Abstract
Although leaf economics spectrum (LES) has been extensively tested with regional and global datasets, the correlation among functional traits of desert plants remains largely unclear. Moreover, examinations on whether and how leaf and root traits are coordinated have yielded mixed results. We investigated variations in leaf and fine-root traits across 48 species in a desert community of northern China to test the hypotheses that (1) the leaf-trait syndrome of plant species in desert shrublands follows the predictions of the global LES, and is paralleled by a similar root-trait syndrome, (2) functional traits related to nutrient contents and resource uptake are tightly coordinated between leaves and fine roots in desert ecosystems where plant growth is limited primarily by dry and nutrient-poor conditions, and (3) traits as well as their relationships vary among functional groups. Our results partially supported the LES theory. Specific leaf area (SLA) was correlated with leaf tissue density, phosphorus content, and carbon-to-nitrogen ratio, but not with leaf nitrogen content. Specific root length (SRL) was not correlated with other fine-root traits, and fine-root traits were largely independent of each other. Therefore, fine-root traits did not mirror the leaf-trait syndrome. Fine-root nitrogen and phosphorus contents, nitrogen-to-phosphorous ratio, and carbon-to-nitrogen ratio all increased with analogous leaf traits, whereas SRL was not correlated with SLA. After phylogenetic effects were considered, nutrient contents and their ratios still displayed stronger coordination between leaves and fine roots than did SRL and SLA. The overall pattern of trait variations and relationships suggested differentiation among functional groups. Our results suggest that despite the absence of a root-trait syndrome, fine-root functions in the studied desert community were probably coordinated with leaf functions with respect to nutrient allocation and use.
Highlights
Leaf functional traits play an important role in plant carbon assimilation, water relations and energy balance (Ackerly et al, 2002), while root traits determine nutrient and water uptake that are crucial for plant survival and growth (McCormack et al, 2015; Weemstra et al, 2016; Wang et al, 2018)
Pairwise trait relationships revealed that Specific leaf area (SLA) was positively correlated with leaf phosphorus content (LP), negative correlated with leaf tissue density (LTD) and LC:leaf nitrogen content (LN), but not correlated with LN and LN:LP across all species (Figure 1)
Leaf principal component analysis (PCA) was generally consistent with pairwise relationships, with PC1 showing that species with low SLA had high LTD and LC:LN, but low LN, LP, and LN:LP (Figure 2A and Table 1)
Summary
Leaf functional traits play an important role in plant carbon assimilation, water relations and energy balance (Ackerly et al, 2002), while root traits determine nutrient and water uptake that are crucial for plant survival and growth (McCormack et al, 2015; Weemstra et al, 2016; Wang et al, 2018). According to leaf and root economics spectrum (LES and RES, respectively), Leaf and Root Traits specific leaf area (SLA) and specific root length (SRL) are two key traits that indicate plant resource strategies (Wright et al, 2004; Cheng et al, 2016). Species with high SLA exhibiting high LN, leaf phosphorus content (LP), high photosynthetic rate and short leaf lifespan, and low leaf tissue density (LTD), i.e., a resource-acquisitive strategy. The opposite is for species with low SLA exhibiting conserved traits (Wright et al, 2004; Pérez-Ramos et al, 2012). Some studies found weak or a lack of correlation between SLA and other leaf traits across species (Zhou et al, 2010; Chen et al, 2013). Existing studies on leaf traits mainly focused on forests and grasslands (He et al, 2008; Fajardo and Siefert, 2016; Hosseini et al, 2019), it remains largely unclear how leaf traits are correlated across species in desert communities
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