Effects of Grazing Intensity on Belowground Carbon and Nitrogen Cycling

Livestock grazing activities substantially affect grassland ecosystem functions such as carbon (C) and nitrogen (N) cycles. Although numerous individual and synthesized studies had been conducted, how grazing, especially its intensity, affects belowground C and N cycling in grasslands remains poorly understood. In this chapter, our previous published studies were summarized to elucidate the 19 variables associated with belowground C and N cycling in response to livestock grazing across global grasslands. Overall, grazing significantly decreased belowground C and N pools in grassland ecosystems, with the largest decreases observed in microbial biomass C and N (21.62 and 24.40%, respectively). However, the response magnitude and directions of belowground C- and N-related variables largely depend on grazing intensities. Specifically, light grazing promoted soil C and N sequestration, whereas moderate and heavy grazing significantly accelerated C and N losses. This study highlights the importance of grazing intensity for belowground C and N cycling, which urges scientists to incorporate it into regional and global models for predicting human disturbance on global grasslands and assessing the climate-biosphere feedbacks accurately

Global systematic review with meta-analysis shows that warming effects on terrestrial plant biomass allocation are influenced by precipitation and mycorrhizal association

Biomass allocation in plants is fundamental for understanding and predicting terrestrial carbon storage. Yet, our knowledge regarding warming effects on root: shoot ratio (R/S) remains limited. Here, we present a meta-analysis encompassing more than 300 studies and including angiosperms and gymnosperms as well as different biomes (cropland, desert, forest, grassland, tundra, and wetland). The meta-analysis shows that average warming of 2.50 °C (median = 2 °C) significantly increases biomass allocation to roots with a mean increase of 8.1% in R/S. Two factors associate significantly with this response to warming: mean annual precipitation and the type of mycorrhizal fungi associated with plants. Warming-induced allocation to roots is greater in drier habitats when compared to shoots (+15.1% in R/S), while lower in wetter habitats (+4.9% in R/S). This R/S pattern is more frequent in plants associated with arbuscular mycorrhizal fungi, compared to ectomycorrhizal fungi. These results show that precipitation variability and mycorrhizal association can affect terrestrial carbon dynamics by influencing biomass allocation strategies in a warmer world, suggesting that climate change could influence belowground C sequestration

Mid-infrared octave-spanning supercontinuum and frequency comb generation in a suspended germanium-membrane ridge waveguide

Stable octave-spanning supercontinuum (SC) in the mid-infrared (MIR) region finds extensive applications in spectroscopy, metrology, biochemistry, etc. The absorption of conventional silicon- or silicon oxide-dominated nonlinear media makes SC generation in MIR region technically challenging. In this paper, we propose ultra-broadband MIR-SC generation using a suspended germanium-membrane ridge waveguide. We theoretically showed that when pump pulses centered at 4.8 um with pulse width at 180 fs and peak power at 800 W are injected into a 4-mm long proposed ridge waveguide, the SC generated ranges from 1.96 ~ 12 um (about 2.6 octaves), extending deep into the “fingerprint” region. The first-order coherence is calculated to confirm the stability of the generated SC. The performance of the SC-based frequency comb is also investigated by assuming a 100-pulses pump source at a repetition rate of 100 KHz

Forest restoration decouple soil C:N:P stoichiometry but has little effects on microbial biodiversity globally

11 páginas.- 7 figuras.- 71 referenciasIntroduction: Forest restoration is an effective way to promote ecosystem functions and mitigate climate change. However, how forest restoration affect soil C:N:P stoichiometry and microbial biodiversity, as well as their linkage across contrasting forest types globally remains largely illusive. Materials and Methods: Here we conducted a global meta-analysis by synthesizing 121 published papers with 1649 observations to explore how forest restoration affect soil C:N:P stoichiometry and microbial biodiversity globally. Results: Forest restoration significantly increased soil total carbon (C), nitrogen (N) and phosphorus (P) content, whereas having no significant impact on most microbial diversity indicator, except for an enhancement in bacterial operational taxonomic unit and fungal Simpson. Meanwhile, forest restoration effects on soil C:N:P stoichiometry varied with different forest types, with promoting more soil C and P in ectomycorrhizal than those in arbuscular mycorrhizal forests. Meanwhile, forest restoration induced changes in soil N and P were positively correlated with microbial Shannon index. More importantly, forest restoration effects on soil C:N:P stoichiometry and microbial biodiversity were regulated by climate factors such as mean annual temperature and mean annual precipitation. Conclusion: Our results highlight the crucial role of forest restoration in decoupling the biogeochemical cycles of C, N and P through changes in microbial biodiversity. Therefore, incorporating the decouple effects of forest restoration on soil C:N:P stoichiometry into Earth system models may improve predictions of climate–forest feedbacks in the Anthropocene. © 2023 The Authors. Journal of Sustainable Agriculture and Environment published by Global Initiative of Sustainable Agriculture and Environment and John Wiley & Sons Australia, Ltd.Guiyao Zhou was supported by Humboldt Research Foundation. This research was financially supported by the National Natural Science Foundation of China (grant numbers 32071593, 31930072, 31770559, 31600387, 31370489 and 42203076).Peer reviewe

Demonstration of intermodal four-wave mixing by femtosecond pulses centered at 1550 nm in an air-silica photonic crystal fiber

In this paper, we demonstrated experimentally the intermodal four-wave mixing effect by launching femtosecond pulses centered at 1550 nm into deeply normal dispersion region in the fundamental guided-mode of an air-silica photonic crystal fiber with two zero dispersion wavelengths. When intermodal phase-matching condition is satisfied, the energy of the pump waves at 1550 nm in the fundamental guided-mode is converted to the anti-Stokes waves around 1258 nm and Stokes waves around 2018 nm both in the second-order guided-mode. When femtosecond pulses at input average power Pav of 90 mW are propagated inside 22 cm long photonic crystal fiber, the conversion efficiencies ηas and ηs of the anti-Stokes and Stokes waves generated are 8.5 and 6.8%, respectively. We also observed that the influences of the fiber bending and walk-off effect between the fundamental and second-order guided-modes on intermodal four-wave mixing-based frequency conversion process are very small

Mycorrhizal associations relate to stable convergence in plant-microbial competition for nitrogen absorption under high nitrogen conditions

117 págibnas.- 4 figuras.- referencias.-Nitrogen (N) immobilization (Nim, including microbial N assimilation) and plant N uptake (PNU) are the two most important pathways of N retention in soils. The ratio of Nim to PNU (hereafter Nim:PNU ratio) generally reflects the degree of N limitation for plant growth in terrestrial ecosystems. However, the key factors driving the pattern of Nim:PNU ratio across global ecosystems remain unclear. Here, using a global data set of 1018 observations from 184 studies, we examined the relative importance of mycorrhizal associations, climate, plant, and soil properties on the Nim:PNU ratio across terrestrial ecosystems. Our results show that mycorrhizal fungi type (arbuscular mycorrhizal (AM) or ectomycorrhizal (EM) fungi) in combination with soil inorganic N mainly explain the global variation in the Nim:PNU ratio in terrestrial ecosystems. In AM fungi-associated ecosystems, the relationship between Nim and PNU displays a weaker negative correlation (r = −.06, p < .001), whereas there is a stronger positive correlation (r = .25, p < .001) in EM fungi-associated ecosystems. Our meta-analysis thus suggests that the AM-associated plants display a weak interaction with soil microorganisms for N absorption, while EM-associated plants cooperate with soil microorganisms. Furthermore, we find that the Nim:PNU ratio for both AM- and EM-associated ecosystems gradually converge around a stable value (13.8 ± 0.5 for AM- and 12.1 ± 1.2 for EM-associated ecosystems) under high soil inorganic N conditions. Our findings highlight the dependence of plant–microbial interaction for N absorption on both plant mycorrhizal association and soil inorganic N, with the stable convergence of the Nim:PNU ratio under high soil N conditions.This research was financially supported by the National Natural Science Foundation of China (grant nos. 32241032, 31930072, 42261144688, 32271713, 32071593, and 42203076), and the Fundamental Research Funds for the Central Universities (grant no. 2572022BA08). MPT acknowledges the support from the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number: M822.00029. G. Zhou acknowledges the support from Ramón y Cajal project (RYC2022-035226-I) funded by the Spanish Ministry of Science and Innovation, the NextGenerationEU program of the European Union (MICIU/AEI/10.13039/501100011033 y el FSE+), and AYUDAS DE EXCELENCIA RYC-MAX 2023 project from Spanish National Research Council.Peer reviewe

New perspectives on microbiome and nutrient sequestration in soil aggregates during long-term grazing exclusion

15 páginas.- 5 figuras.- referencias.-Grazing exclusion alters grassland soil aggregation, microbiome composition, and biogeochemical processes. However, the long-term effects of grazing exclusion on the microbial communities and nutrient dynamics within soil aggregates remain unclear. We conducted a 36-year exclusion experiment to investigate how grazing exclusion affects the soil microbial community and the associated soil functions within soil aggregates in a semiarid grassland. Long-term (36 years) grazing exclusion induced a shift in microbial communities, especially in the 2 mm aggregates, and reduced carbon (C) sequestration potential thus revealing a negative impact of long-term GE. In contrast, 11–26 years of grazing exclusion greatly increased C sequestration and promoted nutrient cycling in soil aggregates and associated microbial functional genes. Moreover, the environmental characteristics of microhabitats (e.g., soil pH) altered the soil microbiome and strongly contributed to C sequestration. Our findings reveal new evidence from soil microbiology for optimizing grazing exclusion duration to maintain multiple belowground ecosystem functions, providing promising suggestions for climate-smart and resource-efficient grasslands.This work was financially supported by the National Natural Science Foundation of China (32061123007, 41977031), the Strategic Priority Research Program of Chinese Academy of Sciences (XDB40020202), and the Natural Science Foundation of Hubei Province, China (2020CFA013). Manuel Delgado-Baquerizo acknowledges support from the Spanish Ministry of Science and Innovation for the I+D+i project PID2020-115813RA-I00 and TED2021-130908B-C41 funded by MCIN/AEI/10.13039/501100011033.Peer reviewe

Disconnection between plant–microbial nutrient limitation across forest biomes

11 páginas.- 7 figuras.- 1 tabla.- 41 referencias.- Additional supporting information can be found online in the Supporting Information section at the end of this article..- Read the free Plain Language Summary for this article on the Journal blog.Nitrogen (N) and phosphorus (P) are essential elements limiting plant–microbial growth in forest ecosystems. However, whether the pattern of plant–microbe nutrient limitation is consistent across forest biomes and the associated potential mechanisms remain largely unclear, limiting us to better understand the biogeochemical processes under future climate change. Here, we investigated patterns of plant–microbial N/P limitation in forests across a wide environmental gradient and biomes in China to explore the divergence of plant–microbial N/P limitation and the driving mechanisms. We revealed that 42.6% of the N/P limitation between plant–microbial communities was disconnected. Patterns in plant–microbial N/P limitations were consistent only for 17.7% of N and 39.7% of P. Geospatially, the inconsistency was more evident at mid-latitudes, where plants were mainly N limited and microbes were mainly P limited. Furthermore, our findings were consistent with the ecological stoichiometry of plants and microbes themselves and their requirements. Whereas plant N and P limitation was more strongly responsive to meteorological conditions and atmospheric deposition, that of microbes was more strongly responsive to soil chemistry, which exacerbated the plant–microbe N and P limitation divergence. Our work identified an important disconnection between plant and microbial N/P limitation, which should be incorporated into future Earth System Model to better predict forest biomes–climate change feedback. Read the free Plain Language Summary for this article on the Journal blog. © 2023 The Authors. Functional Ecology © 2023 British Ecological SocietyNational Natural Science Foundation of China, Grant/Award Number: 42207107; Catalan Government Grant, Grant/Award Number: SGR2017-1005; Fundación Ramón Areces grant, Grant/Award Number: CIVP20A6621; National Key Research and Development Program of China, Grant/Award Number: 2021YFD1901205; Open Fund of Key Laboratory of Agro-Ecological Processes in Subtropical Region, Chinese Academy of Sciences, Grant/Award Number: ISA2021101; Spanish Government, Grant/Award Number: PID2019-110521GB-I00 and PID2020-115770RB-I00; Strategic Priority Research Program of Chinese Academy of Sciences, Grant/Award Number: XDB40020202Peer reviewe

Litter and soil biodiversity jointly drive ecosystem functions

10 páginas.- 4 figuras.- 64 referencias.- Additional supporting information can be found online in the Supporting Information section at the end of this articleThe decomposition of litter and the supply of nutrients into and from the soil are two fundamental processes through which the above- and belowground world interact. Microbial biodiversity, and especially that of decomposers, plays a key role in these processes by helping litter decomposition. Yet the relative contribution of litter diversity and soil biodiversity in supporting multiple ecosystem services remains virtually unknown. Here we conducted a mesocosm experiment where leaf litter and soil biodiversity were manipulated to investigate their influence on plant productivity, litter decomposition, soil respiration, and enzymatic activity in the littersphere. We showed that both leaf litter diversity and soil microbial diversity (richness and community composition) independently contributed to explain multiple ecosystem functions. Fungal saprobes community composition was especially important for supporting ecosystem multifunctionality (EMF), plant production, litter decomposition, and activity of soil phosphatase when compared with bacteria or other fungal functional groups and litter species richness. Moreover, leaf litter diversity and soil microbial diversity exerted previously undescribed and significantly interactive effects on EMF and multiple individual ecosystem functions, such as litter decomposition and plant production. Together, our work provides experimental evidence supporting the independent and interactive roles of litter and belowground soil biodiversity to maintain ecosystem functions and multiple services.SEL acknowledges support from the National Natural Science Foundation of China (grant no. 32101491), fellowship of China Postdoctoral Science Foundation (2022T150375; 2021M701968), and Yunnan Science and Technology Talent and Platform Program (202105AG070002). GYZ acknowledges support from the Humbodlt Research Foundation. JP acknowledges support from the Ramon y Cajal program from the MICINN (RYC-2021-033454). ROH is funded by the Ramon y Cajal program of the MICINN (RYC-2017 22032), by the R & amp;D Project of the Ministry of Science and Innovation PID2019-106004RA-I00 funded by MCIN/AEI/10.13039/501100011033, and by the European Agricultural Fund for Rural Development (EAFRD) through the "Aid to operational groups of the European Association of Innovation (AEI) in terms of agricultural productivity and sustainability", Reference: GOPC-CA-20-0001. BKS acknowledge funding from Australian Research Council (DP210102081). MDB acknowledges support from the Spanish Ministry of Science and Innovation for the I+D+i project PID2020-115813RA-I00 and TED2021-130908B-C41 funded by MCIN/AEI/10.13039/501100011033. Open Access funding enabled and organized by Projekt DEAL.Peer reviewe