Abstract
Nitrogen (N) and phosphorus (P) play important roles in many aspects of plant biology. The allocation of N and P in plant vegetative organs (i.e., leaves, stems, and fine roots) is critical to the regulation of plant growth and development. However, how these elements are allocated in seeds is unclear. The aim of this study was to explore the N and P allocation strategies of seeds in an alpine meadow along an altitudinal gradient. We measured the seed N and P contents of 253 herbaceous species in 37 families along an altitudinal gradient (2,000–4,200 m) in the east Tibetan alpine meadow. The geometric means of seed N and P concentrations and N:P ratios were 34.81 mg g–1, 5.06 mg g–1, and 6.88, respectively. Seed N and P concentrations varied across major taxonomic groups and among different altitude zones. N:P ratios showed no significant variations among different taxonomic groups with the exception of N-fixing species. The numerical value of the scaling exponent of seed N vs. P was 0.73, thus approaching 3/4, across the entire data set, but varied significantly across major taxonomic groups. In addition, the numerical value of the scaling exponent of N vs. P declined from 0.88 in the high altitude zone to 0.63 in the low altitude zone. These results indicate that the variations in the numerical value of the scaling exponent governing the seed N vs. P scaling relationship varies as a function of major taxonomic groups and among different altitude zones. We speculate that this variation reflects different adaptive strategies for survival and germination in an alpine meadow. If true, the data presented here advance our understanding of plant seed allocation strategies, and have important implications for modeling early plant growth and development.
Highlights
Nitrogen (N) and phosphorus (P) are considered the most important resources regulating plant growth and development (Vitousek, 2004), and play pivotal roles in regulating community dynamics and ecosystem function (Güsewell, 2004; Vitousek et al, 2010)
In the context of the N vs. P scaling relationship, when the scaling exponent is less than unity (i.e., α < 1), plants require disproportionately more P than N, perhaps to ensure rapid protein synthesis, whereas when the scaling exponent is greater than unity (i.e., α > 1) the opposite trend holds true (McGroddy et al, 2004; Niklas et al, 2005; Kerkhoff et al, 2006)
We found that N and P concentrations differed across major taxonomic groups (Table 1 and Figure 2)
Summary
Nitrogen (N) and phosphorus (P) are considered the most important resources regulating plant growth and development (Vitousek, 2004), and play pivotal roles in regulating community dynamics and ecosystem function (Güsewell, 2004; Vitousek et al, 2010). The allocation of N and P in plants undoubtedly reflects fundamental adaptive strategies across different species and species groups, which in turn influence the material and energy cycles of ecosystems (Ågren, 2004; Elser et al, 2007). Quantifying how these two elements are allocated in plants is essential to our understanding of ecosystem dynamics. In the context of the N vs. P scaling relationship, when the scaling exponent is less than unity (i.e., α < 1), plants require disproportionately more P than N, perhaps to ensure rapid protein synthesis (as predicted by the growth rate hypothesis proposed by Elser et al, 2000; 2003), whereas when the scaling exponent is greater than unity (i.e., α > 1) the opposite trend holds true (McGroddy et al, 2004; Niklas et al, 2005; Kerkhoff et al, 2006)
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