Climate and soil nutrients differentially drive multidimensional fine root traits in ectomycorrhizal‐dominated alpine coniferous forests

Abstract

1. Fine root traits vary greatly with environmental changes, but the understanding of root trait variation and its drivers is limited over broad geographical scales, especially for ectomycorrhizal (ECM)-dominated conifers in alpine forests. Herein, the covariation patterns of and environmental controls for fine root traits among ECM-dominated conifers were examined to test whether and how climate and soil nutrients differentially affect fine root trait variations. 2. Eight traits of first-and second-order roots were measured, that is, root diameter (RD), specific root length (SRL), branching intensity (BRI), root tissue density (RTD), mycorrhizal colonization rate (MCR) and concentrations of carbon (C), nitrogen (N) and phosphorus (P), across 76 alpine coniferous populations on the eastern Tibetan Plateau, China. 3. Our results showed that variations of the fine root traits fell into two major dimensions: the first dimension (32.39% of the total variance) was mainly represented by RD and SRL, potentially conveying a trade-off between root life span and efficiency of resource foraging; the second dimension (23.70% of the variance) represented coordinated variation for root nutrients (i.e. N and P) and RTD, which depicts the conservation-acquisition trade-off in resource uptake, that is, root economic spectrum. Variations in RD and SRL were mainly driven by climatic variables, characterized by a significant increase in RD and a decrease in SRL with increasing mean annual precipitation. In contrast, variations in fine root nutrients (i.e. N and P) and RTD were primarily driven by soil fertility, showing a significant increase in root N and P concentrations but a decrease in RTD with increasing soil resource levels. 4. Synthesis. Our study clearly shows two distinct dimensions of the variation of fine root traits in ECM-dominated alpine coniferous forests, providing further evidence of the inherent multidimensionality of root traits. Moreover, our findings highlight different roles of climatic and soil variables in driving the variation of fine root traits, potentially leading to the multidimensionality of root traits. This | 2545

Patterns in intraspecific variation in root traits are species‐specific along an elevation gradient

“…Read et al. (2017) found the opposite pattern for SRL, but other studies found outcomes similar to ours (Burton et al., 2017; Ding et al., 2020; Valverde‐Barrantes et al., 2013). Root trait variation at the community level may thus be generally more strongly driven by species' turnover than intraspecific root trait variation, but as species in our study did not make up the majority of the vegetation cover at all elevations, we could not test this potential consequence.…”

“…Our hypothesis (2a) is based on the premise that thicker roots may sustain higher mycorrhizal colonisation rates which benefits resource uptake. However, this relationship is more firmly established for arbuscular mycorrhizal hosts (as thick roots generally have a larger cortex which is directly related to space for arbuscular mycorrhizal fungi; Kong et al., 2014) than for ectomycorrhizal host species (Ding et al., 2020; Kong et al., 2014; McCormack & Iversen, 2019). Thick roots also have lower proliferation rates (Eissenstat, 1991) and foraging precision (Chen et al., 2016); such slower proliferation may be particularly disadvantageous at high altitudes, with typically heterogeneous resource distributions (Holtmeier & Broll, 2005) and short growing seasons that provide limited opportunities to capture sufficient resources, especially in competition with neighbouring plants (Hutchings et al., 2003).…”

Root exudation as a major competitive fine‐root functional trait of 18 coexisting species in a subtropical forest

“…Most studies on root trait coordination put forward hypotheses based on a single‐dimensional spectrum of acquiring resources efficiently or not (Roumet et al ., 2016; Weemstra et al ., 2016) that were in parallel with a single‐dimensional ‘fast–slow growing’ leaf economic spectrum and whole‐plant strategy (Westoby & Wright, 2006; Reich, 2014; Weemstra et al ., 2016). However, field studies have revealed both single‐dimensional (Prieto et al ., 2015; Roumet et al ., 2016; Li et al ., 2017; Wen et al ., 2019) and multidimensional root trait coordination (Valverde‐Barrantes et al ., 2015; Kramer‐Walter et al ., 2016; Liese et al ., 2017; Erktan et al ., 2018; Ding et al ., 2020). One reason is that symbiotic mycorrhizal fungi provide an alternative strategy for plant nutrient acquisition rather than a competitive morphological structure (McCormack & Iversen, 2019; Bergmann et al ., 2020).…”

Topography as a factor driving small‐scale variation in tree fine root traits and root functional diversity in a species‐rich tropical montane forest

“…Resource scarcity, conversely, is believed to exclude fast-growing plants and require species to conserve invested resources (de la Riva et al, 2018;Delpiano et al, 2020). Fine root properties were found to vary along environmental gradients as predicted by the RES framework for different life forms and ecosystems and at different spatial scales (Holdaway et al, 2011;Kramer-Walter et al, 2016;de la Riva et al, 2018;Ding et al, 2020;Fort & Freschet, 2020). While the majority of studies on root trait variation along soil fertility and climate gradients compared different ecosystem types or even different biomes, soil chemical variation also occurs on small spatial scales within ecosystems, for example along smallscale topographic gradients at the same elevation.…”

“…The variation of fine root functional traits along environmental gradients is currently a widely discussed topic in plant functional ecology (e.g. Addo‐Danso et al ., 2020; Delpiano et al ., 2020; Ding et al ., 2020). By contrast with aboveground plant organs, which have been studied extensively (Westoby et al ., 2002; Wright et al ., 2004; Chave et al ., 2009; Díaz et al ., 2016), less is known about the leading dimensions of root functional traits and their association with abiotic factors (Laliberté, 2017).…”