Publications

Abstract Grassland degradation and its impact on soil carbon cycle is of worldwide concern, but optimal restoration strategies remain uncertain. We determined temperature sensitivity of organic cabon mineralization (CO 2 ‐Q 10 ) and the mechanisms underlying changes in soil organic carbon (SOC) content across non‐restored and restored grasslands on the Qinghai‐Tibetan Plateau. Topsoil and subsoil with three SOC contents from non‐restored and passively or actively restored grasslands were incubated for 28 days at 5, 15, and 25°C. We determined the Q 10 of SOC mineralization, and the importance of vegetation, soil physico‐chemical properties and microbial communities regulating CO 2 ‐Q 10 . In C‐poor soil, SOC mineralization rate was slowest with active restoration, but SOC storage increased in both topsoil and subsoil. Increased soil pH and C availability raised CO 2 ‐Q 10 in the actively restored grassland. In subsoil of C‐middle soil, SOC storage in passively and actively restored grasslands were 81% and 25% greater, respectively, than in non‐restored grassland. In the topsoil of C‐rich soil, passively restored grassland had less SOC storage (7.5 kg·m −2 ) than non‐restored grassland (10 kg·m −2 ), because the greater aboveground biomass increased SOC decomposition caused by the priming effects driven by organic inputs from litter. The CO 2 ‐Q 10 in C‐rich topsoil in passively restored grasslands (1.1) was less than in non‐restored grassland (1.3). These findings emphasize that effective restoration management should consider initial organic C content of the degraded grassland to develop the best ecological restoration approaches to maximize C storage and limit CO 2 emission into the atmosphere.

Soil nutrient contents and organic carbon (C) stability are key indicators for restoration of degraded grassland. However, the effects of long‐term active restoration of extremely degraded grassland on soil parameters have been equivocal. The aims of this study were to evaluate the impact of active restoration of degraded alpine grassland on: (a) soil organic matter (SOM) mineralization; and (b) the importance of biotic factors for temperature sensitivity ( Q 10 ) of SOM mineralization. Soils were sampled from intact, degraded and restored alpine grasslands at altitudes ranging between 3,900 and 4,200 m on the Tibetan Plateau. The samples were incubated at 5, 15 and 25°C, and Q 10 values of SOM mineralization were determined. Structural equation modeling was used to evaluate the importance of vegetation, soil physico‐chemical properties and microbial parameters for Q 10 regulation. The Q 10 of N mineralization was similar among intact, degraded and restored soils (0.84–1.24) and was higher in topsoil (1.09) than in subsoil (0.92). The best predictive factor of CO 2 ‐ Q 10 for intact grassland was microbial biomass, for degraded grassland was basal microbial respiration, and for restored grassland was soil bulk density. Restoration by planting vegetation decreased the Q 10 of SOM mineralization as soil bulk density, the most important negative predictor, increased in restored grassland. The Q 10 of SOM mineralization in topsoil was 14% higher than in subsoil because of higher microbial abundance and exo‐enzyme activities. The NH 4 + content was greatest in intact soil, while NO 3 − content was greatest in degraded soil. The SOM mineralization rate decreased with grassland degradation and increased after long‐term (>10 years) restoration. In conclusion, extremely degraded grassland needs proper long‐term management in active restoration projects, especially for improvement of soil nutrients in a harsh environment.

Increased plant carbon (C) input into the soils after cropland abandonment results in not only C accumulation, but also higher microbial activities and consequently faster organic matter decomposition. We investigated the link between soil C accumulation and microbial properties in a chronosequence (0–65 years) of post-agricultural self-restoration of Luvisols - the dominating soil type worldwide. Microbial biomass carbon (MBC) and enzyme activities increased in the top soil (0–20 cm) during the 37-year period of self-restoration. Accumulation of microbial biomass was faster than of soil organic C at earlier stages of self-restoration (0–22 years) because of the fast microbial growth induced by labile litter components. The response of microbial activity was more sensitive to land use changes compared to that of soil organic C. Activities of enzymes responsible for C cycle increased more than that of nitrogen (N) and phosphorus (P) cycles at least up to 37 years after abandonment, indicating microbial adaptations to high input of litter with wide C/N and C/P ratios. Similarly, β-xylosidase was the solely enzyme which reached the activity similar to secondary forest soils after 65 years, due to the accumulation of recalcitrant C in litter with cropland abandonment age. The increased C demand was caused by the higher bacterial portion in soil microbial community (based on PLFA composition), which in turn, resulted in a lower microbial biomass C/N ratio. Enzyme stoichiometry revealed that microorganisms were limited by C and N in the topsoil during the self-restoration up to 37 years. Overall, the quantity and quality of plant C inputs, which changed with post-agricultural land restoration, regulated the microbial activity and enzyme production, offering a profound comprehension of ecosystem succession.

No abstract is provided for this article.

Rhizosphere is a soil volume of high spatio-temporal heterogeneity and intensive plant-soil-microbial interactions, for which visualization and process quantification is of highest scientific and applied relevance, but still very challenging. A novel methodology for quick assessment of two-dimensional distribution of available phosphorus (P) in rhizosphere was suggested, tested, and development up to the application platform. Available P was firstly trapped by an in-situ diffusive gradients in thin-films (DGT) sampler with precipitated zirconia as the binding gel, and subsequently, the loaded gel was analyzed with an optimized colorimetric imaging densitometry (CID). The imaging platform was established linking: i) DGT, ii) planar optode, and iii) soil zymography techniques to simultaneously determine available P, oxygen, and acid phosphatase in rhizosphere at sub-millimeter spatial scales. The DGT identified available P level in rice rhizosphere were spatially overlapping to the localized redox hotspots and phosphatase activity. The spatial relationship between available P and acid phosphatase activity was dependent on root development. The root radial oxygen loss (ROL) remained active during the experimental observations (2–3 days), while a flux of available P of 10 pg cm−2 s−1 was visualized within 2–3 mm of roots, confirming the correlative response of rice roots to oxygen secretion and P uptake. Summarizing, the established imaging platform is suitable to capture spatial heterogeneity and temporal dynamics of root activities, nutrient bioavailability, ROL and enzyme activities in rhizosphere.

Das Tibetische Plateau, mit seinen Kobresia pygmea Weiden, stellt eine globale Senke fur organischen Kohlenstoff (OC) dar. Uberweidung fuhrt zur Zerstorung der Kobresia Wurzelmatten und damit zur Graslanddegradation. Dies hat massive OC Verluste und die Destabilisierung des Okosystems zur Folge. Diese Arbeit analysiert den Effekt der degradationsbedingten veranderten Zusammensetzung der organischen Bodensubstanz (SOM) auf die Zusammensetzung der mikrobiellen Gemeinschaft und deren Funktion entlang einer Sequenz von sechs Degradationsstufen. Dazu wurden die Aktivitaten von sechs extrazellularen Enzyme gemessen sowie die Zusammensetzung der bakteriellen und pilzlichen Gemeinschaft (mittels t-RFLP Analyse gefolgt von Illumina MiSeq Sequenzierung) analysiert. So konnte die Zusammensetzung der mikrobiellen Gemeinschaft mit den vertikalen Gradienten der δ13C und δ15N-Werte, sowie den Neutralzucker-, Cutin-, Suberin- und Ligningehalten in Beziehung gesetzt werden. Mit zunehmender Degradation deuten negativere δ13C-Werte auf eine relative Anreicherung an 13C-armen Makromolekulen wie bspw. Lignin hin. Zusammen mit ebenfalls verringerten δ15N-Werten und veranderten C/N-Verhaltnissen belegt dies einen verstarkten SOM-Abbau. Gleichzeitig nimmt die Aktivitat von hydrolytischen Enzymen, mit fortschreitender Degradation zu. Lediglich in der letzten Degradationsstufe ist ein drastischer Ruckgang der Aktivitat dieser Enzymgruppe zu beobachten. Im Gegensatz dazu zeigen Phenoloxidasen (Mineralisation komplexer SOM) zunehmende Aktivitaten mit steigender Degradation die mit einer Anreicherung dieser Substrate (z.B. Ligin) einhergeht. Die beobachteten Anderungen der Enzymaktivitaten sind mit einer veranderten Zusammensetzung der mikrobiellen Gemeinschaft, besonders des Unterbodens, begleitet. So nehmen Actinobacteria mit der Degradation ab wahrend Nitrosomonas zunehmenden, was einen steigenden Verlust von mineralisiertem N aus dem Boden erklart. Bis jetzt ist unklar ob die degradationsbedingten funktionellen und strukturellen Veranderungen der mikrobiellen Gemeinschaft der Kobresia Graslander reversibel sind, oder ob mit steigendem Verlust an Nahrstoffen und Boden ein Punkt erreicht wird, der eine Erholung der Kobresia-Matten nicht mehr erlaubt.

Plastic film mulching (PM), which contributes to nearly half of the increased crop yields in dryland agroecosystems, exacerbates environmental burdens due to its non-degradable nature. Globally, there is a growing demand to replace non-degradable PM with degradable film mulching (DM), yet its impacts on soil organic carbon (SOC) in dryland agroecosystems remains unknown. Here, using multi-field studies and mesocosm experiments, we found that DM strongly increased but PM reduced SOC storage (0–1 m). This difference is likely attributable to the higher microbial C use efficiency in soil under DM, leading to increased microbial-derived C compared to PM. Under the high roading scenario for 2100, DM could reduce the decomposition of SOC (0–1 m) in China’s drylands by 9.0 ± 1.0 Mg ha–1 year–1 (one standard error) compared with PM. Our findings highlight that DM is a promising alternative to PM for sequestrating SOC and alleviating C loss under climate change in dryland agroecosystems. Sustainable management of soil organic carbon (SOC) in farmland is critical for mitigating climate change and improving soil health. Degradable film mulching is a promising alternative to plastic film mulching, sequestering SOC and reducing C loss in dryland agroecosystems under climate change.

No abstract is provided for this article.

No abstract is provided for this article.

Initiatives to restore soil fertility and mitigate global warming rely on rebuilding soil organic carbon (SOC). Nitrogen (N) fertilization is crucial for crop yields but affects SOC unpredictably due to varying responses of particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) pools to initial SOC levels. To clarify these effects, here, by combining a global meta-analysis with continental-scale field experiments, we determine that an initial SOC threshold of 15 g C kg −1 controls the effect of N fertilization on POC and MAOC. In SOC-poor soils (< 15 g C kg −1 ), N fertilizer increases plant-derived C inputs and promotes soil aggregation, favouring POC accumulation. Conversely, in SOC-rich soils, N fertilizer stimulates microbial metabolic efficiency, leading to larger necromass production and stabilization by mineral protection, observed as more pronounced MAOC accrual. Our findings reveal how SOC thresholds shape the response of active and stable carbon pools to N fertilization, with consequences for SOC accrual in cropland soils globally.