Publications

Biochar (BC) and nitrogen (N) fertilizers are frequently applied to improve soil properties and increase crop productivity. Nonetheless, our mechanistic understanding of plant-soil interactions under single or combined application of BC and N remains incomplete. For the first time, we applied a split-root system to evaluate how BC or N contributes to the changes in soil enzyme activities, N and phosphorus (P) cycling as well as root plasticity. Left and right parts of rhizoboxes were filled with silty-clay loamy soil amended with BC (15 g kg−1 soil, from wheat straw, 300 °C), N (0.05 g KNO3-N kg−1 soil) or a control (no amendments), resulting in the following combinations: BC/Control, N/Control, BC/N. Soil enzyme activities, available N and P, root morphology and plant biomass were analyzed after plant harvest. Plant biomass (shoot + root) ranged from 0.56 g pot−1 (BC/Control) to 0.91 g pot−1(BC/N). The decreased soil bulk density and increased P availability in the BC compartment (BC/Control and BC/N) stimulated root length by 1.4–1.8 times – an effect that was independent of N availability in the same rhizobox. Biochar stimulated activities of β-glucosidase and leucine aminopeptidase (by 33–39%) compared to N due to the coupling of C, N and P cycles in BC/N treated soil. Nitrogen fertilization also increased β-glucosidase activity compared to the unfertilized control, whereas root elongation remained unaffected. Thus, the combined application of BC/N had more efficient benefits for plant growth than BC or N alone. This is linked with i) the stimulation of enzyme activities at the BC locations to reduce N limitation for both microorganisms and plants, and ii) an increase of fine root production to improve N uptake efficiency. Thus, combined BC/N application is potentially especially sustainable to overcome nutrient limitation as well as to maintain crop productivity because it accelerates root-microbial interactions.

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Delineation of microbial habitats within the soil matrix and characterization of their environments and metabolic processes are crucial to understand soil functioning, yet their experimental identification remains persistently limited. We combined single- and triple-energy X-ray computed microtomography with pore specific allocation of 13 C labeled glucose and subsequent stable isotope probing to demonstrate how long-term disparities in vegetation history modify spatial distribution patterns of soil pore and particulate organic matter drivers of microbial habitats, and to probe bacterial communities populating such habitats. Here we show striking differences between large (30-150 µm Ø) and small (4-10 µm Ø) soil pores in (i) microbial diversity, composition, and life-strategies, (ii) responses to added substrate, (iii) metabolic pathways, and (iv) the processing and fate of labile C. We propose a microbial habitat classification concept based on biogeochemical mechanisms and localization of soil processes and also suggests interventions to mitigate the environmental consequences of agricultural management.

No abstract is provided for this article.

Rice paddy conversion to vegetable production is a common agricultural practice driven by economic benefits and shifting diets. However, little is known on the initial effects of this land-use conversion on net ecosystem carbon budget (NECB) and greenhouse gas (GHG) balance. Annual NECB and emissions of CH4 and N2O were measured from a native double rice cropping system (Rice) and a vegetable field recently converted from rice paddy (Veg) under no nitrogen (N) fertilization (Rice-N0 and Veg-N0) and conventional N fertilization (Rice-N+ and Veg-N+) during the initial four years upon conversion in subtropical China. Land-use conversion from rice to vegetable cultivation led to substantial C losses (2.6 to 4.5 Mg C ha−1 yr−1), resulting from strongly reduced C input by 44–52% and increased soil organic matter mineralization by 46–59% relative to Rice. The magnitude of C losses from Veg was highest in the first year upon conversion, and showed a decreasing trend over time. N fertilization shifted rice paddy from a slight C source in Rice-N0 (−1.0 Mg C ha−1 yr−1) to a significant C sink in Rice-N+ (1.1 Mg C ha−1 yr−1) and alleviated the impact of land-use conversion on C loss via increased C input from higher crop productivity. Land-use conversion greatly increased the global warming potential (GWP) from Veg by 116–395% relative to Rice in the first year, primarily due to increased C losses and N2O emission outweighing the decreased CH4 emission. However, the GWP did not show obvious difference between Rice and Veg in the following years. N fertilization and land-use conversion interactively increased GWP in the first year via increased N2O production. Concluding, NECB and GHG emissions in the first year after conversion are crucial and should be considered when evaluating the environmental consequences of land-use conversion.

Effects of light on the short term competition for organic and inorganic nitrogen between maize and rhizosphere microorganisms were investigated using a mi

Overview of all experimental observations from global rice field experiments that were used for calculating paddy SOC stocks and the meta-analysis.

Agriculture and the exploitation of natural resources have transformed tropical mountain ecosystems across the world, and the consequences of these transformations for biodiversity and ecosystem functioning are largely unknown1–3. Conclusions that are derived from studies in non-mountainous areas are not suitable for predicting the effects of land-use changes on tropical mountains because the climatic environment rapidly changes with elevation, which may mitigate or amplify the effects of land use4,5. It is of key importance to understand how the interplay of climate and land use constrains biodiversity and ecosystem functions to determine the consequences of global change for mountain ecosystems. Here we show that the interacting effects of climate and land use reshape elevational trends in biodiversity and ecosystem functions on Africa’s largest mountain, Mount Kilimanjaro (Tanzania). We find that increasing land-use intensity causes larger losses of plant and animal species richness in the arid lowlands than in humid submontane and montane zones. Increases in land-use intensity are associated with significant changes in the composition of plant, animal and microorganism communities; stronger modifications of plant and animal communities occur in arid and humid ecosystems, respectively. Temperature, precipitation and land use jointly modulate soil properties, nutrient turnover, greenhouse gas emissions, plant biomass and productivity, as well as animal interactions. Our data suggest that the response of ecosystem functions to land-use intensity depends strongly on climate; more-severe changes in ecosystem functioning occur in the arid lowlands and the cold montane zone. Interactions between climate and land use explained—on average—54% of the variation in species richness, species composition and ecosystem functions, whereas only 30% of variation was related to single drivers. Our study reveals that climate can modulate the effects of land use on biodiversity and ecosystem functioning, and points to a lowered resistance of ecosystems in climatically challenging environments to ongoing land-use changes in tropical mountainous regions. Elevational trends in biodiversity and ecosystem functions across natural and anthropogenic habitats on Mount Kilimanjaro show that the effects of land use are strongly mediated by climate.

Land use is an important factor affecting soil organic carbon (SOC) dynamics and can produce positive C climate feedback, but its effects remain unknown fo