Leaf shape, planting density, and nitrogen application affect soybean yield by changing direct and diffuse light distribution in the canopy.

When attempting to maximize the crop yield from field-grown soybean (Glycine max (L.) Merr.) by means of improving the light conditions for photosynthesis in the canopy, it is crucial to find the optimal planting density and nitrogen application rate. The soybean plants that were the subject of our experiment were cultivated in N-dense mutual pairs, and included two cultivars with different leaf shapes; one cultivar sported ovate leaves (O-type) and the other lanceolate leaves (L-type). We analyzed the results quantitatively to determine the amount of spatial variation in light distribution and photosynthetic efficiency across the canopy, and to gauge the effect of the experimental parameters on the yield as well as the photosynthetic light and nitrogen use efficiency of the crop. Results indicate that the different leaf shapes were responsible for significant disparities between the photosynthetic utilization of direct and diffuse light. As the nitrogen fertilizer rate and the planting density increased, the soybean plants responded by adjusting leaf morphology in order to maximize the canopy apparent photosynthetic light use efficiency, which in turn affected the leaf nitrogen distribution in the canopy. Despite the fact that the light interception rate of the canopy of the L-type cultivar was lower than that of the canopy of the O-type cultivar, we found its canopy apparent photosynthetic nitrogen and light use efficiency were higher. It was interesting to note, however, that the nitrogen and light use efficiency contributions associated with exposure to diffuse light were greater for the latter than for the former.

Productivity, photosynthetic light-use efficiency, nitrogen metabolism and nutritional quality of C4 halophyte Portulaca oleracea L. grown indoors under different light intensities and durations.

Portulaca oleracea L. (known as purslane), is a nutritious facultative C4 halophyte. Recently, it has been successfully grown indoors under LED lightings by our team. However, basic understanding about the impacts of light on purslanes are lacking. This study aimed to investigate the effects of light intensity and duration on productivity, photosynthetic light use efficiency, nitrogen metabolism and nutritional quality of indoor grown purslanes. All plants were grown in 10% artificial seawater hydroponically under different photosynthetic photon flux densities (PPFDs) and durations and thus different daily light integrals (DLI). They are, L1 (240 µmol photon m-2 s-1, 12 h, DLI = 10.368 mol m-2 day-1); L2 (320 µmol photon m-2 s-1, 18 h, DLI = 20.736 mol m-2 day-1); L3 (240 µmol photon m-2 s-1, 24 h, DLI = 20.736 mol m-2 day-1); L4 (480 µmol photon m-2 s-1, 12 h, DLI = 20.736 mol m-2 day-1), respectively. Compared to L1, higher DLI promoted root and shoot growth and thus increased shoot productivity by 2.63-,1.96-, 3.83-folds, respectively for purslane grown under L2, L3, L4. However, under the same DLI, L3 plants (continuous light, CL) had significantly lower shoot and root productivities compared those with higher PPFDs but shorter durations (L2 and L4). While all plants had similar total chlorophyll and carotenoid concentrations, CL (L3) plants had significantly lower light use efficiency (Fv/Fm ratio), electron transport rate, effective quantum yield of PSII, photochemical- and non-photochemical quenching. Compared to L1, higher DLI with higher PPFDs (L2 and L4) increased leaf maximum nitrate reductase activity while longer durations increased leaf NO 3 - concentrations and total reduced nitrogen. There were no significant differences in leaf total soluble protein, total soluble sugar and total ascorbic acid concentrations in both leaf and stem regardless of light conditions. However, L2 plants had the highest leaf proline concentration but leaf total phenolic compounds concentration was higher in L3 plants instead. Generally, L2 plants had the highest dietary minerals such as K, Ca, Mg and Fe among the four different light conditions. Overall, L2 condition is the most suitable lighting strategy in enhancing productivity and nutritional quality of purslane.

Optimization of Photosynthetic Photon Flux Density and Light Quality for Increasing Radiation-Use Efficiency in Dwarf Tomato under LED Light at the Vegetative Growth Stage.

Dwarf tomatoes are advantageous when cultivated in a plant factory with artificial light because they can grow well in a small volume. However, few studies have been reported on cultivation in a controlled environment for improving productivity. We performed two experiments to investigate the effects of photosynthetic photon flux density (PPFD; 300, 500, and 700 µmol m-2 s-1) with white light and light quality (white, R3B1 (red:blue = 3:1), and R9B1) with a PPFD of 300 µmol m-2 s-1 on plant growth and radiation-use efficiency (RUE) of a dwarf tomato cultivar ('Micro-Tom') at the vegetative growth stage. The results clearly demonstrated that higher PPFD leads to higher dry mass and lower specific leaf area, but it does not affect the stem length. Furthermore, high PPFD increased the photosynthetic rate (Pn) of individual leaves but decreased RUE. A higher blue light proportion inhibited dry mass production with the same intercepted light because the leaves under high blue light proportion had low Pn and photosynthetic light-use efficiency. In conclusion, 300 µmol m-2 s-1 PPFD and R9B1 are the recommended proper PPFD and light quality, respectively, for 'Micro-Tom' cultivation at the vegetative growth stage to increase the RUE.

Light, Not Age, Underlies the Maladaptation of Maize and Miscanthus Photosynthesis to Self-Shading.

Zea mays and Miscanthus × giganteus use NADP-ME subtype C4 photosynthesis and are important food and biomass crops, respectively. Both crops are grown in dense stands where shaded leaves can contribute a significant proportion of overall canopy productivity. This is because shaded leaves, despite intercepting little light, typically process light energy very efficiently for photosynthesis, when compared to light-saturated leaves at the top of the canopy. However, an apparently maladaptive loss in photosynthetic light-use efficiency as leaves become shaded has been shown to reduce productivity in these two species. It is unclear whether this is due to leaf aging or progressive shading from leaves forming above. This was resolved here by analysing photosynthesis in leaves of the same chronological age in the centre and exposed southern edge of field plots of these crops. Photosynthetic light-response curves were used to assess maximum quantum yield of photosynthesis; the key measure of photosynthetic capacity of a leaf in shade. Compared to the upper canopy, maximum quantum yield of photosynthesis of lower canopy leaves was significantly reduced in the plot centre; but increased slightly at the plot edge. This indicates loss of efficiency of shaded leaves is due not to aging, but to the altered light environment of the lower canopy, i.e., reduced light intensity and/or altered spectral composition. This work expands knowledge of the cause of this maladaptive shade response, which limits productivity of some of the world's most important crops.

Diaheliotropic leaf movement enhances leaf photosynthetic capacity and photosynthetic light and nitrogen use efficiency via optimising nitrogen partitioning among photosynthetic components in cotton (Gossypium hirsutum L.).

Phototropic leaf movement of plants is an effective mechanism for adapting to light conditions. Light is the major driver of plant photosynthesis. Leaf N is also an important limiting factor on leaf photosynthetic potential. Cotton (Gossypium hirsutum L.) exhibits diaheliotropic leaf movement. Here, we compared the long-term photosynthetic acclimation of fixed leaves (restrained) and free leaves (allowed free movement) in cotton. The fixed leaves and free leaves were used for determination of PAR, leaf chlorophyll concentration, leaf N content and leaf gas exchange. The measurements were conducted under clear sky conditions at 0, 7, 15 and 30 days after treatment (DAT). The results showed that leaf N allocation and partitioning among different components of the photosynthetic apparatus were significantly affected by diaheliotropic leaf movement. Diaheliotropic leaf movement significantly increased light interception per unit leaf area, which in turn affected leaf mass per area (LMA), leaf N content (NA ) and leaf N allocation to photosynthesis (NP ). In addition, cotton leaves optimised leaf N allocation to the photosynthetic apparatus by adjusting leaf mass per area and NA in response to optimal light interception. In the presence of diaheliotropic leaf movement, cotton leaves optimised their structural tissue and photosynthetic characteristics, such as LMA, NA and leaf N allocation to photosynthesis, so that leaf photosynthetic capacity was maximised to improve the photosynthetic use efficiency of light and N under high light conditions.