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• 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]

Soil moisture is important for plant growth in semi-arid ecosystems. In this study, spatial variations in soil moisture at depths of 0–6 m on seven hillslopes of China's Loess Plateau planted with korshinsk peashrub were analyzed based on soil moisture observations. The objective of this study was to compare the spatial patterns in soil moisture in shallow and deep soil layers at the hillslope scale under the influence of large-scale vegetation restoration. The results showed that: (1) the topographic wetness index was positively correlated with soil moisture near the surface (0–1 m), but negatively correlated with soil moisture at depths below 2 m; and (2) the negative relationship was found between biomass and soil moisture content in deep layers. Soil moisture in shallow layers was more likely to be affected by topographic factors. However, comparisons of soil moisture at different slope positions indicated that the effect of topographic factors on the variability of deep soil moisture was altered, mainly because plants with different biomasses may differ in their consumption of soil water and thus cause greater spatial variations in deep soil moisture. The introduced vegetation may alter the spatial pattern of deep soil moisture influenced by topographic factors at the hillslope scale, and the biomass may have a determining role in the spatial variation of deep-layer soil moisture content. [ABSTRACT FROM AUTHOR]

• Annual mean R s and Q 10 values in HD were significantly higher than those in LD. • R s was mainly controlled by θ in the summer and T s in the other seasons. • Double variable equation was better than single to predict R s at the annual scale. • Annual R s in HD was positively related with θ , NDVI and SOM, negatively with T s. • Annual θ was the main factor controlling annual Q 10 at both sites. Although correlations between soil respiration (R s) and environmental factors in different ecosystems have been extensively investigated, results based on long-term experiments are limited. In this study, we analyzed the correlations between R s and soil temperature (T s), moisture (θ), the normalized difference vegetation index (NDVI), and soil organic matter (SOM) based on an 11-year field campaign in abandoned farmland (HD) and bare land (LD) areas with a Cambisol soil type in the eastern Loess Plateau of China. The results showed that the mean annual R s and annual temperature sensitivity (Q 10) values in HD were significantly larger than those in LD during the measurement period. R s and the annual contribution ratio (R ratio) of root respiration (R r) to R s in HD increased significantly with vegetation recovery years. On the annual scale, R s was controlled primarily by T s at both sites. However, in the summer months, R s was controlled by θ rather than T s. A two-variable model, including T s and θ , could more accurately predict the temporal variations in R s at the annual and seasonal time scales than a single-variable model, and the explanatory power of the equations in HD was significantly larger than that in LD. On the interannual scale, variations in the annual R s and R r showed significant positive correlations with the annual θ and NDVI and SOM, and negative correlations with T s in HD. Moreover, the annual Q 10 was significantly positively related to θ in HD. In LD, the only significant relationship was between the annual Q 10 and the annual θ. All differences between HD and LD in R s , T s , and θ and their correlations were attributed to differences in vegetation. Our findings highlight the importance of long-term observations for the accurate estimation of CO 2 efflux in semiarid regions and the impact of vegetation changes on soil respiration. [ABSTRACT FROM AUTHOR]

Biocrusts are widely distributed throughout the world in dryland ecosystems, but their respiration rate (R s) and responses to soil temperature and mositure have not yet been fully investigated. In a semiarid region of the Loess Plateau in China, the R s of moss-dominated biocrusts was continuously (104 days) measured in summer through an automated soil respiration system, and their relationships with soil temperature and moisture at 2, 5, and 10 cm depths were intensively analyzed. The results showed the biocrusts had 115% higher (t = −3.82, P < 0.001) R s during day and 44% higher (t = −10.22, P < 0.001) R s during night as compared with the underlying soil; they averagely increased R s by 81% (2.52 vs. 1.39 μmol m−2 s−1) across day and night. More specifically, the R s of biocrusts ranged from 0.33 to 6.33 μmol m−2 s−1 in wet conditions (soil moisture ≥ 0.15 cm3 cm−3) and 0.27 to 2.83 μmol m−2 s−1 in dry conditions (soil moisture = 0.05 cm3 cm−3), with a daily mean of 2.11 μmol m−2 s−1. Particularly, in wet conditions the R s of biocrusts had positive responses to increasing temperature, and their relationship was well fitted with an exponential function (R 2 ≥ 0.44; P < 0.001), with a Q 10 value ranging between 1.73 and 2.08. Similarly, the R s of biocrusts was positively correlated with soil moisture, but their relationship was not well fitted with the quadratic function (R 2 ≤ 0.22). A model based on the soil moisture and temperature at 2 cm depth performed much better (R 2 = 0.53; P < 0.001) with R s than that based on the soil moisture and temperature at 5 or 10 cm depth or even air temperature. In conclusion, moss biocrusts made a significant contribution to soil respiration in semiarid ecosystem, firstly (and directly) due to the rich and diversified microbial communities in biocrust layer and secondly (and indirectly) due to the biocrust effects on soil temperature and moisture regimes. The temperature and moisture at 2 cm depth (biocrust layer) should be employed with a higher priority in simulating R s of biocrusted surfaces, rather than the commonly used soil depth (5 cm) in estimating R s of the ordinary soil without biocrusts. Unlabelled Image • Biocrusts increased respiration rate (R s) by 81% as compared with underlying soil. • R s of biocrusts ranged from 0.05 to 9.50 μmol m−2 s−1 with a mean of 2.11 in summer. • R s of biocrusts was highly dependent on moisture and temperature (Q 10 = 1.73–2.08). • Soil temperature and moisture at 2 cm depth are capable of estimating R s of biocrusts. [ABSTRACT FROM AUTHOR]