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Soil Water Status Influences Plant Nitrogen Use: a Case Study

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Soil Water Status Influences Plant Nitrogen Use: a Case Study Plant Soil (2007) 301:303–313 DOI 10.1007/s11104-007-9450-y REGULAR ARTICLE Soil water status influences plant nitrogen use: a case study Zhi-You Yuan & Ling-Hao Li Received: 19 July 2007 /Accepted: 1 October 2007 / Published online: 10 November 2007 # Springer Science + Business Media B.V. 2007 Abstract We studied differences in nitrogen use but lower MRT than the species growing in the river efficiency (NUE) among six species [Calamagrostis bank. There was an inverse relationship between A epigejos (L.) Roth., Carex duriuscula C.A. Mey., and MRT. Consequently, NUE was similar among Phragmites communis (L.) Trin., Salix gordejevii Y.L. species and habitats. These results suggested that Chang, Salix cheilophila Schneid., and Typha minima environmental factors, such as soil water supply, can Funk.] growing in two contrasting habitat types, i.e., a influence N use by plants. riverine wetland with high water supply and a riparian zone with low water supply. The two sites were Keywords Nitrogen use efficiency. Plant strategies . different in soil water supply, but not in nitrogen Riparian areas . Soil water . Wetland vegetation supply. Here, NUE was defined as the total net primary production per unit nitrogen absorbed. There was no significant difference in NUE between the Introduction species growing in the riverine wetland (Carex duriuscula, P. communis, S. cheilophila, T. minima) Nitrogen (N) availability is closely associated with and the species growing in the river bank (Carex plant productivity (Vermeer and Berendse 1983) and duriuscula, Calamagrostis epigejos, P. communis, S. often limits plant N uptake in terrestrial ecosystems gordejevii). We further analyzed NUE as the product (Tilman 1985; Vitousek and Howarth 1991). To adapt of the nitrogen productivity (A, the rate of dry matter to the N limitation, plants should utilize the limited N production per unit of nitrogen in the plant) and the more efficiently. Therefore, it is important to study the mean residence time of nitrogen (MRT, the period of efficiency with which plants use this resource for time a unit of nitrogen is present in the plant). The growth (Vitousek 1982; Aerts and Chapin 2000; Yuan species growing in the riverine wetland had larger A et al. 2006). Nitrogen use efficiency (NUE), a measure of how a plant responds to soil nitrogen, is generally defined as the amount of organic matter lost or produced in a plant per amount of nitrogen used Responsible Editor: Angela Hodge : (Hirose 1971; Vitousek 1982). However, Berendse Z.-Y. Yuan L.-H. Li (*) and Aerts (1987) proposed to redefine the concept of Laboratory of Quantitative Vegetation Ecology, NUE as the product of nitrogen productivity (A, the Institute of Botany, the Chinese Academy of Sciences, Beijing 100093, China rate of dry matter production per unit of nitrogen in e-mail: [email protected] the plant) and the mean residence time of the nitrogen 304 Plant Soil (2007) 301:303–313 in the plant (MRT, the period of time a unit of these species. For perennial herbs, we measured A, nitrogen is present in the plant), i.e., NUE=A×MRT. MRT, and NUE at the aboveground level. The NUE in relation to habitat fertility has been The purpose of this study was to address whether studied in many different species (e.g., Aerts and De NUE and its two components change among species Caluwe 1994; Vázquez de Aldana and Berendse with different water supply. As the amount of soil 1997; Nakamura et al. 2002). However, other factors, water supplied to the plant is reduced, the rate of such as water, could influence plant N use too. Soil photosynthesis will decline (Lambers et al.1998). water supply affects nutrient transport, uptake, and Therefore, we hypothesized that plant nitrogen econ- transformation. It may be the underlying cause of omy, particularly A and MRT, was different when variation in habitat fertility. Plants with different soil growing in habitats with different water supply. water supply can have widely different traits such as Compared with species with low water supply, photosynthetic capacity, growth rate leaf N content species with high water supply would have higher A (Lambers et al.1998), and then N use strategies. To and thus higher NUE. MRT, however, is expected to our knowledge, there are few studies based on the be similar among the species because leaf lifespan NUE index of Berendse and Aerts (1987), and the and N resorption efficiency (REFF, the percentage of N effect of soil water supply on NUE and its two recovered from senescing leaves), both of which components, i.e., A and MRT, has not been studied. strongly affect MRT, do not vary appreciably among Furthermore, most of these studies according to the these species (Eckstein et al. 1999; Yasumura et al. NUE index of Berendse and Aerts (1987)were 2002). In the present study, we tested this hypothesis carried out under controlled conditions (e.g., Aerts by studying the nitrogen economy of six species and de Caluwe 1994; Vázquez de Aldana and growing in two distinct natural habitats with different Berendse 1997; Yuan et al. 2007). Also, the relation- water supply. ship between A and MRT is still under debate: some studies suggest a negative relationship (Yasumura et al. 2002; Silla and Escudero 2004), while others Materials and methods have found no relationship (Aerts and de Caluwe 1994; Nakamura et al. 2002; Yuan et al. 2004). If the Study site and species trade-off between A and MRT exists among plants growing in their natural habitats, is this trade-off The study was carried out in Duolun County, which is related to soil water supply? located on the southern edge of the Hunshandake In this paper, we used the NUE index defined by Sandland in the central part of Inner Mongolia Berendse and Aerts (1987) to study the N economy of Autonomous Region, China. This area belongs to a sixbroadlydistributedspeciesgrowingintwo typical agropastoral ecotone. The climate belongs to contrasting habitats differing in soil water supply. the semiarid monsoon climate of a moderate temper- For woody shrubs, we measured A, MRT, and NUE at ature zone. Mean annual precipitation is around the leaf level. Because leaf production is a major 386 mm and mean annual temperature is 1.6°C, with component of primary production and most N is mean monthly temperature ranging from −18.3°C in invested in leaves, NUE at leaf level could be January to 18.5°C in July. The study site was situated expected to be closely related to that at whole-plant in a riparian zone along the Xiaohezi River, 2 km level, and thus differences in whole-plant NUE could south of Duolun Town (42°11′N, 116°48′E). We be explained largely by leaf-level attributes (Escudero selected two habitat types: riverine wetland and river et al. 1992; Garnier et al. 1995). More recently, bank. The river bank was situated in the riparian zone, Yasumura et al.(2002) studied how the difference in 5–10 m away from the riverine wetland. Table 1 irradiance influenced the leaf-level NUE of canopy contains data on site characteristics of the two and understory species in a beech forest. They habitats. During the growing season (from June to demonstrated that aboveground NUE of three shrub October), we selected five replicates, 50–100 m away species showed the same trend as the leaf-level NUE, from each other, for each habitat. At each replicate, suggesting that aboveground NUE and its compo- three core soil samples, for analysis, were taken at 0– nents could be approximated by leaf-level values in 20 cm depth from the riverine wetland and the river Plant Soil (2007) 301:303–313 305 Table 1 Site characteristics of the riverine wetland and the river bank near Duolun County, China Site Riverine wetland River bank Soil type Coarse sand Coarse sand Dominant plant species Salix cheilophila Salix spp. Phragmites communis Hedysarum leave Typha minima Carex spp. Carex spp. Site management Natural Natural Bulk density (g cm−3) 1.70±0.14a 2.18±0.21b Soil texture Sand (%) 93.7±8.2a 92.5±9.3a Silt (%) 4.6±0.4a 4.8±0.4a Clay (%) 1.7±0.1a 2.7±0.2b pH 7.5±0.6a 7.3±0.5a Water holding capacity (%) 20.5±2.1a 23.2±2.9a −1 Moisture (g H2Og dry soil) 0.185±0.04a 0.055±0.02b Soil organic matter (%) 0.25±0.02a 0.29±0.03a Total N (mg g−1) 0.14±0.01a 0.10±0.02a þ þ À −1 Inorganic N (NH4 NO3 ,mgkg ) 1.5±0.3a 1.2±0.2a Available P (p.p.m) 2.1±0.2a 2.7±0.3b Data are means and standard errors. Each replicate represents the average of eight sampling dates. Different letters indicate significant (P<0.05) differences between habitats after t-test analysis bank each month. Soil organic matter was estimated data in Table 1 were averages of five replicates and from total organic carbon, determined by dry com- eight sampling dates. The results showed that the soils bustion (Nelson and Sommers 1996), total N by the underlying the study site consisted of coarse sand semimicro Kjeldahl technique (Bremner and Mulva- with low soil N availability (Table 1). There was no ney 1982), and available P according to Bray and significant difference in soil N availability between Kurtz (1945). Soil texture was determined by the the two habitats. Soil moisture contents at both pipette method (Gee and Bauder 1986). Soil bulk habitats were lower than their maximum WHC. The density was determined using a soil core (stainless riverine wetland and the river bank sites differed steel cylinders with a volume of 100 cm3).
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