Effects of ammonium application rate on uptake of soil adsorbed amino acids by rice

294 Cao et al. / J Zhejiang Univ-Sci B (Biomed & Biotechnol) 2016 17(4):294-302 Journal of Zhejiang University-SCIENCE B (Biomedicine & Biotechnology) ISSN 1673-1581 (Print); ISSN 1862-1783 (Online) www.zju.edu.cn/jzus; www.springerlink.com E-mail: Effects of ammonium application rate on uptake of soil adsorbed amino acids by rice* Xiao-chuang CAO§†1, Qing-xu MA§2, Liang-huan WU†‡2, Lian-feng ZHU1, Qian-yu JIN1 (1State Key Laboratory of Rice Biology, China National Rice Research Institute, Hangzhou 310006, China) (2Ministry of Education Key Laboratory of Environmental Remediation and Ecosystem Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China) † E-mail: ; Received Aug. 28, 2015; Revision accepted Dec. 8, 2015; Crosschecked Mar. 18, 2016 Abstract: In recent years, excessive use of chemical nitrogen (N) fertilizers has resulted in the accumulation of + + excess ammonium (NH4 ) in many agricultural soils. Though rice is known as an NH4 -tolerant species and can directly + absorb soil intact amino acids, we still know considerably less about the role of high exogenous NH4 content on rice + uptake of soil amino acids. This experiment examined the effects of the exogenous NH4 concentration on rice uptake of soil adsorbed glycine in two different soils under sterile culture. Our data showed that the sorption capacity of glycine was closely related to soils’ physical and chemical properties, such as organic matter and cation exchange capacity. + Rice biomass was significantly inhibited by the exogenous NH4 content at different glycine adsorption concentrations. A three-way analysis of variance demonstrated that rice glycine uptake and glycine nutritional contribution were not + related to its sorption capacity, but significantly related to its glycine:NH4 concentration ratio. After 21-d sterile cultivation, the rice uptake of adsorbed glycine accounted for 8.8%‒22.6% of rice total N uptake, which indicates that soil + adsorbed amino acids theoretically can serve as an important N source for plant growth in spite of a high NH4 application rate. However, further studies are needed to investigate the extent to which this bioavailability is realized in 13 15 the field using the C, N double labeling technology. Key words: Soil adsorbed glycine, Ammonium, Glycine uptake, Glycine bioavailability, Sterile cultivation http://dx.doi.org/10.1631/jzus.B1500203 CLC number: S158.5 1 Introduction Traditionally, the terrestrial nitrogen (N) cycle asserts that soil organic N must be transformed into inorganic N (NO3− and NH4+) by soil microorganisms prior to becoming available to plant roots (Warren and Adams, 2007). However, the role of soil dissolved organic N (DON), such as amino acids, in meeting the ‡ Corresponding author The two authors contributed equally to this work Project supported by the Zhejiang Provincial Natural Science Foundation of China (No. LQ15C130004), the National Basic Research Program (973) of China (No. 2015CB150502), and the National Natural Science Foundation of China (Nos. 31172032 and 31270035) ORCID: Xiao-chuang CAO, http://orcid.org/0000-0002-3630-1556 © Zhejiang University and Springer-Verlag Berlin Heidelberg 2016 § * plant nutritional requirement has since the 1990s received much attention (Jones et al., 2005a; Näsholm et al., 2009; Vinall et al., 2012; Wang et al., 2013; Geisseler and Horwath, 2014). Numerous studies have shown that both mycorrhizal and non-mycorrhizal plants can directly absorb soil amino acids, thereby circumventing the traditional mineralization bottleneck (Näsholm et al., 2001; Persson and Näsholm, 2001; Warren, 2006; Rothstein, 2009; Wang et al., 2014). Especially in some low N-input and cold ecosystems, plant uptake of amino acid has the potential to be a primary factor in ecosystem functioning and vegetation succession (Raab et al., 1999; Henry and Jefferies, 2003; Warren, 2006; Månsson et al., 2014). Cao et al. / J Zhejiang Univ-Sci B (Biomed & Biotechnol) 2016 17(4):294-302 To quantitatively analyze the role of amino acids in plant N uptake, comparisons were always made between the pool of soil extractable organic and inorganic N in different ecosystems. Soil N is dominated by organic forms, of which 30%–45% is present as amino acids after the process of proteolysis (Stevenson, 1994). Many studies have shown that the contents of free amino acids in soil solution are typically less than 1% of the pool of DON at about 0.1–50.0 μmol/L in different ecosystems (Jones et al., 2002; Yu et al., 2002; Christou et al., 2006). However, most studies neglected the fact that amino acid can be readily adsorbed on the soil solid phase, and its content may account for as much as 88%–92% of total soil amino acids (Qualls and Richardson, 2003). It has been reported that soil adsorption capacity is closely related to amino acid concentration (Jones et al., 2013), soil clay content (Gonod et al., 2006), cation exchange capacity (Dashman and Stotzky, 1984), and so on. Therefore, further research on soil organic N composition should include the consideration of soil adsorbed amino acids in different ecosystems. NH4+, one of the two important inorganic N sources used by plants, is beneficial for plant growth under many circumstances, and indeed, serves as a ubiquitous intermediate in plant metabolism (Britto and Kronzucker, 2002). A survey of boreal and temperate forest ecosystems shows forest-floor soil solution NH4+ values ranging from approximately 0.4 to 4.0 mmol/L, with a mean value of 2.0 mmol/L (Bijlsma et al., 2000). In agricultural soils, NH4+ can be even higher, often ranging from 2 to 20 mmol/L (Britto and Kronzucker, 2002). Especially in recent years, the excessive use of N fertilizer leads to N volatilization and subsequent transport and deposition of NH3/NH4+ via the atmosphere, resulting in undesirable accumulation of NH4+ and acidification in agricultural soils (Guo et al., 2010; Li et al., 2011b; Liu et al., 2013). Previous studies have explored several important physiological links in the development of high NH4+ accumulation or NH4+ toxicity, such as rhizosphere acidification, nutrient imbalance, damage to the photosynthesis system, and carbohydrate limitation (Britto and Kronzucker, 2002; Qin et al., 2008; Balkos et al., 2010; Barth et al., 2010; Li et al., 2010; Kempinski et al., 2011). Britto et al. (2001) demonstrated that rice could maintain lower 295 symplastic concentrations of NH4+ than barley (known to be susceptible to NH4+ toxicity) under elevated NH4+ concentration, in part because it is capable of shifting the trans-plasmamembrane electrical potential (Δψ) to more positive values with increasing NH4+ concentration. Though rice is known as an NH4+-tolerant species, we still know considerably less about the effects of the different exogenous NH4+ application rates on rice amino acid uptake. Here, two different soils, differing in soil parent material, texture, l (...truncated)