Journal of Plant Nutrition Identification of ...

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Identification of Phosphorous Efficient Germplasm in Oilseed Rape Hai-Yan Duan

a b b

, Lei Shi

a b

b

, Xiang-Sheng Ye ,

Yun-Hua Wang & Fang-Sen Xu

a b

a

National Key Laboratory of Crop Genetic Improvement , Huazhong Agricultural University , Wuhan, China b

College of Resources and Environment , Huazhong Agricultural University , Wuhan, China Published online: 06 Jun 2009.

To cite this article: Hai-Yan Duan , Lei Shi , Xiang-Sheng Ye , Yun-Hua Wang & FangSen Xu (2009) Identification of Phosphorous Efficient Germplasm in Oilseed Rape, Journal of Plant Nutrition, 32:7, 1148-1163, DOI: 10.1080/01904160902943171 To link to this article: http://dx.doi.org/10.1080/01904160902943171

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Journal of Plant Nutrition, 32: 1148–1163, 2009 Copyright © Taylor & Francis Group, LLC ISSN: 0190-4167 print / 1532-4087 online DOI: 10.1080/01904160902943171


Identification of Phosphorous Efficient Germplasm in Oilseed Rape Hai-Yan Duan,1,2 Lei Shi,1,2 Xiang-Sheng Ye,2 Yun-Hua Wang,2 and Fang-Sen Xu1,2 1

National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan, China 2 College of Resources and Environment, Huazhong Agricultural University, Wuhan, China

ABSTRACT Plant species and genotypes within one species may significantly differ in phosphorus (P) uptake and utilization when they suffer from P starvation. The objective of this research was to screen P-efficient germplasm of oilseed rape (Brassica napus L.) and analyze the possible mechanism responsible for P efficiency by two-steps screening experiments and validation of P efficiency. Phosphorus efficiency coefficient at seedling stage, namely, ratio of shoot dry weight under low P to that under adequate P (PECS) of 194 oilseed rape cultivars varied from 0.050 to 0.62 and was significantly related with shoot dry weight under low P level (r = 0.859∗∗ , P < 0.01). Oilseed rape cultivar ‘Eyou Changjia’ presented the highest P efficiency coefficient in each growth stage and had the highest seed yield at low P, whereas oilseed rape cultivar ‘B104-2’ was the most sensitive to low P stress among the 12 candidate cultivars obtained from the two-steps screening experiments. Under low P condition in validation experiments of soil and solution cultures, ‘Eyou Changjia’ could produce much more dry matter and acquire more P than ‘B104-2.’ Moreover, P efficient coefficient obtained from the pot experiment was comparable to those from the field experiment. This might be attributed to high P uptake efficiency for ‘Eyou Changjia’ when it suffered from low-P stress. Comparison of results from the hydroponics with those from the pot and field experiments led to the conclusion that the P uptake efficiency in the hydroponics is highly related to that in soil culture conditions. These results show that there are large genotypic differences in response to phosphorus deficiency in oilseed rape germplasm (Brassica napus L.) and ‘Eyou Changjia’ is P-efficient and ‘B104-2’ is P-inefficient. By comparing these

Received 20 January 2008; accepted 12 October 2008. Address for correspondence to Feng-sen Xu, National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan 430070, China. E-mail: [email protected] 1148

Identification of P-Efficient Rapeseed Cultivar

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results further, the mechanism responsible for P efficiency was suggested to be mainly due to high P uptake efficiency by forming larger root system, and improving the ability of mobilizing and acquiring soil P in P-efficient oilseed rape under the condition of P starvation.


Keywords: Brassica napus L., germplasm, phosphorous efficiency, PEC, P acquisition

INTRODUCTION Low available phosphorus (P) in soils is a primary constraint for plant growth because it is readily fixed by soil constitutes, such as Fe and Al oxides, and soil organic matter (Marschner et al., 1987; Barber, 1995). Application of P fertilizers has become an important way to maintain and improve crop yield in agricultural production in the world. However, only 10–20% of the applied P can be directly used by crops during the first season and the use of applied phosphate fertilizers by subsequent crops is even low (Bolland and Gilkes, 1998). This large amount of soil phosphate contributed up to 50% for surface water P pollution (Lu, 1998; Li et al., 1998). In addition, intensive P fertilizer use will also be restricted in future by limited, nonrenewable high-grade P ore resources (Cathcart, 1980). Therefore, genetic improvement of P nutrition trait in crops would be more economical and sustainable approach than those which relies on chemical P fertilizers alone (Vance et al., 2003; Yan, 2005). Plant species, as well as genotypes within a species, express significant difference in adaptability to low P stress. Previous studies showed that P uptake efficiency may be achieved through efficient root morphology (Bates and Lynch, 2000; Gitte et al., 2003) and root architecture (Liao et al., 2001; Williamson et al., 2001; He et al., 2003), high affinity phosphate transporters (Dong et al., 1999; Hamburger et al., 2002; Yi et al., 2005), specific P-mobilizing root exudates (Richardson et al., 2001; Dong et al., 2004), reduced tissue P requirement (Halsted and Lynch, 1996; Ciarelli et al., 1998), and efficient P remobilization from senescent organs to growing organs or nonproductive tissues to productive tissues (Smith et al., 1990; Snapp and Lynch, 1996; Frank et al., 2003). Föhse et al. (1991) reported that oilseed rape, cabbage and spinach have high P uptake efficiency. Further study showed that the high P efficiency of cabbage was attributed to a combination of high P mobilization efficiency through exudation of carboxylates and high P use efficiency (Dechassa et al., 2003). Both oilseed rape and cabbage (Brassica oleraceae L.) belong to the Crucifereae family. However, few studies were focused on the genotypic variation in P efficiency among Brassica species. Oilseed rape (Brassica napus L.) is one of the main oil crops in China and is cultivated up to more than six million hectare each year, which is mainly distributed in the east, center, and southwest of China. The soil Olsen-P concentration of about 66.7 million hectare in these regions is less than 10 mg


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kg−1 . In addition, 50%–75% of them showed an Olsen-P concentration below 5 mg P kg−1 (Li et al., 1998). An application of P fertilizer is necessary to maintain seed yield of oilseed rape in these regions. Moreover, low P uptake rate and limited high-grade P ore reserves in China will threat sustainable oilseed rape production in China. The aim of this study was to identify and evaluate P efficient germplasm of oilseed rape (Brassica napus L.) for a long-term goal to elucidate the physiological and molecular mechanisms on high P efficiency in oilseed rape and breeding P-efficient oilseed rape varieties.

MATERIALS AND METHODS Plant Materials Original 194 representative oilseed rape cultivars (Brassica napus L.) were selected from germplasm resource pools at Rapeseed Genetic and Breeding Institute, Huazhong Agricultural University and Oil Crop Research Institute, Agricultural Academy of China, respectively. The screened cultivars with different P efficiency were preserved in our lab by self-pollination for further study.

Germplasm Screening for P Efficiency Phosphorus-efficient germplasms were identified by a two-step screening method under pot culture conditions (Xu et al., 2002). Firstly, biomass production of all selected cultivars was investigated at seedling stage with pot culture at low and adequate P levels, respectively. The ratio of shoot dry weight at low P level to that at adequate P level was defined as P efficiency coefficient at seedling stage (PECS). The cultivars with high, middle and low PECS were selected for screening over whole growth period. Then, these selected cultivars were grown at low P and adequate P levels to harvest seed yield, and P efficiency coefficient at maturity stage (PECM), namely, the ratio of seed yield at low P level to that at adequate P level, was calculated. Finally, P-efficient and P-inefficient cultivars were identified according to the value of the PECS and the PECM combined with its absolute seed yield under low P level. Short-Term Pot Experiment for Seedling Screening Brown-yellow soil was used in the experiment. The soil properties were as follows: pH (1:1 H 2 O) 6.05, organic matter 2.3 g kg−1 , total nitrogen (N) 0.28 g kg−1 , total P 0.193 g kg−1 , Alkali-N 28.8 mg kg−1 , Olsen-P 1.31 mg kg−1 , and



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ammonium acetate (NH 4 OAc)-extracted potassium (K) 93.2 mg kg−1 . Basal fertilizer was applied and mixed thoroughly before sowing according to the rate (g kg−1 soil): N 0.2, K 0.2, magnesium (Mg) 0.025, and Arnon microelements solution (1000 ×) 1 mL kg−1 soil. Each pot was filled with 1.0 kg soil. All of the 194 cultivars were grown in pots at low P level (0.01 g P kg−1 soil) and adequate P level (0.1 g P kg−1 soil) with three replicates, respectively. Six germinated seeds were sown in each pot. 14 d later, three uniform seedlings were remained. Pots were watered with deionized water each day according to the pot weight controlling. The shoots were harvested after 32 d of growth. After harvesting samples were first treated at 105◦ C for 30 min and then dried to constant weight at 65◦ C. The PECS was calculated to evaluate the P efficiency at seedling stage.

Long-Term Pot Experiment for Whole Growth Period (Seed Yield) Screening Soil kind and rate of basal fertilizers were same as above short-term pot experiment. The experiment was designed with two P levels, low P level (−P: 0.02 g P kg−1 soil) and adequate P level (+P: 0.2 g P kg−1 soil), with five replicates. Each pot was filled with 5.0 kg soil. In addition, 0.20 g N per pot was top-dressed at budding stage. Ten germinated uniform seeds were sown in each pot. Two plants per pot were sampled at seedling, bolting, flowering and silique stages, respectively. The last two plants were remained to harvest seed yield at maturity stage and PECM was calculated.

Confirmation of P Efficiency for Candidate Cultivars Pot Culture and Field Trial Three oilseed rape cultivars, ‘Eyou Changjia’, ‘Chuanyou 11’, and ‘B104-2’ with different P-efficiency from the two-steps screening were selected in the experiments. The experiment design for pot culture was the same as described in above long-term pot experiment for the whole growth period screening. For the field trial located at Agricultural Experimental Station of Huazhong Agricultural University, the soil was brown-yellow soil with Olsen-P 6.57 mg P kg−1 . Two treatments, no P (−P) and 43 g P (+P) applied at a plot with 7.0 m2 , were designed with four replicates. A total of 24 plots were conducted with randomized complete block design. The application amount of N, K, and boron (B) fertilizers were calculated according to the following nutrient rates: 180 kg N ha−1 , 83 kg K ha−1 , and 15 kg boric acid (H 3 BO 3 ) ha−1 . The basal fertilizers were applied before transplanting with 60% of N as urea, 100% of P as calcium superphosphate, 100% of K as potassium chloride (KCl) and 100%

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of B as boric acid. The rest N fertilizer was top-dressed at budding stage. After harvesting seed yield was determined and PECM was calculated.


Solution Culture Experiment Solution culture experiment was conducted in a greenhouse with temperature 22 ± 4◦ C, photoperiod 16 hrs/8 hrs (light/dark), light intensity 260 µmol m−2 sec−1 . The nutrient solution contained (mmol L−1 ): ammonium nitrate (NH 4 NO 3 ) 3.0; sodium phosphate (NaH 2 PO 4 ·H 2 O) 0.73; Na 2 HPO 4 ·12 H 2 O 0.28; potassium chloride (KCl) 2.0; calcium chloride (CaCl 2 ) 3.2; magnesium sulfate (MgSO 4 ·7H 2 O) 2.0 and Arnon microelements solution. There were two P treatments, low P (5 µmol L−1 ), and adequate P (1 mmol L−1 ), with four replicates. Seeds of P-efficient cultivar ‘Eyou Changjia,’ and P-inefficient cultivar ‘B104-2’ were soaked with deionized water overnight. Then all seeds were germinated for two d in paper towel moistened with deionized water. Then, uniform seedlings were grown in 1.2 L pot with 1/4 strength nutrient solution for the first week, and replaced with 1/2 strength solution for the second week and full strength solution thereafter. The nutrition solution was changed each week and the pH in the nutrition solution was adjusted to 6.0 ± 0.2 during the plant growth period. Shoots and roots were sampled and washed with deionized water at 21 d after transplanting, and then were dried to constant weight at 65◦ C after treated at 105◦ C for 30 min. The dried samples were grounded to fine powder and then digested with concentrated sulfuric acid–perchloric acid (H 2 SO 4 -HclO 4 ). The P concentration in the digested solution was measured by the molybdate blue method (Murphy and Riley, 1962).

Statistical Analysis Data were tested for ANOVA by SAS software (SAS Institute INC., Cary, NC, USA). Correlation between PECS and shoot dry weight was analyzed by regression analysis.

RESULTS Germplasm Screening of P Efficiency Shoot dry weight of 194 oilseed rape cultivars with sufficient P supply ranged from 0.35 to 1.87 g plant−1 at seedling stage. However, it decreased dramatically under P deficiency, which varied from 0.09 to 0.74 g plant−1 . A highly significant correlation (r = 0.859, P < 0.01) was determined between PECS and shoot dry weight at low P level. However, no significant relationship


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60

Frequency


50 40 30 20 10 0 0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

PECS

Figure 1. Frequency distribution of PECS of 194 oilseed rape cultivars of the seedling screening experiment. PECS indicates phosphorus efficiency coefficient at seedling stage as ratio of shoot dry weight at low P to that at adequate P at seedling stage.

between PECS and shoot dry weight at high P level was found. Using PECS ranged from 0.050 to 0.62 among the 194 oilseed rape cultivars as a parameter to estimate the adaptability of various cultivars to low P stress, most of the cultivars were fell into middle and a few showed significantly high PECS or low PECS (Figure 1). According to the PECS and the shoot dry weight under low P level, twelve representative cultivars, Nos. ‘97009’, ‘97024’, ‘97028’, ‘97029’, ‘97030’, ‘97072’, ‘97073’, ‘97076’, ‘97081’, ‘97105’, ‘97121’, and ‘97142’ were selected for the whole-growth-period screening by a long-term pot experiment. The PECS as well as dry weight of these cultivars at low and adequate P were shown in Table 1. Cv. ‘97081’ (‘Eyou Changjia’) had the highest shoot dry weight at low P and higher PECS, and cv. ‘97009’ (‘B1042’) showed the lowest PECS and lower shoot dry weight among the twelve candidate cultivars. Table 1 shows that the seed yield of the twelve cultivars ranged from 0.78 to 1.69 g plant−1 at low P, and the PECM ranged from 0.11 to 0.31. There was significantly positive relationship between PECM and the seed yield under low P level (r = 0.771, P < 0.01). However, no significant correlation between shoot dry weights obtained in seedling screening and seed yield as well as PECM in the whole-growth-period screening was found. Compared with PECS, ‘Eyou Changjia’ (cv. ‘97081’) had, similarly, the highest seed yield at low P and highest PECM, while ‘B104-2’ (cv. ‘97009’) showed the lowest seed yield under low P condition as well as the lowest PECM among the twelve cultivars. In the long-term pot experiment of whole-growth-period screening, shoot dry weight at seedling, bolting, flowering, silique and maturity stage for six

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Table 1 Shoot dry weight of short-term pot experiment for seedling screening and seed yield of long-term pot experiment for whole growth period at low P and adequate P and the corresponding phosphorus efficiency coefficient of twelve representative cultivars of the field screening


Shoot dry weight (g plant−1 ) Cultivar number 97009 97024 97028 97029 97030 97072 97073 97076 97081 97105 97121 97142

Seed yield (g plant−1 )

−P

+P

PECS −P/+P

−P

+P

PECM −P/+P

0.15f 0.63c 0.61cd 0.64c 0.66c 0.67bc 0.62c 0.70b 0.74a 0.14f 0.22e 0.57d

1.63a 1.37b 1.28c 1.32bc 1.38b 1.31bc 1.12e 1.40b 1.40b 1.01f 1.21d 1.12e

0.09 0.46 0.48 0.49 0.48 0.51 0.55 0.50 0.53 0.14 0.18 0.51

0.78f 0.99d 1.27b 1.06cd 1.10c 1.09c 1.32b 1.16c 1.69a 1.48ab 0.89e 1.16c

7.39c 4.95h 8.95a 7.90b 7.66b 6.12f 6.56e 6.88d 5.55g 6.76d 4.80h 6.53e

0.11 0.20 0.14 0.14 0.14 0.18 0.20 0.17 0.31 0.22 0.19 0.18

The value indicates mean of three replicates per treatment and different letters indicate significant difference at 5% level among the twelve cultivars in the same treatment. PECS indicates phosphorus efficiency coefficient at seedling stage, namely, ratio of shoot dry weight at low P to that at adequate P at seedling stage. PECM indicates phosphorus efficiency coefficient at maturity stage, namely, ratio of seed yield at low P to that at adequate P.

of the twelve cultivars was determined to calculate the P efficiency coefficient (PEC) for investigating the response of different growth stages to low-P stress. The PEC at seedling stage was the highest among the five stages for all of the six cultivars, and then it decreased with plant growth and dropped to the lowest after flowering (Figure 2). As shown in Figure 2, ‘Eyou Changjia’ remained the highest PECs throughout the growth period, and showed the highest PECM among the six cultivars. On the contrary, ‘B104-2’ had the lowest PECs and PECM. In addition, some cultivars showed higher PEC at seedling stage, but it rapidly decreased with the growing stages and produced lower PECM. Such as, PEC of ‘Chuanyou 11’ (cv. ‘97009’) at seedling stage was No. 3 among the six cultivars; however, it decreased to No. 5 at maturity stage. On the other hand, PEC of ‘Quinta’ (cv. ‘97105’) was No. 5 at seedling stage, but it increased to No. 2 at maturity stage. According to the results of the two-steps screening, ‘Eyou Changjia’ was defined as P-efficient germplasm, and ‘B104-2’ was a P-inefficient germplasm.


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1.0 B104-2

0.9

Chuanyou 9

0.8

Chuanyou 11

0.7

Huayou 3

PEC


0.6

Eyou Changjia 0.5 Quinta 0.4 0.3 0.2 0.1 0.0 Seedling

Bolting

Flowering

Siliquing

Maturity

Seed Yield

Growth period

Figure 2. PEC at different growth periods of six representative cultivars. PEC indicates the ratio of shoot dry weight under low P to that under adequate P level at seedling, bolting, flowering, silique stages, respectively, and the ratio of seed yield at low P to that at adequate P (PECM).

Both showed stable response to low-P stress in different growth stages and were used to evaluate the P efficiency in this study further.

Confirmation of P-Efficient Germplasm To further test the responses of P-efficient ‘Eyou Changjia’ to P starvation, both pot and field experiments were conducted, together with middle-efficient cultivar ‘Chuanyou 11’ and P-inefficient cultivar ‘B104-2,’ respectively. Low-P stress significantly inhibited biomass production and seed yield of the three cultivars under pot culture conditions (Figures 3 and 4). The shoot dry weight of three cultivars under low P condition accounted for 41.7% to 76.3% of that under the adequate P condition at seedling stage. The PECS of ‘Eyou Changjia’ and ‘B104-2’ were 0.763 and 0.417, respectively (Figure 3). Seed yield under low P was only 16.0% to 34.8% of that under adequate P condition, and the PECM of ‘Eyou Changjia’ and ‘B104-2’ were 0.348 and 0.160, respectively (Figure 4). Both PECS and PECM of ‘Chuanyou 11’ were in middle of ‘Eyou Changjia’ and ‘B104-2’ (Figures 3 and 4). In the field trial, the response of the selected three cultivars to P deficiency was identical to the results under pot culture (Figure 5). There was no significant

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adequate P

PECS

0.90 0.80

0.35 0.77

0.30

0.70 0.60

0.55

0.50

0.20 0.40

0.42

PECS

0.25

0.15 0.30 0.10

0.20

0.05

0.10 0.00

0.00 B104-2

Chuanyou 11

Eyou Changjia

Cultivars

Figure 3. Effects of P nutrition on shoot dry weight of oilseed rape cultivars with different P efficiency at seedling stage in pot experiment. Left axis and column diagram indicate shoot dry weight in seedling period (g plant−1 ), and right axis and linear diagram indicate PECS (−P/+P). Value indicates mean of three replicates.

8.0

low P

adequate P

PECM

7.0

0.4 0.4

-1

6.0

0.3

5.0

0.3 0.24

4.0 3.0

0.2

PECM

0.35 Seed yield (g plant )


-1

Shoot biomass in seedling period (g plant )

0.40

0.2

0.16

2.0

0.1

1.0

0.1

0.0

0.0 B104-2

Chuanyou 11 Cultivars

Eyou Changjia

Figure 4. Effects of P nutrition on seed yield of oilseed rape cultivars with different P efficiency in pot experiment. Left axis and column diagram indicate seed yield (g plant−1 ), and right axis and linear diagram indicate PECM (−P/+P). Value indicates mean of three replicates.

Identification of P-Efficient Rapeseed Cultivar 20.0

low P

adequate P

PECM

1157 0.4

18.0 0.3 16.0 0.3

12.0

0.2

10.0

6.0

0.2

0.17

8.0 0.13

PECM


-1

Seed yield (g plant )

0.30 14.0

0.1

4.0 0.1 2.0 0.0

0.0 B104-2

Chuanyou 11

Eyou Changjia

Cultivars

Figure 5. Effects of P nutrition on seed yield of oilseed rape cultivars with different P efficiency under field trial. Left axis and column diagram indicate the seed yield (g plant−1 ). Values are means ± SD of three replicates; Right axis and linear diagram indicate PECM (−P/+P).

difference in seed yield among the three cultivars under adequate P condition. However, seed yield of all cultivars decreased dramatically in the absence of P fertilizer and ‘B104-2’ showed a faster decrease than ‘Eyou Changjia.’ The PECM of the P-efficient cultivar ‘Eyou Changjia’ was 0.301, and that of the P-inefficient cultivar ‘B104-2’ was only 0.128. ‘Chuanyou11’ was a middle-efficient genotype with PECM of 0.171. Results from the pot culture and field trial further indicated that ‘Eyou Changjia’ was a P-efficient cultivar and ‘B104-2’ a P-inefficient cultivar.

P Accumulation and Utilization When suffering from low-P stress, plants clearly exhibited growth retardation, i.e., cotyledon became darker green and fell out early, euphylla grew slowly, leaf expansion and number of leaves reduced, taproot became brown, and lateral roots stopped growing. When the P-efficient cultivar ‘Eyou Changjia’ came into the second euphylla, the P-inefficient cultivar ‘B104-2’ had only one small leaf. Root length and number of ‘B104-2’ were less than ‘Eyou Changjia.’ Phosphorus deficiency resulted in increase of root/shoot ratio. Under P deficient condition, ‘Eyou Changjia’ had higher dry weight of shoot and root and root/shoot ratio than ‘B104-2’ (Table 2). Root/shoot ratio of ‘Eyou Changjia’

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Table 2 Shoot and root dry weight and root/shoot ratio of oilseed rape cultivars with different P efficiencies grown with nutrient solution Dry weight (g pot−1 )


Treatment −P +P

Cultivar

Shoot

Root

Total

Root/shoot ratio

‘B104-2’ ‘Eyou Changjia’ ‘B104-2’ ‘Eyou Changjia’

0.325b 0.423a 2.870a 2.727a

0.102b 0.153a 0.748a 0.737a

0.427b 0.576a 3.618a 3.464a

0.31b 0.36a 0.26a 0.27a

The value was mean of three replicates per treatment and the different letters show significant difference at 5% level between the two cultivars in the same treatment.

varied from 0.27 under adequate P to 0.36 under low P, which increased 33.3%. Whereas, root/shoot ratio of ‘B104-2’ was 0.31 at low P and only increased 19.2% compared with that at adequate P as shown in Table 2. However, there was no significant difference in the three parameters between ‘Eyou Changjia’ and ‘B104-2’ under adequate P condition (Table 2). The results showed that P-efficient cultivar ‘Eyou Changjia’ had a larger root system at low P condition than P-inefficient cultivar ‘B104-2.’ Phosphorus concentration and P accumulation of ‘Eyou Changjia’ were significantly higher than ‘B104-2’ at low P level (Table 3). To some extent, total P accumulation in plant indicated the ability of P acquisition from surroundings, while shoot-root ratio of P accumulation implied the distribution of P in the whole plant. No significant change in ratio of P accumulation in shoot to root Table 3 P concentration and accumulation in shoot and root of oilseed rape cultivars with different P efficiency with nutrition solution P concentration (%) Treatment −P +P

P accumulation (mg pot−1 )

Cultivar

Shoot

Root

Shoot

Root

Total

shoot/root

‘B104-2’ ‘Eyou Changjia’ ‘B104-2’ ‘Eyou Changjia’

0.022b 0.053a 0.147a 0.164a

0.038b 0.055a 0.206b 0.230a

0.072b 0.225a 4.219b 4.472a

0.038b 0.085a 1.541b 1.695a

0.110b 0.310a 5.760a 6.167a

1.87b 2.66a 2.74a 2.69a

The value indicates mean of three replicates per treatment and the different letters show significant difference at 5% level between the two cultivars in the same treatment.


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for ‘Eyou Changjia’ was found from adequate P to low P supply. However, the ratio of ‘B104-2’ was decreased from 2.74 at adequate P to 1.87 at low P level. These suggested that ‘Eyou Changjia’ had stronger ability in uptake and transport of P when it suffered from low-P stress.


DISCUSSION The fact that PECS of the 194 oilseed rape cultivars varied from 0.050 to 0.62 in seedling stage (Figure 1) indicated a wide genotype difference in response to low P in oilseed rape germplasms (Brassica napus L.). P-efficient cultivar ‘Eyou Changjia’ selected from the seedling screening experiment, showed higher PECS and PECM in the screening experiment of whole growth period both in pot and field trials. This indicates that the two-step screening method and the parameters of PEC combined with seed yield under low P can be used for screening P-efficient germplasms in oilseed rape. The PECS of the tested cultivars in the seedling screening experiment (Figure 1) was lower than those obtained from the whole growth period experiment (Figure 2). This is attributed to the increase in P supply to the low P treatment from 4.3 mg kg−1 to 8.6 mg kg−1 . Twelve representative oilseed rape genotypes were selected to investigate the PEC correlation between short-term pot experiment for seedling screening and long-term pot experiment for whole growth period. The change in P efficiency of various genotypes was not consistent with developing growth stages (Table 1; Figure 2). The results indicated that the mechanism of P efficiency in oilseed rape was a complex, which could be involved in multi-genes to regulate the adaptability to low-P stress in oilseed rape. P-efficient cultivar, ‘Eyou Changjia’, showed high P efficiency in the whole growth period could attribute to its more P-efficient alleles, and P-inefficient cultivar ‘B104-2’ was failed. The P-efficient alleles could express and improve the adaptability in different growth stages. Thus, stable P-efficient germplasm resulting in P efficiency during the whole growth period should be more valuable for studying the physiological and molecular mechanisms of P efficiency. However, these genotypic differences of various oilseed rapes in response to low P stress were obtained and confirmed based on the used soil with mainly inorganic Ca phosphates. Whether it has the same adaptability responses in soils with dominating Al/Fe phosphates or organic P needs to be investigated further. In general, nutrient efficiency relates to uptake, transport, and utilization within plants (Marschner, 1995). P use efficiency denoting the ability of plants to utilize absorbed P for the production of total biomass was measured by the dry matter (dm) production per unit P absorbed (Blair, 1993). Based on the conventional definition for P use efficiency, ‘Eyou Changjia’ and ‘B104-2’ produced 0.56 g and 0.63 g d.m. per mg P absorbed at adequate P supply level, and 1.86 g and 3.88 g d.m. per mg P absorbed at low P level, respectively


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(calculated according to data of Tables 2 and 3). In this case, ‘Eyou Changjia’ had lower P use efficiency than ‘B104-2’ at low P level. This suggests that P use efficiency could not be an important mechanism of P efficiency for ‘Eyou Changjia.’ Tables 2 and 3 show that P-efficient cultivar ‘Eyou Changjia’ could produce much more dry matter and acquire more P as compared with the Pinefficient ‘B104-2’ under P deficient condition. Therefore, high P efficiency of ‘Eyou Changjia’ might be attributed to its high P uptake efficiency. Nutrient distribution in natural soils is heterogeneous over time and space. For such nutrients with limited mobility as P, distribution is often stratified with higher concentrations in the upper soil layer in association with organic matter or by forming sparingly soluble Ca-P or Al-P compounds. So, the adaptability changes of root space architecture to low-P condition, namely, an increase in proportion of root system in the upper soil layer with an adequate P concentration enables the plant to exploit more P (Lynch, 1995). In this study, there was no significant difference in PEC values between pot and field experiments, indicating that similar efficiency mechanisms were involved in field and pot grown plants. However, considering the limited benefit of the root architecture changes in pots with homogenous soil, the possible mechanisms for P efficiency might be mainly attributed to the acquiring efficiency by forming bigger root system and improving the ability of mobilizing soil P. The higher root dry weight and root/shoot ratio of ‘Eyou Changjia’ under low-P conditions (Table 2) could be one of the indirect proofs. Moreover, the PEC for ‘B104-2’ and ‘Eyou Changjia’ in the solution experiment were 0.118 and 0.166, as calculated from the data in Table 2. This difference between the two genotypes was much smaller than that for soil-grown plants under field and pot experimental conditions (Table 1; and Figures 2, 3, 4, and 5). This indicated that the main mechanisms responsible for P efficiency of oilseed rape plants are related to the soil culture conditions. In addition, total P uptake of the P-inefficient cultivar ‘B104-2’ in the solution experiment was 35.5% of P uptake of the P-efficient cultivar ‘Eyou Changjia’ under low P (Table 3), whereas the root dry weight was 66.6% (Table 2). This result also showed that there are differences in uptake efficiency between the two genotypes. According to the total P supply of 0.576 mg pot−1 with nutrition solution, the P-efficient cultivar ‘Eyou Changjia’ absorbed 0.310 mg pot−1 (Table 3) and this accounted for 53.8% of the total P supply. On the contrary, ‘B104-2’ absorbed only 0.110 mg pot−1 (Table 3) and this only accounted for 19.1% of the total P. This suggests that the efficient genotype could possess a high affinity uptake system and take up most of P, whereas the inefficient one failed. ‘Eyou Changjia’ could absorb more P when suffered P deficiency, which resulted in higher proportion of P allocated in shoot compared with ‘B104-2’ (Table 3). Low P nutrition may induce release of root exudates including carboxylates, phosphatases, and other compounds that can mobilize P from bound P pools. Most of the fixed P is unavailable to plants in short term (Vance et al., 2003). Dong et al. (2004) showed that soybean genotypes contrasting



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in P-efficiency differ in the type and quantity of carboxylates excreted from the roots under P deficient conditions, and such difference may explain the greater P uptake in P-efficient genotypes. Hoffland et al. (1992) reported that phosphate-starved oilseed rape could secrete citric and malate to increase the ability to mobilize soil P. Preliminary data showed that the carboxylates detected in the exudates of the two cultivars increased significantly at low P (data not shown). Compared with adequate P, total organic acid content increased up to 5.1 and 7.2 times for ‘B104-2’ and ‘Eyou Changjia,’ respectively, under low P. Thus, further studies are necessary to focus on analyzing P uptake kinetics of oilseed rape genotypes which significantly differ in P efficiency. In addition, the types and quantity of carboxylates excreted from root under low-P conditions have to be compared between different genotypes. This may provide a base for elucidating the physiological mechanisms responsible for P efficiency and even for breeding P-efficent oilseed rape varieties. ACKNOWLEDGMENTS This work was supported by grants from the National Basic Research and Development Program (2005CB120905), National 863 High Technology Program (2006AA10A112), and Specialized Research Fund for the Doctoral Program of Higher Education (20050504009), China. The authors are grateful to Dr. Feng Yan (Justus Liebig University, Giessen, Germany) for his valuable comments and the correction of manuscript. Haiyan Duan and Lei Shi contributed equally to this work. REFERENCES Barber, S. A. 1995. Soil Nutrient Bioavailability. A Mechanistic Approach. New York: John Wiley & Sons Inc. Bates, T. R., and J. P. Lynch. 2000. The efficiency of Arabidopsis thaliana (Brassicaceae) root hairs in phosphorus acquisition. American Journal of Botany 87: 964–970. Blair, G. 1993. Nutrient efficiency-what do we really mean? In: Genetic Aspects of Plant Mineral Nutrition, eds. P. J. Randall, E. Delhaize, R. A. Richards, and R. Munns, pp. 204–213. Dordrecht, The Netherlands: Kluwer Academic Publishers. Bolland, M. A., and R. J. Gilkes. 1998. The chemistry and agronomic effectiveness of phosphorus fertilizers. In: Nutrient Use in Crop Production, ed. Z. Rengel, pp. 139–163. New York: The Haworth Press. Cathcart, J. B. 1980. World phosphate reserves and resources. In: The Role of P in Agriculture, eds. F. E. Khasawneh, E. C. Sample, and E. J. Kamprath, pp. 1–18. Madison, WI: American Society of Agronomy, Crop Science Society of America, Soil Science Society of America.


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Ciarelli, D. M., A. C. Furlani, A. R. Dechen, and M. Lima. 1998. Genetic variation among maize genotypes for phosphorus-uptake and phosphorus-use efficiency in nutrient solution. Journal of Plant Nutrition 21: 2219–2229. Dechassa, N., M. K. Schenk, N. Claassen, and B. Steingrobe. 2003. Phosphorous efficiency of cabbage (Brassica oleraceae L. var. capitata), carrot (Daucus carota L.), and potato (Solanum tuberosum L.). Plant and Soil 250: 215–224. Dong, D., X. Peng, and X. Yan. 2004. Organic acid exudation induced by phosphorous deficiency and/or aluminum toxicity in two contrasting soybean genotypes. Physiologia Plantarum 122: 190–199. Dong, B., P. R. Ryan, Z. Rengel, and E. Delhaize. 1999. Phosphate uptake in Arabidopsis thaliana: dependence of uptake on the expression of transporter genes and internal phosphate concentrations. Plant Cell Environment 22: 1455–1461. Föhse, D., N. Claassen, and A. Jungk. 1991. Phosphorus efficiency of plants. II. Significance of root radius, root hairs, and cation-anion balance for phosphorus influx in seven plant species. Plant and Soil 132: 261–272. Frank, W. S., R. M. Stephen, L. R. Anne, and G. Donna. 2003. Phosphate transport in plants. Plant and Soil 248: 71–83. Gitte, K., G. Tara, and N. E. Nielsen. 2003. Variation in phosphorus uptake efficiency by genotypes of cowpea (Vigna unguiculata) due to differences in root and root hair length and induced rhizosphere processes. Plant and Soil 251: 83–91. Halsted, M., and J. P. Lynch. 1996. Phosphorous responses of C 3 and C 4 species. Journal of Experimental Botany 47: 497–505. Hamburger, D., E. Rezzonico, J. M. Petétot, C. Somerville, and Y. Poirier. 2002. Identification and characterization of the Arabidopsis PHO1 gene involved in phosphate loading to the xylem. Plant Cell 14: 889–902. He, Y., H. Liao, and X. L. Yan. 2003. Localized supply of phosphorus induces root morphological and architectural changes of rice in split and stratified soil cultures. Plant and Soil 248: 247–256. Hoffland, E., B. R. Van, J. Nelemans, and G. Findenegg. 1992. Biosynthesis and root exudation of citric and malic acids in phosphate-starved rape plants. New Phytologist 122: 675–680. Li, Q., Z. Zhu, and T. Yu. 1998. Fertilizer Problems Existed in the Persistent Development of Agriculture in China. Nanchang, China: Jiangxi Science and Technology Press. Liao, H., G. Rubio, X. Yan, A. Cao, K. M. Brown, and J. P. Lynch. 2001. Effect of phosphorus availability on basal root shallowness in common bean. Plant and Soil 232: 69–79. Lu, R. 1998. Phosphorus in Soil and Phosphate Fertilization. Beijing, China: Chemical Industry Press. Lynch, J. P. 1995. Root architecture and plant productivity. Plant Physiology 109: 7–13.



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Marschner, H. 1995. Mineral Nutrition of Higher Plants. London: Academic Press. Marschner, H., V. Römheld, and I. Cakmak. 1987. Root-induced changes of nutrient availability in the rhizosphere. Journal of Plant Nutrition 10: 1175–1184. Murphy, J., and J. P. Riley. 1962. A modified single solution method for the determination of phosphate in natural waters. Analytica Chimica Acta 27: 31–36. Richardson, A. E., P. A. Hadobas, and J. E. Hayes. 2001. Extracellular secretion of Aspergillus phytase from Arabidopsis roots enables plants to obtain phosphorus from phytate. The Plant Journal 25: 641–649. Smith, F. W., W. A. Jackson, and P. J. V. Berg. 1990. Internal phosphorous flows during development of phosphorous stress in Stylosanthes hammata. Australian Journal of Plant Physiology 17: 451–464. Snapp, S., and J. P. Lynch. 1996. Phosphorus distribution and remobilization in bean plants as influenced by phosphorus nutrition. Crop Science 36: 929–935. Vance, C. P., C. Uhde-Stone, and D. L. Allen. 2003. P acquisition and use: Critical adaptations by plants for securing a nonrenewable resource. New Phytologist 157: 423–447. Williamson, L. C., S. P. Ribrioux, A. H. Fitte, and L. H. Ottoline. 2001. Phosphate availability regulates root system architecture in Arabidopsis. Plant Physiology 126: 875–882. Xu, F., Y. Yang, Y. Wang, and L. Wu. 2002. Boron uptake and retranslocation in cultivars of Brassica napus L. differing in boron efficiency. In: Boron in Plant and Animal Nutrition, eds. H. E. Goldbach, B. Rerkasem, M. A. Wimmer, P. H. Brown, M. Thellier, and R. W. Bell, pp. 127–135. New York: Kluwer Academic/Plenum Publishers. Yan, X. 2005. The roots of phosphorous-efficient soybean: theories and practices. In: Plant Nutrition for Food Security, Human Health and Environmental Protection, eds, C. J. Li, F. S. Zhang, A. Dobermann, P. Hinsinger, H. Lambers, X. L. Li, P. Marschner, L. Maene, S. McGrath, O. Oenema, S. B. Peng, Z. Rengel, Q. R. Shen, R. Welch, N. von Wirén, X. L. Yan, and Y. G. Zhu, pp. 36–37. Beijing: Tsinghua University Press. Yi, K., Z. Wu, J. Zhou, L. Du, L. Guo, Y. Wu, and P. Wu. 2005. OsPTF1, a novel transcription factor involved in tolerance to phosphate starvation in rice. Plant Physiology 138: 2087–2096.