Assessment of the methane mitigation potentials of alternative water regimes in rice fields using a process‐based biogeochemistry model

Rice production is a substantial source of atmospheric CH₄, which is second only to CO₂ as a contributor to global warming. Since CH₄ is produced in anaerobic soil environments, water management is expected to be a practical measure to mitigate CH₄ emissions. In this study, we used a process‐based biogeochemistry model (DNDC‐Rice) to assess the CH₄ mitigation potentials of alternative water regimes (AWR) for rice fields at a regional scale. Before regional application, we tested DNDC‐Rice using site‐scale data from three rice fields in Japan with different water regimes. The observed CH₄ emissions were reduced by drainage of the fields, but were enhanced by organic amendments. DNDC‐Rice gave acceptable predictions of variation in daily CH₄ fluxes and seasonal CH₄ emissions due to changes in the water regime. For regional application, we constructed a GIS database at a 1 × 1 km mesh scale that contained data on rice field area, soil properties, daily weather, and farming management of each cell in the mesh, covering 3.2% of the rice fields in Japan's Hokkaido region. We ran DNDC‐Rice to simulate CH₄ emissions under five simulated water regimes: the conventional water regime and four AWR scenarios with gradually increasing drainage. We found that AWR can reduce CH₄ emission by up to 41% compared with the emission under conventional water regime. Including the changes in CO₂ and nitrous oxide emissions, potential mitigation of greenhouse gas (GHG) was 2.6 Mg CO₂ Eq. ha^?1 yr^?1. If this estimate is expanded to Japan's total rice fields, expected GHG mitigation is 4.3 Tg CO₂ Eq. yr^?1, which accounts for 0.32% of total GHG emissions from Japan. For a reliable national‐scale assessment, however, databases on soil, weather, and farming management must be constructed at a national scale, as these factors are widely variable between regions in Japan.     

Characterizing spatiotemporal dynamics of methane emissions from rice paddies in Northeast China from 1990 to 2010

Background

Rice paddies have been identified as major methane (CH₄) source induced by human activities. As a major rice production region in Northern China, the rice paddies in the Three-Rivers Plain (TRP) have experienced large changes in spatial distribution over the recent 20 years (from 1990 to 2010). Consequently, accurate estimation and characterization of spatiotemporal patterns of CH₄ emissions from rice paddies has become an pressing issue for assessing the environmental impacts of agroecosystems, and further making GHG mitigation strategies at regional or global levels.

Methodology/Principal Findings

Integrating remote sensing mapping with a process-based biogeochemistry model, Denitrification and Decomposition (DNDC), was utilized to quantify the regional CH₄ emissions from the entire rice paddies in study region. Based on site validation and sensitivity tests, geographic information system (GIS) databases with the spatially differentiated input information were constructed to drive DNDC upscaling for its regional simulations. Results showed that (1) The large change in total methane emission that occurred in 2000 and 2010 compared to 1990 is distributed to the explosive growth in amounts of rice planted; (2) the spatial variations in CH₄ fluxes in this study are mainly attributed to the most sensitive factor soil properties, i.e., soil clay fraction and soil organic carbon (SOC) content, and (3) the warming climate could enhance CH₄ emission in the cool paddies.

Conclusions/Significance

The study concluded that the introduction of remote sensing analysis into the DNDC upscaling has a great capability in timely quantifying the methane emissions from cool paddies with fast land use and cover changes. And also, it confirmed that the northern wetland agroecosystems made great contributions to global greenhouse gas inventory.     

Constraining estimates of global soil respiration by quantifying sources of variability

Quantifying global soil respiration (R_SG) and its response to temperature change are critical for predicting the turnover of terrestrial carbon stocks and their feedbacks to climate change. Currently, estimates of R_SG range from 68 to 98 Pg C year^?1, causing considerable uncertainty in the global carbon budget. We argue the source of this variability lies in the upscaling assumptions regarding the model format, data timescales, and precipitation component. To quantify the variability and constrain R_SG, we developed R_SG models using Random Forest and exponential models, and used different timescales (daily, monthly, and annual) of soil respiration (R_S) and climate data to predict R_SG. From the resulting R_SG estimates (range = 66.62–100.72 Pg), we calculated variability associated with each assumption. Among model formats, using monthly R_S data rather than annual data decreased R_SG by 7.43–9.46 Pg; however, R_SG calculated from daily R_S data was only 1.83 Pg lower than the R_SG from monthly data. Using mean annual precipitation and temperature data instead of monthly data caused +4.84 and ?4.36 Pg C differences, respectively. If the timescale of R_S data is constant, R_SG estimated by the first‐order exponential (93.2 Pg) was greater than the Random Forest (78.76 Pg) or second‐order exponential (76.18 Pg) estimates. These results highlight the importance of variation at subannual timescales for upscaling to R_SG. The results indicated R_SG is lower than in recent papers and the current benchmark for land models (98 Pg C year^?1), and thus may change the predicted rates of terrestrial carbon turnover and the carbon to climate feedback as global temperatures rise.     

Regional application of PnET-N-DNDC for estimating the N2O source strength of tropical rainforests in the Wet Tropics of Australia

In contrast to the significant importance of tropical rainforest ecosystems as one of the major sources within the global atmospheric N₂O budget (2.2–3.7 Tg N yr^?1), regional estimates of their N₂O source strength are still limited and highly uncertain. To contribute toward more reliable estimates of the N₂O source strength of tropical rainforest ecosystems on a regional scale, we modified a process‐oriented biogeochemical model, PnET‐N‐DNDC, and parameterized it to simulate C and N turnover and associated N₂O emissions in and from tropical rainforest ecosystems. Model modifications included: (1) new parameterizations associated with plant physiology and soil hydrology and the addition of algorithms relating daily leaf litterfall to water stress as well as to daily rainfall to account for the effects of heavy rainfall damage; (2) the development of a denitrifier activity index that depends on soil moisture conditions and influences N turnover by denitrification; and (3) the addition of a biological N fixation algorithm. Daily simulated N₂O emissions based on site data were in good agreement (model efficiencies up to 0.83) with field observations in the Wet Tropics of Australia and Costa Rica. The model was even able to reproduce the highly dynamic pattern of N₂O emissions with short‐term increases during the wet season. Sensitivity analyses demonstrated that the PnET‐N‐DNDC model was sensitive to changes in soil properties such as pH, clay content, soil organic carbon and climatic factors such as rainfall and temperature. By linking the PnET‐N‐DNDC model to a geographic information systems database, tropical rainforests in a 9000 km² area of the Wet Tropics of Australia are estimated to emit 962 t N₂O‐N yr^?1 (2.4 kg N₂O‐N ha^?1 yr^?1) between July 1997 and June 1998.     

The carbon implications of large‐scale afforestation of agriculturally marginal land with short‐rotation willow in Saskatchewan

Afforestation with short‐rotation coppice (SRC) willow plantations for the purpose of producing bioenergy feedstock was contemplated as one potential climate change mitigation option. The objectives of this study were to assess the magnitude of this mitigation potential by addressing: (i) the land area potentially available for SRC systems in the province of Saskatchewan, Canada; (ii) the potential biomass yields of SRC plantations; and (iii) the carbon implications from such a large‐scale afforestation program. Digital soils and land‐use data were used to identify, map, and group into clusters of similar polygons 2.12 million hectares (Mha) of agriculturally marginal land that was potentially suitable for willow in the Boreal Plains and Prairies ecozones in Saskatchewan. The Physiological Principles in Predicting Growth (3PG) model was calibrated with data from SRC experiments in Saskatchewan, to quantify potential willow biomass yields, and the Carbon Budget Model of the Canadian Forest Sector (CBM‐CFS3), was used to simulate stand and landscape‐level C fluxes and stocks. Short‐rotation willow plantations managed in 3 year rotations for seven consecutive harvests (21 years) after coppicing at Year 1 produced about 12 Mg ha^?1 yr^?1 biomass. The more significant contribution to the C cycle was the cumulative harvest. After 44 years, the potential average cumulative harvested biomass C in the Prairies was 244 Mg C ha^?1 (5.5 Mg C ha^?1 yr^?1) about 20% higher than the average for the Boreal Plains, 203 Mg C ha^?1 (4.6 Mg C ha^?1 yr^?1). This analysis did not consider afforestation costs, rate of establishment of willow plantations, and other constraints, such as drought and disease effects on biomass yield. The results must therefore be interpreted as a biophysical mitigation potential with the technical and economic potential being both lower than our estimates. Nevertheless, short‐rotation bioenergy plantations offer one potential mitigation option to reduce the rate of CO₂ accumulation in the earth's atmosphere and further research is needed to operationalise such a mitigation effort.     

Litterfall and forest floor dynamics in Eucalyptus pilularis forests

Abstract Calculations relating the input of litterfall to litter or forest floor mass in forests generally assume that the forest floor reaches an equilibrium state. Based on this assumption, a decomposition factor (k) can be calculated. In the present paper, this basic assumption is questioned and the implications considered. Data on litterfall and forest floor from blackbutt (Eucalyptus pilularis) regrowth forests and plantations were collated from publications and the authors' studies to evaluate both assumptions and relationships. Blackbutt grows over a wide environmental range but its main distribution is in mild temperate to subtropical conditions. Data were from single‐plot studies, sequential studies and chronosequences in both plantations and native regrowth forests. Stands ranged in age from 3 years to maturity in the case of pure, or almost pure blackbutt stands. The forest floor biomass increased up to 12.3 tha^?1 at 33 years of age with no evidence of steady state. Litterfall increased up to 7.8 t ha^?1 year^?1 and was correlated with crown biomass. Regrowth stands were relatively undisturbed and more than 20 years of age, and litterfall ranged from 4.1 to 11.6 tha^?1 year^?1 and was correlated with stand basal area. Forest floor mass in regrowth forests was variable between the different aged stands but did not exceed 18 tha^?1, and there was no evidence that steady state was achieved. The forest floor mass was related to, and approximately 1.7 times the input of litterfall. Although the assumption of steady state was not valid, a k' factor was estimated that related input to forest floor mass and this was relatively constant across all stands and correlated with generalized environmental data. Although assumptions of forest floor equilibrium cannot be supported for E. pilularis, it still should be possible to predict forest floor mass and decomposition from stand conditions and general environmental data.     

Gene flow of the canker pathogen Botryosphaeria australis between Eucalyptus globulus plantations and native eucalypt forests in Western Australia

Abstract The eucalypt plantation industry in Western Australia provides a unique opportunity to study the movement of pathogens between closely related host taxa. Eucalyptus globulus, a native to Tasmania and south‐eastern Australia, is the predominant species in Western Australian plantations, often being planted adjacent to native forest containing Eucalyptus marginata and Eucalyptus diversicolor. Since the commencement of the plantation industry 20 years ago, several fungal species, previously known only to eastern Australia or overseas, have been reported on E. globulus in Western Australia. Botryosphaeria australis is a newly described species, recently found causing cankers on Acacia spp. in eastern Australia. However, during a routine survey, B. australis was found to be the predominant species associated with E. globulus plantations and native Eucalyptus spp. in Western Australia. In this study, six short simple repeat markers were used to evaluate genetic diversity and gene flow between collections of B. australis from native eucalypt forest and E. globulus plantations at two locations in south‐western Australia. In both cases, there was no restriction to gene flow between the plantations and the adjacent native forest. Botryosphaeria australis has now been isolated from a wide range of hosts across south‐western Australia and was not isolated from E. globulus in Tasmania or South Australia. This extensive distribution and host range suggests B. australis is native to Western Australia. This study demonstrates the ability of a pathogen to move between plantation and forests.     

Annual wood production in a tropical rain forest in NE Costa Rica linked to climatic variation but not to increasing CO2

Increased atmospheric [CO₂] could theoretically lead to increased forest productivity (‘CO₂ fertilization’). This mechanism was hypothesized as a possible explanation for biomass increases reported from tropical forests in the last 30+ years. We used unique long‐term records of annually measured stands (eighteen 0.5 ha plots, 10 years) and focal tree species (six species, 24 years) to assess the effects of rainfall, temperature, and atmospheric [CO₂] on annual wood production in a neotropical rain forest. Our study area was a meso‐scale section (600 ha) of old‐growth Tropical Wet Forest in NE Costa Rica. Using the repeated remeasurements we directly assessed the relative effects of interannual climatic variation and increasing atmospheric [CO₂] on wood production. A remarkably simple two‐factor model explained 91% of the interannual variance in stand‐level tree growth; the statistically independent factors were total dry season rainfall (positive effect, r²=0.85) and night‐time temperature (negative effect, r²=0.42). Stand‐level tree mortality increased significantly with night‐time temperature. After accounting for dry season rainfall and night‐time temperature, there was no effect of annual [CO₂] on tree growth in either the stand or focal species data. Tree growth in this Tropical Wet Forest was surprisingly sensitive to the current range of dry season conditions and to variations in mean annual night‐time temperature of 1–2°. Our results suggest that wood production in the lowland rainforests of NE Costa Rica (and by extension in other tropical regions) may be severely reduced in future climates that are only slightly drier and/or warmer.     

Soil carbon changes under Miscanthus driven by C4 accumulation and C3 decompostion – toward a default sequestration function

Bioenergy has to meet increasing sustainability criteria in the EU putting conventional bioenergy crops under pressure. Alternatively, perennial bioenergy crops, such as Miscanthus, show higher greenhouse gas savings with similarly high energy yields. In addition, Miscanthus plantations may sequester additional soil organic carbon (SOC) to mitigate climate change. As the land‐use change in cropland to Miscanthus involves a C₃‐C₄ vegetation change (VC), it is possible to determine the dynamic of Miscanthus‐derived SOC (C₄ carbon) and of the old SOC (C₃ carbon) by the isotopic ratio of ¹³C to ¹²C. We sampled six croplands and adjacent Miscanthus plantations exceeding the age of 10 years across Europe. We found a mean C₄ carbon sequestration rate of 0.78 ± 0.19 Mg ha^?1 yr^?1, which increased with mean annual temperature. At three of six sites, we found a significant increase in C₃ carbon due to the application of organic fertilizers or difference in baseline SOC, which we define as non‐VC‐induced SOC changes. The Rothamsted Carbon Model was used to disentangle the decomposition of old C₃ carbon and the non‐VC‐induced C₃ carbon changes. Subsequently, this method was applied to eight more sites from the literature, resulting in a climate‐dependent VC‐induced SOC sequestration rate (0.40 ± 0.20 Mg ha^?1 yr^?1), as a step toward a default SOC change function for Miscanthus plantations on former croplands in Europe. Furthermore, we conducted a SOC fractionation to assess qualitative SOC changes and the incorporation of C₄ carbon into the soil. Sixteen years after Miscanthus establishment, 68% of the particulate organic matter (POM) was Miscanthus‐derived in 0–10 cm depth. POM was thus the fastest cycling SOC fraction with a C₄ carbon accumulation rate of 0.33 ± 0.05 Mg ha^?1 yr^?1. Miscanthus‐derived SOC also entered the NaOCl‐resistant fraction, comprising 12% in 0–10 cm, which indicates that this fraction was not an inert SOC pool.     

LAND USE AND SUMMER BIRD POPULATIONS IN NORTHWESTERN GALICIA, SPAIN

Summer bird populations were studied in ten sites: two heathlands, two maritime pine Pinus pinaster plantations, one, four, seven and 13-year-old eucalypt Eucalyptus globulus plantations, one climax oak Quercus robur woodland, and a farmland area in northwestern Galicia, Spain. The farmland and oak wood contained the greatest number of species (24 and 17 respectively) while the one and four-year-old eucalypt stands contained the fewest species (four and six respectively). Avian density was highest in the oak wood (93 birds/ 10 ha) and lowest in a heathland site, the four and one-year-old eucalypt stands (26,13, and seven bird/10 ha respectively). The wren was the most widespread and dominant species occurring in all study areas except the one-year-old eucalypt stand. Mean bird species diversity for the four eucalypt stands was significantly lower than mean bird species diversity for the other wooded habitats. The avian communities of the heathlands, maritime pine and eucalypt plantations, in contrast to the oak wood and farmland, show an excessively high dominance of one species. Using avian dominance as a biological index of habitat perturbation suggests that over half the landscape (4000 km²) in northwestern Galicia is suffering from chronic stress. The newest stress to the avifauna in a long history of land exploitation by man is the importation and cultivation on grand scale of eucalypts. Balancing this tendency, traditional, small-scale farming on the mountainous terrain leads to the development of many tiny parcels whose average size is 0.28 ha; this in turn creates much ‘edge’ in hedgerow which serves to maintain a relatively rich avian species diversity in farmland.     

Conversion of open lands to short‐rotation woody biomass crops: site variability affects nitrogen cycling and N2O fluxes in the US Northern Lake States

Short‐rotation woody biomass crops (SRWC) have been proposed as a major feedstock source for bioenergy generation in the Northeastern US. To quantify the environmental effects and greenhouse gas (GHG) balance of crops including SRWC, investigators need spatially explicit data which encompass entire plantation cycles. A knowledge gap exists for the establishment period which makes current GHG calculations incomplete. In this study, we investigated the effects of converting pasture and hayfields to willow (Salix spp.) and hybrid‐poplar (Populus spp.) SRWC plantations on soil nitrogen (N) cycling, nitrous oxide (N₂O) emissions, and nitrate (NO₃^?) leaching at six sites of varying soil and climate conditions across northern Michigan and Wisconsin, following these plantations from pre conversion through their first 2 years. All six sites responded to establishment with increased N₂O emissions, available inorganic N, and, where it was measured, NO₃^? leaching; however, the magnitude of these impacts varied dramatically among sites. Soil NO₃^? levels varied threefold among sites, with peak extractable NO₃^? concentrations ranging from 15 to 49 g N kg^?1 soil. Leaching losses were significant and persisted through the second year, with 44–112 kg N ha^?1 leached in SRWC plots. N₂O emissions in the first growing season varied 30‐fold among sites, from 0.5 to 17.0 Mg‐CO_2eq ha^?1 (carbon dioxide equivalents). N₂O emissions over 2 years resulted in N₂O emissions due to plantation establishment that ranged from 0.60 to 22.14 Mg‐CO_2eq ha^?1 above baseline control levels across sites. The large N losses we document herein demonstrate the importance of including direct effects of land conversion in life‐cycle analysis (LCA) studies of SRWC GHG balance. Our results also demonstrate the need for better estimation of spatial variability of N cycling processes to quantify the full environmental impacts of SRWC plantations.     

Do the energy fluxes and surface conductance of boreal coniferous forests in Europe scale with leaf area?

Earth observing systems are now routinely used to infer leaf area index (LAI) given its significance in spatial aggregation of land surface fluxes. Whether LAI is an appropriate scaling parameter for daytime growing season energy budget, surface conductance (G_s), water‐ and light‐use efficiency and surface–atmosphere coupling of European boreal coniferous forests was explored using eddy‐covariance (EC) energy and CO₂ fluxes. The observed scaling relations were then explained using a biophysical multilayer soil–vegetation–atmosphere transfer model as well as by a bulk G_s representation. The LAI variations significantly alter radiation regime, within‐canopy microclimate, sink/source distributions of CO₂, H₂O and heat, and forest floor fluxes. The contribution of forest floor to ecosystem‐scale energy exchange is shown to decrease asymptotically with increased LAI, as expected. Compared with other energy budget components, dry‐canopy evapotranspiration (ET) was reasonably ‘conservative’ over the studied LAI range 0.5–7.0 m² m^?2. Both ET and G_s experienced a minimum in the LAI range 1–2 m² m^?2 caused by opposing nonproportional response of stomatally controlled transpiration and ‘free’ forest floor evaporation to changes in canopy density. The young forests had strongest coupling with the atmosphere while stomatal control of energy partitioning was strongest in relatively sparse (LAI ~2 m² m^?2) pine stands growing on mineral soils. The data analysis and model results suggest that LAI may be an effective scaling parameter for net radiation and its partitioning but only in sparse stands (LAI <3 m² m^?2). This finding emphasizes the significance of stand‐replacing disturbances on the controls of surface energy exchange. In denser forests, any LAI dependency varies with physiological traits such as light‐saturated water‐use efficiency. The results suggest that incorporating species traits and site conditions are necessary when LAI is used in upscaling energy exchanges of boreal coniferous forests.     

Determinants of soil organic carbon sequestration and its contribution to ecosystem carbon sinks of planted forests

The area of forest established through afforestation/reforestation has been increasing on a global scale, which is particularly important as these planted forests attenuate climate change by sequestering carbon. However, the determinants of soil organic carbon (SOC) sequestration and their contribution to the ecosystem carbon sink of planted forests remain uncertain. By using globally distributed data extracted from 154 peer‐reviewed publications and a total of 355 sampling points, we investigated above‐ground biomass carbon (ABC) sequestration and SOC sequestration across three different climatic zones (tropical, warm temperate, and cold temperate) through correlation analysis, regression models, and structural equation modeling (SEM). We found that the proportion of SOC sequestration in the ecosystem C sequestration averaged 14.1% globally, being the highest (27.0%) in the warm temperate and the lowest (10.7%) in the tropical climatic zones. The proportion was mainly affected by latitude. The sink rate of ABC (R_ABC) in tropical climates (2.48 Mg C ha^?1 year^?1) and the sink rate of SOC (R_SOC) in warm temperate climates (0.96 Mg C ha^?1 year^?1) were higher than other climatic zones. The main determinants of R_SOC were the number of frost‐free days, latitude, mean annual precipitation (MAP), and SOC density (SOCD) at the initial observation; however, these variables depended on the climatic zone. According to the SEM, frost‐free period, mean annual temperature (MAT) and MAP are the dominant driving factors affecting R_SOC in Chinese plantations. MAT has a positive effect on R_SOC, and global warming may increase R_SOC of temperate plantations in China. Our findings highlight the determinants of SOC sequestration and quantitatively reveal the substantial global contribution of SOC sequestration to ecosystem carbon sink provided by planted forests. Our results help managers identify and control key factors to increase carbon sequestration in forest ecosystems.     

Quantifying above‐ and belowground biomass carbon loss with forest conversion in tropical lowlands of Sumatra (Indonesia)

Natural forests in South‐East Asia have been extensively converted into other land‐use systems in the past decades and still show high deforestation rates. Historically, lowland forests have been converted into rubber forests, but more recently, the dominant conversion is into oil palm plantations. While it is expected that the large‐scale conversion has strong effects on the carbon cycle, detailed studies quantifying carbon pools and total net primary production (NPP_total) in above‐ and belowground tree biomass in land‐use systems replacing rainforest (incl. oil palm plantations) are rare so far. We measured above‐ and belowground carbon pools in tree biomass together with NPP_total in natural old‐growth forests, ‘jungle rubber’ agroforests under natural tree cover, and rubber and oil palm monocultures in Sumatra. In total, 32 stands (eight plot replicates per land‐use system) were studied in two different regions. Total tree biomass in the natural forest (mean: 384 Mg ha^?1) was more than two times higher than in jungle rubber stands (147 Mg ha^?1) and >four times higher than in monoculture rubber and oil palm plantations (78 and 50 Mg ha^?1). NPP_total was higher in the natural forest (24 Mg ha^?1 yr^?1) than in the rubber systems (20 and 15 Mg ha^?1 yr^?1), but was highest in the oil palm system (33 Mg ha^?1 yr^?1) due to very high fruit production (15–20 Mg ha^?1 yr^?1). NPP_total was dominated in all systems by aboveground production, but belowground productivity was significantly higher in the natural forest and jungle rubber than in plantations. We conclude that conversion of natural lowland forest into different agricultural systems leads to a strong reduction not only in the biomass carbon pool (up to 166 Mg C ha^?1) but also in carbon sequestration as carbon residence time (i.e. biomass‐C:NPP‐C) was 3–10 times higher in the natural forest than in rubber and oil palm plantations.     

Application of a process‐based model for predicting the productivity of Eucalyptus nitens bioenergy plantations in Spain

The feasibility of using plantation‐grown biomass to fuel bioenergy plants is in part dependent on the ability to predict the capacity of surrounding forests to maintain a sustainable supply. In this study, the potential productivity of Eucalyptus nitens (Deane and Maiden) Maiden plantations grown for bioenergy in a region of north‐west Spain was quantified using the 3‐PG process‐based model. The model was calibrated using detailed measurements from five permanent sample plots and validated using data from thirty‐five additional permanent sample plots; both sets represented the variability of climate and soils of the region. Plot scale analysis showed that the model was able to reasonably estimate above‐ground biomass and water use when compared with the observed data. Using a representative loam soil characteristic, a spatial analysis was then carried out to predict the potential productivity of E. nitens for bioenergy across a potential area for plantation establishment of 2550 km² and to evaluate different management scenarios related to rotation length and stocking. An increase of only 1.9% in mean annual increment (MAI) of above‐ground biomass (W_AGB) was found between stockings of 3000 and 5000 trees ha^?1; for the lower stocking, MAI of W_AGB increased 4% for rotation lengths between 6 and 8 years. Production was reduced by low summer rainfall and to a lesser extent by high summer and low winter temperatures, and vapour pressure deficit. Above‐ground biomass production was higher by around 12% when average rather than actual climate data were applied. The information from this study can be used to optimize forest management, determine regional relative potential productivity and contribute to decision‐making for bioenergy production from E. nitens plantations in north‐west Spain.     

Experimental validation of in silico estimated biomass yields of Pseudomonas putida KT2440

Pseudomonas putida is rapidly becoming a microbial cell platform for biotechnological applications. In order to understand genotype‐phenotype relationships genome scale models represent helpful tools. However, the validation of in silico predictions of genome scale models is a task that is rarely performed. In this study the theoretical biomass yields of Pseudomonas putida KT2440 were estimated for 57 different carbon sources based on a genome scale stoichiometric model applying flux balance analysis. The batch growth of P. putida KT2440 with six individual carbon sources covering the range of maximal to minimal in silico biomass yields (acetate, glycerol, citrate, succinate, malate and methanol, respectively) was studied in a defined mineral medium in a fully controlled stirred‐tank bioreactor on a 3 L scale. The highest growth rate of P. putida KT2440 was measured with succinate as carbon source (0.51 h^?1). Among the 57 carbon sources tested, glycerol resulted in the highest estimated biomass yield (0.61 molC_Biomass molC^?1_Glycerol) which was experimentally confirmed. The comparison of experimental determined biomass yields with a modified version of the model iJP815 showed deviations of only up to 10%. The experimental data generated in this study can also be used in future studies to further improve the genome scale models of P. putida KT2440. Improved models will then help to gain deeper insights in genotype‐phenotype relationships.     

Regional analysis of soil–atmosphere nitrous oxide emissions in the Northern Atlantic Zone of Costa Rica

Regional analysis of greenhouse gas emissions is becoming increasingly important in answering questions related to environmental change, and typically employs a Geographic Information System (GIS) linked with a process‐based simulation model. For the Northern Atlantic Zone (NAZ) in Costa Rica (281 649 ha), a regional analysis of soil–atmosphere nitrous oxide fluxes from the dominant land‐use types forest, cattle pastures, and banana plantations was performed with both deterministic and stochastic variable representations. The stochastic representation accounted for soil and land management variability across nongeoreferenced fields within 1572 georeferenced land units in 13 relevant classes. Per class, frequency distributions of field‐scale fluxes were simulated with a process‐based model and Monte Carlo methods. Stochastic incorporation of both soil and land use variability resulted in areal (i.e. land unit‐scale) fluxes that were 14–22% lower than estimates based on averaged inputs. Soil heterogeneity was dominant. In addition, spatial flux patterns for current (1992) land use and two alternative land‐use scenarios were evaluated using stochastic inputs. With current management, the regional nitrous oxide‐N flux (standard deviation in parentheses) from agricultural land was 0.43 (0.13) Gg y^?1. Replacing natural grasses with mixtures of grasses and N‐fixing species on relevant soil types and introducing different forms of banana plantation management (alternative I) increased the regional flux by 51% to 0.65 (0.22) Gg y^?1. When all natural grasses were replaced by fertilized improved species and allowing different forms of banana plantation management (alternative II), the regional flux increased by 126% to 0.97 (0.68) Gg y^?1. Using the revised IPCC methodology, the 1992 nitrous oxide emission from agriculture in the NAZ was estimated to be 0.32 Gg y^?1. Due to formidable data requirements, regional analysis may not easily be used to produce country‐level estimates. However, regional analysis does provide a valuable benchmark against which the more straightforward IPCC methodology can be evaluated.     

Quantifying the contribution of land use to N<Subscript>2</Subscript>O,NO and CO<Subscript>2</Subscript> fluxes in a montane forest ecosystem of Kenya

Increasing demand for food and fibre by the growing human population is driving significant land use (LU) change from forest into intensively managed land systems in tropical areas. But empirical evidence on the extent to which such changes affect the soil-atmosphere exchange of trace gases is still scarce, especially in Africa. We investigated the effect of LU on soil trace gas production in the Mau Forest Complex region, Kenya. Intact soil cores were taken from natural forest, commercial and smallholder tea plantations, eucalyptus plantations and grazing lands, and were incubated in the lab under different soil moisture conditions. Soil fluxes of nitrous oxide (N₂O), nitric oxide (NO) and carbon dioxide (CO₂) were quantified, and we approximated annual estimates of soil N₂O and NO fluxes using soil moisture values measured in situ. Forest and eucalyptus plantations yielded annual fluxes of 0.3–1.3 kg N₂O–N ha^?1 a^?1 and 1.5–5.2 kg NO–N ha^?1 a^?1. Soils of commercial tea plantations, which are highly fertilized, showed higher fluxes (0.9 kg N₂O–N ha^?1 a^?1 and 4.3 kg NO–N ha^?1 a^?1) than smallholder tea plantations (0.1 kg N₂O–N ha^?1 a^?1 and 2.1 kg NO–N ha^?1 a^?1) or grazing land (0.1 kg N₂O–N ha^?1 a^?1 and 1.1 kg NO–N ha^?1 a^?1). High soil NO fluxes were probably the consequence of long-term N fertilization and associated soil acidification, likely promoting chemodenitrification. Our experimental approach can be implemented in understudied regions, with the potential to increase the amount of information on production and consumption of trace gases from soils.     

Energy balances and greenhouse gas emissions of palm oil biodiesel in Indonesia

This study presents a cradle‐to‐gate assessment of the energy balances and greenhouse gas (GHG) emissions of Indonesian palm oil biodiesel production, including the stages of land‐use change (LUC), agricultural phase, transportation, milling, biodiesel processing, and comparing the results from different farming systems, including company plantations and smallholder plantations (either out growers or independent growers) in different locations in Kalimantan and Sumatra of Indonesia. The findings demonstrate that there are considerable differences between the farming systems and the locations in net energy yields (43.6–49.2 GJ t^?1 biodiesel yr^?1) as well as GHG emissions (1969.6–5626.4 kg CO_2eq t^?1 biodiesel yr^?1). The output to input ratios are positive in all cases. The largest GHG emissions result from LUC effects, followed by the transesterification, fertilizer production, agricultural production processes, milling, and transportation. Ecosystem carbon payback times range from 11 to 42 years.     

The role of harvest residue in rotation cycle carbon balance in loblolly pine plantations. Respiration partitioning approach

Timber harvests remove a significant portion of ecosystem carbon. While some of the wood products moved off‐site may last past the harvest cycle of the particular forest crop, the effect of the episodic disturbances on long‐term on‐site carbon sequestration is unclear. The current study presents a 25 year carbon budget estimate for a typical commercial loblolly pine plantation in North Carolina, USA, spanning the entire rotation cycle. We use a chronosequence approach, based on 5 years of data from two adjacent loblolly pine plantations. We found that while the ecosystem is very productive (GEP up to 2900 g m^?2 yr^?1, NEE at maturity about 900 g C m^?2 yr^?1), the production of detritus does not offset the loss of soil C through heterotrophic respiration (R_H) on an annual basis. The input of dead roots at harvest may offset the losses, but there remain significant uncertainties about both the size and decomposition dynamics of this pool. The pulse of detritus produced at harvest resulted in a more than 60% increase in R_H. Contrary to expectations, the peak of R_H in relation to soil respiration (SR) did not occur immediately after the harvest disturbance, but in years 3 and 4, suggesting that a pool of roots may have remained alive for the first few years. On the other hand, the pulse of aboveground R_H from coarse woody debris lasted only 2 years. The postharvest increase in R_H was offset by a decrease in autotrophic respiration such that the total ecosystem respiration changed little. The observed flux rates show that even though the soil C pool may not necessarily decrease in the long‐term, old soil C is definitely an active component in the site C cycle, contributing about 25–30% of the R_H over the rotation cycle.