Carbon dioxide fluxes from biologically-crusted Kalahari Sands after simulated wetting

Abstract

Thomas, A. D., Hoon, S. R. (2010). Carbon dioxide fluxes from biologically-crusted Kalahari Sands after simulated wetting. Journal of Arid Environments, 74 (1), 113-139.We report surface CO2 efflux and subsoil CO2 concentrations in biologically-crusted soils from the Kalahari. Fluxes were determined in-situ using a closed chamber coupled to a portable gas chromatograph on dry soils and on soils subject to simulated light and heavy rainfall. Surface efflux was measured in an artificially darkened environment in order to determine by difference, whether photosynthesis was occurring. Dry soil efflux rates were 2.8?14.8 mg Cm2 h1 throughout a diurnal cycle. Light rainfall led to an immediate increase in efflux to a peak of 65.6 mg Cm2 h1. Heavy rainfall resulted in a large pulse of CO2 with efflux rates of 339.2 mg Cm2 h1 over the first hour after wetting. Peak rates remained high over the following 2 days (87.8 and 87.0 mg Cm2 h1). Given sufficient moisture, fluxes increased with temperature. We believe hydration of the subsoil stimulates microorganisms which repsire available C either from extracellular polysaccharide sheaths (EPS) or released into the soil through lysis of microbial cells. Higher fluxes from the soil kept in the dark suggests photosynthesis occurs in wetted crusts during the daytime but net C uptake is masked by respiration from other microorganisms.authorsversionPeer reviewe

Impact of grazing intensity on seasonal variations in soil organic carbon and soil CO 2 efflux in two semiarid grasslands in southern Botswana

“…(a) Biological crusts and soil organic C Dryland savannas are productive areas, accounting for an estimated 13.6 per cent of global NPP and an annual C sink of 1.6 t C ha 21 yr 21 [5,6]. There is, however, significant variability in the distribution of SOC in the landscape.…”

“…The in situ data that are available allow some generalizations to be made and demonstrate that: -annual soil CO 2 efflux in drylands is typically much lower than in mesic systems (see for example [19 -22]). This is because both heterotrophic microbial activity and autotrophic respiration from plant roots are limited by soil moisture for long periods [23]; -immediately following re-wetting, soil CO 2 efflux rates can be very high, often elevated by up to 500 per cent compared with continually moist soil [13,21,24,25]. Re-wetting pulses constitute a significant portion of the total annual CO 2 efflux from soils [24,26,27]; -communities of heterotrophic and autotrophic micro-organisms in BSCs provide an additional, subtle and often overlooked contribution to soil CO 2 efflux [28].…”

Ecophysiological responses of desiccation-tolerant cryptobiotic crusts

“…Therefore, the physiology of these cryptogamic crusts fully depends on the amount of available water or dew [13][14][15]. However, the biological activity of CBCs is based on the time and frequency of dehydration and on the amount of precipitation and light exposure [16,17]. In addition, these crusts composed of mainly cyanobacteria, which have chlorophyll a and also phycobilin pigments, generally have the ability to fix atmospheric nitrogen and improve the nutrient content of the soil in the tropical regions [11,18].…”

Laboratory analysis of the effects of elevated atmospheric carbon dioxide on respiration in biological soil crusts

“…The subsoil (97% fine sand, pH 5.9 ± 0.4, bulk density 1.85 ± 0.03 g cm 3 and porosity 0.34 ± 0.01 v/v) (Thomas and Hoon, 2010) was sieved (853 m), sterilized (autoclaved at 121 °C for 15 min) and then filled (178 g each) in…”

“…Substantial amounts of carbon are also being lost from BSCs via respiration Thomas et al, 2008;Thomas and Hoon, 2010;Thomas et al, 2011) particularly after rainfall events; due to activity and substrate availability increases within microbial populations (Borken and Matzner, 2009). During hours when moisture, temperature and light availability are optimum gain of carbon 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 (photosynthesis) occurs; prior to these optimum conditions (particularly in the absence of light) an initial efflux is observed (Evans and Johansen, 1999;Thomas et al, 2011;Thomas, 2012 treatments cyanobacteria will show a generalized decline with elevated CO 2 though the direct impacts on CO2 efflux rates remains unknown (Steven et al, 2012).…”