Fungi in asymptomatic tissues
Endophytes are microorganisms found inside tissues that show no visible disease symptoms at the time of study. In 2004, material from 21 cactus taxa was collected at six Arizona locations, including field sites and collections. From 1050 surface-disinfected fragments, 900 isolates were obtained, belonging to 22 fungal taxa according to the authors' identifications. The results were published in 2005. [Suryanarayanan et al. 2005]
Culturing on medium and checks of surface disinfection effectiveness were used. The study therefore covers the part of the community capable of growing under those conditions. Frequently isolated fungi included forms identified as Alternaria, Aureobasidium pullulans and the then-recognised Phoma. These names describe the identifications adopted in the publication. [Suryanarayanan et al. 2005]
Culture numbers and diversity
Cylindropuntia ramosissima provided the most isolates, while C. fulgida had the highest value of the diversity index used. These quantities concern different community traits, the frequency of fungal isolation and the distribution of their proportions. Several cultures could grow from one tissue fragment. [Suryanarayanan et al. 2005]
Detecting an endophyte alone documents its presence in the stem. A benefit to the host, an ability to cause disease or involvement in later decomposition requires a separate experiment with a particular plant–fungus pair. The Arizona study primarily compares the composition of culturable communities. [Suryanarayanan et al. 2005]
Drying separated from decomposition
Bilderback and colleagues followed the fate of segments of C. acanthocarpa and Opuntia chlorotica in the Sonoran Desert for almost a year. In both cases, a substantial decline in fresh mass resulted primarily from water loss. Organic matter breakdown was assessed separately by determining ash-free dry mass, the difference between sample dry mass and the mass of ash remaining after combustion. [Bilderback et al. 2021]
After about a year, around 70% of the cholla's initial ash-free dry mass and around 50% of the prickly pear's remained. Elements released during the study included carbon and calcium. Rainfall and water, lignin and polysaccharide content covaried with the rate of material loss. [Bilderback et al. 2021]
Soil responds to weather
Soil CO₂ emissions varied more strongly with moisture and temperature than with the species of cactus lying above it. Winter rainfall and milder temperatures were associated with greater CO₂ flux. The degree of residue decomposition had additional significance under particular weather conditions. [Bilderback et al. 2021]
In cholla, a temporary increase in ash-free mass was found between successive dates. The authors considered contributions from microbial biomass and remains, and deposition of material from the surroundings. Because microbial biomass was not measured directly, the mechanism of this change remained an open question. This illustrates how measurements of matter cycling lead to more detailed studies of processes. [Bilderback et al. 2021]
Prepared from scientific publications. Names follow POWO. Historical names are given in discussions of older papers.
Endophytic fungi associated with cacti in Arizona
Suryanarayanan T. S., Wittlinger S. K., Faeth S. H., Endophytic fungi associated with cacti in Arizona, Mycological Research, 2005, 109(5):635-639, doi: 10.1017/S0953756205002753
Isolation of endophytic fungi from tissues of 21 cactus taxa studied in Arizona. The paper compares the composition of the culturable fraction of communities, isolate numbers and fungal diversity in different hosts.
The structural and nutrient chemistry during early-stage decomposition and desiccation of cacti in the Sonoran Desert
Bilderback A. H., Torres A. J., Vega M., Ball B. A., The structural and nutrient chemistry during early-stage decomposition and desiccation of cacti in the Sonoran Desert, Journal of Arid Environments, 2021, 195:104636, doi: 10.1016/j.jaridenv.2021.104636
A one-year study of drying and decomposition in fragments of Cylindropuntia acanthocarpa and Opuntia chlorotica. It compares losses of water, ash-free dry mass and elements, as well as soil CO₂ emissions under changing moisture and temperature conditions.
