Water availability for plant growth is becoming increasingly limited, whereas rising atmospheric carbon dioxide concentration may have interactive effects with drought stress. The objectives of this study were to determine whether elevated CO2 would mitigate drought-induced water deficit and photosynthesis inhibition and enhance recovery from drought damages on rewatering and to determine whether the mitigating effects during drought stress and the recovery in photosynthesis during rewatering by elevated CO2 were the result of the regulation of stomatal movement or carboxylation activities in tall fescue (Festuca arundinacea Schreb. cv. Rembrandt). Plants were grown in controlled-environment chambers with ambient CO2 concentration (400 μmol·mol−1) or elevated CO2 concentration (800 μmol·mol−1) and maintained well watered (control) or subjected to drought stress and subsequently rewatered. Elevated CO2 reduced stomatal conductance (g S) and transpiration rate of leaves during both drought stress and rewatering. Osmotic adjustment and soluble sugar content were enhanced by elevated CO2. Elevated CO2 enhanced net photosynthetic rate with lower g S but higher Rubisco and Rubisco activase activities during both drought and rewatering. The results demonstrated that elevated CO2 could improve leaf hydration status and photosynthesis during both drought stress and rewatering, and the recovery in photosynthesis from drought damages on rewatering was mainly the result of the elimination of metabolic limitation from drought damages associated with carboxylation enzyme activities.
Yajun Chen, Jingjin Yu, and Bingru Huang
Yu-Wei Liu and Chen-Kang Huang
Hydroponic systems in plant factories can be categorized into recirculating or noncirculating systems. In this study, the effects of various commercially available circulation pumps, including a centrifugal magnetic drive pump, a regenerative self-priming pump, and a submersible pump, were experimentally explored. In addition, the effects of an ultraviolet sterilization system on the ion concentrations in nutrient solutions were examined. The concentrations of sodium, potassium, magnesium, calcium, nitrate, sulfate, and ferric (Fe3+) ions in the nutrient solution were measured. For all three types of pumps, the results indicated that there was no significant effect on the concentrations of ions in the nutrient solution. However, the concentration of Fe3+ ions decreased significantly after the nutrient solution was treated by a ultraviolet sterilization system for 48 hours. In addition, the effects of the three types of pumps on the growth of butterhead lettuce (Lactuca sativa) were examined. The temperature records during the pump circulation tests showed that the nutrient solution temperature of the regenerative self-priming pump increased by 15.5 °C (from 20.5 to 36 °C), which caused yellow seedling, scorching on the leaves, and browning of the roots. The ion concentration in the nutrient solutions and total fresh weight of butterhead lettuce did not show any noticeable difference between the centrifugal magnetic drive pump and the submersible pump. In this paper, we clarify the cause of the decreasing iron concentration and provide a guideline for selecting the pump for circulating hydroponic systems in plant factories.
Yu Huang, John E. Kaminski, and Peter J. Landschoot
Dollar spot, caused by Sclerotinia homoeocarpa F.T. Bennett, is an important disease of creeping bentgrass (Agrostis stolonifera L.) on golf courses in the northern United States. Canopy moisture in the form of dew plays an important role in the development of dollar spot and routine displacement has been shown to reduce disease severity. The use of plant growth regulators (PGRs) is a common management practice for maintaining creeping bentgrass fairways, but their influence on dollar spot is unclear. The objective of this field study was to elucidate the influence of dew removal at the time of fungicide application on dollar spot control in creeping bentgrass regulated by trinexapac-ethyl (TE). Main factors in the study included three dew removal strategies (non-treated, dew removed–mowed, and dew removed–not mowed) before the application of four fungicide treatments (non-treated, chlorothalonil, propiconazole, and iprodione). All fungicide treatments were applied once to turfgrass previously treated with TE or not treated. The presence or absence of dew at the time of fungicide application generally had no influence on fungicide performance with respect to dollar spot control. Based on the results of this study, dew removal before the application of fungicides targeting dollar spot is unnecessary. Applications of TE before fungicides reduced dollar spot severity in some cases, but reductions in symptom expression were limited and did not result in markedly improved dollar spot control.
June Liu, Zhimin Yang, Weiling Li, Jingjin Yu, and Bingru Huang
Cold stress is a major factor limiting the growth of warm-season turfgrass species. Cold tolerance in warm-season turfgrass species could be improved through in vitro selection for somaclonal variations. The objectives of this study were to establish an effective in vitro culture protocol for generating plants from calli using mature seeds of seashore paspalum (Paspalum vaginatum) and to determine whether in vitro cold selection of somaclonal variations would lead to improved cold tolerance in seashore paspalum. The optimal concentrations of supplemental compounds in the culture medium for callus induction, embryogenic callus formation, and plant regeneration were determined. The supplemental compounds included 2,4–dichlorophenoxy acetic acid (2,4-D), 6-benzylaminopurine (6-BA), kinetin (KT), naphthalene-1-acetic acid (NAA), CuSO4, and acidic hydrolysis casein (AHC). The highest rates of callus induction (97.50%), embryogenic callus formation (66.88%), and regeneration (55.94%) were obtained with the supplemental compounds of 3.0 mg·L−1 2,4-D and 10.0 mg·L−1 CuSO4 for callus induction; with 3.0 mg·L−1 2,4-D, 15 mg·L−1 CuSO4, and 1.0 g·L−1 AHC for embryogenic callus formation; and with 8.0 mg·L−1 6-BA, 0.2 mg·L−1 KT, 0.5 mg·L−1 NAA, and 10 mg·L−1 CuSO4 for plant regeneration. Embryogenic calli were subjected to 2 or 6 °C treatment for 90 days for in vitro cold selection of somaclonal variation. Plants regenerated from calli surviving cold treatment (cold-selected) for 45 or 60 days were then exposed to low temperatures [15/10 or 5/3 °C (day/night)]. Plant variants derived from cold-selected calli exhibited significant improvement in their tolerance to low temperature of either 15/10 or 5/3 °C (day/night), as manifested by higher turf quality, leaf chlorophyll content, and membrane stability as well as lower levels of lipid peroxidation compared with the control plants. This study demonstrated the feasibility of in vitro selection for cold tolerance in seashore paspalum. The cold-tolerant variants could be useful germplasm for breeding programs and further molecular characterization of cold tolerance mechanisms.
Jingjin Yu, Mengxian Liu, Zhimin Yang, and Bingru Huang
Drought stress is one of the most important abiotic stresses limiting plant growth, while high recuperative capacity of plants from drought damages is critical for plant survival in periods of drought stress and rewatering. The objective of our study was to determine physiological and growth factors in association with drought tolerance and recuperative capacity of cool-season kentucky bluegrass (Poa pratensis cv. Excursion II) and warm-season zoysigrass (Zoysia matrella cv. Diomand), which were grown in controlled environment chambers and maintained well watered (control) or subjected to drought stress and subsequently rewatering. Compared with kentucky bluegrass, zoysiagrass maintained higher leaf hydration level during drought stress, as shown by greater relative water content (RWC), improved osmotic adjustment (OA), increased leaf thickness, and more extensive root system at deeper soil layers. Turf quality (TQ) and photosynthesis recovered to a greater level and sooner in response to rewatering for zoysiagrass, compared with kentucky bluegrass, which could be due to more rapid reopening of stomata [higher stomatal conductance (g S)] and leaf rehydration (higher RWC). The aforementioned physiological factors associated with leaf dehydration tolerance during drought and rapid resumption in turf growth and photosynthesis in zoysiagrass could be useful traits for improving drought tolerance in turfgrasses.
Hongmei Du, Zhaolong Wang, Wenjuan Yu, and Bingru Huang
The accumulation of different types of metabolites may reflect variations in plant adaptation to different severities or durations of drought stress. The objectives of this project are to examine changes in metabolomic profiles and determine predominant metabolites in response to short-term (6 days) and long-term (18 days) drought stress with gas chromatography–mass spectrometry analysis in a C4 perennial grass species. Plants of hybrid bermudagrass (Cynodon dactylon × C. transvaalensis cv. Tifdwarf) were unirrigated for 18 days to induce drought stress in growth chambers. Physiological responses to drought stress were evaluated by visual rating of grass quality, relative water content, photochemical efficiency, and electrolyte leakage (EL). All parameters decreased significantly at 6 and 18 days of drought stress, except EL, which increased with the duration of drought stress. Under short-term drought stress (6 days), the content did not change significantly for most metabolites, except methionine, serine, γ-aminobutyric acid (GABA), isoleucine, and mannose. Most metabolites showed higher accumulation under long-term drought stress compared with that under the well-watered conditions, including three organic acids (malic acid, galacturonic acid, and succinic acid), 10 amino acids (proline, asparagine, phenylalanine, methionine, serine, 5-hydroxynorvaline, GABA, glycine, theorine, valine), seven sugars (sucrose, glucose, galactose, fructose, mannose, maltose, xylose), one nitrogen compound (ethanolamine), and two-sugar alcohol (myo-inositol). The accumulation of those metabolites, especially malic acid, proline, and sucrose, could be associated with drought adaptation of C4 hybrid bermudagrass to long-term or severe drought stress.
Jingjin Yu, Hongmei Du, Ming Xu, and Bingru Huang
Heat is a major factor limiting growth of C3 grass species. Elevated CO2 may mitigate the adverse effects of heat stress or enhance heat tolerance. The objective of this study was to determine metabolic changes associated with improvement of heat tolerance by elevated atmospheric CO2 concentration in tall fescue (Festuca arundinacea). Plants (cv. Rembrandt) were exposed to ambient day/night temperature (25/20 °C) or heat stress (35/30 °C) and ambient CO2 concentration (400 ± 10 μmol·mol−1) or double ambient CO2 concentration (800 ± 10 μmol·mol−1) in growth chambers. Turf quality (TQ), shoot growth rate, and leaf electrolyte leakage results demonstrated that heat stress at ambient CO2 concentration inhibits turf growth and reduces cell membrane stability, whereas heat-stressed plants under elevated CO2 concentration exhibit improved TQ, shoot growth rate, and membrane stability. Plants exposed to heat stress under elevated CO2 exhibited a significantly greater amount of several organic acids (shikimic acid, malonic acid, threonic acid, glyceric acid, galactaric acid, and citric acid), amino acids (serine, valine, and 5-oxoproline), and carbohydrates (sucrose and maltose) compared with heat-stressed plants at ambient CO2. The increased production or maintenance of metabolites with important biological functions such as those involved in photosynthesis, respiration, and protein metabolism could play a role in elevated CO2 mitigation of heat stress damage. Therefore, elevated CO2 conditions may contribute to improved heat stress tolerance as exhibited by better TQ and shoot growth of heat-stressed plants. Practices to harness the power of CO2 may be incorporated into turfgrass management for plant adaptation to increasing temperatures, particularly during summer months.
Zhimin Yang, Lixin Xu, Jingjin Yu, Michelle DaCosta, and Bingru Huang
Carbohydrate metabolism is important for plant adaptation to drought stress. The objective of this study was to examine major forms of carbohydrates associated with superior drought tolerance and post-drought recovery in kentucky bluegrass (Poa pratensis) by comparing responses of different forms of carbohydrates with drought stress and re-watering in two cultivars contrasting in drought tolerance. Plants of drought-tolerant ‘Midnight’ and drought-sensitive ‘Brilliant’ were maintained well watered or subjected to drought stress for 10 days by withholding irrigation, and drought-stressed plants were re-watered for 3 days. Physiological analysis (turf quality, relative water content, and electrolyte leakage) confirmed the genetic variability of the two cultivars in drought tolerance. The two cultivars exhibited differential responses to drought stress and re-watering for the content of water-soluble sugars (sucrose, fructose, and glucose) and storage carbohydrates (starch and fructan), and ‘Midnight’ maintained higher sucrose content at 10 days of drought stress and more fructan at 3 days of re-watering. The greater accumulation of sucrose in ‘Midnight’ under drought stress corresponded with higher activities of two sucrose-synthesizing enzymes (sucrose phosphate synthase and sucrose synthase) but was not related to the sucrose-degrading enzyme activity (acid invertase). These results suggested that increased sucrose accumulation resulting from the maintenance of active sucrose synthesis could be associated with superior turf performance during drought stress, whereas increased fructan accumulation could contribute to rapid re-growth and post-drought recovery on re-watering in kentucky bluegrass.
Zhimin Yang, Jingjin Yu, Emily Merewitz, and Bingru Huang
Abscisic acid (ABA) and glycine betaine (GB) may regulate plant responses to drought or salinity stress. The objectives of this controlled-environment study were to determine whether foliar application of ABA or GB improves turf quality under drought or salinity and whether improved stress responses were associated changes in antioxidant metabolism in two C3 turfgrass species, creeping bentgrass (Agrostis stolonifera) and kentucky bluegrass (Poa pratensis). Physiological parameters evaluated included turf quality, leaf relative water content, membrane electrolyte leakage (EL), membrane lipid peroxidation [expressed as malondialdehyde (MDA) content], and activity of superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX). Abscisic acid and GB were both effective in mitigating physiological damage resulting from drought or salinity for both grass species, but effects were more pronounced on kentucky bluegrass. The most notable effects of ABA or GB application were the suppression of EL and MDA accumulation and an increase in APX, POD, and SOD activities after prolonged periods of drought (21 days) or salinity stress (35 days). These results suggest foliar application of ABA or GB may alleviate physiological damage by drought or salinity stress in turfgrass and the maintenance of membrane stability and active antioxidant metabolism could contribute to the positive effects in the stress mitigation effects.
Xiaotao Ding, Liyao Yu, Yuping Jiang, Shaojun Yang, Lizhong He, Qiang Zhou, Jizhu Yu, and Danfeng Huang
Changes in leaf length, width, area, weight, chlorophyll and carotenoids contents, and photosynthetic variables with different leaf positions were investigated in fruit cucumber. Plants were grown on rockwool slabs in an environmentally controlled greenhouse and irrigated by drip fertigation. Leaf measurements were conducted from the first to the 15th leaf (the oldest to the youngest). The results showed that fresh weight per unit leaf area decreased from the second to the 15th leaf. Changes in cucumber leaf length, width, and area followed quadratic models from the first to the 15th leaf. The quadratic models of leaf length, width, and area fit the measurements well, with R 2 values of 0.925, 0.951, and 0.955, respectively. The leaf chlorophyll a and b and carotenoid contents increased from the oldest leaf (first leaf) to the youngest leaf and decreased after reaching the highest values. Changes in the net photosynthetic rate (Pn) also followed the quadratic model from the first to the 15th leaf, with R 2 values of 0.975. The leaf transpiration rate (Tr) increased from the first to the 14th leaf. Our results revealed patterns in leaf growth and photosynthetic changes at different leaf positions in fruit cucumber and improved our understanding of the growth and development of fruit cucumber in the greenhouse production system.