Effects of light spectra and 15N pulses on growth, leaf morphology, physiology, and internal nitrogen cycling in Quercus variabilis Blume seedlings

Light Quality Effect on Internal N Retranslocation in Podocarpus macrophyllus Precultured with Exponential Nutrient Loading

Streetlamp light is inevitable in the night landscape of a city and may affect the phenology of newly planted ornamental plants, but it has rarely been fully examined. Newly transplanted ornamental plants probably suffer periodic shocks, which mainly result from the inefficient reuse of internal nutrients for new growth. Exponential nutrient loading (ENL) is well known for its ability to overcome transplant shocks by promoting retranslocation for the reuse of strengthened nutrients from internal reserves in precultured seedlings. Transplantation to urbanized lands is distinct from that of montane areas; this is mainly due to a high frequency of exposure to the artificial illumination of night lighting. It is suspected that this lighting modifies vegetative phenology and generates potential risks by increasing reliance on internal nutrient retranslocation. In this study, Podocarpus macrophyllus seedlings were cultured with ENL at low and high rates of nitrogen (N) deliveries (40 and 120 mg N seedling-1, respectively), and the high-rate treatment was identified as being able to trap seedlings within toxic states. A labeled 15N isotope was pulsed to transplanted seedlings exposed to simulated light qualities in red, green, and blue light spectra. The seedlings harvested at one month showed rare responses to the interactive spectra and preculture treatments, but most of them responded to the low-rate N preculture treatment with stronger abilities in terms of the reuse of internal N and the synthesizing of photosynthetic pigments. In conclusion, it was verified that night light enforces the effect on newly transplanted plants; the red light invoked internal N for reuse, and the blue light promoted the uptake of the current N. The internal N reserve established through preculture ENL rarely made a contribution to the night light effect, except for the enhancement of height growth in the red light. The red light spectrum was recommended for the exposure of newly transplanted seedlings due to its effect on the enhancement of the retranslocation of internal N and the induction of a steady state of uptake from the current N input.

Light-Emitting Diodes Modify Medicinal Quality of Mown Rabdosia rubescens, with Changes in Growth, Physiology, and Antioxidant Activity, under Drought Stress

Medicinal plants accommodated by understory habitats can easily suffer over-exploitation in the heavy harvest of natural products. It is necessary to develop a sustainable cultural protocol to provide high-quality stocks for efficient regeneration. Drought places stress on medicinal plants during their culture by limiting new sprout growth and reducing the quality of medicinal extracts. Artificial mediating approaches should be considered in a sustainable regime of medicinal plant culture to test the potential tradeoff between resistance to drought and production ability. In this study, Rabdosia rubescens seedlings were raised in three light-emitting diode (LED) spectra from red (71.7% red, 14.6% green, 13.7% blue), green (26.2% red, 17.4% green, 56.4% blue), and blue (17.8% red, 33.7% green, 48.5% blue) lights. Mown seedlings were subjected to a simulated drought event. Drought stressed the seedlings by reducing the growth, dry mass, nitrogen (N) uptake, and oridonin content. Mowing increased the oridonin content but decreased total C and N accumulation and the δ13C level. The red light benefitted starch accumulation only under the well-watered condition, and the green light induced an upregulation of δ13C but decreased antioxidant activity. Oridonin content was negatively associated with combined δ13C and catalase activity. Overall, either mowing or blue light can be recommended for the culture of R. rubescens to increase oridonin content, alleviating some of the negative consequences of drought.

Natural Bioactive Substances in Fruits of Aronia melanocarpa (Michx.) Elliott Exposed to Combined Light-Type, Chitosan Oligosaccharide, and Spent Mushroom Residue Treatments

Greenhouse culture is a practical approach to obtain non-wood forest products from berry fruit at a higher efficacy than resource silviculture in natural understory. In this study, three-year old black chokeberry (Aronia melanocarpa (Michx.) Elliott 1821) seedlings were transplanted to a greenhouse where sunlight was complemented by red- (69.4% red, 30.2% green, 0.4% blue) and blue-color (15.3% red, 64.9% green, 19.8% blue) light-emitting diode (LED) illuminations. Half of the planting soils were amended by spent mushroom residue (SMR) (not amendment as the control) and half the seedlings were sprayed by chitosan oligosaccharide (CO) on leaves. All treatments can increase seedling height, but only blue light reinforces the basal diameter growth. Compared to sunlight, exposure to blue light can promote leaf nitrogen and phosphorus concentrations, superoxide dismutase activity, and fruit proanthocyanidin content. The combination with CO addition will further increase chlorophyl a content, acid phosphatase activity, and total phenolics in fruit. SMR amended can induce the steady state uptake of nutrients but failed to impact fruit quality. Overall, we recommend the combination of blue light LED illumination plus CO addition to culture black chokeberry for the purpose to gain natural bioactive compounds.

Forage quality and physiological performance of mowed alfalfa (Medicago sativa L.) subjected to combined light quality and drought

Alfalfa (Medicago sativa) can dwell in water-deficient habitats, where it is difficult to predict dry mass (DM) production and forage quality due to understory transmittance. Mowing is a recommended practice for alfalfa populations under drought, but its effect on forested land receives less attention. In a controlled indoor experiment, we found that drought better reduces shoot DM weight and crude fiber content (CFi) in blue light (33.7% red, 48.5% green, and 17.8% blue lights) than red light (71.7% red, 13.7% green, and 14.6% blue lights). Mowing decreases carbon (C) isotope signature (δ¹³C), CFi, and total C content in shoots but increases their accumulations in DM, nonstructural carbohydrates, and crude fat content (CFa). The results also demonstrated that mown alfalfa has higher starch content when exposed to green light (26.2% red, 56.4% green, and 17.4% blue lights) compared to the other two spectra. Multiple factorial regression indicated that higher soluble sugar content accounted for the increase of CFa and DM weight for CFi. Overall, mowing in blue-light-enriched understory stands is recommended and produces high-forage-quality alfalfa, which can be used as a lowered crude fiber component.

Quality assessment and nutrient uptake and utilization in Luohan pine (Podocarpus macrophyllus) seedlings raised by chitosan spraying in varied LED spectra

Target seedling cultivation pursues high quality and nutrient utilization instead of increasing growth and size. Exposure to light-emitting diode (LED) spectra is a well-known approach that can accelerate growing speed in tree seedlings, but it is still unknown whether seedling quality and nutrient utilization would be further improved with exogeneous polymer additives. Luohan pine (Podocarpus macrophyllus) seedlings were exposed to red (red-green-blue lights, 71.7%-13.7%-14.6%), green (26.2%-56.4%-17.4%), and blue (17.8%-33.7%-48.5%) LED-light spectra with half receiving leaf spray by chitosan oligosaccharides (Cos) at a rate of 2 ppm (w/w) and the other half receiving only water. The red-light spectrum promoted height, biomass, nutrient utilization, and quality assessment (DQI) in water-sprayed seedlings. The Cos spray enhanced fine-root growth, protein, and chlorophyll-b contents with elevated nutrient utilization and quality in seedlings in the green-light spectrum. DQI was found to have a positive relationship with phosphorus utilization. In conclusion, although the red-light LED spectrum can promote seedling growth, green light combined with Cos spray is recommended with the aim of maintaining seedling quality and increasing P utilization in Luohan pine seedlings.

Variations in Acorn Traits in Two Oak Species: Quercus mongolica Fisch. ex Ledeb. and Quercus variabilis Blume

Quercus mongolica Fisch. ex Ledeb. and Q. variabilis Blume are two main oak species in China, producing large amounts of acorns every year. However, the trait variations in acorns, as a promising energy crop material, are not fully understood, hence we compared the traits of acorns from the different populations with the altered geographic distribution in this study. Thirteen acorn traits, including phenotype, proximate compositions and functional compounds, were analyzed in both Quercus L. species collected from 44 populations across China. The results showed that, except large differences found among accessions in acorn sizes, the starch varied from 140.96–297.09 mg/g in Q. mongolica and 130.99–306.28 mg/g in Q. variabilis, indicating its substantial differences among populations. The total polyphenols, total flavonoids and soluble tannins varied from 41.76–158.92, 23.43–91.94, and 15.11–17.81 mg/g, respectively, in Q. mongolica, 89.36–188.37, 50.59–116.07, 15.24–17.33 mg/g, respectively, in Q. variabilis, demonstrating their large variations in the levels of polyphenols among populations. Moreover, the acorns of Q. mongolica in North China and Q. variabilis in Southwest China had higher levels of starch and polyphenols. As the geographical location approached in the distribution of two Quercus species, the difference in acorn sizes gradually increased, while that in polyphenols were opposite. Principal component analysis and cluster analysis further revealed that the acorn sizes became larger and polyphenols became less with the increasing latitudes in both species. In North China, the acorns of Q. mongolica had small sizes and high polyphenols, which was contrary to those in Q. variabilis. These findings indicated that acorn traits were closely associated with the geographical distribution. Thus, our results will provide references for the selection breeding of acorn with the high starch, high or low polyphenols in the different regions.