Microbial Respiration Rates Research Articles

Bulk and Active Sediment Prokaryotic Communities in the Mariana and Mussau Trenches.

Surprisingly high rates of microbial respiration have recently been reported in hadal trench sediment, yet the potentially active microorganisms and specific microbe–microbe relationships in trench sediment are largely unknown. We investigated the bulk and active prokaryotic communities and co-occurrence interactions of different lineages in vertically sectioned sediment cores taken from the deepest points of the Mariana and Mussau Trenches. Analysis on species novelty revealed for the first time the high rate of novel lineages in the microbial communities of the hadal trenches. Using 95, 97, and 99% similarity as thresholds, averagely 22.29, 32.3, and 64.1% of total OTUs retrieved from sediments of the two trenches were identified as the potentially novel lineages, respectively. The compositions of the potentially active communities, revealed via ribosomal RNA (rRNA), were significantly different from those of bulk communities (rDNA) in all samples from both trenches. The dominant taxa in bulk communities generally accounted for low proportions in the rRNA libraries, signifying that the abundance was not necessarily related to community functions in the hadal sediments. The potentially active communities showed high diversity and composed primarily of heterotrophic lineages, supporting their potential contributions in organic carbon consumption. Network analysis revealed high modularity and non-random co-occurrence of phylogenetically unrelated taxa, indicating highly specified micro-niches and close microbial interactions in the hadal sediments tested. Combined analysis of activity potentials and network keystone scores revealed significance of phyla Chloroflexi and Gemmatimonadetes, as well as several potentially alkane-degrading taxa in maintaining microbial interactions and functions of the trench communities. Overall, our results demonstrate that the hadal trenches harbor diverse, closely interacting, and active microorganisms, despite the extreme environmental conditions.

The Influence of Depth on Soil Chemical Properties and Microbial Respiration in the Upper Soil Horizons

Soil microbial respiration is a biological process that converts soil organic matter into atmospheric CO2 via soil microorganisms. It reflects the overall metabolic activity of soil microbial populations and usually used as an indicator of soil health. Soil chemical properties, among others, have an influence on a catabolic capacity of the soil and greatly vary among different soil layers. In this study, we examined patterns of chemical soil properties and soil microbial respiration along 0–10 and 10–25 cm depths of the soil to investigate if soil depth had any effects on soil chemical properties and how these changes with depth could shift the soil microbial respiration. We employed basal respiration method to estimate the rate of soil microbial respiration and measured important chemical properties using standard protocols. The results showed differential effects of soil depth on chemical properties where available nitrogen ( $${\text{NH}}_{{\text{4}}}^{{\text{ + }}}$$ –N, $${\text{NO}}_{3}^{ - }$$ –N, and total N), cation exchange capacity, and Mg2+ were strongly influenced by soil depth. Soil microbial respiration greatly differed among the two soil depths (p = 0.0005) with a higher rate of soil microbial respiration in surface soils compared to subsurface soils. Soil microbial respiration had a significant positive correlation with total N, $${\text{NO}}_{3}^{ - }$$ –N, $${\text{NH}}_{{\text{4}}}^{{\text{ + }}}$$ –N, and soil organic matter (r = 0.98, 0.974, 0.9625, and 0.9455, respectively). The variation of soil microbial respiration was closely linked with the variation of soil organic matter and available nitrogen, implying that these variables were the key drivers of the variation of soil microbial respiration in the study area. Overall, the study highlighted that soil quality assessments and managements should include the depth effects to provide a better understanding of the dynamics of microbial respiration in the soil.

Compensatory Thermal Adaptation of Soil Microbial Respiration Rates in Global Croplands

AbstractUnderstanding whether soil microbial respiration adapts to the ambient thermal climate with an enhanced or compensatory response, hence potentially stimulating or slowing down soil carbon losses with warming, is key to accurately forecast and model climate change impacts on the global carbon cycle. Despite the interest in this topic and the plethora of recent studies in natural ecosystems, it has been seldom explored in croplands. Using two recently published independent datasets of soil microbial metabolic quotient (MMQ; microbial respiration rate per unit biomass) and carbon use efficiency (CUE; partitioning of C to microbial growth vs. respiration), we find a compensatory thermal adaptive response for MMQ in global croplands. That is, mean annual temperature (MAT) has a negative effect on MMQ. However, this compensatory thermal adaptation is only half or less of that found in previous studies for noncultivated ecosystems. In contrast to the negative MMQ‐MAT pattern, microbial CUE increases with MAT across global croplands. By incorporating this positive CUE‐MAT relationship (greater C partitioning into microbial growth rather than respiration with increasing temperature) into a microbial‐explicit soil organic carbon model, we successfully predict the thermal compensation of MMQ observed in croplands. Our model‐data integration and database cross‐validation suggest that a warmer climate may select for microbial communities with higher CUE, providing a plausible mechanism for their compensatory metabolic response. By helping to identify appropriate representations of microbial physiological processes in soil biogeochemical models, our work will help build confidence in model projections of cropland C dynamics under a changing climate.

Low-severity fire as a mechanism of organic matter protection in global peatlands: Thermal alteration slows decomposition.

Worldwide, regularly recurring wildfires shape many peatland ecosystems to the extent that fire-adapted species often dominate plant communities, suggesting that wildfire is an integral part of peatland ecology rather than an anomaly. The most destructive blazes are smoldering fires that are usually initiated in periods of drought and can combust entire peatland carbon stores. However, peatland wildfires more typically occur as low-severity surface burns that arise in the dormant season when vegetation is desiccated, and soil moisture is high. In such low-severity fires, surface layers experience flash heating, but there is little loss of underlying peat to combustion. This study examines the potential importance of such processes in several peatlands that span a gradient from hemiboreal to tropical ecozones and experience a wide range of fire return intervals. We show that low-severity fires can increase the pool of stable soil carbon by thermally altering the chemistry of soil organic matter (SOM), thereby reducing rates of microbial respiration. Using X-ray photoelectron spectroscopy and Fourier transform infrared, we demonstrate that low-severity fires significantly increase the degree of carbon condensation and aromatization of SOM functional groups, particularly on the surface of peat aggregates. Laboratory incubations show lower CO2 emissions from peat subjected to low-severity fire and predict lower cumulative CO2 emissions from burned peat after 1-3years. Also, low-severity fires reduce the temperature sensitivity (Q10 ) of peat, indicating that these fires can inhibit microbial access to SOM. The increased stability of thermally altered SOM may allow a greater proportion of organic matter to survive vertical migration into saturated and anaerobic zones of peatlands where environmental conditions physiochemically protect carbon stores from decomposition for thousands of years. Thus, across latitudes, low-severity fire is an overlooked factor influencing carbon cycling in peatlands, which is relevant to global carbon budgets as climate change alters fire regimes worldwide.

Effect of Lignohumate on Soil Biological Activity on the Bali Island, Indonesia

The effect of commercial humic product Lignohumate® on the biological activity of Latosol under long-term agricultural use with application of pesticides at the Bali Island (Indonesia) was evaluated in model experiments. It was shown that the application of lignohumate in a concentration gradient 0.025–2.5 mg/g resulted in increase in soil microbial community respiration rate by 10–30%, proportionally to the rate applied. As the application rate of Lignohumate increased, a significant threefold increase of nitrogen fixation intensity caused by the activation of bacteria of the Oxalobacteriaceae family was observed. In general, the bacterial community of Latosol consisted of more than 85% of the representatives of four phyla: Proteobacteria, Firmicutes, Chloroflexi, and Acidobacteria. Lignohumate at application rates higher than 0.025 mg/g promoted an increase of methane formation, whereas gaseous nitrogen losses due to denitrification reduced. An important practical conclusion on the reduction of a toxic effect of pesticides in the presence of lignohumate and its positive effect on soil biological activity and nitrogen balance in the Latosol under intensive agricultural use was made.

Lean and keen: Microbial activity in soils from the Maritime Antarctic

AbstractThe soils of the Maritime and sub‐Antarctic experience extreme environmental conditions but nonetheless host biological communities that can survive low temperatures, limited water availability and short day lengths or even the complete absence of solar radiation during the winter. We determined the soil organic carbon (SOC) and total nitrogen (N), soil microbial biomass (SMB), labile carbon (LC) and respiration rate (RR) in soil samples from the longest latitudinal transect (approximately 2,000 km) ever sampled exclusively in the Maritime and sub‐Antarctic, comprising 69 sites located between South Georgia (54°S) and south‐eastern Alexander Island (72°S). With the exception of the most northerly location (South Georgia), the greatest SMB values occurred at 67–68°S, despite the harsh environmental conditions. This is consistent with the relative nutrient richness of the soils at these latitudes, as indicated by large SOC and total soil N concentrations, which are in turn probably linked to more abundant guano and excreta deposition by sea birds and seals, which have fewer and smaller areas of ice‐free terrain to land or haul out on further south. South of 68°S, SOC values declined with increasing latitude, which is probably due to increasingly extreme environmental conditions. We also found that the SOC and SMB values, the proportion of SOC considered labile (LC/SOC) and the carbon mineralization rates expressed as either RR/SOC or RR/SMB were all small compared with values from less extreme temperate and tropical regions. However, the proportion of the SOC in the microbial biomass (SMB/SOC) was substantially greater than that reported for non‐polar soils. We conclude that although the soils of the Maritime and sub‐Antarctic have small and relatively inactive microbial communities, they are characterized by efficient conversion of organic resources into microbial biomass and large affinities for added substrates.Highlights Soil carbon parameters are reported from sites along the longest latitudinal transect in Antarctica ever sampled. The soil microbial biomass tended to peak at 67–68°S, coinciding with relative SOC and N abundance in the soil, probably arising from guano and excreta from sea birds and mammals. The soil microbial community was small but highly efficient at converting organic resources into microbial biomass, as indicated by large microbial biomass/soil organic carbon ratios.

Farm-scale carbon and nitrogen fluxes in pastoral dairy production systems using different nitrogen fertilizer regimes

The nitrogen (N) fertilizer application rate (kg ha−1 year−1) in pastoral dairy systems affects the flow of N through the soil, plant and animal pools of the system. With better understanding of the magnitude of these pools and their fluxes, dairy systems could be managed to improve N use efficiency, therefore reducing losses to the environment. A study with three levels of N fertilizer, 0 (N0), 150 (N150) and 300 (N300) kg N ha−1 year−1, was conducted in the Canterbury region of New Zealand from 1 June 2017 till 31 May 2018. Farm measurements, e.g. pasture and milk production, were used to calibrate three different farm-scale models, DairyNZ’s Whole Farm Model, DairyMod, and Overseer®. The models were used to extrapolate periodic farm measurements to predictions of carbon (C) and N pools and fluxes on an annual basis. Pasture and milk production per hectare increased from N0 to N300 by 70 and 58%, respectively. There was a concomitant increase in farm-gate N surplus (input–output) of 43%, resulting in predicted increases in N leaching and greenhouse gas emissions of 72 and 67%, respectively. By increasing N fertilizer from 0 to 300 kg N ha−1 year−1, 53% more feed N flowed through the dairy herd with surplus N deposited as urinary N increasing by 49%. Plant uptake and soil immobilization increased by 58 and 343%, respectively, but not enough to avoid substantial increases in leaching and emission losses. Carbon flux through the soil system increased through increased litter and faecal deposition, but with very little C sequestration because of accelerated microbial respiration rates.

亚热带森林转换对土壤微生物呼吸及其熵值的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 亚热带森林转换对土壤微生物呼吸及其熵值的影响 DOI: 10.5846/stxb201810142226 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 海峡联合基金项目（U1505233）；国家自然科学基金项目（31670623） Effects of subtropical forest conversion on soil microbial respiration and its entropy Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:土壤微生物呼吸及其熵值是表征土壤质量变化的敏感性指标，不仅能衡量土壤微生物碳利用效率，还能揭示土壤有机碳的变化。通过比较亚热带米槠天然林转换为马尾松人工林和杉木人工林后土壤微生物呼吸速率、土壤微生物生物量碳以及微生物熵、代谢熵的差异，研究亚热带森林转换对土壤微生物碳利用效率的影响。研究结果显示：（1）与天然林相比，马尾松人工林0-10 cm土壤微生物呼吸速率上升32%（P<0.05），马尾松人工林和杉木人工林10-20 cm土壤微生物呼吸速率分别下降26%和24%（P<0.05）；但在20-40 cm土层和40-60 cm土层，天然林土壤微生物呼吸速率比马尾松人工林分别高50%和43%；（2）马尾松人工林和杉木人工林0-10 cm土层土壤微生物生物量碳（MBC）比天然林分别下降19%和40%（P<0.05），但马尾松人工林10-20 cm土壤MBC上升29%（P<0.05）；（3）人工林表层土壤微生物熵与天然林没有显著差异，但与天然林相比，杉木人工林和马尾松人工林20-40 cm土层土壤微生物熵分别下降51%和71%（P<0.05），40-60 cm分别下降52%、66%（P<0.05）。土壤微生物代谢熵的变化主要发生在0-10 cm土层，马尾松人工林和杉木人工林分别比天然林增加38%和29%（P<0.05），在深层土壤，3种林分微生物代谢熵没有显著差异。亚热带森林转换导致表层土壤微生物碳利用效率下降，深层土壤易分解碳在总有机碳库中占比下降，有机碳可利用程度降低。 Abstract:Soil microbial respiration and its entropy, as a sensitive indicator of soil nutrient variation, are usually used to evaluate the microbial carbon use efficiency and soil carbon concentration variation. In this present study, the effects of forest conversion on microbial carbon use efficiency was studied by comparing differences of soil microbial respiration rate, microbial biomass carbon, microbial entropy, and metabolic entropy between Castanopsis carlessi natural forest (NF) and Pinus massoniana Lamb. plantation (PM) and Cunninghamia lanceolata Lamb. Plantation (CL). The results showed that (1) the soil microbial respiration rate in 0-10 cm of PM was 32% higher than that of NF. The soil microbial respiration rate in 10-20 cm of PM and CL were 26% and 24% lower than those of NF, respectively (P<0.05). The microbial respiration rate in 20-40 cm and 40-60 cm soil layer of NF were 50% and 43% higher than that of PM. (2) Soil microbial biomass carbon (MBC) in 0-10 cm of PM and CL were 19% and 40% lower than those of NF, respectively (P<0.05). The MBC in 10-20 cm of PM was 29% higher than that of NF (P<0.05). (3) Soil microbial entropy in 0-10 cm of CL and PM were not significantly different from that in the natural forest. It decreased 51% and 71% in 20-40 cm, 52% and 66% in 40-60 cm (P<0.05). Effects of forest conversion on metabolic entropy could only be found in 0-10 cm soil layer but not subsurface layer. The metabolic entropy in PM and CL 38% and 29% higher than that of NF, respectively (P<0.05). In conclusion, the forest conversion decreased the soil microbial carbon use efficiency in the surface layer, the ratio of labile to total carbon pool in the surface layer, and availability of organic carbon. 参考文献 相似文献 引证文献

Solar Photochemical Emission of CO2 From Leaf Litter: Sources and Significance to C Loss

Although photodegradation can be a significant mechanism of plant litter decay in drylands, the abiotic photochemical emission component of this process is not well characterized. We measured the temperature response of abiotic photochemical emission of CO2 from 12 litter types under midday sunlight in the Sonoran Desert, assessed what litter traits predicted emission rates, and estimated its significance to litter C loss. Emission rates increased exponentially with temperature (Q10= 1.75) and declined as litter decayed. Rates varied substantially among litter types. Microbial respiration rates of litter explained the most variation in emission rates at lower temperature (78% at 45 °C), suggesting that compounds amenable to microbial consumption were major precursors of emission. In contrast, wax concentrations explained the most variation at high temperature (76% at 70 °C), implying that precursors shifted with temperature. Photochemical emission of initial litter at 55 °C was a strong predictor of the mass loss of litter in full sunlight over 34 months in the field, explaining 67% of the variation among litter types. We estimate that photochemical emission of CO2 was responsible for 10% of all C lost from litter in sunlight over 34 months and accounted for 39% of the greater C lost from litter in sunlight compared to litter that did not receive sunlight in the UV to blue wavelength bands. Hence, abiotic photodegradation via photochemical emission appeared to be a significant pathway for C loss from sunlit litter. The substantial exponential increase in photochemical emission with temperature illustrates that temperature needs to be considered in assessments of abiotic photodegradation and implies this process will be greatest in systems where litter is exposed to high solar irradiance in conjunction with high temperatures.

Soil Microbial Metabolic Quotient in Inner Mongolian Grasslands: Patterns and Influence Factors

Microbial metabolic quotient (MMQ) is the rate of soil microbial respiration per unit of microbial biomass, and represents the capacity of soil microbes to utilize soil organic matter. Understanding the regional variation and determinants of MMQ can help predict the responses of soil respiration rate to global climate change. Accordingly, we measured and analyzed MMQ-related data (e.g., soil basic respiration rate at 20°C and soil microbial biomass) from 17 grassland sites, which located in meadow steppe, typical steppe, and desert steppe along a 1000-km transect across the Inner Mongolian grasslands, China. Results showed that MMQ varied significantly among the different grassland types (P typical > meadow) and decreased from southwest to northeast (r = − 0.81) with increasing latitude (r = − 0.50), and with increasing mean annual precipitation (r = − 0.69). Precipitation accounted for 56% of the total variation in MMQ, whereas temperature accounted for 26%. MMQ was negatively correlated with precipitation across the Inner Mongolian grasslands. Therefore, climate change, especially in regard to precipitation, may influence soil microbial respiration and soil carbon dynamics through altering MMQ. These results highlighted the importance of spatial patterns in MMQ for accurately evaluating the responses of soil respiration to climate change at regional and global scales.

Hyporheic Zone Microbiome Assembly Is Linked to Dynamic Water Mixing Patterns in Snowmelt‐Dominated Headwater Catchments

AbstractTerrestrial and aquatic elemental cycles are tightly linked in upland fluvial networks. Biotic and abiotic mineral weathering, microbially mediated degradation of organic matter, and anthropogenic influences all result in the movement of solutes (e.g., carbon, metals, and nutrients) through these catchments, with implications for downstream water quality. Within the river channel, the region of hyporheic mixing represents a hot spot of microbial activity, exerting significant control over solute cycling. To investigate how snowmelt‐driven seasonal changes in river discharge affect microbial community assembly and carbon biogeochemistry, depth‐resolved pore water samples were recovered from multiple locations around a representative meander on the East River near Crested Butte, CO, USA. Vertical temperature sensor arrays were also installed in the streambed to enable seepage flux estimates. Snowmelt‐driven high river discharge led to an expanding zone of vertical hyporheic mixing and introduced dissolved oxygen into the streambed that stimulated aerobic microbial respiration. These physicochemical processes contributed to microbial communities undergoing homogenizing selection, in contrast to other ecosystems where lower permeability may limit the extent of mixing. Conversely, lower river discharge conditions led to a greater influence of upwelling groundwater within the streambed and a decrease in microbial respiration rates. Associated with these processes, microbial communities throughout the streambed exhibited increasing dissimilarity between each other, suggesting that the earlier onset of snowmelt and longer periods of base flow may lead to changes in the composition (and associated function) of streambed microbiomes, with consequent implications for the processing and export of solutes from upland catchments.

Degraded patch formation significantly changed microbial community composition in alpine meadow soils

Approximately half of global grasslands are degraded. Although soil microbes play a key role in ecosystem functioning, their response to grassland degradation has not been fully investigated. In particular, degraded patch formation is the main feature of alpine meadow degradation, but little is known about its effect on soil microbes. In this study, soils were collected from three patch-degraded Tibetan alpine meadows to examine the effects of degraded patch formation on soil microbial communities. The alpine meadows at the three sites were in the third to fifth stages of degradation, respectively. Soil microbial abundance and community structure were determined through real-time PCR and MiSeq sequencing, respectively. The results showed that the degraded patch formation significantly decreased microbial respiration rates, changed the interaction patterns among microbial taxa, and increased fungal diversity, but did not significantly affect microbial abundance. Additionally, both prokaryotic and fungal community composition was significantly altered by the degraded patch formation. The functional predictions based on FAPROTAX and FUNGuild suggested that degraded patch formation significantly increased the proportion of nitrifiers, plant pathogenic fungi, and saprotrophic fungi, especially when mattic epipedons were eroded. The increased relative abundance of nitrifiers and pathogenic fungi can aggravate the risk of nitrogen leaching and plant diseases, respectively. Therefore, degraded patch formation can impede the recovery of degraded alpine meadows by changing soil microbial community composition.

The microbial community size, structure, and process rates along natural gradients of soil salinity

Over 840 M ha of arable land is affected by salinization, and the area is predicted to increase due to global change. Assessments of the status of the microbial community in saline soils have frequently been based on microbial biomass estimates, which might not accurately reflect microbial process rates in soil. Moreover, assessments of how the relative importance of major decomposer groups bacteria and fungi are affected by salinity remain inconclusive. In this study we set out to assess the soil microbial community size, structure and process rates along two salinity gradients. To distinguish between the direct effects of high salinity and indirect effects resulting from reduced soil organic matter (OM) concentrations in saline soils we also assessed the gradients following plant litter amendments to compensate for differences in OM content between soils and isolate the effect of salinity. The research aims were to (i) investigate the microbial biomass responses to salinity as estimated based on both PLFA concentrations and qPCR measurements and to compare these responses to those of respiration and microbial growth, (ii) compare the responses of bacteria and fungi to increased salinity and (iii) assess the responses of these microbial variables to the alleviation of OM scarcity expected in saline soils. Microbial biomass estimates generally were less negatively affected by salinity than bacterial growth and respiration, and were not correlated to rates of microbial growth or respiration rates. While bacterial growth was strongly inhibited by salinity, fungal growth was similar in soils of all salinities, indicating a higher fungal tolerance to salinity. OM additions increased process rates in saline soils and alleviated some of the negative impact of salinity on respiration and growth. In conclusion, this study demonstrates differential responses of saprotrophic fungi and bacteria to increasing salinity and that bacteria are directly impacted by soil salinity while fungi are responding to the indirect effect by salinity related to reduced plant C input.

Historical Drought Affects Microbial Population Dynamics and Activity During Soil Drying and Re-Wet

A history of drought exposure promoted by variable precipitation regimes can select for drought-tolerant soil microbial taxa, but the mechanisms of survival and death of microbial populations through the selective stresses of soil drying and re-wet are not well understood. We subjected soils collected from a 15-year field drought experiment ("Altered" precipitation historywith extended dry periods,versus the "Ambient" field control) to a laboratory drying/re-wetting experiment, to learn whether selective population survival, death, or maintenance of protein synthesis potential and microbial respirationthrough variable soil water conditions was affected by field drought legacy. Microbial community composition, as measured by Illumina MiSeq sequencing of the 16S rRNA and 16S rRNA gene, shifted with laboratory drying/re-wet and field drought treatments. In Ambient soils, there was a higher proportion of reduced OTU abundance (indicative of mortality) during re-wet, whereas Altered soils had a greater proportion of stable OTU populations that did not change in abundance (indicative ofsurvival) through drying/re-wet. Altered soils alsohad a lower proportion of rRNA:rRNA genes (lower protein synthesis potential) during dry-down, a greater weighted mean rRNA operon number (potential growth rate and r-selection) which was associated with higher abundance of Firmicutes (order Bacillales), and lower average microbial respiration rates. These data demonstrate that soils with a weaker historical drought legacy exhibit a higher prevalence of microbial water-stress mortality and differential survival and death at OTU levels following short-term dryingand re-wetting, concurrent with higher carbon loss potential. This work provides novel insight into the mechanisms and consequencesof soil microbial changes resulting fromextended drought conditions.

The sensitivity of soil microbial respiration declined due to crop straw addition but did not depend on the type of crop straw.

An incubation experiment was conducted to investigate whether the type of crop straw added to soil influenced the temperature sensitivity of soil microbial respiration. The soil for incubation was collected from a winter wheat-soybean rotation cropland. Five temperature levels (5, 10, 15, 20, and 25 °C), five crop straw types (soybean, peanut, rice, winter wheat, and maize), and a control (CK, no crop straw addition) were established. Soil microbial respiration rates were measured on days 1, 2, 3, 5, 7, 10, 14, 20, and 27 after crop straw addition using an infrared CO2 analyser. Soil enzyme activities of invertase, urea, and catalase and the dissolved organic carbon (DOC) content were measured after incubation. Estimated Q10 (temperature sensitivity of soil microbial respiration) ranged from 1.472 ± 0.045 to 1.970 ± 0.020 and showed no significant (P > 0.05) difference between straw addition treatments, but there was significantly (P < 0.001) higher temperature sensitivity (1.970 ± 0.020) for CK. A significant (P = 0.002) relationship was found between the Q10 of cumulative soil microbial respiration and basal soil microbial respiration (soil microbial respiration at 0 °C). Moreover, a marginally significant (P < 0.1) relationship was found between the Q10 at different incubation stages and basal soil microbial respiration. A quadratic function was used to explain the relationship between estimated basal microbial respiration and the lignin content. Soil microbial respiration was positively correlated with the activities of invertase, urease, and catalase and the dissolved organic carbon (DOC) content in all treatments. This study indicated that crop straw addition significantly (P < 0.001) reduced the Q10 of soil microbial respiration and that the types of crop straw added to soil did not significantly (P > 0.05) change the Q10 value.

Leaf litter decomposition of sweet chestnut is affected more by oomycte infection of trees than by water temperature

Abstract Riparian forests are subjected to multiple disturbances, such as tree diseases caused by invasive pathogens, whose consequences on stream functioning are unknown. We assessed the impact of Phytophthora cinnamomi infection, and interactions with temperature, on microbial decomposition of Castanea sativa leaves. Leaves from healthy, symptomatic and highly symptomatic trees were incubated in the laboratory at 13 and 18 °C for 64 d. Infection significantly increased polyphenolic concentration and leaf toughness, reducing leaf decomposition and microbial respiration rates irrespective of temperature. Aquatic hyphomycete communities differed significantly in leaves from highly symptomatic trees. Fungal biomass was highest at 18 °C, irrespective of tree health status. None of the parameters were influenced by the tree health status × temperature interaction, suggesting that temperature rise may not synergistically increase the cross-ecosystem effects caused by P. cinnamomi in streams where litter decomposition is microbial-driven. Infection by P. cinnamomi alters the nutritional quality of leaves affecting the functioning of aquatic ecosystems.

Global ecological predictors of the soil priming effect

Identifying the global drivers of soil priming is essential to understanding C cycling in terrestrial ecosystems. We conducted a survey of soils across 86 globally-distributed locations, spanning a wide range of climates, biotic communities, and soil conditions, and evaluated the apparent soil priming effect using 13C-glucose labeling. Here we show that the magnitude of the positive apparent priming effect (increase in CO2 release through accelerated microbial biomass turnover) was negatively associated with SOC content and microbial respiration rates. Our statistical modeling suggests that apparent priming effects tend to be negative in more mesic sites associated with higher SOC contents. In contrast, a single-input of labile C causes positive apparent priming effects in more arid locations with low SOC contents. Our results provide solid evidence that SOC content plays a critical role in regulating apparent priming effects, with important implications for the improvement of C cycling models under global change scenarios.

Litter of the invasive shrub Rhododendron ponticum (Ericaceae) modifies the decomposition rate of native UK woodland litter

Invasive alien plants are a worldwide problem, causing substantial damage to biodiversity as well as economies. Recent studies suggest invasive plants may also alter fundamental ecosystem processes such as nutrient and carbon cycling in soil by depositing chemically distinct leaf litter. Here, we used laboratory microcosms to test whether the chemical properties of Rhododendron ponticum litter, an invasive shrub in Britain, lead to slower decomposition than that of native (or naturalised) species with labile litter (Acer pseudoplatanus and Fraxinus excelsior), but not relative to the recalcitrant litter of Quercus petraea. Leading from this, we hypothesised that the labile native litter decomposition rate is reduced when mixed with R. ponticum litter in non-additive responses, with the strength of these responses increasing with the proportion of R. ponticum in litter mixes (25%, 50% and 75% R. ponticum). Over the incubation period, the decomposition (measured as the microbial respiration rate) of unmixed R. ponticum litter was significantly lower than that of A. pseudoplatanus and F. excelsior, but not Q. petraea. When mixed with R. ponticum (50%), F. excelsior litter decomposition was slowed, whilst no effect was seen for Q. petraea. However, A. pseudoplatanus litter decomposition was enhanced, contrary to expectation. The strength of the non-additive decomposition responses did not vary with different proportions of R. ponticum to the other species, with only the 50% mixtures showing significant non-additive respiration rates. Litter chemical properties were highly associated with decomposition rates, with both phenolic content and C:N ratio negatively correlated with microbial respiration. To test the influence of phenolics on litter decomposition, leachates of R. ponticum litter with phenolics present or removed (via activated carbon) were added to microcosms containing the native species litter. Microbial respiration in F. excelsior microcosms was lower when R. ponticum leachate contained phenolics. For A. pseudoplatanus and Q. petraea litter, no effect of leachate treatment was observed. Our results show that invasive litter chemistry can alter the decomposition of native litter, with the impact varying between species. Altered decomposition rates could cause plant-soil feedbacks, leading to altered soil nutrient concentrations. The novel soil conditions may favour the invader, increasing its dominance, whilst negatively influencing native species possessing greater nutrient demands.

Temperature Sensitivity of Soil Respiration in Palsa Peatlands of the North of Western Siberia

Palsa peatland soils are known as significant terrestrial storage of the Earth’s soil carbon. The response of these soils to changing climate may result in a strong feedback to global carbon balance. In laboratory, we investigated the effect of rising temperatures on the upper (T1) and lower (T2) horizons of Turbic Histic Cryosols using sequential (S) and equal-time (ET) methods. The S method was applied to estimate the response of organic carbon mineralization rate (R) to sequential temperature increase from 5 to 30°C; the ET method was used to study the response of the basal (microbial) respiration rate to equal-time incubation at 5, 15, and 25°C. The Q10 coefficient was calculated. In the T1 horizon, both methods (S and ET) demonstrated a positive response of respiration to the rise in temperature. The respiration intensity increased by 91 and 84%, respectively. In the T2 horizon, it increased by 93 and 91%, respectively. However, despite the overall positive response of soil respiration to the rise in temperature, the Q10 values demonstrated differences in the temperature sensitivity of soil respiration. These values were maximal in the cold (5–15°C) range for both horizons. For most of temperature ranges, Q10 was higher for T2 than for T1. For the T1 horizon and S method, Q10 slightly varied (2.7–3.0), whereas in the case of the ET method, it decreased by 3.3 times from the cold (4.9) to the warm 15–25°C (1.5) temperature range. For the T2 horizon, the S method also did not cause significant shifts in Q10 (3.0–3.5); the ET method caused a decrease in Q10 by 1.5 times from the cold (4.3) to the warm (2.8) temperature range. To sum up, the ET method leads to a wider variation of Q10 values in comparison with the S method thus indicating its better applicability for temperature sensitivity studies with palsa peatland soils under laboratory conditions.

Diverse recalcitrant substrates slow down decomposition of leaf litter from trees in a serpentine ecosystem

Litter decomposition in serpentine ecosystems has been studied solely addressing heavy metals like Ni. We aimed to show how leaf nutrients, cell-wall components and lamina mass per area and microbial communities affect litter decomposition in a cool-temperate serpentine ecosystem. Reciprocal transplant leaf-litter decomposition was observed in three tree species (Clethra barbinervis, Magnolia obovata, and Quercus serrata) common to serpentine and non-serpentine ecosystems. Thirteen litter quality variables of the initial litter and microbial respirations from decomposed litter were assessed. Litter from the serpentine ecosystem decomposed slower than that from the non-serpentine ecosystem. Compared with all species, C. barbinervis showed high heavy metal concentration, cellulose content, and lamina dry mass per area; M. obovata showed low Ca concentration; and Q. serrata exhibited high lignin/N ratio in litter from the serpentine ecosystem. Litter placed in the serpentine site decomposed faster than that placed in the non-serpentine site, but basal microbial respiration rates from litter did not differ between decomposition sites. Litter from serpentine ecosystems adversely influenced decomposition rate owing to its diverse recalcitrant litter quality. Our study suggested the feasibility of litter quality evaluation based on multiple litter traits for better-understanding of litter decomposition in serpentine ecosystems.