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Article

Effects of Precipitation Variation on Annual and Winter Soil Respiration in a Semiarid Mountain Shrubland in Northern China

by
Huitao Shen
1,
Tao Zhang
1,
Yanxia Zhao
1,
Aibin Wu
1,
Zhenhua Zheng
1,* and
Jiansheng Cao
2,*
1
Hebei Engineering Research Center for Geographic Information Application, Institute of Geographical Sciences, Hebei Academy of Sciences, Shijiazhuang 050021, China
2
Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang 050021, China
*
Authors to whom correspondence should be addressed.
Sustainability 2023, 15(9), 7461; https://doi.org/10.3390/su15097461
Submission received: 14 March 2023 / Revised: 22 April 2023 / Accepted: 26 April 2023 / Published: 1 May 2023
(This article belongs to the Section Air, Climate Change and Sustainability)
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Abstract

:
In response to global climate change, future precipitation changes are expected to profoundly influence soil respiration in arid and semiarid areas. However, few studies focus on CO2 emissions from soils undergoing precipitation changes in semiarid mountain shrublands in winter. A precipitation-manipulation experiment with three levels of precipitation (30% decreased precipitation (DP), ambient precipitation (AP), and 30% increased precipitation (IP)) was performed to examine the effects of variable precipitation on soil respiration (SR) and wintertime contributions to annual SR emissions in Vitex negundo var. heterophylla shrub ecosystems located on the Middle Taihang Mountain in Hebei Province, northern China. The results showed that the average annual SR rates and winter SR rates ranged from 1.37 to 1.67 μmol m−2 s−1 and 0.42 to 0.59 μmol m−2 s−1 among the different precipitation treatments. The model based on soil moisture better represented the soil-respiration rates, suggesting that the variable precipitation extended the water’s limitation of the soil’s CO2 emissions. The cumulative annual soil CO2 emissions were 523, 578, and 634 g C m−2 in response to the DP, AP, and IP treatments, respectively. The ratio of the soil CO2 emissions in winter to the annual CO2 emissions varied from 7.6 to 8.8% in response to the different precipitation treatments. Therefore, ignoring the soil CO2 emissions in winter leads to the underestimation of the carbon losses in semiarid shrublands. Our results highlight that variable precipitation significantly influences soil-respiration rates, and soil CO2 emissions in winter must not be ignored when predicting the future feedback between SR and climate change in semiarid regions.

1. Introduction

Soil respiration is a significant process involved in land–atmosphere carbon (C) exchange [1,2,3]. Even a subtle change in soil respiration may cause a huge fluctuation in the global terrestrial C budget [4]. The predicted increase in global temperatures is expected to alter the hydrological cycle and change the frequency and duration of precipitation events [5]. These changes in precipitation are expected to greatly affect terrestrial carbon C cycling [6]. In general, manipulation experiments on precipitation reduction significantly inhibited [7], substantially stimulated [8], and had no effect [9] on soil respiration. These inconsistent results may have resulted from the different ecosystems and the level of precipitation reduction across the experiments. Moreover, increased precipitation can improve soils’ water content, which in turn benefits root growth and stimulates microbial activity [10], thus improving soil respiration [11]. The quantification of the variable precipitation effects on soil respiration may allow us to reduce uncertainty in the simulation of terrestrial C cycles in response to future climate change. It is imperative to focus on this issue because climate change due to emissions negatively affects production systems [12,13,14,15].
Soil temperature and soil moisture are the critical environmental variables affecting soil respiration [16,17]. Previous studies reported that soil respiration increased exponentially with soil temperature [18,19,20], due to the temperature sensitivity of the metabolic breakdown of stable C pools, microbial adaptation, and the depletion of labile substrates [21,22]. Soil moisture, a key driver of biological processes [19], directly affects soil respiration through physiological processes and indirectly influences soil respiration using oxygen diffusion through the substrate [18]. The relationships between soil respiration and soil moisture were proposed to be a linear, quadratic, and exponential in previous studies [16], attributable to differences between soil textures, plant roots, and soil microbial activities [23,24]. Thus, the identification between soil respiration variations and their control factors could decrease some of the uncertainties related to climate–carbon feedback projections [16].
Many of the measurements of soil respiration in different ecosystems were only performed during growing seasons [18,25,26]. The researchers who conducted these studies assumed that soil respiration in winter can be ignored due to the negligible soil microbial activity [27,28]. However, the small but continuous soil respiration in winter can play a significant role in the annual C budget in arctic and boreal ecosystems [29,30]. For example, Brooks et al. [31] indicated that on average, 50% of the growing-season carbon uptake is currently respired during winter. Mast et al. [32] observed that soil CO2 fluxes in winter accounted for 23% of the gross annual CO2 emissions in the Rocky Mountain National Park, Colorado. Compared with arctic and boreal ecosystems, arid and semi-arid regions which account for 45% of the global land area and feature shorter winters, are believed to be major sources of the terrestrial carbon sink [28,33].
Artificial drought treatments have been devised by experimentally excluding precipitation using a system of plastic panels and drainage tubes in arid and semi-arid regions [34]. These have been used to investigate the impact of precipitation reduction on soil respiration in different shrubland ecosystems [35,36,37]. However, the contribution of winter soil respiration to annual soil CO2 fluxes under variable precipitation in shrublands in arid and semi-arid regions is still unclear. In this study, we hypothesized that variable precipitation would have a large effect on annual and winter soil-respiration rates. We performed a field-manipulation experiment with three levels of precipitation treatment (ambient precipitation as control, 30% decreased precipitation, and 30% increased precipitation) in semiarid shrubland plots on the Taihang Mountain, in northern China. The objectives of this study were (1) to assess the annual soil CO2 emissions and the magnitude of the winter contributions to the annual soil respiration in response to variable precipitation treatments; and (2) to explore the responses of the soil respiration to the soil temperature and soil moisture. We proposed that the soil respiration’s response to changes in precipitation are related to changes in soil moisture (Figure 1).

2. Materials and Methods

2.1. Site Description and Experimental Design

The study site was located at the Taihang Mountain Experimental Station of the Chinese Academy of Science (114°15′50″ E, 37°52′44″ N, 350 m a.s.l.) in northern China (Figure 2). The research area has a semi-arid continental climate. The mean annual atmospheric temperature is 13 °C, with the lowest at −4 °C, in January, and the highest at 26 °C, in July, respectively [38]. The mean annual precipitation is approximately 560 mm, mainly falling from June to September [39]. According to the Chinese soil taxonomy, the soil is classified as cinnamon soil, equivalent to Ustalf in the USDA soil taxonomy [38]. The Vitex negundo var. heterophylla is the predominant shrub species [38].
Three sites were established in June 2016 in areas with similar topographies and aspects. On three plots (10 m × 10 m each) at each site, about 10 to 15 m apart from each other, we performed one of three precipitation treatments: ambient precipitation as control (AP), 30% decreased precipitation (DP), and 30% increased precipitation (IP). The precipitation treatments were conducted throughout the whole experimental period, from August 2017 to July 2018. The precipitation levels −30% and +30% of ambient precipitation were selected based on the interannual fluctuation magnitudes of annual precipitation (−28% to +27%) over the previous 30 years at the experimental site. In DP plots, plastic rainout shelters were used to remove 30% of the natural precipitation, as described by Sherman et al. [40]. Although the shelters caused a slight interception of incoming light, Zhang et al. [41] showed that interception has little effect on plant responses. In IP plots, 30% of the precipitation was added immediately after more than 2 mm of precipitation. All the added water was collected from precipitation removed by the shelters [11]. Any snowfall in winter was also collected by the shelters and evenly added to the IP plots before it melted [10].

2.2. Measurement of Soil Respiration and Environmental Variables

In each plot, three PVC collars (diameters of 20.3 cm and heights of 8 cm) were randomly inserted 5 cm into the soil to monitor soil respiration. All collars were left at the site for the entire study period [42]. Before every measurement, living plants inside the collars were carefully removed by hand [43]. Soil-respiration data were measured once every month using a soil CO2 flux system (LI-8100, LI-COR Inc., Lincoln, NE, USA) from August 2017 to July 2018. Soil-respiration measurements were carried out between 9:00 a.m. and 11:30 a.m., local time. The winter length in this study was 3 months, from December to February, during which the mean diel soil temperature at a depth of 5 cm was continuously <0.5 °C, as defined by Grogan and Jonasson [44]. Temporal soil temperature (°C) and soil moisture (%) at a soil depth of 5 cm near each collar were recorded at the same time as soil-respiration measurements, using soil temperature and humidity sensors equipped with the LI-8100 system [39].

2.3. Response of Soil Respiration to Soil Temperature and Moisture

An exponential function was used to explore the relationship between soil respiration and soil temperature, as follows [20]:
S R = a ⋅ e b ⋅ S T
where SR and ST are soil respiration (μmol m−2 s−1) and soil temperature (°C) at a depth of 5 cm, respectively, and a and b are constant coefficients. The temperature sensitivity (Q10) of the SR based on Equation (1) was calculated as:
Q 10 = e 10 ⋅ b
A quadratic least-squares regression was fitted to assess the effect of soil moisture on soil respiration, as follows [37]:
S R = a ⋅ S M 2 + b ⋅ S M + c
where a, b, and c are fitted constants and SM is the soil moisture (%) at a depth of 5 cm.
Considering the effect of interaction of soil temperature and soil moisture on soil respiration, a two-variable regression model was also used to fit soil respiration, as follows [20]:
S R = a ⋅ e b ⋅ S T ⋅ S M c
where a, b, and c are fitted parameters.

2.4. Scaling for Winter and Annual Soil CO2 Emissions

Further estimates of winter and annual soil CO2 emissions for different precipitation treatments were obtained by interpolating measured SR rates between respective sampling dates, and then computing the sum to obtain winter or annual values [28,42], as follows:
T S R = ∑ k = 1 n − 1 S R m , k Δ t k
where Δtk = tk+1 − tk is the number of days between each field measurement within the season, TSR is total soil CO2 emissions during the measurement period, SRm,k is the average SR rate over the interval tk+1 − tk recorded by the LI-8100 system, and n is the number of soil-respiration measurements made within each measurement period [42].

2.5. Statistical Analysis

The relationships between soil respiration and environmental variables were explored by non-linear regression using Sigmaplot 12 software (Systat Inc., Point Richmond, Chicago, IL, USA). Analysis of variance (ANOVA) was used to detect the significance of soil respiration, soil temperature, soil moisture, and cumulative soil CO2 emissions in response to different precipitation treatments using Duncan’s test at p < 0.05. The SPSS 18.0 software (SPSS Inc., Chicago, IL, USA) was used to calculate the statistical analysis.

3. Results

3.1. Temporal Dynamics of Soil Temperature, Soil Moisture, and Soil Respiration

The soil temperature showed a strong seasonal pattern, from a trough of −2.6 °C, in January 2018, to a peak of 26.5 °C, in July 2018, with no significant differences between the three precipitation treatments (Figure 3A). The mean monthly soil temperatures of the DP, AP, and IP were 14.1, 14.0, and 13.9 °C, respectively.
The soil moisture exhibited similarly seasonal variations and was significantly affected by the precipitation manipulation (p < 0.01) (Figure 3B). On average, the soil moisture was 9.7%, 10.2%, and 10.7% in the DP, AP, and IP treatments, respectively.
The soil respiration followed a similarly seasonal pattern to the soil temperature, ranging from a minimum of 0.33 μmol m−2 s−1, in January 2018, to a maximum of 4.02 μmol m−2 s−1, in July 2018 (Figure 3C). Across the whole study period, the soil respiration was significantly influenced by the precipitation treatments (p < 0.01). The AP treatment’s monthly average soil-respiration rate was 1.52 μmol m−2 s−1, which was 10.9% higher than the DP treatment and 9.0% lower than the IP treatment. In the winter season, the mean SR in the IP was 0.59 μmol m−2 s−1, which was significantly higher than the SR measured in the DP and AP treatments (Figure 4). The results showed that the soil respiration in this study was significantly influenced by the precipitation variation, either through the winter period or through the whole experimental period.

3.2. Winter Soil CO2 Emissions

The interpolated annual and winter soil CO2 emissions under different precipitation treatments are presented in Figure 5. The annual soil CO2 emissions were as follows, in descending order: IP (634 g C m−2) > AP (578 g C m−2) > DP (523 g C m−2). The soil CO2 emissions during the winter season had a similar ranking, in which the IP had the highest emissions (56 g C m−2), followed by the AP (45 g C m−2), and then the DP (39 g C m−2). Higher levels of precipitation increased the winter soil CO2 emissions in the present study. The contribution of the winter soil CO2 emissions to the annual soil CO2 emissions ranged from 7.6% to 8.8% in all the precipitation treatments, with the largest ratio occurring with the IP treatment and the lowest in DP treatment.

3.3. Relationships between Soil Respiration and Environmental Variables

During all three precipitation treatments, the soil-respiration rate was significantly correlated and increased exponentially with the soil temperature (Table 1 and Figure 6). Based on the exponential models, the soil temperature explained 76.6% to 78.7% of the seasonal changes in the soil-respiration rates. The Q10 values ranged from 2.64 to 4.57, and significantly decreased with the precipitation increment. A parabolic relationship between the soil-respiration rate and the soil moisture was observed among all three precipitation treatments, while the soil moisture explained 78.7% to 81.3% of the variation in the soil-respiration rates (Table 2 and Figure 7). The soil-respiration rates were more dependent on the soil moisture than on the soil temperature, as indicated by the higher R2 in the relationships (Table 1 and Table 2). The two-variable regression model (equation 4) explained 63.1% to 76.3% of the variation in the soil-respiration rate (Table 3), suggesting that the two-variable function did not represent the relationship better than the single-factor functions using either soil temperature or soil moisture.

4. Discussion

4.1. Effects of Changing Precipitation on Soil Respiration

Changing precipitation is expected to profoundly affect terrestrial C fluxes [10]. Water is the most important factor driving CO2 fluxes in semiarid ecosystems, and ecological processes are directly restricted by water limitation [26,45]. Consistent with previous studies [46,47], the DP treatments reduced the soil respiration by 9.9% in this study (Figure 3C). The soil respiration was inhibited by the precipitation-exclusion treatment because soil-organic-matter decomposition rates, soil microbial activities, and enzymatic activities are suppressed in semiarid ecosystems due to the limited water content in the soil [48]. In contrast, increases in precipitation led to greater soil respiration (1.67 μmol m−2 s−1) in the IP treatments compared to the AP treatments, in a manner that was consistent with grassland ecosystems [49,50]. These results suggested that the direct and critical role of soil water availability and the synergistic increases in bacterial and fungal abundance under increasing precipitation were responsible for the enhancement of the soil respiration [51,52]. However, other studies, on tropical rainforests, reported that reductions in precipitation increased soil respiration, positing that the soil-moisture levels were within the range required for optimal microbial and root activities under precipitation-reduction conditions [20,53]. Conversely, Wei et al. [19] observed no effects on soil respiration from changing precipitation levels, speculating that offsets occurred among the numerous changes in C cycling processes. The disagreements between these results are not surprising because the studies of the effects of changing precipitation on soil respiration were conducted in diverse ecosystems, and the measurements were made within different temporal scales [45,54].

4.2. The Importance of Winter Soil CO2 Emissions

Soil CO2 emissions during winter months represent a considerable proportion of annual CO2 emissions [42]. In the semiarid shrubland sites investigated here, the average soil-respiration rates in winter varied from 0.42 to 0.59 μmol m−2 s−1, falling within the range of previously reported values in different shrubland sites (0.17–0.80 μmol m−2 s−1) [28,42,55]. Similar ranges of average winter soil-respiration rates were also recorded in China: 0.17–0.69 μmol m−2 s−1 in different vegetation patches in the Yellow River Delta [56], and 0.43–0.55 μmol m−2 s−1 in a spruce forest [57]. However, several studies reported higher values in different forest ecosystems. For instance, the average soil-respiration rates in winter ranged from 0.74–1.41 μmol m−2 s−1 on Pinus massoniana plantations in southern China [58], and 1.3 μmol m−2 s−1 at European beech stands in Romania [27]. The measurements of winter soil-respiration rates vary across ecosystems, and they may be influenced by interactive factors, such as the composition of the vegetation, the length of winter season, snow covering the soils, and various physical and chemical properties of different soils [59]. In our study area, the snow cover was thin and its duration was short. Snow cover with a depth of less than 30 cm may not effectively decouple soil temperatures from those of the atmosphere, resulting in lower respiration rates [28]. The associated CO2 losses from respiration in winter might offset a major portion of the carbon fixed during the growing season and were not negligible, in one study, in the determination of the annual soil CO2 emissions [56]. In this study, the ratio of winter-season soil respiration to the annual total emissions (7.6–8.8%) fell within the previously reported range values (3.5–19.0%) from other ecosystems [28,42,59]. The soils released considerable amounts of CO2 into the atmosphere during winter in response to the different precipitation treatments. These emissions need to be considered when assessing annual carbon budgets in similar semiarid shrubland sites.

4.3. Dependence of Soil Respiration on Soil Moisture and Temperature

Higher soil temperatures are likely to significantly enhance soil microbial and root activity, accelerating the decomposition of soil organic matter, which further increases soil respiration rates [59]. In this study, the soil respiration enhanced exponentially with increases in the soil temperature (Figure 6). Similar trends were also found in cropland [26,60], shrubland [61], grassland [19], and broadleaved ever-green forest [62] ecosystems. Compared with the non-winter seasons, the soil temperature was more important in the winter for soil respiration, as the plant activity was strongly reduced, and soil the respiration typically took the form of microbial respiration [42].
Understanding the sensitivity of soil respiration to changes in soil temperature (Q10) makes it possible to accurately evaluate the response of the terrestrial C balance to climate change [60]. In this study, the Q10 values ranged between 2.64 and 4.57, similar to the reported values (1.33–5.18) in other ecosystems [59,62,63]. Several studies suggested that higher soil moisture increased Q10, while drought suppressed Q10 [18,19]. These results were attributed to the diffusion rate of extracellular enzymes produced by microbes to break down organic matter as the soil moisture increases [61]. Higher water availability is also related to higher C accumulation and allocation, resulting in a higher Q10 [64]. In contrast, our study suggested that reductions in the precipitation increased the Q10, which was consistent with other previous works [26,65]. These findings create a need for more data sets to determine whether increases in Q10 in response to decreased precipitation is common or an anomaly in semi-arid regions.
In addition to soil temperature, soil moisture has been recognized as another important driver of soil respiration [20,27,61]. Our results provided evidence that the changes in precipitation significantly influenced the soil moisture and that the quadratic functions of the soil moisture exerted stronger effects than the exponential functions of the soil temperature. Changes in soil moisture affect the allocation of assimilates in plant–soil systems, controlling microbial biomass and enzymatic activities in the rhizosphere [19,61]. Additionally, the quadratic functions of the soil moisture indicated that soil respiration might become depressed when soil moisture is either excessively low or overly high. Escolar et al. [66] suggested that the soil moisture might limit soil respiration in two ways, either by limiting soil aeration under high-moisture conditions or by stressing microorganisms under lower-moisture conditions. In addition, the two-variable function of soil respiration appeared to be weaker than the model based on soil moisture in our analysis only, suggesting that changes in precipitation might amplify the effects of the limitation of soil moisture on soil respiration [51,52]. A meta-analysis study also suggested that soil respiration was mainly driven by soil-moisture changes rather than by soil temperature across different biomes [23]. Variations in soil respiration were also ascribed to changes in other biotic factors, such as plant-community structures, roots, vegetation cover, and microbial communities [67]. These factors might respond differently to alterations in precipitation. As a result, conclusions regarding the relationships between soil respiration and environmental factors should be further studied in future research.

5. Conclusions

A better understanding of the response of soil respiration to alterations in precipitation has important practical implications for global carbon cycles under climate change. Based on the three-level precipitation-manipulation experiment in a semiarid shrubland, the reduced-precipitation treatment led to lower soil respiration (1.37 μmol m−2 s−1) than the control treatment (1.52 μmol m−2 s−1). The increased-precipitation treatment stimulated soil respiration (1.67 μmol m−2 s−1). The most significant difference in soil-respiration levels was between the IP and DP treatments (p < 0.01). Moreover, the winter-season soil-CO2-emissions ratio accounted for 7.6% to 8.8% of the total yearly emissions. Hence, winter soil CO2 emissions should be considered when evaluating the reactions of ecosystem C balances in response to climate change. In addition, the soil respiration was best represented by the quadratic model based on the soil moisture. The precipitation-reduction treatment increased the Q10 value in our study, highlighting the need to evaluate whether this phenomenon occurs across other shrubland ecosystems. This study is important for the carbon cycling of shrubland ecosystems in response to changes in the climate. However, the effects of biotic factors on the total soil respiration were not considered in this study, and future research is necessary to evaluate the effects of alterations in precipitation on soil respiration through various biotic and abiotic factors.

Author Contributions

Conceptualization, H.S. and J.C.; investigation, H.S., T.Z. and Y.Z.; data curation, T.Z., Y.Z. and A.W.; writing—original draft preparation, H.S.; writing—review and editing, Z.Z. and J.C.; project administration, A.W.; funding acquisition, H.S. and Z.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Natural Science Foundation of Hebei Province (no. C2019302018), the Natural Science Foundation of China (no. 31500448), the Youth Talent Project of Hebei Province, and the Talent Training Program of Hebei Academy of Sciences (2017G01).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Conceptual framework of the effect of precipitation changes on the relationship between soil respiration and soil moisture.
Figure 1. Conceptual framework of the effect of precipitation changes on the relationship between soil respiration and soil moisture.
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Figure 2. Research location (red triangle) of the study site. Note: Red five-pointed star represents the location of Beijing City; Red solid circle represents the location of Tianjin City; Red double circle represents the location of Shijiazhuang City.
Figure 2. Research location (red triangle) of the study site. Note: Red five-pointed star represents the location of Beijing City; Red solid circle represents the location of Tianjin City; Red double circle represents the location of Shijiazhuang City.
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Figure 3. Soil temperature (°C) at depth of 5 cm (A), moisture (%) at depth of 5 cm (B), and respiration (μmol m−2 s−1) (C) of each precipitation treatment in semiarid shrubland sites in northern China between August 2017 and July 2018. Data are the mean ± SD values (n = 3). The inset graphs show the mean values of soil temperature, moisture, and respiration, respectively, throughout the experimental period. Letters on the tops of the bars indicate significant differences between the precipitation treatments when p < 0.05. DP: 30% decreased precipitation; AP: ambient precipitation as control; IP: 30% increased precipitation.
Figure 3. Soil temperature (°C) at depth of 5 cm (A), moisture (%) at depth of 5 cm (B), and respiration (μmol m−2 s−1) (C) of each precipitation treatment in semiarid shrubland sites in northern China between August 2017 and July 2018. Data are the mean ± SD values (n = 3). The inset graphs show the mean values of soil temperature, moisture, and respiration, respectively, throughout the experimental period. Letters on the tops of the bars indicate significant differences between the precipitation treatments when p < 0.05. DP: 30% decreased precipitation; AP: ambient precipitation as control; IP: 30% increased precipitation.
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Figure 4. Soil respiration (μmol m−2 s−1) of each precipitation treatment during winter and non-winter seasons in semiarid shrubland sites of northern China. Data are the mean ± SD values (n = 3). Letters on the tops of the bars indicate significant differences between the precipitation treatments when p < 0.05. DP: 30% decreased precipitation; AP: ambient precipitation as control; IP: 30% increased precipitation.
Figure 4. Soil respiration (μmol m−2 s−1) of each precipitation treatment during winter and non-winter seasons in semiarid shrubland sites of northern China. Data are the mean ± SD values (n = 3). Letters on the tops of the bars indicate significant differences between the precipitation treatments when p < 0.05. DP: 30% decreased precipitation; AP: ambient precipitation as control; IP: 30% increased precipitation.
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Figure 5. Winter and non-winter soil CO2 emissions (WSCE and NWSCE) of each precipitation treatment in semiarid shrubland sites in northern China. Letters on the tops of the bars indicate significant differences between the precipitation treatments when p < 0.05. DP: 30% decreased precipitation; AP: ambient precipitation as control; IP: 30% increased precipitation.
Figure 5. Winter and non-winter soil CO2 emissions (WSCE and NWSCE) of each precipitation treatment in semiarid shrubland sites in northern China. Letters on the tops of the bars indicate significant differences between the precipitation treatments when p < 0.05. DP: 30% decreased precipitation; AP: ambient precipitation as control; IP: 30% increased precipitation.
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Figure 6. Relationships between soil respiration (μmol m−2 s−1) and soil temperature (°C) at depth of 5 cm under different precipitation treatments in semiarid shrubland sites in northern China.
Figure 6. Relationships between soil respiration (μmol m−2 s−1) and soil temperature (°C) at depth of 5 cm under different precipitation treatments in semiarid shrubland sites in northern China.
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Figure 7. Relationships between soil respiration (μmol m−2 s−1) and soil moisture (%) at depth of 5 cm in response to different precipitation treatments in semiarid shrubland sites in northern China.
Figure 7. Relationships between soil respiration (μmol m−2 s−1) and soil moisture (%) at depth of 5 cm in response to different precipitation treatments in semiarid shrubland sites in northern China.
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Table
Table 1. Relationships between soil respiration (SR, μmol m−2 s−1) and soil temperature (ST, °C) in response to different precipitation treatments, showing R2, p, and Q10 values.
Table 1. Relationships between soil respiration (SR, μmol m−2 s−1) and soil temperature (ST, °C) in response to different precipitation treatments, showing R2, p, and Q10 values.
TreatmentEquationR2pQ10
Decrease in precipitation of 30% (DP)SR = 0.061 e0.152 ST0.774<0.014.57
Ambient precipitation (AP)SR = 0.125 e0.126 ST0.787<0.013.52
Increase in precipitation of 30% (IP)SR = 0.266 e0.097 ST0.766<0.012.64
Table
Table 2. Relationships between soil respiration (SR, μmol m−2 s−1) and soil moisture (SM, %) in response to different precipitation treatments, showing R2 and p values.
Table 2. Relationships between soil respiration (SR, μmol m−2 s−1) and soil moisture (SM, %) in response to different precipitation treatments, showing R2 and p values.
TreatmentEquationR2p
Decrease in precipitation of 30% (DP)SR = 0.039 SM2 − 0.430 SM + 1.4510.787<0.01
Ambient precipitation (AP)SR = 0.041 SM2 − 0.495 SM + 1.7970.797<0.01
Increase in precipitation of 30% (IP)SR = 0.034 SM2 − 0.419 SM + 1.7800.813<0.01
Table
Table 3. Combined effects of soil temperature (ST, °C) and soil moisture (SM, %) on the variation in soil respiration (SR, μmol m−2 s−1) in response to different precipitation treatments, showing R2 and p values.
Table 3. Combined effects of soil temperature (ST, °C) and soil moisture (SM, %) on the variation in soil respiration (SR, μmol m−2 s−1) in response to different precipitation treatments, showing R2 and p values.
TreatmentEquationR2p
Decrease in precipitation of 30% (DP)SR = 0.303 e0.058ST SM0.1640.631<0.01
Ambient precipitation (AP)SR = 0.313 e0.056ST SM0.2140.642<0.01
Increase in precipitation of 30% (IP)SR = 0.357 e0.048ST SM0.2700.763<0.01
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Shen, H.; Zhang, T.; Zhao, Y.; Wu, A.; Zheng, Z.; Cao, J. Effects of Precipitation Variation on Annual and Winter Soil Respiration in a Semiarid Mountain Shrubland in Northern China. Sustainability 2023, 15, 7461. https://doi.org/10.3390/su15097461

AMA Style

Shen H, Zhang T, Zhao Y, Wu A, Zheng Z, Cao J. Effects of Precipitation Variation on Annual and Winter Soil Respiration in a Semiarid Mountain Shrubland in Northern China. Sustainability. 2023; 15(9):7461. https://doi.org/10.3390/su15097461

Chicago/Turabian Style

Shen, Huitao, Tao Zhang, Yanxia Zhao, Aibin Wu, Zhenhua Zheng, and Jiansheng Cao. 2023. "Effects of Precipitation Variation on Annual and Winter Soil Respiration in a Semiarid Mountain Shrubland in Northern China" Sustainability 15, no. 9: 7461. https://doi.org/10.3390/su15097461

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