Soil respiration responses of moss and lichen biocoenoses to moderate and severe rain events after summer drought in a temperate early‐successional ecosystem

Abstract

It is commonly accepted that CO2 efflux increases with soil water content in aerated soils and that rewetting after periods of soil drying can result in respiration pulses. It has further been shown that soil pores may become water logged which can impede soil gas exchange. The present study aimed to quantify the carbon response of moss (Polytrichum piliferum) and lichen (Cladonia coniocraea) biocoenoses to different quantities of rain in an artificial catchment, which granted that the starting point of the development of both biocoenoses was the same. To address this aim, we conducted in situ soil moisture and soil respiration measurements, where soil respiration was hypothesised to emerge from a cryptogamic vegetation layer and from mineral soil beneath. We found that higher water‐holding capacity of the moss layer and higher accumulation of organic matter in the upper mineral soil under mosses result in higher amounts of water stored near the surface. As a consequence, evaporation of water as well as pulses of CO2 efflux after moderate rain following a period of drought were higher in the moss biocoenosis, where the upper mineral soil was of key importance. In contrast, the lichen biocoenosis facilitated penetration of rainwater into the deep soil. Superimposing rewetting pulses, near‐saturation of soil pores with water after severe rain resulted in gas exchange inhibition and diminished soil respiration until subsequent aeration in both biocoenoses.

A false paradigm? Do biocrust types necessarily reflect ‘successional stages’?

“…The examples are ample (Büdel et al, 2009;Cole et al, 2010;Eldridge & Greene, 1994;Lalley & Viles, 2008;Lan et al, 2012;Li et al, 2022;Redfield et al, 2002;Shields & Durrell, 1964;Thomas & Dougill, 2006;Wang et al, 2023;Williams et al, 2018;Zhuang et al, 2009). This notion is supported by the gradual increase in crust thickness (Kidron et al, 2010;Lan et al, 2012), which reflects higher carbon fixation (Fischer et al, 2023). This notion is also supported by the increase in biodiversity with crust development, as found by many researchers (Büdel et al, 2009;Miralles et al, 2020), which correspond to plant succession, that is, with annuals being succeeded by shrubs that are later succeeded by trees.…”

“…In contrast to vascular plants that showed high correlation with the soil water amount, biocrusts showed higher correlation with water duration (Kidron & Benenson, 2014). As found during detailed measurements, a thick film of water blocks the carboxylation centres of the microorganism cell, impeding gas exchange (O 2 , CO 2 ), thus negatively impacting the rate of respiration (Fischer et al, 2023) and photosynthesis (Lange & Tenhunen, 1981). As far as the cyanobacteria are concerned, a relatively thin water film, equivalent to 0.2-0.6 mm (a quarter or half of the maximum thickness), yielded the highest photosynthesis (Lange et al, 1992).…”

“…By fixing organic carbon (Fischer et al, 2023;Lange et al, 1992;Su et al, 2012Su et al, , 2013Wilske et al, 2008), cyanobacteria and green algae serve as an important nutrient source. Certain cyanobacteria also fix nitrogen (Brankatschk et al, 2013;Strauss et al, 2012), all playing an important role in ecosystem development (Odum, 1969).…”