Woody plants have received considerable attention for the phytoremediation of heavy metal-contaminated soil. This study aimed to investigate the changes in antioxidant enzyme activity, macroelement uptake and microstructure of the woody plant Robinia pseudoacacia (black locust) for the phytoremediation of cadmium (Cd) and lead (Pb) co-contaminated soil based on dynamic sampling. The results show that black locust demonstrates strong tolerance in Cd and Pb co-contaminated soil. After 30-120 days of cultivation, the activities of superoxide dismutase, peroxidase and the macroelement (potassium [K] and calcium [Ca]) content in plant leaves significantly declined in response to Cd and Pb. However, after 160 d of cultivation, the antioxidant enzyme activities, chlorophyll, sulfhydryl and soluble protein contents, as well as Ca and magnesium content in plant leaves were returned to normal levels under the 40 mg kg(-1) Cd and 1000 mg kg(-1) Pb contaminated soil (CdPb3). Meanwhile, K content in plant leaves under the CdPb3 treatment was significantly (P < 0.05) increased by 68.9% compared with the control. Cadmium and Pb were primarily accumulated in black locust roots. Scanning electron microscope analysis indicated that the sieve tubes in the roots and stems of plant might block the transport of Cd and Pb. Transmission electron microscope analysis indicated that the number and volume of osmiophilic particles in plant leaves were increased and the cell walls were thickened in response to Cd and Pb stress. Path analysis further indicated that the growth of plant was related to macroelements uptake and physiological change (photosynthesis, antioxidant enzyme activity and chelation). Thus, black locust could effectively regulate the antioxidant defense system, macroelement absorption and microstructure to enhance plant tolerance to Cd and Pb stress. Moreover, black locust could maintain the normal urease, acid phosphatase and sucrase activities in the Cd and Pb co-contaminated soil. These findings suggest that black locust could be considered as a useful woody plant for the phytostabilization in Cd- and Pb-contaminated soil.

Uncertainties about the ecophysiological response of plants to elevated temperature limit our ability to predict the impact of climate change on plants, especially in tropical and subtropical forests. One important source of the uncertainties is that the vast majority of warming studies manipulated only aboveground or only belowground temperature when in the real word warming takes place both aboveground and belowground. We used a full factorial design of air warming and soil warming with four temperature treatments: (1) unwarmed, (2) soil warming, (3) air warming, (4) soil plus air warming to explore the effects of warming on ecophysical processes/ characteristics of leaves and fine roots of Chinese-fir saplings. We measured photosynthesis, concentrations of oxidant substances, activity of antioxidant enzymes, and osmoregulatory substances in leaves and fine roots. We found that the soil warming increased photosynthetic rate by 68.9%, but air warming and soil plus air warming treatments did not. The concentrations of oxidant compounds, superoxide anion (O2- ), hydrogen peroxide (H2O2) and malondialdehyde (MDA) were higher in leaves than in fine roots under all treatments, possibly due to their differences in the degree of oxidative damage. Soil warming increased leaf catalase (CAT) activity by 58.5%, soil warming and air warming increased leaf peroxidase (POD) activity by 31% and 42.3%, respectively, and soil plus air warming increased leaf ascorbic acid peroxidase (APX) activity by 31%. These increases in antioxidant enzyme concentrations indicated that warming activated leaf antioxidant systems. The CAT activity was lower in leaves than in fine roots, while the POD activity and concentrations of osmoregulatory substances were higher in leaves than in fine roots across all treatments. Our study clearly illustrated that different warming treatments (aboveground and belowground) had different effects on plant growth and physiological processes. The differences in oxidant compounds and activities of antioxidant enzymes between leaves and fine roots indicated that warming affect different organs differently. This study provides insights into how climate warming may affect important physiological and biochemical processes in subtropical forests.

Spring, especially the freeze-thaw season, is considered the key period for the growth and carbon sequestration of desert mosses. It is not clear how the change in environment water and temperature affects the physiological characteristics of desert mosses in freeze-thaw season. In this study, the effects of water and freeze-thaw cycles on the physiological characteristics of Syntrichia caninervis were assessed by manipulating the increase or removal of 65% snow and changes in the freeze-thaw cycles. The results showed that the changes in snow depth, freeze-thaw cycles, and their interaction significantly affected the plant water content, osmoregulatory substances content, antioxidant substance, and antioxidant enzyme activities. The contents of free proline, soluble sugar, ascorbic acid (AsA), reduced glutathione (GSH), and malondialdehyde (MDA), and superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities increased significantly with the decrease in snow depth and freeze-thaw cycles. POD and free proline were the most sensitive to the snow depth and freeze-thaw cycles, while SOD and CAT were the least sensitive. Therefore, compared with the increase in freeze-thaw cycles, the reduction in freeze-thaw cycles weakened the physiological sensitivity of S. caninervis to snow depth changes.