More intense, more frequent, and longer heat waves are expected in the future due to global warming, which could have dramatic ecological impacts. However, few studies have involved invasive species. The aims of this study were to examine the effect of extreme heating (40/35 degrees C for 30 d) on the growth and photosynthesis of an alien invasive species Wedelia trilobata and its indigenous congener (Wedelia chinensis) in South China, and to determine the development of this invasive species and its potential adaptive mechanism. In comparison with W. chinensis, W. trilobata suffered less inhibition of the relative growth rate (RGR) and biomass production due to high temperature, which was consistent with the changes of photosystem II (PSII) activity and net photosynthetic rate (P(n)). High temperature caused a partial inhibition of PSII, but the adverse effect was more severe in W. chinensis. Measurement of the minimum fluorescence (F(o)) versus temperature curves showed that W. trilobata had a higher inflexion temperature of F(o) (T(i)), indicating greater thermostability of the photosynthetic apparatus. Moreover, comparisons of absorbed light energy partitioning revealed that W. trilobata increased xanthophyll-dependent thermal dissipation (Phi(NPQ)) under high temperature, while retaining the higher fraction of absorbed light allocated to photochemistry (Phi(PSII)) relative to W. chinensis. The results suggest that the invasive W. trilobata has a high thermostability of its photosynthetic apparatus and an effective regulating mechanism in energy partitioning of PSII complexes to minimize potential damage and to retain greater capability for carbon assimilation. These factors confer greater heat stress tolerance compared with the native species. Therefore, the invasive W. trilobata may become more aggressive with the increasingly extreme heat climates.

Low temperature (LT) is one of the major factors that limit crop production and reduce yield. To better understand the cold-tolerance mechanism in the plantains, a sensitive cultivar Williams (Musa acuminata AAA cv. Williams) and a tolerant cultivar Cachaco (Musa paradisiaca ABB cv. Dajiao) were used. LT resulted in increased malondialdehyde (MDA) content, elevated contents of hydrogen peroxide (H 2 O 2 ) and superoxide radical (O 2• -), and decreased photochemical efficiency (F v /F m ) and net photosynthetic rate (P N ), but cv. Cachaco showed better LT tolerance than cv. Williams. After LT treatment for 120 h, total scavenging capability (DPPH • scavenging capability) in Williams showed a significant decrease but no significant alternations was found in Cachaco. Ascorbate peroxidase (APX) and peroxidase (POD) displayed a significant increase but superoxide dismutase (SOD) showed no significant alternations and catalase (CAT) showed a significant decrease in Cachaco after 120 h of LT treatment. All the four antioxidant enzymes above showed a significant decrease in Williams after 120 h of LT treatment. Our results suggest that higher activities of APX, POD, SOD, and DPPH • scavenging capability to a certain extent can be used to explain the higher cold tolerance in the plantain, which would provide a theoretical guidance for bananas production and screening cold-resistant variety.

A potted soil experiment was conducted to investigate the effects of bensulfuron-methyl (BSM) residue on the growth and photosynthesis of seedlings of a local cucumber variety (Xia Feng No.1). When the residue of bensulfuron-methyl in soil exceeded 50μg kg -1 , it significantly inhibited the growth of cucumber, chlorophyll content and photosynthetic capacity of cucumber. BSM treatment caused significant decreases in the biomass, chlorophyll content, net photosynthesis rate, stomatal conductance, and transpiration rate, photosystem II (PSII) maximum quantum yield, actual quantum yield, photochemical quenching coefficient, and electron transport rate in cucumber seedlings, but increased the minimal fluorescence yield and dark respiration rate. Moreover, comparisons of the patterns of absorbed light energy partitioning revealed that the fractions of excess and thermally dissipated energy increased with rising concentrations of the BSM residue, but the fraction of PSII photochemistry declined. The BSM residues caused reversible destruction in the PSII reaction centers and decreased the proportion of available excitation energy used in PSII photochemistry. The results suggested that rice or wheat fields sprayed with BSM will not be suitable for planting cucumbers in succession or rotation.

We selected five typical tree species, including one early-successional species (ES) Pinus massoniana Lamb., two mid-successional species (MS) Schima superba Gardn. et Champ. and Castanopsis fissa (Champ. ex Benth.) Rehd. et Wils. and two late-successional species (LS) Cryptocarya concinna Hance. and Acmena acuminatissima (BI.) Merr et Perry., which represent the plants at three successional periods in Dinghushan subtropical forest succession of southern China. Potted seedlings of the five species were grown under 12% of full sunlight for 36 months. The ES and MS showed the slowest and fastest responses to lightflecks, respectively, which correlated with the rate of stomatal opening. In contrast to P. massoniana and C. concinna, the other three species exhibited a high induction loss. Early-successional species showed the lowest specific leaf area and chlorophyll content, the highest photosynthetic capacity (A(max)) and respiratory carbon losses (R(d)). Compared with ES and MS, LS showed lower A(max) and R(d). The five tree species showed a similar chlorophyll a/b ratio after long-term low-light adaptations. On the other hand, LS had a relatively higher de-epoxidation state to protect themselves from excess light during lightflecks. Our results indicated that (i) slower responses to lightflecks could partially explain why ES species could not achieve seedling regeneration in low-light conditions; (ii) fast responses to lightflecks could partially explain why MS species could achieve seedling regeneration in low-light conditions; and (iii) smaller respiratory carbon losses might confer on the LS species a competitive advantage in low-light conditions.