Coarse roots are the thick, woody transport and structural organs of the root system, distinct from the fine roots that handle most nutrient absorption. While fine roots have attracted decades of stoichiometric research, coarse roots remained a blind spot, even though they represent an enormous reservoir of biomass and nutrients in forests worldwide. To fill this gap, an international team led by Siying Gong and Yang Li of the Central South University of Forestry and Technology, together with colleagues at the Chinese Academy of Sciences, compiled a global dataset of nitrogen and phosphorus concentrations in woody plant coarse roots and subjected it to rigorous scaling analysis.

The headline numbers are striking in their own right. Across the globe, coarse root nitrogen concentrations averaged 5.67 milligrams per gram of tissue, while phosphorus averaged just 0.76 milligrams per gram, a ratio of roughly seven to one. When the researchers plotted nitrogen against phosphorus across all species and sites, they found a statistically significant relationship, but one that was loose rather than tight. The overall scaling exponent came out at 0.81, meaning that nitrogen concentrations increase more slowly than phosphorus concentrations as plants become more phosphorus-rich. An exponent of exactly 1.0 would indicate isometric scaling, where both nutrients change in lockstep; anything below it suggests a degree of decoupling between the two elements.

The real surprise emerged when the team broke the global picture down by plant functional group. Angiosperms, the flowering trees and shrubs that dominate most of the world’s forests, showed scaling exponents close to isometry, hinting that their nitrogen and phosphorus economies are relatively coordinated. Gymnosperms, the conifers and their allies, displayed significantly lower exponents, indicating that their coarse root nitrogen and phosphorus contents are far less tightly coupled. This phylogenetic split suggests that hundreds of millions of years of divergent evolution have left distinct chemical fingerprints in the underground tissues of these two great lineages of seed plants.

Functional traits beyond lineage mattered just as much. Evergreen species, which hold their leaves year-round and typically conserve nutrients intensively, exhibited higher scaling exponents than deciduous species that shed their foliage each autumn. Even more intriguing was the role of mycorrhizal symbiosis, the ancient partnership between plant roots and fungi. Species associated with arbuscular mycorrhizal fungi, which penetrate root cells and are especially adept at scavenging phosphorus, showed higher exponents than species partnered with ectomycorrhizal fungi, which sheath the roots and dominate in many temperate and boreal conifer forests. The finding aligns with a growing body of evidence that mycorrhizal type fundamentally reshapes plant nutrient economics, from carbon allocation to decomposition rates.

Geography left its mark as well. Coarse root nitrogen concentrations were lowest in boreal regions, echoing the well-documented pattern that cold, high-latitude environments constrain nitrogen availability and plant nutrient concentrations. Yet the scaling exponents themselves told a subtler story: they were higher in tropical and boreal forests than in temperate forests. The temperate zone, with its intermediate climates and mixed forests of deciduous angiosperms and evergreen gymnosperms, appears to host a particularly heterogeneous mix of nutrient strategies, flattening the global relationship when all species are pooled together.

Perhaps the most consequential finding concerns what drives these patterns below ground. When the researchers tested the influence of environmental variables on the variation in scaling exponents, soil total phosphorus emerged as a significant driver, whereas soil total nitrogen did not. In other words, the availability of phosphorus in the ground, not nitrogen, appears to govern how flexibly trees balance the two nutrients in their coarse roots. This makes ecological sense: phosphorus is chemically scarcer, geologically patchy and slower to cycle than nitrogen, so plants may have evolved more plastic responses to its availability. It also echoes the classic Walker and Syers model of phosphorus depletion during soil development, which predicts that phosphorus becomes an increasingly limiting resource over time.

Why does this matter beyond the world of root ecology? Coarse roots store a substantial fraction of forest carbon and nutrients, and their chemistry influences decomposition rates, nutrient return to the soil and the residence time of carbon in biomass. Global vegetation models that simulate forest growth and biogeochemical cycling often rely on simplified assumptions about how nutrients scale across plant organs. If coarse root nitrogen and phosphorus relationships shift systematically across lineages, mycorrhizal types and climate zones, then models built on a single universal exponent could misestimate nutrient limitation, biomass allocation and carbon storage, particularly as forests respond to rising carbon dioxide, nitrogen deposition and shifting disturbance regimes.

The study’s authors argue that these context-dependent scaling patterns should be woven into the root economics spectrum, the framework that describes how root traits trade off between fast resource acquisition and slow, conservative resource use. Just as leaves follow a worldwide fast-slow economic spectrum, roots appear to occupy a multidimensional space shaped by fungal collaboration gradients and structural roles. Coarse roots, as the transport backbone of that system, now have their own quantified position within it, and it is not the rigid one that a universal law would predict.

The work also highlights how much remains to be learned beneath the soil surface. Fine roots have been mapped, measured and modeled far more intensively, yet coarse roots may hold the key to understanding how forests allocate nutrients over decades and centuries. As global databases of plant traits expand and mycorrhizal associations are catalogued at ever-finer resolution, ecologists are discovering that the underground world is governed less by grand unifying equations and more by a rich interplay of history, partnership and environment. For the trees of the world’s forests, the rules of nutrient balance are not written in stone; they are negotiated with their fungi, their soils and their climates, one coarse root at a time.

Subject of Research: Global patterns and drivers of nitrogen-phosphorus stoichiometric scaling in woody plant coarse roots

Article Title: Global patterns of coarse root N-P stoichiometry: divergent scaling relationships across woody plant functional groups

Article References: Gong, S., Li, Y., Tian, Q., Zhao, R., Chen, L., Cheng, S., Yang, Y., Liu, F., & Zhao, X. (2026). Global patterns of coarse root N-P stoichiometry: divergent scaling relationships across woody plant functional groups. Plant and Soil. https://doi.org/10.1007/s11104-026-09098-y

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09098-y

Keywords: coarse roots, stoichiometry, nitrogen, phosphorus, scaling exponent, plant functional groups, mycorrhiza, angiosperms, gymnosperms, forest ecology, root economics spectrum, biogeochemistry

The research team, working in collaboration with the Swedish University of Agricultural Sciences (SLU), constructed a gene atlas of the Norway spruce cone, a map that records when and where individual genes are switched on as the tree’s seed-bearing reproductive organs take shape. The atlas identifies key genes involved in cone development and, in a surprise to the researchers themselves, uncovered an entirely previously unknown gene, designated DAL55. Together, these results begin to decode the molecular switch that tells a spruce to stop investing in vegetative growth and start building the structures that carry seeds.

What makes the achievement remarkable is the sheer difficulty of the study organism. Conifers such as Norway spruce carry among the largest genomes in the plant kingdom, orders of magnitude bigger than the human genome, and their long life cycles make classical genetic experiments slow and cumbersome. Generations cannot be crossed quickly, and the infrequency of cone production means that even obtaining the right tissue at the right developmental stage is a logistical challenge. These obstacles have left fundamental questions about cone development unanswered, despite the species’ enormous ecological and economic importance across Northern Europe.

The methodological heart of the study is a technology called spatial transcriptomics, developed at KTH and since commercialized as Visium by 10x Genomics. Conventional gene-expression measurements tell researchers which genes are active in a sample, but they destroy the spatial context, blending the signals of many different cell types into a single average. Spatial transcriptomics preserves that context. It allows scientists to see which genes are active in a tissue and exactly where that activity occurs, effectively producing a molecular map layered directly onto the anatomy of the organ being studied.

Stefania Giacomello, associate professor at the Department of Gene Technology at KTH, emphasized the power of this approach for the spruce work. The technology, she said, enables the study of the expression patterns of all genes simultaneously. To achieve this, the researchers cut sections of spruce cone tissue to extraordinary thinness, just 10 micrometers, or 0.01 millimeters, and measured gene activity across those sections. The result is a spatiotemporal record of reproductive development: not merely a list of genes involved in cone formation, but a picture of how genetic programs unfold across the tissue as the cone grows and differentiates.

The practical motivation behind the research is straightforward. Forest tree breeding depends on the ability to produce seed, and in spruce the long juvenile period and erratic flowering make that production inefficient. Breeders seeking to develop improved varieties, whether for timber quality, growth rate or resilience, are constrained by how rarely their breeding material sets cones. By identifying the genes that govern the transition from vegetative to reproductive development, the new atlas provides molecular targets that could eventually help breeders induce or accelerate cone formation, shortening breeding cycles that currently stretch across decades.

Giacomello pointed to the climate dimension of this goal. By learning more about the molecular mechanisms that regulate cone formation, she said, the team hopes to accelerate breeding efforts and facilitate the production of climate-adapted spruce seedlings for forest owners across the country. As warming shifts the conditions under which Northern European forests grow, the demand for seedlings bred from trees suited to future climates is expected to rise. A faster, more controllable route to reproductive maturity in spruce would directly support that effort, allowing desirable genetic combinations to be captured in seed more quickly than natural flowering schedules permit.

The study also reaches beyond forestry into one of the deepest questions in plant evolutionary biology. Flowering plants, the angiosperms, dominate the modern landscape, but cone-bearing trees such as spruce belong to the gymnosperms, a far older lineage. Both groups descend from a common seed-plant ancestor, and a central open question is whether some of the genetic mechanisms that control reproduction in flowering plants, including familiar crops and trees such as apple, were inherited from that shared ancestor rather than invented independently along the flowering lineage. Comparing the gene programs active in spruce cones with those known from flowers offers a way to test this.

Jens Sundström, a researcher in plant biotechnology at SLU, framed the findings in these evolutionary terms. The results, he said, improve understanding of the evolutionary processes that contributed to the development of all living seed plants, including both flowering plants and conifers. In other words, the cone atlas is not only a breeding tool; it is a window into the ancient genetic toolkit that has governed seed production for hundreds of millions of years. Shared patterns of gene activity between cones and flowers would suggest deep conservation of reproductive control, while differences would point to lineage-specific innovations in each group.

Sundström also stressed the relevance of the work to economies that depend on forestry, singling out Sweden and Finland, where Norway spruce underpins the sector. For those countries, the gap between a fundamental genetic discovery and a commercial seed orchard may still be long, but the direction of travel is clear. A species that once resisted molecular study because of its giant genome and glacial life cycle has now yielded a high-resolution map of its reproductive development, complete with a new gene to investigate. The decades-long wait for a spruce to reproduce may not be shortened overnight, but the genetic instructions behind that wait are, for the first time, coming into view.

Subject of Research: Genetic regulation of the vegetative-to-reproductive transition and cone development in Norway spruce

Article Title: Why do spruce take decades to reproduce? A genetic study offers some clues

Article References: Why do spruce take decades to reproduce? A genetic study offers some clues. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Norway spruce, spatial transcriptomics, cone development, gene atlas, conifer reproduction, forestry breeding, DAL55, gymnosperms, plant evolution, KTH Royal Institute of Technology, SLU, climate-adapted seedlings