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Soil respiration ( R s ), conventionally considered as net soil CO 2 flux, is an important link in the terrestrial carbon cycle. However, existing estimates of R s in drylands may be erroneous, because of the abiotic soil CO 2 flux. This may seriously hamper our understanding of the carbon cycle of desert ecosystems. In this study, we monitored CO 2 flux of natural and sterilized soils, and obtained the net and abiotic soil CO 2 flux in a desert ecosystem in Ningxia, China, and then computed R s by using these data. Daily R s was much larger than the net soil CO 2 flux both in the growing and non-growing season. Further analysis indicated that R s was controlled by soil temperature ( T s ) over the annual cycle, and an exponential model could provide a good prediction of R s . During the growing season, R s increased significantly with rising soil water content ( VWC ) ( P < 0.05). A bivariate ( T s and VWC ) exponential–power model had a better performance for predicting R s in the growing season than a T s -only model. However, during the non-growing season, this model failed to simulate R s . Our results suggest that R s is greatly underestimated, and the exponential model is more applicable for annual R s prediction. [ABSTRACT FROM AUTHOR]

In natural ecosystems, soil respiration is one of the important components of carbon emission into the atmosphere – CO 2 efflux. Soil CO 2 efflux has both temporal (due to temperature and moisture changes) and spatial variability, which can be explained by different types of soil, soil use and management, as well as the influence of vegetation on CO 2 efflux. The aim of this study was to measure the spatial variability of soil CO 2 efflux, soil temperature and soil moisture in areas of archaeological dark earth cultivated with the guandu bean (GB) and pasture (PT), compared to soil use in natural forests (NF) in Amazonas state, Brazil. To that end, regular meshes were marked out in areas of forest (6 × 6 m spacing), guandu bean (4 × 5 m spacing) and pasture (8 × 8 m spacing) measuring 2500 m 2 , 1700 m 2 and 4800 m 2 , respectively, with 88 sample points georeferenced in each area. Soil CO 2 efflux (FCO 2 ) and soil temperature (ST) were measured at the intersection points of the meshes, and soil samples were collected at a depth of 0.00–0.10 m to determine soil moisture (SM) in the laboratory. FCO 2 measurements were taken using LI-6400 systems. Soil temperature (ST) was measured at 0.00–0.10 m, using a portable thermistor thermometer, and soil moisture (SM) using soil samples collected at 0.00–0.10 m. FCO 2 and ST were lower in the forest area, with higher SM content, no difference between FCO 2 and ST in GB and PT, but with lower SM content in PT. The models of the experimental semivariogram were predominantly spherical, except for FCO 2 in the NF and GB areas, and SM in the PT area, which were fit to the exponential model. The maps of spatial distribution patterns indicate a trend in concentration, with a positive correlation between FCO 2 and SM and negative correlation between FCO 2 and ST in natural forest. Positive correlations were observed between FCO 2 and ST and SM in GB, but in PT, FCO 2 correlations were restricted to SM. [ABSTRACT FROM AUTHOR]

In this work, we investigated how the reindeer grazing in subarctic boreal Scots pine forests and climate (air temperature and the amount of precipitation) affects soil temperature, soil water content, and ultimately the CO 2 efflux from forest soils. The study was carried out in years 2013 and 2014, where 2013 was an extremely dry year (especially the summer), while 2014 was a “normal” year. Our work showed that in subarctic mature pine forests, soil temperatures were higher, and soil water content was fluctuating more on grazed areas compared to non-grazed areas in both years. On both years, the soil water content on the grazed area was higher in June and the situation changed in the second half of July when the moisture content in the non-grazed area remained higher. There was a negative correlation between soil water content and soil temperature. The soil CO 2 effluxes were mostly affected by the year of measurement, time of measurement (different months through growing season), soil temperature and also by the management (grazed or non-grazed) resulting in higher CO 2 emissions on the grazed areas. Soil moisture content was not affecting the soil CO 2 efflux. The average soil CO 2 efflux values were significantly higher in the year 2014 compared to the year 2013 mainly due to differences in soil temperature at the beginning of season. [ABSTRACT FROM AUTHOR]

• The meadow-rice mixed ecosystem acted as CO 2 sink and CH 4 source. • CH 4 emissions were regulated by soil moisture during the dry period. • The seasonal dynamics of GPP, R eco , and CH 4 throughout the growing season were mainly regulated by T s and T a. Although previous studies have illustrated the variations in carbon dioxide (CO 2) and methane (CH 4) fluxes for different types of wetlands, there have been few reports on those of meadow-rice mixed ecosystems in semi-arid regions. In this study, eddy covariance (EC) technique was utilized to measure CO 2 and CH 4 fluxes for a meadow-rice mixed ecosystem during the growing season in 2020 in the Horqin Sandy Land, North China. The results indicated obvious diurnal and seasonal variations in gross primary productivity (GPP), ecosystem respiration (R eco), net CO 2 exchange (NEE), and CH 4 flux, with high levels during the vigorous growing stage and low levels during the early and late growing stages. The mean daily GPP, R eco , NEE, and CH 4 were 11.33 g CO 2 m−2 d−1, 6.37 g CO 2 m−2 d−1, −4.96 g CO 2 m−2 d−1, and 81.97 mg CH 4 m−2 d−1, respectively. The accumulated values of GPP, R eco , NEE, and CH 4 during the growing season were 1,756.54 g CO 2 m−2 (478.62 g C m−2), 987.30 g CO 2 m−2 (269.02 g C m−2), −769.24 g CO 2 m−2 (−209.60 g C m−2), and 12.7 g CH 4 m−2 (9.55 g C m−2), respectively, showing that the meadow-rice mixed ecosystem acted as CO 2 sink and CH 4 source. Low intensity CH 4 emissions were maintained during the dry period and were controlled by soil moisture (SM). The seasonal dynamics of GPP, R eco , and CH 4 throughout the growing season were mainly controlled by soil temperature (T s) and air temperature (T a). [ABSTRACT FROM AUTHOR]