Patterns Of Rs Research Articles

Flooding Length Mediates Fencing and Grazing Effects on Soil Respiration in Meadow Steppe.

Grassland management affects soil respiration (Rs, consists of heterotrophic respiration and autotrophic respiration) through soil micro-ecological processes, such as hydrothermal, plant root, organic carbon decomposition and microbial activity. Flooding, an irregular phenomenon in grasslands, may strongly regulate the response of soil respiration and its components to grassland management, but the regulatory mechanism remains unclear. We conducted a 3-year experiment by grassland management (fencing and grazing) and flooding conditions (no flooding (NF), short-term flooding (STF) and long-term flooding (LTF)) to study their effects on Rs and its components in a meadow steppe in the Hui River basin of Hulunbuir. We found differences in the patterns of Rs and its components under grassland management and flooding conditions. In 2021-2023, the temporal trends of Rs, heterotrophic respiration (Rh) and autotrophic respiration (Ra) were generally consistent, with peaks occurring on days 190-220, and the peaks of grazing were higher than that of fencing. In NF, Rs of grazed grassland was significantly higher than that of fenced grassland in 2021-2022 (p < 0.05). In STF and LTF, there was no significant difference in Rs between fenced and grazed grassland (p > 0.05). The dependence of Rs on soil temperature (ST) decreased with increasing flooding duration, and the dependence of Rs on ST of grazed grassland was higher than fenced grassland under NF and STF, but there was no difference between fenced grassland and grazed grassland under LTF. In addition, Rh was more sensitive to ST than Ra. This may be due to the different pathways of ST effects on Rs under grazing in different flooding conditions. Our study indicates that the effect of flooding on Rs is the key to the rational use of grassland under future climate change. To reduce regional carbon emissions, we recommend grazing on flooding grassland and fencing on no-flooding grassland.

Temperature and moisture sensitivities of soil respiration vary along elevation gradients: An analysis from long-term field observations

Based on long-term field observation data over 11 years at 23 sites in two mountainous areas (TS1 and TS2) at elevations from 829 to 2700 m, where the dominant vegetation type of TS1 and TS2 was temperate mixed broadleaf-coniferous forest and cold temperate coniferous forest, respectively, we analyzed the correlations between soil respiration (Rs) and abiotic and biotic factors to explore the response patterns of Rs to environmental factors within and between the sites along the elevation gradient. We found that soil moisture (θ) and its combinations (Ts × θ and θ/Ts) with soil temperature (Ts) increased significantly with increasing elevation, while Ts, soil bulk density (SBD), C/N ratio, and pH decreased significantly with increasing elevation. Within each site, both exponential- Ts (ET) and Gaussian-Ts (GT) models could be used for predicting the Rs seasonal variation, except for two sites in the area of TS1, where θ was a better predictor than Ts. The integrated ET–θ and GT–θ models could be applied to all sites except for 22S, and both were superior to the ET and GT models. The mean Rs of each site over the measurement period ranged from 3.07 to 6.94 μmol CO2 m−2 s−1 and showed a quadratic increase along the elevation gradient. Among the 23 sites, Q10 ranged from 1.15 to 3.79, and it increased with elevation, reaching a maximum at an elevation of 2366 m; the θ sensitivity parameter (d) decreased significantly with elevation and reached a minimum at an elevation of 1975 m. Both the d and Ts sensitivity parameter (b) of Rs were complementary to each other along the elevation gradient. Among the sites, Ts, θ, and combinations of the two were more important drivers for both Rs and Q10 variations than microbial and physicochemical indicators.

Temporal Variation and Hysteresis of Soil Respiration and Sap Flow of Pinus densiflora in a Cool Temperate Forest, Japan

Soil respiration (Rs) consists of autotrophic (Ra) and heterotrophic (Rh) respiration, and the metabolic responses of Ra and Rh are supposedly affected by environmental factors. Our hypothesis was that the contribution of Ra and Rh would be affected by seasons. To characterize seasonal patterns of Rs, sap flow (as an indicator of photosynthetic activity), and environmental factors, we continuously measured temporal variation in Rs using an automated opening and closing chamber system in a cool temperate forest. Rs had counterclockwise hysteresis (Rs: spring &lt; autumn) with soil temperature at a depth of 5 cm. Daily maximum Rs had a significant positive relationship with daily maximum sap flow over three seasons, and daily maximum sap flow was lower in autumn than in spring (Ra: spring &gt; autumn). The amount of leaf litterfall increased significantly from August to October; the high Rs in autumn would be due to an increase in Rh (Rh: spring &lt; autumn). These results suggest that Ra contributes more in spring than in autumn, and the contribution of Rh is high from summer through autumn.

Elevation of NO3−-N from biochar amendment facilitates mitigating paddy CH4 emission stably over seven years

Biochar application into paddy is an improved strategy for addressing methane (CH4) stimulation of straw biomass incorporation. Whereas, the differentiative patterns and mechanisms on CH4 emission of straw biomass and biochar after long years still need to be disentangled. Considering economic feasibility, a seven-year of field experiment was conducted to explore the long-term CH4 mitigation effect of annual low-rate biochar incorporation (RSC, 2.8 t ha−1), with annual rice straw incorporation (RS, 8 t ha−1) and control (CK, with no biochar or rice straw amendment incorporation) as a comparation. Results showed that RSC mitigated CH4 emission while RS stimulated CH4 significantly (p < 0.05) and stably over 7 experimental years compared with CK. RSC mitigated 14.8–46.7% of CH4 emission compared with CK. In comparison to RSC, RS increased 111–950.5% of CH4 emission during 7 field experimental years. On the 7th field experimental year, pH was significantly increased both in RS and RSC treatment (p < 0.05). RSC significantly (p < 0.05) increased soil nitrate (NO3−-N) compared with RS while RS significantly (p < 0.05) increased dissolved carbon (DOC) compared to RSC. Soil NO3−-N inhibition on methanogens and promotion on methanotrophs activities were verified by laboratory experiment, while soil pH and DOC mainly promoted methanogens abundance. Significantly (p < 0.05) increased DOC and soil pH enhanced methanogens growth and stimulated CH4 emission in RS treatment. Higher soil NO3−-N content in RSC than CK and RS contributed to CH4 mitigation. Soil NO3−-N and DOC were identified as the key factors differentiating CH4 emission patterns of RS and RSC in 2019. Collectively, soil NO3−-N impacts on CH4 flux provide new ideas for prolonged effect of biochar amendment on CH4 mitigation after years.

Soil Respiration Variation among Four Tree Species at Young Afforested Sites under the Influence of Frequent Typhoon Occurrences

Afforestation is an effective solution for restoring forest ecosystems and mitigating climate change in the tropics. In this study, we analyzed the soil respiration (Rs) at four afforested sites with different tree species exposed to a monsoon climate with frequent typhoon occurrences in southern Taiwan. The aim of this study is to examine (1) the distinct seasonal variation that strongly affects the Rs among four tree species at afforested sites, (2) the patterns of Rs that differ among the four species at the afforested sites, and (3) the influence of typhoons on forest structure and consequently the degree of Rs. The annual mean Rs among the four tree species at the afforested sites in the pretyphoon disturbance year was approximately 7.65 t C ha−1, with the post-typhoon year having an annual mean Rs of approximately 9.13 t C ha−1. Our results clearly show Rs variations in the four tree species at the young afforested sites under the influence of typhoon disturbances. The high seasonal variations in Rs were controlled by soil temperature and soil moisture. The different tree species also led to variations in litterfall production and consequently influenced Rs variation. Forest structures, such as aboveground biomass and consequently the degree of Rs, were disturbed by severe typhoon impacts in 2016, resulting in high aboveground biomass with tree height losses and litterfall accumulation. Furthermore, Rs increased immediately after litterfall input to the soil, and the addition effect of litter and the soil C release occurred throughout the year after typhoon disturbances. Our results contribute to understanding impact of typhoon disturbances on the degree of Rs at tropical afforested sites.

High-resolution assessment of solar radiation and energy potential in China

Global solar radiation (Rs) is a key parameter for determining the energy yields of solar photovoltaic (PV) systems. However, long-term Rs data are not available in most regions of China, impeding the management and development of PV systems. In this study, a novel model for estimating Rs was developed and coupled with a PV power model and inverse distance weighting model to generate high-resolution Rs and PV power data over China. A large network of observations was used to provide forcing inputs (daily observations from 1961 to 2018, from 2123 meteorological stations). The spatiotemporal patterns of Rs and PV power in China were further quantified. The results indicate that the newly developed Rs model accurately represents the decadal variability of Rs in China during 1961–2018. Annual potential PV power exhibited a significantly decreasing trend from 1961 to 2018, with a significant decrease from 1961 to 1991 (−0.35 ± 0.06 kWh m−2 yr−1, p < 0.01) and non-significant decrease from 1992 to 2018 (−0.14 ± 0.12 kWh m−2 yr−1, p > 0.05). Owing to air quality improvements in the future, the potential PV power may increase over China, leading to large economic benefits. Western China is favored for its abundant PV power, whereas central and eastern China are the least favorable for PV power generation. Thus, the western part of China, with its excellent geographical potential, is an optimal location for the installation of solar PV power plants. Our findings provide practical information to solar energy industries, and can help in energy structure transitions, meeting the energy demand and contributing to carbon neutrality.

Biochar Mitigated Paddy CH &lt;sub&gt;4&lt;/sub&gt; Emission Stably Over Seven Years with NO &lt;sub&gt;3&lt;/sub&gt; &lt;sup&gt;-&lt;/sup&gt;-N Elevation the Decisive Factor the Last Year

Biochar application into paddy is an improved strategy for addressing methane (CH4) stimulation of straw biomass incorporation. Whereas, the differentiative patterns and mechanisms on CH4 emission of straw biomass and biochar after long years are still blur. Considering economic feasibility, a seven-year of field experiment was conducted to explore the long-term CH4 mitigation effect of annual low-rate biochar incorporation (RSC, 2.8 t ha-1), with annual rice straw incorporation (RS, 8 t ha-1) and control (CK, with no biochar or rice straw amendment incorporation) as a comparation. Results showed that RSC mitigated CH4 emission while RS stimulated CH4 significantly (p < 0.05) and stably over 7 experimental years compared with CK. RSC mitigated 14.8 ~ 46.7% of CH4 emission compared with CK. In comparison to RSC, RS increased 111 ~ 950.5% of CH4 emission during 7 field experimental years. On the 7th field experimental year, pH was significantly increased both in RS and RSC treatment (p < 0.05). RSC significantly (p < 0.05) increased soil nitrate (NO3--N) while RS significantly (p < 0.05) increased dissolved carbon (DOC) when compared to each other. Soil NO3--N inhibitory on methanogens and promotion on methanotrophs was verified by laboratory experiment, while soil pH and DOC mainly promoted methanogens abundance. Significantly (p < 0.05) increased DOC and soil pH enhanced methanogens growth and stimulated CH4 emission in RS treatment. Higher soil NO3--N in RSC than CK and RS contributed to CH4 mitigation. Soil NO3--N and DOC were identified as the key factors differentiating CH4 emission patterns of RS and RSC in 2019. Collectively, soil NO3--N impacts on CH4 flux provide new ideas for prolonged effect of biochar on CH4 mitigation after years.

Soil respiration of alpine meadow is controlled by freeze–thaw processes of active layer in the permafrost region of the Qinghai–Tibet Plateau

Abstract. Freezing and thawing action of the active layer plays a significant role in soil respiration (Rs) in permafrost regions. However, little is known about how the freeze–thaw processes affect the Rs dynamics in different stages of the alpine meadow underlain by permafrost in the Qinghai–Tibet Plateau (QTP). We conducted continuous in situ measurements of Rs and freeze–thaw processes of the active layer at an alpine meadow site in the Beiluhe permafrost region of the QTP and divided the freeze–thaw processes into four different stages in a complete freeze–thaw cycle, comprising the summer thawing (ST) stage, autumn freezing (AF) stage, winter cooling (WC) stage, and spring warming (SW) stage. We found that the freeze–thaw processes have various effects on the Rs dynamics in different freeze–thaw stages. The mean Rs ranged from 0.12 to 3.18 µmol m−2 s−1 across the stages, with the lowest value in WC and highest value in ST. Q10 among the different freeze–thaw stages changed greatly, with the maximum (4.91±0.35) in WC and minimum (0.33±0.21) in AF. Patterns of Rs among the ST, AF, WC, and SW stages differed, and the corresponding contribution percentages of cumulative Rs to total Rs of a complete freeze–thaw cycle (1692.98±51.43 g CO2 m−2) were 61.32±0.32 %, 8.89±0.18 %, 18.43±0.11 %, and 11.29±0.11 %, respectively. Soil temperature (Ts) was the most important driver of Rs regardless of soil water status in all stages. Our results suggest that as climate change and permafrost degradation continue, great changes in freeze–thaw process patterns may trigger more Rs emissions from this ecosystem because of a prolonged ST stage.

Stand ages adjust fluctuating patterns of soil respiration and decrease temperature sensitivity after revegetation

AbstractRevegetation plays an essential role in controlling soil erosion and influencing soil respiration (Rs) by changing the vegetation coverage and soil biochemical characteristics. Soil respiration and its temperature sensitivity (Q10) have been studied comprehensively. However, the effect of stand age after revegetation on Rs and Q10 remains unclear. We selected four stands (i.e., eroded hillslopes [EBs] and 0‐ to 5‐yr, 5‐ to 10‐yr, and 10‐yr apple orchards) to investigate the changes in Rs and Q10 values. A soil CO2 flux system (Li‐8100) was used to measure Rs in situ from July 2018 to December 2018 in the Luoyugou watershed on the Chinese Loess Plateau. The average Rs rate showed decreased and increased periods with stand age. Changes in Rs were mainly induced by soil nutrient status, which accounted for 44.5% of the heavy weight in principal component analysis. The Q10 values decreased with stand age after revegetation and followed the order EB (4.96) &gt; 0‐ to 5‐yr apple orchard (3.02) &gt; 5‐ to 10‐yr apple orchard (2.25) &gt; 10‐yr apple orchard (1.67). Our results suggest that Rs is substantially influenced by fungal richness and soil microbial biomass carbon (C), and the Q10 values are explained by the nonmetric multidimensional scaling ordinations of bacteria, which in turn are influenced by labile organic C. We demonstrate that converting EBs to apple orchards could be an effective way to decrease Rs and Q10 values. The fluctuating patterns of Rs with stand age should be considered when accurately evaluating the global C balance and predicting future climate change.

Machine learning models to quantify and map daily global solar radiation and photovoltaic power

Global solar radiation (Rs) reaching Earth's surface is the primary information for the design and application of solar energy-related systems. High-resolution Rs measurements are limited owing to the high costs of measuring devices, and their stringent operational maintenance procedures. This study evaluated a newly developed machine learning model, namely the hybrid particle swarm optimization and extreme learning machine (PSO-ELM), to accurately predict daily Rs. The newly proposed model was compared with five other machine learning models, namely the original ELM, support vector machine, generalized regression neural networks, M5 model tree, and autoencoder, under two training scenarios using long-term Rs and other climatic data taken during 1961–2016 from seven stations located on the Loess Plateau of China. Overall, the PSO-ELM with full climatic data as inputs provided more accurate Rs estimations. We also calculated the daily Rs at fifty other stations without Rs measurements on the Loess Plateau using the PSO-ELM model, as well as the potential photovoltaic (PV) power using an empirical PV power model, and then generated high-resolution (0.25°) Rs and PV power data to investigate the patterns of Rs and PV power. Significant reductions in Rs (−6.49 MJ m−2 per year, p < 0.05) and PV power (−0.46 kWh m−2 per year, p < 0.05) were observed. The northwestern parts of the study area exhibited more Rs and PV power and are therefore considered more favorable for solar energy-related applications. Our study confirms the effectiveness of the PSO-ELM for solar energy modeling, particularly in areas where in-situ measurements are unavailable.

Comparison of automatic and manual chamber methods for measuring soil respiration in a temperate broad-leaved forest

BackgroundStudying the ecosystem carbon cycle requires analysis of interrelationships between soil respiration (Rs) and the environment to evaluate the balance. Various methods and instruments have been used to measure Rs. The closed chamber method, which is currently widely used to determine Rs, creates a closed space on the soil surface, measures CO2 concentration in the inner space, and calculates Rs from the increase. Accordingly, the method is divided into automatic or manual chamber methods (ACM and MCM, respectively). However, errors of these methods and differences in instruments are unclear. Therefore, we evaluated the characteristics and difference of Rs values calculated using both methods with actual data.ResultsBoth methods determined seasonal variation patterns of Rs, reflecting overall changes in soil temperature (Ts). ACM clearly showed detailed changes in Rs, but MCM did not, because such small changes are unknown as Rs values are collected monthly. Additionally, Rs measured using MCM was higher than that using ACM and differed depending on measured plots, but showed similar tendencies with all measurement times and plots. Contrastingly, MCM Rs values in August for plot 4 were very high compared with ACM Rs values because of soil disturbances that easily occur during MCM measurements. Comparing Rs values calculated using monthly means with those calculated using MCM, the ACM calculated values for monthly averages were higher or lower than those of similar measurement times using the MCM. The difference between the ACM and MCM was attributed to greater or lesser differences. These Rs values estimated the carbon released into the atmosphere during measurement periods to be approximately 57% higher with MCM than with ACM, at 5.1 and 7.9 C ton ha−1, respectively.ConclusionACM calculated average values based on various Rs values as high and low for measurement periods, but the MCM produced only specific values for measurement times as representative values. Therefore, MCM may exhibit large errors in selection differences during Rs measurements. Therefore, to reduce this error using MCM, the time and frequency of measurement should be set to obtain Rs under various environmental conditions. Contrastingly, the MCM measurement is obtained during CO2 evaluation in the soil owing to soil disturbance caused by measuring equipment, so close attention should be paid to measurements. This is because the measurement process is disturbed by high CO2 soil concentration, and even small soil disturbances could release high levels into the chamber, causing large Rs errors. Therefore, the MCM should be adequately mastered before using the device to measure Rs.

Responses of soil respiration to rainfall addition in a desert ecosystem: Linking physiological activities and rainfall pattern

The tight linkage between photosynthesis (An) and soil respiration (Rs) has been verified in many terrestrial ecosystems. However, it remains unclear whether this linkage occurs in desert ecosystems, where water is considered an important trigger of carbon cycling. A field experiment was performed under seven simulated rainfall amounts (0, 3, 5, 10, 15, 25, and 40 mm) with two co-existing desert plants (Reaumuria soongorica and Nitraria sphaerocarpa) in June (early growing season, EGS) and August (middle growing season, MGS) in 2016. An, Rs, predawn water potential (Ψpd), soil temperature (Ts) and soil moisture (Swc) were measured for each treatment or control plot for 3 weeks. Our objective was to examine the effects of rainfall pattern on Rs and physiological responses of the two plants and the relationships between Rs and biotic and abiotic factors. No obvious variations in Ψpd or An were found under small rainfall events. However, when the rainfall amount exceeded 10 mm, both plants responded strongly, and the response patterns of Rs showed trends similar to those of An, which varied between species and seasons. Moreover, rain additions of 3–40 mm significantly increased Rs, and the relative changes in Rs (ΔRs) of both species were much larger in the EGS than in the MGS. Importantly, abiotic factors may have controlled the variations in Rs under small rain events while An played a more important role in regulating the variations in Rs when the rainfall amount exceeded 10 mm for both species, suggest that the rainfall pattern–driven changes in Rs composition interact with physiological activity and abiotic factors to regulate the response of Rs to rainfall variability in desert ecosystems. Thus, climate change in the coming decades may lead to carbon sequestration by desert plants, which may cause desert ecosystems to act as carbon sinks.

Seasonal and diurnal patterns of soil respiration in an evergreen coniferous forest: Evidence from six years of observation with automatic chambers.

Soil respiration (Rs) plays a key role in the carbon balance of forest ecosystems. There is growing evidence that Rs is strongly correlated with canopy photosynthesis; however, how Rs is linked to aboveground attributes at various phenological stages, on the seasonal and diurnal scale, remains unclear. Using an automated closed dynamic chamber system, we assessed the seasonal and diurnal patterns of Rs in a temperate evergreen coniferous forest from 2005 to 2010. High-frequency Rs rates followed seasonal soil temperature patterns but the relationship showed strong hysteresis. Predictions of Rs based on a temperature-response model underestimated the observed values from June to July and overestimated those from August to September and from January to April. The observed Rs was higher in early summer than in late summer and autumn despite similar soil temperatures. At a diurnal scale, the Rs pattern showed a hysteresis loop with the soil temperature trend during the seasons of high biological activity (June to October). In July and August, Rs declined after the morning peak from 0800 to 1400 h, although soil temperatures continued to increase. During that period, figure-eight-shaped diurnal Rs patterns were observed, suggesting that a midday decline in root physiological activity may have occurred in early summer. In September and October, Rs was higher in the morning than in the night despite consistently high soil temperatures. We have characterised the magnitude and pattern of seasonal and diurnal Rs in an evergreen forest. We conclude that the temporal variability of Rs at high resolution is more related to seasons across the temperature dependence.

Technical note: Differences in the diurnal pattern of soil respiration under adjacent &amp;lt;i&amp;gt;Miscanthus&amp;lt;/i&amp;gt; × &amp;lt;i&amp;gt;giganteus&amp;lt;/i&amp;gt; and barley crops reveal potential flaws in accepted sampling strategies

Abstract. For convenience, measurements used to compare soil respiration (Rs) from different land uses, crops or management practices are often made between 09:00 and 16:00 UTC, convenience which is justified by an implicit assumption that Rs is largely controlled by temperature. Three months of continuous data presented here show distinctly different diurnal patterns of Rs between barley (Hordeum vulgare) and Miscanthus × giganteus (Miscanthus) grown on adjacent fields. Maximum Rs in barley occurred during the afternoon and correlated with soil temperature, whereas in Miscanthus after an initial early evening decline, Rs increased above the daily average during the night and in July maximum daily rates of Rs were seen at 22:00 and was significantly correlated with earlier levels of solar radiation, probably due to delays in translocation of recent photosynthate. Since the time of the daily mean Rs in Miscanthus occurred when Rs in the barley was 40 % greater than the daily mean, it is vital to select appropriate times to measure Rs especially if only single daily measurements are to be made.

Nonlinear response of soil respiration to increasing nitrogen additions in a Tibetan alpine steppe

Nitrogen (N) availability is a key regulator of carbon (C) cycling in terrestrial ecosystems. Anthropogenic N input, such as N deposition and fertilization, increases N availability in soil, which has important implications for an ecosystem’s C storage and loss. Soil respiration (Rs), which is the second largest C flux from terrestrial ecosystems to the atmosphere, plays an important role in terrestrial C cycles. The direction and magnitude of the responses of Rs and its components to N addition have been widely evaluated, but it remains unclear how these processes change across multiple N addition levels. Here we conducted a two-year field experiment to examine the changes of Rs and its autotrophic respiration (Ra) and heterotrophic respiration (Rh) components along a gradient of eight N levels (0, 1 2, 4, 8, 16, 24, 32 g m−2 yr−1) in a Tibetan alpine steppe, and used structural equation modeling (SEM) to explore the relative contributions of biotic and abiotic variables and their direct and indirect pathways regulating the Ra and Rh. Our results indicated that both Rs and Ra exhibited first increasing and then subsequent decreasing trends at the threshold of 8 g N m−2 yr−1. In contrast, the Rh declined linearly with the N addition rate continuously increasing. SEM analysis revealed that, among various environmental factors, soil temperature was the most important one modulating Rs, which not only had a direct effect on the two Rs components, but also indirectly regulated the Ra and Rh via root and microbial biomass. These findings suggest that the nonlinear response patterns of Rs should be considered for better predicting terrestrial C balance, given that anthropogenic N input to the terrestrial ecosystems is increasing continuously.

Spatial Upscaling of Soil Respiration under a Complex Canopy Structure in an Old‐Growth Deciduous Forest, Central Japan

The structural complexity, especially canopy and gap structure, of old‐growth forests affects the spatial variation of soil respiration (Rs). Without considering this variation, the upscaling of Rs from field measurements to the forest site will be biased. The present study examined responses of Rs to soil temperature (Ts) and water content (W) in canopy and gap areas, developed the best fit modelof Rs and used the unique spatial patterns of Rs and crown closure to upscale chamber measurements to the site scale in an old‐growth beech‐oak forest. Rs increased with an increase in Ts in both gap and canopy areas, but the effect of W on Rs was different between the two areas. The generalized linear model (GLM) analysis identified that an empirical model of Rs with thecoupling of Ts and W was better than an exponential model of Rs with only Ts. Moreover, because of different responses of Rs to W between canopy and gap areas, it was necessary to estimate Rs in these areas separately. Consequently, combining the spatial patterns of Rs and the crown closure could allow upscaling of Rs from chamber‐based measurements to the whole site in the present study.

Spatial Heterogeneity of Soil Respiration in the Soil Erosion Area of West Mountains in Fujian Province, China

The spatial heterogeneity of soil respiration (Rs) is of great significance in accurately estimating the carbon budget in erosion areas. This study investigated the soil respiration (Rs), total nitrogen (TN), carbon-nitrogen ratio (C/N), soil organic carbon content (SOC), leaf area index (LAI), soil temperature (T10), and soil moisture (W) in 59 soil samples collected from Hetian Town in Fujian Province. Both classical statistics and geostatistics were used to analyze the spatial heterogeneity of soil respirations and other measured factors. The variability of Rs and other measured factors in the samples ranked from the largest to the smallest: LAI > SOC > TN > Rs > C/N > T10 > W. Rs was positively correlated with T10 (P<0.01) and with TN (P<0.05), but not significantly correlated with other factors (P>0.05); TN, SOC and T10 could be used to explain the spatial variation of soil respiration among the samples. The results from geo-statistical analysis showed that Rs was in a medium spatial autocorrelation, with 52.89% of spatial heterogeneity caused by structural factors and 47.11% of spatial heterogeneity resulted from random factor; the fractal dimensions of soil respiration and its interacted factors were ranked as: Rs > LAI > C/N > T10 > SOC > W > TN; the spatial distribution patterns of Rs were similar with those of TN and T10, but different from those of C/N, SOC or LAI. At the 95% confidence level and 90% estimation accuracy, the reasonable sampling number of Rs was 62.

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.

Upscaling plot-scale soil respiration in winter wheat and summer maize rotation croplands in Julu County, North China

Soil respiration (Rs) data from 45 plots were used to estimate the spatial patterns of Rs during the peak growing seasons of winter wheat and summer maize in Julu County, North China, by combining satellite remote sensing data, field-measured data, and a support vector regression (SVR) model. The observed Rs values were well reproduced by the model at the plot scale, with a root-mean-square error (RMSE) of 0.31μmolCO2m−2s−1 and a coefficient of determination (R2) of 0.73. No significant difference was detected between the prediction accuracy of the SVR model for winter wheat and summer maize. With forcing from satellite remote sensing data and gridded soil property data, we used the SVR model to predict the spatial distributions of Rs during the peak growing seasons of winter wheat and summer maize rotation croplands in Julu County. The SVR model captured the spatial variations of Rs at the county scale. The satellite-derived enhanced vegetation index was found to be the most important input used to predict Rs. Removal of this variable caused an RMSE increase from 0.31μmolCO2m−2s−1 to 0.42μmolCO2m−2s−1. Soil properties such as soil organic carbon (SOC) content and soil bulk density (SBD) were the second most important factors. Their removal led to an RMSE increase from 0.31μmolCO2m−2s−1 to 0.37μmolCO2m−2s−1. The SVR model performed better than multiple regression in predicting spatial variations of Rs in winter wheat and summer maize rotation croplands, as shown by the comparison of the R2 and RMSE values of the two algorithms. The spatial patterns of Rs are better captured using the SVR model than performing multiple regression, particularly for the relatively high and relatively low Rs values at the center and northeast study areas. Therefore, SVR shows promise for predicting spatial variations of Rs values on the basis of remotely sensed data and gridded soil property data at the county scale.

Biotic and abiotic controls on the diel and seasonal variation in soil respiration and its components in a wheat field under long-term nitrogen fertilization

Characterization of the dynamics of soil respiration (Rs) and its components under long-term nitrogen (N) fertilization is necessary to understand the mechanisms that regulate soil carbon (C) emissions. We continuously monitored Rs and its components (heterotrophic respiration (Rh) and autotrophic respiration (Ra)) for 3 years in farmland planted with winter wheat that had been fertilized with N for 10 years to investigate the seasonal and diurnal responses of Rs and its components under different N fertilization rates. The seasonal dynamics of Rs and its components were regulated by biotic factors (leaf area index and photosynthesis) and abiotic factors (soil temperature (ST) and moisture). N addition altered the Rh-to-Rs ratio and resulted in different Rs responses. Moderate N addition increased the C efflux, but excess N fertilization caused no significant change in Rs compared to the treatment without N. Diel Rs and ST are decoupled in farmland. Higher Rs was observed when the temperature increased, which demonstrates the hysteresis effect. N fertilization increased the peak Rs values in the diurnal pattern. N addition changed the seasonal and diurnal patterns of Rs by regulating both biotic and abiotic factors, and Rs did not linearly increase with the N addition rate.