The research, published in the journal Plant and Soil, was led by Sophia Moracchioli Philadelphi of the University of Hohenheim in Germany, together with colleagues at Hohenheim and Aarhus University in Denmark. The team set out to answer a question that most drought experiments have sidestepped: what happens when a compound drought-heatwave, or CDHW, hits a young grassland community that is still assembling itself? Mature swards have been studied extensively, but during establishment the competitive hierarchies, root systems and canopies that underpin complementarity are still forming. Stress at this stage can leave lasting legacies for productivity, species composition and the ecosystem services a sward will deliver for years afterward.

To simulate a realistic western European summer extreme, the researchers ran a 112-day controlled growth-chamber experiment at Hohenheim. They grew mesocosms containing three functionally contrasting forage species: perennial ryegrass (Lolium perenne), a fast-growing grass; white clover (Trifolium repens), a nitrogen-fixing legume; and chicory (Cichorium intybus), a deep-rooted non-leguminous forb. Each species was grown alone, and three mixture types were created: a binary grass-forb mixture and two three-species mixtures with either 33 or 67 percent legume. Climate profiles followed weekly averages recorded at Stuttgart Airport between 1991 and 2005, mimicking a typical regional growing season. For the first 90 days after sowing, all mesocosms were kept identical and well watered at 65 percent of field capacity.

Then came the stress. From day 91, a nine-day CDHW event was imposed in three of the chambers: irrigation was withheld to create an edaphic drought while air temperatures were raised by up to 8 degrees Celsius at the daily maximum and 3.4 degrees at the minimum, with relative humidity cut by 17 percent. The result was a doubling of the vapour pressure deficit, from about 1.1 to 2.21 kilopascals, a measure of how hard the atmosphere pulls water out of leaves. Dry soils suppress evapotranspiration and cloud formation, amplifying surface heating, which is precisely why drought and heat so often arrive together. The team tracked the consequences daily, measuring gross primary production, evapotranspiration, gravimetric soil water content and leaf water potential, then harvested all biomass at the end.

The physiological responses were strikingly species-specific. White clover proved the most resistant: its photosynthetic rate per unit of canopy area barely declined during stress and showed only weak coupling to soil moisture, evapotranspiration or leaf water status. Chicory took the opposite path, losing 24 percent of its normalised gross primary production during the event, the highest hydraulic sensitivity, but then staging the most dramatic recovery, rebounding to an average of 204 percent of control levels once water returned. Perennial ryegrass was the least resistant, its photosynthesis tracking soil drying closely, with reductions of roughly 37 to 47 percent in the grass monoculture and all mixtures. Leaf water potential, a direct indicator of plant hydraulic strain, diverged from control values within just two to four days of stress onset in all three species.

Yet here lay the study’s central paradox: this rich physiological diversity never scaled up to the community level. In mixtures, the photosynthetic trajectories closely followed those of the dominant ryegrass, regardless of whether the more resistant clover or the faster-recovering chicory were present. The authors point to the mass-ratio hypothesis, which holds that ecosystem functioning is governed primarily by the traits of the most abundant species. Because ryegrass already accounted for the bulk of the biomass, the physiological strengths of the subordinate species were simply underrepresented at the canopy scale, and no community-level physiological buffering could be detected.

The biomass data told a subtler story. Across all communities, the CDHW event cut aboveground shoot dry weight by about 20 percent, an estimated mean loss of 147 grams per square metre. All three monocultures ended with harvest ratios significantly below one relative to their controls, with chicory suffering the steepest decline at 41 percent, followed by clover at 28 percent and ryegrass at 20 percent. The mixtures, by contrast, all showed ratios that did not differ significantly from one, indicating greater biomass stability, exactly as the team’s first hypothesis predicted. Net diversity effects, the difference between observed mixture biomass and the sown-proportion-weighted expectation from monocultures, were positive in both climates and grew substantially under stress, rising on average by nearly 88 grams per square metre under CDHW.

But that stability came at a hidden cost. The diversity effects were non-transgressive: mixtures matched, but never exceeded, the best-performing monoculture, which was ryegrass itself. And beneath the stable totals, the community composition was being rewritten. Under control conditions, ryegrass already dominated the mixtures, contributing roughly 69 to 75 percent of shoot dry weight. Under CDHW, its share surged to 94 to 97 percent, a statistically significant reinforcement of grass dominance, while chicory and clover were squeezed down to minor fractions of 1 to 5 percent, though neither species was completely eliminated. Crucially, both subordinates experienced more negative leaf water potentials in mixtures than in their own monocultures during the stress, direct evidence that the dominant grass intensified their hydraulic stress through competition for belowground water.

The mechanism, the authors argue, is structural rather than physiological. Ryegrass entered the stress period with greater canopy development and finished with by far the largest root biomass, about 2,300 grams per square metre, significantly more than any other community. That early structural pre-emption, combined with rapid regrowth capacity, allowed it to convert the disturbance into a competitive legacy. Clover, despite its physiological resistance, lacked the structural reserves to capitalise on it, while chicory lost too much tissue during the event to recover its position. Rapid photosynthetic recovery after rewatering, the study shows, was simply not enough to restore biomass within the experiment’s timeframe, because shallow roots and limited carbon reserves constrained compensatory growth in these young swards.

The implications reach well beyond the growth chamber. A grassland mixture can hold its yield steady through a compound extreme and still lose the functional diversity that underpins biological nitrogen fixation, forage quality and long-term multifunctionality. If CDHW events, which are becoming a defining feature of western European summers, increasingly strike during establishment, farmers may end up with swards that look diverse on the seed label but function as near-monocultures in the field. The authors suggest that management strategies promoting balanced early establishment, such as optimised sowing rates and sowing timing, may be essential if mixtures are to deliver their promised benefits under climate change. Short-term biomass stability, this study makes clear, is no guarantee of compositional stability, and the most important battle for diversity in a grassland may be fought in its first few months of life.

Subject of Research: Effects of compound drought-heatwave events on species interactions and community assembly during grassland establishment

Article Title: Compound drought-heatwave events during establishment reinforce perennial ryegrass dominance in grassland mixtures

Article References: Philadelphi, S. M., Berauer, B. J., Eriksen, J., Schweiger, A., Högy, P., & Malisch, C. S. (2026). Compound drought-heatwave events during establishment reinforce perennial ryegrass dominance in grassland mixtures. Plant and Soil. https://doi.org/10.1007/s11104-026-09168-1

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09168-1

Keywords: grassland ecology, compound drought-heatwave, perennial ryegrass, white clover, chicory, plant diversity, drought resistance, gross primary production, species dominance, establishment phase, climate extremes, ecosystem services

The research team, led by Masoud Andideh and corresponding author Alireza Yadavi, set out to tackle two pressing challenges at once: the need for sustainable forage production in a changing climate and the degradation of soil biological function that often accompanies intensive agriculture. Their approach was to test whether intercropping chicory (Cichorium intybus L.), a deep-rooted perennial herb valued for its mineral-rich forage, with berseem clover (Trifolium alexandrinum L.), an annual legume that fixes atmospheric nitrogen, could be enhanced further by manipulating the soil’s fungal and chemical environment.

The experimental design was deliberately comprehensive. The researchers compared pure stands of each species against three intercropping arrangements: alternating single rows of chicory and clover, two rows of chicory with one row of clover, and one row of chicory with two rows of clover. Each planting configuration was crossed with five fertilization treatments: no fertilizer, mycorrhizal inoculation alone, 75 kilograms per hectare of triple superphosphate, 150 kilograms per hectare of the same fertilizer, and a combined treatment pairing mycorrhiza with the lower 75-kilogram phosphorus rate. This factorial structure allowed the team to separate the effects of cropping pattern, biology, and chemistry.

The results were striking. Intercropping systems consistently outperformed monocultures, and the treatments that included mycorrhizal inoculation produced the highest levels of soil biological activity, including greater bacterial populations, elevated microbial respiration, and enhanced enzyme activities. These indicators matter because they reflect the living engine of the soil: microbes that decompose organic matter, cycle nutrients, and make minerals available to plant roots. Perhaps counterintuitively, the chemical superphosphate applications on their own reduced soil biological activity, suggesting that heavy-handed fertilization can suppress the very organisms that sustain long-term fertility.

To move beyond simple correlations, the team employed Bayesian Structural Equation Modeling, a statistical framework that can test hypothesized chains of cause and effect among many variables simultaneously. The modeling revealed that for chicory, the leaf area index and chlorophyll content were the key physiological drivers of forage yield, while soil microbial respiration and gram-positive bacteria influenced the degree of root colonization by mycorrhizal fungi, which in turn shaped leaf development. In other words, a biologically active soil appeared to set the stage for fungal partnership, and that partnership fed directly into the plant’s photosynthetic capacity.

Berseem clover told a more nuanced story. For the legume, both leaf area index and mycorrhizal root colonization positively affected forage yield, but the modeling also exposed a trade-off: the clover’s famous rhizobium symbiosis, in which root nodules house nitrogen-fixing bacteria, appeared to compete with aboveground development. This finding has practical implications, because it suggests that the energetic cost of hosting nitrogen-fixing bacteria is not trivial, and that maximizing clover biomass requires balancing the benefits of biological nitrogen fixation against the carbon the plant must spend to maintain its nodules.

The bottom line for farmers came down to two efficiency metrics. The highest land equivalent ratio, a measure of how much more productive intercropping is compared with growing each crop separately, reached 1.107 in the two-row clover to one-row chicory arrangement. A land equivalent ratio above 1.0 means the intercrop uses the land more efficiently than monocultures, and a value of 1.107 indicates roughly a 10 percent advantage. Meanwhile, the combined treatment of mycorrhiza plus 75 kilograms per hectare of triple superphosphate achieved the highest K value of 1.628, indicating a substantial synergistic gain when biological and chemical inputs were paired at moderate levels.

Why would mycorrhizal fungi and phosphorus fertilizer work better together than either alone? The answer lies in the biology of the symbiosis. Arbuscular mycorrhizal fungi colonize plant roots and extend networks of hyphae far into the soil, accessing phosphorus that is beyond the reach of root hairs and delivering it to the plant in exchange for photosynthetic carbon. When soil phosphorus is extremely low, the fungi have little to mine; when it is very high, plants have less incentive to support the fungal partnership. A moderate fertilizer dose appears to hit the sweet spot, providing enough phosphorus to fuel early growth while keeping the symbiosis active and the soil microbial community engaged.

The suppression of soil biological activity under higher superphosphate rates adds to a growing body of evidence that fertilizer intensity shapes microbial communities in ways that can undermine their contributions. Enzyme activities and microbial respiration are sensitive indicators of soil function, and their decline under heavy chemical inputs suggests a simplification of the belowground community. For forage systems, where soil health directly underpins multi-year productivity, this is a warning worth heeding: more fertilizer is not always better, and the cheapest inputs may be the living ones already present in the soil.

The study also carries broader significance for climate-resilient agriculture. Intercropping legumes with grasses or herbs is a time-honored strategy that reduces the need for synthetic nitrogen, improves diet diversity for grazing animals, and buffers against weather extremes. By demonstrating that mycorrhizal inoculation can amplify these benefits while a reduced phosphorus dose preserves soil life, the Iranian team provides a template for low-input forage systems that could be adapted across semi-arid regions. As the authors frame it, the work addresses the twin demands of climate change adaptation and sustainable food production, showing that the path to higher yields may run not through the fertilizer bag but through the fungal threads threading quietly through the soil.

Subject of Research: Effects of arbuscular mycorrhizal fungi and phosphorus fertilization on chicory–berseem clover intercropping systems

Article Title: Synergistic effects of arbuscular mycorrhizal inoculation and phosphorus fertilization on soil microbial properties, plant physiological characteristics, in chicory–berseem clover intercropping

Article References: Andideh, M., Yadavi, A., Balouchi, H., & Farajee, H. (2026). Synergistic effects of arbuscular mycorrhizal inoculation and phosphorus fertilization on soil microbial properties, plant physiological characteristics, in chicory–berseem clover intercropping. BMC Plant Biology. https://doi.org/10.1186/s12870-026-09989-3

Image Credits: AI Generated

DOI: 10.1186/s12870-026-09989-3

Keywords: arbuscular mycorrhiza, intercropping, chicory, berseem clover, phosphorus fertilization, soil microbiology, forage yield, microbial respiration, Bayesian structural equation modeling, land equivalent ratio, rhizobial symbiosis, sustainable agriculture

Spirulina, the dried biomass of Limnospira platensis and its congener L. maxima, is cultivated worldwide at industrial scale, exceeding 12,000 tons per year, and holds GRAS status from both the U.S. Food and Drug Administration and the European Food Safety Authority. Its market value rests on an exceptional nutritional profile, including protein content reaching up to 70 percent of dry weight, essential amino acids, vitamins B12 and E, bioactive lipids such as gamma-linolenic acid, and a suite of photosynthetic pigments. Among these, C-phycocyanin is the most valuable, prized as a natural colorant and functional ingredient across the food, cosmetic, and pharmaceutical sectors for its antioxidant, immunomodulatory, and anti-inflammatory properties. But extracting this pigment leaves behind a mountainside of residual material whose fate has remained largely unexamined, despite European policies that strongly encourage waste valorization and circular economy approaches in agriculture.

Researchers at Tor Vergata University of Rome, working with biomass supplied by the Italian producer Algaria Srl, set out to determine whether the residue left after phycocyanin extraction, which they call POST biomass, could serve as an effective biofertilizer. They compared it with untreated biomass collected before extraction, termed PRE biomass, and with a commercial NPK fertilizer, using chicory (Cichorium intybus) as the test plant. Chicory is a leafy vegetable of high nutritional and cultural importance in the Mediterranean diet, making it an ideal candidate for a fertilizer destined for sustainable horticulture. The team grew the cyanobacterium in a 300 square meter open raceway pond under natural sunlight, collected both biomass fractions, centrifuged and freeze-dried them, and then characterized their chemical composition.

The compositional analysis delivered the first encouraging surprise. Although phycocyanin extraction removed some of the protein, the POST biomass still contained 50.2 percent protein by dry weight, alongside 6.8 percent total nitrogen and 0.78 percent phosphorus, only moderately lower than the intact PRE biomass. In other words, the industrial extraction process strips out the blue pigment but leaves behind a nutrient-dense matrix. This matters because cyanobacterial biomass is known to carry phytohormones including auxins, cytokinins, gibberellins, and abscisic acid, plus amino acids, carbohydrates, and exopolymeric substances with documented biostimulant effects on plants.

Germination experiments revealed a nuanced early response. Seeds treated with POST biomass suspensions showed a transient delay in radicle emergence during the first days, an effect that strengthened with increasing concentration. Yet by day six, final germination had caught up with, or exceeded, the water control, with the 5 milligrams per milliliter treatment reaching a germination percentage of 96.6 percent against the control’s 91.6 percent. The researchers interpret this pattern of initial slowdown followed by equal or improved final germination as a priming-like response, in which bioactive compounds activate metabolic pathways associated with germination without harming the seed. By contrast, PRE biomass proved more inhibitory, significantly reducing germination at intermediate and high concentrations, suggesting the extraction process actually improves the bioavailability profile of the residual material.

The growth results were even more striking. Under controlled laboratory conditions, POST biomass increased shoot fresh weight in a dose-dependent fashion, with values of 0.76 grams at 7.5 milligrams per milliliter and 1.06 grams at 10 milligrams per milliliter, far exceeding the commercial fertilizer’s 0.39 grams. Leaf fresh weight followed the same trend, peaking at 0.94 grams versus 0.31 grams for the fertilizer control. Under greenhouse conditions, where temperature ranged from 19.7 to 32.5 degrees Celsius and humidity fluctuated naturally, the effects grew stronger rather than weaker. The highest POST treatment pushed shoot fresh weight to 4.0 grams, nearly triple the 1.47 grams achieved by the commercial product, and roots benefited significantly as well. The robustness of the response under variable environmental conditions is critical evidence that the effect can survive the messiness of real-world agriculture.

Photosynthetic pigment measurements helped explain where the extra biomass came from. POST-treated plants accumulated significantly more chlorophyll a and chlorophyll b than either control, reaching 981.9 micrograms per gram fresh weight of chlorophyll a in the laboratory and 578.3 micrograms per gram in the greenhouse, compared with 641.9 and 320.9 micrograms per gram respectively for fertilizer-treated plants. Carotenoid levels rose in parallel. The coordinated increase in chlorophyll b is particularly telling, since this pigment anchors the light-harvesting antenna complexes of photosystem II; its accumulation implies an expanded photosynthetic apparatus and greater capacity to capture light, which plausibly drove the observed gains in plant mass. PRE biomass produced weaker and less consistent pigment responses, with chlorophyll b often lagging behind the control and the chlorophyll a to chlorophyll b ratio rising, a signature of limited antenna development.

Just as important was what the researchers did not find. Phenolic compounds and flavonoids are classic markers of oxidative and environmental stress in plants, so their accumulation would have signaled that the biofertilizer was stressing the crop rather than helping it. In POST-treated greenhouse plants, total phenolic and flavonoid contents remained essentially unchanged relative to controls at most concentrations, confirming that the growth promotion was achieved without triggering adverse physiological responses. The residue acts as a genuine biostimulant, not a low-grade stressor masquerading as one. This biochemical evidence complements the growth and pigment data in portraying the leftover biomass as a safe and multifunctional agricultural input.

The study builds on the group’s earlier demonstration that spirulina processing waste can fertilize lettuce in aquaponic systems, and together the two works suggest the activity of L. platensis leftovers holds across different crops, substrates, and cultivation environments. The broader implications touch the economics of the entire spirulina sector. Commercial cyanobacterial biostimulants remain scarce largely because production costs exceed those of conventional fertilizers, and nearly half of all research on cyanobacteria in agriculture between 2006 and 2020 focused on L. platensis without translating into widespread products. By folding agricultural reuse into the existing phycocyanin biorefinery chain, producers could convert a disposal liability into a second revenue stream while reducing the environmental footprint of both the pigment industry and the farms that adopt the residue. The researchers conclude that integrating this upcycling step into spirulina biorefineries could substantially improve the economic and environmental sustainability of cyanobacterial production, turning process waste into functional bio-based products for sustainable agriculture. Remaining questions include optimizing dosing for different species and soils and validating performance at field scale, but the central message of this work is clear: the blue gold of the spirulina industry may be hiding a green treasure in what it throws away.

Subject of Research: Upcycling of industrial Limnospira platensis residual biomass as a biofertilizer for chicory cultivation

Article Title: From waste to resource: agricultural potential of Limnospira platensis (spirulina) leftovers in chicory cultivation

Article References: Savio, S., Di Cave, A., Ortenzi, F., Rugnini, L., Scuderi, F., Migliore, G., Canini, A., Braglia, R., & Congestri, R. (2026). From waste to resource: agricultural potential of Limnospira platensis (spirulina) leftovers in chicory cultivation. Plant Biosystems, 160(5), Article 265. https://doi.org/10.1007/s44473-026-00249-8

Image Credits: AI Generated

DOI: 10.1007/s44473-026-00249-8

Keywords: spirulina, Limnospira platensis, biofertilizer, phycocyanin, chicory, circular economy, biostimulant, plant biotechnology, cyanobacteria, sustainable agriculture, seed priming, industrial leftovers