The root as a site of association
Arbuscular mycorrhiza is an association between a fungus and plant roots. Structures formed within a root include arbuscules, small branched structures involved in exchange between the partners. Fungal hyphae also extend through the soil. In this association, the fungus uses plant photosynthetic products, while its presence can increase the plant's access to mineral nutrients. The magnitude of any benefit depends on partners and conditions. Identifying fungal structures in a root documents colonization. Measuring plant growth, nutrition or survival allows the subsequent functional consequences of that presence to be assessed. [Blanco-Valenzuela et al. 2024] [Jiménez-Martínez et al. 2026]
A nurse plant changes the surroundings of a young cactus through its canopy, litter and roots. At the same site, fungal propagules, structures capable of initiating further colonization, may also occur. Combining these processes raises a question about the relationship between mycorrhiza and tree neighbourhood. Graciela Blanco-Valenzuela and colleagues investigated this in Sonora by comparing cacti beneath Olneya tesota canopies with those outside them. They selected four columnar species and described roots and surrounding soil using several independent indicators. Their picture of the microsite consequently included both the plant and fungal stages in soil. [Blanco-Valenzuela et al. 2024]
Twenty-four cacti in Sonora
Samples were collected in October 2020 near the road from Hermosillo to Bahía de Kino. Each of four species was represented by three plants beneath trees and three outside canopies, giving 24 individuals in total. Plants of similar size were selected before their reproductive stage and without visible damage. This selection reduced some differences attributable to age or cactus condition. Material consisted of fine roots and neighbouring soil collected to a depth of 15 cm. The study compared existing microsites without moving plants or experimentally adding fungi. [Blanco-Valenzuela et al. 2024]
Roots were stained and examined microscopically to identify hyphae and other mycorrhizal structures. One indicator measured the proportion of root portions colonized, another fungal tissue occupancy. Soil spores were counted, while soil chemistry and cactus root hairs were assessed separately. Each measurement describes a different part of the relationship. A colonized root indicates a current association, spores indicate structures occurring in the sampled soil, and chemical composition describes the local environment. Combining these data allows sites beneath and beside trees to be compared without reducing the whole result to one number. [Blanco-Valenzuela et al. 2024]
A pooled result and differences among species
Mycorrhiza was recorded in all four species in both microsites. Across the pooled sample, mean root colonization was 38.93% beneath trees and 28.22% outside canopies. The difference associated with location was statistically significant. Fungal tissue occupancy within roots and the number of soil spores were also greater beneath trees. A pooled mean nevertheless describes the set of species, with each species represented by a small sample. In senita, treated in the paper as Pachycereus schottii, colonization differed in the opposite direction. The combined result therefore requires its original scope to be retained. [Blanco-Valenzuela et al. 2024]
Soil beneath Olneya tesota contained more organic matter, nitrate and some measured phosphorus fractions. Other properties, including total nitrogen, showed nonsignificant differences. Cactus root hairs varied among species, while canopy location itself had no significant effect on them. These observations associate mycorrhiza with the different environment beneath a tree. Separating the causal contributions of soil, shade and fungi would require another experiment. The authors also note that a cactus currently outside a canopy could previously have benefited from a nurse plant that subsequently died. [Blanco-Valenzuela et al. 2024]
The milpa-chichipera mosaic
In the Tehuacán-Cuicatlán Valley, relationships between cacti and fungi form part of a traditional agricultural landscape. Near San Luis Atolotitlán, milpa-chichipera combines native vegetation patches dominated by Polaskia chichipe with areas growing maize, beans and squash. Retained patches also contain other cacti, agaves, shrubs and trees. Different portions of a field vary in vegetation composition and human intervention. For fungi this creates neighbouring sets of hosts and soil conditions. The arrangement can be compared both with preserved dry scrub and with intensive monocropping. [Jiménez-Martínez et al. 2026]
Arturo Jiménez-Martínez and colleagues distinguished four sampling categories. These were preserved scrub, native patches within milpa-chichipera, open cropping areas of that system and monocropped fields. Five plots represented each category. A composite sample was prepared from soil collected to a depth of 15 cm in every plot. Sampling was repeated during the dry and rainy seasons, producing 40 composite samples in total. This distinction captures variation within a traditional field. A vegetation patch and an open cropping area can belong to the same management system while supporting different communities of soil organisms. [Jiménez-Martínez et al. 2026]
Recognizing fungi through their spores
Fungi were identified from spore characteristics, including wall structure and reactions used in identification. Maize trap cultures helped obtain additional material for identification. Across the study, 58 species-level morphotypes belonging to 17 genera and 10 families were distinguished. Of these, 38 were identified to species and 20 remained identified at genus level. Reporting the result in this form retains the actual resolution of identification. All 58 units contributed to analyses of community richness, although some had no complete species name assigned. [Jiménez-Martínez et al. 2026]
Spores occurred in every land-use category. Preserved scrub and native patches of the traditional system generally supported greater richness and diversity than monocropped fields. Open milpa-chichipera areas occupied a position that depended on the indicator and season analysed. Community composition associated native patches with preserved scrub, while intensive management favoured a different representation of individual fungi. Change therefore involved both the number of recognized units and their relative occurrence. The data describe community reorganization under land use, with mycorrhizal fungi persisting in agricultural fields as well. [Jiménez-Martínez et al. 2026]
Season and soil properties
Dry-season samples contained more spores and showed greater richness of recognized fungi than rainy-season samples. Spore abundance is therefore an indicator that changes seasonally. Individual fungi may differ in the timing of spore formation, while vegetation activity also changes through the year. A single sampling visit would describe only one state of the system. Repeating soil sampling allowed the researchers to recognize both persistent land-use differences and seasonal shifts in the community. A high spore count at a particular time is not itself a direct measurement of water or mineral nutrients transferred to a plant. [Jiménez-Martínez et al. 2026]
Soil organic carbon was associated with preserved scrub and native patches, while individual nitrogen and phosphorus forms had their own patterns. Moisture changed strongly with season, whereas differences among land-use categories were nonsignificant. The results therefore require comparison of particular properties rather than describing one habitat as richer in everything. Statistical associations between soil characteristics and fungal composition help identify possible sources of variation. The observational design leaves causal contributions of vegetation, cultivation and soil conditions partly interdependent. Measurements were made in existing land-use landscapes during two seasons. [Jiménez-Martínez et al. 2026]
What the two comparisons connect
The Sonoran study measured root colonization in four cacti and spores in their immediate surroundings. The Tehuacán-Cuicatlán study described soil fungal communities across an entire vegetation mosaic. These scopes complement one another while retaining different units of analysis. A finding about milpa-chichipera soil does not attribute every fungus exclusively to Polaskia chichipe, because numerous hosts grow there. Likewise, higher mean root colonization in Sonora concerns the species and sampling period studied. Extending these findings to other cacti or unrelated succulents would require appropriate evidence about their own roots and environments. [Blanco-Valenzuela et al. 2024] [Jiménez-Martínez et al. 2026]
Retained vegetation was associated in both studies with a richer or more strongly colonized mycorrhizal environment within the measurements made. This agreement supports conserving habitat mosaics as places maintaining diverse hosts and fungi. The milpa-chichipera authors interpret native patches as local refuges for mycorrhizal communities within agricultural landscapes. Measuring crop productivity and experimentally tracing substance movement through a shared fungal network remain separate tasks. The study demonstrated community structure and its relationships with land use. That result gives retained patches a specific role in describing soil biological diversity. [Blanco-Valenzuela et al. 2024] [Jiménez-Martínez et al. 2026]
Practical scope and publication date
For cactus propagation, understanding mycorrhiza helps organize questions about substrates and root partners. An experiment with a particular inoculum should establish its identity, colonization capacity and effect on a specified plant species and developmental stage. Neither study discussed here tested a commercial preparation in pots. Their direct findings are field differences, ranging from structures within roots to the composition of soil communities. Retaining this distinction allows knowledge of natural environments to be used without assigning it an unmeasured treatment efficacy. A mycorrhizal association is described through its actual partners and their shared growing conditions. [Blanco-Valenzuela et al. 2024] [Jiménez-Martínez et al. 2026]
The paper by Jiménez-Martínez and colleagues carries a citation in volume 100 of Agroforestry Systems for 2026, while its first online publication occurred on 9 December 2025. Both dates concern one article and one DOI. Preserving their distinct meanings allows the knowledge to be dated accurately. The researchers documented fungal communities associated with a local land-use system. At this scale, milpa-chichipera retains native patches beside crops whose mycorrhizal diversity is closer to preserved scrub than to intensively managed fields. This is a characteristic of a particular landscape of cacti and traditional agriculture in central Mexico. [Jiménez-Martínez et al. 2026]
Enhanced mycorrhization in four species of columnar cacti under the Sonoran Desert tree Olneya tesota
Blanco-Valenzuela G., Calderón K., Ochoa-Meza A., Peñalba M. C., Tinoco-Ojanguren C., Enhanced mycorrhization in four species of columnar cacti under the Sonoran Desert tree Olneya tesota, Botanical Sciences, 2024, 102(3):765-778, doi: 10.17129/botsci.3454
A field comparison of four columnar cacti in Sonora documents arbuscular mycorrhiza in roots beneath Olneya tesota trees and outside their canopies. In the pooled sample, root colonization and fungal tissue occupancy were higher beneath trees, as was the number of soil spores. The direction of the colonization difference nevertheless depended on cactus species. The observational study also describes soil properties and root hairs, keeping association distinct from experimental demonstration of benefit.
The “milpa-chichipera” ethno-agroforestry system as a buffer against land-use change impacting arbuscular mycorrhizal fungi in a semiarid Mexican ecosystem
Jiménez-Martínez A., Montaño N. M., Chimal-Sánchez E., Varela L., Montaño-Arias S. A., Salazar-Ortuño B. L., Villarreal-García M. E., Camargo-Ricalde S. L., The “milpa-chichipera” ethno-agroforestry system as a buffer against land-use change impacting arbuscular mycorrhizal fungi in a semiarid Mexican ecosystem, Agroforestry Systems, 2026, 100:26, doi: 10.1007/s10457-025-01405-3
A study of mycorrhizal fungi near San Luis Atolotitlán compares preserved dry scrub, native vegetation patches and open cropping areas within milpa-chichipera, and monocropped fields. Samples from two seasons distinguished 58 species-level fungal morphotypes, of which 38 were identified to species and 20 to genus. Scrub and retained vegetation patches supported greater richness and diversity than monocropped fields. The article appeared online on 9 December 2025 and received a 2026 volume citation.