Global meta‐analysis reveals different patterns of root tip adjustments by angiosperm and gymnosperm trees in response to environmental gradients

Abstract

Aim Rising air temperature and changing precipitation patterns already strongly influence forest ecosystems, yet large‐scale patterns of belowground root trait variation and their underlying drivers are poorly understood. Here, we investigated general patterns of root tip adjustments within fine‐root systems and the potential ecological implications of these patterns. Location Global. Methods We synthesize key fine‐root traits related to resource acquisition and determined their responses along climate and edaphic gradients. We specifically identified patterns of root tip abundance (number of root tips per dry biomass of fine roots ≤2 mm in diameter), and root tip density (number of root tips per soil volume) among angiosperm and gymnosperm trees to climate, edaphic gradients and stand properties. Results We found that angiosperm trees, which were more common in warmer, sometimes drier climates with more fertile soil, formed more root tips (higher root tip abundance, root tip density and higher slope of root tip density vs. fine‐root biomass) than gymnosperm trees, which lived in cooler, wetter climates with poor soil. Angiosperm and gymnosperm trees exhibited opposing trends in response to gradients in climate as gymnosperm trees tended to decrease root tip abundance and root tip density but alternatively increase mycorrhizal mycelial biomass with increasing MAT/MAP (ratio of mean annual temperature to mean annual precipitation), while angiosperm trees tended to increase root tip abundance and root tip density with increasing MAT/MAP. However, the individual trends of root tip abundance and root tip density for angiosperm and gymnosperm trees to MAT or MAP were more similar and often non‐significant. Main conclusions These results suggest disparate carbon or biomass adjustment strategies within gymnosperm and angiosperm tree fine‐root systems along climate gradients. Differences in angiosperm and gymnosperm tree adjustments in their fine‐root systems to changing environments have implications for how these plant groups are likely to perform in different environments and how their responses to future climate change should be modelled.

Faculty Opinions recommendation of Robust leaf trait relationships across species under global environmental changes.

“…6a). This result suggests a more conserved trait adjustment strategy in gymnosperms than angiosperms, which has also been found in the root traits 50 . Due to the higher nitrogen use efficiency in C 4 than C 3 herbs 51 , it is expected that the elevation of A m -N m relationship is greater in C 4 than C 3 herbs ( Supplementary Fig.…”

Environmental drivers of plant distributions at global and regional scales

“…A large proportion of angiosperms and gymnosperms, with complex interaction system of plant–soil feedback, are more likely to be influenced by temperature‐related factors that shape spatial patterns of mycorrhizal host plants (Barceló et al., 2019). Moreover, variations in eco‐physiological traits lead to angiosperm trees occurring in warmer climates with more fertile soil and gymnosperm trees to distribute in wetter and cooler climates with poor soil (Wang et al., 2019). This illustrates why gymnosperms are distributed more widely and cover a broader range of latitudes, and are more likely to appear in higher latitude areas, compared with angiosperms (Supporting Information Appendix S1: Figure S1.4).…”

Future direction of searching for root economics spectrum: focusing on the fibrous roots “absorptive unit”

“…], and root tip density [number of root tips per soil volume; Wang et al. ]) of the absorptive unit in future studies. What should be emphasized is that although the standardized sampling protocol we proposed is widely applicable, there are still some exceptions.…”

“…The branching architecture of roots seems to be independent from phylogeny and is an expression of responses and adaptations to the environment (Kong et al 2014, Liese et al 2017. It might be significant to pay more attention to the architecture traits (e.g., specific root tip density [number of root tips divided by root dry mass, SRTD; Isaac et al 2017], root length density [root length per soil volume, RLD; Comas et al 2012], and root tip density [number of root tips per soil volume; Wang et al 2019]) of the absorptive unit in future studies. What should be emphasized is that although the standardized sampling protocol we proposed is widely applicable, there are still some exceptions.…”