Effects of elevated CO2 concentration and nitrogen addition on the chemical compositions, construction cost, and payback time of subtropical trees in Cd-contaminated mesocosm soil

Rising atmospheric CO2 concentration ([CO2]) and nitrogen (N) deposition are changing plant growth, physiological characteristics, and chemical compositions; however, few studies have explored such impacts in a heavy-metal-contaminated environment. In this study, we conducted an open-top chamber experiment to explore the impacts of two years of elevated atmospheric [CO2] and N addition on the growth, physiological characteristics, and chemical compositions of five subtropical tree species in a cadmium (Cd)-contaminated environment. Results showed that N addition significantly increased concentration of leaf N and protein in five tree species, and also decreased payback time (PBT) and leaf C:N ratios and increased tree relative height growth rate (RGR-H) and basal diameter growth rate (RGR-B) in Liquidambar formosana and Syzygium hainanense. Elevated [CO2] increased leaf maximum photosynthetic rate (Amax) and concentration of total non-structural carbohydrates (TNC) and shortened PBT to offset the negative effect of Cd contamination on RGR-B in A. auriculiformis. The combined effects of elevated [CO2] and N addition did not exceed their separate effects on RGR-H and RGR-B in Castanopsis hystrix and Cinnamomum camphora. N addition significantly increased the concentration of leaf Cd by 162.1% and 338.0%, and plant Cd bio-concentration factor (BCF) by 464% and 861% in C. hystrix, and C. camphora, respectively, compared to Cd addition. Among the five tree species, the decreases in PBT and the increases in Amax, RGR-B, and concentrations of leaf protein in response to N and Cd addition under elevated [CO2] were average higher 86.7% in A. auriculiformis than other species, suggesting that the mitigation of the negative effects of Cd pollution by elevated [CO2] and N addition among five species was species-specific. Overall, we concluded that N addition and elevated [CO2] reduced Cd toxicity, and increased the growth rate in A. auriculiformis, S. hainanense and L. formosana, while maintained the growth rate in C. hystrix, and C. camphora by differently increasing photosynthetic rate, altering the leaf chemical compositions, and shortening PBT.

Carbon allocation strategies and water uptake in young grafted and own-rooted hazelnut (Corylus avellana L.) Cultivars

In this study, grafted and own-rooted young hazelnut plants of three high-quality cultivars were cultivated in Central Italy to investigate possible differences in growth, fruit and flower production, and physiological processes encompassing water uptake, photosynthetic variables, and non-structural carbohydrates (NSC) allocation. Stable isotopes and photosynthetic measurements were used to study carbon and water fluxes in plants. For the first time an ecophysiological study was carried out to understand the seasonal growth dynamics of grafted plants in comparison with own-rooted plants. The own-rooted hazelnuts showed rapid aboveground development with large canopy volume, high amount of sprouts and earlier yield. The grafted plants showed greater belowground development with lower canopy volumes and lower yield. However, later, the higher growth rates of the canopy led these plants to achieve the same size as that of the own-rooted hazelnuts and to enter the fruit production phase. Different seasonal behavior in root water uptake and leaf photosynthetic-related variables were detected between the two types of plants. The grafted plants showed root development that allowed deeper water uptake than that of the own-rooted hazelnuts. Moreover, the grafted plants were characterized by a higher accumulation of carbohydrate reserves in their root tissues and by higher stomatal reactivity, determining a major plasticity in response to seasonal thermal variations.

Comparable and adaptable strategies to waterlogging stress regulated by adventitious roots between two contrasting species

Cleistocalyx operculatus and Syzygium cumini possess a certain waterlogging tolerance. However, the comparable and adaptable strategies to waterlogging stress between these two species on the basis of waterlogging adventitious root (AR) regulation were still unclear. In this study, the plant performances in response to AR regulation based on AR removal and exogenous hormone application were investigated in terms of plant morphology, physiology, photosynthesis, and AR traits. Results showed that C. operculatus possesses stronger waterlogging tolerance than S. cumini based on waterlogging tolerance coefficient, which is mainly due to the higher root biomass, root porosity, and length and activity of ARs, and shorter emergence time of ARs in C. operculatus than in S. cumini. The AR-R treatment increased activity and porosity of primary root, and induce a large amount of up-vertical ARs from the primary root systems in C. operculatus, while similar adaptive morphological changes in roots did not occur in AR-R treated S. cumini. Exogenous ABA application had better effects on alleviating waterlogging damages than exogenous IAA in balancing endogenous hormones (ABA and ZR), promoting ARs development (porosity and activity, and the ratio of cortex area to stele area), improving photosynthesis process and antioxidant system (soluble protein, free proline, and peroxidase). Moreover, under waterlogging conditions, exogenous ABA application induced greater increases in net photosynthesis rate (A), stomatal conductance (gs), chlorophyll b (Chl b), and carotenoid (Caro) in S. cumini than in C. operculatus, which suggested that S. cumini responded more positively and efficiently to exogenous ABA application than C. operculatus under waterlogging conditions. Thus, the findings provided new insights into the waterlogging adaptable strategies in waterlogging tolerant woody species on the basis of ARs, and could provide scientific guidance for the application of these two species during revegetation activities in wetlands.