The effects of rain shelter coverings on the vegetative growth and fruit characteristics of Chinese cherry (Prunus pseudocerasus Lindl.)

Scientia Horticulturae 254 (2019) 228–235

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The effects of rain shelter coverings on the vegetative growth and fruit characteristics of Chinese cherry (Prunus pseudocerasus Lindl.) Tian Tiana,b, Guang Qiaoa, Bin Denga, Zhuang Wena, Yi Honga, Xiaopeng Wena,b,

T

⁎

a

Key Laboratory of Plant Resource Conservation and Germplasm Innovation in Mountainous Region (Ministry of Education), Institute of Agro-bioengineering/ College of Life Science, Guizhou University, Guiyang, 550025, PR China b Institute for Forest Resources & Environment of Guizhou/ College of Forestry, Guizhou University, Guiyang, 550025, PR China

ARTICLE INFO

ABSTRACT

Keywords: Chineses cherry Rain shelter cultivation Photosynthesis Fruit quality Fruit yield

Throughout the whole process from the onset of blossoming to fruit maturity, rain and hail can cause severe losses in cherry (Prunus pseudocerasus Lindl.) yields, e.g., up to 90%, under the conventional shelter-free (control) conditions in Southwest China. Recently, rain shelters have been increasingly applied worldwide to prevent flowers and fruit from damage by excessive rainfall and hail, and the utility of rain shelters was preliminarily proven to benefit cherry production due to yield improvements, especially in Southwest China. However, the effects of rain shelter coverings on the vegetative growth, photosynthesis and fruit characteristics of cherry have not yet been fully explored. In the present study, the 5-year-old field-grown plants were covered with polyethylene (PE) film from the preflowering stage until fruit harvested for one year (1a-shelter) or two years (2ashelter) as part of trials in Guizhou Province, Southweste China. Compared with that under the control conditions, the leaf area under 1a- and 2a-shelter conditions significantly increased by 23.0% and 26.87%, respectively, at the 55 days after flowering (DAF) (DAF55); conversely, the leaf thickness clearly decreased by 17.67% and 19.7%, respectively. Similar trends in leaf area and thickness were also observed under the 2a-shelter, but no marked differences occurred between the 1a-shelter and 2a-shelter. Regardless of the covering cycle, the rain shelters somewhat promoted shoot elongation, although the differences were not statistically significant. Compared with the control, the 1a-shelter and 2a-shelter caused considerable increases in chlorophyll contents in the leaves. Interestingly, the rain shelters strongly increased the carotenoid (Cx) contents in the leaves under both the 1a- shelter and 2a-shelter, indicating an obvious improvement in the ability to use weak sunlight. Compared with those in the control, the diurnal fluctuations in the photosynthetic rate (Pn) of the leaves under both 1a- shelter and 2a-shelter characterized by a single peak; the Pn of the control exhibited a typical noonslump pattern, which accordingly led to an increase in the total daily photosynthetic accumulation within the sheltered leaves. Compared with those in the control, the mean weight and size of fruit from plants under the shelters significantly increased, and the cracking rate greatly decreased from 95% (control) to approximately 4% (1a-shelter and 2a-shelter), giving rise to an approximately fourfold increase in yield of the sheltered trees. Furthermore, the contents of the total soluble solids (TSSs), soluble sugars (SSs), ascorbic acid (AsA) and anthocyanins of the sheltered fruit differentially increased; conversely, the rain shelters reduced the titratable acid (TA) titers. Therefore, rain shelter cultivation may substantially contribute to the total photosynthetic accumulation and increased fruit yield and has no obvious negative effects on the vegetative growth or fruit quality of cherry trees in Southwest China, which may benefit the cherry industry in this region.

1. Introduction Cherry (Prunus pseudocerasus Lindl.) is widely grown in Southwest China because it ripens early, is succulent, and is rich in nutrients. The yield and synthesis of nutrients in the plants depend on environment

factors, i.e., light intensity, rainfall and temperature (Solovchenko and Schmitz-Eiberger, 2003). However, adverse weather conditions such as frequent rainfall, ‘late spring cold’ and hail from February to May are unavoidable obstacles to the cherry industry and can severely inhibit yield and quality (Xu et al., 2013; Li et al., 2014a,b).

⁎ Corresponding author at: Key Laboratory of Plant Resource Conservation and Germplasm Innovation in Mountainous Region (Ministry of Education), Institute of Agro-bioengineering/ College of Life Science, Guizhou University, Guiyang, 550025, PR China. E-mail addresses: [email protected] (T. Tian), [email protected] (X. Wen).

https://doi.org/10.1016/j.scienta.2019.04.030 Received 5 January 2019; Received in revised form 18 March 2019; Accepted 11 April 2019 Available online 06 May 2019 0304-4238/ © 2019 Elsevier B.V. All rights reserved.

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To date, increasing numbers of protected facilities have been used in the horticulture industry to promote yield and quality (Trivedi and Singh, 2015). Shelter cultivation is widely used for fruit production in Europe. During the period of maturity and at harvest, the yield loss from rainfall and hail can reach 90%, and the average yields are significantly higher under rain shelters than in conventional open cultivation (Schmitz-Eiberger and Blanke, 2012). Recent studies have shown that the minimum and maximum temperatures can be regulated by simple rain shelter cultivation, whilst the soil water content under shelters was found to be significantly lower than that under shelter-free (control) conditions (Long et al., 2018). Morphological, anatomical and physiological characteristics also change in response to limitations of the low light intensity, e.g., leaf area, palisade and spongy parenchyma thickness, and pigment contents vary in response to low light intensity (Amani et al., 2018). In Nova Gorica, coverings significantly reduced the percentage of cracked (by 13.6%) and rotten (by 4.6%) as well as fruit weight (by 19.9%) in sweet cherry orchards but did not significantly influence the contents of sugars, organic acids, polyphenols or anthocyanins (Usenik et al., 2009). Shelter cultivation is also often used in the grape and strawberry industries in China (Meng et al., 2013; Yu et al., 2015). A large amount of viticulture practices have indicated that, by keeping rainwater away from leaves and fruit, rain shelter cultivation can effectively eliminate the cracking incidence associated with major diseases as well as rip rot (Li et al., 2014a,b), even delaying leaf senescence (Du et al., 2015), thereby improving fruit quality and yield (Tangolar et al., 2007). In Germany, the new technique of covering cherry trees in the spring promotes flowering and enhances ripening, thus improving the synthesis of bioactive compounds and providing consumers with early high-quality fruit (Overbeck et al., 2017). Early apple blooming was shown to be caused by warming spring seasons in France, and shelters significantly influenced the crop growth, yield and production (El Yaacoubi et al., 2014). The improvement of tangerine fruit sweetness and pectin content was investigated via simple rain shelter cultivation (Long et al., 2018); however, the ascorbic acid (AsA) content in tomato decreased under low light intensity (Zushi et al., 2014). Diametrically, the two consecutive years of shelter conditions in Rome did not affect apple maturity, but reduced the skin color vibrancy and sugar content, generally, the fruit produced under shelters presented greater reductions than did those from control trials (Baiamonte, et al., 2016). Recently, shelter facilities were applied to sweet cherry production in northern, central and eastern China. Li et al. (2014a,b) reported that rain shelters might effectively increase yields and advance the maturity date of sweet cherry in Shandong Province (China). Additionally, the phenological periods of cherry plants grown under several rain shelter cases have been preliminarily investigated. In fact, rain shelters may attenuate the light intensity; this phenomenon presumably reduces the photosynthesis ability, consequently influencing the vegetative and reproductive characteristics of plants. Moreover, how does the vegetative growth and fruit setting characteristics changes in response to shelter covering? No reports on these issues in cherry are available, especially concerning cherry growth in Southwest China. This lack of data is a bottleneck for the cherry industry in the region. Therefore, in the present study, the vegetative and reproductive growth characteristics of cherry plants subjected to one year and two years of shelter covering were monitored. The objectives were to determine the effects of shelter covering on leaf and shoot growth, photosynthetic characteristics, fruit yield and quality, etc., which may benefit the cherry industry.

Fuquan (26°70′N; 107°51′E), which is in the middle of Guizhou Province, China. The climate of the region is characterized as subtropical monsoon, with an average temperature of 14 °C (-1˜ 33 °C), a relative humidity of 88% and an annual total precipitation of 1220 mm. The experimental trees were spaced 3.0 m between rows and 3.0 m within rows, and similarly growing trees were chosen for shelter covering, i.e., under a rain shelter for one year (1a-shelter) or two years (2a-shelter), and shelter-free (control) conditions served as the control. The shelters were covered with the colorless polyethylene (PE) film, and the shelter length, width and height of the steel frame were 30 m, 10 m, and 5 m (aboveground), respectively. The PE film with (which had a high transmission) was used from January 15 (before blossoming) to May 20 (after fruit harvest). All the trees were managed with the same practical techniques, and forty trees (20 trees were covered for one year; 20 trees, two years) were grown under PE film. Three trees per treatment were selected for inclusion in a completely randomized design at three stages: 35 days after flowering (DAF35), 45 DAF (DAF45), 55 DAF (DAF55). Forty shoots and leaves (the fifth leaf from the base of the shoots) from four directions were tagged to observe their vegetative parameters. The anatomical characteristics and photosynthetic pigment contents in the leaves adjacent to those used were investigated to determine their morphological indexes. Nine leaves from the southern canopy of three trees were tagged for measuring their photosynthetic characteristics. The leaves and shoots of three individual trees per treatment at three development stages were investigated throughout the experiment. 2.2. Observations of leaf morphological and anatomical characteristics At every stage, 40 shoots from four directions per tree were investigated for their vegetative growth characteristics, e.g., length and diameter (just below the fifth leaf). Moreover, the length and width of 40 leaves per tree were measured and then scanned (MFC8510DN, Brother, Japan); the leaf area was quantified from DAF35 to DAF55 using Adobe Photoshop (Adobe Systems, San Jose, CA). Eight well-developed leaves per tree were fixed in formalin–acetic acid–alcohol (FAA) solution (50% ethanol: 90:5:5 ratio by volume). They were subsequently dehydrated in a graded ethanol series (Zhang et al., 2016). Twenty-four sections of each treatment were selected, and six random visual fields (20) per section were chosen for observations of anatomical characteristics including the thickness, upper epidermis, palisade tissue, spongy tissue, and lower epidermis of leaves by a CX41RF Olympus microscope (Japan), and the characteristics were measured with a micrometer. 2.3. Determination of photosynthetic characteristics For each trial, a total of nine fully expanded leaves were used for photosynthetic investigation during fruit development (from DAF35 to DAF55). The photosynthetically active radiation (PAR) and diurnal courses of photosynthesis measurements were taken at hourly intervals, which started at 7:00 h and terminated at 18:00 h. The incident radiation of the leaf chamber was applied at a right angles with a portable photosynthesis system (Li-6400XT, Li-Cor, Inc., USA) to prevent shading inside the cuvette (Naidoo and Naidoo, 2018). The daily photosynthetic accumulation (relative values) was estimated through via the diurnal integral values (DIVs) of the photosynthetic rate (Pn) with coordinate axes by Origin 9.0 (Guan et al., 2015). The same expanded leaves were measured from 9:00 h to 11:30 h with Li-6400XT to construct photosynthesis light-response curves. Moreover, the apparent quantum yield (AQY) was obtained by linear regression under a PAR range of 0–200 μmol m−2·s-1 (SPSS statistics package) (Zhou et al., 2015). The light compensation point (LCP), maximum net photosynthetic rate (Amax) and dark respiration (Rd) parameters were calculated from the photosynthetic light-response curves in accordance with the Farquhar mathematical model (Prioul and Chartier, 1977).

2. Material and methods 2.1. Plant material and shelter covering The experiment was carried out using 5-year-old cherry plants (cultivar ‘Manaohong’) from 2016 to 2018 in a public orchard in 229

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2.4. Quantification of photosynthetic pigment contents

(Table 2). Additionally, the shelter covering strongly affected the anatomical characteristics of the leaves. Compared with that in the control, the leaf thickness in the 1a- shelter and 2a-shelter (DAF55) clearly decreased by 17.67% and 19.67%, respectively. The thickness of both palisade tissue and spongy tissue was highly reduced in response to the 1a- and 2a-shelter covering; for example, the palisade tissue decreased by 15.10% and 18.17%, respectively, and the spongy tissue decreased by 19.07% and 21.09%, at DAF55, indicating negative effects of the reduced PAR on leaf thickness (Table 3). In particular, the reduction in thickness of the palisade tissues was not as severe as that of the spongy tissues, which somehow attenuated the loss of chloroplasts during low PAR acclimatization.

To quantify the contents of photosynthetic pigments, 20 leaves of the tagged shoots from four directions of each canopy were sampled to minimize the errors as caused by light intensity differences. The pigments were extracted by 80% acetone, and the absorbance at 470 nm (A470), 663 nm (A663) and 646 nm (A646) of the extracts was measured via a microplate spectrophotometer (Thermo Scientific, USA). The contents of chlorophyll a (Ca), chlorophyll b (Cb), and Cx were calculated as described by Shi et al. (2013). Ca = 12.21A663 − 2.81A646

(1)

Cb = 20.13A646 − 5.03A663

(2)

Cx = (1000A470 − 3.27Ca − 104Cb) /229

(3)

3.2. Photosynthetic characteristics

The Duncan test was used to assess significant differences of all the parameters using the SPSS 21.0 statistics package (Chicago, IL, USA). The percentage values of fruit quality were subjected to arc sin transformation before ANOVA. All the presented data are the means and standard deviations (SDs) of at least three replicates. The graphs were constructed with Origin 9.0 (Origin Lab, Northampton, MA, USA).

Shelter covering might mitigate the PAR within the canopy (Fig. 1A–C); however, more than 70% of the PAR could reach the sheltered leaves. During three stages of fruit development, as shown in Fig. 1D–F, the diurnal Pn patterns were characterized as single-peak types; however, the pattern of the control displayed an obvious noonslump. The diurnal maximum Pn in the 1a- shelter and 2a-shelter was as high as 15.89 μmol m−2·s-1 and 15.98 μmol m−2·s-1, respectively, at DAF55, and the Pn of both the 1a- and 2a-sheltered leaves was even greater than that of the control leaves after 14:00 h (Fig. 1F). Moreover, Pn DIVs were used to show the daily photosynthetic accumulation of the trees; interestingly, these values in the 1a-shelter and 2a-shelter were distinctly greater than those in control during the three development stages (P < 0.05) (Fig. 2), which suggests that the shelter covering possibly results in an increased daily photosynthetic accumulation in this region. Compared with that of the control leaves, the AQY of the 2a-shelter leaves increased (Table 4) by 22.22%, 18.92% and 17.95% at DAF35, DAF45 and DAF55, respectively, suggesting the strong adaptability of sheltered leaves to low light intensity. Additionally, compared with that of the control leaves, the LCP of the 1a- and 2a-sheltered leaves (DAF55) dramatically decreased by 18.96% and 35.43%, respectively, throughout the whole fruits development period, strongly justifying that shelter covering might improve the effectiveness of low light usage. The Amax of different leaf conditions gradually increased with the progression of fruit development. The Amax of the control leaves peaked at DAF 55; however, the reduction in the leaves under the shelters was not as high as that in the control, e.g., the values decreased by only 7.44% and 15.27% in the 1a-shelter and 2a-shelter, respectively (Table 4). Additionally, the Rd in both the 1a-shelter and 2a-shelter was significantly decreased during the fruit development stages, indicating the reduced respiratory consumption of photosynthetic products. Therefore, overall, shelter coverings resulted in a tendency for improved low-intensity light use, which may be attributed to the successful adaptation to the reduced PAR.

3. Results

3.3. Photosynthetic pigment contents

3.1. Morphological characteristics and anatomical structure

The leaf photosynthetic pigments contents, including those of Ca, Cb and Cxs, under the rain shelter were significantly greater than those in the control (Table 5). The highest contents of Ca, Cb and Cxs were recored at DAF 55, and those of the 2a-sheltered leaves were 2.27 mg g−1, 0.81 mg·g−1, and 0.41 mg·g−1, respectively, which were 26.1%, 42.1% and 36.7% greater, respectively, than those of the control leaves (Table 5). Compared to the Ca content under the shelter coverings, the Cb and Cx contents were more abundant, regardless of the development stages, which reflects a stronger low-light-use ability of the sheltered trees.

2.5. Measurements of the fruit cracking rate and yield After the fruit were harvested, the total numbers of unscathed and cracking fruit were determined for each tagged tree (n = 3), and the cracking rates were calculated. The total undamaged fruit were weighed for to determine the yield. 2.6. Determination of fruit quality parameters A total of 40 mature fruits (per tree) were randomly collected from the middle part of a canopy to determine the exterior and interior quality parameters. The exterior quality indexes, which included the vertical diameter, transect diameter, weight, and edible portion (flesh) weight, were measured. The interior quality indexes were subsequently measured. The percentage of total soluble solids (TSSs) and titratable acid (TA) content were determined (Goldenberg, 2014), and the soluble sugar (SS) content was measured as described by Junfeng (2000). The AsA content was determined using an enzyme-linked immunosorbent assay (ELISA) kit (Suzhou Comin Biotechnology Co., LtD., China). Anthocyanins were extracted overnight in the dark at 4 °C by 1% HCl in methanol (v/v), and the absorbance values of the supernatant at 530 and 657 nm was measured, followed by their inclusion into the following calculation: A530 - 0.25 A657 (Jeong et al., 2010). 2.7. Statistical analysis

The morphological characteristics of the shoots, including their length and diameter, were differentially affected by shelter covering from the onset of fruit set to the full maturity. The rain shelters somewhat promoted shoot elongation and reduced the shoot diameter, but no significant differences in shoot characteristics were observed between the sheltered and control conditions (Table 1). These measurements indicated that the rain shelters did not significantly affect the vegetative growth of the shoots. Compared with those in the control, the leaf width, length and area morphological characteristics in the 1a-shelter and 2a-shelter were significantly increased; e.g., the leaf area in the 1a- shelter and 2ashelter (DAF55) increased by 22.96% and 26.87%, respectively

3.4. Fruit cracking rate and yield Shelter covering markedly reduced the fruit cracking rates (Fig. 3A). 230

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Table 1 Dynamic effects of rain shelters on shoot growth characteristics. Treatment

Shoot length/cm

2a-shelter 1a-shelter Shelter-free

Shoot diameter/cm

DAF35

DAF45

DAF55

DAF35

DAF45

DAF55

24.22 ± 5.62 23.85 ± 6.12 20.65 ± 4.02

27.65 ± 4.68 27.92 ± 4.86 24.26 ± 3.86

33.25 ± 4.81 32.97 ± 4.97 30.80 ± 3.97

0.49 ± 0.09 0.48 ± 0.10 0.50 ± 0.08

0.57 ± 0.09 0.56 ± 0.12 0.60 ± 0.08

0.69 ± 0.09 0.69 ± 0.10 0.70 ± 0.06

The values represent the means ± SDs of 3 trees (40 shoots·tree−1). The means followed by different letters in the same columns are significantly different at P < 0.05. Table 2 Dynamic effects of rain shelters on leaf characteristics. Leaf area/cm2

　

Leaf width/cm

Leaf length/cm

Treatment

DAF35

DAF45

DAF55

DAF35

DAF45

DAF55

DAF35

DAF45

DAF55

2a-shelter 1a-shelter Shelter-free

9.41 ± 0.28a 8.84 ± 0.78a 7.65 ± 0.44b

9.51 ± 0.16a 9.36 ± 0.46a 8.21 ± 0.19b

9.67 ± 0.16a 9.65 ± 0.20a 8.59 ± 0.48b

19.69 ± 0.53a 19.56 ± 0.39a 16.41 ± 1.05b

20.46 ± 0.46a 20.03 ± 0.42a 16.95 ± 0.71b

21.58 ± 0.17a 21.37 ± 0.69a 17.96 ± 0.42b

131.18 ± 4.47a 125.15 ± 3.24a 90.47 ± 2.13b

146.60 ± 10.23a 134.86 ± 3.79a 106.81 ± 4.89b

173.48 ± 9.04a 167.94 ± 4.05a 136.68 ± 8.52b

The values represent the means ± SDs of 3 trees (40 leaves·tree−1). The means followed by different letters in same columns are significantly different at P < 0.05. Table 3 Microscopic structural characteristics of mature leaves under sheltered conditions. Treatment

Leaf thickness/μm

Upper epidermis/μm

Palisade tissue/μm

Spongy tissue/μm

Lower epidermis/μm

2a-shelter 1a-shelter Shelter-free

212.88 ± 6.62b 218.17 ± 8.45b 265.00 ± 15.80a

21.86 ± 4.26b 22.03 ± 2.86b 32.95 ± 9.24a

85.62 ± 5.74b 88.83 ± 6.15b 104.63 ± 7.41a

85.67 ± 5.16b 87.86 ± 4.37b 108.56 ± 7.54a

12.27 ± 2.04b 12.45 ± 2.42b 18.92 ± 3.26a

The values represent the means ± SDs of 3 trees (8 leaves·tree−1). The means followed by different letters in the same columns are significantly different at P < 0.05.

Fig. 1. The fluctuations in PAR (A–C) and daily leaf Pn (D–F) during different fruit development stages of cherry.

For example, the rates under the 1a-shelter and 2a-shelter were 2.6% and 2.3%, respectively; however, the rate in the control was as high as 53% in 2017, and 92% in 2018. Further, the rain-shelters substantially improved the fruit yield. For example, the average yields per tree under the 1a-shelter and 2a-shelter were as high as 9.7 kg and 12.9 kg,

respectively; however, the yield in the control was just 3.5 kg (Fig. 3B). The shelters might also differentially affect the fruit sizes (Table 6), and the fruit diameters and fruit weight were significantly greater than those of the control. The greatest fruit weight (6.45 g) was recorded under the 2a-shelter, the value was 19.44% greater than greatest value 231

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232

0.69 ± 0.02b 0.87 ± 0.02a 0.88 ± 0.06a 1.08 ± 0.04 0.97 ± 0.07 1.12 ± 0.08 1.20 ± 0.04c 1.51 ± 0.05b 1.87 ± 0.02a 21.53 ± 0.58b 23.52 ± 0.45a 25.41 ± 0.63a 21.00 ± 0.49b 20.48 ± 0.37b 22.67 ± 0.52a 16.29 ± 0.35 17.33 ± 0.43 16.54 ± 0.42 12.43 ± 0.38c 15.60 ± 0.46b 19.25 ± 0.71a 14.32 ± 0.41c 16.26 ± 0.46b 26.99 ± 0.58a 15.88 ± 0.34c 26.03 ± 0.48b 39.07 ± 0.62a 0.046 ± 0.001a 0.042 ± 0.001b 0.039 ± 0.001c

The values represent the means ± SDs of 3 trees (3 leaves·tree−1). The means followed by different letters in the same columns are significantly different at P < 0.05.

DAF45

0.044 ± 0.000a 0.041 ± 0.002b 0 .037 ± 0.001c

DAF45 DAF35 DAF35 DAF35

DAF55

LCP/ (μmol·m−2·s-1)

The photosynthetic characteristics of plants may be regulated by environmental factors, of which PAR provides the necessary energy not only for leaf growth and development but also for fruit yield and quality improvement (Zoran, et al., 2012). Shelter covering unavoidably mitigates the PAR of the canopy (Guo et al., 2006), thus presumably leading to a reduction in photosynthetic ability. However, available evidence has proven that plants can successfully adapt to low-PAR conditions under rain shelters, which can improve cumulative photosynthesis (Kaiser et al., 2015), accordingly, somewhat attenuated the negative effects of shelters on photosynthesis (Jiang et al., 2016). In the present study, the PAR of the sheltered cherry canopy under the shelter was weakened by approximately 30% (Fig. 1A–C), while compared with that in the control, the leaf areas of the trees under the sheltered increased (Table 2), which might, as a compensatory effect, improve the use of the reduced PAR. Additionally, although the rain shelter reduced the effective radiation, the shelter may attenuate the damage to leaves caused by UV-B at noon, thus protecting photosystem II (PSII) from high radiation damage (Berli et al., 2011) and delaying the senescence of the green leaves (Li et al., 2014a,b). Furthermore, the quantification of several photosynthetic parameters, i.e., increased AQY and decreased LCP and Rd, demonstrated a superior tendency for increased Pn in response to the shelter conditions (Table 4), which may be due to the

AQY

4.1. Effects of shelter covering on the photosynthetic ability of cherry

Treatment

Table 4 Responses of photosynthesis to different conditions in leaves during three stages.

4. Discussion

DAF45

DAF55

Shelter covering strongly affected the interior quality of the fruit. Compared with those of the control fruit, the TSS, SS, AsA and anthocyanin contents of the sheltered fruit were much greater, conversely, the TA was somewhat lower (Table 7). The greatest average values of TSSs and SSs in the 2a-sheltered fruit were 16.1% and 10.2%, respectively, and no significant differences were observed between the 1aand 2a-shelter covering conditions (Table 7). Compared with the control, covering resulted in greater AsA and anthocyanin contents, and the greatest values (increases of 15.8% and 20.1%, respectively) occurred under the 2a-shelter.

0.044 ± 0.001a 0.045 ± 0.001a 0.036 ± 0.001b

3.5. Fruit interior quality

2a-shelter 1a-shelter Shelter-free

Amax / (μmol·m−2·s-1)

in the control (5.40 g). Interestingly, the flesh weights of fruit from the sheltered trees were also significantly higher than those from the control trees (Table 6).

DAF35

Fig. 2. The diurnal integral Pn values during different fruit development stages trees. The values marked with different letters are significant at P < 0.05.

DAF45

DAF55

Rd/ (μmol·m−2·s-1)

DAF55

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Table 5 The leaf contents of Ca, Cb and Cxs of cherry under sheltered conditions. Treatment

2a-shelter 1a-shelter Shelter-free

Chlorophyll a/(mg·g−1)

Chlorophyll b/(mg·g−1)

Carotenoid/(mg·g−1)

DAF35

DAF45

DAF55

DAF35

DAF45

DAF55

DAF35

DAF45

DAF55

1.78 ± 0.02a 1.76 ± 0.02b 1.60 ± 0.02c

2.00 ± 0.02a 1.90 ± 0.01b 1.71 ± 0.02c

2.25 ± 0.02a 2.06 ± 0.02b 1.80 ± 0.02c

0.60 ± 0.02a 0.59 ± 0.02a 0.51 ± 0.05b

0.68 ± 0.02a 0.63 ± 0.02b 0.55 ± 0.05c

0.81 ± 0.03a 0.75 ± 0.02b 0.57 ± 0.04c

0.33 ± 0.01a 0.30 ± 0.01b 0.24 ± 0.02c

0.39 ± 0.01a 0.35 ± 0.02b 0.28 ± 0.02c

0.41 ± 0.03a 0.39 ± 0.01a 0.30 ± 0.02b

The values represent the means ± SDs of 3 trees (20 20 leaves·tree−1).The means followed by different letters in the same columns are significantly different at P < 0.05.

Fig. 3. Fruit cracking rates and yields of cherry under sheltered and control conditions. The vertical bars represent standard of the means (n = 3). The values marked with different letters are significant at P < 0.05.

neither a significantly negative impact on photosynthetic ability, nor an accumulation of photosynthetic products, which was attributed to the comprehensive adjustment mechanism in response to the relatively weaker light intensity.

Table 6 Fruit exterior indicators and yield of cherry. Treatment

Fruit vertical diameter/cm

Fruit transect diameter/cm

Fruit weight/g

Flesh weight/g

2a-shelter 1a-shelter Shelter-free

2.68 ± 0.10a 2.62 ± 0.20a 2.25 ± 0.11b

2.42 ± 0.11a 2.36 ± 0.06a 2.18 ± 0.10b

6.75 ± 0.54a 6.56 ± 0.36a 5.69 ± 0.34b

6.45 ± 0.12a 6.06 ± 0.20b 5.40 ± 0.18c

4.2. Effects of shelter covering on the fruit yield and quality of cherry Many factors, including environmental alternations and cultivar characteristics, can cause fruit dropping and cracking (Simon, 2006), and it is difficult to recommend the corresponding defensive measures (Khadivi-Khub, 2015). Shelter covering can markedly increase the rate of fruit set (Usenik et al., 2009), strongly reduce the fruit cracking rate and increase fruit yields (Khadivi-Khub, 2015). Our findings showed that rain shelters markedly reduced the fruit cracking rates (Fig. 3A); the same results have also been reported in sweet cherry (Usenik et al., 2009), grape (Tangolar et al., 2007; Li et al., 2014a,b), and strawberry (Yu et al., 2015). Rain shelters have been proven to be a preferable means to ensure regular yields of cherry by protecting the fruit against adverse weather factors (Overbeck et al., 2017), thereby significantly improving fruit appearance and quality (Polat et al., 2005; Kim et al., 2011). Detoni et al (2007) reported that the TSSs of grapes increased under coverings, but other studies indicated that the TSSs varied depending on the fruit cultivar (Novello and Palma, 2008；Meng et al., 2013). Overbeck et al. (2017) reported that the TSS, SS and AsA contents in sweet cherry increased under shelters but that the TA content was little

The values represent the means ± SDs of 3 trees (40 fruits·tree−1). The means followed by different letters in the same columns are significantly different at P < 0.05.

adaptation to low PAR. Previously, the appropriate sheltered conditions were shown to result in daily photosynthetic accumulation that was greater than that under control conditions in black pepper (Zu et al., 2016) and tomato (Jiang et al., 2017). Currently, the diurnal patterns of the Pn of the sheltered cherry trees were single-peak type ones, in contrast to an obvious noon-slump pattern of the control trees (Fig. 2), suggesting that the former could probably mitigate the excessive PAR at noon and somewhat compensate for the reduction in photosynthesis (Júnior et al., 2011). In actually, the accumulation of diurnal photosynthesis, which reflected the daily photosynthetic accumulation of the 1a- shelter and 2a-shelter, was greater under the shelters than in the control during flowering and fruit development (Fig. 2). Therefore, covering cherry trees with rain shelters from the onset of fruit set to maturity resulted in Table 7 Fruit interior quality indicators of cherry. Treatment

TSSs/%

SSs/%

TA/%

AsA (mg/100 g)

Anthocyanins (mg/100 g)

2a-shelter 1a-shelter Shelter-free

12.61 ± 0.75a 12.40 ± 0.65a 10.86 ± 0.80b

10.59 ± 0.04a 10.52 ± 0.07a 9.61 ± 0.10b

0.45 ± 0.11 0.50 ± 0.07 0.64 ± 0.09

9.69 ± 0.80a 8.21 ± 0.64b 6.72 ± 0.74c

8.95 ± 0.38a 8.52 ± 0.42a 7.45 ± 0.31b

The values represent the means ± SDs of 3 trees (40 fruits·tree−1). The means followed by different letters in the same columns are significantly different at P < 0.05. 233

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affected. In the present study, the SS content of cherry under shelter was greater than in the control (Table 7) in the rainy areas of Southwest China (Guizhou Province). It was speculated that shelter covering the cherry trees with shelters did not clearly give negatively affect the accumulation of photosynthesis, and rain shelters might prevent leaves from coming into contacting with frequent rainwater and reduce the water content of the soil when there is an abundant of rainwater during the fruit development stage (Long, et al., 2018). Most related studies have suggested that the anthocyanin content in fruit under the shelter decreases because of the weakened light intensity (Downey et al., 2010; Koyama et al., 2012); however, the opposite result was obtained in the present work (Table 7), which was probably attributable to the increase in canopy temperature (available upon query), because the accumulation of anthocyanins in fruit depends on the increase in temperature enhancement under the shelter (Wang, 2006). Overall, shelter covering did not significantly inhibit the photosynthesis of cherry and substantially increased the diurnal photosynthetic accumulation, thereby leading to no obviously negative effects on the vegetative growth. Additionally, the fruit cracking rate sharply decreased; thus, the yield markedly increased in response to cover provided by rain-shelters. Further, all the data were analyzed by Pearson’s correlation coefficients, which revealed that the SSs and anthocyanins in the fruit considerably increased under shelter covering, which was presumably attributed to the increase in diurnal photosynthetic accumulation. Therefore, the use of rain shelters was an effective technique for cherry cultivation in the rainy regions of Southwest China, such as Guizhou Province.

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