Temporal Variation In Soil Respiration Research Articles

A biophysical model to simulate seasonal variations of soil respiration in agroecosystems in China

Characterizing the seasonal patterns of soil respiration using a biophysical model is crucial for understanding the mechanisms of the terrestrial carbon (C) cycle. We developed a biophysical soil respiration model including four submodels that were associated with the functions of soil temperature, moisture, leaf area index (LAI), and soil organic C, and the model parameters were determined and calibrated. The modeling reproducibility was examined in various crop fields at our study site, and the modeling performance was also validated in twenty-five other agroecosystems in China. The monthly and annual soil respiration was estimated using the model, and the modeling uncertainty was evaluated. The results showed that the soil respiration model had good modeling reproducibility in various crop fields at our site. The measured soil respiration in the different agroecosystems in China validated our model well. The R2, root mean squared error (RMSE), model efficiency (ME), and mean absolute error (MAE) were within the ranges of 0.449‒0.932, 0.526‒1.465 μmol m−2 s−1, 0.176‒0.796, and 0.312‒1.377 μmol m−2 s−1, respectively, across the twelve agroecosystem sites for validation. The measured soil respiration was significantly (P < 0.001) correlated with the modeled soil respiration across all twenty-six validation sites. Adding LAI significantly improved the modeling of soil respiration when the performance of the model (with LAI) vs. that without LAI was compared. The modeled monthly soil respiration was within the range of 0.016 ± 0.001‒0.117 ± 0.006 Pg C mo−1 in 2010 in agroecosystems in China. The black soils in Northeast China are fertile, which resulted in high temperature sensitivity and a clear increasing tendency of soil respiration from winter to summer in 2010 in agroecosystems in Northeast China. The established biophysical soil respiration model was proven to be effective for characterizing the temporal variations of soil respiration in various agroecosystems in China.

SOIL RESPIRATION UNDER DIFFERENT LAND USE SYSTEMS IN THE KUMAON REGION OF CENTRAL HIMALAYA, INDIA

Soil respiration (SR) is chiefly controlled by microclimatic conditions, microbial activity, and land use management practices of the particular ecosystem. In the present study, SR was measured under three different land-use systems viz. arable land (AL), a kitchen garden (KG), and peach orchard (PO) in the Almora and Nainital districts of Uttarakhand to observe the effect of soil temperature (ST) and soil moisture (SMC) on the rate of SR. The cumulative seasonal mean SR rate (g CO 2 m -2 h -1 ) was 2.67 ± 0.33, 4.3 ± 0.06, 8.29 ± 2.59 for the year 2017‒18, and 1.37 ± 0.28, 1.85 ± 0.05 and 2.27 ± 0.03 for the year 2018‒19 in AL, KG and PO respectively. The highest SR was found in PO followed by KG and AL. This study also found the spatial and temporal variations of SR in the selected land-use systems. The SR was positively correlated with SMC but negatively correlated with ST. Thus the ST explained the maximum variability of SR in the selected land-use systems. Overall, the results of this study clearly indicate that the microclimatic variables and land use management practices have a greater role in changes in SR of the studied region.

Influence of straw mulch and no-tillage on soil respiration, its components and economic benefit in a Chinese wheat–maize cropping system

Optimizing economic benefit while reducing soil CO2 emissions in cropping systems has become the focus of agricultural study. We assessed the influence of short-term straw mulch and no-tillage on soil respiration (Rs), heterotrophic respiration (Rh), and autotrophic respiration (Ra), as well as economic benefit, in a traditional Chinese winterwheat and summermaize rotation system. Combinations of four treatments were tested: NS (no straw), SM (straw mulch), CT (conventional tillage) and NT (no-tillage). For wheat, SM significantly increased Rs in 2019 but significantly decreased Rs in 2020 relative to NS. NT significantly decreased Rs by 5.8% compared to CT from 2019 to 2020. For maize, during all three annual cycles, SM increased Rs relative to NS. NT increased Rs in 2018 with respect to CT but decreased it in 2019 and 2020. From the perspective of annual Rs both wheat and maize, SM increased Rs by 34.8%, 19.8%, and 18.8% in 2018, 2019, and 2020, respectively. NT increased Rs by 4.9%, −1.6%, and −0.7% in 2018, 2019, and 2020, respectively. The lowest annual Rs occurred for SM+NT in 2020. Relative to NS and CT, SM and NT promoted Rh but inhibited Ra for wheat during 2019 and 2020. For maize, SM increased Rh and suppressed Ra while NT had no significant effect on Rh and suppressed Ra. Therefore, SM increased Rs by promoting Rh, while NT decreased Rs by inhibiting Ra. In all treatments, Rh averaged 1.82–3.36 times higher than Ra. Soil temperature had a greater influence on temporal variations in soil respiration than soil moisture. Averaged from 2018 to 2020, the annual economic benefit was increased by 11.7% and 15.3% in SM and NT than NS and CT, respectively. Our results suggest that straw mulch and no-tillage should be promoted as an environment-friendly agroecosystem management practice for wheat and maize, as these practices can achieve a balance between improving economic benefit and reducing soil CO2 emissions, contributing to the mitigation of climate change and the early achievement of carbon neutrality goals.

Spatial variation in soil respiration is determined by forest canopy structure through soil water content in a mature beech forest

For accurate estimation of soil respiration (SR) in forest ecosystems, temporal and spatial variation in SR and the factors that control these variations must be considered. Although some of the factors underlying temporal variation in SR have been elucidated in recent decades, a large part of spatial variation in SR remains unexplained especially in forest ecosystems with complex structures. Our objectives were to demonstrate spatial variation in daily summed SR (SRdaily) and to examine if spatial variation in SRdaily can be explained by canopy openness which is one of the indexes of forest structure. We conducted simultaneous measurements of SRdaily, soil temperature (ST), and soil water content (SWC) at 121 points. We also measured canopy openness and some forest stand structure indexes in different seasons in 2012 and 2013. The coefficient of variation (CV) of SRdaily ranged from 25 % to 28 %, which was similar to that of SWC (21 % to 28 %). We also found that the spatial variation in SR in other forest ecosystems ranged widely (CV = 14 % to 62 %), and that in our site fell within the range. There was no significant relationship between ST and spatial variation in SRdaily; however, a significant relationship was observed between SWC and spatial variation in SRdaily (P < 0.01) excepted for the measurement conducted in June 2013. Multiple linear regression analysis indicated that canopy openness showed significant positive correlations with SWC during the growing season. And there was no significant relationships between SWC and forest stand structure indexes.In this study, we found that canopy structure influenced SWC, which in turn determined the spatial variation in SR in this mature beech forest. The possible connections could give us new insight for adequate forest carbon management.

Effects of Amendments on Physicochemical Properties and Respiration Rate of Soil from the Arid Region of Northwest China

In arid regions, decreased soil fertility has adversely affected agricultural sustainability. The effects of different amendments in alleviating these issues and increasing soil fertility remain unclear. Herein, a two-year field experiment was conducted to evaluate the properties of grey desert soil and soil respiration (SR) dynamics under six different treatment groups: biochar (BC), leonardite (LD), anionic polyacrylamide (PAM−), cationic polyacrylamide (PAM+) powder, anionic polyacrylamide solution in water (PAM−W), and control (CK). We observed that the BC and LD amendments significantly altered soil pH, organic matter, available nitrogen, available phosphorus, cation exchange capacity, and SR. PAM amendment increased the SR as compared to the control, except in autumn, but PAM did not affect the soil properties. SR under different amendments showed strong seasonal patterns, the highest and lowest SR rates were observed in June and January, respectively. Amendments and seasonal dynamics significantly affected SR, but no interaction was observed between these factors. Temporal variation of SR was substantially influenced by soil temperature at 15 cm of soil depth. Temperature sensitivity of SR (Q10) increased with soil depth and decreased with amendment addition. SR was significantly affected by soil temperature, moisture, air temperature, and their interactions. The outcomes of this study suggested that the BC and LD amendments improved soil fertility and negated the net carbon accumulation by increasing the SR and Q10 in arid agriculture soil.

Soil Respiration Characteristics and Influencing Factors for Apple Orchards in Different Regions on the Loess Plateau of Shaanxi Province

To explore the characteristics of the spatial and temporal variation in soil respiration (SR) in orchard ecosystems in different regions of the Loess Plateau of Shaanxi Province and to distinguish the controlling factors, representative orchards were studied from April to October 2019. We conducted SR measurements in five locations, including Mizhi dangta (MZ), Ansai Liuzhuang (AS), Luochuan houzitou (LC), Fuping meijiaping (FP), and Yangling Wuquan (YL). The results indicated that the SR of each orchard showed clear seasonal variation. The SR increased with the distance from the trunk at the tree scale, while gradually increasing from north to south on the regional scale (p &lt; 0.05). The soil temperature and soil moisture were the main factors controlling the seasonal changes in SR in the orchards. On the tree scale, the fine root biomass was the main factor causing the tree-scale spatial variability. At the regional scale, SR was mainly influenced by the differences in the soil temperature, soil moisture, soil organic carbon, soil bulk density and pH. In agricultural management practices, the cumulative soil respiration was higher with irrigated treatment than with non-irrigated (NI) treatment (p &lt; 0.05). In addition, traditional surface drip irrigation (SDI) and root injection irrigation (RII) showed great differences in soil respiration in the early and late stages of irrigation (p &lt; 0.05), and the soil moisture was the main controlling factor. Compared with no tillage (NI), green cover (GC), deep tillage (DT), and shallow tillage (ST) increased the SR by 57%, 36% and 14%, respectively (p &lt; 0.05). Due to the great temporal and spatial variation in the SR in our study area, we determined that the soil respiration in the orchards was affected not only by environmental factors but also by agricultural measures. Therefore, greater attention should be paid to human factors when exploring SR to ensure that orchard management can promote the economic benefits of the orchards without greatly impacting the environment.

Responses of soil respiration to N fertilization and grazing in a Keerqin sandy grassland in northeast China

Nitrogen (N) deposition and grazing (G) are two disturbances of grassland ecosystems and these can greatly affect soil respiration. To date, few studies have investigated this topic in sandy grasslands. Here, we conducted a manipulative experiment in a sandy grassland in Inner Mongolia, China in the year 2013 and 2014, to investigate the effects of N addition and grazing on soil respiration. The results showed that N addition significantly accelerated soil respiration in both 2013 and 2014. The respiration enhancement under N addition varied during the growing season, being larger in early May 2014 (0.40 μmol·m−2·s−1) and early July 2014 (1.29 μmol·m−2·s−1) than in October 2014 (0.03 μmol·m−2·s−1). Grazing plots yielded a lower cumulative soil respiration rate than the control plots (−5,68% in 2013 and −1.07% in 2014), although the difference was not significant. In this study, soil temperature rather than soil moisture was the main factor affecting the temporal variation in soil respiration during the growing season. The inter-plot analysis showed that the soil ammonium nitrogen (NH4 +–N) content, C:N ratio, and root biomass were significantly correlated with soil respiration, indicating that soil respiration under N-addition or grazing treatment could be affected by changing soil microhabitat conditions, thus affecting soil respiration.

Controls of Temporal Variations on Soil Respiration in a Tropical Lowland Rainforest in Hainan Island, China

Soil respiration represents the largest carbon (C) flux from terrestrial ecosystems to the atmosphere. We created a study site in tropical lowland rainforest and used static chamber method to measure the temporal variations of soil respiration and their relationship with environmental factors at monthly time scale. The temporal variations of soil respiration showed a seasonal pattern related to soil temperature (p < .01) and soil moisture (p < .05). We tested different regression models to explore the relationship between soil respiration and environmental factors. Soil respiration had a better fit with soil temperature than with soil moisture in single-factor models. At different temperatures, the Q10 values from different models changed in rather different ways. We found that the mixed quadratic model composite of soil temperature and moisture had the best-fitting effect (R2 = .74) on soil respiration and could better explain the seasonal variation. In a certain soil moisture range close to 15%, soil respiration increased with soil temperature. However, soil respiration became restricted when the moisture was greatly higher or lower than this value. Furthermore, at low soil temperatures (lower than 16°C), higher soil moisture could decrease soil respiration rapidly. Thus, soil respiration in a tropical lowland rainforest is co-controlled by soil temperature and moisture. This study expands our observations of soil respiration in tropical forests and how it responds to environmental factors, which is important for reducing errors in evaluation and scaling up of soil carbon flux in climate change studies.

Temporal variation in soil respiration and its sensitivity to temperature along a hydrological gradient in an alpine wetland of the Tibetan Plateau

Wetlands are predicted to experience lowered water tables due to permafrost degradation in the Tibetan Plateau. These changes may affect carbon cycle processes such as soil respiration (Rs). However, the magnitude, patterns and controls of Rs remain poorly understood in alpine wetlands with their distinct hydrological regimes. Here, we conducted a field study on Rs from 2012 to 2014 in three alpine ecosystems on the Tibetan Plateau—fen, wet meadow and meadow—with soil water decreases along hydrological gradients. From 2012 to 2014, the annual Rs was 128.9–193.3 g C m−2yr−1, 281.5–342.9 g C m−2yr−1, and 663.4–709.1 g C m−2yr−1 for the fen, wet meadow, and meadow, respectively. An abrupt increase in CO2 emissions was caused by the spring thawing of the frozen soil in the fen and wet meadow, contributing 20.4–37.6% and 13.2–17.4%, respectively, to the annual Rs. The diurnal variation in the Rs was site specific among the three ecosystems, with one peak at 1300 h in the fen and meadow and two peaks at 1300 h and 1900 h in the wet meadow. The temperature-independent components of the diurnal variation in Rs were generally explained by photosynthetically active radiation in the fen and wet meadow, but not in the meadow. The temperature sensitivity of the Rs (unconfounded Q10) varied significantly among the three ecosystems, with the highest values occurring in the wet meadow, implying that permafrost thaw-induced wetland drying from the fen to the wet meadow could enhance the response of CO2 emissions to climate warming but that further drying from the wet meadow to the meadow probably weakens the effect of warming on the Rs. Our study emphasized the important role of the hydrological regime in regulating the temporal variation in Rs and its response to climate warming.

Soil respiration of four forests along elevation gradient in northern subtropical China.

Background and aimsSoil respiration is the second‐largest terrestrial carbon (C) flux, and soil temperature and soil moisture are the main drivers of temporal variation in soil respiration and its components. Here, we quantified the contribution of soil temperature, soil moisture, and their intersection on the variation in soil respiration and its components of the evergreen broad‐leaved forests (EBF), mixed evergreen and deciduous broad‐leaved forests (MF), deciduous broad‐leaved forests (DBF), and subalpine coniferous forests (CF) along an elevation gradient.MethodsWe measured soil respiration of four types of forests along the elevation gradient in Shennongjia, Hubei China based on the trenching experiments. We parameterized the relationships between soil respiration and soil temperature, soil moisture, and quantified the intersection of temperature and moisture on soil respiration and its components.ResultsTotal soil respiration (R S), heterotrophic respiration (R H), and autotrophic respiration (R A) were significantly correlated with soil temperature in all four forests. The Q 10 value of soil respiration significantly differed among the four types of forest, and the Q 10 was 3.06 for EBF, 3.75 for MF, 4.05 for DBF, and 4.49 for CF, respectively. The soil temperature explained 62%–81% of the variation in respiration, while soil temperature and soil moisture together explained 91%–97% of soil respiration variation for the four types of forests. The variation from the intersection of soil temperature and moisture were 12.1%–25.0% in RS, 1.0%–7.0% in R H, and 17.1%–19.6% in R A, respectively.ConclusionsOur results show that the temperature sensitivity (Q 10) of soil respiration increased with elevation. The intersection between soil temperature and soil moisture had strong effects on soil respiration, especially in R H. We demonstrated that the intersection effects between soil temperature and soil moisture on soil respiration were essential to understand the response of soil respiration and its components to climate change.

Topographic controls on the variability of soil respiration in a humid subtropical forest

Knowledge of the spatial and temporal variabilities of soil respiration is important in estimating the soil carbon budget and in understanding how soils may respond to global changes. In areas with complex terrain, the topography can modify the hydrological conditions and other biophysical variables, which complicates the spatial and temporal heterogeneity of soil respiration. Herein, we investigated soil respiration along topographic transects with ridge, middle slope, lower slope and valley positions in a humid subtropical mountain forest in China to assess the driving factors of the variations in soil respiration. Our results showed that there were substantial temporal and spatial variations in soil respiration. The temporal variation of soil respiration could be well explained by the dynamics of soil temperature and moisture. Soil respiration rates also showed clear topographic pattern and decreased significantly from the ridge to valley soils, with the mean rates equaled 3.43 ± 0.13, 2.64 ± 0.30, 2.13 ± 0.26 and 1.88 ± 0.24 μmol m−2 s−1 at the ridge, middle slope, lower slope, and valley, respectively. Correlation analyses revealed that the spatial variation of soil respiration could be explained by multiple variables (e.g., soil temperature, basal area of the trees, thickness of the forest floor, root biomass and stock of soil dissolved carbon, soil C/N and soil bulk density). Results from partial least squares path modeling suggested that the topography modified the fine root distribution and the lateral losses of light and dissolved organic materials that created areas of high carbon sources for soil respiration at the ridge. The topographically regulated processes further resulted in a high soil C/N at the ridge that favored SOC decomposition. The higher respiration rate for the ridge soil and its higher sensitivity to soil temperature and moisture changes suggested that the ridge position was a potential hot spot for future environmental changes. Future studies and management practices regarding the soil carbon efflux in forest ecosystems with topographical variations should take into account the topographic effects.

Effects of Understory Shrub Biomass on Variation of Soil Respiration in a Temperate-Subtropical Transitional Oak Forest

Quantification of the temporal and spatial variations of soil respiration is an essential step in modeling soil carbon (C) emission associated with the spatial distribution of plants. To examine the temporal and spatial variations of soil respiration and its driving factors, we investigated soil respiration, microclimate, and understory vegetation in a 50 m × 70 m plot in a climatic transitional zone oak forest in Central China. The temporal variation of soil respiration based on the 21 measurements ranged from 15.01% to 30.21% across the 48 subplots. Structural equation modeling showed that soil temperature and understory shrub biomass had greater positive effects on the seasonal variability of soil respiration. The spatial variation of soil respiration of the 48 subplots varied from 3.61% to 6.99% during the 21 measurement campaigns. Understory shrub biomass and belowground fine root biomass positively regulated the spatial variation of soil respiration. Soil respiration displayed strong spatial autocorrelation, with an average spatial correlation length of 20.1 m. The findings highlight the importance of understory shrub and belowground biomass in regulating the temporal and spatial heterogeneity of soil respiration in forest ecosystems, and the need to carefully address it to robustly estimate the contribution of soil C emission in terrestrial C cycling.

Assessment of the effect of plastic mulching on soil respiration in the arid agricultural region of China under future climate scenarios

The application of plastic film to agricultural fields has been widely used in the arid and semi-arid regions of China to improve crop productivity and soil organic carbon storage. However, the impact of this practice on soil respiration under future climate scenarios remains poorly understood. Process-based model is a useful tool for simulating the effect of this practice on soil biochemical processes and for predicting future changes in soil respiration under different climate scenarios. In this study, the denitrification-decomposition (DNDC) model was evaluated against measured soil respiration. The DNDC model was used to simulate the temporal variation of soil respiration, and the application of plastic film increased the cumulative carbon dioxide (CO2) emissions compared with that of the fields without plastic film. Sensitivity tests indicated that plastic mulching decreased the sensitivity of DNDC-simulated soil respiration and plant biomass to changes in the temperature, precipitation and CO2 concentration. Across different climate scenarios, the DNDC model predicted that both soil respiration and plant biomass in the mulched treatment slightly changed from −0.2% to 2.1% and from −0.7% to 1.2%, respectively; and in the non-mulched treatment, soil respiration and biomass changed from −4.7% to 10.9% and from −8.7% to 7.8%, respectively. In the arid agricultural region of China, if the pollution of residual mulch film in the fields can be effectively controlled, the application of plastic film is an efficient method for increasing crop productivity and would likely mitigate changes in soil respiration under future climate scenarios.

Plant functional groups regulate soil respiration responses to nitrogen addition and mowing over a decade

Abstract Nitrogen (N) deposition and land‐use practice (e.g. mowing) could have profound effects on soil respiration. However, the changes in other ecosystem components, such as plant functional groups (PFGs), may control soil carbon (C) efflux response to long term global change. A 10‐year (2005–2014) field experiment was conducted with both N addition (10 g N m−2 year−1) and mowing (once a year) in a northern Chinese temperate grassland. We collected continuous data on soil respiration over 10 years accompanied with data on abiotic and biotic factors, and attempted to determine (i) the temporal variation in soil respiration and its responses to N addition and mowing, (ii) the regulation of soil respiration by PFGs and the underlying long‐term mechanisms of control. Soil respiration varied significantly among years. This was mainly caused by changes in precipitation pattern (e.g. frequency and distribution) during the growing‐season rather than total rainfall. N addition significantly suppressed soil respiration by 10.4% whereas mowing stimulated it by 8.4% over the 10 years. The interaction of N addition with mowing had little effect on soil respiration. However, the significant effects of both N addition and mowing appeared only in the third year and thereafter, indicating the differences between long‐ and short‐term responses. These long‐term effects of N addition and mowing were mainly caused by changes in the PFGs of covers (e.g. grasses and forbs) and in soil pH rather than in soil microclimate. Forb‐dominant patches had greater soil respiration than grass patches owing to their higher litter quality and photosynthetic capacity. Our results highlight that shifts in above‐ground plant community could play an important role in regulating soil respiration responses to N addition and mowing in the long‐term. This is potentially important for improving our understanding of the link between above‐ and below‐ground ecological processes. A plain language summary is available for this article.

Spatial and temporal variations in soil respiration among different land cover types under wet and dry years in an urban park

Soil respiration (Rs) determines land surface carbon balance; however, there have been few studies that measured Rs in heterogeneous urban landscapes. Here, we investigated the spatial and temporal variations in Rs in six land cover types (mixed forest, deciduous broadleaf forest, evergreen needleleaf forest, lawn, wetland, and bare land) in Seoul Forest Park, Republic of Korea, between March 2013 and September 2014, which included a wet (2013) and an extremely dry (2014) summer. Spatially, there was a three-fold difference (0.48–1.45kgCm−2) in annual Rs among the six land cover types. The soil organic carbon stock at a depth of 0.1m explained 72% of the spatial variation in the annual Rs across the land cover types. During the entire study period, the soil temperature explained 82–97% of the temporal variation in Rs among different land cover types. Comparing the two summers, the 2014 drought only resulted in a decrease in Rs in the lawn plots (25%), which was driven by a reduction in the leaf area index and the fine root density. The temperature sensitivity of Rs in 2014 (dry summer) compared to 2013 (wet summer) was significantly lower in mixed forest, deciduous broadleaf forest, and lawn, and did not change in evergreen needleleaf forest, wetland, or bare land. The differences in Rs in these drought responses highlight the importance of the careful selection of land cover type during park planning to better manage carbon cycles.

Response of soil respiration to a severe drought in Chinese Eucalyptus plantations

Extreme droughts can adversely affect the dynamics of soil respiration in tree plantations. We used a severe drought in southwestern China as a case study to estimate the effects of drought on temporal variations in soil respiration in a plantation of Eucalyptus globulus. We documented a clear seasonal pattern in soil respiration with the highest values (100.9 mg C–CO2 m−2 h−1) recorded in June and the lowest values (28.7 mg C–CO2 m−2 h−1) in January. The variation in soil respiration was closely associated with the dynamics of soil water driven by the drought. Soil respiration was nearly twice as great in the wet seasons as in the dry seasons. Soil water content accounted for 83–91% of variation in soil respiration, while a combined soil water and soil temperature model explained 90–99% of the variation in soil respiration. Soil water had pronounced effects on soil respiration at the moisture threshold of 6–10%. Soil water was strongly related to changes in soil parameters (i.e., bulk density, pH, soil organic carbon, and available nitrogen). These strongly influenced seasonal variation in soil respiration. We found that soil respiration was strongly suppressed by severe drought. Drought resulted in a shortage of soil water which reduced formation of soil organic carbon, impacted soil acid–base properties and soil texture, and affected soil nutrient availability.

Temporal variations of soil respiration at multiple timescales in a spruce-fir valley forest, northeastern China

There is a paucity of data regarding the multiple timescale variations of heterotrophic respiration (R H) and autotrophic respiration (R A) as well as the primary controlling factors. The objective of this study is to find the temporal variations of total soil respiration (R S) and its components, revealing the driving factors at different timescales. A trenching method was used to distinguish R S, R H, and R A in a spruce-fir valley forest in northeastern China. We used the closed dynamic chamber method to measure the soil respiration rate. Analyses of R S, R H, and R A in relation to biotic and abiotic factors were conducted to realize the temporal variations at different timescales. Only R S and R H showed a distinct diurnal variation and soil temperature (T S) can explain 68 and 59 % of the daily variation, respectively. R S, R H, and R A showed a pronounced, single peak curve seasonally, and T S can explain 11–95 % of the seasonal variation. Soil moisture (W S) maintained at a relatively high level and was not related to R S, R H, or R A on a seasonal scale, and there was no significant relationship between the seasonal R S, R A, and root biomass. However, for 5 years, only the mean R A of the growing season was significantly related to the mean W S, which can explain 39 % of the inter-annual variation of R A. The annual variations of litterfall and the relative growth rate of stems were not related to R S, R H, or R A. The contribution of R H to R S was larger, and the temperature sensitivity was 2.01–3.71 for R S, 1.90–3.08 for R H, and 2.20–5.65 for R A. R S, R H, and R A show different temporal variations at multiple timescales. When W S is not restricted, T S is the primary driving factor of daily and seasonal variation of R S and R H. In this site, R H accounts for a large proportion of R S and plays a crucial role in determining the magnitude and temporal variation of R S.

Microbial properties explain temporal variation in soil respiration in a grassland subjected to nitrogen addition.

The role of soil microbial variables in shaping the temporal variability of soil respiration has been well acknowledged but is poorly understood, particularly under elevated nitrogen (N) deposition conditions. We measured soil respiration along with soil microbial properties during the early, middle, and late growing seasons in temperate grassland plots that had been treated with N additions of 0, 2, 4, 8, 16, or 32 g N m−2 yr−1 for 10 years. Representing the averages over three observation periods, total (Rs) and heterotrophic (Rh) respiration were highest with 4 g N m−2 yr−1, but autotrophic respiration (Ra) was highest with 8 to 16 g N m−2 yr−1. Also, the responses of Rh and Ra were unsynchronized considering the periods separately. N addition had no significant impact on the temperature sensitivity (Q10) for Rs but inhibited the Q10 for Rh. Significant interactions between observation period and N level occurred in soil respiration components, and the temporal variations in soil respiration components were mostly associated with changes in microbial biomass carbon (MBC) and phospholipid fatty acids (PLFAs). Further observation on soil organic carbon and root biomass is needed to reveal the long-term effect of N deposition on soil C sequestration.

Soil respiration and carbon balance in a Moso bamboo (Phyllostachys heterocycla (Carr.) Mitford cv. Pubescens) forest in subtropical China

Abstract: Understanding spatial and temporal variation in soil respiration (RS) in different forest ecosystems is crucial to estimate the global carbon balance. Bamboo forest is a special forest type in southern China covering an area of 5.38 million ha, 70% of which are Moso bamboo (Phyllostachys heterocycla (Carr.) Mitford cv. Pubescens) forests. Bamboo forests contribute more than 10% to the whole carbon stock of forest ecosystems in China, and therefore play a critical role in the regional and national carbon balance. However, little information on the seasonal dynamic of RS and the carbon balance of Moso bamboo forests is available. In this study, litter removal and trenching methods were applied to partition RS into root respiration (RR), litter respiration (RL) and soil organic matter derived respiration (RM), and to study their seasonal dynamics and carbon balance in a pure Moso bamboo forest. Monthly RS, its source components and combined monthly environmental factors were measured. RS and its source components showed a significant seasonal variability with higher values from June to August and lower values from December to February driven by soil temperature and moisture (P < 0.001). Annual average RS, RR, RL and RM were 2.37, 0.69, 0.58 and 1.10 μmol m-2 s-1 with Q10 values of 1.25, 1.15, 1.19 and 1.26, respectively. Annual RS was 8.97 t C ha-1, and RR, RL and RM contributed 29%, 22% and 49%, respectively. Annual NEP was 4.72 t C ha-1 y-1, indicating that the Moso bamboo forest studied is a significant carbon sink.

Comparison of the Variation of Soil Respiration in Carbon Cycle in Temperate and Subtropical Forests and the Relationship with Climatic Variables

ABSTRACT Forest soil respiration (SR) has become a vital issue in global change ecology because of its critical role in global warming processes. However, SR remains the least understood component of the terrestrial carbon cycle because of its high spatial-temporal variability, inaccessibility of the soil substrate, and the high cost of measurement equipment. This study investigated the spatial and temporal variations of SR in six temperate and subtropical forest sites in eastern China. Seasonal variations of SR, the relationship between SR and soil temperature (ST) and volumetric water content (SW) were analyzed. Mean monthly SR varied seasonally and peaked in summer. SR varied temporally with ST (R2 = 0.43∼0.79) in different sites and varied spatially with latitude (R2 = 0.68). The responses of SR to the changes of SW varied across different sites and forest types. Their relationships were simulated by piecewise functions in the north three sites. The modules of ST and SW showed that ST is the dominant ...