Tung tree is a member of the Euphorbiaceae family, a native tree species that has been cultivated for more than 1000 years in China. Along with the oil-tea tree (Camellia oleifera), walnut (Juglans regia), and tallow tree (Sapium sebiferum), tung tree is one of the four major woody oil trees in China. Tung trees have been cultivated in central and southern areas of China (lat. 22°15′–34°30′N; long. 99°41′–122°07′E) and are usually cultivated in mountainous and hilly areas at less than 1000 m above sea level. Mature tung trees can reach ≈5 m, with a crown circumference of ≈4.5 m (Tan et al., 2011). Tung oil, which is extracted from tung seeds, exhibits traits that are highly valued in many industries (Park et al., 2008; Pfister et al., 2008), including rapid drying, chemical resistance, adhesiveness, and sleekness. These properties make tung oil a valuable drying ingredient in paints, varnishes, and other coatings and finishes (Cao and Shockey, 2012; Li et al., 2017b). With recent human population increases, tung trees have become a valuable biofuel species, with the potential to help resolve energy shortage problems (Tan et al., 2011). Furthermore, tung trees grow quickly, yielding fruit within 3 years as a result of their high photosynthetic efficiency (Li et al., 2017a).
The primary problem in tung tree production is the weak or dead lower branches of mature tung trees caused by heavy shade of the upper branches, resulting in a lower yield. For example, tung trees in a shady, sloped planting site had a 58.4% yield reduction with smaller fruit than those grown in a sunny planting site (Li and Zhu, 2014). In addition, most of the lower branches of mature tung trees appear to be dead, which seriously affects the healthy development of the tung tree industry in China (Fig. 1). To date, there have not been any studies on the effects of growth and photosynthesis of tung trees under different light intensities. Currently, the lowest DLI for suitable for tung tree growth is not known, especially in southern China, which has frequent cloudy and rainy days. By studying the growth and physiological responses of tung tree seedlings to different light intensities, the minimum DLI requirement can be determined for the growth of tung trees, which provides a theoretic basis and technical support for the determination of a suitable planting density of tung trees.
The productivity of plants depends on soil, LA index and efficiency of light conversion, and CO2 absorption (Lone and Khan, 2007). Light is a major environmental factor that affects leaf photosynthesis, traits, and plant growth, and determines the geographic distribution of plants (Kim et al., 2011). Plants experiencing shade stress often exhibit serious dysfunctions in terms of appearance and physiology, including reduced photosynthetic potential, stomatal density, and damage to various cellular structures (Holland and Richardson, 2009; Kim et al., 2011; Nobel et al., 1993; Tsukaya, 2005). Reduced photosynthesis may be the result of either stomatal closure restricting the availability of CO2 for carboxylation or nonstomatal inhibition caused by abiotic stress on the photosynthetic apparatus (Chen et al., 2009; Colla et al., 2012b; Rivelli et al., 2002). However, plants adopt different strategies to adapt to shade stress. For example, to absorb sufficient light energy, LA and plant height increase under shade conditions, increasing light-harvesting capabilities in a light-limited environment (Huang et al., 2016; Johnston and Onwueme, 1998; Khan et al., 2000). Similarly, superoxide dismutase and peroxidase in leaves increase in response to shade stress (Ou et al., 2015). Many authors (Morandi et al., 2011; Zibordi et al., 2009) have reported that shade causes a decrease in the net C exchange rates in young apple canopies. The decrease in fruit growth rate in young apple trees is mainly the result of a reduction in import through the phloem rather than a direct effect of shading on fruit sink strength. Iqbal et al. (2012) hypothesized that the photosynthetic potential of leaves that were lower on the plant axis was less than that of the upper leaves in the plant canopy. Previous studies have shown that light-use efficiency and decreased photosynthetic activity from the apex of the plant to the lower axis (Khan and Lone, 2005; Lone et al., 2008). Lugassi-Ben-Hamo et al. (2010) reported that shade treatments may have an adverse effect on plant growth or flower yield and quality in Lisianthus. Several studies have shown that shade tolerance is associated with a wide range of traits, including pigment biosynthesis, photosynthesis, and morphological and physiological traits (Huang et al., 2016; Khan et al., 2000; Kim et al., 2011).
In our study, we investigated the changes in growth, chlorophyll content, relative water content, photosynthesis, and enzyme activity under different light intensities. The aim of our study was to understand the acclimation mechanism under lower light conditions and to determine the optimal DLI for tung tree seedlings. From this DLI, we can determine the proper planting density and cultivation technique, such as pruning, to prevent mutual shading and ensure sufficient light for tung tree growth and high yield.
BlakeyR.J.BowerJ.P.2009Bertling I.: Influence of water and ABA supply on the ripening pattern of avocado (Persea americana Mill.) fruit and the prediction of water content using near infrared spectroscopyPostharvest Biol. Technol.537276
BowerJ.P.1985Some aspects of water relations on avocado (Persea americana Mill.) tree and fruit physiology. Department of Horticultural Science University of Natal Pietermaritzburg PhD Diss.
BowerJ.P.CuttingJ.G.M.1988Avocado fruit development and ripening physiology p. 229–271. In: J. Janick (ed.). Horticultural reviews 10. Timber Press Portland OR
BrodribbT.1996Dynamics of changing intercellular CO2 concentration (Ci) during drought and determination of minimum functional CiPlant Physiol.111179185
CaoH.P.ShockeyJ.M.2012Comparison of TaqMan and SYBR green qPCR methods for quantitative gene expression in tung tree tissuesJ. Agr. Food Chem.601229612303
ChenS.P.BaiY.F.ZhangL.X.HanX.G.2005Comparing physiological responses of two dominant grass species to nitrogen addition in Xilin River Basin of ChinaEnviron. Exp. Bot.536575
ChenL.H.GongP.YangW.Q.ZhangJ.HuT.X.2012Effects of allelopathy from the early decomposition of Eucalyptus leaf litter on the photosynthetic characteristics of Brassica chinensis LJ. Sichuan Agr. Univ.30174180
ChenB.L.YangH.K.MaY.N.LiuJ.R.LvF.J.ChenJ.2016Effect of shading on yield, fiber quality and physiological characteristics of cotton subtending leaves on different fruiting positionsPhotosynthetica111
ChenW.ZouD.GuoW.XuH.ShiD.YangC.2009Effects of salt stress on growth, photosynthesis and solute accumulation in three poplar cultivarsPhotosynthetica47415421
CollaG.RouphaelY.CardarelliM.2012aVegetable crops: Improvement of tolerance to adverse chemical soil conditions by grafting. In: Improving Crop Resistance to Abiotic Stress Vol. 1 and Vol. 2.
CollaG.RouphaelY.LeonardiC.BieZ.L.CollaG.2010Role of grafting in vegetable crops grown under saline conditionsScientia Hort.127147155
CollaG.RouphaelY.ReaE.CardarelliM.2012bGrafting cucumber plants enhance tolerance to sodium chloride and sulfate salinizationScientia Hort.135177185
HuL.YuJ.LiaoW.ZhangG.XieJ.LvJ.XiaoX.YangB.ZhouR.BuR.2015Moderate ammonium:nitrate alleviates low light intensity stress in mini Chinese cabbage seedling by regulating root architecture and photosynthesisScientia Hort.186143153
HuangW.HuH.HuT.ChenH.WangQ.ChenG.2015Impact of aqueous extracts of Cinnamomum septentrionale leaf litter on the growth and photosynthetic characteristics of Eucalyptus grandis seedlingsNew For.46561576
HuangC.J.WeiG.JieY.C.XuJ.J.AnjumS.A.TanveerM.2016Effect of shade on plant traits, gas exchange and chlorophyll content in four ramie cultivarsPhotosynthetica54390395
IqbalN.MasoodA.KhanN.A.2012Analyzing the significance of defoliation in growth, photosynthetic compensation and source-sink relationsPhotosynthetica50161170
JohnstonM.OnwuemeI.C.1998Effects of shade on photosynthetic pigments in the tropical root crops: Yam, taro, tannia, cassava and sweet potatoExp. Agr.34301312
KhanN.A.LoneP.M.2005Effects of early and late season defoliation on photosynthesis, growth and yield of mustard (Brassica juncea L.)Braz. J. Plant Physiol.17181186
KhanS.R.RoseR.HaaseD.L.SabinT.E.2000Effects of shade on morphology, chlorophyll concentration, and chlorophyll fluorescence of four Pacific Northwest conifer speciesNew For.19171186
KimS.J.YuD.J.KimT.C.LeeH.J.2011Growth and photosynthetic characteristics of blueberry (Vaccinium corymbosum, cv. Bluecrop) under various shade levelsScientia Hort.129486492
LiZ.LongH.X.ZhangL.LiuZ.M.CaoH.P.ShiM.W.TanX.F.2017aThe complete chloroplast genome sequence of tung tree (Vernicia fordii): Organization and phylogenetic relationships with other angiospermsSci. Rep.71869doi: 10.1038/s41598-017-02076-6.
LiZ.TanX.F.LuK.LiuZ.M.WuL.L.2017bThe effect of CaCl2, on calcium content, photosynthesis, and chlorophyll fluorescence of tung tree seedlings under drought conditionsPhotosynthetica55553560
LichtenthalerH.K.BabaniF.LangsdorfG.2007Chlorophyll fluorescence imaging of photosynthetic activity in sun and shade leaves of treesPhotosynth. Res.93235244
LoneP.M.KhanN.A.2007The effects of rate and timing of N fertilizer on growth, photosynthesis, N accumulation and yield of mustard (Brassica juncea) subjected to defoliationEnviron. Exp. Bot.60318323
LoneP.M.NazarR.SinghS.KhanN.A.2008Effects of timing of defoliation on nitrogen assimilation and associated changes in ethylene biosynthesis in mustard (Brassica juncea)Biologia63207210
Lugassi-Ben-HamoM.KitronM.BustanA.ZaccaiM.2010Effect of shade regime on flower development, yield and quality in LisianthusScientia Hort.124248253
MorandiB.ZibordiM.LoscialeP.ManfriniL.PierpaoliE.GrappadelliL.C.2011Shading decreases the growth rate of young apple fruit by reducing their phloem importScientia Hort.127347352
NobelP.S.ForsethI.N.LongS.P.1993Canopy structure and light interception p. 79–90. In: D.O. Hall J.M.O. Scurlock H.R. Bolhar-Nordenkampf R.C. Leegood and S.P. Long (eds.). Photosynthesis and production in a changing environment. Chapman and Hall London UK
OuL.J.WeiG.ZhangZ.Q.DaiX.Z.ZouX.X.2015Effects of low temperature and low irradiance on the physiological characteristics and related gene expression of different pepper speciesPhotosynthetica538594
ParkJ.Y.KimD.K.WangZ.M.LuP.ParkS.C.LeeJ.S.2008Production and characterization of biodiesel from tung oilAppl. Biochem. Biotechnol.148109117
PfisterD.P.BakerJ.R.HennaP.H.LuY.LarockR.C.2008Preparation and properties of tung oil-based composites using spent germ as a natural fillerJ. Appl. Polym. Sci.10836183625
RivelliA.R.LovelliS.PerinolaM.2002Effects of salinity on gas exchange, water relations and growth of sunflower (Helianthus annuus)Funct. Plant Biol.2914051415
SarijevaG.KnappM.LichtenthalerH.K.2007Differences in photosynthetic activity, chlorophyll and carotenoid levels, and in chlorophyll fluorescence parameters in green sun and shade leaves of Gingko and FagusJ. Plant Physiol.164950955
SchwarzD.IerselM.W.V.IngramK.T.KläringH.P.HorstW.J.SchenkM.K.2001Nutrient solution concentration effects on growth and photosynthesis of tomato grown hydroponically: Plant nutrition. Springer Netherlands
ShiJ.N.WuM.X.ChaJ.J.1979Studies on plant phosphoenolpyruvate carboxylase I: Separation and properties of PEP carboxylase isoenzymesJ. Plant Physiol.5225236
SuiX.L.MaoS.L.WangL.H.ZhangB.X.ZhangZ.X.2012Effect of low light on the characteristics of photosynthesis and chlorophyll a fluorescence during leaf development of sweet pepperJ. Integr. Agr.1116331643
TaltsP.PärnikT.GardeströmP.KeerbergO.2004Respiratory acclimation in Arabidopsis thaliana leaves at low temperatureJ. Plant Physiol.161573579
YanN.WangX.Q.XuX.F.GuoD.P.WangZ.D.ZhangJ.Z.HydeK.D.LiuH.L.2013Plant growth and photosynthetic performance of Zizania latifolia are altered by endophytic Ustilago esculenta infectionPhysiol. Mol. Plant Pathol.837583