The cushion and its surroundings
On the Talabre–Lejía transect in the Chilean Atacama, Maihueniopsis camachoi forms cushions at around 2800–3800 m above sea level. Díaz and colleagues compared vegetation inside cushions with nearby open surfaces of similar size. They analysed 20 such pairs at each elevation. The study covered several seasons and 11 elevation levels. [Díaz et al. 2024]
Eighteen species were found with the cactus at least at one level. A particularly consistent association occurred in Atriplex imbricata and Baccharis tola. Inside the cushion, the companion plant's roots could develop in accumulated, decomposing plant material. This microenvironment links physical shelter with rooting conditions. [Díaz et al. 2024]
Temperature measured beneath the plant
Sensors were placed 5 cm deep beneath the cushion and at an open site, with four replicates of each position. In measurement series from different elevations, soil beneath the cactus warmed less during the day and maintained a higher temperature at night. The greatest differences reached about 20°C by day and 8°C at night. These are extreme soil temperature differences relating to specific measurements. [Díaz et al. 2024]
The cushion thus reduced the daily temperature range in the zone where companion plants' roots developed. The mean night-time difference depended on elevation and cactus size. A model comparing vegetation cover with thermal conditions indicated that moderation of night-time cold could explain part of the observed nurse effect. [Díaz et al. 2024]
Shifting limits on the slope
Atriplex imbricata reached around 3300 m on open ground and around 3700 m above sea level in association with the cactus. The difference was therefore about 400 m. In Baccharis tola, the shift concerned the lower limit of occurrence studied, from about 3600 to 3400 m. The companion plants' responses depended on their position within their ecological ranges. [Díaz et al. 2024]
The results combine environmental measurements, plant distribution and modelling. They indicate a consistent link between thermal shelter and site colonisation. The roles of water, nutrients and other microenvironmental components remain part of explaining the whole system. [Díaz et al. 2024]
Metabolites in the sheltered plant
Chemical signals in A. imbricata leaves were measured using metabolomics. From a pool of thousands of analytical features, 93 were selected that were consistently associated with growth beside the cactus. Some substances were identified, including flavonoids, while numerous signals remained chemically unidentified. The number 93 refers to measurement features, some of which may represent different signals from the same compound. [Díaz et al. 2024]
Many signals had lower intensity in sheltered plants. The authors considered reduced costs of stress responses and different resource use. This interpretation agrees with the change in microclimate and metabolite profile. The study did not directly measure carbon flux or the total cost of synthesising these substances. [Díaz et al. 2024]
Prepared from the publications read. Metrics, experimental conditions and tabular data were checked against the source material.
Ecological and metabolic implications of the nurse effect of Maihueniopsis camachoi in the Atacama Desert
Díaz F. P., Dussarrat T., Carrasco-Puga G., Colombié S., Prigent S., Decros G., Bernillon S., Cassan C., Flandin A., Guerrero P. C., Gibon Y., Rolin D., Cavieres L. A., Pétriacq P., Latorre C., Gutiérrez R. A., Ecological and metabolic implications of the nurse effect of Maihueniopsis camachoi in the Atacama Desert, New Phytologist, 2024, 241(3):1074-1087, doi: 10.1111/nph.19415
A field and metabolomic study of the role of Maihueniopsis camachoi as a nurse plant. It compares vegetation cover, soil temperature and the metabolite composition of associated plants along an elevational gradient in the Atacama. It analyses the cactus's relationship with Atriplex imbricata in detail.
