9 research outputs found
Impacts of slurry acidification and injection on fertilizer nitrogen fates in grassland
Low nitrogen (N) use efficiency of broadcast slurry application leads to nutrient losses, air and water pollution, greenhouse gas emissions andâin particular in a warming climateâto soil N mining. Here we test the alternative slurry acidification and injection techniques for their mitigation potential compared to broadcast spreading in montane grassland. We determined (1) the fate of N labelled slurry in the plant-soil-microbe system and soil-atmosphere exchange of greenhouse gases over one fertilization/harvest cycle and (2) assessed the longer-term contribution of fertilizer N to soil organic N formation by the end of the growing season. The isotope tracing approach was combined with a space for time climate change experiment. Simulated climate change increased productivity, ecosystem respiration, and net methane uptake irrespective of management, but the generally low NO fluxes remained unchanged. Compared to the broadcast spreading, slurry acidification showed lowest N losses, thus increased productivity and fertilizer N use efficiency (38% N recovery in plant aboveground plant biomass). In contrast, slurry injection showed highest total fertilizer N losses, but increased fertilization-induced soil organic N formation by 9â12 kg N ha season. Slurry management effects on NO and CH fluxes remained negligible. In sum, our study shows that the tested alternative slurry application techniques can increase N use efficiency and/or promote soil organic N formation from applied fertilizer to a remarkable extent. However, this is still not sufficient to prevent soil N mining mostly resulting from large plant N exports that even exceed total fertilizer N inputs
Temperatureâsensitive biochemical Oâfractionation and humidityâdependent attenuation factor are needed to predict ÎŽ O of cellulose from leaf water in a grassland ecosystem
We explore here our mechanistic understanding of the environmental and physiological processes that determine the oxygen isotope composition of leaf cellulose (ÎŽO) in a droughtâprone, temperate grassland ecosystem.
A new allocationâandâgrowth model was designed and added to an Oâenabled soilâvegetationâatmosphere transfer model (MuSICA) to predict seasonal (AprilâOctober) and multiâannual (2007â2012) variation of ÎŽO and Oâenrichment of leaf cellulose (ÎO) based on the BarbourâFarquhar model.
Modelled ÎŽO agreed best with observations when integrated over c. 400 growingâdegreeâdays, similar to the average leaf lifespan observed at the site. Over the integration time, air temperature ranged from 7 to 22°C and midday relative humidity from 47 to 73%. Model agreement with observations of ÎŽO (R = 0.57) and ÎO (R = 0.74), and their negative relationship with canopy conductance, was improved significantly when both the biochemical Oâfractionation between water and substrate for cellulose synthesis (Δ, range 26â30â°) was temperatureâsensitive, as previously reported for aquatic plants and heterotrophically grown wheat seedlings, and the proportion of oxygen in cellulose reflecting leaf water Oâenrichment (1 â pp, range 0.23â0.63) was dependent on air relative humidity, as observed in independent controlled experiments with grasses.
Understanding physiological information in ΎO requires quantitative knowledge of climatic effects on pp and Δ
Lysimeter-based full fertilizer 15N balances corroborate direct dinitrogen emission measurements using the 15N gas flow method
The N gas flux (NGF) method allows for direct in situ quantification of dinitrogen (N) emissions from soils, but a successful cross-comparison with another method is missing. The objectives of this study were to quantify N emissions of a wheat rotation using the NGF method, to compare these N emissions with those obtained from a lysimeter-based N fertilizer mass balance approach, and to contextualize N emissions with N enrichment of N in soil air. For four sampling periods, fertilizer-derived N losses (NGF method) were similar to unaccounted fertilizer N fates as obtained from the N mass balance approach. Total N emissions (NGF method) amounted to 21â±â3 kg N haââ1, with 13â±â2 kg N haââ1 (7.5% of applied fertilizer N) originating from fertilizer. In comparison, the N mass balance approach overall indicated fertilizer-derived N emissions of 11%, equivalent to 18â±â13 kg N haââ1. Nitrous oxide (NO) emissions were small (0.15â±â0.01 kg N haââ1 or 0.1% of fertilizer N), resulting in a large mean N:(NOâ+âN) ratio of 0.94â±â0.06. Due to the applied drip fertigation, ammonia emissions accounted for <â1% of fertilizer-N, while N leaching was negligible. The temporal variability of N emissions was well explained by the ÎŽN in soil air down to 50 cm depth. We conclude the NGF method provides realistic estimates of field N emissions and should be more widely used to better understand soil N losses. Moreover, combining soil air ÎŽN measurements with diffusion modeling might be an alternative approach for constraining soil N emissions
The 18O ecohydrology of a grassland ecosystem - predictions and observations
This research has been supported by the Deutsche Forschungsgemeinschaft (grant no. SCHN 557/9-1), the Agence Nationale de la Recherche (grant no. ANR-13-BS06-0005), and the European Commission (grant no. SOLCA 338264). This work was supported by the German Research Foundation (DFG) and the Technical University of Munich (TUM) in the framework of the Open Access Publishing Program.Peer reviewedPublisher PD
Fluxes in central carbohydrate metabolism of source leaves in a fructan-storing C-3 grass: rapid turnover and futile cycling of sucrose in continuous light under contrasted nitrogen nutrition status
International audienceThis work assessed the central carbohydrate metabolism of actively photosynthesizing leaf blades of a C3 grass (Lolium perenne L.). The study used dynamic C-13 labelling of plants growing in continuous light with contrasting supplies of nitrogen ('low N' and 'high N') and mathematical analysis of the tracer data with a four-pool compartmental model to estimate rates of: (i) sucrose synthesis from current assimilation; (ii) sucrose export/use; (iii) sucrose hydrolysis (to glucose and fructose) and resynthesis; and (iv) fructan synthesis and sucrose resynthesis from fructan metabolism. The contents of sucrose, fructan, glucose, and fructose were almost constant in both treatments. Labelling demonstrated that all carbohydrate pools were turned over. This indicated a system in metabolic steady state with equal rates of synthesis and degradation/consumption of the individual pools. Fructan content was enhanced by nitrogen deficiency (55 and 26% of dry mass at low and high N, respectively). Sucrose content was lower in nitrogen-deficient leaves (2.7 versus 6.7%). Glucose and fructose contents were always low (< 1.5%). Interconversions between sucrose, glucose, and fructose were rapid (with half-lives of individual pools ranging between 0.3 and 0.8 h). Futile cycling of sucrose through sucrose hydrolysis (67 and 56% of sucrose at low and high N, respectively) and fructan metabolism (19 and 20%, respectively) was substantial but seemed to have no detrimental effect on the relative growth rate and carbon-use efficiency of these plants. The main effect of nitrogen deficiency on carbohydrate metabolism was to increase the half-life of the fructan pool from 27 to 62 h and to effectively double its size