Short-Term Root-Zone Temperature Treatment Enhanced the Accumulation of Secondary Metabolites of Hydroponic Coriander (Coriandrum sativum L.) Grown in a Plant Factory

Plant secondary metabolic responses to global climate change: A meta-analysis in medicinal and aromatic plants

Plant secondary metabolites (SMs) play crucial roles in plant-environment interactions and contribute greatly to human health. Global climate changes are expected to dramatically affect plant secondary metabolism, yet a systematic understanding of such influences is still lacking. Here, we employed medicinal and aromatic plants (MAAPs) as model plant taxa and performed a meta-analysis from 360 publications using 1828 paired observations to assess the responses of different SMs levels and the accompanying plant traits to elevated carbon dioxide (eCO₂ ), elevated temperature (eT), elevated nitrogen deposition (eN) and decreased precipitation (dP). The overall results showed that phenolic and terpenoid levels generally respond positively to eCO₂ but negatively to eN, while the total alkaloid concentration was increased remarkably by eN. By contrast, dP promotes the levels of all SMs, while eT exclusively exerts a positive influence on the levels of phenolic compounds. Further analysis highlighted the dependence of SM responses on different moderators such as plant functional types, climate change levels or exposure durations, mean annual temperature and mean annual precipitation. Moreover, plant phenolic and terpenoid responses to climate changes could be attributed to the variations of C/N ratio and total soluble sugar levels, while the trade-off supposition contributed to SM responses to climate changes other than eCO₂ . Taken together, our results predicted the distinctive SM responses to diverse climate changes in MAAPs and allowed us to define potential moderators responsible for these variations. Further, linking SM responses to C-N metabolism and growth-defence balance provided biological understandings in terms of plant secondary metabolic regulation.

A short-term cooling of root-zone temperature increases bioactive compounds in baby leaf Amaranthus tricolor L

Leafy vegetables that are offered as seedling leaves with petioles are referred to as baby leaf vegetables. One of the most nutritious baby leaves, amaranth (Amaranthus tricolor L.), contains several bioactive compounds and nutrients. Here, we investigated the growth and quality of baby leaf amaranth using a variety of short-term cooling root-zone temperatures (RZT; 5, 10, 15, and 20°C), periods (1, 3, 5, and 7 days), and combinations thereof. We observed that exposing amaranth seedlings to RZT treatments at 5 and 10°C for 1-3 days increased the antioxidant capacity and the concentrations of bioactive compounds, such as betalain, anthocyanin, phenolic, flavonoid, and ascorbic acid; however, extending the treatment period to 7 days decreased them and adversely affected growth. For RZT treatments at 20°C, leaf photosynthetic pigments, bioactive compounds, nutrients, and antioxidant capacity increased gradually as the treatment period was extended to 7 days. The integration of RZTs at 5 and 10°C for one day preceded or followed by an RZT treatment at 20°C for 2 days had varied effects on the growth and quality of amaranth leaves. After one day of RZT treatment at 5°C followed by 2 days of RZT treatment at 20°C, the highest concentrations of bioactive compounds, nutrients, and antioxidant capacity were 1.4-3.0, 1.7, and 1.7 times higher, respectively, than those of the control, and growth was not impaired. The short-term cooling RZT treatments under controlled environments were demonstrated to be adequate conditions for the improvement of target bioactive compounds in amaranth baby leaf without causing leaf abnormality or growth impairment.

Optimization of the Yield, Total Phenolic Content, and Antioxidant Capacity of Basil by Controlling the Electrical Conductivity of the Nutrient Solution

Hydroponic cultivation using nutrient solution (NS) is the main cultivation method employed by plant factories with artificial lighting (PFALs). The electrical conductivity (EC) of NSs influences the yield and quality of vegetables. The purpose of this study was to optimize the yield and antioxidant accumulation of basil in a PFAL by EC management. In experiment 1, basil plants were grown under four different ECs (0.5, 1.0, 3.0, and 5.0 dS m−1) after transplanting. At 18 days after treatment, the highest levels of shoot fresh and dry weights, leaf fresh and dry weights, and leaf area were observed at an EC of 3.0 dS m−1. However, low-EC treatments (0.5 and 1.0 dS m−1) generated total phenolic content (TPC) and antioxidant capacities that were higher than those of other EC treatments (3.0 and 5.0 dS m−1). In experiment 2, basil plants were grown at an EC of 3.0 dS m−1 for 13 or 15 days, then treated with water or NS with low ECs (0.5 and 1.0 dS m−1) for 5 or 3 days before harvest. The short-term low-EC treatments, especially, water for 3 days and 0.5 dS m−1 for 5 days, significantly increased the TPC and antioxidant capacity of leaves without significantly decreasing the yields of basil, compared with the control. In conclusion, yield of basil was optimized with an EC of 3.0 dS m−1; however, the TPC and antioxidant capacity of basil were significantly increased by low ECs of 0.5 and 1.0 dS m−1. Short-term low-EC treatments (0.5 dS m−1 for 5 days or water for 3 days) could be used to promote the TPC and antioxidant capacity in leaves without sacrificing yield of basil significantly.

Influence of Nitrogen Sources Applied by Fertigation to an Enriched Soil with Organic Compost on Growth, Mineral Nutrition, and Phytochemicals Content of Coriander (Coriandrum sativum L.) in Two Successive Harvests

The aim of the present study was to evaluate the effects of nitrogen source applied by fertigation to an enriched soil with organic compost on plant growth, mineral nutrition, and phytochemical contents in two successive harvests in coriander. The treatments were as follows: unfertilized soil, soil enriched with organic compost, and soil enriched with organic compost to which 60 kg N ha^-1 as ammonium nitrate and as ammonium sulfate applied by fertigation were added. Ammonium nitrate addition allowed to obtain a high total fresh yield (3.6 kg m^-2) with a low inorganic nitrogen input. Ammonium nitrate increased plant shoot dry weight; fresh yield; and shoot N, K, and Ca uptake in the first harvest. Ammonium nitrate relative to organic compost and to ammonium sulfate increased fresh yield by approximately 57 and 25%, respectively. However, ammonium sulfate in the first harvest greatly increased shoot total phenols, from 137 mgGAE/100 g FW in ammonium nitrate to 280.4 mgGAE/100 g FW. Coriander's fresh yield, in the second harvest, was unaffected by nitrogen addition. However, ammonium nitrate increased shoot total phenols and FRAP activity. Overall, the shoot phytochemical accumulation in the second harvest was lower than in the first. The combined application of ammonium nitrate and organic compost is a strategy to reduce inorganic nitrogen application.

Effects of Root Temperature on the Plant Growth and Food Quality of Chinese Broccoli (Brassica oleracea var. alboglabra Bailey)

Root temperature has long been considered an essential environmental factor influencing the plant’s physiology. However, little is known about the effect of root temperature on the quality of the food produced by the plant, especially that of horticultural crops. To fill this gap, two independent root cooling experiments (15 °C vs. 20 °C and 10 °C vs. 20 °C) were conducted in autumn 2017 and spring 2018 in hydroponics with Chinese broccoli (Brassica oleracea var. alboglabra Bailey) under greenhouse conditions. The aim was to investigate the effect of root temperature on plant growth (biomass, height, yield) and food quality (soluble sugars, total chlorophyll, starch, minerals, glucosinolates). A negative impact on shoot growth parameters (yield, shoot biomass) was detected by lowering the root temperature to 10 °C. Chinese broccoli showed no response to 15 °C root temperature, except for an increase in root biomass. Low root temperature was in general associated with a higher concentration of soluble sugars and total chlorophyll, but lower mineral levels in stems and leaves. Ten individual glucosinolates were identified in the stems and leaves, including six aliphatic and four indolic glucosinolates. Increased levels of neoglucobrassicin in leaves tracked root cooling more closely in both experiments. Reduction of root temperature by cooling could be a potential method to improve certain quality characters of Chinese broccoli, including sugar and glucosinolate levels, although at the expense of shoot biomass.