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N Ratio of Subtending Leaf of Cotton Boll and Its Relationship with Cotton Boll Dry Matter Accumulation and Distribution
ACTA AGRONOMICA SINICA Volume 34, Issue 2, February 2008 Online English edition of the Chinese language journal Cite this article as: Acta Agron Sin, 2008, 34(2): 254–260.
RESEARCH PAPER
Changes in C/N Ratio of Subtending Leaf of Cotton Boll and Its Relationship with Cotton Boll Dry Matter Accumulation and Distribution HU Hong-Biao, ZHANG Wen-Jing, CHEN Bing-Lin, WANG You-Hua, SHU Hong-Mei**, and ZHOU Zhi-Guo* Key Laboratory of Crop Growth Regulation, Ministry of Agriculture, Nanjing Agricultural University, Nanjing 210095, China
Abstract: Fourteen cotton (Gossypium hirsutum L.) cultivars differing in yield were used to study the C/N ratio in the subtending leaf of cotton boll and its effect on boll dry matter accumulation and distribution. The 14 cultivars were clustered into 3 groups according to different changing patterns of C/N ratio in the subtending leaf of cotton boll. There were significant differences in dynamic changes of the C/N ratio and dry weight per boll among the 3 groups. Group III show much higher C/N ratio than Groups I and II from 10 to 17 d of boll age, and it maintained the C/N ratio of approximately 2.5 after 24 d of boll age. Group III also showed the widest changing range and the highest average values during the whole boll development. The boll dry matter accumulation of Group III took the longest time period and the lowest accumulating rate, which resulted in the highest final dry weight per boll and boll weight. The distributions of dry matter in cotton boll (percentages of boll-shell, seed, and lint) were not significantly different among the 3 groups. The C/N ratio in the subtending leaf of boll had no correlation to lint percentage and lint yield. The results indicated that the dynamics of the C/N ratio in the subtending leaf of cotton boll are significantly different among genotypes. A favorable pattern for dry matter accumulation in cotton boll is the sharp decrease in C/N ratio from 10 to 17 d of boll age, which is maintained at a relatively higher level after 24 d of boll age. Keywords:
subtending leaf of cotton boll; C/N ratio; dry matter accumulation and distribution
The source–sink relationship is crucial in crop production. The growth rate of sink tissues and organs is limited by photosynthate supplies from source leaves (source limitation). The sink in cotton (Gossypium hirsutum L.) changes with the plant developing status because cotton is a continuous growth plant. Cotton bolls are always the strongest sink with key stage of boll-forming. In this stage, carbohydrate of cotton boll is mainly supplied from the subtending leaf of the cotton boll, the subtending leaf of the adjacent fruiting position, and the corresponding main-stem leaf. The subtending leaf is the main source of the dry matter of cotton boll by translocating 85.6% of the photosynthate [1]. Carbon metabolism and nitrogen metabolism are the 2 basic metabolism processes in crop development. They directly affect the formation and transformation of the photosynthetic product, mineral nutrition absorption, and
protein synthesis [2]. The ratio of carbon and nitrogen affect source-to-sink ratio and crop yield [3–5]. In cotton, previous studies on carbon and nitrogen metabolism is to understand the differences of transgenic Bt cotton and conventional cotton [6–12]. Very few experiments, however, were conducted to disclose the changes of the C/N ratio in the subtending leaf of cotton boll in the boll-forming stage, and its relationship with boll dry matter accumulation and distribution. The contents of soluble sugar and total free amino acids in leaves are regarded as important indicators of carbon and nitrogen metabolism, respectively, and their ratio (C/N ratio) reflects the accordant status of carbon and nitrogen metabolism [5]. In this article, we took these indices to investigate the relationship between C/N ratio and dry matter accumulation and distribution in bolls as well as the
Received: 28 March 2007; Accepted: 17 August 2007. * Corresponding author. E-mail: [email protected] ** Author for English translation. Copyright © 2008, Crop Science Society of China and Institute of Crop Sciences, Chinese Academy of Agricultural Sciences. Published by Elsevier BV. All rights reserved. Chinese edition available online at http://www.chinacrops.org/zwxb/
HU Hong-Biao et al. / Acta Agronomica Sinica, 2008, 34(2): 254–260
yield responses to the changes of the C/N ratio in the subtending leaf of cotton boll.
1 1.1
Materials and methods Experimental design
Field experiments were conducted with 14 cotton cultivars (Sumian 15, Sumian 17, Sumian 19, Sumian 22, Zhongmiansuo 29, Zhongmiansuo 35, Zhongmiansuo 38, Zhongmiansuo 39, Zhongmiansuo 41, Lumian 15, Lumian 18, Kemian 1, Dexiamian 1, and AC-33B) in Jiangsu Academy of Agricultural Sciences, Nanjing, China (118º50’ E, 32º02’ N) in 2004. The experimental soil was yellow-brown loam. In 0–20 cm soil layer, it contained 2.5% organic matter, 12.0 g kg−1 total N, 85.1 mg kg−1 available N, 13.0 mg kg−1 available P, and 91.6 mg kg−1 available K (pH 7.5). All cultivars were planted in a nursery on April 15, 2004 and transplanted to the field on May 10. Field experiment was arranged in random design with 3 replicates in each treatment. The plot was 4 m wide and 15 m long. Field managements followed the high-yielding cultivation techniques in cotton production. 1.2
Sample collection and measurements
Flowers were labeled at the anthesis day (the day when the cotton flower opens). From the 10 d of boll age till boll opening, the bolls and its subtending leaves were collected from the 1st and 2nd fruiting positions of 6–10 sympodial branches every 7 d at 9:00–10:00 am. The middle part of the sampled subtending leaves were scissored and rapidly put into liquid nitrogen for measurements. Cotton fibers and seeds were excised from the bolls and dried at 80ºC. Dry weight per boll was comprised of dry weights of boll shell, seed, and fiber dry matter. Boll weight was the total of seed and fiber dry matter weights per boll. Boll-shell percentage, seed percentage, and fiber percentage are the proportions of the corresponding dry weights to boll dry matter, respectively. The soluble sugar content was determined by anthrone assay [13]. The total free amino acid content was determined by ninhydrin assay, and the absorbance readings were converted to microgram amino acid g−1 fresh weight using a glycine standard curve. The C/N ratio in the subtending leaf of cotton boll was the ratio of the soluble sugar content and the total free amino acid content. Data analysis
All data were statistically analyzed with the software SPSS and Microsoft Excel. Cluster analysis was conducted according to squared Euclidean distance and between-groups linkage. The following Logistic regression model
1+ae
bt
was used to describe dry matter accumulation [14, 15], where W is dry weight per boll, t is boll age, Wm is the maximum dry weight per boll, and a and b are parameters. Two variables, t1 and t2, were designated as the starting and termination time of cellulose rapid accumulation period with the following equations: t1 =
1 b
ln
2+
3
a
t2 =
,
1 b
ln
2−
3
a
The average rate of boll dry matter accumulation during the speedy accumulation period (VT) was expressed as VT =
W 2 − W1 t 2 − t1
where W1 and W2 are the dry weights per boll at t1 and t2, respectively.
2
Results
2.1 Cluster analysis on C/N ratio in the subtending leaf of cotton boll The dynamic changes of the C/N ratio in the subtending leaf of cotton boll were simulated with the quadratic of 2
y=at +bt +c, where y stands for the C/N ratio and t stands for the boll age (Table 1). Correlation analysis indicated that a, b, c, and the maximum C/N ratio were significantly correlated with dry weight per boll and boll weight but not with lint percentage and boll-shell percentage (Table 2).
Table 1
Equation of dynamic changes in C/N ratio in the subtending leaf of cotton boll with boll age
Cultivar Sumian 15 Sumian 17 Sumian 19 Sumian 22 Zhongmiansuo 29 Zhongmiansuo 35 Zhongmiansuo 38 Zhongmiansuo 39
1.3
Wm
W =
Zhongmiansuo 41 Lumian 15 Lumian 18 Kemian 1 Dexiamian 1 AC-33B *
Equation
P
R2
2
0.023
0.920*
2
0.011
0.951*
2
0.000
0.998**
2
0.014
0.942*
2
0.015
0.940*
2
0.006
0.965**
2
0.013
0.944*
2
0.022
0.921*
2
0.041
0.882*
2
0.024
0.916*
2
0.018
0.931*
2
0.014
0.943*
2
0.037
0.963*
2
0.026
0.912*
y = 0.0011t − 0.0767t + 2.5120 y = 0.0025t − 0.1895t + 5.1369 y = 0.0023t − 0.1686t + 5.1515 y = 0.0032t − 0.2438t + 6.4687 y = 0.0013t − 0.0942t + 3.6454 y = 0.0054t − 0.3984t + 9.4091 y = 0.0083t − 0.5543t + 10.6627 y = 0.0027t − 0.1826t + 5.2937 y = 0.0004t − 0.0302t + 2.2103 y = 0.0014t − 0.0929t + 3.3754 y = 0.0018t − 0.1269t + 3.5720 y = 0.0044t − 0.3045t + 7.4775 y = 0.0010t − 0.0916t + 4.7978 y = 0.0013t − 0.0953t + 3.9452
Significant at P < 0.05. ** Significant at P < 0.01.
HU Hong-Biao et al. / Acta Agronomica Sinica, 2008, 34(2): 254–260
Table 2 Correlation coefficients between parameters of C/N ratio dynamic changes and single boll dry matter weight, boll weight, lint percentage, and boll-shell percentage Parameter
Dry matter
Boll
Lint
Boll-shell
weight per boll
weight
percentage
percentage
A
0.691**
0.674**
0.060
0.532
b
−0.706**
−0.700**
−0.072
−0.538*
c
0.728**
0.722**
0.011
0.516
Max.
0.729**
0.721**
−0.003
0.481
Min.
0.308
0.202
−0.367
0.007
AV
0.560*
0.520
−0.261
0.258
n = 14, r0.05 = 0.533, r0.01 = 0.661. * Significant at P < 0.05. ** Significant at P < 0.01. a, b, and c are the parameters in equation of C/N ratio dynamic changes along with boll age in the leaf subtending cotton boll. Max., Min., and AV are the maximum, minimum, and the average values of the C/N ratio, respectively.
According to these results, we selected a, b, c, and the maximum C/N ratio as the variables for clustering analysis. The 14 cotton cultivars were clustered into 3 groups including 6, 6, and 2 cultivars, respectively (Fig. 1). 2.2
C/N ratio in the subtending leaf of cotton boll
As shown in Fig. 2, the C/N ratio showed a decreasing trend with boll age in all groups. Cultivars in the same group had a similar trend, which was quite different among groups. The change of C/N ratio in Group I was rather gently during
the whole boll development with an average of 1.94 but that in Group III had the largest changes. The onset value of Group III was up to 6.0 (10 d of boll age), which was much higher than that of Groups I and II. It declined sharply but still it was significantly higher than that of Groups I and II. From the 24 d of boll age, there were no significant differences among the 3 groups. 2.3
Boll dry matter accumulation and distribution
The response of dry matter weight of single boll (the value of each group was calculated with the average of all cultivars involved in the group) to boll age presented a “slow–quick–slow” changing pattern in all 3 groups. The dynamic changes were described with Logistic equations shown in Table 3. In different parts of cotton boll (boll shell, seed, and fiber), no significant differences were detected in the dry matter distribution among groups during the whole period of boll development (Fig. 3). As shown in Table 3, boll dry matter accumulation differed significantly among groups and the differences reflected the duration for boll dry matter speedy accumulation. In Group I, the duration of speedy accumulation was the shortest resulting in the lowest boll dry weight ultimately although the average of the accumulation rate was the highest. However, in Group III, the longest duration of speedy accumulation led to the highest final cotton boll dry weight.
Sumian 17 Sumian 19 Zhongmiansuo 39 Dexiamian 1 Sumian 22 Kemian 1 Sumian 15 Zhongmiansuo 41 Zhongmiansuo 29 Lumian 15 Lumian 18 AC-33B Zhongmiansuo 35 Zhongmiansuo 38
Fig. 1
Dendrogram based on dynamic changes in C/N ratio in the subtending leaf of cotton boll
HU Hong-Biao et al. / Acta Agronomica Sinica, 2008, 34(2): 254–260
5.5 C/N ratio
4.5 3.5 2.5 1.5 0.5
A
6.5
Group I
5.5
B
5
4.5
5
3.5
5
2.5
5
1.5
5
0.5 10 17 10 17
Group III
Group II
5
7 6
C/N ratio
6.5
5 4 3 2 1 0
5 24 31 38 45 24 31 38
10 45 10
17 45 17 2424 31 3138 38 Boll age (d)
S um ian 15 Zhongm iansuo 29 Zhongm iansuo 41 Lum m ian 15 Lum ian 18 AC -33B
45 10
17
24
38
45
10 17
24 31 38 45 Boll age (d) Group I Group II Group III
Zhongmiansuo 35
S um ian 17 S um ian 19 S um ian 22 Zhongm iansuo 39 Kem ian 1 Dexiam ian 1
Fig. 2
31
Zhongmiansuo 38
Dynamic changes of C/N ratio in the subtending leaf of cotton boll
Panel A shows the dynamic changes of C/N ratio in the boll subtending leaf for each cultivar; Panel B shows dynamic changes of C/N ratio in the boll subtending leaf for each cluster.
Table 3 Equations of dynamic change in cotton boll dry matter weight with boll age and its eigen values Group
Equation
t1 (d)
t2 (d)
T (d)
VT (g d-1)
Wo (g)
I
W = 6.38486 / (1 + 26.71382 e−0.16266t)
0.9980**
12.10 aA
28.29 bB
16.19 cC
0.23 aA
6.35 cC
II
W = 6.83374 / (1 + 16.51484 e−0.14440t)
0.9865**
10.30 bB
28.54 bB
18.24 bB
0.22 bB
6.75 bB
0.9949**
8.73 cC
30.05 aA
21.32 aA
0.20 cC
7.26 aA
−0.12355t
III **
R2
W = 7.44723 / (1 + 10.97259 e
)
Determination coefficient significant at 0.01 probability level (n = 7, R20.01 = 0.7653).
Values followed by the same capital or lowercase letter within columns are not significantly different at 0.01 or 0.05 probability level, respectively. t1: start date of the speedy accumulation period of boll dry matter; t2: termination day of the speedy accumulation period of boll dry matter; T: duration for cotton boll dry matter speedy accumulation, T = t2−t1; VT: average rate of cotton boll dry matter accumulation during the speedy accumulation period; Wo: final dry weight of cotton boll.
Boll shell ratio (%)
Boll shell ratio (%)
60 50 40
30 Boll shell ratio (%)
50
70
40
30
30
25 20 15 10
20
20 10
17
24
31
38
45 BO
Boll age (d) Group I Group II Group III
Fig. 3
5 10
17
24
31
38
45
BO
10
Boll age (d) Group I Group II Group III
Dynamic changes of distribution ratios in cotton boll dry matter BO: date of boll opening.
17
24
31
38
Boll age (d) Group I Group II Group III
45 BO
HU Hong-Biao et al. / Acta Agronomica Sinica, 2008, 34(2): 254–260
2.4 Relationship between changes of C/N ratio in the subtending leaf of cotton boll and boll dry matter accumulation and distribution
middle of Group I and Group III (Fig. 4 and Table 3). 2.5 Relationship between C/N ratio in the subtending leaf of cotton boll and cotton yield and the yield traits
In Group I, the C/N ratio of the subtending leaf of cotton boll maintained was approximately 2.0 during the whole boll development, and the boll dry matter accumulation was the lowest in the 3 groups with highest accumulation rate and the duration of boll dry matter accumulation was the shortest. In Group III, the C/N ratio was rather high at beginning but declined sharply in the following 14 d and accorded with the levels of Groups I and II ultimately. The duration of boll dry matter accumulation in Group III was of lowest rate, resulting in the highest final dry weight per boll and boll weight. In Group II, the above indices were in the
The yields were significantly different among the 14 cultivars (Table 4). With respect to lint yield and lint percentage, Group II was significantly higher than Groups I and III, which were equivalent in lint yield with no significant difference (Fig. 5). With regard to cotton boll weight, it showed that Group III > Group II > Group I with significant differences. This was in agreement with the group ranks on dry weight per boll among groups. The C/N ratio in the subtending leaf of cotton boll was not correlated with the final lint percentage and lint yield.
70
8
60 6
50 40
4
30 20
2
10 0
0 10
17
24
31
38
45
BO
10
17
24
31
38
45
BO
10
17
24
31
38
45
BO
Boll age (d) Boll shell ratio
Seed ratio
Fiber ratio C/N ratio in cotton boll subtending leaf
Dry matter weigth per boll
Fig. 4
Relationship between C/N dynamic changes in the subtending leaf of cotton boll and boll dry matter accumulation and distribution
Table 4 Source of variance
Degree of freedom
Blocks
Variance analysis of cotton yield
Sum of squares
Mean squares
2
11442.43
5721.22
Cultivars
13
1357344.44
104411.11
Errors
26
70355.48
2705.98
3.37
5.53
38.59**
2.12
2.91
1000 900 800
5.5 5.3 5.1 4.9 4.7
II Group
III
39 38 37 36 35
4.5 I
F0.01
40 Lint percentage (%)
Boll weight (g)
Lint yield (kg ha−1)
F0.05
2.11
5.7
1100
Fig. 5
F-value
I
II Group
III
I
II
III
Group
Relationship between changes of C/N in the subtending leaf of cotton boll and lint yield, boll weight and lint percentage
HU Hong-Biao et al. / Acta Agronomica Sinica, 2008, 34(2): 254–260
3
Discussion
In this study, 14 cotton cultivars were clustered into 3 groups on the basis of the C/N ratio in the subtending leaf of cotton boll indicating the probable difference by genotypes on this index. In the regressive equation between the C/N ratio in the subtending leaf of boll and the boll age, parameters of a, b, c, and the maximum C/N ratio were significantly correlated with dry weight per boll and boll weight but not with lint percentage and boll-shell percentage (Table 2). This indicated that the C/N ratio in the subtending leaf of cotton boll show significant effect on the dry matter accumulation but not on the dry matter distribution. We also found that the average rate of cotton boll dry matter accumulation was not crucial for the final cotton boll dry weight. In fact, it was determined by the duration for cotton boll dry matter speedy accumulation (Table 3 and Fig. 4). The duration was determined by the sink size and the supply capacity of photosynthate from source leaves (the subtending leaf of cotton boll). Nakamura et al. [16] reported that high yield was determined not only by photosynthesis capability but also by the capacity of translocation of photosynthesis products represented by the ratio of carbon and nitrogen in the subtending leaf of cotton boll. Gao et al. [17] and Zhao et al. [18] revealed that the flag leaf maintained a high capacity for carbon metabolism and photosynthate supply in large-spike wheat (Triticum aestivum L.) at middle-to-late filling stage. This implied that the proper ratio of carbon and nitrogen in functional leaf can promote dry matter accumulation in late developmental stages. At the onset (from 10 to 24 d of boll age), cotton boll needs much carbohydrate. In Group I cultivars, the C/N ratio in the subtending leaf of cotton boll of Group I was only about 2.0 in this time period, which cannot meet the requirement of boll development. In addition, the C/N ratio was reduced to less than 2.0 after 24 d of boll age. Accordingly, the dry matter accumulation, dry weight per boll, and boll weight were restricted by the low activity of carbon metabolism. In Group III cultivars, the C/N ratio was approximately 5.0 d from 10 to 17 d of boll age, which was favorable for carbohydrate supply in speedy accumulation period in the boll. After 24 d of boll age, the C/N ratio declined to approximately 2.5, implying relatively strong activities of carbon and nitrogen metabolism. This is the fundamental for high boll weight formation. According to these results, fertilizers in blossoming and boll-forming stages can be reduced in cotton production for controlling the metabolic activity of nitrogen from 10 to 17 d of boll age and increasing the dry weight per boll and boll weight. The dry matter distributions (boll shell percentage, seed percentage, and fiber percentage) were not significantly different among the 3 groups in this study, which indicates no correlation between cotton lint percent and C/N ratio in
the subtending leaf of cotton boll. Dry matter distribution is a process of re-allocating dry matter in the boll, which is not directly correlated with physiological characteristics of the subtending leaf of cotton boll. It is probably determined by the physiological characteristics of cotton boll differing from genotypes. The C/N ratio in the subtending leaf of boll was significantly correlated with dry weight per boll and boll weight but not with lint yield. The lint weight is mostly correlated with the number of mature bolls per plant under the same planting density, which is not associated with the C/N ratio in the subtending leaf of boll.
4
Conclusions
The dynamic characters of the C/N ratio in the subtending leaf of cotton boll are significantly different among genotypes, and the C/N ratio declined dramatically from 10 to 17 d of boll age and maintained at a relative higher level after 24 d of boll age, which is favorable for cotton boll dry matter accumulation.
Acknowledgments This study was funded by the National Natural Science Foundation of China (30571095 and 30600378), the Jiangsu Provincial Natural Science Foundation (BK 2006141), and the Special Research Funds for Doctoral Program of Higher Education (20050307028).
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RESEARCH PAPER
Changes in C/N Ratio of Subtending Leaf of Cotton Boll and Its Relationship with Cotton Boll Dry Matter Accumulation and Distribution HU Hong-Biao, ZHANG Wen-Jing, CHEN Bing-Lin, WANG You-Hua, SHU Hong-Mei**, and ZHOU Zhi-Guo* Key Laboratory of Crop Growth Regulation, Ministry of Agriculture, Nanjing Agricultural University, Nanjing 210095, China
Abstract: Fourteen cotton (Gossypium hirsutum L.) cultivars differing in yield were used to study the C/N ratio in the subtending leaf of cotton boll and its effect on boll dry matter accumulation and distribution. The 14 cultivars were clustered into 3 groups according to different changing patterns of C/N ratio in the subtending leaf of cotton boll. There were significant differences in dynamic changes of the C/N ratio and dry weight per boll among the 3 groups. Group III show much higher C/N ratio than Groups I and II from 10 to 17 d of boll age, and it maintained the C/N ratio of approximately 2.5 after 24 d of boll age. Group III also showed the widest changing range and the highest average values during the whole boll development. The boll dry matter accumulation of Group III took the longest time period and the lowest accumulating rate, which resulted in the highest final dry weight per boll and boll weight. The distributions of dry matter in cotton boll (percentages of boll-shell, seed, and lint) were not significantly different among the 3 groups. The C/N ratio in the subtending leaf of boll had no correlation to lint percentage and lint yield. The results indicated that the dynamics of the C/N ratio in the subtending leaf of cotton boll are significantly different among genotypes. A favorable pattern for dry matter accumulation in cotton boll is the sharp decrease in C/N ratio from 10 to 17 d of boll age, which is maintained at a relatively higher level after 24 d of boll age. Keywords:
subtending leaf of cotton boll; C/N ratio; dry matter accumulation and distribution
The source–sink relationship is crucial in crop production. The growth rate of sink tissues and organs is limited by photosynthate supplies from source leaves (source limitation). The sink in cotton (Gossypium hirsutum L.) changes with the plant developing status because cotton is a continuous growth plant. Cotton bolls are always the strongest sink with key stage of boll-forming. In this stage, carbohydrate of cotton boll is mainly supplied from the subtending leaf of the cotton boll, the subtending leaf of the adjacent fruiting position, and the corresponding main-stem leaf. The subtending leaf is the main source of the dry matter of cotton boll by translocating 85.6% of the photosynthate [1]. Carbon metabolism and nitrogen metabolism are the 2 basic metabolism processes in crop development. They directly affect the formation and transformation of the photosynthetic product, mineral nutrition absorption, and
protein synthesis [2]. The ratio of carbon and nitrogen affect source-to-sink ratio and crop yield [3–5]. In cotton, previous studies on carbon and nitrogen metabolism is to understand the differences of transgenic Bt cotton and conventional cotton [6–12]. Very few experiments, however, were conducted to disclose the changes of the C/N ratio in the subtending leaf of cotton boll in the boll-forming stage, and its relationship with boll dry matter accumulation and distribution. The contents of soluble sugar and total free amino acids in leaves are regarded as important indicators of carbon and nitrogen metabolism, respectively, and their ratio (C/N ratio) reflects the accordant status of carbon and nitrogen metabolism [5]. In this article, we took these indices to investigate the relationship between C/N ratio and dry matter accumulation and distribution in bolls as well as the
Received: 28 March 2007; Accepted: 17 August 2007. * Corresponding author. E-mail: [email protected] ** Author for English translation. Copyright © 2008, Crop Science Society of China and Institute of Crop Sciences, Chinese Academy of Agricultural Sciences. Published by Elsevier BV. All rights reserved. Chinese edition available online at http://www.chinacrops.org/zwxb/
HU Hong-Biao et al. / Acta Agronomica Sinica, 2008, 34(2): 254–260
yield responses to the changes of the C/N ratio in the subtending leaf of cotton boll.
1 1.1
Materials and methods Experimental design
Field experiments were conducted with 14 cotton cultivars (Sumian 15, Sumian 17, Sumian 19, Sumian 22, Zhongmiansuo 29, Zhongmiansuo 35, Zhongmiansuo 38, Zhongmiansuo 39, Zhongmiansuo 41, Lumian 15, Lumian 18, Kemian 1, Dexiamian 1, and AC-33B) in Jiangsu Academy of Agricultural Sciences, Nanjing, China (118º50’ E, 32º02’ N) in 2004. The experimental soil was yellow-brown loam. In 0–20 cm soil layer, it contained 2.5% organic matter, 12.0 g kg−1 total N, 85.1 mg kg−1 available N, 13.0 mg kg−1 available P, and 91.6 mg kg−1 available K (pH 7.5). All cultivars were planted in a nursery on April 15, 2004 and transplanted to the field on May 10. Field experiment was arranged in random design with 3 replicates in each treatment. The plot was 4 m wide and 15 m long. Field managements followed the high-yielding cultivation techniques in cotton production. 1.2
Sample collection and measurements
Flowers were labeled at the anthesis day (the day when the cotton flower opens). From the 10 d of boll age till boll opening, the bolls and its subtending leaves were collected from the 1st and 2nd fruiting positions of 6–10 sympodial branches every 7 d at 9:00–10:00 am. The middle part of the sampled subtending leaves were scissored and rapidly put into liquid nitrogen for measurements. Cotton fibers and seeds were excised from the bolls and dried at 80ºC. Dry weight per boll was comprised of dry weights of boll shell, seed, and fiber dry matter. Boll weight was the total of seed and fiber dry matter weights per boll. Boll-shell percentage, seed percentage, and fiber percentage are the proportions of the corresponding dry weights to boll dry matter, respectively. The soluble sugar content was determined by anthrone assay [13]. The total free amino acid content was determined by ninhydrin assay, and the absorbance readings were converted to microgram amino acid g−1 fresh weight using a glycine standard curve. The C/N ratio in the subtending leaf of cotton boll was the ratio of the soluble sugar content and the total free amino acid content. Data analysis
All data were statistically analyzed with the software SPSS and Microsoft Excel. Cluster analysis was conducted according to squared Euclidean distance and between-groups linkage. The following Logistic regression model
1+ae
bt
was used to describe dry matter accumulation [14, 15], where W is dry weight per boll, t is boll age, Wm is the maximum dry weight per boll, and a and b are parameters. Two variables, t1 and t2, were designated as the starting and termination time of cellulose rapid accumulation period with the following equations: t1 =
1 b
ln
2+
3
a
t2 =
,
1 b
ln
2−
3
a
The average rate of boll dry matter accumulation during the speedy accumulation period (VT) was expressed as VT =
W 2 − W1 t 2 − t1
where W1 and W2 are the dry weights per boll at t1 and t2, respectively.
2
Results
2.1 Cluster analysis on C/N ratio in the subtending leaf of cotton boll The dynamic changes of the C/N ratio in the subtending leaf of cotton boll were simulated with the quadratic of 2
y=at +bt +c, where y stands for the C/N ratio and t stands for the boll age (Table 1). Correlation analysis indicated that a, b, c, and the maximum C/N ratio were significantly correlated with dry weight per boll and boll weight but not with lint percentage and boll-shell percentage (Table 2).
Table 1
Equation of dynamic changes in C/N ratio in the subtending leaf of cotton boll with boll age
Cultivar Sumian 15 Sumian 17 Sumian 19 Sumian 22 Zhongmiansuo 29 Zhongmiansuo 35 Zhongmiansuo 38 Zhongmiansuo 39
1.3
Wm
W =
Zhongmiansuo 41 Lumian 15 Lumian 18 Kemian 1 Dexiamian 1 AC-33B *
Equation
P
R2
2
0.023
0.920*
2
0.011
0.951*
2
0.000
0.998**
2
0.014
0.942*
2
0.015
0.940*
2
0.006
0.965**
2
0.013
0.944*
2
0.022
0.921*
2
0.041
0.882*
2
0.024
0.916*
2
0.018
0.931*
2
0.014
0.943*
2
0.037
0.963*
2
0.026
0.912*
y = 0.0011t − 0.0767t + 2.5120 y = 0.0025t − 0.1895t + 5.1369 y = 0.0023t − 0.1686t + 5.1515 y = 0.0032t − 0.2438t + 6.4687 y = 0.0013t − 0.0942t + 3.6454 y = 0.0054t − 0.3984t + 9.4091 y = 0.0083t − 0.5543t + 10.6627 y = 0.0027t − 0.1826t + 5.2937 y = 0.0004t − 0.0302t + 2.2103 y = 0.0014t − 0.0929t + 3.3754 y = 0.0018t − 0.1269t + 3.5720 y = 0.0044t − 0.3045t + 7.4775 y = 0.0010t − 0.0916t + 4.7978 y = 0.0013t − 0.0953t + 3.9452
Significant at P < 0.05. ** Significant at P < 0.01.
HU Hong-Biao et al. / Acta Agronomica Sinica, 2008, 34(2): 254–260
Table 2 Correlation coefficients between parameters of C/N ratio dynamic changes and single boll dry matter weight, boll weight, lint percentage, and boll-shell percentage Parameter
Dry matter
Boll
Lint
Boll-shell
weight per boll
weight
percentage
percentage
A
0.691**
0.674**
0.060
0.532
b
−0.706**
−0.700**
−0.072
−0.538*
c
0.728**
0.722**
0.011
0.516
Max.
0.729**
0.721**
−0.003
0.481
Min.
0.308
0.202
−0.367
0.007
AV
0.560*
0.520
−0.261
0.258
n = 14, r0.05 = 0.533, r0.01 = 0.661. * Significant at P < 0.05. ** Significant at P < 0.01. a, b, and c are the parameters in equation of C/N ratio dynamic changes along with boll age in the leaf subtending cotton boll. Max., Min., and AV are the maximum, minimum, and the average values of the C/N ratio, respectively.
According to these results, we selected a, b, c, and the maximum C/N ratio as the variables for clustering analysis. The 14 cotton cultivars were clustered into 3 groups including 6, 6, and 2 cultivars, respectively (Fig. 1). 2.2
C/N ratio in the subtending leaf of cotton boll
As shown in Fig. 2, the C/N ratio showed a decreasing trend with boll age in all groups. Cultivars in the same group had a similar trend, which was quite different among groups. The change of C/N ratio in Group I was rather gently during
the whole boll development with an average of 1.94 but that in Group III had the largest changes. The onset value of Group III was up to 6.0 (10 d of boll age), which was much higher than that of Groups I and II. It declined sharply but still it was significantly higher than that of Groups I and II. From the 24 d of boll age, there were no significant differences among the 3 groups. 2.3
Boll dry matter accumulation and distribution
The response of dry matter weight of single boll (the value of each group was calculated with the average of all cultivars involved in the group) to boll age presented a “slow–quick–slow” changing pattern in all 3 groups. The dynamic changes were described with Logistic equations shown in Table 3. In different parts of cotton boll (boll shell, seed, and fiber), no significant differences were detected in the dry matter distribution among groups during the whole period of boll development (Fig. 3). As shown in Table 3, boll dry matter accumulation differed significantly among groups and the differences reflected the duration for boll dry matter speedy accumulation. In Group I, the duration of speedy accumulation was the shortest resulting in the lowest boll dry weight ultimately although the average of the accumulation rate was the highest. However, in Group III, the longest duration of speedy accumulation led to the highest final cotton boll dry weight.
Sumian 17 Sumian 19 Zhongmiansuo 39 Dexiamian 1 Sumian 22 Kemian 1 Sumian 15 Zhongmiansuo 41 Zhongmiansuo 29 Lumian 15 Lumian 18 AC-33B Zhongmiansuo 35 Zhongmiansuo 38
Fig. 1
Dendrogram based on dynamic changes in C/N ratio in the subtending leaf of cotton boll
HU Hong-Biao et al. / Acta Agronomica Sinica, 2008, 34(2): 254–260
5.5 C/N ratio
4.5 3.5 2.5 1.5 0.5
A
6.5
Group I
5.5
B
5
4.5
5
3.5
5
2.5
5
1.5
5
0.5 10 17 10 17
Group III
Group II
5
7 6
C/N ratio
6.5
5 4 3 2 1 0
5 24 31 38 45 24 31 38
10 45 10
17 45 17 2424 31 3138 38 Boll age (d)
S um ian 15 Zhongm iansuo 29 Zhongm iansuo 41 Lum m ian 15 Lum ian 18 AC -33B
45 10
17
24
38
45
10 17
24 31 38 45 Boll age (d) Group I Group II Group III
Zhongmiansuo 35
S um ian 17 S um ian 19 S um ian 22 Zhongm iansuo 39 Kem ian 1 Dexiam ian 1
Fig. 2
31
Zhongmiansuo 38
Dynamic changes of C/N ratio in the subtending leaf of cotton boll
Panel A shows the dynamic changes of C/N ratio in the boll subtending leaf for each cultivar; Panel B shows dynamic changes of C/N ratio in the boll subtending leaf for each cluster.
Table 3 Equations of dynamic change in cotton boll dry matter weight with boll age and its eigen values Group
Equation
t1 (d)
t2 (d)
T (d)
VT (g d-1)
Wo (g)
I
W = 6.38486 / (1 + 26.71382 e−0.16266t)
0.9980**
12.10 aA
28.29 bB
16.19 cC
0.23 aA
6.35 cC
II
W = 6.83374 / (1 + 16.51484 e−0.14440t)
0.9865**
10.30 bB
28.54 bB
18.24 bB
0.22 bB
6.75 bB
0.9949**
8.73 cC
30.05 aA
21.32 aA
0.20 cC
7.26 aA
−0.12355t
III **
R2
W = 7.44723 / (1 + 10.97259 e
)
Determination coefficient significant at 0.01 probability level (n = 7, R20.01 = 0.7653).
Values followed by the same capital or lowercase letter within columns are not significantly different at 0.01 or 0.05 probability level, respectively. t1: start date of the speedy accumulation period of boll dry matter; t2: termination day of the speedy accumulation period of boll dry matter; T: duration for cotton boll dry matter speedy accumulation, T = t2−t1; VT: average rate of cotton boll dry matter accumulation during the speedy accumulation period; Wo: final dry weight of cotton boll.
Boll shell ratio (%)
Boll shell ratio (%)
60 50 40
30 Boll shell ratio (%)
50
70
40
30
30
25 20 15 10
20
20 10
17
24
31
38
45 BO
Boll age (d) Group I Group II Group III
Fig. 3
5 10
17
24
31
38
45
BO
10
Boll age (d) Group I Group II Group III
Dynamic changes of distribution ratios in cotton boll dry matter BO: date of boll opening.
17
24
31
38
Boll age (d) Group I Group II Group III
45 BO
HU Hong-Biao et al. / Acta Agronomica Sinica, 2008, 34(2): 254–260
2.4 Relationship between changes of C/N ratio in the subtending leaf of cotton boll and boll dry matter accumulation and distribution
middle of Group I and Group III (Fig. 4 and Table 3). 2.5 Relationship between C/N ratio in the subtending leaf of cotton boll and cotton yield and the yield traits
In Group I, the C/N ratio of the subtending leaf of cotton boll maintained was approximately 2.0 during the whole boll development, and the boll dry matter accumulation was the lowest in the 3 groups with highest accumulation rate and the duration of boll dry matter accumulation was the shortest. In Group III, the C/N ratio was rather high at beginning but declined sharply in the following 14 d and accorded with the levels of Groups I and II ultimately. The duration of boll dry matter accumulation in Group III was of lowest rate, resulting in the highest final dry weight per boll and boll weight. In Group II, the above indices were in the
The yields were significantly different among the 14 cultivars (Table 4). With respect to lint yield and lint percentage, Group II was significantly higher than Groups I and III, which were equivalent in lint yield with no significant difference (Fig. 5). With regard to cotton boll weight, it showed that Group III > Group II > Group I with significant differences. This was in agreement with the group ranks on dry weight per boll among groups. The C/N ratio in the subtending leaf of cotton boll was not correlated with the final lint percentage and lint yield.
70
8
60 6
50 40
4
30 20
2
10 0
0 10
17
24
31
38
45
BO
10
17
24
31
38
45
BO
10
17
24
31
38
45
BO
Boll age (d) Boll shell ratio
Seed ratio
Fiber ratio C/N ratio in cotton boll subtending leaf
Dry matter weigth per boll
Fig. 4
Relationship between C/N dynamic changes in the subtending leaf of cotton boll and boll dry matter accumulation and distribution
Table 4 Source of variance
Degree of freedom
Blocks
Variance analysis of cotton yield
Sum of squares
Mean squares
2
11442.43
5721.22
Cultivars
13
1357344.44
104411.11
Errors
26
70355.48
2705.98
3.37
5.53
38.59**
2.12
2.91
1000 900 800
5.5 5.3 5.1 4.9 4.7
II Group
III
39 38 37 36 35
4.5 I
F0.01
40 Lint percentage (%)
Boll weight (g)
Lint yield (kg ha−1)
F0.05
2.11
5.7
1100
Fig. 5
F-value
I
II Group
III
I
II
III
Group
Relationship between changes of C/N in the subtending leaf of cotton boll and lint yield, boll weight and lint percentage
HU Hong-Biao et al. / Acta Agronomica Sinica, 2008, 34(2): 254–260
3
Discussion
In this study, 14 cotton cultivars were clustered into 3 groups on the basis of the C/N ratio in the subtending leaf of cotton boll indicating the probable difference by genotypes on this index. In the regressive equation between the C/N ratio in the subtending leaf of boll and the boll age, parameters of a, b, c, and the maximum C/N ratio were significantly correlated with dry weight per boll and boll weight but not with lint percentage and boll-shell percentage (Table 2). This indicated that the C/N ratio in the subtending leaf of cotton boll show significant effect on the dry matter accumulation but not on the dry matter distribution. We also found that the average rate of cotton boll dry matter accumulation was not crucial for the final cotton boll dry weight. In fact, it was determined by the duration for cotton boll dry matter speedy accumulation (Table 3 and Fig. 4). The duration was determined by the sink size and the supply capacity of photosynthate from source leaves (the subtending leaf of cotton boll). Nakamura et al. [16] reported that high yield was determined not only by photosynthesis capability but also by the capacity of translocation of photosynthesis products represented by the ratio of carbon and nitrogen in the subtending leaf of cotton boll. Gao et al. [17] and Zhao et al. [18] revealed that the flag leaf maintained a high capacity for carbon metabolism and photosynthate supply in large-spike wheat (Triticum aestivum L.) at middle-to-late filling stage. This implied that the proper ratio of carbon and nitrogen in functional leaf can promote dry matter accumulation in late developmental stages. At the onset (from 10 to 24 d of boll age), cotton boll needs much carbohydrate. In Group I cultivars, the C/N ratio in the subtending leaf of cotton boll of Group I was only about 2.0 in this time period, which cannot meet the requirement of boll development. In addition, the C/N ratio was reduced to less than 2.0 after 24 d of boll age. Accordingly, the dry matter accumulation, dry weight per boll, and boll weight were restricted by the low activity of carbon metabolism. In Group III cultivars, the C/N ratio was approximately 5.0 d from 10 to 17 d of boll age, which was favorable for carbohydrate supply in speedy accumulation period in the boll. After 24 d of boll age, the C/N ratio declined to approximately 2.5, implying relatively strong activities of carbon and nitrogen metabolism. This is the fundamental for high boll weight formation. According to these results, fertilizers in blossoming and boll-forming stages can be reduced in cotton production for controlling the metabolic activity of nitrogen from 10 to 17 d of boll age and increasing the dry weight per boll and boll weight. The dry matter distributions (boll shell percentage, seed percentage, and fiber percentage) were not significantly different among the 3 groups in this study, which indicates no correlation between cotton lint percent and C/N ratio in
the subtending leaf of cotton boll. Dry matter distribution is a process of re-allocating dry matter in the boll, which is not directly correlated with physiological characteristics of the subtending leaf of cotton boll. It is probably determined by the physiological characteristics of cotton boll differing from genotypes. The C/N ratio in the subtending leaf of boll was significantly correlated with dry weight per boll and boll weight but not with lint yield. The lint weight is mostly correlated with the number of mature bolls per plant under the same planting density, which is not associated with the C/N ratio in the subtending leaf of boll.
4
Conclusions
The dynamic characters of the C/N ratio in the subtending leaf of cotton boll are significantly different among genotypes, and the C/N ratio declined dramatically from 10 to 17 d of boll age and maintained at a relative higher level after 24 d of boll age, which is favorable for cotton boll dry matter accumulation.
Acknowledgments This study was funded by the National Natural Science Foundation of China (30571095 and 30600378), the Jiangsu Provincial Natural Science Foundation (BK 2006141), and the Special Research Funds for Doctoral Program of Higher Education (20050307028).
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