Temperature Sensitivity Of Rs Research Articles

Divergent seasonal patterns and drivers of soil respiration in alpine forests of northwestern China

Uncertainty about winter carbon (C) fluxes and their drivers hinders the accurate estimation of C budgets in high-latitude and high-altitude ecosystems. We conducted 3-year-long field observations of soil respiration (Rs) in an alpine forest in northwestern China. The results showed that the mean winter Rs ranged from 193.79 to 233.03 g C m−2 year−1 and significantly increased with elevation, while the mean growing season Rs ranged from 467.29 to 711.25 g C m−2 year−1 and significantly decreased with elevation. The ratio of winter to annual soil CO2 emissions ranged from 21.96 to 34.24 %. The Q10 value (temperature sensitivity of Rs) also varied seasonally, with significantly higher values in winter (3.00–3.85) than in the growing season (2.08–2.22). During the growing season, the Rs was directly regulated by soil temperature (ST), fine root biomass, and microbial activity and indirectly regulated by nitrate nitrogen via an increase in fine root biomass and microbial activity. In addition to the direct effects of soil moisture (SM), ST, and the ratio of fungi to bacteria (F/B) on winter Rs, we revealed another effect: the indirect effect on Rs of the interaction of ST with SM (decreasing ST and increasing SM) with elevation by reducing the soil aggregate stability, probably improving the organic substrate availability, and decreasing the F/B. The ST was the most important factor affecting the growing season Rs, and SM had the greatest effect on the winter Rs. Overall, our findings indicated that the patterns and underlying mechanisms of Rs dynamics in alpine forests in winter are different from those in the growing season and that research on winter Rs dynamics in alpine forests under future climate conditions is needed due to the greater temperature response of Rs in winter than in the growing season.

The long-term effects of thinning on soil respiration vary with season in subalpine spruce plantations

Thinning is a principal silvicultural practice in temperate plantations with potential impacts on soil respiration (Rs). However, most of the existing measurements of Rs dynamics after thinning have been performed during the growing season, while those in the nongrowing season have been seldom determined, even though recent evidence demonstrates that the nongrowing season Rs occupied a considerable proportion of the annual carbon (C) budgets in temperate forests. Here, we investigated the long-term (17 years) impacts of thinning on Rs in middle-aged subalpine spruce plantations in northwestern China. We found that thinning significantly (p < 0.001) increased Rs from 3.00 to 4.18 μmol m−2 s−1 in the growing season while significantly (p < 0.001) decreasing Rs from 1.05 to 0.90 μmol m−2 s−1 in the nongrowing season; additionally, thinning had no significant (p = 0.0989) effect on the Q10 value (temperature sensitivity of Rs) in the growing season, with values ranging from 2.10 to 2.44, while it significantly (p < 0.01) increased the Q10 value from 2.91 to 3.48 in the nongrowing season. In the growing season, increased nitrate nitrogen due to elevated soil moisture (SM) played a fundamental role in stimulating Rs by improving microbial biomass (MB) and fine root biomass, and increased soil temperature (ST) also contributed to the increases in MB and Rs. However, these variables and pathways were not applicable in the nongrowing season, when decreased dissolved organic C induced by decreased ST explained most of the decline in MB and Rs. Our results revealed that the long-term effects of thinning on the nongrowing season Rs were completely different from those in the growing seasons in subalpine spruce plantations. Furthermore, the greatly increased Q10 value in the nongrowing season indicated that a substantial increase in Rs can be expected in subalpine forests after thinning due to nongrowing season warming at high altitudes.

Moss biocrusts buffer soil CO2 effluxes in a subtropical karst ecosystem

Biocrusts, specialized communities comprised of mosses, lichens, cyanobacteria, fungi, and bacteria occurring on the ground surface, are famous as ecological engineers on Earth, but less is understood in humid karst areas, where they are often widespread and provide important ecosystem services. To better understand how biocrusts affect soil carbon cycles, we performed an in situ study monitoring net soil exchange (NSE) of CO2, soil respiration (Rs), soil temperature and moisture, and determined soil nutrient contents and carbon-related enzyme activities over three different microcosms (soils covered by moss biocrusts, soils deprived of biocrust-forming mosses, and bare soils) in a subtropical karst ecosystem in southwest China. The results showed that, in comparison with bare soils, moss biocrusts increased Rs by 40% but decreased NSE by 49% and the temperature sensitivity of Rs by 35%. However, disturbance to moss biocrusts decreased Rs by 26% but increased NSE by 104% and the temperature sensitivity of Rs by 93%. Although moss biocrusts increased the content of soil organic carbon and total nitrogen and the activity of β-glucosidase, this effect was reversed by disturbance to moss biocrusts. While Rs was significantly correlated with soil temperature and moisture, the effect of moss biocrusts on Rs was partly explained by soil organic carbon, total nitrogen, and β-glucosidase. Overall, this study adds to the scarce number of experiments characterizing biocrust ecology in humid karst ecosystems and calls for management efforts to protect and restore biocrusts to buffer soil CO2 emissions under global change scenarios.

Phenological season-dependent temperature effects on soil respiration in a subtropical Pinus massoniana forest

Soil respiration (Rs) is a major flux of the carbon cycle in forest ecosystems, and time-scale-dependent variations in Rs are critical for evaluating carbon sequestration capacity, which is not fully understood. In this study, we investigated diurnal, phenological seasonal and annual variations in Rs over three years (2015–2017) in a Pinus massoniana forest in subtropical China based on automated Rs chamber measurements at hourly intervals. Soil temperature and moisture at the 5 cm soil depth were simultaneously measured, and precipitation data were collected to examine their influences on Rs. Our results showed that the daytime mean and total Rs were significantly higher than their respective nighttime counterparts over the course of a year. Daily Rs ranged from 0.42 to 4.63 µmol CO2m−2s−1, with the maximum value in August and the minimum value in February. The temperature sensitivity of Rs (Q10) did not significantly differ between daytime and nighttime, but it was significantly higher at the end-season (autumn) than during the nongrowing season. The effects of soil temperature but not soil moisture on Rs varied with phenological season, showing significant soil temperature effects in the active phenological seasons (spring and autumn) but not in the steady-state phenological seasons (growing season and nongrowing season). This seasonal-dependent temperature effect on Rs may be a result of the effect of rapidly changing temperature in spring and autumn on leaf phenology, plant growth and physiological activity, soil microbial and enzyme activity, and litter decomposition rate. Our results suggest that long-term data covering monthly, seasonal, and annual variations in Rs and its biotic and abiotic environments are needed for more precisely calculating and predicting the carbon balance of forest ecosystems on various time scales.

Nitrogen Addition Decreases Soil Respiration without Changing the Temperature Sensitivity in a Semiarid Grassland

The mechanisms underlying the response of soil respiration (Rs) to nitrogen (N) addition remain to be explored in semiarid ecosystems. This study was conducted to determine the effect of N addition on soil microbial composition, Rs and the temperature sensitivity of Rs (Q10). The N addition experiment was carried out in a semiarid grassland in China, with N fertilizer application rates of 0, 2, 4, 8, 16, or 32 g N m–2 yr–1. Microbial phospholipid fatty acids (PLFAs), Rs and Q10 were measured, and their relationships with soil properties were determined for three growing seasons. The results showed that N addition significantly increased the content of soil dissolved organic carbon (DOC) and inorganic nitrogen (IN), and decreased soil pH. With respect to soil microbes, N addition reduced soil PLFAs, reduced the fungi to bacteria ratio (F:B) and increased the gram-positive bacteria to gram-negative bacteria ratio (G+:G–). Rs under the N2, N4, N8, N16 and N32 treatments decreased by 2.58%, 14.86%, 22.62%, 23.97% and 19.87%, respectively, compared to the N0 (control) treatment. The results of structural equation models showed that N addition reduced Rs by lowering soil PLFAs and altering the microbial composition. However, N addition had no significant effect on either Q10, soil total organic carbon (TOC) or total nitrogen (TN), indicating that N addition alleviated soil carbon loss and was unlikely to change the potential for a bigger loss under global warming.

Localized basal area affects soil respiration temperature sensitivity in a coastal deciduous forest

Abstract. Soil respiration (Rs), the flow of CO2 from the soil surface to the atmosphere, is one of the largest carbon fluxes in the terrestrial biosphere. The spatial variability of Rs is both large and poorly understood, limiting our ability to robustly scale it in space. One factor in Rs spatial variability is the autotrophic contribution from plant roots, but it is uncertain how the presence of plants affects the magnitude and temperature sensitivity of Rs. This study used 1 year of Rs measurements to examine the effect of localized basal area on Rs in the growing and dormant seasons, as well as during moisture-limited times, in a temperate, coastal, deciduous forest in eastern Maryland, USA. In a linear mixed-effects model, tree basal area within a 5 m radius (BA5) exerted a significant positive effect on the temperature sensitivity of soil respiration. Soil moisture was the dominant control on Rs during the dry portions of the year, while soil moisture, temperature, and BA5 all exerted significant effects on Rs in wetter periods. Our results suggest that autotrophic respiration is more sensitive to temperature than heterotrophic respiration at these sites, although we did not measure these source fluxes directly, and that soil respiration is highly moisture sensitive, even in a record-rainfall year. The Rs flux magnitudes (0.46–15.0 µmol m−2 s−1) and variability (coefficient of variability 10 %–23 % across plots) observed in this study were comparable to values observed in similar forests. Six Rs observations would be required in order to estimate the mean across all study sites to within 50 %, and 518 would be required in order to estimate it to within 5 %, with 95 % confidence. A better understanding of the spatial interactions between plants and microbes, as well as the strength and speed of above- and belowground coupling, is necessary to link these processes with large-scale soil-to-atmosphere C fluxes.

Soil respiration in relation to cropping sequence, nutrient management and environmental variables

ABSTRACT Soil respiration (Rs) measurements in relation to agricultural management and environmental variables are necessary to improve our understanding of net ecosystem carbon balance (NECB) and to predict soil’s feedback to climate change. The objectives of this study were to analyze the seasonal dynamics of Rs in maize-wheat and cotton-wheat crop rotations and to quantify the effects of temperature, moisture and management on Rs, and NECB. Rs was measured in situ by open chambers over 2 years. In-season Rs varied with crop growth and peak rates coincided with the maximum growth stage of a crop. Rs rate was higher in maize than in cotton. Mean Rs in winter wheat was about one-third of that in preceding maize or cotton. Root respiration comprised 13–29% of Rs in different crops. The NECB suggested that soil could be losing organic C at 381–643 g C m−2 y−1. Application of organic amendments along with inorganic fertilizers improved NECB underpinning their role in converting a cropping sequence from potential source to sink of carbon. Temperature sensitivity of Rs was strongly modulated by soil moisture suggesting that increased Rs due to warming coupled with high moisture could provide a positive feedback to climate change.

Microbe-mediated attenuation of soil respiration in response to soil warming in a temperate oak forest

Soil respiration (Rs) in response to climate warming received a wide concern due to its important role in terrestrial ecosystem carbon (C) cycling, but the warming-induced effects of soil microbes on soil respiration are still less understood, especially over time. Our study aims to understand the long-term warming induced effects of soil microbes on Rs. A field soil warming experiment using a completely randomized design was conducted in a naturally regenerated oak forest (Quercus aliena) in central China. Soil warming was executed by infrared heater throughout the period from 2011 to 2015. Our results showed that soil temperature was a main factor in regulating Rs in a temperate oak forest throughout the experiment, while soil water content determined Rs only when a naturally dry year occurred. The positive effect of soil warming on Rs that was observed (i.e., 37.5 to 42.0% in the first two years) gradually diminished in the following three years (i.e., 0.9 to 15.4%). Significant positive warming effects on the temperature sensitivity of Rs (Q10) only occurred in the second year. Continuous soil warming caused the decline in nitrogen (N) availability, with a significant increase in microbial biomass-specific enzyme activities for N-acquisition. The attenuation of microbial biomass increment and the decreased ratio of enzymatic C:N acquisition contributed to the diminished warming effect on Rs over time. Our study suggests that microbe-mediated attenuation of Rs, accompanied by the concomitant decline in soil N availability in response to warming, should be taken into consideration in global C cycle modeling.

Soil respiration and its Q10 response to various grazing systems of a typical steppe in Inner Mongolia, China.

BackgroundAs one of the important management practices of grassland ecosystems, grazing has fundamental effects on soil properties, vegetation, and soil microbes. Grazing can thus alter soil respiration (Rs) and the soil carbon cycle, yet its impacts and mechanisms remain unclear.MethodsTo explore the response of soil carbon flux and temperature sensitivity to different grazing systems, Rs, soil temperature (ST), and soil moisture (SM) were observed from December 2014 to September 2015 in a typical steppe of Inner Mongolia under three grazing systems: year-long grazing, rest-rotation grazing, and grazing exclusion. In addition, plant aboveground and root biomass, soil microbial biomass and community composition, and soil nutrients were measured during the pilot period.ResultsSoil respiration was significantly different among the three grazing systems. The average Rs was highest under rest-rotation grazing (1.26 μmol·m−2·s−1), followed by grazing exclusion (0.98 μmol·m−2·s−1) and year-long grazing (0.94 μmol·m−2·s−1). Rs was closely associated with ST, SM, potential substrate and root, and soil microbe activity. The effects of grazing among two grazing systems had generality, but were different due to grazing intensity. The root biomass was stimulated by grazing, and the rest-rotation grazing system resulted in the highest Rs. Grazing led to decreases in aboveground and microbial biomass as well as the loss of soil total nitrogen and total phosphorus from the steppe ecosystem, which explained the negative effect of grazing on Rs in the year-long grazing system compared to the grazing exclusion system. The temperature sensitivity of Rs (Q10) was higher in the rest-rotation and year-long grazing systems, likely due to the higher temperature sensitivity of rhizosphere respiration and higher “rhizosphere priming effect” in the promoted root biomass. The structural equation model analysis showed that while grazing inhibited Rs by reducing soil aeration porosity, ground biomass and SM, it increased Q10 but had a lower effect than other factors. A better understanding of the effects of grazing on soil respiration has important practical implications.

Forest Floor and Mineral Soil Respiration Rates in a Northern Minnesota Red Pine Chronosequence

We measured total soil CO2 efflux (RS) and efflux from the forest floor layers (RFF) in red pine (Pinus resinosa Ait.) stands of different ages to examine relationships between stand age and belowground C cycling. Soil temperature and RS were often lower in a 31-year-old stand (Y31) than in 9-year-old (Y9), 61-year-old (Y61), or 123-year-old (Y123) stands. This pattern was most apparent during warm summer months, but there were no consistent differences in RFF among different-aged stands. RFF represented an average of 4–13% of total soil respiration, and forest floor removal increased moisture content in the mineral soil. We found no evidence of an age effect on the temperature sensitivity of RS, but respiration rates in Y61 and Y123 were less sensitive to low soil moisture than RS in Y9 and Y31. Our results suggest that soil respiration’s sensitivity to soil moisture may change more over the course of stand development than its sensitivity to soil temperature in red pine, and that management activities that alter landscape-scale age distributions in red pine forests could have significant impacts on rates of soil CO2 efflux from this forest type.

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.

Spatio-temporal distribution of soil respiration in dune-meadow cascade ecosystems in the Horqin Sandy Land, China

PurposeThis study investigated soil respiration (Rs) in adjacent ecosystems with a cascade distribution in the semi-arid region of the Horqin Sandy Land (HSL) and determined the spatio-temporal distribution of Rs as well as its relationship with the influencing factors. MethodsFour ecosystems with a cascade distribution (i.e., cascade ecosystems) were selected from the dune–meadow area of the HSL, including sandy bare ground (SBG), a sandy Caragana microphylla community (SCC), transitional artificial Populus forest (TPF), and a meadow Phragmites communis community (MPC). In 2014 and 2015, Rs, soil temperature (Ts) and soil moisture content (Ms) were measured every 10–15days during the growing season, and 24-h continuous observations were carried out during the early, middle and late stages of growth. In addition, landforms, soil properties, vegetation characteristics and groundwater table depths of the cascade ecosystems were surveyed. ResultsThe Rs values of the cascade ecosystems showed significantly different seasonal variations (P<0.05). During the growing season, the mean, coefficient of variation, and temperature sensitivity of Rs were in order of SBG<SCC<TPF<MPC, which was consistent with landforms, soil properties and vegetation characteristics. Due to the differences in landforms, soil properties, vegetation characteristics and groundwater table depth, the Rs values of SBG and SCC were significantly positively correlated with Ms. but not with Ts. TPF had the optimum Ms. for Rs, while the Rs value of MPC was significantly negatively correlated with Ms. Further, the Rs values of TPF and MPC were significantly positively correlated with Ts. Ts and Ms. together explained 49.9%, 74.8%, 79.5%, 92.1% of Rs in the cascade ecosystems(SBG, SCC, TPF, MPC). At the diurnal scale, the Rs values of SBG, TPF and MPC had different relationships with Ts and Ms. during different stages of the growing season. The Rs values of SBG and TPF also had different diurnal patterns during these stages. ConclusionThe critical factors that led to the spatial variation of Rs in the cascade ecosystems in the study area were root biomass, vegetation cover, soil organic matter and Ms. These factors also resulted in the complex relationships of Rs with its influencing factors. The critical factors that led to the temporal variation of Rs in the cascade ecosystems were Ts, Ms. and plant growth. Cascade ecosystems should be considered when estimating the terrestrial carbon balance, and caution must be taken to select the appropriate relation between Rs and its influencing factors. Results of this study will contribute to the accurate estimation of terrestrial carbon emissions and our understanding of the carbon cycle process.

Different Response Patterns of Soil Respiration to a Nitrogen Addition Gradient in Four Types of Land-Use on an Alluvial Island in China

It has been well documented that nitrogen (N) additions significantly affect soil respiration (R s) and its components [that is, autotrophic (R a) and heterotrophic respiration (R h)] in terrestrial ecosystems. These N-induced effects largely result from changes in plant growth, soil properties (for example, pH), and/ or microbial community. However, how R s and its components respond to N addition gradients from low to high fertilizer application rates and what the differences are in diverse land-use types remain unclear. In our study, a field experiment was conducted to examine response patterns of R s to a N addition gradient at four levels (0, 15, 30, and 45 g N m−2 y−1) in four types of land-use (paddy rice–wheat and maize–wheat croplands, an abandoned field grassland, and a Metasequoia plantation) from December 2012 to September 2014 in eastern China. Our results showed that N addition significantly stimulated R s in all four land-use types and R h in croplands (paddy rice–wheat and maize–wheat). R s increased linearly with N addition rates in croplands and the plantation, whereas in grassland, it exhibited a parabolic response to N addition rates with the highest values at the moderate N level in spite of the homogeneous matrix for all four land-use types. This suggested higher response thresholds of R s to the N addition gradient in croplands and the plantation. During the wheat-growing season in the two croplands, R h also displayed linear increases with rising N addition rates. Interestingly, N addition significantly decreased the apparent temperature sensitivity of R s and increased basal R s. The different response patterns of R s to the N addition gradient in diverse land-use types with a similar soil matrix indicate that vegetation type is very important in regulating terrestrial C cycle feedback to climate change under N deposition.

N and P fertilization reduced soil autotrophic and heterotrophic respiration in a young Cunninghamia lanceolata forest

Understanding the response of heterotrophic (Rh) and autotrophic (Ra) components of soil respiration (Rs) to fertilization is important to evaluate the effects of management practices on soil carbon cycling in plantation forest ecosystems. Therefore, we investigated Ra and Rh using a trenching method in a young Cunninghamia lanceolata plantation, subjected to N and P fertilization in subtropical China. Soil CO2 efflux was measured from December 2013 to November 2015. Mean annual Rs, Ra, and Rh rates decreased on average by 18.6%, 23.6%, and 17.1% after fertilization. The contribution of Rh to Rs ranged from 70.9% to 76.7%. This contribution was greater in P-fertilized plots, suggesting that fertilization changed the contribution of Rh and Ra to Rs. The reduced rate of Rh induced by fertilization contributed on average 66.9% to the decrease in Rs rate. This contribution for Rh was higher in NP-fertilized plots than in other plots Based on a bivariate model, 51.2%–69.3% and 53.6%–66.7% of the variations in Rs and Rh among different treatments were explained by soil temperature and moisture. However, temperature sensitivity of Rs and Rh were not affected by fertilization. Ra and Rh were positively related to fine root biomass. Rh was also positively related to soil organic C, dissolved organic C, and microbial biomass C, but negatively related to soil mineral N content. Our results highlight the importance of fertilization on soil CO2 efflux and its significance to the estimation of forest C sink potential.

Soil microbial respiration rate and temperature sensitivity along a north‐south forest transect in eastern China: Patterns and influencing factors

AbstractSoil organic matter is one of the most important carbon (C) pools in terrestrial ecosystems, and future warming from climate change will likely alter soil C storage via temperature effects on microbial respiration. In this study, we collected forest soils from eight locations along a 3700 km north‐south transect in eastern China (NSTEC). For 8 weeks these soils were incubated under a periodically changing temperature range of 6–30°C while frequently measuring soil microbial respiration rate (Rs; each sample about every 20 min). This experimental design allowed us to investigate Rs and the temperature sensitivity of Rs (Q10) along the NSTEC. Both Rs at 20°C (R20) and Q10 significantly increased (logarithmically) with increasing latitude along the NSTEC suggesting that the sensitivity of soil microbial respiration to changing temperatures is higher in forest soils from locations with lower temperature. Our findings from an incubation experiment provide support for the hypothesis that temperature sensitivity of soil microbial respiration increases with biochemical recalcitrance (C quality‐temperature hypothesis) across forest soils on a large spatial scale. Furthermore, microbial properties primarily controlled the observed patterns of R20, whereas both substrate and microbial properties collectively controlled the observed patterns of Q10. These findings advance our understanding of the driving factors (microbial versus substrate properties) of R20 and Q10 as well as the general relationships between temperature sensitivity of soil microbial respiration and environmental factors.

Effects of harvest residue management on soil carbon and nitrogen processes in a Chinese fir plantation

Plantation management can affect ecosystem soil carbon (C) and nitrogen (N) cycles. However, how different harvest residue management strategies impact soil C and N processes over the long term is largely unclear. In this study, we examined effects of harvest residue management on soil C and N concentrations, labile soil C and N pools and soil CO2 efflux (Rs) at different stages after Chinese fir (Cunninghamia lanceolata) was replanted in subtropical China. The residue management treatments were slash and burning, whole-tree harvesting, stem-only harvesting and stem only harvesting with double residue retention. Our results showed that the harvest residue management treatments did not differ significantly in their effect on soil C and N, mineral N (NH4+-N plus NO3−-N), dissolved organic C or total dissolved N concentrations, except for soil N concentrations in surface soil (0–10cm) at year 3 and soil total dissolved N concentrations at year 12, which were significantly lower where the slash was burnt than in the double residue retention treatment. Similarly, Rs did not differ significantly among the four residue management strategies at year 15. Topsoil temperature and topsoil moisture were also unaffected by harvest residue management treatment. Soil temperature was found to be the most important factor controlling the temporal pattern of Rs, accounting for 65.8% of seasonal variation of Rs. There was no significant difference in temperature sensitivity of Rs (Q10) or annual Rs among the four treatments. These results indicated that harvest residue management may not significantly cause long-term effects on soil C cycling and N availability in subtropical Chinese fir plantations.