Other Life Forms

Biological Crusts

Not only is water a limiting factor here in the desert, but our lower and mid-elevation ecosystems are short on macro and micro nutrients for plant growth, thus the beginning of the food web here at Saguaro. Algae, cyanobacteria (pictured), mosses and liverworts exist on the soil's surface here. This is only possible in warm areas of the world because colder weather north of the subtropics prevents biotic crusts from thriving at the surface. They are exceptionally slow-growing and while they may appear lifeless, they are far from it. Rain brings them back to life, and they store vital nutrients for symbiotic reactions with plantlife, sharing nitrogen (among other nutrients) with plant species in exchange for the byproducts of photosynthesis. Be careful as you hike, as these are easily damaged and killed by human and livestock trampling.

 

Fungi, Nitrogen Fixing Bacteria & Lichen

Nitrogen fixation through bacteria of legume species is absolutely critical here at Saguaro National Park. Much like Biological Crusts, these bacteria help mitigate the lack of nitrogen in the soil here. Nitrogen is extracted from the atmosphere and converted to a usable form for plant life and thus growth/ fruit production. This can double or even triple the available nitrogen underneath mesquite and palo verde trees.

Fungal associations through their hyphae in the roots of vascular plants is now thought to be the sole reason plants were able to establish on terrestrial surfaces, away from a constant water supply. Hyphae attached to roots has been seen to increase absorptive surfaces in the roots 100-fold! However, sometimes fungi associate with photosynthetic algae & cyanobacteria, since they cannot perform photosynthesis, to form composite organisms called lichen (pictured in the yellow on the rock face). These organisms combine to provide nutrients and water, with the photosynthetic organism completing the process of photosynthesis. They then share the end results with the fungi, completing the mutualistic relationship.