- Email: [email protected]
Selective uptake of nitrogen by Suaeda salsa under drought and salt stresses and nitrogen fertilization using 15N
Ecological Engineering 102 (2017) 542–545
Contents lists available at ScienceDirect
Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng
Short communication
Selective uptake of nitrogen by Suaeda salsa under drought and salt stresses and nitrogen fertilization using 15 N Junhong Bai a,∗ , Jia Jia a , Chen Huang b , Qinggai Wang c,∗ , Wei Wang a , Guangliang Zhang a , Baoshan Cui a , Xinhui Liu a a
State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, PR China Fujian Forestry Survey and Planning Institute, Fujian 350003, PR China c Apprisal Center for Environment and Engineering, Ministry of Environmental Protection, Beijing 100012, PR China b
a r t i c l e
i n f o
Article history: Received 6 December 2016 Received in revised form 15 February 2017 Accepted 18 February 2017 Keywords: Nitrate Ammonium Glycine Drought Salt stress Nitrogen fertilization
a b s t r a c t Plant nitrogen uptake can be influenced by drought and salt stresses and nitrogen fertilization; however, the selective uptake of different forms of nitrogen is poorly understood. We conducted a short-term 15 Nlabeling experiment to investigate the preferences of Suaeda salsa for nitrate, ammonium and amino acid. Our results indicated that nitrate and glycine, especially nitrate, were major nitrogen sources and glycine was absorbed after decompostion. Drought and salt stresses had no significant effect on the uptake of ammonium (p > 0.05). However, nitrate uptake was strongly related to water content and nitrogen application (p < 0.05) instead of salinity (p > 0.05). Drought and nitrogen application reduced the uptake of nitrate by almost 65.73% and 90.29%, respectively, suggesting appropriate soil water content and nitrogen deficiency could promote nitrate uptake. The uptake of glycine was mainly influenced by water content, and drought stress decreased glycine uptake by almost 89.74%. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Nitrogen (N) is one of the most limiting elements for plants in coastal wetlands (Mitsch and Gosselink, 2015). Generally, nitrate and ammonium are the two main forms of N assimilated by plants, and their relative availability has been considered to be an important factor controlling the distribution of plant species (Mitsch and Gosselink, 2015). However, some studies have indicated that plants can take up organic N directly or indirectly, especially simple forms such as amino acid (Schimel and Bennett, 2004). Some studies have even exhibited that amino acids can be assimilated by plants as fast as, or faster than, inorganic N sources (Persson et al., 2003). Species vary in their preferences for different forms of N, and environmental factors may exert a significant impact on these preferences (Buckeridge and Jefferies, 2007). Previous studies have reported that the selection of N forms is highly influenced by species at different succession stages (Warren, 2009). Nordin et al. (2001) showed correlations between amino acids and nitrate levels in soil and plant preferences for these N forms. Miller and Bowman
∗ Corresponding authors. E-mail addresses: [email protected] (J. Bai), [email protected] (Q. Wang). http://dx.doi.org/10.1016/j.ecoleng.2017.02.046 0925-8574/© 2017 Elsevier B.V. All rights reserved.
(2003) studied alpine plant uptake of organic and inorganic N along a moisture gradient, and reported that all species appeared to take up glycine at rates comparable to or greater than those of ammonium or nitrate, and species from the same community showed different uptake rates of ammonium, nitrate and glycine. Shao et al. (2015) found that the salt stress-induced growth inhibition of cucumber seedlings might disrupt N uptake and decrease the activities of enzymes. However, in coastal wetlands, little information is available on organic and inorganic nitrogen uptake by plants under drought, salt stresses and N fertilization. Isotope tracer technique can improve the understanding of plant N preference, which in turn is expected to aid in the prediction of plant growth and evolutionary trends and contribute to coastal wetland health and management. The primary objectives of this work were to reveal the main sources of inorganic and organic N for S. salsa as well as the preferences of S. salsa for N under drought and salt stresses, and N fertilization using the 15 N isotope tracer technique.
J. Bai et al. / Ecological Engineering 102 (2017) 542–545
1.2
-5
1.0
-10
0.8
c
0.6
a
a
15
NH4+-N
0
0.4
δ 13C PBD %
N Atom %
Control
b
1.4
15
(B)
(A)
1.6
543
-15 -20 -25 -30
0.2
-35
0.0
Control
15
+
NH4 -N
15
-
NO3 -N
15
N-glycine
a
a
-40
Fig 1. 15 N uptake by S. salsa under different N application treatments (A) and 13 C uptake under glycine application treatment (B) (abc represent the differences in 15 N uptake under different 15 N forms application).
2. Materials and methods 2.1. Site description The Yellow River Delta National Reserve (118◦ 33 ∼ 119◦ 20 E, 37◦ 35 ∼ 38◦ 12 N) is located in Dongying City, Shandong Province. It is the most complete and youngest wetland in the warm temperate zone, with a typical continental monsoon climate and distinctive seasons. Its annual average temperature and frost-free period are 12.3 ◦ C and 196 days, respectively. The annual evaporation is 1962 mm and annual precipitation is 551.6 mm, with approximately 70% of precipitation and rainfall occurring between June and August. The shallow salt groundwater, loose rock class and high evaporation in the Yellow River Delta subject the region to the risk of salinization, and the seasonal fresh water deficiency would aggravate the environmental stresses of drought and salinization on plants. In addition, to solve the sedimentation of the Yellow River, the flow-sediment regulation engineering has been carried out in June or July since 2002, and it brings plenty of freshwater to the Yellow River Delta during this period. The subsequent freshwater deficit would cause the region suffering from drought. The dominate soil types are fluvo-aquic soil and salt soil (Bai et al., 2012) and the dominate vegetation is Suaeda salsa, Tamarix chinensis and Phragmite australis. As a pioneer plant in the Yellow River Delta, Suaeda salsa is an euhalophytic herb that naturally grows on highly salt soil and it has strong adaptations to environmental stresses.
13 C, 15 N(98
atom% 15 N; 99 atom% 13 C) (Sigma-Aldrich company). We injected 1.0 mmol/L N solutions (0.6 mmol/L 15 N fertilizer in treatment + 0.2 mmol/L 14 N of one of the two remaining N fertilizer + 0.2 mmol/L 14 N of the remaining N fertilizer) into the soil at depths of 5 cm and 10 cm in the four corners of a 2 × 2 cm2 area around the plant. The injection concentration ensured the detection of plant uptake and prevented the plant from being injured, and the injection procedure ensured the label was spread evenly throughout the soil. The plants were harvested after 6 h. Plant samples were sent to the Nanjing Normal University for 13 C and 15 N analysis by isotope ratio mass spectrometry (IRMS) at the SerCon 20–22 Stable Isotope Facility. Soil salinity was measured using a salinity meter, respectively (soil/water, 1:5), and soil water content was determined by drying soil samples at 105 ◦ C for 24 h in an oven. The grain size fractions of soil were measured on a Laser Size Analyzer (Microtrac S3500) and classified into clay (<0.002 mm), silt (0.002–0.02 mm), and sand (0.02–2 mm). The contents of total nitrogen of soil were determined by CHNOS Elemental Analyzer (Vario EL, German). One-way variance analysis (ANOVA) was conducted to identify the significant effects of the water content, salinity and nitrogen application on the plant nitrogen uptake. Statistical analysis was carried out using SPSS 16.0 software package. The difference was considered to be significant if p < 0.05.
3. Results and discussion 3.1. Different forms of nitrogen absorbed by S. salsa
2.2. Experimental design and statistical analysis An outdoor shed (2 m height and 12 m2 area) at the Yellow River Delta management station was used as the test site in April 2012. Soils for experiment were collected at a depth of 15 cm near the test site. S. salsa seedlings with similar growth characteristics were collected around the soil sampling site. Soil samples were brought to the laboratory and air-dried at room temperature, and then grounded through a 2-mm sieve to remove the coarse plant residues and stones. Plants were divided into three groups and transplanted to the plastic pots filled with 2 kg air-dried soils. The salinity, total nitrogen, and water content of initial experimental soils are 1.87 g/kg, 209 mg/kg, and 26%, respectively. The particle size of soil is mainly composed of sand (about approximately 75.84%). After the plant adaptive phase, experiment was carried out with two moisture treatments (i.e., 26% and 14%), four salinity treatments (i.e., 8 g/kg, 6 g/kg, 4 g/kg, and 2 g/kg) and two N-application treatments (i.e., 0 N mg/kg and 200 N mg/kg). Each treatment included four replicates. The isotopic labeled substrates were (15 NH4 )2 SO4 (98 atom%), K15 NO3 (98 atom%) and Glycine-2-
S. salsa showed significant uptake of nitrate and glycine (p < 0.05) other than ammonium (p > 0.05) (Fig. 1A), indicating that nitrate and amino acids, especially nitrate, were the main sources of N for S. salsa. This result is partly consistent with results of Goloran et al. (2015), who presented H. violacea and L. rigidum mainly absorbed nitrate, which might be explained by low toxicity of nitrate and species preference. In addition, Moneta et al. (2014) studied the seasonal uptake of N and observed ammonium was preferentially assimilated, whereas nitrate was preferred in spring and summer, owing to the competition between plants and microbes. However, other researchers have reported that ammonium was the main inorganic source of N in coastal wetlands, and this preference was related to the amounts of different forms of N in soil (Kirk and Kronzucker, 2005). Nordin et al. (2001) reported that in a boreal forest, all plants preferred ammonium, but ammonium and nitrate showed equivalent plant uptake when their abundances were equal. One probable explanation for this inconsistency is associated with species and seasonal variations. The 13 C DeltaPBD% in the 15 N-Glycine treatment was not significantly different from the
544
J. Bai et al. / Ecological Engineering 102 (2017) 542–545
2.0 a
a
1.4
Glycine nitrogen
a
a
0.8 a a a
15
a 0.1 0.0
(B) a Nitrate nitrogen Glycine nitrogen
1.2 N Atom %
Nitrate nitrogen
15
N Atom %
1.6 1.2
1.6
(A)
1.0 0.8 b
0.6 0.4
a
0.2 2
4 6 Salinity (g/kg) 1.8
a
0.0
8
Control
Drought
(C)
a
1.6
15
N Atom %
1.4 Nitrate nitrogen Glycine nitrogen
1.2 1.0 0.8 0.6
b
0.4
a
0.2
a
0.0 N application
Control
Fig. 2. Effects of salinity, water content and N application on nitrate and glycine nitrogen uptake by S. salsa (ab represent the differences in under salt, drought stresses and N application).
15
N uptake in the same form
Table 1 Statistical results of one-way ANOVA testing the effects of salinity, drought and N application on the uptake of 15 NO3 − -N and 15 N-Glycine by S. salsa.
Salinity Water content N application
F value (15 NO3 − -N)
P value (15 NO3 − -N)
F value (15 N-Glycine)
P value (15 N-Glycine)
0.029 7.505 23.184
0.993 0.023* 0.001**
0.079 4.988 0.063
0.970 0.052 0.808
control (p > 0.05) (Fig. 1B), suggesting that glycine was assimilated after decomposition. However, Nasholm et al. (2000) reported that glycine was assimilated in the form of intact amino acids, and the uptake capacity differs among plant species. The soil type (acidic or alkaline), which can have a great effect on the rate of N mineralization (Yang, 2014), might be the probable explanation for the inconsistency. 3.2. Nitrogen uptake of S. salsa affected by drought and salt stress and N fertilization Nitrate uptake was significantly reduced by drought and N application (p < 0.05) (Fig. 2B and C) (Table 1). Drought and N application reduced the uptake of nitrate by almost 65.73% and 90.29%, respectively, indicating that appropriate water content and N deficiency would enhance nitrate uptake. This result is supported by the finding of Subasinghe (2007) that N starvation improved nitrate uptake capacity. In addition, plants suffering from N deficiency tended to recover their nitrate uptake rapidly and offset the feedback regulation by the internal nitrate (Jackson et al., 1976). Water deficit caused by drought could decrease nitrate uptake by influencing stomatal conductance and injuring membrane permeability and active transport (Tezara, 2003; Ali and Golombek, 2016), which agrees with the result of Gonzalez et al. (2008) that drought affected nutrient uptake through impairing acropetal translocation of some nutrients (Song et al., 2010). In our study, the assimilated nitrate by S. salsa showed no significant correlation
with soil salinity (p > 0.05, Fig. 2A). However, Botella et al. (1994) reported that salinity pretreatments increased the net uptake rates of nitrate and ammonium. Unconspicuous difference under salt stress treatments might be attributed to the active absorption way of nitrate, which was not affected in 8 g/kg or lower salinity treatments, and plant species differ greatly in the salinity effects on their and nutrient uptake. N-Glycine uptake showed an obvious difference between the moisture treatments although there was no significant statistical difference (p > 0.05) (Fig. 2B), and drought stress decreased glycine uptake by almost 89.74%. These indicated that water content influences glycine uptake. Miller and Bowman (2003) also reported that plants exhibited species-level differences in the uptake of organic nitrogen among nine species in dry, moist and wet soils. The differences of organic nitrogen uptake among the species and under environmental stresses are still unknown and further studies on the detailed mechanisms of glycine uptake are still needed. 4. Conclusions S. salsa mainly assimilated nitrate, followed by decomposition products of glycine, but rather than ammonium. Nitrate uptake was prohibited under drought and N application treatments. When the soil salinity was lower than 8 g/kg, salt stress had little effect on nitrate and glycine uptake. Drought and salt stress had almost no effect on glycine uptake, but soil water content exhibited a marked effect (p > 0.05). Our study was only a pilot study for the N prefer-
J. Bai et al. / Ecological Engineering 102 (2017) 542–545
ence of S. salsa in coastal wetlands. Further studies are needed to explore the mechanisms influencing glycine uptake during drought to testify the conclusion. Acknowledgements This study was financially supported by the National Basic Research Program of China (no. 2013CB430406), the National Natural Science Foundation of China (no. 51379012) and the Young Top-Notch Talent Support Program of China. References Ali, Z.L., Golombek, S.D., 2016. Effects of drought and nitrogen availability on osmotic adjustment of five Pearl Milled Cultivars in the vegetative growth stage. J. Agro. Crop. Sci. 202, 433–444, http://dx.doi.org/10.1111/jac.12163. Bai, J.H., Ye, X.F., Zhi, Y., et al., 2012. Nitrate – nitrogen transport in horizontal soil columns of the yellow river delta wetland, China. Clean – Soil Air Water 40 (10), 1106–1110. Botella, M.A., Cerda, A., Lips, S.H., 1994. Kinetics of NO3 (−) and NH4 (+) uptake in wheat seedlings. Effect of salinity and nitrogen source. J. Plant Physiol. 144, 51–53. Buckeridge, K.M., Jefferies, R.L., 2007. Vegetation loss alters soil nitrogen dynamics in an Arctic salt marsh. J. Ecol. 95, 283–293. Goloran, J.B., et al., 2015. Transformation and plant uptake of 15 N-labeled fertilizers mediated by ammonia-oxidizing bacteria in alkaline bauxite-processing residue sand amended with greenwaste compost. Ecol. Eng. 74, 68–78. Gonzalez, A., Martin, I., Ayerbe, L., 2008. Yield and osmotic adjustment capacity of barley under terminal water-stress conditions. J. Agron. Crop Sci. 194, 81–91. Jackson, W.A., Kwik, K.D., Volk, R.J., 1976. Nitrate uptake during recovery from nitrogen deficiency. Physiol. Plant. 36 (2), 174–181.
545
Kirk, G.J.D., Kronzucker, H.J., 2005. The potential for nitrification and nitrate uptake in the rhizosphere of wetland plants: a modelling study. Ann. Bot. 96, 639–646. Miller, A.E., Bowman, W.D., 2003. Alpine plants show species-level differences in the uptake of organic and inorganic nitrogen. Plant Soil 250, 283–292. Mitsch, W.J., Gosselink, J.G., 2015. Wetlands, 5th ed. John Wiley & Sons, Inc, New York. Moneta, A., et al., 2014. Dissolved inorganic and organic nitrogen uptake in the coastal North Sea: a seasonal study. Estuar. Coast. Mar. Sci. 147, 78–86. Nasholm, T., Huss-Danell, K., Hogberg, P., 2000. Uptake of organic nitrogen in the field by four agriculturally important plant species. Ecology 81, 1155–1161. Nordin, A., Högberg, P., Näsholm, T., 2001. Soil nitrogen form and plant nitrogen uptake along a boreal forest productivity gradient. Oecologia 129, 125–132. Persson, J., Högberg, P., Ekblad, A., Högberg, M.N., Nordgren, A., Näshom, T., 2003. Nitrogen acquisition from inorganic and organic sources by boreal forest plants in the field. Oecologia 137, 252–257. Schimel, J.P., Bennett, J., 2004. Nitrogen mineralization: challenges of a changing paradigm. Ecology 85, 591–602. Shao, Q.S., Shu, S., Du, J., Xing, W.W., Guo, R.S., Sun, J., 2015. Effects of NaCl stress on nitrogen metabolism of cucumber seedlings. Russ. J. Plant Physiol. 62 (5), 595–603. Song, L., Zhang, D.W., Li, F.M., et al., 2010. DROUGHT STRESS: soil water availability alters the inter- and intra-Cultivar competition of three spring wheat cultivars bred in different eras. J. Agrono. Crop Sci. 196 (5), 323–335. Subasinghe, R., 2007. Effect of nitrogen and potassium stress and cultivar differences on potassium ions and nitrate uptake in sugarcane. J. Plant Nutr. 29, 809–825. Tezara, W., 2003. Photosynthetic responses of the tropical spiny shrub lycium nodosum (Solanaceae) to drought, soil salinity and Saline spray. Ann. Bot. 92 (6), 757–765. Warren, C.R., 2009. Uptake of inorganic and amino acid nitrogen from soil by Eucalyptus regnans and Eucalyptus pauciflora seedlings. Tree Physiol. 29 (3), 401–409. Yang, J.J., 2014. Relationship Between Soil Gross Nitrogen Transformation Rates and Nitrogen Fatse in Purple Soils and Countermeasures. Nanjing Normal University (in Chinese).
Contents lists available at ScienceDirect
Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng
Short communication
Selective uptake of nitrogen by Suaeda salsa under drought and salt stresses and nitrogen fertilization using 15 N Junhong Bai a,∗ , Jia Jia a , Chen Huang b , Qinggai Wang c,∗ , Wei Wang a , Guangliang Zhang a , Baoshan Cui a , Xinhui Liu a a
State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, PR China Fujian Forestry Survey and Planning Institute, Fujian 350003, PR China c Apprisal Center for Environment and Engineering, Ministry of Environmental Protection, Beijing 100012, PR China b
a r t i c l e
i n f o
Article history: Received 6 December 2016 Received in revised form 15 February 2017 Accepted 18 February 2017 Keywords: Nitrate Ammonium Glycine Drought Salt stress Nitrogen fertilization
a b s t r a c t Plant nitrogen uptake can be influenced by drought and salt stresses and nitrogen fertilization; however, the selective uptake of different forms of nitrogen is poorly understood. We conducted a short-term 15 Nlabeling experiment to investigate the preferences of Suaeda salsa for nitrate, ammonium and amino acid. Our results indicated that nitrate and glycine, especially nitrate, were major nitrogen sources and glycine was absorbed after decompostion. Drought and salt stresses had no significant effect on the uptake of ammonium (p > 0.05). However, nitrate uptake was strongly related to water content and nitrogen application (p < 0.05) instead of salinity (p > 0.05). Drought and nitrogen application reduced the uptake of nitrate by almost 65.73% and 90.29%, respectively, suggesting appropriate soil water content and nitrogen deficiency could promote nitrate uptake. The uptake of glycine was mainly influenced by water content, and drought stress decreased glycine uptake by almost 89.74%. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Nitrogen (N) is one of the most limiting elements for plants in coastal wetlands (Mitsch and Gosselink, 2015). Generally, nitrate and ammonium are the two main forms of N assimilated by plants, and their relative availability has been considered to be an important factor controlling the distribution of plant species (Mitsch and Gosselink, 2015). However, some studies have indicated that plants can take up organic N directly or indirectly, especially simple forms such as amino acid (Schimel and Bennett, 2004). Some studies have even exhibited that amino acids can be assimilated by plants as fast as, or faster than, inorganic N sources (Persson et al., 2003). Species vary in their preferences for different forms of N, and environmental factors may exert a significant impact on these preferences (Buckeridge and Jefferies, 2007). Previous studies have reported that the selection of N forms is highly influenced by species at different succession stages (Warren, 2009). Nordin et al. (2001) showed correlations between amino acids and nitrate levels in soil and plant preferences for these N forms. Miller and Bowman
∗ Corresponding authors. E-mail addresses: [email protected] (J. Bai), [email protected] (Q. Wang). http://dx.doi.org/10.1016/j.ecoleng.2017.02.046 0925-8574/© 2017 Elsevier B.V. All rights reserved.
(2003) studied alpine plant uptake of organic and inorganic N along a moisture gradient, and reported that all species appeared to take up glycine at rates comparable to or greater than those of ammonium or nitrate, and species from the same community showed different uptake rates of ammonium, nitrate and glycine. Shao et al. (2015) found that the salt stress-induced growth inhibition of cucumber seedlings might disrupt N uptake and decrease the activities of enzymes. However, in coastal wetlands, little information is available on organic and inorganic nitrogen uptake by plants under drought, salt stresses and N fertilization. Isotope tracer technique can improve the understanding of plant N preference, which in turn is expected to aid in the prediction of plant growth and evolutionary trends and contribute to coastal wetland health and management. The primary objectives of this work were to reveal the main sources of inorganic and organic N for S. salsa as well as the preferences of S. salsa for N under drought and salt stresses, and N fertilization using the 15 N isotope tracer technique.
J. Bai et al. / Ecological Engineering 102 (2017) 542–545
1.2
-5
1.0
-10
0.8
c
0.6
a
a
15
NH4+-N
0
0.4
δ 13C PBD %
N Atom %
Control
b
1.4
15
(B)
(A)
1.6
543
-15 -20 -25 -30
0.2
-35
0.0
Control
15
+
NH4 -N
15
-
NO3 -N
15
N-glycine
a
a
-40
Fig 1. 15 N uptake by S. salsa under different N application treatments (A) and 13 C uptake under glycine application treatment (B) (abc represent the differences in 15 N uptake under different 15 N forms application).
2. Materials and methods 2.1. Site description The Yellow River Delta National Reserve (118◦ 33 ∼ 119◦ 20 E, 37◦ 35 ∼ 38◦ 12 N) is located in Dongying City, Shandong Province. It is the most complete and youngest wetland in the warm temperate zone, with a typical continental monsoon climate and distinctive seasons. Its annual average temperature and frost-free period are 12.3 ◦ C and 196 days, respectively. The annual evaporation is 1962 mm and annual precipitation is 551.6 mm, with approximately 70% of precipitation and rainfall occurring between June and August. The shallow salt groundwater, loose rock class and high evaporation in the Yellow River Delta subject the region to the risk of salinization, and the seasonal fresh water deficiency would aggravate the environmental stresses of drought and salinization on plants. In addition, to solve the sedimentation of the Yellow River, the flow-sediment regulation engineering has been carried out in June or July since 2002, and it brings plenty of freshwater to the Yellow River Delta during this period. The subsequent freshwater deficit would cause the region suffering from drought. The dominate soil types are fluvo-aquic soil and salt soil (Bai et al., 2012) and the dominate vegetation is Suaeda salsa, Tamarix chinensis and Phragmite australis. As a pioneer plant in the Yellow River Delta, Suaeda salsa is an euhalophytic herb that naturally grows on highly salt soil and it has strong adaptations to environmental stresses.
13 C, 15 N(98
atom% 15 N; 99 atom% 13 C) (Sigma-Aldrich company). We injected 1.0 mmol/L N solutions (0.6 mmol/L 15 N fertilizer in treatment + 0.2 mmol/L 14 N of one of the two remaining N fertilizer + 0.2 mmol/L 14 N of the remaining N fertilizer) into the soil at depths of 5 cm and 10 cm in the four corners of a 2 × 2 cm2 area around the plant. The injection concentration ensured the detection of plant uptake and prevented the plant from being injured, and the injection procedure ensured the label was spread evenly throughout the soil. The plants were harvested after 6 h. Plant samples were sent to the Nanjing Normal University for 13 C and 15 N analysis by isotope ratio mass spectrometry (IRMS) at the SerCon 20–22 Stable Isotope Facility. Soil salinity was measured using a salinity meter, respectively (soil/water, 1:5), and soil water content was determined by drying soil samples at 105 ◦ C for 24 h in an oven. The grain size fractions of soil were measured on a Laser Size Analyzer (Microtrac S3500) and classified into clay (<0.002 mm), silt (0.002–0.02 mm), and sand (0.02–2 mm). The contents of total nitrogen of soil were determined by CHNOS Elemental Analyzer (Vario EL, German). One-way variance analysis (ANOVA) was conducted to identify the significant effects of the water content, salinity and nitrogen application on the plant nitrogen uptake. Statistical analysis was carried out using SPSS 16.0 software package. The difference was considered to be significant if p < 0.05.
3. Results and discussion 3.1. Different forms of nitrogen absorbed by S. salsa
2.2. Experimental design and statistical analysis An outdoor shed (2 m height and 12 m2 area) at the Yellow River Delta management station was used as the test site in April 2012. Soils for experiment were collected at a depth of 15 cm near the test site. S. salsa seedlings with similar growth characteristics were collected around the soil sampling site. Soil samples were brought to the laboratory and air-dried at room temperature, and then grounded through a 2-mm sieve to remove the coarse plant residues and stones. Plants were divided into three groups and transplanted to the plastic pots filled with 2 kg air-dried soils. The salinity, total nitrogen, and water content of initial experimental soils are 1.87 g/kg, 209 mg/kg, and 26%, respectively. The particle size of soil is mainly composed of sand (about approximately 75.84%). After the plant adaptive phase, experiment was carried out with two moisture treatments (i.e., 26% and 14%), four salinity treatments (i.e., 8 g/kg, 6 g/kg, 4 g/kg, and 2 g/kg) and two N-application treatments (i.e., 0 N mg/kg and 200 N mg/kg). Each treatment included four replicates. The isotopic labeled substrates were (15 NH4 )2 SO4 (98 atom%), K15 NO3 (98 atom%) and Glycine-2-
S. salsa showed significant uptake of nitrate and glycine (p < 0.05) other than ammonium (p > 0.05) (Fig. 1A), indicating that nitrate and amino acids, especially nitrate, were the main sources of N for S. salsa. This result is partly consistent with results of Goloran et al. (2015), who presented H. violacea and L. rigidum mainly absorbed nitrate, which might be explained by low toxicity of nitrate and species preference. In addition, Moneta et al. (2014) studied the seasonal uptake of N and observed ammonium was preferentially assimilated, whereas nitrate was preferred in spring and summer, owing to the competition between plants and microbes. However, other researchers have reported that ammonium was the main inorganic source of N in coastal wetlands, and this preference was related to the amounts of different forms of N in soil (Kirk and Kronzucker, 2005). Nordin et al. (2001) reported that in a boreal forest, all plants preferred ammonium, but ammonium and nitrate showed equivalent plant uptake when their abundances were equal. One probable explanation for this inconsistency is associated with species and seasonal variations. The 13 C DeltaPBD% in the 15 N-Glycine treatment was not significantly different from the
544
J. Bai et al. / Ecological Engineering 102 (2017) 542–545
2.0 a
a
1.4
Glycine nitrogen
a
a
0.8 a a a
15
a 0.1 0.0
(B) a Nitrate nitrogen Glycine nitrogen
1.2 N Atom %
Nitrate nitrogen
15
N Atom %
1.6 1.2
1.6
(A)
1.0 0.8 b
0.6 0.4
a
0.2 2
4 6 Salinity (g/kg) 1.8
a
0.0
8
Control
Drought
(C)
a
1.6
15
N Atom %
1.4 Nitrate nitrogen Glycine nitrogen
1.2 1.0 0.8 0.6
b
0.4
a
0.2
a
0.0 N application
Control
Fig. 2. Effects of salinity, water content and N application on nitrate and glycine nitrogen uptake by S. salsa (ab represent the differences in under salt, drought stresses and N application).
15
N uptake in the same form
Table 1 Statistical results of one-way ANOVA testing the effects of salinity, drought and N application on the uptake of 15 NO3 − -N and 15 N-Glycine by S. salsa.
Salinity Water content N application
F value (15 NO3 − -N)
P value (15 NO3 − -N)
F value (15 N-Glycine)
P value (15 N-Glycine)
0.029 7.505 23.184
0.993 0.023* 0.001**
0.079 4.988 0.063
0.970 0.052 0.808
control (p > 0.05) (Fig. 1B), suggesting that glycine was assimilated after decomposition. However, Nasholm et al. (2000) reported that glycine was assimilated in the form of intact amino acids, and the uptake capacity differs among plant species. The soil type (acidic or alkaline), which can have a great effect on the rate of N mineralization (Yang, 2014), might be the probable explanation for the inconsistency. 3.2. Nitrogen uptake of S. salsa affected by drought and salt stress and N fertilization Nitrate uptake was significantly reduced by drought and N application (p < 0.05) (Fig. 2B and C) (Table 1). Drought and N application reduced the uptake of nitrate by almost 65.73% and 90.29%, respectively, indicating that appropriate water content and N deficiency would enhance nitrate uptake. This result is supported by the finding of Subasinghe (2007) that N starvation improved nitrate uptake capacity. In addition, plants suffering from N deficiency tended to recover their nitrate uptake rapidly and offset the feedback regulation by the internal nitrate (Jackson et al., 1976). Water deficit caused by drought could decrease nitrate uptake by influencing stomatal conductance and injuring membrane permeability and active transport (Tezara, 2003; Ali and Golombek, 2016), which agrees with the result of Gonzalez et al. (2008) that drought affected nutrient uptake through impairing acropetal translocation of some nutrients (Song et al., 2010). In our study, the assimilated nitrate by S. salsa showed no significant correlation
with soil salinity (p > 0.05, Fig. 2A). However, Botella et al. (1994) reported that salinity pretreatments increased the net uptake rates of nitrate and ammonium. Unconspicuous difference under salt stress treatments might be attributed to the active absorption way of nitrate, which was not affected in 8 g/kg or lower salinity treatments, and plant species differ greatly in the salinity effects on their and nutrient uptake. N-Glycine uptake showed an obvious difference between the moisture treatments although there was no significant statistical difference (p > 0.05) (Fig. 2B), and drought stress decreased glycine uptake by almost 89.74%. These indicated that water content influences glycine uptake. Miller and Bowman (2003) also reported that plants exhibited species-level differences in the uptake of organic nitrogen among nine species in dry, moist and wet soils. The differences of organic nitrogen uptake among the species and under environmental stresses are still unknown and further studies on the detailed mechanisms of glycine uptake are still needed. 4. Conclusions S. salsa mainly assimilated nitrate, followed by decomposition products of glycine, but rather than ammonium. Nitrate uptake was prohibited under drought and N application treatments. When the soil salinity was lower than 8 g/kg, salt stress had little effect on nitrate and glycine uptake. Drought and salt stress had almost no effect on glycine uptake, but soil water content exhibited a marked effect (p > 0.05). Our study was only a pilot study for the N prefer-
J. Bai et al. / Ecological Engineering 102 (2017) 542–545
ence of S. salsa in coastal wetlands. Further studies are needed to explore the mechanisms influencing glycine uptake during drought to testify the conclusion. Acknowledgements This study was financially supported by the National Basic Research Program of China (no. 2013CB430406), the National Natural Science Foundation of China (no. 51379012) and the Young Top-Notch Talent Support Program of China. References Ali, Z.L., Golombek, S.D., 2016. Effects of drought and nitrogen availability on osmotic adjustment of five Pearl Milled Cultivars in the vegetative growth stage. J. Agro. Crop. Sci. 202, 433–444, http://dx.doi.org/10.1111/jac.12163. Bai, J.H., Ye, X.F., Zhi, Y., et al., 2012. Nitrate – nitrogen transport in horizontal soil columns of the yellow river delta wetland, China. Clean – Soil Air Water 40 (10), 1106–1110. Botella, M.A., Cerda, A., Lips, S.H., 1994. Kinetics of NO3 (−) and NH4 (+) uptake in wheat seedlings. Effect of salinity and nitrogen source. J. Plant Physiol. 144, 51–53. Buckeridge, K.M., Jefferies, R.L., 2007. Vegetation loss alters soil nitrogen dynamics in an Arctic salt marsh. J. Ecol. 95, 283–293. Goloran, J.B., et al., 2015. Transformation and plant uptake of 15 N-labeled fertilizers mediated by ammonia-oxidizing bacteria in alkaline bauxite-processing residue sand amended with greenwaste compost. Ecol. Eng. 74, 68–78. Gonzalez, A., Martin, I., Ayerbe, L., 2008. Yield and osmotic adjustment capacity of barley under terminal water-stress conditions. J. Agron. Crop Sci. 194, 81–91. Jackson, W.A., Kwik, K.D., Volk, R.J., 1976. Nitrate uptake during recovery from nitrogen deficiency. Physiol. Plant. 36 (2), 174–181.
545
Kirk, G.J.D., Kronzucker, H.J., 2005. The potential for nitrification and nitrate uptake in the rhizosphere of wetland plants: a modelling study. Ann. Bot. 96, 639–646. Miller, A.E., Bowman, W.D., 2003. Alpine plants show species-level differences in the uptake of organic and inorganic nitrogen. Plant Soil 250, 283–292. Mitsch, W.J., Gosselink, J.G., 2015. Wetlands, 5th ed. John Wiley & Sons, Inc, New York. Moneta, A., et al., 2014. Dissolved inorganic and organic nitrogen uptake in the coastal North Sea: a seasonal study. Estuar. Coast. Mar. Sci. 147, 78–86. Nasholm, T., Huss-Danell, K., Hogberg, P., 2000. Uptake of organic nitrogen in the field by four agriculturally important plant species. Ecology 81, 1155–1161. Nordin, A., Högberg, P., Näsholm, T., 2001. Soil nitrogen form and plant nitrogen uptake along a boreal forest productivity gradient. Oecologia 129, 125–132. Persson, J., Högberg, P., Ekblad, A., Högberg, M.N., Nordgren, A., Näshom, T., 2003. Nitrogen acquisition from inorganic and organic sources by boreal forest plants in the field. Oecologia 137, 252–257. Schimel, J.P., Bennett, J., 2004. Nitrogen mineralization: challenges of a changing paradigm. Ecology 85, 591–602. Shao, Q.S., Shu, S., Du, J., Xing, W.W., Guo, R.S., Sun, J., 2015. Effects of NaCl stress on nitrogen metabolism of cucumber seedlings. Russ. J. Plant Physiol. 62 (5), 595–603. Song, L., Zhang, D.W., Li, F.M., et al., 2010. DROUGHT STRESS: soil water availability alters the inter- and intra-Cultivar competition of three spring wheat cultivars bred in different eras. J. Agrono. Crop Sci. 196 (5), 323–335. Subasinghe, R., 2007. Effect of nitrogen and potassium stress and cultivar differences on potassium ions and nitrate uptake in sugarcane. J. Plant Nutr. 29, 809–825. Tezara, W., 2003. Photosynthetic responses of the tropical spiny shrub lycium nodosum (Solanaceae) to drought, soil salinity and Saline spray. Ann. Bot. 92 (6), 757–765. Warren, C.R., 2009. Uptake of inorganic and amino acid nitrogen from soil by Eucalyptus regnans and Eucalyptus pauciflora seedlings. Tree Physiol. 29 (3), 401–409. Yang, J.J., 2014. Relationship Between Soil Gross Nitrogen Transformation Rates and Nitrogen Fatse in Purple Soils and Countermeasures. Nanjing Normal University (in Chinese).