Nicolas Brüggemann

Monitoring the soil mineral nitrogen (SMN) status of cropland is challenging due to large spatiotemporal variability. Here, we present a novel approach that correlates NH ₃ , NO, and HONO emissions with SMN content, pH, and soil moisture, eliminating the need for destructive soil sampling. We conducted incubation experiments with five soils with different pH, texture, and organic matter content, using SMN and soil water gradients. In all soils, NH ₄ ⁺ soil content was positively correlated with NH ₃ emission as a function of soil pH and water content. For soil with pH 6.2 and 50% maximum water holding capacity (mWHC), the limit of detection (LOD) was comparable to established methods for total soil NH ₄ ⁺ analysis (LOD = 2.17 mg NH ₄ ⁺ ‐N kg ⁻¹ ) and was as low as 0.16 mg NH ₄ ⁺ ‐N kg ⁻¹ at pH 7.3 and 50% mWHC. In contrast, a significant correlation was found in only one of the soils between NO/NO ₂ ⁻ ( R ²  = 0.73, p < 0.001) and HONO/NO ₂ ⁻ ( R ²  = 0.57, p < 0.001). Furthermore, NO (LOD = 37.65 µg NO ₂ ⁻ ‐N kg ⁻¹ ) analysis was preferable to HONO (LOD = 56.14 µg NO ₂ ⁻ ‐N kg ⁻¹ ) due to its lower LOD and 14‐fold higher accuracy. However, the LOD was slightly higher than that of established photometric methods for NO ₂ ⁻ analysis.

Black soil (Mollisol), characterized by high soil organic matter (SOM), is becoming more vulnerable to extreme heat events, yet the effects of heat on decomposition of SOM, thus N ₂ O emission remain unclear. Here, we investigated the residual effect of temporal heat exposure on subsequent N losses and N ₂ O production pathways in a cultivated black soil in Northeast China. Soil samples were exposed to 25°C, 35°C, 45°C, and 50°C for 12 h, followed by a 7‐day recovery period, after which N ₂ O “hot moment” events (i.e., rewetting with N addition and aerobic‐to‐anaerobic transition) were set up using a robotized continuous‐flow incubation system. We then performed high‐frequency automated monitoring of CO ₂ , N ₂ O, and N ₂ fluxes, and analyzed N ₂ O isotopocules, bacterial community composition, and N‐cycling functional genes to elucidate the underlying mechanisms. Compared with the 25°C control, heat‐exposed soils exhibited 28%–94% higher N ₂ O emissions during the hot moment events. The ¹⁵ N site preference values of N ₂ O indicated that the short‐term heat exposure prior to rewetting enhanced the contribution of denitrification‐derived N ₂ O. The N ₂ O/(N ₂ O + N ₂ ) ratio increased in the extreme heat treatments, indicating a shift toward less complete denitrification. Heating caused modest shifts in bacterial community composition and selectively altered N‐cycling functional gene abundances, including increased AOB amoA and narG abundance in the 50°C treatment. The higher mineral N content and the reduced total N content (by 7%–13%) in heat‐exposed soils after incubation suggest that extreme heat accelerated the decomposition of soil organic N, thereby triggering greater N ₂ O emissions during subsequent hot moment events. The findings have important implications for predicting greenhouse gas feedbacks in black soils under intensifying climate extremes, particularly the potential amplification of soil N ₂ O emissions.

Knowledge about plant water stress regulation mechanisms (e.g., plant stem capacitance) from in situ observation is crucial for the study and modeling of plant root water uptake (RWU). We present a proof of concept and a first application of a simple method for online, minimally invasive monitoring of the water stable isotopic composition of sap xylem water of Helianthus annuus (sunflower) by inserting a sampling tube connected to a laser spectrometer in the plant stem. After careful calibration of our method, we applied it successfully to individual sunflower plants grown in soil columns. We followed the dynamics in stem water isotopic composition in response to changing light intensity and to depth-specific, isotopically labeled water pulses. We further establish that these isotopic dynamics matched changes in RWU profiles monitored simultaneously, independently, and non-destructively by the Soil Water Profiler. We finally highlight from modeling exercises the significance of the role of plant stem capacitance: water exchanges between xylem and stem non-conducting tissues were estimated to amount to about one sixth of RWU of Helianthus annuus , showing that the stem itself can be expected to be a quickly accessible reservoir of water for transpiration, very similar to what is found in trees.

Residual mineral nitrogen (Nmin) in arable soils after harvest represents a major source of N loss. The addition of carbon (C) -rich materials can stimulate microbial immobilization of Nmin, but the stability of the immobilized pool under warming and drought remains uncertain. We conducted a field experiment with winter wheat in Germany, combining ¹⁵N-labelled Nmin with wheat straw, cellulose, or starch, and applying warming, drought, or both. Using in situ mesh bags, we traced N dynamics from the post-harvest period to the following harvest across mineral and organic N pools. Cellulose and starch strongly increased N immobilization after harvest, retaining 47.7% and 72.2% of added Nmin in organic pools, respectively, compared to weaker effects of straw. A substantial proportion (27-46%) of immobilized N was retained as mineral-associated organic matter, which persisted until harvest under all climate conditions. However, warming combined with drought enhanced N remobilization during the growing season, resulting in increased Nmin accumulation at harvest, particularly in cellulose- and starch-amended soils. These results show that C-rich, N-free substrates promote microbial N immobilization and stabilization in soil organic matter. However, subsequent warming and drought can accelerate microbial turnover and mineralization, potentially increasing Nmin losses during the post-harvest period by 2.8 to 3.6 times relative to current climatic conditions. This indicates a climate-sensitive balance between N retention and release, with implications for the effectiveness of high soil C amendments in mitigating N losses.

Knowledge about plant water stress regulation mechanisms (e.g., plant stem capacitance) from in-situ observation is crucial for the study and modeling of plant root water uptake (RWU). We present a proof of concept and a first application of a simple method for online, minimally invasive monitoring of the water stable isotopic composition of sap xylem water of Helianthus annuus (sunflower) by inserting a sampling tube connected to a laser spectrometer in the plant stem. After careful calibration of our method, we applied it successfully to individual sunflower plants grown in soil columns. We followed the dynamics in stem water isotopic composition in response to changing light intensity and to depth-specific, isotopically labeled water pulses. We further establish that these isotopic dynamics matched changes in RWU profiles monitored simultaneously, independently, and non-destructively by the Soil Water Profiler. We finally highlight from modeling exercises the significance of the role of plant stem capacitance: water exchanges between xylem and stem non-conducting tissues were estimated to amount to about one sixth of RWU of Helianthus annuus, showing that the stem itself can be expected to be a quickly accessible reservoir of water for transpiration, very similar to what is found in trees.

Knowledge about plant water stress regulation mechanisms (e.g., plant stem capacitance) from in-situ observation is crucial for the study and modeling of plant root water uptake (RWU). We present a proof of concept and a first application of a simple method for online, minimally invasive monitoring of the water stable isotopic composition of sap xylem water of Helianthus annuus (sunflower) by inserting a sampling tube connected to a laser spectrometer in the plant stem. After careful calibration of our method, we applied it successfully to individual sunflower plants grown in soil columns. We followed the dynamics in stem water isotopic composition in response to changing light intensity and to depth-specific, isotopically labeled water pulses. We further establish that these isotopic dynamics matched changes in RWU profiles monitored simultaneously, independently, and non-destructively by the Soil Water Profiler. We finally highlight from modeling exercises the significance of the role of plant stem capacitance: water exchanges between xylem and stem non-conducting tissues were estimated to amount to about one sixth of RWU of Helianthus annuus, showing that the stem itself can be expected to be a quickly accessible reservoir of water for transpiration, very similar to what is found in trees.

Knowledge about plant water stress regulation mechanisms (e.g., plant stem capacitance) from in-situ observation is crucial for the study and modeling of plant root water uptake (RWU). We present a proof of concept and a first application of a simple method for online, minimally invasive monitoring of the water stable isotopic composition of sap xylem water of Helianthus annuus (sunflower) by inserting a sampling tube connected to a laser spectrometer in the plant stem. After careful calibration of our method, we applied it successfully to individual sunflower plants grown in soil columns. We followed the dynamics in stem water isotopic composition in response to changing light intensity and to depth-specific, isotopically labeled water pulses. We further establish that these isotopic dynamics matched changes in RWU profiles monitored simultaneously, independently, and non-destructively by the Soil Water Profiler. We finally highlight from modeling exercises the significance of the role of plant stem capacitance: water exchanges between xylem and stem non-conducting tissues were estimated to amount to about one sixth of RWU of Helianthus annuus, showing that the stem itself can be expected to be a quickly accessible reservoir of water for transpiration, very similar to what is found in trees.

Knowledge about plant water stress regulation mechanisms (e.g., plant stem capacitance) from in-situ observation is crucial for the study and modeling of plant root water uptake (RWU). We present a proof of concept and a first application of a simple method for online, minimally invasive monitoring of the water stable isotopic composition of sap xylem water of Helianthus annuus (sunflower) by inserting a sampling tube connected to a laser spectrometer in the plant stem. After careful calibration of our method, we applied it successfully to individual sunflower plants grown in soil columns. We followed the dynamics in stem water isotopic composition in response to changing light intensity and to depth-specific, isotopically labeled water pulses. We further establish that these isotopic dynamics matched changes in RWU profiles monitored simultaneously, independently, and non-destructively by the Soil Water Profiler. We finally highlight from modeling exercises the significance of the role of plant stem capacitance: water exchanges between xylem and stem non-conducting tissues were estimated to amount to about one sixth of RWU of Helianthus annuus, showing that the stem itself can be expected to be a quickly accessible reservoir of water for transpiration, very similar to what is found in trees.

Knowledge about plant water stress regulation mechanisms (e.g., plant stem capacitance) from in-situ observation is crucial for the study and modeling of plant root water uptake (RWU). We present a proof of concept and a first application of a simple method for online, minimally invasive monitoring of the water stable isotopic composition of sap xylem water of Helianthus annuus (sunflower) by inserting a sampling tube connected to a laser spectrometer in the plant stem. After careful calibration of our method, we applied it successfully to individual sunflower plants grown in soil columns. We followed the dynamics in stem water isotopic composition in response to changing light intensity and to depth-specific, isotopically labeled water pulses. We further establish that these isotopic dynamics matched changes in RWU profiles monitored simultaneously, independently, and non-destructively by the Soil Water Profiler. We finally highlight from modeling exercises the significance of the role of plant stem capacitance: water exchanges between xylem and stem non-conducting tissues were estimated to amount to about one sixth of RWU of Helianthus annuus, showing that the stem itself can be expected to be a quickly accessible reservoir of water for transpiration, very similar to what is found in trees.