Linking Plant Leaf Nutrients/Stoichiometry to Water Use Efficiency On
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Ecological Engineering 87 (2016) 124–131 Contents lists available at ScienceDirect Ecological Engineering jo urnal homepage: www.elsevier.com/locate/ecoleng Linking plant leaf nutrients/stoichiometry to water use efficiency on the Loess Plateau in China a a a,b a,∗ Weiming Yan , Yangquanwei Zhong , Shuxia Zheng , Zhouping Shangguan a State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A&F University, Yangling, Shaanxi 712100, PR China b State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China a r t a b i s c l e i n f o t r a c t Article history: Nutrient and hydrological cycles are tightly coupled in ecosystems. However, little is known about the Received 30 January 2015 relationship between leaf nutrient stoichiometry (nutrient mass ratios) and water use efficiency (WUE) Received in revised form 22 October 2015 in ecosystems. To fill this knowledge gap, we examined 132 plant samples distributed from the Qinling Accepted 18 November 2015 Mountains to the north of the Loess Plateau of China and observed the relationship between leaf nutrient stoichiometry and WUE in various ecosystems. Our findings suggest that a positive correlation exists Keywords: between the leaf nitrogen:phosphorus (N:P) ratio and WUE, and this relationship is sensitive to plant life Leaf nutrients forms and growth conditions. Additionally, potassium (K) was related to WUE in herbs and plants under Stoichiometry WUE P limitation. These results link plant nutrient stoichiometry to hydraulic processes in terrestrial plants and provide useful information for ecologists studying nutrient and hydrological cycles in ecosystems. Life form Nutrient limitation © 2015 Elsevier B.V. All rights reserved. 1. Introduction required for the synthesis of proteins, which contain large amounts of N and P (Cernusak et al., 2010). The N:P ratio (ratio of the N to Carbon (C), nitrogen (N), phosphorus (P) and potassium (K) are P concentration) in terrestrial plant leaves can provide important considered essential elements for plant growth and play a vital role information about potential nutrient limitation, which may affect in plant functions (Marschner and Marschner, 2012). C provides primary productivity (Ågren, 2008; Cernusak et al., 2010). The bal- the structural basis of the plant, constituting a relatively stable ance of N and P can influence the growth rate of plants, and the 50% of the dry mass; N is an important constituent of proteins and leaf N:P mass ratio has been widely used as an indicator of N or P plays an essential role in all enzymatic activities; and P is involved deficit. For example, based on studies conducted on European wet- in energy transfer in cells. Additionally, P and N are important land plants, it has been suggested that an N:P ratio above a given structural elements in nucleic acids (Ågren, 2008; Marschner and threshold (16 on a mass basis) indicates P limitation of biomass pro- Marschner, 2012). These three elements (C, N and P) are strongly duction, whereas a ratio below a given threshold (c. 14 on a mass coupled in terms of their biochemical functions. N and P, which basis) indicates N limitation (Koerselman and Meuleman, 1996; are required for plant growth in relatively large quantities, are Aerts and Chapin, 1999; Tessier and Raynal, 2003; Güsewell, 2004; classified as macronutrients and cannot be substituted with other Reich and Oleksyn, 2004; Cernusak et al., 2010). This parameter elements in metabolic functions (Aerts and Chapin, 1999; Ågren, offers a powerful tool for ecological and physiological investiga- 2008). K is involved in the plant–water relationship (Babita et al., tions by providing a straightforward means of characterising the 2010) through plant osmotic control and improvement of stoma- relative availability of N vs. P (Cernusak et al., 2010). Relation- tal function (Sangakkara et al., 2000; Babita et al., 2010; Laus et al., ships between N:P ratios and vegetation characteristics have also 2011; Rivas-Ubach et al., 2012). been used to describe functional differences between naturally N- Plant growth requires photosynthetic products, and proteins are or P-limited plant communities and their responses to environ- required for photosynthesis and growth. In addition, ribosomes are mental change or human management (Tessier and Raynal, 2003; Güsewell, 2004; Reich and Oleksyn, 2004). K is also important, but less information is available regarding the quantitative require- ∗ ments for this element (Reich and Oleksyn, 2004). Correspondence to: Xinong Rd. 26, Institute of Soil and Water Conservation, In many terrestrial ecosystems, soil water is variable and often Yangling, Shaanxi, 712100, PR China. Tel.: +86 29 87019107; fax: +86 29 87012210. the most important limiting soil resource. Therefore, plant water E-mail addresses: [email protected] (W. Yan), [email protected] (Y. Zhong), [email protected] (S. Zheng), [email protected] (Z. Shangguan). use efficiency (WUE) is of major importance for the survival, http://dx.doi.org/10.1016/j.ecoleng.2015.11.034 0925-8574/© 2015 Elsevier B.V. All rights reserved. W. Yan et al. / Ecological Engineering 87 (2016) 124–131 125 ◦ ◦ productivity and fitness of individual plants (Ponton et al., 2006) broadleaf forest located at 108 26 E and 33 26 N, all of the other and is a measure of plant performance that has long been of inter- investigated stands, i.e., Yangling, Yongshou, Tongchuan, Fuxian, est to agronomists, foresters and ecologists (Cernusak et al., 2007a; Ansai, Mizhi and Shenmu, are distributed from south to north on Raven et al., 2009). In plant physiological ecology, leaf carbon-13 the Loess Plateau of China (Fig. 1). These stands are located at ␦13 ◦ ◦ ◦ ◦ ( C) data are a useful index for assessing WUE when the leaf- 34 16 –38 47 N and 108 02 –110 21 E within the temperate zone, to-air vapour pressure difference is known (Farquhar et al., 1989; and the vegetation type ranges from semi-humid forests to arid Dawson et al., 2002), and these data have been widely used to eval- desert grasslands. The altitude, latitude and longitude were deter- uate plant WUE under various environmental conditions and in mined using a global positioning system (GPS) at the sampling sites. response to climatic variables (Hietz et al., 2005; Silva et al., 2009; The sampling sites were located far from human habitation (more 13 Nock et al., 2011; Penuelas˜ et al., 2011). Leaf ␦ C data not only than 1 km) to minimise the influence of human disturbance. The precisely reflect water conditions but also reflect the physiologi- detailed geographical and climatic conditions of the eight sampling cal status of the plant and have been proven to be the best means sites are summarised in Table 1. of investigating WUE. As one of the most important physiological characteristics involved in plant growth, WUE is considered to be an 2.2. Plant materials objective index for evaluating water conditions (Cabrera–Bosquet et al., 2007) and drought tolerance characteristics and is capable A total of 132 plant samples (118 from the Loess Plateau and of providing a theoretical basis for studying such characteristics 14 from the Qinling Mountains) belonging to 39 different species in specific environments (Livingston et al., 1999; Condon et al., and 17 families, including 10 types of trees, 20 types of shrubs 2004). In addition, transpiration plays a role in modulating nutrient and 10 types of herbaceous species, were collected at the eight uptake by delivering nutrients to root surfaces through mass flow sites. Species from the 3 different plant life forms (herbs, shrubs (Cernusak et al., 2011). However, little is known about the relation- and trees) were selected based on the following criteria: the target ship between plant WUE and nutrients in ecosystems. Therefore, species should be the dominant species and relatively abundant studying the relationship between WUE and nutrients across plant at each site. Sun foliage samples were mainly collected from the life forms and nutrient conditions would help us to better under- upper canopies. Three to five healthy and fully expanded leaves stand ecosystems. from individual plants were randomly selected, and each sample It has been reported that the leaf N:P ratio is positively correlated included leaves from 4–5 individual plants of the same species. with plant WUE in seedlings of tropical pioneer tree species, and it has been suggested that the N:P ratio is expected to be correlated 13 with WUE according to the following argument (Cernusak et al., 2.3. C (carbon isotope discrimination) and calculation of 2007b): positive increases in plant C require N-rich proteins for WUE plants to assimilate C and grow, as shown in the following equation (Ågren, 2004): dC/dt = ˚CN NP (C, amount of carbon; t, time; CN, The leaf samples were ultrasonically washed with distilled ◦ rate factor; NP, amount of nitrogen in proteins used for growth). In water, air-dried, oven-dried at 70 C for at least 48 h to a con- addition, P-rich ribosomes are required for protein synthesis. The stant weight, then ground to a fine powder using a plant sample amounts of N and P in plants exceed those required for growth and mill (Cyclotec sample Mill 1093; FOSS Tecator, Hoganas, Sweden), 13 ␦ protein synthesis, but a balance between N and P is necessary for and finally sieved through a 1-mm mesh screen. C was ana- normal plant functioning and could affect the normal growth of lysed using a MAT-251 mass spectrometer (Finnegan, San Jose, USA) plants. Mass flow, which partly depends on plant transpiration, is at the State Key Laboratory of Soil and Sustainable Agriculture, the process by which P in the soil solution is transported to the Institute of Soil Science, Chinese Academy of Sciences.