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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. Eight traits of first-
and second-order roots were measured, i.e., 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. 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 tradeoff between root lifespan 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 tradeoff in resource
uptake, i.e., root economic spectrum (RES). 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. 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 study provides new insights for understanding and predicting
shifts in plant belowground strategies in climate-sensitive alpine forests
worldwide.
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