Desert terraria, characterization of a Mojave Desert moss community under quartz rocks

Abstract

Important ecosystem functions take place in dryland biological soil crusts, which are communities of lichens, microbes, and mosses living on and in the soil in arid environments. Desert mosses are extremely desiccation-tolerant and all their biological functions are limited to infrequent post-rainfall periods. We discovered that some Mojave Desert moss species find refuge under semi-translucent quartz rocks where moisture seems to persist for a longer period of time than in adjacent hyperlithic (above rock) environments. This study characterized the moss communities growing in quartz hyperlithic and hypolithic (below rock) microenvironments in a western, high-elevation Mojave Desert site in Sheep Creek Wash near Wrightwood California. Restriction of the hypolithic moss community to quartz rocks was first verified by pairing inspection under quartz rocks with inspection under non-quartz rocks of similar size within a randomly selected 2 m x 2 m quadrat. Study samples were then collected by sampling each unique moss species or distinct morphology in approximately 0.5 cm clumps around and under each quartz rock along two 15 m linear north-south transects. Collections were analyzed in the lab for species identification and length of previous year’s growth. Of the 53 total samples, 67.9% were Syntrichia caninervis (Pottiaceae), the dominant species of the Mojave Desert biological soil crust. Tortula inermis (Pottiaceae) accounted for 28.3% of the samples and 3.8% were Bryum argenteum (Bryaceae). Of note, T. inermis was significantly more likely to be found in hypolithic microenvironments while S. caninervis was more likely to be in hyperlithic environments (p-value < 0.01). Low light and lower evapotranspiration rates under quartz may be more conducive to T. inermis growth than conditions in adjacent hyperlithic positions. The previous year’s shoot growth of S. caninervis samples in hyperlithic and hypolithic environments also differed significantly. Recent growth of hypolithic shoots of this species was 62.2% longer than that of hyperlithic shoots (p-value < 0.001), perhaps due to higher water retention under the protection of quartz rocks. Additionally, hypolithic S. caninervis shoots appeared to have less of the characteristic brown or black pigment of that species. These results indicate that western high elevation Mojave Desert quartz rocks provide hypolithic environments for some moss species to flourish and that the hypolithic microenvironment is distinct from the surface one. Quartz rocks may prevent small, respiratory carbon loss-inducing rainfalls from ever reaching hypolithic mosses while allowing larger rainfalls to keep tissues hydrated for longer.

Date
Aug 1, 2016
Location
Savannah, Georgia, USA
Jenna Ekwealor
Jenna Ekwealor
PhD Candidate

I am a UC Berkeley PhD Candidate studying evolution & eco-physiology of desiccation-tolerant desert mosses.