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Effects of Nitrogen Application on Chlorophyll Fluorescence Parameters and Leaf Gas Exchange in Naked Oat
Journal of Integrative Agriculture 2013, 12(12): 2164-2171
December 2013
RESEARCH ARTICLE
Effects of Nitrogen Application on Chlorophyll Fluorescence Parameters and Leaf Gas Exchange in Naked Oat LIN Ye-chun1, HU Yue-gao1, REN Chang-zhong2, GUO Lai-chun2, WANG Chun-long2, JIANG Ying1, WANG Xue-jiao1, Phendukani Hlatshwayo1, 3 and ZENG Zhao-hai1 1
College of Agronomy and Biotechnology, China Agricultural University, Beijing 100193, P.R.China Baicheng Academy of Agricultural Sciences, Baicheng 137000, P.R.China 3 KZN Department of Agriculture, Nquthu 3135, Republic of South Africa 2
Abstract Naked oat (Avena nuda L.) was originated from China, where soil nitrogen (N) is low availability. The responses of chlorophyll (Chl.) fluorescence parameters and leaf gas exchange to N application were analysed in this study. After the N application rate ranged from 60 to 120 kg ha-1, variable fluorescence (Fv), the maximal fluorescence (Fm), the maximal photochemical efficiency (Fv/Fm), quantum yield (ΦPS II) of the photosynthetic system II (PS II), electron transport rate (ETR), and photochemical quenching coefficient (qP) increased with N application level, however, non-photochemical quenching coefficient (qN) decreased. Moreover, there was no difference in initial fluorescence (Fo) with further more N enhancement. The maximum net photosynthetic rate (Pmax), apparent dark respiration rate (Rd) and light saturation point (LSP) were improved with 40-56 kg N ha-1 as basal fertilizer and 24-40 kg N ha-1 as top dressing fertilizer applied at jointing stage. Initial quantum yield (α) was decreased with 24 kg N ha-1 as basal fertilizer and 56 kg N ha-1 as top dressing fertilizer. Flag-leaf net photosynthetic rate (Pn) was significantly enhanced at the jointing and heading stages with 40-56 kg N ha-1 as basal fertilizer; in addition, increased at grain filling stage of naked oat with 40-56 kg N ha-1 as top dressing fertilizer. 90 kg N ha-1 (50-70% as basal fertilizer and 30-50% as top dressing fertilizer) application is recommended to alleviate photodamage of photosystem and improve the photosynthetic rate in naked oat. Key words: Avena nuda, nitrogen fertilizer, nitrogen application, chlorophyll fluorescence, gas exchange
INTRODUCTION Despite water deficit, nitrogen (N) nutrient is the main constraint restricting yield of crops in many environmental factors (Passioura 2002). Increase in vegetative and reproductive growth and yield is dependent upon the adequate N application (Lawlor 2002). However, overuse of N fertilizer did not significantly improve the grain yield in oat (Xiao et al. 2011), contrarily that
would even lead to environmentally negative impacts such as global warming (Giles 2005; Zhang et al. 2010). Therefore, most of studies have been investigating how to maximize crop yields while reducing N fertilizer input (Baethgen et al. 1995; Ankumah et al. 2003; Iqbal et al. 2005; Caliskan et al. 2008; Li et al. 2012; Qiao et al. 2012). Furthermore, several attempts have been accomplished to assess the relationship between N supply and physiological responses in crops. Chlorophyll
Received 1 November, 2012 Accepted 15 January, 2013 LIN Ye-chun, E-mail: [email protected]; Correspondence ZENG Zhao-hai, Tel: +86-10-62733847, E-mail: [email protected]
© 2013, CAAS. All rights reserved. Published by Elsevier Ltd. doi: 10.1016/S2095-3119(13)60346-9
Effects of Nitrogen Application on Chlorophyll Fluorescence Parameters and Leaf Gas Exchange in Naked Oat
(Chl.) fluorescence parameters are usually used to evaluate the functionality of photosynthetic apparatus and the effects of environmental stresses (Baker et al. 1983; Wang et al. 2009; Shen and Li 2011). The Chl. fluorescence parameters, potential photochemical efficiency (Fv/Fo) of PS II, Fv/Fm, ΦPS II, and qP were enhanced with N fertilizer application in winter wheat and tobacco (Ma et al. 2010; Yun et al. 2010). However, Liu et al. (2008) found that Fv/Fm, ΦPS II, ETR, and qP to water stress decreased with the excessive N fertilizer supply (480 kg N ha-1) in cotton. The Chl. content and the area of leaves were clearly increased with increasing N fertilizer application; otherwise, Pn, Gs and E were significantly improved in oat (Dong et al. 2008). Jiang et al. (2011) showed that Chl. content, Pn, nitrate reductase activity, and soluble protein content of leaves were significantly raised when N fertilizer topdressing increased at jointing stage in winter wheat. Naked oat is the most widely cultivated oat in terms of growing area in the farming-pastoral ecotone of China, which is the major producer all over the world (Ren 2010). The objective of this study was to demonstrate that how N fertilizer application affect Chl. fluorescence parameters and gas exchange characteristics of naked oat with alternate partial root-zone irrigation.
RESULTS Effects of nitrogen fertilizer on Chl. fluores cence parameters Fig. 1 illustrates the effects of N fertilizer application rate on initial fluorescence (Fo), the maximal fluorescence (Fm), variable fluorescence (Fv), and the maximal photochemical efficiency (Fv/Fm). The ANOVA for Fo values showed that there were no significant differences with the different N fertilizer supply levels. Fm, Fv and Fv/Fm were significantly (P<0.05) decreased at low N supply compared to the moderate and high N supply; however, N did not induce significant differences between moderate and high N application. Quantum yield of PS II (ΦPS II), electron transport rate (ETR), photochemical quenching coefficient (qP), and non-photochemical quenching coefficient (qN) were showed in Fig. 2. Similarly, Φ PS II, ETR and qP were significantly lower at low than the ones at moderate and high N supply; moreover, no significant differences were found between moderate and high N supply. qN was significantly improved at low N fertilizer supply (Fig. 3).
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Fig. 1 Effects of different nitrogen application rates on Fo, Fm, Fv, and Fv/Fm of the flag leaves in naked oat. Different letters mean significant difference at 0.05 level. The same as below. © 2013, CAAS. All rights reserved. Published by Elsevier Ltd.
LIN Ye-chun et al.
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Responses of net photosynthetic rate (P n) to photosynthetically active radiation (PAR) with different ratios of basal and top dressing nitrogen fertilizer F3 reduced the photosynthetic activity strongly at light saturation compared to CK, however, F1 and F2 in reverse (Fig. 4); the parameters fitted by a non-rectangular hyperbola are reported in Table 1. Initial quantum yield (α) was decreased with the basal N fertilizer rate reduced, especially in F3. The Pmax, exceeded 31.15 μmol m-2 s-1 in F1 and F2, whilst in CK and F3, it exhibited lower values (28.47 and 22.09 μmol m-2 s-1, respectively). The similar trend was observed for dark respiration (Rd) and light saturation point (LSP), where the values for Rd registered in F1 and F2 were 1.8 times higher than in CK and F3, moreover, exceeded a 1.4-fold for LSP. Light compensation point (LCP) varied little with the different ratios of basal to top dressing N fertilizer, with a mean value of 11.2 μmol m-2 s-1. Table 2 shows the summary of ANOVA for the values of net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci),
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Fig. 3 Effects of nitrogen application rates on qP and qN of the flag leaves in naked oat.
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Fig. 2 Effects of nitrogen application rates on ΦPS II and ETR of the flag leaves in naked oat.
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and transpiration rate at 60 (jointing stage), 75 (heading stage) and 87 d after sowing (DAS, grain filling stage). There was no significant difference between F1 and CK for Pn, but significant differences in F2 and F3 at 60 DAS; at 75 DAS, Pn only significantly decreased by 6% in F3 to CK; otherwise, F2 showed the greatest value for Pn at 87 DAS. It was found that Gs was significantly reduced both in F2 and F3, but no significant
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Effects of Nitrogen Application on Chlorophyll Fluorescence Parameters and Leaf Gas Exchange in Naked Oat
difference between F1 and CK at 60 DAS; the values of Gs were higher in F1, F2 and F3 than in CK at 75 DAS; the similar trend was reported at 87 DAS. Ci was generally higher in F3 than in other treatments, and Ci was increased with the top dressing N fertilizer enhanced from 60 to 87 DAS. A linear relationship between P n and G s represents the contribution of Gs on photosynthetic CO2 assimilation. A similar relationship was observed
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in leaves of naked oat in this study (Fig. 5). It was a positive relationship (R 2=0.685) between P n and Gs, and Pn decreased as Gs reduced. Pn and Gs were lower at 87 DAS than at 60 and 75 DAS. The positive relationship (R2=0.536) between Pn and E had the similar behavior than Pn and Gs (Fig. 6). As the photosynthetic rates of the functional leaves of naked oat declined, the transpiration rates of the target leaves decreased.
Table 1 Effects of different nitrogen application on the light response parameters in naked oat Treatment CK F1 F2 F3 Mean
Pmax (μmol m-2 s-1) 28.47 36.72 37.32 22.09 31.15
α (μmol m-2 s-1/μmol m-2 s-1) 0.065 0.062 0.063 0.056 0.062
Rd (μmol m-2 s-1) 1.34 2.45 2.73 1.33 1.96
LSP (μmol m-2 s-1) 1 623.72 2 210.92 2 212.69 1 304.59 1 837.98
LCP (μmol m-2 s-1) 11.20 11.19 11.20 11.20 11.20
R2 0.999 0.999 0.999 0.995 0.998
Table 2 Effects of different nitrogen application on leaf gas exchange at the different stages in naked oat DAS
Treatments
Pn (μmol m-2 s-1)
Gs (mol m-2 s-1)
Ci (μmol mol-1)
E (mmol m-2 s-1)
CK F1 F2 F3
25.31±2.08 a 25.02±2.59 ab 23.52±2.93 b 17.56±1.31 c
0.67±0.08 a 0.66±0.06 a 0.60±0.08 b 0.58±0.08 b
278.30±11.71 b 280.13±7.52 b 277.75±10.09 b 299.89±6.24 a
12.72±0.95 a 12.28±1.15 ab 11.37±0.83 c 11.64±1.05 bc
CK F1 F2 F3
24.05±2.43 ab 24.09±1.94 ab 25.25±3.43 a 22.60±2.17 b
0.66±0.14 b 0.67±0.14 ab 0.73±0.11 ab 0.75±0.08 a
257.30±10.53 c 261.15±17.44 bc 267.52±4.58 ab 271.45±6.20 a
8.61±0.86 b 8.69±0.95 b 9.29±0.73 a 9.85±0.80 a
CK F1 F2 F3
8.41±2.38 c 7.00±3.08 c 12.27±1.15 a 10.52±2.74 b 18.80
0.15±0.12 b 0.28±0.18 a 0.37±0.19 a 0.36±0.23 a 0.54
257.49±54.25 b 306.82±56.72 a 308.00±30.52 a 315.52±27.32 a 281.78
3.53±2.04 b 5.62±3.16 a 6.88±2.29 a 6.87±2.73 a 8.95
60 (June 9)
75 (June 24)
87 (July 6)
Mean
Different letters mean significant difference at 0.05 level.
DISCUSSION N is one of the most important nutrients needed by crop growth and development. Crop yield and yield components were increased as N fertilizer was enhanced (Ma et al. 2010); in addition, it was found that leaf Chl. content was higher in high N than in low N supply (Ciompi et al. 1996; Dordas and Sioulas 2008). Since, N affected leaf photosynthesis (Shen and Li 2011), we illustrated the effect of N fertilizer application rate on the Chl. fluorescence parameters. In the present research, it was observed that Chl. fluorescence parameters showed significant differences with
the different N application levels, except the values of Fo (Figs. 1, 2 and 3). This is in agreement with most of data (e.g., Fo, Fm, Fv, Fv/Fm, and ΦPS II) reported in the literature regarding N fertilizer application (Zhang et al. 2003) to upland winter wheat. Ciompi et al. (1996) indicated the different results for sunflower. They found that Fm was significantly increased and Fv/Fm was not affected by N stress. In this study, qP was enhanced and qN decreased as N fertilizer application rate was increased. The yield of Chl. fluorescence of photosynthetic organisms is determined by two distinct quenching processes: photochemical quenching coefficient (qP) and non-photochemical
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LIN Ye-chun et al.
2168 35 Jointing stage Heading stage Filling stage
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Fig. 5 Relationship between net photosynthetic rate (P n) and stomatal conductance (Gs) to nitrogen application levels in naked oat. Data from 60, 75 and 87 DAS are presented. There were 18 replicates taken from the target leaves in each treatment. The same as below. Regression eq. is y=26.354x+4.566; R2=0.685; P<0.0001.
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CONCLUSION
14 7 0
and it was in agreement with the results reported by Huang et al. (2004). N concentration of plant was increased as N fertilizer supply increased, meanwhile, plant N concentration was positively correlated with leaf photosynthetic rate at light saturation (Pmax) to some degree (Press et al. 1993). Pmax was enhanced with top dressing N fertilizer increasing, however, being reduced as the excessive top dressing N fertilizer were supplied (Table 1). Otherwise, lower N fertilizer application decreased initial quantum yield (α) and light saturation point (LSP) in the literature reported by Yang et al. (2011). There was no effect of the ratios of basal and top dressing N fertilizer applicationon light compensation point (LCP) in this study. Wang et al. (1998) indicated that the photosynthetic capacity of winter wheat was clearly improved as the top dressing N fertilizer enhanced appropriately. A similar result was showed in this research. Moreover, it was a linear relationship between Pn and Gs (Fig. 5), and a similar correlation found with Pn and E (Fig. 6). Cechin and Fumis (2004) demonstrated that Gs of the sunflower leaf declined with the photosynthetic rate of the target leaf.
0
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6 9 E (mmol m-2 s-1)
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Fig. 6 Relationship between net photosynthetic rate (P n) and transpiration rate (E) to nitrogen application levels in naked oat. Regression eq. is y=1.690x+3.684; R2=0.536; P<0.0001.
quenching coefficient (qN). Ma et al. (2007) reported similar trend for rise both qP and ΦPS II with N fertilizer supply improving. The observed increase in qN at low N fertilizer level, and it was found that qN was in contrast in the high N fertilizer application (Zhang et al. 2010). This change may be due to the effect of N deficiency (Ciompi et al. 1996). The electron transport rate (ETR) was linearly related to oxygen evolution as an indirect measure of photosynthetic rate (Zhang et al. 2010). ETR was decreased in low N fertilizer supply,
The chlorophyll fluorescence parameters were increased as nitrogen fertilizer application rate enhanced except initial fluorescence (Fo) in naked oat. 90 kg N ha-1 was the optimum level for naked oat. 90 kg N ha-1 (50-70% as basal fertilizer and 30-50% as top dressing fertilizer) application is recommended to alleviate photodamage of photosystem and improve the photosynthetic rate in naked oat.
MATERIALS AND METHODS Growth conditions and materials The field experiment was performed in the arid and semiarid areas at the experimental station of Baicheng Academy of Agricultural Sciences, Jilin Province of China (latitude 45°37´N, longitude 122°48´E, 152 m asl). This station is within a continental monsoon climate area in the northwestern part of Jilin Province, with the average annual sunshine duration 2 919 h, average annual temperature 4.9°C. The frost-free period is 157 d, and average annual
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Effects of Nitrogen Application on Chlorophyll Fluorescence Parameters and Leaf Gas Exchange in Naked Oat
precipitation is 380 mm (the precipitation during JuneSeptember accounts for 83% of the annual precipitation). The soil type in the site was chernozem; the filed capacity of the 0-20 cm topsoil was 23.65% water by weight, and the bulk density was 1.53 g cm -3 . The soil contained 15.03 g organic matter, 0.15 g total N, 14.17 mg available phosphorus and 48.57 mg available potassium kg-1; the soil test indicated mean values of pH (soil:water=1:5) was 7.4. Naked oat (Avena nuda L. cv. Baiyan 2) was sowed in the columns in field with 180 kg ha-1 seed rate.
Experimental design Three levels of N fertilizer application, 60, 90 and 120 kg N ha-1, were used to analyze the effects of N supply rate on the Chl. fluorescence characteristics at the grain filling stage in naked oat. With 90 kg N ha-1 applied in the growing season of naked oat, there were four ratios of basal and top dressing N fertilizer: 1:0 (CK), 5:5 (F1), 7:3 (F2), and 3:7 (F3); in addition, basal and top dressing N fertilizer was supplied at sowing and jointing stage, respectively. 45 kg P2O5 and 45 kg K2O ha-1 were recommended as the basal fertilizer when sowing, moreover, 90 mm irrigation amount was applied between jointing and grain filling stage by the alternate partial root-zone irrigation (APRI) according to Lin et al. (2012).
Chlorophyll fluorescence and gas exchange measurements The Chl. fluorescence parameters of naked oat functional leaves were measured by an integrated fluorescence chamber head (LI6400XT-40 leaf chamber fluorometer, LICOR, Inc., USA) coupled with an open gas exchange system (LI6400XT, LICOR Inc., Lincoln, NE, USA) at grain filling stage. Leaves enclosed with silver paper were acclimatized to dark for 30 min at room temperature before measurements taken. The initial (F o) and the maximal (Fm) Chl. fluorescence were measured, then, the variable fluorescence (Fv) and maximal photochemical efficiency (Fv/ Fm) were calculated. Quantum yield of PS II (ΦPS II), electron transport rate (ETR), photochemical quenching coefficient (qP), and non-photochemical quenching coefficient (qN) were obtained as described by Li and Chen (2009). The photosynthesis was determined on a random sample of the youngest fully expanded leaves from each treatment using LI-6400XT at jointing (60 DAS), heading (75 DAS) and grain filling (87 DAS) stage. This instrument provided steady CO2, H2O, light, and temperature conditions in this study. Inside the leaf chamber of an infrared gas analysis system (IRGA), the programmed ambient concentration of CO2 was 400 μmol mol-1. A 6400-02 LED Source (LiCor) provided photosynthetic photon flux density (PPFD) and ambient CO2 partial pressure in the leaf chamber (Ca) to
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obtain light and CO2 response curves. Light response curves were measured with a series of intensity levels (2 800, 2 400, 1 800, 1 400, 1 000, 800, 400, 200, 100, 60, 40, 20, 10, and 0 μmol m-2 s-1) using the “Auto Light Curve Program”. For the photosynthetic measurement, leaves were allowed to equilibrate in the leaf chamber for about 20 min (MorenoSotomayor et al. 2002). Then, light was decreased by steps using the light source, after each decrease, there was at least 200 s before the next measurement started.
Statistical analysis Light response curve was fitted by a non-rectangular hyperbola, and fixed parameters of the model were estimated using an IBM SPSS 19.0 statistical package (Marshall and Biscoe 1980). ANOVA was used to test for statistical significance using Statistical Analysis Software (SAS 8.2, SAS Institute Inc., USA), moreover, means were separated using Duncan’s multiple comparison test at P=0.05. Regression and correlation coefficients were calculated by standard methods with SAS.
Acknowledgements We are grateful to the study grants from the Special Fund for Agro-Scientific Research in the Public Interest, China (nyhyzx07-009-2) and the Earmarked Fund for China Agriculture Research System (CARS-08-B-1).
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Effects of Nitrogen Application on Chlorophyll Fluorescence Parameters and Leaf Gas Exchange in Naked Oat
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December 2013
RESEARCH ARTICLE
Effects of Nitrogen Application on Chlorophyll Fluorescence Parameters and Leaf Gas Exchange in Naked Oat LIN Ye-chun1, HU Yue-gao1, REN Chang-zhong2, GUO Lai-chun2, WANG Chun-long2, JIANG Ying1, WANG Xue-jiao1, Phendukani Hlatshwayo1, 3 and ZENG Zhao-hai1 1
College of Agronomy and Biotechnology, China Agricultural University, Beijing 100193, P.R.China Baicheng Academy of Agricultural Sciences, Baicheng 137000, P.R.China 3 KZN Department of Agriculture, Nquthu 3135, Republic of South Africa 2
Abstract Naked oat (Avena nuda L.) was originated from China, where soil nitrogen (N) is low availability. The responses of chlorophyll (Chl.) fluorescence parameters and leaf gas exchange to N application were analysed in this study. After the N application rate ranged from 60 to 120 kg ha-1, variable fluorescence (Fv), the maximal fluorescence (Fm), the maximal photochemical efficiency (Fv/Fm), quantum yield (ΦPS II) of the photosynthetic system II (PS II), electron transport rate (ETR), and photochemical quenching coefficient (qP) increased with N application level, however, non-photochemical quenching coefficient (qN) decreased. Moreover, there was no difference in initial fluorescence (Fo) with further more N enhancement. The maximum net photosynthetic rate (Pmax), apparent dark respiration rate (Rd) and light saturation point (LSP) were improved with 40-56 kg N ha-1 as basal fertilizer and 24-40 kg N ha-1 as top dressing fertilizer applied at jointing stage. Initial quantum yield (α) was decreased with 24 kg N ha-1 as basal fertilizer and 56 kg N ha-1 as top dressing fertilizer. Flag-leaf net photosynthetic rate (Pn) was significantly enhanced at the jointing and heading stages with 40-56 kg N ha-1 as basal fertilizer; in addition, increased at grain filling stage of naked oat with 40-56 kg N ha-1 as top dressing fertilizer. 90 kg N ha-1 (50-70% as basal fertilizer and 30-50% as top dressing fertilizer) application is recommended to alleviate photodamage of photosystem and improve the photosynthetic rate in naked oat. Key words: Avena nuda, nitrogen fertilizer, nitrogen application, chlorophyll fluorescence, gas exchange
INTRODUCTION Despite water deficit, nitrogen (N) nutrient is the main constraint restricting yield of crops in many environmental factors (Passioura 2002). Increase in vegetative and reproductive growth and yield is dependent upon the adequate N application (Lawlor 2002). However, overuse of N fertilizer did not significantly improve the grain yield in oat (Xiao et al. 2011), contrarily that
would even lead to environmentally negative impacts such as global warming (Giles 2005; Zhang et al. 2010). Therefore, most of studies have been investigating how to maximize crop yields while reducing N fertilizer input (Baethgen et al. 1995; Ankumah et al. 2003; Iqbal et al. 2005; Caliskan et al. 2008; Li et al. 2012; Qiao et al. 2012). Furthermore, several attempts have been accomplished to assess the relationship between N supply and physiological responses in crops. Chlorophyll
Received 1 November, 2012 Accepted 15 January, 2013 LIN Ye-chun, E-mail: [email protected]; Correspondence ZENG Zhao-hai, Tel: +86-10-62733847, E-mail: [email protected]
© 2013, CAAS. All rights reserved. Published by Elsevier Ltd. doi: 10.1016/S2095-3119(13)60346-9
Effects of Nitrogen Application on Chlorophyll Fluorescence Parameters and Leaf Gas Exchange in Naked Oat
(Chl.) fluorescence parameters are usually used to evaluate the functionality of photosynthetic apparatus and the effects of environmental stresses (Baker et al. 1983; Wang et al. 2009; Shen and Li 2011). The Chl. fluorescence parameters, potential photochemical efficiency (Fv/Fo) of PS II, Fv/Fm, ΦPS II, and qP were enhanced with N fertilizer application in winter wheat and tobacco (Ma et al. 2010; Yun et al. 2010). However, Liu et al. (2008) found that Fv/Fm, ΦPS II, ETR, and qP to water stress decreased with the excessive N fertilizer supply (480 kg N ha-1) in cotton. The Chl. content and the area of leaves were clearly increased with increasing N fertilizer application; otherwise, Pn, Gs and E were significantly improved in oat (Dong et al. 2008). Jiang et al. (2011) showed that Chl. content, Pn, nitrate reductase activity, and soluble protein content of leaves were significantly raised when N fertilizer topdressing increased at jointing stage in winter wheat. Naked oat is the most widely cultivated oat in terms of growing area in the farming-pastoral ecotone of China, which is the major producer all over the world (Ren 2010). The objective of this study was to demonstrate that how N fertilizer application affect Chl. fluorescence parameters and gas exchange characteristics of naked oat with alternate partial root-zone irrigation.
RESULTS Effects of nitrogen fertilizer on Chl. fluores cence parameters Fig. 1 illustrates the effects of N fertilizer application rate on initial fluorescence (Fo), the maximal fluorescence (Fm), variable fluorescence (Fv), and the maximal photochemical efficiency (Fv/Fm). The ANOVA for Fo values showed that there were no significant differences with the different N fertilizer supply levels. Fm, Fv and Fv/Fm were significantly (P<0.05) decreased at low N supply compared to the moderate and high N supply; however, N did not induce significant differences between moderate and high N application. Quantum yield of PS II (ΦPS II), electron transport rate (ETR), photochemical quenching coefficient (qP), and non-photochemical quenching coefficient (qN) were showed in Fig. 2. Similarly, Φ PS II, ETR and qP were significantly lower at low than the ones at moderate and high N supply; moreover, no significant differences were found between moderate and high N supply. qN was significantly improved at low N fertilizer supply (Fig. 3).
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Fig. 1 Effects of different nitrogen application rates on Fo, Fm, Fv, and Fv/Fm of the flag leaves in naked oat. Different letters mean significant difference at 0.05 level. The same as below. © 2013, CAAS. All rights reserved. Published by Elsevier Ltd.
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Responses of net photosynthetic rate (P n) to photosynthetically active radiation (PAR) with different ratios of basal and top dressing nitrogen fertilizer F3 reduced the photosynthetic activity strongly at light saturation compared to CK, however, F1 and F2 in reverse (Fig. 4); the parameters fitted by a non-rectangular hyperbola are reported in Table 1. Initial quantum yield (α) was decreased with the basal N fertilizer rate reduced, especially in F3. The Pmax, exceeded 31.15 μmol m-2 s-1 in F1 and F2, whilst in CK and F3, it exhibited lower values (28.47 and 22.09 μmol m-2 s-1, respectively). The similar trend was observed for dark respiration (Rd) and light saturation point (LSP), where the values for Rd registered in F1 and F2 were 1.8 times higher than in CK and F3, moreover, exceeded a 1.4-fold for LSP. Light compensation point (LCP) varied little with the different ratios of basal to top dressing N fertilizer, with a mean value of 11.2 μmol m-2 s-1. Table 2 shows the summary of ANOVA for the values of net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci),
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Fig. 3 Effects of nitrogen application rates on qP and qN of the flag leaves in naked oat.
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Fig. 2 Effects of nitrogen application rates on ΦPS II and ETR of the flag leaves in naked oat.
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and transpiration rate at 60 (jointing stage), 75 (heading stage) and 87 d after sowing (DAS, grain filling stage). There was no significant difference between F1 and CK for Pn, but significant differences in F2 and F3 at 60 DAS; at 75 DAS, Pn only significantly decreased by 6% in F3 to CK; otherwise, F2 showed the greatest value for Pn at 87 DAS. It was found that Gs was significantly reduced both in F2 and F3, but no significant
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Effects of Nitrogen Application on Chlorophyll Fluorescence Parameters and Leaf Gas Exchange in Naked Oat
difference between F1 and CK at 60 DAS; the values of Gs were higher in F1, F2 and F3 than in CK at 75 DAS; the similar trend was reported at 87 DAS. Ci was generally higher in F3 than in other treatments, and Ci was increased with the top dressing N fertilizer enhanced from 60 to 87 DAS. A linear relationship between P n and G s represents the contribution of Gs on photosynthetic CO2 assimilation. A similar relationship was observed
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in leaves of naked oat in this study (Fig. 5). It was a positive relationship (R 2=0.685) between P n and Gs, and Pn decreased as Gs reduced. Pn and Gs were lower at 87 DAS than at 60 and 75 DAS. The positive relationship (R2=0.536) between Pn and E had the similar behavior than Pn and Gs (Fig. 6). As the photosynthetic rates of the functional leaves of naked oat declined, the transpiration rates of the target leaves decreased.
Table 1 Effects of different nitrogen application on the light response parameters in naked oat Treatment CK F1 F2 F3 Mean
Pmax (μmol m-2 s-1) 28.47 36.72 37.32 22.09 31.15
α (μmol m-2 s-1/μmol m-2 s-1) 0.065 0.062 0.063 0.056 0.062
Rd (μmol m-2 s-1) 1.34 2.45 2.73 1.33 1.96
LSP (μmol m-2 s-1) 1 623.72 2 210.92 2 212.69 1 304.59 1 837.98
LCP (μmol m-2 s-1) 11.20 11.19 11.20 11.20 11.20
R2 0.999 0.999 0.999 0.995 0.998
Table 2 Effects of different nitrogen application on leaf gas exchange at the different stages in naked oat DAS
Treatments
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Gs (mol m-2 s-1)
Ci (μmol mol-1)
E (mmol m-2 s-1)
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25.31±2.08 a 25.02±2.59 ab 23.52±2.93 b 17.56±1.31 c
0.67±0.08 a 0.66±0.06 a 0.60±0.08 b 0.58±0.08 b
278.30±11.71 b 280.13±7.52 b 277.75±10.09 b 299.89±6.24 a
12.72±0.95 a 12.28±1.15 ab 11.37±0.83 c 11.64±1.05 bc
CK F1 F2 F3
24.05±2.43 ab 24.09±1.94 ab 25.25±3.43 a 22.60±2.17 b
0.66±0.14 b 0.67±0.14 ab 0.73±0.11 ab 0.75±0.08 a
257.30±10.53 c 261.15±17.44 bc 267.52±4.58 ab 271.45±6.20 a
8.61±0.86 b 8.69±0.95 b 9.29±0.73 a 9.85±0.80 a
CK F1 F2 F3
8.41±2.38 c 7.00±3.08 c 12.27±1.15 a 10.52±2.74 b 18.80
0.15±0.12 b 0.28±0.18 a 0.37±0.19 a 0.36±0.23 a 0.54
257.49±54.25 b 306.82±56.72 a 308.00±30.52 a 315.52±27.32 a 281.78
3.53±2.04 b 5.62±3.16 a 6.88±2.29 a 6.87±2.73 a 8.95
60 (June 9)
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Mean
Different letters mean significant difference at 0.05 level.
DISCUSSION N is one of the most important nutrients needed by crop growth and development. Crop yield and yield components were increased as N fertilizer was enhanced (Ma et al. 2010); in addition, it was found that leaf Chl. content was higher in high N than in low N supply (Ciompi et al. 1996; Dordas and Sioulas 2008). Since, N affected leaf photosynthesis (Shen and Li 2011), we illustrated the effect of N fertilizer application rate on the Chl. fluorescence parameters. In the present research, it was observed that Chl. fluorescence parameters showed significant differences with
the different N application levels, except the values of Fo (Figs. 1, 2 and 3). This is in agreement with most of data (e.g., Fo, Fm, Fv, Fv/Fm, and ΦPS II) reported in the literature regarding N fertilizer application (Zhang et al. 2003) to upland winter wheat. Ciompi et al. (1996) indicated the different results for sunflower. They found that Fm was significantly increased and Fv/Fm was not affected by N stress. In this study, qP was enhanced and qN decreased as N fertilizer application rate was increased. The yield of Chl. fluorescence of photosynthetic organisms is determined by two distinct quenching processes: photochemical quenching coefficient (qP) and non-photochemical
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Fig. 5 Relationship between net photosynthetic rate (P n) and stomatal conductance (Gs) to nitrogen application levels in naked oat. Data from 60, 75 and 87 DAS are presented. There were 18 replicates taken from the target leaves in each treatment. The same as below. Regression eq. is y=26.354x+4.566; R2=0.685; P<0.0001.
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CONCLUSION
14 7 0
and it was in agreement with the results reported by Huang et al. (2004). N concentration of plant was increased as N fertilizer supply increased, meanwhile, plant N concentration was positively correlated with leaf photosynthetic rate at light saturation (Pmax) to some degree (Press et al. 1993). Pmax was enhanced with top dressing N fertilizer increasing, however, being reduced as the excessive top dressing N fertilizer were supplied (Table 1). Otherwise, lower N fertilizer application decreased initial quantum yield (α) and light saturation point (LSP) in the literature reported by Yang et al. (2011). There was no effect of the ratios of basal and top dressing N fertilizer applicationon light compensation point (LCP) in this study. Wang et al. (1998) indicated that the photosynthetic capacity of winter wheat was clearly improved as the top dressing N fertilizer enhanced appropriately. A similar result was showed in this research. Moreover, it was a linear relationship between Pn and Gs (Fig. 5), and a similar correlation found with Pn and E (Fig. 6). Cechin and Fumis (2004) demonstrated that Gs of the sunflower leaf declined with the photosynthetic rate of the target leaf.
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Fig. 6 Relationship between net photosynthetic rate (P n) and transpiration rate (E) to nitrogen application levels in naked oat. Regression eq. is y=1.690x+3.684; R2=0.536; P<0.0001.
quenching coefficient (qN). Ma et al. (2007) reported similar trend for rise both qP and ΦPS II with N fertilizer supply improving. The observed increase in qN at low N fertilizer level, and it was found that qN was in contrast in the high N fertilizer application (Zhang et al. 2010). This change may be due to the effect of N deficiency (Ciompi et al. 1996). The electron transport rate (ETR) was linearly related to oxygen evolution as an indirect measure of photosynthetic rate (Zhang et al. 2010). ETR was decreased in low N fertilizer supply,
The chlorophyll fluorescence parameters were increased as nitrogen fertilizer application rate enhanced except initial fluorescence (Fo) in naked oat. 90 kg N ha-1 was the optimum level for naked oat. 90 kg N ha-1 (50-70% as basal fertilizer and 30-50% as top dressing fertilizer) application is recommended to alleviate photodamage of photosystem and improve the photosynthetic rate in naked oat.
MATERIALS AND METHODS Growth conditions and materials The field experiment was performed in the arid and semiarid areas at the experimental station of Baicheng Academy of Agricultural Sciences, Jilin Province of China (latitude 45°37´N, longitude 122°48´E, 152 m asl). This station is within a continental monsoon climate area in the northwestern part of Jilin Province, with the average annual sunshine duration 2 919 h, average annual temperature 4.9°C. The frost-free period is 157 d, and average annual
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Effects of Nitrogen Application on Chlorophyll Fluorescence Parameters and Leaf Gas Exchange in Naked Oat
precipitation is 380 mm (the precipitation during JuneSeptember accounts for 83% of the annual precipitation). The soil type in the site was chernozem; the filed capacity of the 0-20 cm topsoil was 23.65% water by weight, and the bulk density was 1.53 g cm -3 . The soil contained 15.03 g organic matter, 0.15 g total N, 14.17 mg available phosphorus and 48.57 mg available potassium kg-1; the soil test indicated mean values of pH (soil:water=1:5) was 7.4. Naked oat (Avena nuda L. cv. Baiyan 2) was sowed in the columns in field with 180 kg ha-1 seed rate.
Experimental design Three levels of N fertilizer application, 60, 90 and 120 kg N ha-1, were used to analyze the effects of N supply rate on the Chl. fluorescence characteristics at the grain filling stage in naked oat. With 90 kg N ha-1 applied in the growing season of naked oat, there were four ratios of basal and top dressing N fertilizer: 1:0 (CK), 5:5 (F1), 7:3 (F2), and 3:7 (F3); in addition, basal and top dressing N fertilizer was supplied at sowing and jointing stage, respectively. 45 kg P2O5 and 45 kg K2O ha-1 were recommended as the basal fertilizer when sowing, moreover, 90 mm irrigation amount was applied between jointing and grain filling stage by the alternate partial root-zone irrigation (APRI) according to Lin et al. (2012).
Chlorophyll fluorescence and gas exchange measurements The Chl. fluorescence parameters of naked oat functional leaves were measured by an integrated fluorescence chamber head (LI6400XT-40 leaf chamber fluorometer, LICOR, Inc., USA) coupled with an open gas exchange system (LI6400XT, LICOR Inc., Lincoln, NE, USA) at grain filling stage. Leaves enclosed with silver paper were acclimatized to dark for 30 min at room temperature before measurements taken. The initial (F o) and the maximal (Fm) Chl. fluorescence were measured, then, the variable fluorescence (Fv) and maximal photochemical efficiency (Fv/ Fm) were calculated. Quantum yield of PS II (ΦPS II), electron transport rate (ETR), photochemical quenching coefficient (qP), and non-photochemical quenching coefficient (qN) were obtained as described by Li and Chen (2009). The photosynthesis was determined on a random sample of the youngest fully expanded leaves from each treatment using LI-6400XT at jointing (60 DAS), heading (75 DAS) and grain filling (87 DAS) stage. This instrument provided steady CO2, H2O, light, and temperature conditions in this study. Inside the leaf chamber of an infrared gas analysis system (IRGA), the programmed ambient concentration of CO2 was 400 μmol mol-1. A 6400-02 LED Source (LiCor) provided photosynthetic photon flux density (PPFD) and ambient CO2 partial pressure in the leaf chamber (Ca) to
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obtain light and CO2 response curves. Light response curves were measured with a series of intensity levels (2 800, 2 400, 1 800, 1 400, 1 000, 800, 400, 200, 100, 60, 40, 20, 10, and 0 μmol m-2 s-1) using the “Auto Light Curve Program”. For the photosynthetic measurement, leaves were allowed to equilibrate in the leaf chamber for about 20 min (MorenoSotomayor et al. 2002). Then, light was decreased by steps using the light source, after each decrease, there was at least 200 s before the next measurement started.
Statistical analysis Light response curve was fitted by a non-rectangular hyperbola, and fixed parameters of the model were estimated using an IBM SPSS 19.0 statistical package (Marshall and Biscoe 1980). ANOVA was used to test for statistical significance using Statistical Analysis Software (SAS 8.2, SAS Institute Inc., USA), moreover, means were separated using Duncan’s multiple comparison test at P=0.05. Regression and correlation coefficients were calculated by standard methods with SAS.
Acknowledgements We are grateful to the study grants from the Special Fund for Agro-Scientific Research in the Public Interest, China (nyhyzx07-009-2) and the Earmarked Fund for China Agriculture Research System (CARS-08-B-1).
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