Uptake of nitrogen forms by diploid and triploid white poplar depends on seasonal carbon use strategy and elevated summer ozone

A wider spectrum of avoidance and tolerance mechanisms explained ozone sensitivity of two white poplar ploidy levels

BACKGROUND AND AIMS

Polyploidization can improve plant mass yield for bioenergy support, yet few studies have investigated ozone (O3) sensitivity linked to internal regulatory mechanisms at different ploidy levels.

METHODS

Diploid and triploid Populus tomentosa plants were exposed to ambient and ambient plus 60 ppb [O3]. We explored their differences in sensitivity (leaf morphological, physiological and biochemical traits, and plant mass) as well as mechanisms of avoidance (stomatal conductance, xanthophyll cycle, thermal dissipation) and tolerance (ROS scavenging system) in response to O3 at two developmental phases.

KEY RESULTS

Triploid plants had the highest plant growth under ambient O3, even under O3 fumigation. However, triploid plants were the most sensitive to O3 and under elevated O3 showed the largest decreases in photosynthetic capacity and performance, as well as increased shoot:root ratio, and the highest lipid peroxidation. Thus, plant mass production could be impacted in triploid plants under long-term O3 contamination. Both diploid and triploid plants reduced stomatal aperture in response to O3, thereby reducing O3 entrance, yet only in diploid plants was reduced stomatal aperture associated with minimal (non-significant) damage to photosynthetic pigments and lower lipid peroxidation.

CONCLUSIONS

Tolerance mechanisms of plants of both ploidy levels mainly focused on the enzymatic reduction of hydrogen peroxide through catalase and peroxidase, yet these homeostatic regulatory mechanisms were higher in diploid plants. Our study recommends triploid white poplar as a bioenergy species only under short-term O3 contamination. Under continuously elevated O3 over the long term, diploid white poplar may perform better.

Integrative physiological, metabolomic and transcriptomic analysis reveals nitrogen preference and carbon and nitrogen metabolism in blackberry plants

Nitrogen (N) is an indispensable element for plant growth and development. To understand the regulation of underlying carbon (C) and N metabolism in blackberry plants, we performed integrated analyses of the physiology, metabolome and transcriptome. Blackberry plants were subjected to no N, nitrate (NO₃⁻)-N, ammonium (NH₄⁺)-N and urea treatments. Our results showed that the NH₄⁺-N treatment yielded higher values for the biomass, chlorophyll, antioxidants, N contents and antioxidant enzyme activities, as well as lower levels of free radicals and the C/N ratio compared with other treatments. Transcriptome analysis showed that different N forms significantly affected photosynthesis, flavonoid biosynthesis and the TCA cycle. Metabolome analysis indicated that the levels of lipids, carbohydrates, flavonoids and amino acids were markedly changed under different N treatments. Integrated transcriptomic and metabolomic data revealed that amino acids, including proline, arginine, L-isoleucine, L-aspartate, threonine, and L-glutamate, played important roles in maintaining normal plant growth by regulating N metabolism and amino acid metabolism. Overall, blackberry plants preferentially take up NH₄⁺-N. Under the NH₄⁺-N treatment, N assimilation was stronger, flavonoid biosynthesis was decreased, and the promoting influence of NH₄⁺-N on N metabolism was better than that of NO₃⁻-N. However, the NO₃⁻-N treatment enhanced the C/N ratio, accelerated the process of C metabolism and increased the synthesis of flavonoids, thereby accelerating the flow of N metabolism to C metabolism. These results provide deeper insight into coordinating C and N metabolism and improving N use efficiency in blackberry plants.

Elevated ozone inhibits isoprene emission of a diploid and a triploid genotype of Populus tomentosa by different mechanisms

Ozone (O3) pollution affects plant growth and isoprene (ISO) emission. However, the response mechanism of isoprene emission rate (ISOrate) to elevated O3 (EO3) remains poorly understood. ISOrate was investigated in two genotypes (diploid and triploid) of Chinese white poplar (Populus tomentosa Carr.) exposed to EO3 in an open top chamber system. The triploid genotype had higher photosynthetic rate (A) and stomatal conductance (gs) than the diploid one. EO3 significantly decreased A, gs, and ISOrate of middle and lower leaves in both genotypes. In the diploid genotype, the reduction of ISOrate was caused by a systematic decrease related to ISO synthesis capacity, as indicated by decreased contents of the isoprene precursor dimethylallyl diphosphate and decreased isoprene synthase protein and activity. On the other hand, the negative effect of O3 on ISOrate of the triploid genotype did not result from inhibited ISO synthesis capacity, but from increased ISO oxidative loss within the leaf. Our findings will be useful for breeding poplar genotypes with high yield and lower ISOrate, depending on local atmospheric volatile organic compound/NOx ratio, to cope with both the rising O3 concentrations and increasing biomass demand. They can also inform the incorporation of O3 effects into process-based models of isoprene emission.