Yong-Jiao Zhou, Institute of Applied Ecology, Chinese Academy of Sciences, discusses their article: Trait networks and the whole-plant economics spectrum: Uncovering key determinants of growth rate across 33 temperate tree species
Why do some trees grow fast, while others always seem to lag behind?
For decades, ecologists have strived to answer this question. Past research has predominantly focused on above-ground traits, such as leaf photosynthetic capacity or wood density. However, in reality, tree growth is driven by the collective performance of different organs: leaves fix carbon, stems and coarse roots transport resources, and fine roots absorb water and nutrients. How exactly functional traits of above- and below-ground organs coordinate to influence tree growth has long remained unclear.
The whole-plant approach
In a common garden, we conducted a study on 33 temperate deciduous broad-leaved tree species co-occurring in the Changbai Mountains, Northeast China. By integrating a decade of tree-ring data (2010–2020) with 24 functional traits spanning leaves, stems, coarse roots, and fine roots, we brought the full picture into focus from a holistic perspective of “resource acquisition–transportation–utilization”, systematically unravelling the intrinsic physiological mechanisms of multi-organ coordination that underpin tree growth.
Deconstructing organs: How do fast-growing trees “arm” their organs?
By dissecting individual traits, we found that fast-growing tree species evolve more efficient characteristics across all their organs:
- Leaves: They possess higher photosynthetic rates and denser vein networks. Interestingly, they also exhibit a greater leaf mass per area (LMA). In temperate forests, a higher LMA may not always imply a conservative strategy; instead, it may represent a thicker mesophyll layer that supports greater photosynthetic capacity.
- Stems: They feature wider vessels and higher hydraulic conductance while allocating more stem xylem per unit leaf area (Hv), essentially building a wider, more stable “water highway” to supply the canopy.
- Coarse roots: They similarly possess wider vessels and higher hydraulic efficiency, ensuring that water encounters almost “no traffic jams” on its way into the trunk.
- Fine roots: Fast-growing trees tend to have thicker fine roots rather than thinner ones. This suggests that in natural forest ecosystems, thicker fine roots may imply stronger mycorrhizal symbiosis and a more efficient resource-exchange system.
Who are the “hubs” within the trait network?
Beyond looking at individual traits, we constructed a “functional trait network”. We discovered that leaf photosynthetic rate, stem hydraulic conductance, and coarse-root vessel diameter exhibit exceptionally high centrality within the network. Acting like “hubs” in a transportation system, these traits establish more connections with other traits and show stronger correlations with tree growth rates.
This underscores that what is more critical to tree growth is the hub traits coordinating multiple organ functions.
Strategy showdown: Fast-paced vs. slow-living
Furthermore, our study successfully validated the existence of a clear “Whole-Plant Economics Spectrum”.
- The “fast-paced” acquisitive strategy: Tree species at one end of the spectrum combine stronger photosynthesis, more efficient water transport across organs, and thicker fine roots with lower investment in wood construction costs, supporting rapid radial growth.
- The “slow-living” conservative strategy: Tree species at the opposite end of the spectrum, by contrast, exhibit weaker carbon fixation and lower water transport efficiency, but prioritize investing in high-cost tissue construction, corresponding to a conservative slow-growth strategy.
We found that tree growth rates are well explained by individual above- and below-ground traits associated with resource economics and tree hydraulics, with leaf photosynthetic rate and both stem and coarse-root hydraulic efficiency identified as hub traits that strongly influence growth by simultaneously mediating multiple plant functions. Moreover, the acquisitive–conservative strategies along the PES showed strong alignment with the fast–slow growth pattern. Taken together, this work reveals the functional integration of leaves, stems, and roots as a “whole-plant symphony” that underpins tree growth. We hope that this study, with its identification of these key traits and their connections, will promote more studies and better understanding of the whole plant economic spectrum.
