Publications

<p>In year 1974, Monsanto introduced the glyphosate [N-(phosphonomethyl) glycine] product RoundUp and in the 1990s also glyphosate resistant crops. Since then, and increasingly after the expiry of the patent, glyphosate has become the most commonly used herbicide worldwide. The estimation of the worldwide use of glyphosate as an active ingredient amounts to more than 800,000 tons/year (estimation from 2014). A herbicide of such wide spread use, commercial in agriculture and for personal use in gardens, has been found in many different environmental compartments (e.g. surface waters and food) and with negative impact on non-target organisms (e.g. glyphosate resistance in weeds, or bactericidal effects). Glyphosate persistence and degradation of the compound differ between strongly between soils. In this study, we focus on elucidating the factors contributing to the persistence and degradation of glyphosate in two contrasting soils. Different chemical additives (N, P, DOM), as well as pH change and microbial transfer alongside glyphosate application were investigated in a <sup>14</sup>C-glyphosate multi-labeling approach, upon their effect on the glyphosate degradation. The study shows that pH initially has a strong positive impact the mineralization in both soils and the DOM addition only increased the mineralization slightly. On the other hand, phosphate addition shows contrasting results in both soils, and nitrate addition lowered the mineralization significantly. Microbial transfer did not have any significant effect on the mineralization. Furthermore, we identify the impact of adsorption of glyphosate in soil as one of the major factors reducing glyphosate degradation.</p>

The location of microorganisms and substrates within soil pore networks plays a crucial role in organic carbon (C) processing, and its microbial utilization and turnover, and has direct consequences for C and nutrient cycling. An optimal approach to quantify responses to new C inputs from microorganisms residing in specific pores is the addition of new C to pores of target sizes in undisturbed soil cores. We used the matric potential approach to add 14 C‐labelled glucose to small (< 40 μm, root free) or large (60–180 μm, potentially inhabited by roots) pores of undisturbed soil cores. Localization of glucose‐derived C via 14 C imaging was related to pore size distributions and connectivity, characterized via X‐ray computed microtomography (μCT), and to β‐glucosidase activity, characterized via zymography. After 2‐week incubations, 1.3 times more glucose was mineralized ( 14 CO 2 ) when it was added to the large pores; however, more 14 C remained in microbial biomass when glucose was added to the small pores. Consequently, although utilizing the same amounts of easily available C, the microorganisms localized in the large pores had faster turnover compared to microorganisms in small pores. Stronger associations between β‐glucosidase activity and glucose‐derived C were observed when glucose was added to the large pores. We conclude that (a) the matric potential approach allows placing, albeit not exactly, of soluble substrates into pores of target diameter range, and (b) microorganisms localized in large pores respond to new C inputs with faster turnover, greater growth and more intensive enzyme production compared to those inhabiting the small pores.

No abstract is provided for this article.

Consequences of interactions between ectomycorrhizal fungi (EcMF) and non‐mycorrhizal rhizosphere fungi (NMRF) for plant carbon (C) allocation belowground and nutrient cycling in soil remain unknown. To address this topic, we performed a mesocosm study with Norway spruce seedlings [ Picea abies (L.) H. Karst] inoculated with EcMF, NMRF, or a mixture of both (MIX). 14 CO 2 pulse labelling of spruce was applied to trace and visualize the 14 C incorporation into roots, rhizohyphosphere and hyphosphere. Activities and localization of enzymes involved in the C, nitrogen (N) and phosphorus (P) cycling were visualized using zymography. Spruce seedlings inoculated with EcMF and NMRF allocated more C to soils (EcMF: 10.7%; NMRF: 3.5% of total recovered C) compared to uninoculated control seedlings. The 14 C activity in the hyphosphere was highest for EcMF and lowest for NMRF. In the presence of both, NMRF and EcMF (MIX), the 14 C activity was 64% lower compared with EcMF inoculation alone. This suggests a suppressed C allocation via EcMF likely due to the competition between EcMF and NMRF for N and P. Furthermore, we observed 57% and 49% higher chitinase and leucine‐aminopeptidase activities in the rhizohyphosphere of EcMF compared to the uninoculated control, respectively. In contrast, β‐glucosidase activity (14.3 nmol cm −2 h −1 ) was highest in NMRF likely because NMRF consumed rhizodeposits efficiently. This was further supported by that enzyme stoichiometry in soil with EcMF shifted to a higher investment of nutrient acquisition enzymes (e.g., chitinase, leucine‐aminopeptidase, acid phosphatase) compared to NMRF inoculation, where investment in β‐glucosidase increased. In conclusion, the alleviation of EcMF from C limitation promotes higher activities of enzymes involved in the N and P cycle to cover the nutrient demand of EcMF and host seedlings. In contrast, C limitation of NMRF probably led to a shift in investment towards higher activities of enzymes involved in the C cycle.

It is crucial to promote soil carbon sequestration while reducing CO2 emissions to mitigate climate change. However, the extent of increasing actual soil carbon storage depends on the amount and composition of organic matter input, including its fate during decomposition and soil organic matter (SOM) formation via microbial transformation. With respect to the need to increase carbon sequestration in soil and sustain soil fertility, it is of great interest to better understand how soils with different organic matter content react to amendment with fresh organic matter. Here, we incubated three agricultural soils representing a gradient in C content, adding two different 13C labeled plant residues varying in carbon-to-nitrogen ratio. Carbon mineralization was monitored together with the analysis of the 13CO2 signatures. After the incubation, 13C compound-specific PLFAs, microbial necromass, and enzyme activities were analyzed. This study demonstrates that the carbon return on investment, thus the amount of retained fresh carbon in relation to the amount of added organic matter, clearly depends on the amount of native soil carbon. Notably, the addition of fresh organic matter to carbon-deficient soils leads to a higher specific CO2 release compared to soils with high carbon loading, which can be attributed to the differences in the soil microorganisms' response. The CO2 release of the soil with the lowest C-content was 2.1 and 2.0 mg g−1 soil for treatment with oat and pea litter addition, respectively, whereas for the soil with the highest C-content, CO2 release was 1.7 mg g−1 soil for oat treatment and 1.6 mg g−1 soil for pea treatment. Thus, higher SOC contents sustain a higher 'return on investment' for the fresh carbon that is amended to soils. With plant litter amendments the microbial community shifted towards a higher fungi-to-bacteria ratio (F/B). This shift in the microbial community was more pronounced (F/B ranging from 0.04 to 0.11) with the addition of oat litter (low quality) compared to pea litter (high quality). Hence, it is important to consider the fate of organic amendments with different N availability when aiming to rebuild soil carbon stocks in degraded soils. Soil management should focus on sustaining soil carbon in balance with current carbon stocks to avoid the vicious circle of soils losing carbon in conjunction with increased greenhouse gas release.

Microorganisms are critical for litter decomposition, organic carbon (C) and nutrient transformations in soil, corresponding to the vegetation succession. The dynamics of microbial activities and ecological functions during the soil recovery after agricultural land use (post-agricultural restoration) remains unclear. We investigated the effects of vegetation and soil restoration duration on active microbial biomass, microbial growth rates, C use efficiency (CUE, analyzed by 14C glucose utilization), and enzyme activities in three soil types of Russia: Haplic Luvisol in a deciduous forest (chronosequence from 0 to 37 years), Luvic Phaeozem in forest steppe (0–66 years), and Haplic Phaeozem in forest steppe (0–42 years). The microbial CUE (0.66–0.82) decreased during restoration and was highly dependent on soil type: the lowest in Luvisol and the highest in Haplic Phaeozem. The activities of β-1,4-glucosidase, β-1,4-N-acetylglucosaminidase, leucine aminopeptidase, and acid phosphatase increased during post-agricultural restoration. Microbial growth rates and the proportion of active microorganisms increased with restoration, reflecting a shift of microbial community to fast-growing decomposers (mainly r strategists) caused by large litterfall from recovered natural vegetation. The increase of the portion of active microorganisms and microbial growth rates was correlated with activities of enzymes responsible for C, N and P cycling. In conclusion, the post-agricultural restoration activates microorganisms, raises microbial growth, increases enzyme activities and accelerates microbially-mediated C and nutrient turnover.

Drought impacts microbial carbon cycling, and thus the fate of carbon in soils. Carbon allocation to energy via CO 2 producing respiration and to biosynthesis via volatile organic compound (VOC) emissions both represent consequent carbon loss to the atmosphere, although only the former is well studied. Here, we examined drought impacts on carbon allocation by soil microbes to CO 2 and VOCs using position-specific 13 C-labeled pyruvate and multi-omics in an artificial tropical rainforest. During drought, 13 C-VOCs efflux increased, driven by increased production and buildup of intermediate metabolites due to decreased interconnectivity between central carbon metabolism pathways, and 13 C-CO 2 efflux decreased, driven by an overall decrease in microbial activity. However, internal carbon allocation to energy relative to biosynthesis did not change, signifying maintained energy demand toward biosynthesis of VOCs and drought-stress induced biosynthesis pathways. Therefore, while carbon loss to the atmosphere via CO 2 decreases during drought, carbon loss via VOCs may increase.

No abstract is provided for this article.

Interactions between the atmosphere, biosphere, cryosphere, hydrosphere, and geosphere are most active in the critical zone, a region extending from the tops of trees to the top of unweathered bedrock. Changes in one or more of these spheres can result in a cascade of changes throughout the system in ways that are often poorly understood. Here we investigate how past and present climate change have impacted permafrost, hydrology, and ecosystems on the Tibetan Plateau. We do this by compiling existing climate, hydrologic, cryosphere, biosphere, and geologic studies documenting change over decadal to glacial-interglacial timescales and longer. Our emphasis is on showing present-day trends in environmental change and how plateau ecosystems have largely flourished under warmer and wetter periods in the geologic past. We identify two future pathways that could lead to either a favorable greening or unfavorable degradation and desiccation of plateau ecosystems. Both paths are plausible given the available evidence. We contend that the key to which pathway future generations experience lies in what, if any, human intervention measures are implemented. We conclude with suggested management strategies that can be implemented to facilitate a future greening of the Tibetan Plateau.