. Between the two test greenhouse gases, CH4 was the main one emitted under perennial water-logging, while CO2 was that under no water-logging. Moreover, the wetland under perennial water-logging had the strongest carbon sink function, while that under no water-logging was in adverse.