Foliar, root and rhizospheric soil C:N:P stoichiometries of overstory and understory species in subtropical plantations
Introduction
Ecological stoichiometry represents the balance of energy and nutrient and provides important information on biogeochemical processes in terrestrial ecosystems (Reiners, 1986, Elser et al., 1996, Elser et al., 2000). Carbon (C) is the basis of plant growth, reproduction and structure, and constructs about 50% of plant dry weight (Liu et al., 2011). Nitrogen (N) is the major component of all enzymes and chlorophyll in plants which plays an important role in controlling carbon uptake and primary production (Chen et al., 2016). Phosphorus (P) is a key element in plant ribosome production and responsible for the construction of RNA, DNA and ATP, playing an important role in genetic information transmission, energy storage and cell construction (Bai et al., 2012, Chen et al., 2013). Stoichiometric research has paid most attention to C, N and P due to their crucial roles in plant growth and physiological metabolism (Finzi et al., 2011, Zechmeister-Boltenstern et al., 2015, Zhang et al., 2018a).
In recent decades, C:N:P stoichiometry has been increasingly used to explore the relationships between above- and below-ground components of ecosystems (Zeng et al., 2016, Zeng et al., 2017, Yang et al., 2018a, Bai et al., 2019). Specifically, foliar and root nutrient stoichiometries vary among species due to their specific strategies for the assimilation and allocation of C and to their demand and resorption of nutrients, and which would influence ecosystem processes and functions eventually (Bell et al., 2014, Bu et al., 2019). For example, shifts in abundances of plant species can alter the nutrient stoichiometry of the soil (Li et al., 2011), showing that soil C:N, C:P and N:P ratios can vary simultaneously with the dynamic variation of plant communities because of different substrate inputs (e.g. rhizodeposition) (Zechmeister-Boltenstern et al., 2015, Zhang et al., 2018b). Meanwhile, the status of soil resources can further affect the compositions of specific plant communities (Bell et al., 2014) and the abundance of plant species (Li et al., 2011). Plant-soil feedbacks can strongly influence the coexistence of competing plant species and thus ecosystem structure and function (Diez et al., 2010, Bell et al., 2014). However, most studies were focused on composited bulk soil samples, and ignored the small-scale heterogeneity associated with individual plants (Bell et al., 2014). The research of Yang, Zhu et al. (2018) indicated that rhizosphere is a powerful tool for understanding the linkage between plant and soil.
The rhizosphere is a focus of plant-soil feedbacks due to the strong association between plants and soil due to specific root processes, such as exudation and microbe symbiosis, etc (Carrillo et al., 2017). Rhizosphere stoichiometry is thus particularly important to assess the links between plant species and soil nutrient status (Bell et al., 2014, Carrillo et al., 2017), especially for forest ecosystems with different functional groups to coexist and interact, such as overstory trees and understory shrubs and herbs (Liu et al., 2017). Limited evidence has indicated that the rhizospheric soil C:N:P stoichiometries of overstory trees and shrubs differ markedly in plantation ecosystems (Dai et al, 2018), but whether or not differences in rhizosphere stoichiometry among coexisting species induce variations in foliar and root stoichiometries remains unknown.
Understory vegetation is an important component and plays a key role in ecosystem functions in forests (Gilliam, 2007, Wan et al., 2014). For example, understory vegetation can affect soil temperature and moisture content (Wang et al., 2014), increase soil C and N contents and potential enzymatic activities (Yang, Liu et al., 2018), promote litter decomposition (Cleveland et al., 2006) and alter soil food webs (Zhao et al., 2012). As an important driver of soil ecological processes in plantation ecosystems, understory vegetation has been increasingly studied in interactions between plants and soil (Jiang et al., 2020). Xie et al. (2019) found that understory plant species with different functional types impacted the correlations in C, N, and P stoichiometric ratios between plants and soil. Furthermore, Zhang et al. (2019) found that overstory trees and understory plants on Loess Plateau in China responded oppositely to soil N:P ratios due to their different use efficiencies and acquiring patterns of nutrient. Therefore, the study of coexisting species (including overstory trees and understory plant species) in the forest ecosystem can provide deeper insights into the role of plant species in driving ecosystem function (Weidenhamer and Callaway, 2010, Bell et al., 2014).
Evergreen broadleaved forest, the zonal vegetation in subtropical China, was destroyed by human activity prior to the 1980s, which severely degraded the soil. Cunninghamia lanceolata, Pinus massoniana and Pinus elliottii have been widely reforested since the 1980s to combat erosion (Dai et al., 2018). Plantations of these species have abundant understory vegetation and have since become important forest resources in subtropical China. We examined the C, N and P stoichiometries of leaves, roots and rhizosphere soils of overstory trees and understory shrubs and herbs in coniferous plantations of C. lanceolata, P. massoniana and P. elliottii. We hypothesized that 1) the C, N and P stoichiometries of leaves, roots and rhizosphere soils would differ among coexisting overstory trees and understory shrubs and herbs, thus inducing the difference among the three forest types and 2) the C, N and P stoichiometries of leaves and roots across all species would vary greatly with constraints of the rhizosphere soils.
Section snippets
Site description
This study was conducted at the Qianyanzhou Ecological Research Station of the Chinese Academy of Sciences in Taihe County, Jiangxi Province, China (26°44′48″N, 115°04′13″E). This region has a typical subtropical monsoon climate with mean annual temperature and precipitation of 17.9 °C and 1489 mm, respectively. The soil is a typical red soil that has been weathered from red sandstone and mudstone, and classified as Typic Dystrudept and Udept Inceptisol based on the USDA soil taxonomy (Jiang et
Plants and soil C:N:P stoichiometry
The foliar and rhizosphere soil C:N and C:P ratios were significantly affected by forest type (P < 0.05, Fig. 1). The foliar and rhizosphere soil C:N ratios of the P. elliottii forest were significantly higher than the ratios of the C. lanceolata and P. massoniana forests. Foliar and rhizosphere soil C:P ratios differed significantly between the P. elliottii and C. lanceolata forests, but there was no significant difference between P. massoniana and C. lanceolata forests. The foliar C:N ratios
Variations of the C, N and P stoichiometries among the plant species
Plants need to maintain relatively stable nutrient ratios (stoichiometric homeostasis) for optimal growth (Spohn, 2016), which is critical for maintaining the structure, function and stability of ecosystems (Zeng et al., 2013). Different species, especially those with different life forms, however, have different capacities of photosynthesis and C allocation relative to various demands for N and P, which produce different nutrient ratios (Zechmeister-Boltenstern et al., 2015). Our first
Conclusions
We studied the C:N:P stoichiometries of leaves, roots and rhizosphere soil of co-existing plant species in detail in three forest ecosystems. The C, N and P stoichiometries differed significantly among species with different life forms (trees, shrubs and herbs) with various survival abilities and growth strategies. The C, N and P stoichiometries of the leaves, roots and rhizosphere soil were strongly correlated, indicating substantial plasticity of C:N:P stoichiometry in leaves and roots across
Declaration of Competing Interest
This paper is not being considered nor has it been accepted for publication in any other journal. Further, the manuscript contains only original data, and it has not been published elsewhere in part or in its entirety. The authors further declare that they have no conflicts of interest, financial or otherwise.
Acknowledgments
This study was financially supported by the National Natural Science Foundation of China (31730014, 41830860). We thank Xueli Mo and Yuqiu Gao for their assistance in field and laboratory work. We thank Ye Yuan for her valuable comments regarding earlier versions of the manuscript. We also thank the academic editor and anonymous reviewers for their constructive comments, which helped in improving the manuscript.
References (78)
- et al.
Response of forest species to C:N: P in the plant-litter-soil system and stoichiometric homeostasis of plant tissues during afforestation on the Loess Plateau
China. Catena
(2019) - et al.
Soil microbial activities and carbon and nitrogen fixation
Res. Microbiol.
(2003) - et al.
Understory vegetation leads to changes in soil acidity and in microbial communities 27 years after reforestation
Sci. Total Environ.
(2015) - et al.
Facilitative effects of shrubs in shifting sand on soil macro-faunal community in Horqin Sand Land of Inner Mongolia, Northern China
Eur. J. Soil Biol.
(2011) Chloroplasts: a structural approach
J. Plant Physiol.
(1998)- et al.
The implications of exoenzyme activity on microbial carbon and nitrogen limitation in soil: a theoretical model
Soil Biol. Biochem.
(2003) Element cycling as driven by stoichiometric homeostasis of soil microorganisms
Basic Appl. Ecol.
(2016)- et al.
Does stoichiometric homeostasis differ among tree organs and with tree age?
Forest Ecol. Manag.
(2019) - et al.
Ecological stoichiometry in leaves, roots, litters and soil among different plant communities in a desertified region of Northern China
Catena
(2018) - et al.
The linkage between vegetation and soil nutrients and their variation under different grazing intensities in an alpine meadow on the eastern Qinghai-Tibetan Plateau
Ecol. Eng.
(2018)