Publications

Root detritusphere is one of the most important sources of N2O, however, understanding of how N2O emission from the detritusphere is influenced by soil properties remains elusive. Here, we evaluated the effects of pore architecture and soil moisture on N2O emission during the decomposition of in-situ grown roots of switchgrass, an important bioenergy crop. We combined dual isotope labeling (15C and 15N) with zymography to gain insights into the location of the microbial N2O production in soils with contrasting pore architectures. In the studied soil, the effect of soil pore architecture on N2O emissions was 6 times greater than that of soil moisture. Soil dominated by > 30 μm Ø pores (i.e., large-pore soil) had higher chitinase activity than the soil dominated by < 10 μm Ø pores (i.e., small-pore soil), especially near the decomposing roots. The chitinase activity on the decomposing roots was positively correlated with emission of root-derived N2O, indicating that N released from root decomposition was an important source of N2O. Greater N2O and N2 emission was induced by switchgrass roots in soils dominated by the large- compared to the small-pore soils. The microenvironment developed near decomposing roots of the large-pore soil also resulted in positive N2O priming. Our study challenged the traditional view on soil moisture as the main factor of N2O production. Production and emission of N2O was most intensive in microbial activity hotspots (i.e., rhizosphere legacy) in the large pores, where decomposed roots release mineral N as the main N2O source.

Since the late 1950s, governmental rangeland policies have changed the grazing management on the T ibetan P lateau ( TP ). Increasing grazing pressure and, since the 1980s, the privatization and fencing of pastures near villages has led to land degradation, whereas remote pastures have recovered from stronger overgrazing. To clarify the effect of moderate grazing on the carbon ( C ) cycle of the TP , we investigated differences in below‐ground C stocks and C allocation using in situ 13 CO 2 pulse labeling of (i) a montane K obresia winter pasture of yaks, with moderate grazing regime and (ii) a 7‐year‐old grazing exclosure plot, both in 3440 m asl. Twenty‐seven days after the labeling, 13 C incorporated into shoots did not differ between the grazed (43% of recovered 13 C ) and ungrazed (38%) plots. In the grazed plots, however, less C was lost by shoot respiration (17% vs. 42%), and more was translocated below‐ground (40% vs. 20%). Within the below‐ground pools, &lt;2% of 13 C was incorporated into living root tissue of both land use types. In the grazed plots about twice the amount of 13 C remained in soil (18%) and was mineralized to CO 2 (20%) as compared to the ungrazed plots (soil 10%; CO 2 9%). Despite the higher contribution of root‐derived C to CO 2 efflux, total CO 2 efflux did not differ between the two land use types. C stocks in the soil layers 0–5 and 5–15 cm under grazed grassland were significantly larger than in the ungrazed grassland. However, C stocks below 15 cm were not affected after 7 years without grazing. We conclude that the larger below‐ground C allocation of plants, the larger amount of recently assimilated C remaining in the soil, and less soil organic matter ‐derived CO 2 efflux create a positive effect of moderate grazing on soil C input and C sequestration.

The rates of soil carbon renewal were determined by the method of natural 13C abundance in a chernozem under a 40-year-long monoculture of corn and in a gr

Soil microbial alpha diversity is essential for driving ecosystem functions and processes. However, little is known about the beta-diversity affect communi

Carbon (C) and nitrogen (N) input strongly influence the formation, turnover, and sequestration of soil organic carbon (SOC) in agricultural ecosystems. However, it is not yet clear how N inputs regulate the contributions of plant- and microbially-derived C to SOC sequestration under straw return. To fill this knowledge gap, a long-term (18 years) field experiment was conducted to elucidate the response of SOC sequestration to straw return and N fertilization assessed by plant and microbial biomarkers, and enzyme activities. Straw returns increased SOC content and the proportion of total lignin (mainly vanillyl and syringyl) phenols in SOC. In contrast, straw return decreased the contribution of cinnamyl phenols to SOC. In addition, straw return increased phospholipid fatty acids (PLFA) content and enzyme activities, which indicated the acceleration of straw decomposition. Therefore, this contradiction means that lignin alone is not sufficient to assess the contribution of plant-derived C to SOC under straw return. N fertilization increased the contents of SOC, PLFA and microbial necromass, as well as activity of C and N-acquiring enzymes. N fertilization decreased the maximal plant residue contribution to SOC, but raised the portion of microbial necromass (especially bacterial necromass) C. Accordingly, N fertilization accelerated the microbial utilization of straw and consequently microbial necromass formation. In terms of PLFA composition and necromass content, Ascomycota and Basidiomycota, Actinobacteria, and Gram-negative bacteria were the key groups forming microbial necromass and consequently SOC. N fertilization boosted the involvement of bacterial necromass in nutrient cycling, which in turn stimulated plant and microbial growth. Although the bacterial necromass contribution to SOC was increased under N fertilization, the relative importance of fungal necromass C in SOC sequestration was highest compared to bacterial necromass and lignin phenols. Concluding, N fertilization and straw return accelerated straw utilization, microbial turnover and necromass formation, thereby increasing SOC sequestration.

Agricultural practices such as tillage, cover crops, and nitrogen (N) fertilization affect physico-chemical and biological soil parameters. However, these factors were often studied separately and their combined effects remain unclear, especially with respect to soil microbial functional diversity and carbon (C) and N content. Thereafter, we aim to assess the links between cropping systems and functional response of microbial communities by using a large range of soil chemical and biological measurements. A 5-yr field experiment was conducted in Northern France using a combination of three factors: i) no-till (NT) vs. conventional tillage (CT); ii) with or without winter cover crops (bare fallow; cover crops with a low prevalence of legumes; cover crop with a high prevalence of legumes); and iii) with or without N fertilization. C and N inputs from cover crops and crop residues, C and N content, enzyme activities, and microbial functional diversity in the topsoil (0–10cm) were measured over an industrial crop rotation: wheat, pea, corn, wheat, flax. No-till combined with any of the cover crops was characterized by increased total soil organic C and N contents by more than 20% between 2010 and 2015. Dehydrogenase and urease activities were significantly greatest under NT, irrespective of the presence of cover crops. Cover crops without N fertilization under no-till led to higher microbial functional activity (faster carbohydrate and phenolic compound degradation) and diversity. Bare fallow had lower soil microbial functional diversity and C and N contents compared with soil under NT and cover crops. On the other hand, NT associated with cover crops allowed to maintain the soil in both C and N, and to promote microbial activities without N fertilization. In conclusion, winter cover crops and/or NT are sustainable agricultural practices resulting in a greater soil quality index. These results demonstrate that NT and use of standard cover crops or cover crops with legumes for 5 years under a low biomass return in industrial crop production have a positive effect on: i) upper soil C content and microbial enzymes, irrespective of N fertilization regime; ii) soil microbial functional diversity in the absence of N fertilization.

Straw incorporation into soils is an effective and low-cost approach to sequester organic carbon (C) and improve soil quality. However, the interactive effects of soil moisture and temperature on soil organic matter (SOM) mineralization were unclear in the presence of plant residues. We evaluated influences of 13C labeled maize (Zea mays) straw on SOM mineralization in two soils with contrasting soil C content (3.0% and 6.8%) under two moisture levels (45% or 65% water-holding capacity (WHC)) and two temperatures (12°C or 22°C) by an experiment incubation. Without straw addition, CO2 production at 22°C was 2-3 times more than at 12°C, and was 31-40% higher at 65% WHC than at 45% WHC in both soils. Soil temperature and moisture interactively affected straw decomposition. After a 66-day incubation, approximately 7-11% of straw was decomposed to CO2, contributing 44-67% to the total CO2 production. Straw addition increased SOM mineralization at all temperature and moisture levels resulting in positive priming effect (PE), with the highest PE in 45% WHC at 22℃ in both soils. Temperature sensitivity (Q10 value) of native SOM mineralization decreased with straw addition due to higher quality SOM (i.e., higher the basal microbial respiration rate per unit organic C at 0°C and DOC/SOC) compared with control (no straw addition). The Q10 values of SOM and straw decomposition was higher at 65% WHC compared to 45% WHC, implying that the drought condition has potential to dampen effects of temperature on the decomposition. We also found the Q10 was positively correlated with activation energy and negatively with soil C quality, which supporting the C quality–temperature hypothesis. Summarizing, our findings contribute to the better understanding of soil C dynamic response to exogenous C input under environment change.

Increasing soil organic carbon (SOC) in agroecosystems is necessary to mitigate climate change and soil degradation. Management practices designed to reach this goal call for a deeper understanding of the processes and drivers of soil carbon input stabilization. We identified main drivers of SOC stabilization in oil palm plantations using the well‐defined spatial patterns of nutrients and litter application resulting from the usual management scheme. The stabilization of oil palm‐derived SOC (OP‐SOC) was quantified by δ 13 C from a shift of C4 (savanna) to C3 (oil palm) vegetations. Soil organic carbon stocks under frond piles were 20% and 22% higher compared with harvest paths and interzones, respectively. Fertilization and frond stacking did not influence the decomposition of savanna‐derived SOC. Depending on management zones, net OP‐SOC stabilization equalled 16–27% of the fine root biomass accumulated for 9 years. This fraction was similar between frond piles and litter‐free interzones, where mineral NPK fertilization is identical, indicating that carbon inputs from dead fronds did not stabilize in SOC. A path analysis confirmed that the OP‐SOC distribution was largely explained by the distribution of oil palm fine roots, which itself depended on management practices. SOC mineralization was proportional to SOC content and was independent on phosphorus availability. We conclude that SOC stabilization was driven by C inputs from fine roots and was independent of alteration of SOC mineralization due to management. Practices favouring root growth of oil palms would increase carbon sequestration in soils without necessarily relying on the limited supply of organic residues.

No abstract is provided for this article.

Background Soil organic matter (SOM) formed under legume‐based grasslands may serve as an important source of nitrogen (N) for subsequent maize growth. Aim We aimed at studying effects of fertilizer type (organic and mineral N and phosphorus (P) fertilizers) on N release from recently formed SOM and N utilization by plants. Methods The effects of mineral and organic (meat and bone meal) N and P fertilization on SOM turnover were examined under maize ( Zea mays L.) on a sand loamy typic hapludult in an outdoor pot experiment over 55 days. The plant uptake of N derived from recently formed SOM was investigated by dual labeling this SOM pool with 15 N and 13 C. Results Organic and mineral fertilized maize acquired similar amounts of N derived from recently formed SOM, which was twice as high as for unfertilized plants. Rhizosphere soil with organic fertilizer had higher 13 C loss than unplanted soil, whereas no extra 13 C was lost under mineral fertilization. On the contrary, a lower 13 C loss from planted compared to unplanted soil was observed in unfertilized soil. Conclusions Both mineral and organic fertilizers increased plant growth and N uptake, whereas only organic fertilizers accelerated SOM turnover in the rhizosphere as compared to bulk soil. Thus, this study implies that the fertilizer types differently affected the mechanisms controlling the utilization of N bound in recently formed SOM.

No abstract is provided for this article.