Response of carbon fixation, allocation, and growth to source-sink manipulation by defoliation in vegetative citrus trees.

Source-sink balance in plants determines carbon distribution, and altering it can impact carbon fixation, transport, and allocation. We aimed to investigate the effect of altered source-sink ratios on carbon fixation, transport, and distribution in 'Valencia' sweet orange (Citrus x sinensis) by various defoliation treatments (0%, 33%, 66%, and 83% leaf removal). Gas exchange parameters were measured on 0 and 10 days after defoliation using A/Ci response curves, and leaf export was measured two days after defoliation using radioisotope tracer techniques. Greater defoliation increased the maximum rate of carboxylation (Vcmax), electron transport rate (J1200), and triose-phosphate utilization rate (TPU). Leaf export was unaffected by defoliation but increased in leaves closer to the shoot apex. Basipetal translocation velocity in the trunk remained unaltered, indicating that more photosynthates remained in the shoot rather than being transported directly to the root sink. Defoliated plants initiated more new flush shoots but accumulated less shoot biomass per plant after 8 weeks. Carbon allocation to fine roots was smaller in defoliated plants, suggesting defoliation led to retention of carbohydrates in aboveground organs such as the trunk and other shoots from previous growing cycles. In conclusion, the low source-sink ratio increased carbon fixation without impacting individual leaf export in citrus. The results suggest that intermediate sinks such as the aboveground perennial organs play a role in mediating the translocation velocity. Further research is necessary to better understand the dynamics of source-sink regulation in citrus trees.

Root:shoot balance controls flush phenology and carbohydrate translocation dynamics in citrus (Citrus x sinensis) trunk.

Flush shoot growth presents a fluctuation pattern alternating with root growth. The cyclic pattern determines the balance of root:shoot and can affect the direction and speed of carbohydrate translocation during the vegetative growth period. In this study, we used water deficit to limit corresponding growth in sweet orange (Citrus x sinensis) "OLL 4" grafted on "US-942" rootstock, and then observed the changes of translocation dynamics between two flush statuses. Our first hypothesis was that water deficit would reduce root growth and extend the root growth phase during the growth cycle, delaying the following flush. We then tested the related second hypothesis that shoot flushes would switch the direction and slow the speed of carbohydrate transport due to fluctuation between single and dual sinks. After recovery from a severe deficit, the flush was synchronized and emerged within 2 weeks. Mild and moderate water-deficit plants showed a delayed new flush. Next, we used a 14 C-labeling method to test whether translocation was affected by the presence of new flush. Basipetal translocation was dominant, but the new flush increased the likelihood of acropetal translocation. Translocation speeds were not different in both directions regardless of flushing status, though speed estimates were highly variable, even though 14 C export from the source leaf increased when new flush was present. The results suggest that flush timing across an environmental gradient is governed by source-sink dynamics. The presence of new flush altered the direction of photoassimilate translocation and rate of leaf export, but stem transport speeds were not distinguishably different.

Fast-Charging Nonaqueous Potassium-Ion Batteries Enabled by Rational Construction of Oxygen-Rich Porous Nanofiber Anodes.

Practical applications of carbon anodes in high-power potassium-ion batteries (PIBs) were hampered by their limited rate properties, due to the sluggish K+ transport kinetics in the bulk. Constructing convenient ion/electron transfer channels in the electrode is of great importance to realize fast charge/discharge rates. Here, cross-linked porous carbon nanofibers (inner porous carbon nanotubes and outer soft carbon layer) modified with oxygen-containing functional groups were well designed as anodes to realize robust de-/potassiation kinetics. The novel anode delivered excellent rate capabilities (107 mAh g-1 at 20 A g-1 and 78 mAh g-1 at 40 A g-1) and superior cycling stability (76% capacity retention after 14,000 cycles at 2 A g-1). In situ XRD measurement, in situ Raman spectra, and galvanostatic intermittent titration verified its surface-dominated potassium storage behavior with fast de-/potassiation kinetics, excellent reversibility, and rapid ion/electron transport. Moreover, theoretical investigation revealed that the carboxyl groups in the carbon offered additional capacitive adsorption sites for K+, thus significantly enhancing the reversible capacity. Surprisingly, a full cell using the anode and perylene-3,4,9,10-tetracarboxylic dianhydride cathode achieved an outstanding power density of 23,750 W kg-1 and superior fast charge/slow discharge performance.

Metabolomic analysis elucidates how shade conditions ameliorate the deleterious effects of greening (Huanglongbing) disease in citrus.

Under tropical and subtropical environments, citrus leaves are exposed to excess sunlight, inducing photoinhibition. Huanglongbing (HLB, citrus greening), a devastating phloem-limited disease putatively caused by Candidatus Liberibacter asiaticus, exacerbates this challenge with additional photosynthetic loss and excessive starch accumulation. A combined metabolomics and physiological approach was used to elucidate whether shade alleviates the deleterious effects of HLB in field-grown citrus trees, and to understand the underlying metabolic mechanisms related to shade-induced morpho-physiological changes in citrus. Using metabolite profiling and multinomial logistic regression, we identified pivotal metabolites altered in response to shade. A core metabolic network associated with shade conditions was identified through pathway enrichment analysis and metabolite mapping. We measured physio-biochemical responses and growth and yield characteristics. With these, the relationships between metabolic network and the variables measured above were investigated. We found that moderate-shade alleviates sink limitation by preventing excessive starch accumulation and increasing foliar sucrose levels. Increased growth and fruit yield in shaded compared with non-shaded trees were associated with increased photosystem II efficiency and leaf carbon fixation pathway metabolites. Our study also shows that, in HLB-affected trees under shade, the signaling of plant hormones (auxins and cytokinins) and nitrogen supply were downregulated with reducing new shoot production likely due to diminished needs of cell damage repair and tissue regeneration under shade. Overall, our findings provide the first glimpse of the complex dynamics between cellular metabolites and leaf physiological functions in citrus HLB pathosystem under shade, and reveal the mechanistic basis of how shade ameliorates HLB disease.

Photo-oligomerization by shifting the coordination site in a luminescent coordination polymer.

A layered coordination polymer (CP) with the fine-tuned alignment of four diolefinic ligands has been designed by shifting the coordination site of the ligand. The trimeric and tetrameric cyclobutane derivatives were reversely achieved by the photoinitiated [2+2] cycloaddition of the CP due to the favorable Schmidt's distance. More interestingly, a dynamic fluorescence shift was observed during the photo-oligomerization and heat-cycloreversion of the CP system.