Relationships between temperature-light meteorological factors and seedcotton biomass per boll at different boll positions

Key Laboratory of Crop Physiology Ecology and Production Management, Ministry of Agriculture/Jiangsu Collaborative Innovation Center for Modern Crop Production (JCIC-MCP), Nanjing Agricultural University, Nanjing 210095, P.R.China

1. Introduction

Cotton (Gossypium hirsutumL.) is an important economic crop and raw material for the textile industry which originates from tropical and subtropical latitudes, and is accustomed to warm conditions (Lee 1984). Seedcotton biomass per boll is the decisive factor in cotton yield and value, and depends on genotypes, environmental conditions, and agronomic managements (Gormus and Yucel 2002; Percyet al. 2006;Dai and Dong 2014). Temperature and light are the most important environmental constraints for cotton growth in agriculture (Janaset al. 2002; Yeateset al. 2010; Lvet al.2013). Cotton-growing regions usually were combined with the main food crop-growing regions in China. As a result of double cropping systems such as cotton-wheat and cottonrapeseed rotation systems, cotton often suffers from cool temperature and low light due to late planting along the middle and lower reaches of the Yangtze River. In addition,shading resulted from air pollutants and overcast weather is wide spread in this region. However, global warming has the potential to increase air temperatures by 1.8 to 4.0°C by the end of the 21st century (IPCC 2007), therefore cotton will be grown in a different environments at that time. Hence,it is important to explore the effects of temperature-light meteorological factors and their relationship with seedcotton biomass per boll, and to find out the main effects of these meteorological factors and their optimum range for cotton yield (seedcotton biomass per boll).

Cotton experiences temperature and solar radiation change ranging from 12–36°C and 10.9–16.9 MJ m–2throughout the growing season, which influence cotton growth and development (Chenet al. 2013; Liuet al. 2013).Mean daily temperature, mean daily maximum temperature,mean daily minimum temperature, mean diurnal temperature difference, growing degree-days, mean daily sunshine hours, and mean daily radiation also vary with the different boll positions. It is of utmost importance to understand and quantify thoroughly that how plant responses to various temperature regimes and light conditions.

Previously, different planting dates and shading treatments were established to explore the effects of temperature and light on cotton growth (Zhaoet al. 2012;Lvet al. 2013; Lokhande and Reddy 2014; Liuet al. 2015a,b). Researchers had analyzed the effect of cool temperature due to late planting on seedcotton biomass per boll (Baueret al. 1998; Donget al. 2006; Jalotaet al. 2008; Wratheret al. 2008; Boquet and Clawson 2009; Zhaoet al. 2012).It was reported that days from anthesis to boll opening were prolonged by cool temperature (Viatoret al. 2005) and seedcotton biomass per boll was significantly decreased under cool temperature condition (Pettigrew 1994; Zhao and Ooterhuis 2000; Dusserreet al. 2002; Arshadet al.2007; Caoet al. 2011; Lvet al. 2013; Liuet al. 2015a, b).Seedcotton biomass per boll decreased with increasing shading treatments (Dusserreet al. 2002; Lüet al. 2013).Previous researches usually focus on the single factor of cool temperature or low light, however, cool temperature and low light often appear together during cotton growth season in the Yangtze River Valley Cotton Belt. In recent years, a few studies had paid attention to the interaction of planting date and shading, however, they mainly focused on the effects on the entire cotton plant, and no detailed research on effects of cool temperature and shading combined on cotton yield at each boll position was found.

In our study, seedcotton biomass per boll is measured from bolls that develop under different environments, including spatial and temporal differences due to the indeterminate growth habit of cotton. Most researches focused on assessing seedcotton biomass per boll using the average of seedcotton biomass per boll within a whole cotton plant.However, little attention has been paid to quantifying the spatial distribution of seedcotton biomass per boll, although earlier studies have showed that seedcotton biomass per boll varied among bolls that develop at different times and different boll positions (Davidoniset al. 2004; Baueret al.2009; Maet al. 2014; Kuaiet al. 2015) due to cotton boll maturity period, as well as the difference of environment and fertilizer supply (Jenkinset al. 1990; Zhaoet al. 2012).Previous researches have concentrated on the effects of meteorological factors on seedcotton biomass per boll in a whole plant or concentrated on different fruiting branches of the main stem, few studies have been done at different fruiting positions of the same fruiting branch (Heitholt 1997; Anjumet al. 2002). Therefore, it is important to study the effects of temperature-light meteorological factors on seedcotton biomass per boll at different boll positions and find out the optimum range of the main factor for cotton yield.

The primary objective of this research was to explore the effects of various temperature-light meteorological factors on seedcotton biomass per boll at different boll positions,which could provide information for formulating predictions as to the effect of certain meteorological conditions on cotton production. It also will be useful to minimize the negative effects of environment conditions through utilizing proper cultivation managements based on optimum temperature and light to improve cotton yield.

2. Materials and methods

2.1. Experimental design

Field experiments in 2010 and 2011 were conducted at the Pailou Experimental Station of Nanjing Agricultural University, Jiangsu Province, China (118°50´E, 32°02´N).The soil at the experimental site was clay, mixed, thermic,Typic alfisols (udalfs; FAO luvisol) with 18.3 and 16.3 g kg–1organic matter, 1.1 and 1.0 g kg–1total nitrogen (N), 64.5 and 50.2 mg kg–1available N, 17.9 and 16.8 mg kg–1available phosphorus (P), and 102.3 and 96.4 mg kg–1available potassium (K) in the depth of 20 cm of the soil profile before planting cotton in 2010 and 2011, respectively.

Kemian 1 (a cool temperature-tolerant cultivar) and Sumian 15 (a cool temperature-sensitive cultivar) were sown on 25 April, 25 May, and 10 Jun in both 2010 and 2011. Planting date of 25 April is comparatively appropriate for cotton growing in the Yangtze River Valley Cotton Belt(Jianget al. 2006), and 25 May and 10 June are late planting dates (Shuet al. 2009; Liuet al. 2013). Cotton seeds were sown in a nursery bed, and seedlings with three true leaves were transplanted to the field at a spacing of 80 cm×25 cm.When flowers at the 1st node of the 7th main-stem sympodial fruiting branch for a given planting date bloomed, three shading levels were imposed for that planting date. Shading cloths were removed after cotton bolls on the 3rd node of the 7th sympodial branch became maturity. Shading levels included an unshaded control (crop relative light rate (CRLR)100%), light shade (CRLR 80%), and severe shade (CRLR 60%) achieved with white nylon cloth. Nitrogen fertilizer was applied 40% as basal, 30% at first flowering stage, and 30%at peak flowering stage.

Experiments were arranged as a randomized complete block design in the field with three replications. Each plot was 6 m wide and 11 m long, and the shade cloth over each plot was 7 m wide, 12 m long, and 2 m above the ground.Furrow-irrigation was applied as needed during cotton seasons. Conventional insect and weed control methods were utilized as needed.

2.2. Sampling and processing

Ten consecutive cotton plants were randomly selected in each experimental plots. All white flowers in selected cotton plants were tagged and labeled with small plastic tags at the same day to ensure the tagged bolls were equivalent metabolic and developmental ages. Fruiting branches and fruiting nodes were noted on the tags, and cotton boll opening date was marked on the same tags when the tagged cotton boll was opened. All tagged cotton bolls were harvested and air-dried, and then were divided in 14 groups according to similar anthesis date and neighbouring boll position. The first sympodial branch was designated as fruiting branch 1(FB1), the first fruiting node on a sympodial branch was designated as fruiting node 1 (FN1), and the rest was deduced by analogy. Longitudinally, fruiting branches were divided into five groups as FB1–3, FB4–6, FB7–9, FB10–12, and FB13–15, and fruiting nodes for each fruiting branch were divided into three groups as FN1, FN2, and FN3, horizontally, which assured the uniformity of anthesis time and the days from anthesis to boll opening. FB2, FB5, FB8, FB11, and FB14were chosen for representative examples, respectively, for FB1–3, FB4–6,FB7–9, FB10–12, and FB13–15at each plot.

The dried cotton bolls were used to determine seedcotton biomass per boll weighed by an electronic balanceafter shelling.

2.3. Weather data

Weather data were collected from an established station(Nanjing Weather Station). The temperature-light meteorological factors used in this study were mean daily temperature (MDT,X1), mean daily maximum temperature(MDTmax,X2), mean daily minimum temperature (MDTmin,X3),mean diurnal temperature difference (MDTdif,X4), growing degree-days above the threshold of 15°C (GDD,X5), mean daily sunshine hours (MDSH,X6), and mean daily radiation(MDR,X7). Through analyzing meteorological data, it was clarified that the environmental difference during cotton boll development period among three planting dates of 25 April,25 May, and 10 Jun was primarily on temperature, especially MDTmin(Liuet al. 2013; Maet al. 2013). The range of MDTminof cotton boll maturation period was reduced from 25.9 to 16.5°C in 2010 and from 24.0 to 16.0°C in 2011 (Chenet al.2013, 2014; Liuet al. 2013; Lvet al. 2013; Maet al. 2013).

2.4. Microclimate measurement

Since microclimate factors would be affected by planting date and shading cloth, photosynthetically active radiation(PAR) was measured using a Decagon AccuPAR LP-80 Ceptometer (Decagon Devices, Logan, UT, USA) which was diagonal across the cotton row within the canopy to ensure accuracy of PAR measurement. Canopy air temperature and relative humidity (RH) were monitored with a Hygro-Thermometer Psychrometer (DT-8892, CEM, Shenzhen,China). These microclimate factors were measured every two hours from 06:00 to 18:00 near the 2nd, 8th, and 11th fruiting branch on 15 d after initiation of shading, with three replications per plot. Measurements were done only when the direct sunlight was not blocked by clouds.

2.5. Data analysis

Data were subjected to an analysis of variance with the SPSS statistical package version 20.0. Differences at theP＜0.05 level were considered statistically significant using the least significant difference (LSD) test. Correlation coefficients and Stepwise regression were also calculated by SPSS 20.0.

3. Results

3.1. Cotton canopy microclimate

Microclimate data in cotton canopy were expressed as the mean of measured data from 06:00 to 18:00 on 15 d after initiation of shading (Table 1). Shading reduced air temperature and PAR, whereas increased relative humidity in two experimental years. The differences of air temperature and relative humidity among three shading levels were little,which were no more than 1.5°C and 5.5%. Based on the

coefficient of variation (CV) of three microclimate factors,PAR was the key factor affected by shading and strongly reduced. PAR in FB8was most affected by shading, which decreased by 30 and 47% under CRLR 80% and CRLR 60%,respectively, followed by FB2and FB12. Two cultivars Sumian 15 and Kemian 1 reacted in the same way, but the decreased magnitude of Sumian 15 was more than that of Kemian 1. The results suggest that PAR was the primary meteorological factor affected by shading, and the influences varied among different fruiting branches and cultivars. FB8was most affected of any fruiting branch, and Sumian 15 changed more than Kemian 1, which may result in different responses of seedcotton biomass per boll to shading.

Table 1 Air temperature, potosynthetically active radiation, and relative humidity at different canopy heights for combinations of planting dates and shading treatments for cultivar Sumian 15 and Kemian 1 in 2010 and 20111)

3.2. Environmental conditions during days from anthesis to boll opening in different fruiting branches

Cotton boll with the same anthesis time had the nearest days from anthesis to boll opening stages. The anthesis date and days from anthesis to boll opening stages were affected by boll positions and planting dates (Table 2). Vertical anthesis intervals (number of days between the 1st node flowers in successive main stem) firstly increased and then decreased,except for cotton grew in the planting date of 25 April in 2010,which was changeless. Data of temperature (MDT, MDTmax,and MDTmin) and MDR in FB2were the highest. As fruiting branch upward, data of temperature and solar radiation decreased, which resulted in shorter days from anthesis to boll opening stages in FB2. Temperature and solar radiation were higher in 2010 than those in 2011, which resulted in shortening the days from anthesis to boll opening stages,especially for the bolls in the upper fruiting branch and outside bolls (bolls on the 3rd and more than 3rd node). The days from anthesis to boll opening stages were affected by planting date, besides boll positions (Table 2). 25 April was the normal planting date in theYangtze River Valley Cotton Belt, which had the shortest days from anthesis to boll opening in these three planting dates. However, late planting prolonged daysfrom anthesis to boll opening stages from 44 to 63 d in 2010 and from 50 to 65 d in 2011, respectively. MDT, MDTmax,MDTmin, and MDR during days from anthesis to boll opening stages decreased as planting date delayed, but the CVs of MDT, MDTmax, and MDTminwere higher than those of MDR,except FB2and FB5in 2010. Among three temperature factors, the CVs of MDTminwas higher than those MDT and MDTmax, which was 24.9 and 21.1% in 2010 and 2011. The effect of late planting on bolls in the upper fruiting branch was greater than bolls in the lower and middle fruiting branches,whose MDTminreduced from 22.5 to 11.8°C in 2010 and from 19.9 to 12.6°C in 2011.

Table 2 Mean daily temperature (MDT), mean daily maximum temperature (MDTmax), mean daily minimum temperature (MDTmin),and mean daily radiation (MDR) during boll development from anthesis to boll opening stages on different fruiting branches in 2010 and 20111)

Therefore, the decline of MDTminwas the key factor for the adverse effect on cotton growth and development caused by late planting. Environmental conditions in the upper fruiting branch and outside bolls were most affected.

3.3. Relationships between temperature-light meteorological factors and seedcotton biomass per boll at different boll positions

Correlation estimatesResults of simple correlation coefficients between temperature-light meteorological factors and seedcotton biomass per boll on different boll positions were shown in Table 3. The simple correlation values indicated clearly that temperature factors seem to be more important than light factors especially MDT, MDTmax,MDTmin, and GDD as they showed higher correlation values.MDT, MDTmax, MDTmin, GDD, and MDR had significant positive relation with seedcotton biomass per boll, while MDTdifshowed a negative relation.

Stepwise regression modelDue to the correlation among above temperature-light meteorological factors, they might have strengthening or weakening effects on the seedcotton biomass per boll. Therefore, the effects of meteorological factors were analyzed by stepwise regression analysis(Table 4). Base on the standardized coefficients of variables entered in stepwise regression models (Table 5), the effects of each meteorological factor could be judged.

The main temperature-light meteorological factors which affect seedcotton biomass per boll varied among different boll positions. GDD was the most important temperaturelight meteorological factor for bolls on FB2FN1for both cultivars. For bolls on their positions, MDR was chosen, butthe influence of MDR on seedcotton biomass per boll was lower than temperature factors, especially GDD.

Table 3 Correlation coefficients of seedcotton biomass per boll against different temperature-light meteorological factors during boll development period on different boll positions of Sumian 15 and Kemian 11)

Table 4 Stepwise regression models of seedcotton biomass per boll against meteorological factors during boll development period on different boll positions of Sumian 15 and Kemian 1

Regression equationBy regression analysis, fitting predictive equations (Table 6) were computed for seedcotton biomass per boll using selected significant factors (Table 5)from the seven temperature-light meteorological factors studied in this study.

MDTmaxand MDR had the most significant effect on seedcotton biomass per boll for bolls grew at late growth stage (FB14FN3). Based on the border effect models, the optimum MDTmaxwas 32.4°C, and the optimum MDR was 15.8 MJ m–2for Sumian 15. The optimum MDTmaxwas 29.9°C, and the optimum MDR was 17.5 MJ m–2for Kemian 1.

4. Discussion

4.1. Cotton canopy microclimate

Cool temperature and low light caused by late planting,cloudy and overcast weather during cotton flowering and boll formation often appear together in the Yangtze River Valley Cotton Belt (Pettigrew 2001; Shuet al. 2009; Liuet al. 2015a, b). In this experiment, different planting dates plus shading were used to bring out different combinations of temperature and light. Based on our experiments in 2010 and 2011, through analyzing weather data and microclimate factors in the field (Tables 1 and 2), it was clarified that air temperature was the dominant factor of planting date, especially MDTmin(Liuet al. 2013).In addition, compared with PAR, the differences of air temperature and relative humidity would have only a minor effect on cotton growth and development among the three shading treatments. PAR was reduced by 21–29% and 31–41% for CRLR 80% and CRLR 60%, respectively in the upper fruiting branch, which was consistent with the design of the experiment. The effects of shading on PAR varied with cultivars and fruiting branches, which might result in different responses of seedcotton biomass per boll to shading. The changes of temperature and light might have influences on cotton growth and development, but it needed a deeper investigation.

Table 5 Standardized coefficients of variables entered in stepwise regression model of seedcotton biomass per boll against meteorological factors during boll development period on different boll positions of Sumian 15 and Kemian 11)

4.2. Days from anthesis to boll opening

Anthesis date and days from anthesis to boll opening are determined by genotypes and environmental conditions(Roussopouloset al. 1998; Bednarz and Nichols 2005).Vertical anthesis intervals were the greatest in the middle fruiting branch, which was similar to previous research(Bednarz and Nichols 2005). Bednarz found flowering and the number of developing bolls were the greatest in the middle fruiting branch in a plant, thus the source-to-link ratio in the middle fruiting branch was most likely reduced,resulting in extended vertical anthesis intervals. The days from anthesis to boll opening stages were prolonged as fruiting branch upward and fruiting node outward because of the gradual reduction of temperature during the growing season. Late planting extended the days from anthesis to boll opening. Average across the 2 years, days from anthesis to boll opening stages increased by 11 and 17 d in planting date of 25 May and 10 Jun (Table 2). The differences of meteorological conditions at different boll positions altered days from anthesis to boll opening stages,which was 6–9 d longer on FB14than that on FB2in 25 April in the two years. As planting date postponed, the difference value increased. The low temperature is the main limited factor for cotton flowering and boll setting at late growth stages (Gormus and Yucel 2002; Boquet and Clawson 2009). Therefore, suitable planting date was beneficial for bolls in the upper fruiting branch and bolls on the 3rd and more than 3rd nodes to avoid low temperature. Previous researches found that light has significant influences on days from anthesis to boll opening stages (Bednarz and Nichols 2005; Liet al. 2009), but in our experiment, shading had little effect on it. In this study, there were no significant differences in anthesis date and days from anthesis to boll opening between two cultivars.

4.3. Seedcotton biomass per boll

Numerous studies have measured the effects of temperature or light on cotton growth and yield (Wratheret al. 2008; Zhaoet al. 2012; Lvet al. 2013; Liuet al. 2015a, b). However,several studies referred to the effect of meteorologicalfactors on seedcotton biomass per boll. Mergeai and Demol(1991) found that cotton yield was favoured by temperature between 24 to 28°C. Reddyet al. (1962) reported that optimum temperature for boll production was 30/22°C (day/night temperature regimes). Sawan found that evaporation,sunshine duration, humidity, surface soil temperature at 1 800 h, and the maximum air temperature were the important meteorological factors that significantly affect boll production of Egyptian cotton (Sawanet al. 2002).Lokhande and Reddy reported that boll mass per unit total weight, peaked at 25.5°C and was reduced by 21% at 18.1°C and 53% at 29.5°C (Lokhande and Reddy 2014).

Table 6 Relationship models and border effect models of seedcotton biomass per boll to meteorogical factors during boll development period on different boll positions of Sumian 15 and Kemian 1

4.4. Relationships between temperature-light factors and seedcotton biomass per boll

In most studies, seedcotton biomass per boll was measured from the bolls collected from the entire plant or the bolls just collected from the middle fruiting branch (Chenet al. 2013,2014; Lvet al. 2013). Thus, the effects of temperature and light on different boll positions were averaged. In this study, deeper investigation was conducted on the main temperature-light meteorological factors affect seedcotton biomass per boll at different boll positions.

The positive correlation between each of MDT, MDTmax,MDTmin, GDD, or MDR and seedcotton biomass per boll revealed that the increasing in the values of those factors had beneficial effects on cotton production. On the other hand, there was a negative correlation between MDTdifand seedcotton biomass per boll. The negative relationship between MDSH and seedcotton biomass per boll might due to the fact that cotton is a short-day plant. Hence, the increasing of MDSH over requirement of cotton plant growth would decrease seedcotton biomass per boll.

Standardized coefficients of variables entered in stepwise regression models of seedcotton biomass per boll against meteorological factors at different boll positions obtained from Sumian 15 and Kemian 1 indicated that relationships of some temperature-light meteorological factors varied markedly among different boll positions and cultivars.For example, MDT showed a negative relationship with seedcotton biomass per boll on FB2FN2and FB8FN3for Sumian 15, while that trend differed on FB5FN1and FB14FN1for Kemian 1.

The optimum MDTmaxwas 32.4°C, and the optimum MDR for seedcotton biomass per boll on FB11FN3was 15.8 MJ m–2for Sumian 15. While the optimum MDTmaxwas 29.9°C,and the optimum MDR was 17.5 MJ m–2for Kemian 1. In cotton-wheat rotation systems, winter wheat was harvested in June. Direct-seeded cotton after wheat harvest had poor yield and fiber quality because of the shorter growth period.Seedling transplanting of cotton was an effective way to solve the interaction effect of these two crops. In reality,MDTmaxranged from 18.7 to 27.8°C, MDR ranged from 6.5 to 12.7 MJ m–2among three planting dates in 2010 and 2011,which were lower than the optime values. In order to catch up with better temperature-light environment, one way was to cultivate early-maturing wheat, rape, and cotton varieties to relieve the conflict of time, the other way was to transform current planting patterns to simplified cultivation and mechanization. Through replacing soil clay with seedling substrate, mechanized transplanting and harvest instead of manual managements, we could increase efficiency on cotton production and decrease labor cost.

5. Conclusion

Based on experiments in 2010 and 2011, two-factor interactions of late planting and shading were designed to study the relationships between meteorological factors and seedcotton biomass per boll at different boll positions.Results obtained from this study indicate that the main meteorological factors varied among different boll positions.MDR affected seedcotton biomass per boll at all boll positions, except FB2FN1, but its influence was less than temperature factors, especially GDD. The optimum MDTmaxwas 29.9–32.4°C, and the optimum MDR was 15.8–17.5 MJ m–2on FB11FN3.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (31471444, 31401327), the Special Fund for Agro-scientific Research in the Public Interest of China (Impact of Climate Change on Agriculture Production,201203096), and the Jiangsu Overseas Research and Training Program for University Prominent Young and Middle-aged Teachers and President , China (2016).

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