Annual Cumulative CO2 Emissions Research Articles

Effects of Long-Term Nitrogen Fertilization and Ground Water Level Changes on Soil CO2 Fluxes from Oil Palm Plantation on Tropical Peatland

A long-term study on the effect of nitrogen (N) fertilization on soil carbon dioxide (CO2) fluxes in tropical peatland was conducted to (1) quantify the annual CO2 emissions from an oil palm plantation under different N application rates and (2) evaluate the temporal effects of groundwater level (GWL) and water-filled pore space (WFPS) on soil organic carbon (SOC) and CO2 fluxes. Monthly measurement of soil CO2 fluxes using a closed chamber method was carried out from January 2010 until December 2013 and from January 2016 to December 2017 in an oil palm plantation on tropical peat in Sarawak, Malaysia. Besides the control (T1, without N fertilization), there were three N treatments: low N (T2, 31.1 kg N ha−1 year−1), moderate N (T3, 62.2 kg N ha−1 year−1), and high N (T4, 124.3 kg N ha−1 year−1). The annual CO2 emissions ranged from 7.7 ± 1.2 (mean ± SE) to 16.6 ± 1.0 t C ha−1 year−1, 9.8 ± 0.5 to 14.8 ± 1.4 t C ha−1 year−1, 10.5 ± 1.8 to 16.8 ± 0.6 t C ha−1 year−1, and 10.4 ± 1.8 to 17.1 ± 3.9 t C ha−1 year−1 for T1, T2, T3, and T4, respectively. Application of N fertilizer had no significant effect on annual cumulative CO2 emissions in each year (p = 0.448), which was probably due to the formation of large quantities of inorganic N when GWL was temporarily lowered from January 2010 to June 2010 (−80.9 to −103.4 cm below the peat surface), and partly due to low soil organic matter (SOM) quality. A negative relationship between GWL and CO2 fluxes (p < 0.05) and a positive relationship between GWL and WFPS (p < 0.001) were found only when the oil palm was young (2010 and 2011) (p < 0.05), indicating that lowering of GWL increased CO2 fluxes and decreased WFPS when the oil palm was young. This was possibly due to the fact that parameters such as root activity might be more predominant than GWL in governing soil respiration in older oil palm plantations when GWL was maintained near or within the rooting zone (0–50 cm). This study highlights the importance of roots and WFPS over GWL in governing soil respiration in older oil palm plantations. A proper understanding of the interaction between the direct or indirect effect of root activity on CO2 fluxes and balancing its roles in nutrient and water management strategies is critical for sustainable use of tropical peatland.

N and P addition increase soil respiration but decrease contribution of heterotrophic respiration in semiarid grassland

Fertilization is an effective measure to decrease soil erosion by promoting vegetation restoration, while it affects soil respiration (Rs) greatly through influencing soil properties and plant root growth. A factorial combination of N addition (0, 50 and 100 kg N ha-1 yr-1 defined as N0, N50, and N100) and P addition (0, 40 and 80 kg P2O5 ha-1 yr-1 defined as P0, P40, and P80) experiment was conducted in a farming-withdrawn grassland to investigate the Rs and its components (heterotrophic respiration, Rh; autotrophic respiration, Ra) in responses to different nitrogen (N) and phosphorus (P) addition levels from May 2018 to October 2019 on the semiarid Loess Plateau. Results showed that Rs, Rh and Ra presented single-peak curves both in diurnal and seasonal variations across all N and P addition treatments. The highest Rs, Rh and Ra values during the day occurred at 12:00–14:00 and the highest values during the year appeared in July, which were consistent with soil temperature changes. Rs, Rh and Ra increased significantly under N and/or P addition from May to September. Compared with no fertilization, Rh and Ra significantly increased by 4.2–5.1% and 43.9–46.4%, and by 13.2–15.8% and 23.0–34.2% under N or P addition alone, respectively. N and P combined addition increased Rh and Ra by 25.4–30.7% and 62.0–111.4% than N or P addition alone. Rs and Ra reached the highest values under N100 combined with P80 addition, but Rh reached the highest values under N50 combined with P80 addition treatment. Annual cumulative CO2 emission increased by 24.4%−26.5% under N addition alone, 17.0–27.4% under P addition alone and 42.2–68.7% under N and P combined addition. Compared with no fertilization, root biomass and soil microbial biomass carbon significantly increased by 15.8–122% and 5.2–92.5% after N and P additions, respectively. However, the positive effect of N and P addition on Rh was weaker than that of Ra, which decreased the contribution of Rh to Rs. Our findings point to the need of rational N and P combination to tradeoff biomass production improvement and soil carbon emission when applying fertilization to promote grassland restoration in semiarid Loess Plateau.

Carbon Balance under Organic Amendments in the Wheat-Maize Cropping Systems of Sloppy Upland Soil

With an increasing interest in closing the nutrient loop in agroecosystems, organic amendments are highly recommended as a reliable resource for soil nutrient recycling. However, from a carbon sequestration perspective, not much has been reported on the contribution of different organic amendments to soil organic carbon (SOC), crop carbon (C) uptake, and soil carbon dioxide (CO2) emissions in wheat-maize cropping systems of sloppy upland soil. To fill the knowledge gap, a two-year lysimeter-field plots experiment was conducted in a sloppy upland purplish soil under wheat-maize cropping systems. The experiments were arranged in a complete random block design with five treatment plots, namely; fresh pig slurry as organic manure (OM), crop residues (CR), conventional mineral fertilizers (NPK) as the control, organic manure plus mineral fertilizers (OMNPK), and crop residues plus mineral fertilizers (CRNPK). Our results showed the leaf photosynthesis rate was not significantly increased by organic amendment application treatments compared to NPK treatment, and was within a range of 4.8 to 45.3 µmol m−2 s−1 for the wheat season and −20.1 to 40.4 µmol m−2 s−1 for the maize season across the five treatments and the measured growth stages. The soil CO2 emissions for the maize season (in the range of 203 to 362 g C m−2) were higher than for the wheat season (in the range of 118 to 252 g C m−2) on average across the different experimental treatments over the two-year experiment. The organic amendment application increased annual cumulative CO2 emissions from 30% to 51% compared to NPK treatment. Over the two years, the average crop C uptake ranged from 174 to 378 g C m−2 and from 287 to 488 g C m−2 for the wheat and maize seasons, respectively, and the organic amendment application increased the crop C uptake by 4% to 23% compared to NPK treatment. In the organic amendment treatments, the C balance ranged from −160 to 460 g C m−2 and from −301 to 334 g C m−2 for the wheat and the maize seasons, respectively, which were greater than those in the NPK treatment. Overall, the present study results suggest incorporation of organic amendments could be an effective strategy for increasing C sequestration and sustaining crop productivity in sloppy upland soil.

Long-term harvesting of reeds affects greenhouse gas emissions and microbial functional genes in alkaline wetlands

Reed (Phragmites australis) is dominant vegetation in alkaline wetlands that is harvested annually due to its economic value. To reveal the effects of harvesting reeds on the emission of greenhouse gases (GHG), the annual soil physicochemical characteristics and flux of GHGs in a reed wetland without harvesting (NHRW) and with harvesting (HRW) were measured. The results showed that after the harvesting of reeds, the total organic carbon (TOC) and total nitrogen (TN) significantly decreased, and soil temperature significantly increased. The annual cumulative N2O emissions decreased from 0.73 ± 0.20 kg ha−1 to −0.57 ± 0.49 kg ha−1 with the harvesting of reeds. The annual cumulative CH4 emissions also decreased from 561.88 ± 18.61 kg ha−1 to 183.13 ± 18.77 kg ha−1 with the harvesting of reeds. However, harvesting of reeds had only a limited influence on the annual cumulative CO2 emissions. A Pearson correlation analysis revealed that the CO2 and N2O emissions were more sensitive to temperature than the CH4 emissions. Both structural equation modeling (SEM) analysis and slurry incubation confirmed that higher temperatures offset the reduction of CO2 emissions after reed harvesting. Metagenomics showed that the abundance of functional genes involved in both GHG sink and source decreased with reed harvesting. This study presents a comprehensive view of reed harvesting on GHG emissions in alkaline wetlands, yielding new insight into the microbial response and offering a novel perspective on the potential impacts of wetland management.

Effects of different nitrogen fertilizers on annual emissions of greenhouse gas from maize field in Northeast China

A field experiment was conducted to investigate the greenhouse gas emission at high latitude farmland in Northeast China. We monitored the greenhouse gas emission using the static chamber-gas chromatography method. Four nitrogen (N) fertilizers were used: conventional N fertilization (CN), slow release fertilizer (SLN), urea plus nitrification inhibitor and urease inhibitor (NIUI), and no nitrogen fertilizer (NN). The results showed that the yields under CN, SLN and NIUI treatments were 9618, 9376 and 9645 kg·hm-2, respectively. Compared with CN treatment, SLN increased soil N2O emission in the growing season and decreased N2O emission in the non-growing season. The cumulative N2O emission flux of NIUI treatment was 39.0% lower than that of CN. There were no significant differences in the annual cumulative CO2 emission flux among the treatments. The spring maize field in Northeast China was a weak CH4 sink. NIUI treatment promoted soil CH4 absorption in maize growing season compared with CN treatment. In summary, urea plus nitrification inhibitor and urease inhibitor could significantly reduce soil greenhouse gas emissions with high yield of maize.

Effect of plough pan thickness on crop growth parameters, nitrogen uptake and greenhouse gas (CO2 and N2O) emissions in a wheat-maize double-crop rotation in the Northern China Plain: A one-year study

Plough pan can affect crop growth, nutrient uptake and the fates of substances in the environment. To determine the effects of plough pan thickness on crop and environment, a field survey and a field experiment were conducted on a typical calcareous fluvo-aquic soil in a winter wheat-summer maize rotation system in Northern China Plain from 2014 to 2016. Specifically, the thickness of plough pans was surveyed in 108 field plots in 2014, and then based on the survey results a field experiment was established to study the effects of different plough pan thicknesses (PP15: 15 cm of plough pan; PP10: 10 cm of plough pan; PP5: 5 cm of plough pan; PP0: 0 cm of plough pan) on crop growth, nitrogen (N) utilization and the environment. The survey showed that the thickness of topsoil averaged at 14.7 cm, and the plough pan was approximately 15 cm deep. The plough pan was found at 76% of the survey locations, and it was distributed commonly from 15 to 30 cm beneath the soil surface. Breaking the original plough pan partially or completely could promote the net photosynthesis rate, leaf water use efficiency, crop yield, and N use efficiency, decrease N2O emission, but increase CO2 emission. Among all treatments, breaking plough pans completely (PP0) and by 2/3 (PP5) resulted in best crop performance, whose photosynthetic parameters (especially net photosynthetic rate and leaf water use efficiency) were significantly higher than PP10 and PP15. For both wheat and maize, PP5 resulted in greater yield (7 130 kg ha−1 for wheat and 8 240 kg ha−1 for maize) than other treatments. Although it did not differ with PP0 significantly, PP5 had significantly higher N uptake (410 kg ha−1) and N use efficiency (40.1%) than PP10 and PP15. The magnitude of N2O emission peak decreased with an increasing degree of plough pan breakage. The cumulative N2O emission and intensity in PP5 was obviously lower than that in PP10 and PP15. Annual cumulative CO2 emission did not differ significantly among PP5, PP10 and PP15. Net ecosystem productivity (NEP) of the rotation system increased as the thickness of plough pan decreased, so PP5 had relative higher NEP (9 740 kg C ha−1) than PP10 and PP15. Thus, considering better crop growth, higher yield, optimized N utilization, lower N2O and CO2 emissions, as well as higher NEP and less mechanical costs, breaking the original plough pan partially is a good choice to ameliorating the plough pan restrictions in the Northern China Plain.

Towards a baseline for reducing the carbon budget in sugarcane: three years of carbon dioxide and methane emissions quantification

Sugarcane straw burning or removal and N fertilization are management practices that modify the input of carbon (C) to the soil affecting greenhouse gases emissions and the potential of the soil for C sequestration. This study aimed to determine the effect of post-harvest straw burning and synthetic N fertilization on the dynamics of CO2 and CH4 fluxes in the sugarcane-soil system of Tucuman, Argentina; it also compared these emissions with those of a native forest and discussed a theoretical soil C balance based on C emissions. Close-vented chambers were used to capture CO2 and CH4 during three consecutive growing seasons. The higher CO2 emissions coincided with the period of high soil and air temperatures and rainfalls. There was not a clear pattern in the dynamics of CH4 flux for all sugarcane treatments, while the native forest consistently captured CH4; however, the cumulative CH4 flows were negligible in term of C mass. Annual cumulative CO2 emissions were 12.4–61.4 and 5.9–51.5% higher (for N-fertilized and unfertilized treatments, respectively) when straw was not burned regarding to the burned treatment. However, C losses -as CO2 emissions- in unburnt treatments were lower than the C input from straw and roots, while C losses in burnt treatments were higher than C input from straw and roots. The soil-sugarcane system of Tucuman has a potential C sequestration estimated of 2.03 Mg of C ha−1 yr−1. The results of this manuscript highlighted the importance of preserving straw as a way to maintain or increase soil organic carbon. They also demonstrated the importance of considering management practices when measuring CO2 fluxes during the crop cycle for determining the soil C balance.

Soil carbon dioxide emissions due to oxidative peat decomposition in an oil palm plantation on tropical peat

Soil carbon dioxide (CO2) efflux was measured continuously for two years using an automated chamber system in an oil palm plantation on tropical peat. This study investigated the factors controlling the CO2 efflux and quantified the annual cumulative CO2 emissions through soil respiration and heterotrophic respiration, which is equivalent to oxidative peat decomposition. Soil respiration was measured in close-to-tree (<2.5m, CT) and far-from-tree (>3m, FT) plots, and heterotrophic respiration was measured in root-cut (RC) plots by a trenching method. The daily mean CO2 efflux values (mean±1 standard deviation) were 2.80±2.18, 1.59±1.18, and 1.94±1.58μmolm−2s−1 in the CT, FT, and RC plots, respectively. Daily mean CO2 efflux increased exponentially as the groundwater level or water-filled pore space decreased, indicating that oxidative peat decomposition and gas diffusion in the soil increased due to enhanced aeration resulting from lower groundwater levels. Mean annual gap-filled CO2 emissions were 1.03±0.53, 0.59±0.26, and 0.69±0.21kgCm−2 yr−1 in the CT, FT, and RC plots, respectively. Soil CO2 emissions were significantly higher in the CT plots (P<0.05), but did not differ significantly between the FT and RC plots. This implies that root respiration was negligible in the FT plots. Heterotrophic respiration accounted for 66% of soil respiration. Annual CO2 emissions through both soil and heterotrophic respiration were smaller than those of other oil palm plantations on tropical peat, possibly due to the higher groundwater levels, land compaction, and continuous measurement of soil CO2 efflux in this study. Mean annual total subsidence was 1.55 to 1.62cmyr−1, of which oxidative peat decomposition accounted for 72 to 74%. In conclusion, water management to raise groundwater levels would mitigate soil CO2 emissions from oil palm plantations on tropical peatland.

Soil CO2 emissions from different slope gradients and positions in the semiarid Loess Plateau of China

Knowledge of CO2 emissions under different slope gradients and positions and its controlling factors is critical in accurately estimating CO2 emissions and carbon cycling on the slopes of eroded regions. In this study, three east-facing plots of 100m2 (20m×5m) with a slope gradient of 0.5° (S0.5), 1° (S1), and 3° (S3) were established in an eroded gully of the semi-arid Loess Plateau, China. The CO2 emission, temperature, moisture, runoff, sediment, fine root biomass and grain yield of these three plots were measured from October 2013 to September 2015 to investigate the relationship between slope gradients and soil CO2 emissions. The results showed that the mean annual cumulative CO2 emissions at S1 and S3 (731.0±65.1 and 628.3±74.8gCm−2year−1) were about 13.4% and 25.5% lower than that at S0.5 (843.7±84.9gCm−2year−1). The CO2 emissions were higher at bottom slope than at upper slope, with an increase of 26.2% at S3, 22.9% at S1 and 14.5% at S0.5, respectively. The mean soil moisture ranged from 40.8% to 44.8% water-filled pore space (WFPS) among the slope gradients, and from 35.8% to 45.6% WFPS among the slope positions. There was a significant difference in mean fine root biomass among different slope gradients (S0.5>S1> S3,P<0.05), but no significant difference among different slope positions. The mean soil organic carbon (SOC) ranged from 8.8gkg−1 at S3 to 9.9gkg−1 at S0.5, and that at the bottom and middle slope were higher than that at the upper slope at S1 and S3. Slope differentiated soil moisture content and redistribution, and the thus derived spatial differences in fine root biomass and crop yields, was the major factor influencing the soil CO2 emissions among slope gradients and positions. Slope gradients and positions should be considered when estimating soil CO2 emissions and carbon cycling in the complex and fragmented topography regions.

Impact of Grazing Intensity and Seasons on Greenhouse Gas Emissions in Tropical Grassland

Greenhouse gases (GHG) can be affected by grazing intensity, soil, and climate variables. This study aimed at assessing GHG emissions from a tropical pasture of Brazil to evaluate (i) how the grazing intensity affects the magnitude of GHG emissions; (ii) how season influences GHG production and consumption; and (iii) what are the key driving variables associated with GHG emissions. We measured under field conditions, during two years in a palisade-grass pasture managed with 3 grazing intensities: heavy (15 cm height), moderate (25 cm height), and light (35 cm height) N2O, CH4 and CO2 fluxes using static closed chambers and chromatographic quantification. The greater emissions occurred in the summer and the lower in the winter. N2O, CH4, and CO2 fluxes varied according to the season and were correlated with pasture grazing intensity, temperature, precipitation, % WFPS (water-filled pores space), and soil inorganic N. The explanatory variables differ according to the gas and season. Grazing intensity had a negative linear effect on annual cumulative N2O emissions and a positive linear effect on annual cumulative CO2 emissions. Grazing intensity, season, and year affected N2O, CH4, and CO2 emissions. Tropical grassland can be a large sink of N2O and CH4. GHG emissions were explained for different key driving variables according to the season.

CO2 Emission Increases with Damage Severity in Moso Bamboo Forests Following a Winter Storm in Southern China.

Despite the prevalence of disturbances in forests, the effects of disturbances on soil carbon processes are not fully understood. We examined the influences of a winter storm on soil respiration and labile soil organic carbon (SOC) of a Moso Bamboo (Phyllostachys heterocycle) plantation in the Wuyi Mountains in Southern China from May 2008 to May 2009. We sampled stands that were damaged at heavy, moderate, and light levels, which yielded aboveground biomass inputs to the soil at 22.12 ± 0.73 (mean ± 1 s.e.m.), 10.40 ± 1.09, and 5.95 ± 0.73 Mg per hectare, respectively. We found that soil respiration rate and annual cumulative CO2 emissions were significantly higher in heavily damaged sites than moderately and lightly damaged sites. Soil temperature was the most important environmental factor affecting soil respiration rate across all studied stands. However, soil respiration sensitivity to temperature (Q10) decreased in heavily damaged sites. Microbial biomass carbon and its proportion to total SOC increased with damage intensity. Soil respiration rate was positively correlated to microbial biomass carbon and soil moisture. Our results indicated that the increase of soil respiration following canopy disturbance from winter storm resulted from increased microbial biomass carbon, soil moisture, and temperature.

Life Cycle Inventory Analysis for a Small-Scale Trawl Fishery in Sendai Bay, Japan

A reduced environmental burden, while maintaining high quality and low cost, has become an important factor for achieving sustainability in the fisheries sector. The authors performed life cycle inventory (LCI) analysis targeting the fish production for a small-scale trawl fishery including small trawlers operating in Sendai Bay, Japan. The average annual cumulative CO2 emissions for the small trawlers were 4.7 ton-CO2/ton-product and 8.3 ton-CO2/million Japanese yen (JPN). Total fuel consumption contributed to 97% of the global warming potential. The range of variation in the basic unit of CO2 for each small trawler was also elucidated. Energy conservation through lower fuel consumption is shown to be an effective measure for reducing CO2 in a small trawler fishery. Moreover, the authors examined the system boundary, the determination of the functional unit, and the allocation method of applying LCI analysis to fisheries. Finally, the economy and environment of small trawler fisheries are discussed as important factors for sustainable fisheries, and the life cycle approach is applied to a new fishery type in Japan.

Greenhouse Gas Emissions Dynamics as Influenced by Corn Residue Removal in Continuous Corn System

The removal of corn residue for bioethanol may require changes in current tillage and fertilization practices to minimize potential alterations to the soil environment that may lead to increase in greenhouse gas (GHG) emission. The objectives of this study were to examine how tillage, N fertilization rates, residue removal, and their interactions affect CO2, and N2O soil surface emissions. Greater CO2 emission coincided with higher soil temperatures typically observed with conventional tillage (CT) compared with no-tillage (NT), resulting in greater annual cumulative CO2 emission in CT (18.1 CO2 Mg ha−1 yr−1) compared with NT (16.2 CO2 Mg ha−1 yr−1) in 2009 and 2010 across sites. However, drier soil conditions during the growing season in 2011 lead to higher soil temperatures compared with 2009 and 2010. Consequently, annual cumulative CO2 emission from NT with 50 and 100% residue removal was (19.5 CO2 Mg ha−1 yr−1) greater than that from CT (17.8 CO2 Mg ha−1 yr−1) across all residue removal rates and from NT (17.5 CO2 Mg ha−1 yr−1) with no residue removal, respectively across all N rates in the Ames central site (AC) in 2011. In the Armstrong southwest site (ASW) site, there were no significant differences between tillage or residue removal rates for annual cumulative CO2 emission (19.9 CO2 Mg ha−1 yr−1) in 2011. Although N2O emission was considerably lower than CO2 emission, differences in N fertilization rates did have a significant impact on global warming potential once these gases were converted on the basis of their radiative forcing of the atmosphere.

施肥方式对紫色土土壤异养呼吸的影响

Recent studies have shown that soil respiration is the critical importance in determining the carbon balance of terrestrial ecosystems. Respiration from soils is comprised of both the heterotrophic respiration of microorganisms( soil bacteria,fungi,and fauna) and autotrophic respiration from roots and mycorrhizae. Precise assessment of these components is important for calculating the carbon budgets of vegetation and the turnover rate of soil organic matter,as well as for understanding sources and sinks of carbon in terrestrial ecosystems in the face of global climate change. Although soil heterotrophic respirations have received considerable attention in recent decades,much less is known about the effects of various natural or artificial factors such as temperature,precipitation or fertilization etc. on it. The field study was conducted at a sloping cropland in Yanting Agro-ecological Station of Purple Soil,Chinese Academy of Science under Chinese Ecosystem Research Network( CERN),situated at N31°16°,E105°28',with the altitude of 400 to 600 meters in the middle of Sichuan Basin,where a set of long-term research plots is located. Three plots were randomly assigned to oneof the following treatments: conventional chemical fertilizer( NPK),organic manure( pig slurry,OM) and crop residue with chemical fertilizer( RSDNPK). Total nitrogen for each fertilization treatment was applied at the same rate with 130 and150 kgN /hm2 for wheat and maize seasons,respectively. The results showed that soil heterotrophic respiration exhibited pronounced seasonal variations that clearly reflected those of soil temperature,with minimum values in winter and maximum values in summer. There was a pulse of soil heterotrophic respiration induced by fertilization at the 5th day after fertilization. The peak rate for OM treatment was 2356. 8 mgCO2m-2h-1and it was significantly higher than that for both RSDNPK and NPK treatments( P0. 01). Meanwhile,the respiration rate and the annual cumulative CO2 emission in OM and RSDNPK treatments were higher than those in NPK treatment. During wheat growing season,average respiration rate for NPK,OM and RSDNPK treatments were 212. 9,285. 8 and 305. 8 mgCO2m-2h-1,respectively,which were all lower than that in maize growing season. The cumulative soil CO2 emissions from NPK,OM and RSDNPK were 255. 1,342. 3and 369. 5 gC /m2 for wheat season,and 344. 7,542. 8 and 376. 9 gC /m2 for maize season,while 599. 8,885. 1 and 746. 4gCm-2for the whole year,respectively. The results implied that lower C /N ratio organic material was the primary driving force for increasing soil heterotrophic rate and cumulative soil CO2 emissions. The values of temperature sensitivity( Q10)for soil heterotrophic respiration in wheat season and maize season were also measured. The results showed that Q10 values in wheat season always higher than that in maize season at all plots. During the whole experiment time,the magnitudes of Q10 both followed the order of OM NPK RSDNPK,which was clearly reflected that Q10 was sensitive to lower C /N organic materials. Q10 values obtained from soil temperature at soil surface( 0 cm) and soil 5 cm depth in OM and RSDNPK were2. 64,2. 77 and 1. 88,1. 99,respectively. It indicated that the Q10 values for soil heterotrophic respiration rates were higher at lower temperatures and lower at higher temperature.