Abstract
Soil respiration induced by biological soil crusts (BSCs) is an important process in the carbon (C) cycle in arid and semi-arid ecosystems, where vascular plants are restricted by the harsh environment, particularly the limited soil moisture. However, the interaction between temperature and soil respiration remains uncertain because of the number of factors that control soil respiration, including temperature and soil moisture, especially in BSC-dominated areas. In this study, the soil respiration in moss-dominated crusts and lichen-dominated crusts was continuously measured using an automated soil respiration system over a one-year period from November 2015 to October 2016 in the Shapotou region of the Tengger Desert, northern China. The results indicated that over daily cycles, the half-hourly soil respiration rates in both types of BSC-covered areas were commonly related to the soil temperature. The observed diel hysteresis between the half-hourly soil respiration rates and soil temperature in the BSC-covered areas was limited by nonlinearity loops with semielliptical shapes, and soil temperature often peaked later than the half-hourly soil respiration rates in the BSC-covered areas. The average lag times between the half-hourly soil respiration rates and soil temperature for both types of BSC-covered areas were two hours over the diel cycles, and they were negatively and linearly related to the volumetric soil water content. Our results highlight the diel hysteresis phenomenon that occurs between soil respiration rates and soil temperatures in BSC-covered areas and the negative response of this phenomenon to soil moisture, which may influence total C budget evaluations. Therefore, the interactive effects of soil temperature and moisture on soil respiration in BSC-covered areas should be considered in global carbon cycle models of desert ecosystems.
Highlights
Soil respiration accounts for the largest proportion of the total ecosystem respiration [1], and its global integration is an order of magnitude larger than that of anthropogenic CO2 releases from burning fossil fuels and deforestation [1,2]
Diel hysteresis between soil respiration and soil temperature in BSCcovered areas Over the course of the diurnal cycles, our results demonstrate that a significant time lag occurred between the half-hourly soil respiration rates and soil temperature at a depth of 5 cm in both types of Biological soil crusts (BSCs)-covered areas, with the soil respiration peaking earlier than the soil temperature (Figs 2 and 3)
Autotrophic respiration is affected by photosynthetically active radiation [34] and air temperatures, whereas heterotrophic respiration is primarily affected by soil temperature [35,36], and the different responses of autotrophic respiration and heterotrophic respiration to environmental factors may explain the observed diel hysteresis [16]
Summary
Soil respiration accounts for the largest proportion of the total ecosystem respiration [1], and its global integration is an order of magnitude larger than that of anthropogenic CO2 releases from burning fossil fuels and deforestation [1,2]. Biological soil crusts (BSCs) are widespread communities that consist of cyanobacteria, green algae, lichens, mosses and other organisms, and they are closely integrated with particles of the soil surface in arid and semi-arid regions [6]. These communities have long been acknowledged as one of the major components of arid and semi-arid ecosystems [7,8], where up to 70% of the living ground is covered by BSCs in certain plant communities [9]. BSCs need to be considered when estimating the C budgets in desert ecosystems because of their major contribution to the total C release by soil respiration
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