Impact of nitrogen input from biosolids application on carbon sequestration in a Pinus radiata forest

Background:Forest management practices(e.g.choice of stand density,fertilisation)are just as important in carbon(C)forestry as in other types of forestry and will affect the level of C sequestration and profitability.Because C stored in wood is approximately proportional to the product of its volume and density,it is necessary to account for both volume growth and wood density when assessing the effects of fertilisation on C sequestration in pine forests.Methods:The effects of nitrogen(N)input from biosolids application on forest C sequestration were quantified from an intensively monitored biosolids field trial in a Pinus radiata plantation on a sandy soil in New Zealand.The field trial tested the application of three biosolids rates:Control(no application),Standard(300 kg N⋅ha^(-1) applied every three years),and High(600 kg N⋅ha^(-1) applied every three years),across three levels of stand density:300,450,and 600 stems⋅ha^(-1).Carbon sequestration was estimated using the C-Change model from annual plot measurements of stand density,stem height and diameter,and annual breast height wood densities obtained from increment cores.Results:By age 24 years,N-fertilised trees had sequestered 40 t C⋅ha^(-1) more than unfertilised trees,an increase of 18%.Fertilisation increased stem volume by 23%but reduced stem wood density by 2.5%.Most of the increased C sequestration occurred between age 6 and age 17 years and the Standard rate gave the same increase in C sequestration as the High rate.On average,there was no significant difference in growth rate between fertilised and unfertilised trees after the 17th growth year,but the increased growth ceased earlier at higher stand densities,and later at lower stand densities.Conclusions:This study indicates that 2–3 applications of the Standard rate would have been sufficient to achieve the increased C sequestration,with an applied N to C conversion ratio of 43–65 kg C⋅kg^(-1) N.Our results highlight that N fertilisation will become more widespread under greenhouse gas emissions trading schemes which en-courages forest management practices that improve C sequestration in young forests in New Zealand in particular and other countries in general.

Land-use induced changes in topsoil organic carbon stock of paddy fields using MODIS and TM/ETM analysis:A case study of Wujiang County,China

Topsoil soil organic carbon (SOC) that plays an important role in mitigating atmospheric carbon dioxide (CO_2) buildup is greatly affected by human activities.To evaluate the influence of land-use changes on SOC stocks in paddy soils,a new algorithm was developed by integrating MODIS (moderate resolution imaging spectral-radiometer) and TM/ETM data for timely monitoring the land-use change in Wujiang County.Thereafter,the land-use class-maps derived from MODIS and TM/ETM analyses were further used to estima...

Litter decomposition and C and N dynamics as affected by N additions in a semi-arid temperate steppe, Inner Mongolia of China

Litter decomposition is the fundamental process in nutrient cycling and soil carbon（C） sequestration in terrestrial ecosystems. The global-wide increase in nitrogen（N） inputs is expected to alter litter decomposition and,ultimately, affect ecosystem C storage and nutrient status. Temperate grassland ecosystems in China are usually N-deficient and particularly sensitive to the changes in exogenous N additions. In this paper, we conducted a 1,200-day in situ experiment in a typical semi-arid temperate steppe in Inner Mongolia to investigate the litter decomposition as well as the dynamics of litter C and N concentrations under three N addition levels（low N with 50 kg N/（hm2？a）（LN）, medium N with 100 kg N/（hm2？a）（MN）, and high N with 200 kg N/（hm2？a）（HN）） and three N addition forms（ammonium-N-based with 100 kg N/（hm2？a） as ammonium sulfate（AS）, nitrate-N-based with 100 kg N/（hm2？a） as sodium nitrate（SN）, and mixed-N-based with 100 kg N/（hm2？a） as calcium ammonium nitrate（CAN）） compared to control with no N addition（CK）. The results indicated that the litter mass remaining in all N treatments exhibited a similar decomposition pattern： fast decomposition within the initial 120 days, followed by a relatively slow decomposition in the remaining observation period（120–1,200 days）. The decomposition pattern in each treatment was fitted well in two split-phase models, namely, a single exponential decay model in phase I（〈398 days） and a linear decay function in phase II（≥398 days）. The three N addition levels exerted insignificant effects on litter decomposition in the early stages（〈398 days, phase I; P〉0.05）. However, MN and HN treatments inhibited litter mass loss after 398 and 746 days, respectively（P〈0.05）. AS and SN treatments exerted similar effects on litter mass remaining during the entire decomposition period（P〉0.05）. The effects of these two N addition forms differed greatly from those of CAN after 746 and 1,053 days, respectively（P〈0.05）. During the decomposition period, N concentrations in the decomposing litter increased whereas C concentrations decreased, which also led to an exponential decrease in litter C：N ratios in all treatments. No significant effects were induced by N addition levels and forms on litter C and N concentrations（P〉0.05）. Our results indicated that exogenous N additions could exhibit neutral or inhibitory effects on litter decomposition, and the inhibitory effects of N additions on litter decomposition in the final decay stages are not caused by the changes in the chemical qualities of the litter, such as endogenous N and C concentrations. These results will provide an important data basis for the simulation and prediction of C cycle processes in future N-deposition scenarios.

Assessing productivity and carbon sequestration capacity of subtropical coniferous plantations using the process model PnET-CN

A generalized, lumped-parameter ecological model PnET-CN was calibrated and validated for a subtropical coniferous plantation in southern China. PnET-CN model describes the biogeochemical cycles of carbon （C） and nitrogen （N） and can assist in estimating carbon sequestration potential. For validation of PnET-CN, data from coniferous forest plantations in southern China was used. Simulated daily gross primary productivity （GPP） from 2005 to 2007 agreed well with observations （R2=0.56, S.D.=0.009）. Simulations of monthly soil respiration （Rs） from 2005-2007 agreed well with Rs observations （R2=0.67, S.D. =0.03）. Simu- lated annual net primary productivity （NPP） from 1998-2006 was 803＋33 gCm 2a-1, about 4% higher than NPP observation （752＋51 gCm-2a-1）. Simulations of annual NEP from 2005-2007 only overestimate 9 gCm-2a-1 （4%）, 4 gCm 2a-1 （1%） and 34 gCm 2a-1 （8%） compared to NEP observations, respectively. Simulated annual foliar N concentration （FolNCon） （1.09%） is 10% lower than observed monthly FolNCon （0.87%-1.58%）. Simulated annual N leaching （0.26 gNm-2） is about 10% lower than leaching observation （0.29 gNm-2）. PnET-CN model validation indicates that PnET-CN is capable to simulate daily GPP, annual NPP, annual NEP, monthly Rs, annual FolNCon and annual nitrate N leaching for subtropical coniferous planta- tions in southern China. The results obtained from the validation test revealed that PnET-CN model can be used to simulate carbon sequestration of planted coniferous forests in southern China to a high level of precision. Sensitivity analysis suggests that great care should be taken in developing generalizations as to how forests will respond to a changing climate. PnET-CN performed satisfactorily in comparison to other models that have already been calibrated and validated in coniferous planted subtropical forests in China. Based on PnET-CN validation and its comparison to other models, future improvement of PnET-CN should focus on seasonal foliar N dynamics and the effects of water stress on autotrophic respirations in subtropical coniferous plantations in southern China.

Interactive effects of elevated CO2 and nitrogen fertilization levels on photosynthesized carbon allocation in a temperate spring wheat and soil system

Increasing atmospheric CO2 concentration impacts the terrestrial carbon(C) cycle by affecting plant photosynthesis, the flow of photosynthetically fixed C belowground, and soil C pool turnover. For managed agroecosystems, how and to what extent the interactions between elevated CO2 and N fertilization levels influence the accumulation of photosynthesized C in crops and the incorporation of photosynthesized C into arable soil are in urgent need of exploration.We conducted an experiment simulating elevated CO2 with spring wheat(Triticum aestivum L.) planted in growth chambers.13C-enriched CO2 with an identical 13C abundance was continuously supplied at ambient and elevated CO2 concentrations(350 and 600 μmol mol-1, respectively) until wheat harvest.Three levels of N fertilizer application(equivalent to 80, 120, and 180 kg N ha-1 soil) were supplied for wheat growth at both CO2 concentrations. During the continuous 62-d 13CO2 labeling period, elevated CO2 and increased N fertilizer application increased photosynthesized C accumulation in wheat by 14%–24% and 11%–20%, respectively, as indicated by increased biomass production, whereas the C/N ratio in the roots increased under elevated CO2 but declined with increasing N fertilizer application levels. Wheat root deposition induced 1%–2.5% renewal of soil C after 62 d of 13CO2 labeling. Compared to ambient CO2, elevated CO2 increased the amount of photosynthesized C incorporated into soil by 20%–44%. However, higher application rates of N fertilizer reduced the net input of root-derived C in soil by approximately 8% under elevated CO2. For the wheat-soil system, elevated CO2 and increased N fertilizer application levels synergistically increased the amount of photosynthesized C. The pivotal role of plants in photosynthesized C accumulation under elevated CO2 was thereby enhanced in the short term by the increased N application. Therefore, robust N management could mediate C cycling and sequestration by influencing the interactions between plants and soil in agroecosystems under elevated CO2.

Biochar addition to vineyard soils:effects on soil functions,grape yield and wine quality

In response to increasing concerns over climate change,soil health and wine quality,grape growers are seeking new practices(e.g.,biochar application)to minimize their environmental footprint while increasing productivity and the quality of their products.To explore the potential of biochar-based amendments to achieve these goals in wine grape production,vineyard trials were established in the fall of 2018.Two Oregon sites were chosen with distinct soil types and climates(Willamette Valley and Rogue Valley)but planted with the same grapevine scion/rootstock Pinot noir combination.Four treatments were applied under vines at each location:no biochar-no tillage(NT);no biochar+tillage(B0);18 tons ha^(−1)biochar+tillage(B18);35 tons ha^(−1)biochar+tillage(B35).In 2019,a suite of soil health,plant,and crop variables were measured,and wines were produced after harvest.The incorporation of biochar modified the chemical and physical composition of soils at the two studied locations,increasing the bioavailability of carbon and nitrogen,their gravimetric water content and the concentration of plant available micro and macro nutrients.No responses of plant physiology parameters or productivity at either site were found after biochar incorporation when compared with controls.Conversely,a significant and gradual decrease in the amount of wine tannins was found as a result of biochar application in wines produced from grapes from the Woodhall location.Long-term field experiments are required to assess the effects of biochar on soil properties,vine physiol-ogy,productivity,and grape and wine quality several years after incorporation.