[Tillage Depth Regulation and the Effect of Straw Return on Soil Respiration in Farmland].

Straw return and tillage depth treatments are one of the most important agricultural management measures that affect farmland soil respiration, but the mechanism of their interaction affecting farmland soil respiration remains unclear. Therefore, 116 published research articles were used through Meta-analysis technology for dryland farmland ecosystems in China to explore the effects of straw return and tillage depth treatments and their interaction on farmland soil respiration and its regulatory factors, which will provide important data support and a theoretical basis for achieving "carbon neutrality" in farmland ecosystems. The results showed that no tillage reduced soil respiration by 8.3%, and the effects of shallow and deep tillage treatments on soil respiration were not significant, but the increase in soil respiration still showed a trend of deep tillage>shallow tillage>no tillage. However, both shallow and deep tillage had relatively small effects on soil respiration and soil organic carbon (SOC), whereas no tillage reduced soil respiration by 8.3% and increased SOC by 7.05%. Therefore, implementing no tillage measures is of great significance for soil carbon sequestration and emission reduction in farmland ecosystems. In addition, tillage depth significantly regulated the impact of straw return on soil respiration, and the increase in soil respiration showed a trend of deep tillage straw return>shallow tillage straw return>no tillage straw return, with an overall average increase of 14.51%. The increase in soil respiration under different tillage depth treatments after straw return was closely related to the change in soil bulk density, crop yield, SOC, soil temperature, and moisture, and the contribution to the increase in soil respiration showed a trend of soil bulk density>crop yield>soil organic carbon>soil moisture>soil temperature. However, SOC increased by 29.32%, 10.12%, and 23.94%, respectively, in the deep tillage straw return, shallow tillage straw return, and no tillage straw return treatments, whereas soil respiration increased by 29.32% and 18.92%, respectively, in the deep tillage straw return and shallow tillage straw return treatments, and it only increased by 1.2% in the no tillage straw return treatment. Therefore, no tillage straw return was also beneficial to soil carbon sequestration and emission reduction in farmland ecosystems. Thus, in the dryland farmland ecosystem of China, tillage depth treatments regulated the impact of straw return on soil respiration, which was mainly related to soil physical and chemical properties, especially being closely related to soil bulk density. Moreover, no tillage and no tillage straw return are important agricultural management measures that are conducive to soil carbon sequestration and emission reduction.

Global patterns of plant and microbial biomass in response to CO2 fumigation.

Introduction: The stimulation of plant and microbial growth has been widely observed as a result of elevated CO2 concentrations (eCO2), however, this stimulation could be influenced by various factors and their relative importance remains unclear. Methods: A global meta-analysis was performed using 884 lines of observations collected from published papers, which analyzed the eCO2 impact on plant and microbial biomass. Results: A significant positive impact of eCO2 was observed on various biomass measures, including aboveground biomass (20.5%), belowground biomass (42.6%), soil microbial biomass (10.4%), fungal biomass (11.0%), and bacterial biomass (9.2%). It was found that eCO2 levels above 200 ppm had a greater impact on plant biomass compared to concentrations at or below 200 ppm. On the other hand, studies showed that positive effects on microbial biomass were more prominent at lower eCO2 levels (≤200 ppm) than at higher levels (>200 ppm), which could be explained by soil nitrogen limitations. Importantly, our results indicated that aboveground biomass was controlled more by climatic and experimental conditions, while soil properties strongly impacted the stimulation of belowground and microbial biomass. Discussion: Our results provided evidence of the eCO2 fertilization effect across various ecosystem types, experimental methods, and climates, and provided a quantitative estimate of plant and soil microbial biomass sensitivity to eCO2. The results obtained in this study suggest that ecosystem models should consider climatic and edaphic factors to more accurately predict the effects of global climate change and their impact on ecosystem functions.

Interactions between nitrogen and phosphorus in modulating soil respiration: A meta-analysis.

BACKGROUND: Economic and social development worldwide increases the input of nutrients, especially nitrogen (N) and phosphorus (P), to soils. These nutrients affect soil respiration (Rs) in terrestrial ecosystems. They may act independently or have interactive effects on Rs. The effect of N and P on Rs and its components (autotrophic respiration [Ra] and heterotrophic respiration [Rh]), however, either individually or together, is poorly understood. We performed a meta-analysis of 130 studies to examine the effects of different fertilization treatments on Rs and its components across terrestrial ecosystems. RESULTS: Our results showed that (1) The impact of fertilizer addition on Rs varies among different fertilizer types. N addition reduced Rs and Rh significantly but did not affect Ra; P addition had no significant effect on Rs, Rh, and Ra; NP addition increased Rs significantly but did not affect Rh and Ra. (2) Ecosystem type, duration of fertilization, fertilization rate, and fertilizer form influenced the response of Rs and its components to fertilizer application. (3) Based on our study, the annual average temperature may be a driving factor of Rs response to fertilizer addition, while soil total nitrogen may be an important predictor of Rs response to fertilizer addition. CONCLUSION: Overall, our study highlights the complex and multifaceted nature of the response of soil Rs and its components to fertilizer application, underscoring the importance of considering multiple factors when predicting and modeling future Rs and its feedback to global change.

Dominant role of nitrogen stoichiometric flexibility in ecosystem carbon storage under elevated CO2.

Interactions between the carbon (C) and nitrogen (N) cycles can impact on the sensitivity of terrestrial C storage to elevated atmospheric carbon dioxide (CO2) concentrations (eCO2). However, the underlying mechanisms associated with CN interactions that influence terrestrial ecosystem C sequestration (Cseq) remains unclear. Here, we quantitatively analyzed published C and N responses to experimentally eCO2 using a meta-analysis approach. We determined the relative importance of three principal mechanisms (changes in the total ecosystem N amount, redistribution of N between plant and soil pools, and flexibility of the C:N ratio) that contribute to increases in ecosystem C storage in response to eCO2. Our results showed that eCO2 increased C and N accumulation, resulted in higher C:N ratios in plant, litter, and soil pools and induced a net shift of N from soils to vegetation. These three mechanisms largely explained the increment of ecosystem Cseq under eCO2, although the relative contributions differed across ecosystem types, with changes in the C:N ratio contributing 50% of the increment in forests Cseq, while the total N change contributed 60% of the increment in grassland Cseq. In terms of temporal variation in the relative importance of each of these three mechanisms to ecosystem Cseq: changes in the C:N ratio was the most important mechanism during the early years (~5 years) of eCO2 treatment, whilst the contribution to ecosystem Cseq by N redistribution remained rather small, and the contribution by total N change did not show a clear temporal pattern. This study highlights the differential contributions of the three mechanisms to Cseq, which may offer important implications for future predictions of the C cycle in terrestrial ecosystems subjected to global change.

Degradation of recalcitrant organic matter in SAARB leachate by a combined process of coagulation and catalytic ozonation.

A combined coagulation and γ-Al2O3 catalytic ozonation process was used to treat semi-aerobic aged refuse biofilter (SAARB) effluent from treating mature landfill leachate. First, the coagulant providing the best pretreatment performance was selected. Then, the coagulated SAARB leachate was further treated in an optimized γ-Al2O3-catalyzed ozonation process. Characteristics of the γ-Al2O3-catalyzed ozonation process were determined, and a reaction mechanism was proposed. FeCl3 provided the best treatment efficiency (chemical oxygen demand (COD) removal of 65.8%, absorbance at 254 nm (UV254) removal of 68.55%, and color number (CN) removal of 79.4%). Under optimized O3 dosage (18.92 mg/min) and γ-Al2O3 dosage (10 g/L), efficiencies of removing COD, UV254, and CN were 54.3%, 82.9%, and 95.9%, respectively, at 30 min. In addition, spectral analysis indicated that fulvic-like substances in ultraviolet and visible regions were effectively degraded in the γ-Al2O3-O3 process and some smaller organic products were produced. Characterization of γ-Al2O3 showed that γ-Al2O3 was relative stable; its morphology and constituent elements did not change much after reaction. In addition, ozonation capacity was enhanced by heterogeneous catalytic effects of γ-Al2O3. The combined coagulation and γ-Al2O3 catalytic ozonation process was proven to be an efficient treatment method for removing bio-refractory organic matter contained in SAARB leachate.

Effect of soil microorganisms and labile C availability on soil respiration in response to litter inputs in forest ecosystems: A meta-analysis.

Litter inputs can influence soil respiration directly through labile C availability and, indirectly, through the activity of soil microorganisms and modifications in soil microclimate; however, their relative contributions and the magnitude of any effect remain poorly understood. We synthesized 66 recently published papers on forest ecosystems using a meta-analysis approach to investigate the effect of litter inputs on soil respiration and the underlying mechanisms involved. Our results showed that litter inputs had a strong positive impact on soil respiration, labile C availability, and the abundance of soil microorganisms, with less of an impact related to soil moisture and temperature. Overall, soil respiration was increased by 36% and 55%, respectively, in response to natural and doubled litter inputs. The increase in soil respiration induced by litter inputs showed a tendency for coniferous forests (50.7%)> broad-leaved forests (41.3%)> mixed forests (31.9%). This stimulation effect also depended on stand age with 30- to 100-year-old forests (53.3%) and ≥100-year-old forests (50.2%) both 1.5 times larger than ≤30-year-old forests (34.5%). Soil microbial biomass carbon and soil dissolved organic carbon increased by 21.0%-33.6% and 60.3%-87.7%, respectively, in response to natural and doubled litter inputs, while soil respiration increased linearly with corresponding increases in soil microbial biomass carbon and soil dissolved organic carbon. Natural and doubled litter inputs increased the total phospholipid fatty acid (PLFA) content by 6.6% and 19.7%, respectively, but decreased the fungal/bacterial PLFA ratio by 26.9% and 18.7%, respectively. Soil respiration also increased linearly with increases in total PLFA and decreased linearly with decreases in the fungal/bacterial PLFA ratio. The contribution of litter inputs to an increase in soil respiration showed a trend of total PLFA > fungal/bacterial PLFA ratio > soil dissolved organic carbon > soil microbial biomass carbon. Therefore, in addition to forest type and stand age, labile C availability and soil microorganisms are also important factors that influence soil respiration in response to litter inputs, with soil microorganisms being more important than labile C availability.

Effects of nitrogen application rate and leaf age on the distribution pattern of leaf SPAD readings in the rice canopy.

A Soil-Plant Analysis Development (SPAD) chlorophyll meter can be used as a simple tool for evaluating N concentration of the leaf and investigating the combined effects of nitrogen rate and leaf age on N distribution. We conducted experiments in a paddy field over two consecutive years (2008-2009) using rice plants treated with six different N application levels. N distribution pattern was determined by SPAD readings based on the temporal dynamics of N concentrations in individual leaves. At 62 days after transplantation (DAT) in 2008 and DAT 60 in 2009, leaf SPAD readings increased from the upper to lower in the rice canopy that received N levels of 150 to 375 kg ha(-1)The differences in SPAD readings between the upper and lower leaf were larger under higher N application rates. However, as plants grew, this atypical distribution of SPAD readings in canopy leaf quickly reversed to the general order. In addition, temporal dynamics of the leaf SPAD readings (N concentrations) were fitted to a piecewise function. In our model, changes in leaf SPAD readings were divided into three stages: growth, functioning, and senescence periods. The leaf growth period lasted approximately 6 days, and cumulative growing days were not affected by N application rates. The leaf functioning period was represented with a relatively stable SPAD reading related to N application rate, and cumulative growing days were extended with increasing N application rates. A quadratic equation was utilized to describe the relationship between SPAD readings and leaf age during the leaf senescence period. The rate of decrease in SPAD readings increased with the age of leaves, but the rate was slowed by N application. As leaves in the lower canopy were physiologically older than leaves in the upper canopy, the rate of decrease in SPAD readings was faster in the lower leaves.

[Effects of nitrogen fertilization, soil moisture and soil temperature on soil respiration during summer fallow season].

On the loess plateau, summer fallow season is a hot rainy time with intensive soil microbe activities. To evaluate the response of soil respiration to soil moisture, temperature, and N fertilization during this period is helpful for a deep understanding about the temporal and spatial variability of soil respiration and its impact factors, then a field experiment was conducted in the Changwu State Key Agro-Ecological Experimental Station, Shaanxi, China. The experiment included five N application rates: unfertilized 0 (N0), 45 (N45), 90 (N90), 135(N135), and 180 (N180) kg x hm(-2). The results showed that at the fallow stage, soil respiration rate significantly enhanced from 1.24 to 1.91 micromol x (m2 x s)(-1) and the average of soil respiration during this period [6.20 g x (m2 x d)(-1)] was close to the growing season [6.95 g x (m2 x d)(-1)]. The bivariate model of soil respiration with soil water and soil temperature was better than the single-variable model, but not so well as the three-factor model when explaining the actual changes of soil respiration. Nitrogen fertilization alone accounted for 8% of the variation soil respiration. Unlike the single-variable model, the results could provide crucial information for further research of multiple factors on soil respiration and its simulation.