Global Change Reshapes Forest Elementomes, Offering Clues for Better Management

Forests are far more than reservoirs of carbon, and a sweeping new review argues that science has been underestimating them precisely because it has often treated them that way. An international team of researchers led by Zhenhong Hu of Northwest A&F University and CREAF, together with Marcos Fernández-Martínez, Josep Peñuelas, Alessio Collalti and colleagues, has synthesized the latest evidence on how global environmental change is reshaping the elemental composition of forest ecosystems — from the chemistry of tree leaves and roots to the communities of microbes that govern soil fertility. Their conclusion is striking: the balance of chemical elements within trees, soils and microorganisms, a property scientists call the elementome, is being systematically altered by rising carbon dioxide, nitrogen pollution, warming and drought, and those shifts ripple outward to control how much carbon forests can store, how nutrients cycle, and even which animals and insects can survive on forest foliage.

The elementome is the full suite of chemical elements an organism contains and the proportions in which it holds them. Ecological stoichiometry, the discipline behind this concept, rests on a simple but powerful principle: life is built from a handful of elements, chiefly carbon, nitrogen, phosphorus, potassium and a suite of micronutrients, and the ratios among them constrain growth, reproduction, decomposition and energy flow through food webs. Every organism maintains a characteristic elemental signature — its biogeochemical niche — and deviations from that signature carry consequences for function. Trees with phosphorus-poor leaves grow more slowly; microbes whose bodies demand more nitrogen than their food supplies must excrete excess carbon; herbivores feeding on foliage diluted in protein face chronic undernutrition. The review, published in Current Climate Change Reports, argues that these atomic-scale details are among the most important, and most neglected, levers controlling the fate of the world’s forests under climate change.

The first driver the authors examine is the relentless rise of atmospheric carbon dioxide, which has now climbed well beyond 420 parts per million. Higher CO2 stimulates photosynthesis — the so-called CO2 fertilization effect — and much of the additional carbon that forests fix ends up in wood and soil, contributing to the land carbon sink that currently absorbs roughly a third of human emissions. But the review makes clear that this fertilization is not free. Because plants take up carbon from the air while extracting nitrogen, phosphorus and other nutrients from finite soil pools, elevated CO2 progressively dilutes the nutrient concentration of plant tissues. Tissue nitrogen and phosphorus concentrations typically decline even as carbon accumulates, raising the nitrogen-to-phosphorus and carbon-to-nitrogen ratios of leaves, roots and litter. This “nutrient dilution” has been documented across European forests, where declining nutritional status correlates with rising CO2, and it echoes findings in crop plants that point toward globally imbalanced plant stoichiometry. For forest fauna, the implications are sobering: foliage that is less nutritious per bite may force herbivores to eat more, potentially intensifying insect damage while populations of nutrient-sensitive species decline — a phenomenon researchers have described as nutrient dilution with consequences for entire food webs.

Crucially, the authors argue that nutrient availability may be the master variable deciding whether CO2 fertilization continues at its current pace. Evidence from long-term experiments, including mature-forest carbon dioxide enrichment studies, suggests that where soil nitrogen or phosphorus is scarce, the capacity of forests to translate extra CO2 into extra carbon storage is constrained. Recent global syntheses point in the same direction: analyses of vegetation dynamics indicate that the global CO2 fertilization effect on photosynthesis has already begun to decline, and models that ignore the stoichiometric constraints imposed by nitrogen and phosphorus consistently overestimate future carbon uptake. Incorporating the availability and composition of essential elements such as nitrogen, phosphorus and potassium into the plant–soil system, the review finds, substantially improves projections of the forest carbon cycle — especially when simulating how much of the rising atmospheric CO2 humanity has been relying on forests to absorb.

Nitrogen deposition tells a more double-edged story. Industrial agriculture and fossil fuel combustion have loaded enormous quantities of reactive nitrogen onto landscapes, and in many temperate and boreal regions nitrogen was historically the limiting nutrient, so modest additions can act as fertilizer, boosting growth and carbon storage. But the review highlights a growing catalogue of costs. Excess nitrogen acidifies soils, leaches base cations such as potassium, calcium and magnesium, and can push forests toward phosphorus limitation — a shift documented in European forests where nitrogen enrichment has been linked to reduced water use efficiency when phosphorus availability is low. Long-term nitrogen deposition drives foliar nitrogen-phosphorus ratios upward in China’s subtropical forests, alters fungal communities that decompose wood and litter, reduces soil bacterial richness in nitrogen-rich tropical forests, and reshapes the fine-root dynamics that govern soil carbon storage. Meta-analyses compiled by the authors show that nitrogen addition effects on plant multi-element composition vary with ecosystem type, nitrogen form and the presence of other nutrients, underscoring that there is no single, predictable “nitrogen response” — instead, outcomes depend on the initial stoichiometric position of each system.

Drought emerges as perhaps the most acutely dangerous driver, because it couples water stress directly with nutrient stress. The review assembles evidence from rainfall-exclusion experiments in beech forests, tree-ring studies of declining silver fir, and global meta-analyses showing that drought coherently alters carbon-to-nitrogen stoichiometry across plants, soils and microorganisms. When soils dry, the physical transport of nutrients to roots slows, phosphorus mineralization declines, and roots lose access to the water films that carry dissolved ions. Drought also decreases nutrient resorption from senescing leaves, meaning trees abandon valuable nitrogen and phosphorus in their autumn litter rather than conserving them. The consequences can be lethal: nutritional impairment — the failure of a tree to maintain adequate nutrient concentrations under water stress — is increasingly implicated in drought-induced tree mortality and dieback, alongside the better-known hydraulic failure of xylem transport. Studies of drought-stricken pines, oaks and firs across the Mediterranean and temperate Europe reveal that trees with poorer nutritional status, or with root systems unable to maintain nutrient uptake under dry conditions, are far more likely to die. Some species, notably those relying on bedrock-stored water, can buffer this coupling; many cannot.

Warming, the fourth driver, acts in a subtler and sometimes paradoxical manner. Warmer temperatures generally accelerate decomposition and nitrogen mineralization, potentially easing nutrient limitations, and meta-analyses show biomass accumulation often increases under experimental warming. But warming also dries soils, shifts microbial community composition, and can decouple nutrient supply from water availability in vertical soil profiles, reducing plant nutrient uptake and productivity. Global syntheses find that warming changes the carbon-nitrogen-phosphorus stoichiometry of plants, soils and microbes in distinct directions depending on the ecosystem component, and that temperature-driven shifts in leaf nutrient concentrations can reduce photosynthesis, growth and survival in water-limited environments. Because warming interacts with every other driver — amplifying drought intensity, modifying nitrogen cycling, and changing the soil enzyme activities that liberate phosphorus — the authors stress that its net effect on forest elementomes is strongly context-dependent, varying with climate zone, soil type and forest composition.

What unites these threads is the recognition that elemental composition sits at the hub of forest functioning. The elemental makeup of foliage and roots determines litter quality, which governs decomposition rates, which in turn control the release of nutrients back to plants and the residence time of carbon in soil. Microbial communities — ectomycorrhizal fungi, saprotrophs, bacteria — have their own elemental demands and can either accelerate or suppress carbon cycling depending on the stoichiometric match between their needs and their substrates. Recent work showing that microbial carbon use efficiency promotes global soil carbon storage demonstrates that even a single stoichiometric parameter of microbial physiology can tip continental carbon balances. The review also emphasizes biogeography and evolution: global maps of forest foliar elemental composition reveal that evolutionary history, not just contemporary climate, shapes which elements each species concentrates and releases, meaning that species composition — a lever humans can actually pull — matters as much as climate.

That is precisely where the management implications become concrete. The authors argue that forest management can be reframed as elementome stewardship. Silvicultural choices alter soil organic carbon, nutrient stocks and microbial stoichiometry; thinning can relieve microbial metabolic limitations and enhance microbial carbon use efficiency in secondary forests; retaining and encouraging tree species diversity strengthens soil carbon and nitrogen accrual over decades, as shown in large-scale experiments, and mixtures of species with complementary elemental requirements can balance ecosystem-level carbon, nitrogen and phosphorus pools. Selecting species and provenances whose elementomes confer resilience — trees with efficient nutrient resorption, deep or rock-penetrating roots, and associations with drought-tolerant mycorrhizae — could buffer stands against the combined stresses ahead. Composting, biochar amendment and judicious fertilization offer tools to correct diagnosed nutrient imbalances, and earlier monitoring frameworks that track foliar nutrient concentrations across Europe have already revealed widespread nutrient deficiencies that management could target before they escalate into decline.

The authors also lay out an agenda for closing the knowledge gaps that currently limit prediction. Monitoring networks measuring a handful of elements should expand toward full elementome characterization — including micronutrients and trace elements — using remote sensing, foliar sampling and high-throughput chemical analysis. Earth system models must build in multi-element constraints on carbon fixation rather than treating nitrogen as the sole limiter. And because global change drivers do not act in isolation, future experiments should deliberately test interactions: how does elevated CO2 alter drought-nutrition feedbacks, and how does nitrogen deposition change the warming sensitivity of soil carbon? The review concludes that integrating multi-source information on elementomes will not only sharpen forecasts of forest carbon sinks but also guide management decisions that help forests adapt to conditions they have never experienced. In an era when the world is counting on forests to blunt climate change, the atomic composition of a leaf may prove to be as consequential as the temperature record itself.