Publications

The photosynthate carbon (C) released in the rhizosphere plays a crucial role in C sequestration, microbial activities and nutrient availability in soil. Nitrogen (N) fertilization modifies the allocation and dynamics of photosynthates in paddy rice systems, but these effects depend on plant growth stages. Rice ( Oryza sativa L.) plants were pulse labelled with 13 CO 2 at the tillering, elongation, heading and grain‐filling stages with 0 and 225 kg N ha −1 fertilizer. The plants and soil were sampled shortly after each pulse labelling and at harvest. Relative 13 C (as % of assimilated C) in the roots and rhizosphere soil was largest at the early growth stage (tillering) and subsequently decreased. At harvest, 68% of the rhizodeposited C remained in bulk soil without N fertilizer, which corresponded to 6.2% of the net assimilated 13 C. The absolute amount of net belowground C input (root + rhizodeposition) by rice was 268 and 468 kg C ha −1 under 0 and 225 kg N ha −1 fertilizer, of which rhizodeposition accounted for 60 and 40%, respectively. We concluded that N fertilization raised the belowground C input by rice mainly by increasing root biomass rather than by rhizodeposition. Highlights Rice photosynthesis‐derived carbon (C) was quantified in soil by multiple pulse labelling with 13 CO 2 Young rice plants allocated more assimilates into the soil compared to mature plants Nitrogen deficiency led to greater C retention in bulk soil than in the rhizosphere Nitrogen fertilization increased the net belowground C input mainly with larger root biomass

Abstract Plant‐microbial interactions under N‐limiting conditions are governed by competitive abilities of plants for N. Our study aimed to examine how two plant species of strawberry, Fragaria vesca L. (native species) and Duchesnea indica (Andrews) Focke (an invasive plant in central Europe), growing in intra‐specific and inter‐specific competition alter the functions of rhizosphere microorganisms in dependence on N availability. By intra‐specific competition at low N level, a 2.4‐fold slower microbial‐specific growth rate was observed under D. indica characterized by smaller root biomass and lower N content in roots compared with F. vesca. By inter‐specific competition of both plants at low N level, microbial growth rates were similar to those for D. indica indicating that plants with stronger competitive abilities for N controls microbial community in the rhizosphere. Since a high N level smoothed the differences between plant species in root and microbial biomass as well as in microbial growth rates under both intra‐specific and inter‐specific competition, we conclude that competitive abilities of plant species were crucial for microbial growth in the rhizosphere only under N imitation. Keywords: Plant‐microbial interactionsr‐ and K‐strategiesN limitationrhizosphere Acknowledgment The study was supported by the European Commission (Marie Curie IIF program, project MICROSOM).

In situ 13CO2 pulse labeling was conducted in temperate grasslands, managed by no grazing, rotational, or continuous overgrazing, to trace the allocation p

Soil organic matter (SOM) mineralization is affected by various abiotic and biotic factors, as well as the input of exogenous organic substances. Our previous studies have shown that SOM mineralization in flooded rice paddies is lower than that in adjacent upland soils in subtropical agro-ecosystems. However, the main factors contributing to the differences in SOM mineralization remain unclear. To compare the effects of biotic and abiotic factors on SOM mineralization between upland and paddy soils, we incubated upland and paddy (flooded) soils with three low molecular weight organic substances (LMWOS, i.e., glucose, acetic acid, or oxalic acid) for 30 days under field conditions. Generally, the average CO2 efflux from upland soil was higher than that in paddy soil with the same LMWOS addition. The total content of phospholipid fatty acids (PLFAs) in paddy soil was 2–5 times higher than that of upland soil, irrespective of the LMWOS added. Redundancy analyses indicated that microbial community composition was influenced mainly by the low redox potential (Eh) and dissolved organic carbon in paddy soil. Structural equation modeling revealed that, among abiotic factors, temperature exerted indirect effects on SOM mineralization by influencing biotic factors in both soils; Eh has a positive and direct effect on SOM mineralization in paddy soil. In terms of biotic factors, SOM mineralization in upland soil was mainly regulated by the quantity of bacteria. In paddy soil, SOM mineralization was largely influenced by the ratio of fungal to bacterial PLFAs and peroxidase activity.

Although root mucilage plays a prominent role in soil-plant-water relations, especially under drought, its persistence in soil and its microbial decomposition remain unknown. The aim of this study was to investigate: 1) the effect of soil moisture on mucilage decomposition, 2) the effect of mucilage on enzyme activities, and 3) the effect of mucilage on soil organic matter (SOM) decomposition. We hypothesized that mucilage benefits soil microorganisms by compensating for the detrimental effects of drought. Consequently, low water content was expected to reduce SOM mineralization and enzyme activities only in soil without mucilage. High moisture was predicted to support high microbial activities and therefore rapid decomposition of the mucilage. Two doses of maize root mucilage (40 and 200 μg C g−1 soil; C4 plant derived) were added to a C3 soil at optimum moisture (80% WHC) and under drought (30% WHC) to test these hypotheses. Under optimum moisture conditions, CO2 efflux from soil increased in proportion to mucilage addition. In contrast, there was no effect of mucilage on CO2 efflux under drought. At 80% WHC, mucilage was nearly completely decomposed (98% and 88% for low and high dose, respectively) after 15 days. Drought significantly suppressed mucilage mineralization. Microbial uptake of mucilage C was independent of soil moisture, suggesting that its bioavailability is regulated not by the water content of the whole soil, but by the water within the swollen mucilage. The high mucilage dose increased microbial biomass at both moisture levels compared to the soil without mucilage. Positive priming of soil organic matter decomposition was induced by mucilage at 80% WHC, whereas at 30% WHC, mucilage caused slightly negative priming. Mucilage addition counteracted the decrease of enzyme activities at 30% WHC, and so, stabilized the catalytic activity irrespective of soil moisture content. We conclude that mucilage provides biofilm-like properties that maintain microbial and exoenzymatic activities, even under drought. The slow decomposition of mucilage in drying soils suggests that mucilage maintains moist conditions around the roots for a long period, supporting beneficial root-microbial interactions at low water availability. This would result in a positive ecological feedback for microbial life in the rhizosphere and enhance nutrient release for roots under water scarcity.

The soil microbial carbon pump (MCP) is increasingly acknowledged as being directly linked to soil organic carbon (SOC) accumulation and stability. Given the close coupling of carbon (C) and nitrogen (N) cycles and the constraints imposed by their stoichiometry on microbial growth, N addition might affect microbial growth strategies with potential consequences for necromass formation and carbon stability. However, this topic remains largely unexplored. Based on two multi-level N fertilizer experiments over 10 years in two soils with contrasting soil fertility located in the North (Cambisol, carbon-poor) and Southwest (Luvisol, carbon-rich), we hypothesized that different resource demands of microorganism elicit a trade-off in microbial growth potential (Y-strategy) and resource-acquisition (A-strategy) in response to N addition, and consequently on necromass formation and soil carbon stability. We combined measurements of necromass metrics (MCP efficacy) and soil carbon stability (chemical composition and mineral associated organic carbon) with potential changes in microbial life history strategies (assessed via soil metagenomes and enzymatic activity analyses). The contribution of microbial necromass to SOC decreased with N addition in the Cambisol, but increased in the Luvisol. Soil microbial life strategies displayed two distinct responses in two soils after N amendment: shift toward A-strategy (Cambisol) or Y-strategy (Luvisol). These divergent responses are owing to the stoichiometric imbalance between microbial demands and resource availability for C and N, which presented very distinct patterns in the two soils. The partial correlation analysis further confirmed that high N addition aggravated stoichiometric carbon demand, shifting the microbial community strategy toward resource-acquisition which reduced carbon stability in Cambisol. In contrast, the microbial Y-strategy had the positive direct effect on MCP efficacy in Luvisol, which greatly enhanced carbon stability. Such findings provide mechanistic insights into the stoichiometric regulation of MCP efficacy, and how this is mediated by site-specific trade-offs in microbial life strategies, which contribute to improving our comprehension of soil microbial C sequestration and potential optimization of agricultural N management.

Ridge and furrow (RF) crop cultivation systems with crops planted in furrows or on ridges, modifies soil properties by altering field topography and optimizing water and N fluxes as well as temperature regime. The RF cultivation can be used to mitigate environmental stresses that restrict crop production, such as drought, low temperatures, high soil bulk density, and even flooding. There is broad diversity of RF systems, each of which is tailored to specific objectives under local climatic and soil conditions. Despite the worldwide spread and importance of these cultivation systems, there is no clear systematization of RF fields or evaluation of changes in water and N fluxes compared with flat cultivation. Here, we performed a meta-analysis and literature review to provide a comprehensive characterization of RF cultivation on the basis of the main aims, and management of water and nutrients. The most important difference between RF and flat cultivation practices is the complete change in water infiltration and fluxes in soils as well as associated nutrient losses, especially nitrogen (N). Furrow planting involves the collection of rainwater in the rooted zone, providing an advantage under droughts. Increasing the N content in rooted soil is the main advantage of ridge planting, but the low soil moisture in ridges may limit N availability. Covering ridges with mulch optimizes water redistribution and reduces N leaching, NH3 volatilization and N2O emissions, which in turn increases the benefits of RF cultivation. With a broad range of crops, RF cultivation raises yield and N uptake, and generally increase N use efficiency (NUE; yield / N uptake) and water use efficiency (WUE; yield/evapotranspiration (ET)), and reduce ET, compared with flat planting. RF cultivation has good adaptability to climate change, effectively addressing various environmental stresses. Moderate temperatures maximize the rate of yield increase under RF cultivation. Furrow planting can more effectively increases yields in dry climates than in wet climates. Under humid conditions, ridge planting retains moisture in the ridges, thereby increasing WUE, NUE and yield, while reducing waterlogging. Factors such as microtopography, mulch coverage, stemflow, irrigation, climate, and plant uptake influence water and N redistribution, vertical and lateral infiltration. Lateral infiltration is critical in regulating soil moisture and water storage in the root zone, thereby reducing water loss and raising water uptake by roots. Preventing fertilizer N loss through water infiltration and maintaining N availability increase NUE and WUE, while reducing N losses. Modelling and upscaling of water and N fluxes in RF systems are highly challenging. Future research should focus on the redistribution of factors limiting crop growth via RF topography and mulching as well as to consider the specifics of soil surface modification.

No abstract is provided for this article.

No abstract is provided for this article.

This dataset is composed of two datasets. Dataset1 includes geographic location, soil layer thickness, soil organic carbon, bulk density, soil organic carbon density, basal mirobial respiration, cumulative priming effect and relative priming effect across 24 sampling sites on the Tibetan Plateau. Dataset2 includes CO2 emission rate and δ13C values across 24 sampling sites during the 60-day incubation. At each site, both CO2 emission rate and δ13C values of three parallel samples were measured for 9 times on days 1, 2, 4, 9, 15, 22, 30, 45, and 60.

Soil nitrogen (N) is frequently limiting forest productivity, especially in plantations. To investigate the soil N dynamics and the consequences of N accumulation as well as the losses in the ecosystem, we studied a chronosequence of Chinese-fir (Cunninghamia lanceolata [Lamb.] Hook) plantations with stands aged 3, 16, 25, 32, and >80 years. Total N (TN), dissolved organic N (DON), microbial biomass N (MBN) and mineral N (i.e., ammonium (NH4 +) and nitrate (NO3 −)) in the top 0–5 cm and 5–15 cm soils were compared with the annual N accumulation by trees, annual litter N return and microbial N transformation rates. Stronger changes with stand age were observed in all N forms in the top 5 cm compared to the 5–15 cm layer. Topsoil TN and DON increased steadily in stands from ages 3- to >80-years-old by 1.9-times and 2.1-times, respectively. MBN increased from 206 mg kg−1 to 327 mg kg−1 in the first 25 years and stabilized thereafter. NH4 + content increased sharply from 3 to 16 years and then stabilized, while NO3 − increased linearly with stand age. Both N demand of Chinese-fir and litter N input were clearly age dependent and defined the soil N status: rapid tree biomass accumulation in younger stands greatly depleted soil N, while the older stands with larger litter return and slower growth enabled N re-accumulation in the topsoil. The close positive correlation between total mineral N and gross mineralization rate, as well as between NO3 − and gross nitrification rate indicated that the mineralization of soil organic matter and the nitrification of released NH4 + were the two primary microbial processes controlling the available N supply. The topsoil NO3 −: NH4 + ratio in older stands (32- and >80 years) was greater than 1.0, and the MBN: (NH4 + + NO3 −) ratio was greatly reduced. This indicates that N availability increase and N cycling is accelerated with stands age.