Isotopic composition (δ13C and δ15N) in the soil-plant system of subtropical urban forests.

This study brings information on the dynamics of C and N in urban forests in a subtropical region. We tested the hypothesis that C and N isotopic sign of leaves and soil and physiological traits of trees would vary from center to periphery in a megacity, considering land uses, intensity of automotive fleet and microclimatic conditions. 800 trees from four fragments were randomly chosen. Soil samples were collected at every 10 cm in trenches up to 1 m depth to analyze C and N contents. Both, plants and soil were assessed for δ13C, δ15N, %C and %N. Physiological traits [carbon assimilation (A)], CO2 internal and external pressure ratio (Pi/Pa) and intrinsic water use efficiency iWUE were estimated from δ13C and Δ Î´13C in leaves and soil ranged from -27.42 ‰ to -35.39 ‰ and from -21.22 ‰ to -28.18 ‰, respectively, and did not vary along the areas. Center-periphery gradient was not evidenced by C. Emissions derived from fossil fuel and distinct land uses interfered at different levels in δ13C signature. δ15N in the canopy and soil varied clearly among urban forests, following center-periphery gradient. Leaf δ15N decreased from the nearest forest to the city center to the farthest, ranging from <3 ‰ to <-3 ‰. δ15N was a good indicator of atmospheric contamination by NOx emitted by vehicular fleet and a reliable predictor of land use change. %N followed the same trend of δ15N either for soils or leaves. Forest fragments located at the edges of the center-periphery gradient presented significantly lower A and Pi/Pa ratio and higher iWUE. These distinct physiological traits were attributed to successional stage and microclimatic conditions. Results suggest that ecosystem processes related to C and N and ecophysiological responses of urban forests vary according to land use and vehicular fleet.

Regulatory mechanisms behind the phenotypic plasticity associated with Setaria italica water deficit tolerance.

Drought is one of the main environmental stresses that negatively impacts vegetative and reproductive yield. Water deficit responses are determined by the duration and intensity of the stress, which, together with plant genotype, will define the chances of plant survival. The metabolic adjustments in response to water deficit are complex and involve gene expression modulation regulated by DNA-binding proteins and epigenetic modifications. This last mechanism may also regulate the activity of transposable elements, which in turn impact the expression of nearby loci. Setaria italica plants submitted to five water deficit regimes were analyzed through a phenotypical approach, including growth, physiological, RNA-seq and sRNA-seq analyses. The results showed a progressive reduction in yield as a function of water deficit intensity associated with signaling pathway modulation and metabolic adjustments. We identified a group of loci that were consistently associated with drought responses, some of which were related to water deficit perception, signaling and regulation. Finally, an analysis of the transcriptome and sRNAome allowed us to identify genes putatively regulated by TE- and sRNA-related mechanisms and an intriguing positive correlation between transcript levels and sRNA accumulation in gene body regions. These findings shed light on the processes that allow S. italica to overcome drought and survive under water restrictive conditions.

Elevated CO2 increases photosynthesis, biomass and productivity, and modifies gene expression in sugarcane.

Because of the economical relevance of sugarcane and its high potential as a source of biofuel, it is important to understand how this crop will respond to the foreseen increase in atmospheric [CO(2)]. The effects of increased [CO(2)] on photosynthesis, development and carbohydrate metabolism were studied in sugarcane (Saccharum ssp.). Plants were grown at ambient (approximately 370 ppm) and elevated (approximately 720 ppm) [CO(2)] during 50 weeks in open-top chambers. The plants grown under elevated CO(2) showed, at the end of such period, an increase of about 30% in photosynthesis and 17% in height, and accumulated 40% more biomass in comparison with the plants grown at ambient [CO(2)]. These plants also had lower stomatal conductance and transpiration rates (-37 and -32%, respectively), and higher water-use efficiency (c.a. 62%). cDNA microarray analyses revealed a differential expression of 35 genes on the leaves (14 repressed and 22 induced) by elevated CO(2). The latter are mainly related to photosynthesis and development. Industrial productivity analysis showed an increase of about 29% in sucrose content. These data suggest that sugarcane crops increase productivity in higher [CO(2)], and that this might be related, as previously observed for maize and sorghum, to transient drought stress.