不同颜色遮阳网防止脐橙高温日灼的效应

赖恒鑫,李文广a,彭良志*,何义仲,凌丽俐,淳长品

(西南大学·中国农业科学院柑桔研究所·国家柑桔工程技术研究中心,重庆 400712)

摘 要:【目的】探究覆盖不同颜色遮阳网防止脐橙高温日灼的效果。【方法】在重庆8月高温期,用相同规格(纬编6针)5种不同颜色(黑、黄、红、绿、蓝)遮阳网覆盖纽荷尔脐橙,对照不覆盖任何材料,测定对照和各色遮阳网覆盖处理的光质和光照度、叶面和果面温度、光合作用指标、相对叶绿素含量、果实生长量和果实品质。【结果】与对照相比,各色遮阳网覆盖的遮光率为59.9%~75.4%,叶面和果面温度降低7.0~10.0 ℃,春梢相对叶绿素含量SPAD 值提高1.6~5.8;各色遮阳网覆盖均无叶片和果实日灼,且提高了叶片净光合速率和单果质量。在所有处理中,蓝网和黑网显著提高净光合速率(Pn)且显著增加果实横径和单果质量,蓝网显著提高果实可溶性固形物(TSS)含量,蓝网和绿网显著提高果实维生素C(Vc)含量。【结论】覆盖各色遮阳网均可完全防止脐橙果实和叶片日灼且改善高温时段的Pn,其中,蓝网对提高Pn、促进果实增大和改善品质的效果最好。

关键词:纽荷尔脐橙;8月高温;彩色遮阳网;日灼防控

我国柑橘产区普遍存在高温伏旱,在此期间,高温和强光照抑制柑橘光合作用、阻碍果实生长发育,严重时引起叶片和果实日灼,导致产量和品质下降[1-2],特别是外围结果较多的沃柑、茂谷柑、温州蜜柑、南丰蜜橘、脐橙等品种,日灼果比例可占1/3[3-4],给生产带来严重损失。目前柑橘生产上防止或减轻日灼的措施主要有树冠覆盖遮阳网[5-6]、果实套袋[7]、果实涂白[8-9]、喷水[10-11]、放夏梢遮阴[12]、生草栽培[13]和建设防护林[14]等。其中,遮阳网对日灼和高温有良好防护效果,在蔬菜等作物上有较系统的研究[15-17],已在生产上得到广泛应用,取得良好增产提质效果[18-19]。但有关柑橘的遮阳网研究少,少量的研究也仅局限于黑色遮阳网试验[5,20-21]。黑色遮阳网主要影响光照度和温度,对光质的影响很小[22]。然而,众多研究表明,光照度、温度、光质对植物光合作用和生长发育等都有重要影响[23-26],不同颜色遮阳网对光质有较大影响,但生产上有关不同颜色遮阳网的研究很少,在柑橘上则未见报道。为此,笔者在本研究中以不同颜色遮阳网为材料,在高温强日照期覆盖纽荷尔脐橙树冠,研究光照度、光质和温度的变化,以及对光合作用和果实生长与品质的影响,以期为柑橘生产上适宜遮阳网颜色的选择提供理论依据和参考。

1 材料和方法

1.1 试验材料与处理

试验于2019—2021 年的8—9 月在重庆北碚西南大学柑桔研究所试验园进行,2019年初步试验发现不同颜色遮阳网存在较大差异,2020—2021年开展系统性研究,选择生长相对一致的枳砧成年纽荷尔脐橙树,7月底在脐橙树四周搭设支架,上盖遮阳网,遮阳网与脐橙树冠顶部间距0.6~0.7 m。共设置5个处理和1个对照,5个处理分别是覆盖黑色遮阳网(T1)、黄色遮阳网(T2)、红色遮阳网(T3)、绿色遮阳网(T4)、蓝色遮阳网(T5),遮阳网均为高密度聚乙烯材质、纬编6 针,RGB 强度值依次为(26,31,32)、(192,153,3)、(157,28,17)、(48,110,92)、(31,82,128),以不覆盖遮阳网为对照(CK)。在树冠中部南面约1.5 m 高度安装徐州数智电子科技有限公司的gsp-6自动温湿度记录仪(单株小区,3个重复;2021 年改为3 株1 小区,3 小区1 个重复),每15 min自动记录1次。记录显示:2020年8月7日至9月15日覆盖期间,41 d 中有24 d 田间气温在35 ℃以上,其中有5 d 田间气温≥40 ℃,高温天气基本为连续性;2021 年8 月1 日至10 月4 日覆盖期间,64 d 中有35 d 田间气温在35 ℃以上,其中有6 d 田间气温≥40 ℃,但高温天气断断续续,最迟在10 月1—4 日还出现37 ℃高温。

1.2 各处理下的光强和光质成分测定

试验期间,选高温晴天(气温≥38 ℃,下同)和阴天两种天气,在8:00—18:00时段,每隔1 h使用植物光合作用检测仪(TES-1339P)在处理和对照树冠顶部同时进行测定,并取晴天光合有效辐射(PAR)最大值计算各色遮阳网的遮光率(遮光率/%=1-网内PAR/网外PAR×100)。使用植物光照分析仪(杭州雷迈科技有限公司PLA-20)测定晴天12:00 各处理树冠顶部的光质成分。

1.3 叶面和果面温度测定

试验期间,选高温晴天、多云、阴天三种天气,在8:00—18:00时段,每隔1 h使用红外测温仪(福禄克FLUCK 62MAX)对树冠南面的叶面、果面温度进行测定,每处理在树冠南面分别选12枚叶片和12个果实测定,各3个重复。

1.4 叶片和果实日灼程度的统计

高温结束后,统计各处理果实、叶片日灼占比,果实、叶片日灼分级参考王敏[9]标准,计算日灼发生率(%)和日灼程度(0~4级)。

日灼发生率(%)=统计日灼数/统计总数×100;

日灼程度=(0级×0+1级数×1+2级数×2+3级数×3+4级数×4)/日灼果数。

1.5 叶片相对叶绿素含量、光合速率和果实横径测定

在各处理选取30 枚当年春梢末端倒数第3 片叶固定标记,使用叶绿素测定仪(欧柯奇OKY104),测定高温初期、高温末期两个时间段的叶片相对叶绿素含量。

选高温晴天,在10:00—11:00、14:00—15:00 时段,用Li-6400 便携式光合仪,选配2 cm×3 cm 标准叶室,在大气CO2浓度下测定各处理树冠中部南面叶片的光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)、胞间CO2浓度(Ci)。

各处理标记21个果实,使用游标卡尺测定高温初期、高温末期果实横径。

1.6 果实品质测定

分别在高温刚结束(拆网时期)和果实成熟时(花后220 d左右)采集各处理南面果实,每个处理每个重复采集15个果实。果实品质测定参考王敏[6]方法。

1.7 数据处理

采用Microsoft Office Excel 2010对数据进行处理及作图,并用SPSS 24.0进行方差分析和显著性分析。采用单因素ANOVA的LSD比较统计数据的差异显著水平(α=0.05)。表中数据均以(平均值±标准差)表示。

2 结果与分析

2.1 不同颜色遮阳网覆盖对柑橘光环境的影响

图1显示,光合有效辐射最大值出现在13:00附近,遮阳网覆盖显著降低树冠的光合有效辐射(PAR),不同颜色遮阳网的遮光率为黑网>蓝网>红网≈黄网≈绿网。在晴天,对照有8 h PAR≥600 μmol·m-2·s-1,最高1579.5 μmol·m-2·s-1;黑网有8 h PAR≥200 μmol·m-2·s-1,最高388.0 μmol·m-2·s-1;黄网有9 h PAR≥200 μmol·m-2·s-1,最高631.4 μmol·m-2·s-1;红网有9 h PAR≥200 μmol·m- 2·s- 1,最高625.3 μmol·m-2·s-1;绿网有9 h PAR≥200 μmol·m-2·s-1,最高632.9 μmol · m- 2 · s- 1;蓝网有9 h PAR≥200 μmol·m-2·s-1,最高581.8 μmol·m-2·s-1。从晴天PAR日变化来看,对照一天至少有8 h 受到了超过600 μmol·m-2·s-1强光损害,而所有覆盖遮阳网处理基本未受到高于600 μmol·m-2·s-1的强光损害(柑橘光饱和点在600 μmol·m-2·s-1附近),但彩色遮阳网有9 h PAR≥200 μmol·m-2·s-1,比黑网多1 h,最高光强比黑网高193.8~244.9 μmol·m-2·s-1且不至于受到强光损害,显然,彩色遮阳网在重庆高温晴天更有利于柑橘光合作用。柑橘光合作用的适宜PAR 为200~600 μmol·m-2·s-1,然而在阴天,无论哪种颜色遮阳网覆盖,一天也只有0~3 h PAR≥200 μmol·m-2·s-1,而对照有6 h PAR≥200 μmol·m-2·s-1,最高634.4 μmol·m-2·s-1(图1-B)。由此可见,在高温伏旱期,无论何种颜色遮阳网覆盖纽荷尔脐橙的PAR 变化在晴天都是有利的,在阴天都是不利的。不过,高温伏旱期通常绝大多数是晴天,覆盖遮阳网利远大于弊。

图1 不同颜色遮阳网覆盖纽荷尔脐橙的树冠顶部光合有效辐射日变化
Fig.1 Changes of diurnal photosynthetically active radiation on tree canopy top of Newhall navel orange covered with different color shading-nets

植物在波长380~780 nm 的可见光光谱上有蓝紫光(400~500 nm)和红橙光(600~700 nm)两个吸收高峰,而对黄光(580~600 nm)、绿光(500~580 nm)吸收较少。将植物吸收光谱分为蓝紫光区(400~500 nm)、黄绿光区(500~600 nm)、红橙光区(600~700 nm)三个光区并测定其相应辐射照度。表1 结果显示,与对照相比,蓝紫光区的照度占比在蓝网中显著提高5.7%,在黄网和红网中则分别显著降低7.4%和4.8%;黄绿光区的照度占比在黄网和绿网中分别显著提高2.5%和2.4%,在蓝网中只提高0.6%,在红网中则显著降低3.4%;红橙光区的照度占比在黄网和红网中分别显著提高5.0%和8.2%,在绿网和蓝网中分别显著降低1.3%和6.3%。总体上,黑网和绿网的光质变化小,基本与外界光质一致;蓝网、黄网和红网则分别提高了相应网颜色所在光区的透射光占比。

表1 不同颜色遮阳网覆盖纽荷尔脐橙树的遮光率和光质变化
Table 1 Changes of shading rate and spectral proportion on tree canopy top of Newhall navel orange covered with different color shading-nets

注:同列数值后不同小写字母表示差异显著(p <0.05)。下同。
Note:Values in the same column with differens small letters mean significant difference(p <0.05).The same below.

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2.2 不同颜色遮阳网覆盖的脐橙叶片和果面温度比较

2020年测定结果显示,遮阳网显著降低叶面和果面温度,叶面和果面的温度日变化趋势一致,其中,覆盖遮阳网在晴天的最大降温幅度在叶面为7.4~10.0 ℃、果面为7.0~8.3 ℃,≥40 ℃高温延迟3~4 h到来。不同颜色遮阳网降温效果为黑网>黄网≈红网≈绿网≈蓝网。图2-A 和图2-B 显示,在晴天8:00—18:00 叶面和果面最高温度对照分别为49.7 ℃和47.3 ℃,黑网分别为39.8 ℃和39.0 ℃,黄网分别为41.6 ℃和39.7 ℃,红网分别为41.2 ℃和40.3 ℃,绿网分别为42.3 ℃和39.2 ℃,蓝网分别为40.8 ℃和39.1 ℃。在多云天8:00—18:00 树冠中部的南面,对照有3~4 h的叶面温度达到35 ℃以上、最高40.0 ℃,有2~3 h 果面温度达到35 ℃以上、最高39.2 ℃,而不同颜色遮阳网下的叶面和果面温度基本不超过35 ℃(图2-C,图2-D),处于光合适温中;由于覆盖遮阳网后最高温度都不超过42 ℃,各色遮阳网均可保护叶片和果实不受高温灼伤。在阴天8:00—18:00树冠中部南面,对照和处理的叶面和果面温度基本不超过30 ℃,适合柑橘叶片和果实生长发育(图2-E~F)。2021年的叶片和果面温度变化特征和2020年基本相同。

图2 2020 年不同颜色遮阳网覆盖纽荷尔脐橙的树冠中部叶面(A、C、E)和果面(B、D、F)温度日变化
Fig.2 Changes of diurnal temperature on leaf surfaces(A,C,E)and fruit surfaces(B,D,F)of Newhall navel orange covered with different color shading-nets in 2020

2.3 不同颜色遮阳网覆盖对脐橙光合作用的影响

表2显示,覆盖遮阳网后,在高温晴天11:00,各色遮阳网处理的净光合速率(Pn)大小依次为:蓝网>黑网>黄网≈红网≈绿网>对照;各处理的气孔导度值(Gs)、水分蒸腾速率(Tr)变化趋势与Pn变化趋势基本一致,其中,蓝网和黑网的PnGs显著高于对照和其他处理,分别为对照Pn的2.1~2.4倍和1.8~2.3倍,分别为对照Gs的1.8~2.0倍和1.5~1.9倍;各处理的胞间CO2浓度(Ci)都低于对照但无显著差异。在高温晴天14:00,与对照相比,各处理Pn显著提高,Ci显著降低,各处理的GsTr的变化趋势与Pn变化趋势基本一致。但由于柑橘光合作用存在“午休”现象,14:00 的光合作用受到抑制,缩小了处理之间的差异。由此可见,覆盖遮阳网提高了叶片PnGsTr,降低了Ci,所有颜色遮阳网均能显著提升高温晴天的Pn,其中蓝色提升幅度最大。

表2 不同颜色遮阳网覆盖纽荷尔脐橙在11:00 和14:00 的光合参数变化
Table 2 Photosynthesis of Newhall navel orange covered with different color shading-nets at 11:00 am and 14:00 pm on clear day

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2.4 不同颜色遮阳网覆盖对脐橙叶绿素含量和果实生长的影响

覆盖遮阳网提高了高温期间的叶片相对叶绿素含量和促进了果实的膨大(表3),各色遮阳网覆盖的叶片相对叶绿素含量均显著增加,对照则显著降低,各处理之间无显著差异。各色遮阳网覆盖均有利于高温期间果实的增大,使果实横径增长量显著高于对照,其中,蓝网和黑网覆盖的果实横径增长量又显著高于其他颜色遮阳网。

表3 不同颜色遮阳网覆盖纽荷尔脐橙的叶片相对叶绿素含量变化和果实横径增长量
Table 3 Changes in leaf relative chlorophyll content and fruit diameter increase of'Newhall'navel orange covered with different color shading-nets during high temperature season

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2.5 不同颜色遮阳网对脐橙日灼程度的影响

在高温结束后对各处理叶片、果实进行日灼率统计和程度分级(0~4 级),2020 年对照叶片日灼率为50.41%、日灼程度为1.87 级;果面日灼率为43.70%、日灼程度为1.88 级;2021 年对照叶片日灼率为72.34%、日灼程度为2.07 级;果面日灼率为69.42%、日灼程度为1.98 级;2020 年和2021 年各处理的叶片和果实均未受到日灼伤害,日灼程度和日灼率均为0,表明覆盖纬编6针各色遮阳网均可完全防止日灼的发生。

2.6 不同颜色遮阳网覆盖的脐橙品质比较

由表4可知,高温结束后,各色遮阳网处理的单果质量和可滴定酸(TA)含量、维生素C(Vc)含量均高于对照,可溶性固形物含量(TSS)均低于对照。其中,蓝网、黄网和黑网的单果质量显著高于对照;蓝网、绿网和黄网的Vc 含量显著高于对照;各色遮阳网处理的TSS和TA含量与对照无显著差异,但黑网的TSS含量最低。

表4 高温期结束后不同颜色遮阳网覆盖纽荷尔脐橙的果实品质比较
Table 4 Comparison of fruit quality of Newhall navel orange covered with different color shading-nets after the end of high temperature period

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果实成熟时,外观品质方面,各色遮阳网覆盖的单果质量、横径均高于对照,其中蓝网和黑网显著高于对照;各色网覆盖的纵径、果形指数、果皮亮度、红色度、黄色度与对照相比多数无显著差异。内在品质方面,各色网覆盖的TSS 和Vc 含量均高于对照,其中蓝网的TSS 含量显著高于对照,蓝网和绿网的Vc含量显著高于对照。各色遮阳网的TA含量均略低于对照而无显著差异(表5~表6)。

表5 2020 年成熟期不同颜色遮阳网覆盖纽荷尔脐橙的果实外观品质比较
Table 5 Comparison of external quality of Newhall navel orange covered with different color shading-nets at mature stage in 2020

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表6 2021 年成熟期不同颜色遮阳网覆盖纽荷尔脐橙的果实外观品质比较
Table 6 Comparison of external quality f Newhall navel orange covered with different color shading-nets at mature stage in 2021

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结合高温结束后和成熟期两个时间段的果实品质变化可知,蓝网和黑网果实的单果质量在两个时期均显著最高,这是蓝网和黑网的果实横径显著增加的缘故。蓝网和绿网果实的Vc 含量在两个时期均显著最高。各处理的TSS含量在拆除遮阳网后上升较快并最终高于对照,其中蓝网显著高于其他处理和对照。各色遮阳网覆盖使果实TA 含量略高于对照,但拆除遮阳网后随着果实进入成熟期而下降,最终略低于对照(表4~表6)。

3 讨 论

黑色遮阳网的编织材料不透光、不反光,网下的光照来自透过网孔的光和周边的散射光[27-28];而彩色遮阳网的编织材料有一定透光性,网下的光照除了来自透过网孔的光和周边的散射光,还有直接透过编织材料的光,以及编织材料反射的光[22,29-32],后两部分光的光质有较大比例的是材料的颜色波长。因此,与相同编织规格的黑色遮阳网相比,彩色遮阳网下的光照度略高,与网颜色对应的光质比例也升高,在此二者的共同作用下,不同颜色网下防止高温日灼的效果存在差异。不过,就温度而言,不同颜色遮阳网在高温晴天均可降低脐橙叶面果面温度7~10 ℃,使得最高温度都在40 ℃左右,低于42 ℃的柑橘高温伤害温度[33-34],可完全防止日灼的发生,并减缓相对叶绿素含量的下降;在光照度和光质变化方面则有所不同,与黑色遮阳网相比,彩色遮阳网能延长高温晴天脐橙的适宜光照度(PAR=200~600 μmol·m-2·s-1)时间[33, 35-36],每天要比黑色遮阳网多1 h;不同颜色网的光质也有较大差异,导致与网颜色对应的光质占比显著提高,从而对脐橙光合作用产生较大影响。从本研究看,蓝色遮阳网显著促进气孔开放(Gs更高),Pn高于黑色和其他颜色遮阳网,这与前人研究发现蓝光可促进叶片气孔的开放和提高Pn[37-39]应有相同的机制;通常,红光可以提高叶片表观量子效率,降低光补偿点,在光照不足时可提高叶片净光合速率[40-41],但笔者在本研究中发现,红色遮阳网Pn往往较低,这可能是试验测定Pn都在中午,光照充足,不存在光照不足的条件所致;对于绿色和黄色遮阳网Pn高于红色遮阳网这一现象,这可能是网内黄绿波段光增加不多的原因,不至于对光合作用产生明显影响,另外,Terashima 等[42]发现在中强光下绿光比红光可更有效地促进光合作用,其机制尚不太清楚。

果实产量和质量是柑橘生产最重要的指标,7—8月是柑橘果实膨大期,而此期间却是高温强日照,影响果实生长。从本研究结果看,高温期覆盖不同颜色遮阳网对果实增大作用表现出较大差异,此期的果实直径增大,对照最小,蓝色和黑色遮阳网最大,红、黄、绿色遮阳网居中,与各自在此期间的Pn大小趋势基本相同;到果实成熟时,不同颜色遮阳网处理的果实大小依然表现相同规律,只是差距缩小。果实TSS含量的变化有所不同,在高温结束后,对照和各处理果实TSS和TA含量无显著差异,但到果实成熟时,对照TSS含量最低,蓝色遮阳网最高且显著高于对照,其他颜色遮阳网居中,说明各处理在拆除遮阳网后果实TSS 含量的增加速度高于对照,主要原因可能是各处理的相对叶绿素含量在高温结束后显著高于对照,而9—12 月重庆大部分是阴雨寡照天气,更高的叶绿素含量有利于低光照下的光合作用和糖分累积。各种颜色遮阳网的果实Vc 含量一直高于对照,且以蓝色最高,高温加快Vc 降解并抑制其合成[43],这应是对照果实Vc含量较低的主要原因。

秋梢是成年柑橘树主要的结果母枝,重庆等我国大部分中亚热带柑橘产区,8 月上中旬萌发的早秋梢是良好的结果母枝,但在重庆气候条件下,因高温强日照,7—8 月很难抽发新梢,绝大多数年份是在9 月降温降雨后才萌发质量较差的中晚秋梢,促进早秋梢萌发一直是重庆柑橘生产希望解决的问题。王登亮等[21]发现在高温期覆盖遮阳网可促进秋梢的生长发育,利于翌年结果母枝的形成,笔者在本研究中也发现覆盖遮阳网可以促进早秋梢萌发,但数量很少,主要还是以中晚秋梢为主,可能与试验树树龄较大和结果较多有关。

日灼一直困扰柑橘生产,尤其是重庆高温伏旱期气温为40~42 ℃,并伴随干旱和强烈日照,柑橘叶片和果实最高温度可达55 ℃[44]。虽然目前防止柑橘日灼的方法有很多[5-14],但仍缺乏能同时兼具高效、简便、经济和操作性强的方法,生产上应用最多的还是喷布石灰水等白色防晒剂[8-9],虽然较简便且能有效防日灼,但高温过后仍黏附在叶片和果面的白色防晒剂既影响光合作用,又影响果实外观,大大增加果面清洗难度,成为一大难题,而遮阳网则完全没有这方面的缺点,重庆无台风影响,遮阳网基本不会被风吹坏,且可以重复使用2~3 a(年),具经济性和可操作性。从本试验看,无论哪种颜色的遮阳网,都能达到100%的防日灼效果,这是其他防日灼方法难以达到的[5-6,20]。在6针纬编的各种颜色遮阳网中,综合而言,蓝色最好,其次是黑色,然后是黄、红、绿色。由于6针纬编不同颜色遮阳网的遮光度存在较大差异,下一步值得研究不同颜色相同遮光度遮阳网的效果。

4 结 论

使用6针纬编各色遮阳网均可完全防止脐橙日灼,提高高温晴天叶片净光合速率,促进果实增大并改善品质。其中,蓝色遮阳网和黑色遮阳网在提高叶片净光合速率、促进果实生长方面效果显著,蓝色遮阳网还能显著提高果实TSS和Vc含量,优于黑色和其他颜色遮阳网。

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Effects of different color shading nets on preventing sunburn of Newhall navel orange during high temperature season

LAI Hengxin,LI Wenguanga,PENG Liangzhi*,HE Yizhong,LING Lili,CHUN Changpin
(Citrus Research Institute,Southwest University/CAAS/National Citrus Engineering Research Center,Chongqing 400712,China)

Abstract:【Objective】In the early autumn,high temperature and strong light often inhibit the photosynthesis of citrus leaves and fruit development, and cause sunburn on leaves and fruits in severe cases,leading to the decline of fruit yield and quality. Covering shading net above tree canopy is one of the main and effective measures to reduce the harm of high temperature and high light intensity in citrus production,which has good effects on increasing fruit production and improving quality.Color shading nets maybe a new choice for preventing citrus sunburn, and it not only has the effect of shading and cooling, but also plays a role in regulating the light quality under the net. Previous studies have shown that the light quality has a significant role in regulating plant growth, development and physiological metabolism. Therefore, in order to provide a basis for the selection of the appropriate shade net color,we studied the effects of different color shading net coverings on light intensity, light quality and temperature under the net, as well as the photosynthesis and fruit growth and quality of Newhall navel orange.MethodsIn high temperature season(Aug.)in Chongqing,weft knitting 6 stitches of color shading nets(yellow,red,green,blue)and black sunshade nets were selected for tree canopy sunshade treatments for Newhall navel orange.The diurnal changes of light quality, light intensity, leaf and fruit surface temperature, leaf photosynthesis and relative chlorophyll content in the leaves, and the increase of the fruit diameter were measured during the net covering period.The fruit growth increment and quality indexes, including peel color, contents of vitamin C (Vc), titratable acids (TA) and total soluble solids(TSS)were measured just post high temperature season and during the harvest time.【Results】Different color shading nets had different shading rates on tree canopy and the shading rate was 59.9%-75.4%.However,yellow,red,green and blue nets basically had the same shading rate,but black net had 75.4%shading rate,which was 12.2%-15.5%higher than those of color nets (59.9%-63.2%). Compared with the control(no shading net covering),the cooling effect of all color nets was basically the same,and the temperature decreased on the leaves and fruits by 7.4-10.0 ℃and 7.0-8.3 ℃,respectively.All the treatments had no sun burning damage on the leaves and fruits,and significantly increased the relative chlorophyll contents and photosynthesis. The color shading nets covering treatments, especially the blue net,yellow net,black net also incresed the fruit diameter and fruit weight in just after the high temperature season.In terms of internal quality,the color shading nets decreased the fruit TSS and increased the fruit TA,although the difference between the control and each treatment was not significant.The color shading nets increased the fruit Vc and the increase of the fruit Vc by the green and blue shading net was significant compared with the control. In harvest time, the color shading nets increased the weight of fruit and transverse diameter and the increase by the blue and black nets was significant compared with the control.There were no significant differences in the longitudinal diameter, the fruit Index, and the fruit surface color between the various color shading net treatments and the control. In terms of internal quality, the contents of TSS and Vc treated with the various color shading-net treatments were higher than those of the control, while the content of TA was lower than that of the control. The fruit TSS content treated with the blue shading net treatment was significantly higher than that of the control,and the fruit Vc content of the green and blue shading net was significantly higher than that of control.Comparing the changes of fruit quality at the end of high temperature and ripening stage,the single fruit weight and transverse diameter treated with the blue and black shading net treatments was significantly the highest in both periods.The fruit Vc content treated with the blue and green shading net treatments was significantly the highest in both periods.The fruit TSS of all the treatments increased rapidly after removing the shading nets, and finally higher than that of control, in which blue net was significantly higher than that of the other treatments and the control. The TA content of fruits treated with the color shading-nets was slightly higher than that of the control in just after high temperature season, but after removing the shading nets,it decreased as the fruits entered the mature stage,and finally it was slightly lower than that of the control.ConclusionThe covering with black, yellow, red, green or blue weft knitting 6 stitches shading nets could completely control sunburn damage,increase the net photosynthetic rate and improve fruit growth and quality of Newhall navel orange,and blue or black shading net covering increased the leaf net photosynthetic rate, promoted the fruit enlargement and increased the fruit weight significantly.Generally,the blue shading net had the best effects on improving fruit internal quality,including increasing the fruit TSS and Vc,reducing the fruit TA.Therefore,blue shading net would be suitable application for navel orange in high temperature season for controlling sunburn.

Key words:Newhall navel orange;High temperature in August;Color shading net;Sunburn control

中图分类号:S666.4

文献标志码:A

文章编号:1009-9980(2022)07-1241-11

DOI:10.13925/j.cnki.gsxb.20210329

收稿日期2021-07-15

接受日期:2022-03-03

基金项目国家重点研发计划课题[柑橘优质轻简高效栽培技术集成与示范(2020YFD1000102)];财政部和农业农村部:国家现代农业产业技术体系(CARS-26-01A)

作者简介赖恒鑫,男,在读硕士研究生,主要从事果树栽培与生理研究。Tel:13576779585,E-mail:laihengxin_jiangxi@163.com。a为共同第一作者。

*通信作者Author for correspondence.Tel:023-68349725,E-mail:pengliangzhi@cric.cn