Effects of long-term warming on microbial nutrient limitation of soil aggregates on the Qinghai-Tibet Plateau

Background and aims Global warming has increasingly serious impacts on the structure and function of the Tibetan Plateau ecosystem. However, the mechanism by which warming affects the biogeochemical processes, and consequently the microbial nutrient limitation in soil aggregates, is not clear. Methods In the present study, we used open-top chamber experiments to simulate warming in an alpine meadow and an alpine shrubland on the Qinghai-Tibet Plateau, and we measured the C, N, and P-acquiring enzyme (β-1, 4-glucosidase, BG; leucine aminopeptidase, LAP; β-N-acetylglucosaminidase, NAG; alkali phosphatase, AP) activities and their stoichiometry to understand how warming affects microorganism-limiting mechanisms in soil aggregates. Results The results showed that long-term warming treatment significantly decreased soil organic carbon (SOC) and total nitrogen (TN) concentrations of large macroaggregates (LMGA) and small macroaggregates (SMGA) in alpine meadows, but significantly increased SOC concentration of LMGA in alpine shrubland. The SOC and TN concentrations of alpine meadows increased with the decrease of soil aggregate size and the concentrations in microaggregate (MIGA) were significantly higher than those LMGA. Soil enzyme activity increased with the decrease in aggregate size and was not significantly affected by warming treatment. Enzyme stoichiometry results demonstrated that soil microbes in alpine meadows and shrubland were limited by nutrient P relative to nitrogen; moreover, the long-term warming treatment aggravated the P limitation of soil microorganisms in the shrubland, and it had significant differences in LMGA and MIGA. At the same time, the long-term warming treatment had no significant effect on C limitation in the alpine shrubland and alpine meadows, but soil aggregate size affected the C limitation patterns of microorganisms and showed the greatest limitations in MIGA. Conclusions The microbial P limitation in shrubland is more sensitive to warming than that in meadow. Soil aggregates mediate the acquisition of C by microorganisms, and the C limitation in MIGA is the greatest. By providing a new perspective on this topic, our study increased our understanding of the effects of warming on microbial nutrient utilization and restriction patterns in soil aggregates.

Enhanced carbon acquisition and use efficiency alleviate microbial carbon relative to nitrogen limitation under soil acidification

Background Soil microbial communities cope with an imbalanced supply of resources by adjusting their element acquisition and utilization strategies. Although soil pH has long been considered an essential driver of microbial growth and community composition, little is known about how soil acidification affects microbial acquisition and utilization of carbon (C) and nitrogen (N). To close the knowledge gap, we simulated soil acidification and created a pH gradient by adding eight levels of elemental sulfur (S) to the soil in a meadow steppe. Results We found that S-induced soil acidification strongly enhanced the ratio of fungi to bacteria (F:B) and microbial biomass C to N (MBC:MBN) and subsequently decreased the C:N imbalance between microbial biomass and their resources. The linear decrease in the C:N imbalance with decreasing soil pH implied a conversion from N limitation to C limitation. To cope with enhanced C versus N limitation, soil microbial communities regulated the relative production of enzymes by increasing the ratio of β-glucosidase (BG, C-acquiring enzyme) to leucine aminopeptidase (LAP, N-acquiring enzyme), even though both enzymatic activities decreased with S addition. Structural equation modeling (SEM) suggested that higher C limitation and C:N-acquiring enzyme stimulated microbial carbon-use efficiency (CUE), which counteracted the negative effect of metal stress (i.e., aluminum and manganese) under soil acidification. Conclusions Overall, these results highlight the importance of stoichiometric controls in microbial adaption to soil acidification, which may help predict soil microbial responses to future acid deposition.

The light-to-nutrient ratio in alpine lakes: different scenarios of bacterial nutrient limitation and community structure in lakes above and below the treeline

The light-to-nutrient hypothesis proposes that under high light-to-nutrient conditions, bacteria tend to be limited by phosphorus (P), while under relatively low light-to-nutrient conditions, bacteria are likely driven towards carbon (C) limitation. Exploring whether this light-to-nutrient hypothesis is fitting for alpine lakes has profound implications for predicting the impacts of climatic and environmental changes on the structures and processes of aquatic ecosystems in climate-sensitive regions. We investigated the environmental conditions and bacterioplankton community compositions of 15 high-elevation lakes (7 above and 8 below treeline). High light-to-nutrient conditions (denoted by the reciprocal value of the attenuation coefficient (1/K) to total phosphorus (TP)), high chlorophyll a (Chl a) concentrations, low TP concentrations and low ratios of the dissolved organic carbon concentration to the dissolved total nitrogen concentration (DOC: DTN) were detected in above-treeline lakes. Significant positive correlations between the bacterioplankton community compositions with 1/K:TP ratios and Chl a concentrations indicated that not only high light energy but also nutrient competition between phytoplankton and bacteria might induce P limitation for bacteria. In contrast, low light-to-nutrient conditions and high allochthonous DOC input in below-treeline lakes lessen P limitation and C limitation. The most abundant genus, Polynucleobacter, was significantly enriched and more diverse oligotypes of Polynucleobacter OTUs were identified in the below-treeline lakes, indicating the divergence of niche adaptations among Polynucleobacter oligotypes. The discrepancies in the light-to-P ratio and the components of organic matter between the above-treeline and below-treeline lakes have important implications for the nutrient limitation of bacterioplankton and their community compositions.

Interactive Effects of Nitrogen and Water Addition on Soil Microbial Metabolic Limitation in Temperate Desert Shrublands

Aims Soil microbes play critical roles in regulating the turnover of soil organic carbon (SOC) and nutrients, and microbial metabolic limitation should draw more attention in desert ecosystems. However, soil extracellular enzymes activity (EEA) response and microbial metabolic limitation to atmospheric N deposition and increased precipitation in desert-shrubland are still poorly understood. Methods The study examined the effects of long-term (9 year) N and water additions (i.e., 5 g N m−2 yr−1, 30% ambient precipitation increase and their combination) on EEAs and soil microbial resource limitation, as well as explored their controlling factors in the Gurbantunggut Desert in northwestern China. Results The results showed that N and water additions significantly enhanced soil EEAs and considerably aggravated microbial phosphorous (P) limitation. Water addition and the N-water combination addition alleviated carbon (C) limitation, but N addition alone strengthened microbial C limitation. The interaction of N and water additions relieved the negative impact of N addition on soil microbial C limitation, and positively aggravated microbial P limitation. Soil microbial C limitation was primarily driven by soil moisture and organic C concentration, while the soil microbial N/P limitation was chiefly controlled by soil water and available P contents. Conclusions The influences of either N- or water addition alone on desert ecosystem biogeochemical processes may be altered by their concurrent occurrence. Overall, these findings highlight water availability is more effective at modifying microbial metabolisms than N accumulation in desert ecosystems. Altogether, this may help to predict how terrestrial C and nutrient flow could be induced by global change factors..

Parent material and organic matter control soil microbial processes in African tropical rainforests

<p>Microbial processes are one of the key factors driving carbon (C) and nutrient cycling in terrestrial ecosystems, and are strongly controlled by the equilibrium between resource availability and demand. In deeply weathered tropical rainforest soils of Africa, it remains unclear whether patterns of microbial processes differ between soils developed from geochemically contrasting parent material. Here, we investigate patterns of soil microbial processes and their controls in tropical rainforests of Africa. We used soil developed from three geochemically distinct parent material (mafic, felsic, mixed sedimentary rocks) and three soil depths (0−70 cm). We measured microbial biomass C and enzyme activity at the beginning and end of a 120-day incubation experiment. We also conducted a vector analysis based on ecoenzymatic stoichiometry to assess microbial C and nutrient limitations. We found that microbial C limitation was highest in the mixed sedimentary region and lowest in the felsic region, which we propose was related to the strength of contrasting C stabilization mechanisms and varying C quality. None of the investigated regions and soil depths showed signs of nitrogen (N) limitation for microbial processes. Microbial phosphorus (P) limitation increased with soil depth, indicating that subsoils in the investigated soils were depleted in rock-derived nutrients and are therefore dependent on efficient nutrient recycling. Microbial C limitation was lowest in subsoils, indicating that subsoil microbes cannot significantly participate in C cycling and limit C storage if oxygen is not available, but can do so in our laboratory incubation experiment under well aerated conditions. Using multivariable regressions, we demonstrate that microbial biomass C normalized to soil organic C content (MBC<sub>SOC</sub>) is controlled by soil geochemistry and substrate quality, while microbial biomass C normalized to soil weight (MBC<sub>Soil</sub>) is predominantly driven by resource distribution (i.e., depth distribution of organic C). We conclude that due to differences in resource availability, microbial processes in deeply weathered tropical rainforest soils greatly vary across geochemical regions.</p>

Patterns of microbial processes shaped by parent material and soil depth in tropical rainforest soils

Microbial processes are one of the key factors driving carbon (C) and nutrient cycling in terrestrial ecosystems, and are strongly driven by the equilibrium between resource availability and demand. In deeply weathered tropical rainforest soils of Africa, it remains unclear whether patterns of microbial processes differ between soils developed from geochemically contrasting parent materials. Here we show that resource availability across soil depths and regions from mafic to felsic geochemistry shape patterns of soil microbial processes. During a 120-day incubation experiment, we found that microbial biomass C and extracellular enzyme activity were highest in the mafic region. Microbial C limitation was highest in the mixed sedimentary region and lowest in the felsic region, which we propose is related to the strength of contrasting C stabilization mechanisms and varying C quality. None of the investigated regions and soil depths showed signs of nitrogen (N) limitation for microbial processes. Microbial phosphorus (P) limitation increased with soil depth but was similar across geochemical regions, indicating that subsoils in the investigated soils were depleted in rock-derived nutrients and are therefore dependent on efficient biological recycling of nutrients. Microbial C limitation was lowest in subsoils, indicating that subsoil microbes can significantly participate in C cycling and limit C storage if increased oxygen availability is prevalent. Using multivariable regressions, we demonstrate that microbial biomass C normalized to soil organic C content (MBCSOC) is controlled by soil geochemistry and substrate quality, while microbial biomass C normalized to soil weight (MBCSoil) is predominantly driven by resource distribution. We conclude that due to differences in resource availability, microbial processes in deeply weathered tropical rainforest soils greatly vary across geochemical regions which must be considered when assessing soil microbial processes in organic matter turnover models.

Limiting factors for soil microbial growth in climate change simulation treatments in the Subarctic

<p>Soil microorganisms play a crucial role in the regulation of nutrient cycling, and are thought to be either limited by low nutrient availability, or by labile carbon supplied by nutrient limited plant productivity. It remains unknown how climate change will affect the rate-limiting resources for decomposer microorganisms in the Arctic, rendering feedbacks to climate change highly uncertain. In this study, we focused on the responses of soil microbial community processes to simulated climate change in a subarctic tundra system in Abisko, Sweden, using litter additions to represent arctic greening and inorganic N fertilizer additions to represent a faster nutrient cycling due to arctic warming. We hypothesized that 1) the plant community would shift and plant productivity would increase in response to N fertilization, 2) microbial process rates would be stimulated by both plant litter and fertilizer additions, and 3) the growth limiting factors for decomposer microorganisms would shift toward nutrient limitation in response to higher plant material input, and towards C-limitation in response to N-fertilizer additions.</p><p> </p><p>We assessed the responses of the plant community composition (vegetation surveys) and productivity (NDVI), microbial processes (bacterial growth, fungal growth, C and N mineralization) along with an assessment of the limiting factors for fungal and bacterial growth. The growth-limiting factors were determined by full factorial additions of nutrients (C, N, P), with measurement of microbial growth and respiration following brief incubations in the laboratory. We found that plant productivity was ca. 15% higher in the N fertilized plots. However, field-treatments had limited effects on bacterial growth, fungal growth and the fungal-to-bacterial growth ratio in soils. Field-treatments also had no significant effect on the rate of soil C mineralization, but did affect rates of gross N mineralization. Gross N mineralization was twice as high in N fertilized plots compared to the control. In control soils, bacterial growth increased 4-fold in response to C, indicating that bacterial growth was C limited. Bacterial growth remained C limited in soils from all field-treatments. However, in the N fertilized soils, the C limitation was 1.8-times greater than the control, while in soils with litter input, the C limitation was 0.83-times the control, suggesting that the N fertilized soils were moving towards stronger C-limitation and the litter addition soils were becoming less C-limited. The limiting factor for fungal growth was difficult to resolve. We presumed that the competition of fungi with bacteria decreased our resolution to detect the limiting factor. Therefore, factorial nutrient addition were combined with low amount of bacterial specific inhibitors.</p>

Indio (denominación) = Indian (denomination)

ResumenEl artículo mostrará cómo las distintas denominaciones: indio, pueblo indio o indígena, campesino, comunidad indígena u originaria, etnia, nación y nacionalidad, otorgadas a los aymaras, quechuas (Bolivia) y kichwas (Ecuador) son una deconstrucción histórica social de casi cinco siglos hacia su identidad milenaria e histórica, que causan tres efectos: a) dominación (tutela), b) desestructuración territorial, por ende, desarticulación político-administrativa, económica y social, y c) limitación en su lucha por la emancipación.Así, las distintas denominaciones usadas por los Estados plurinacionales de Bolivia y Ecuador, son un lenguaje hegemónico-histórico deconstructivo por medio de significantes y significaciones que impregnará un “signo” colonial y postcolonial a los jaques, runas, ayllus, markas, suyus, señoríos aymaras, quechuas, y kichwas convirtiéndose a largo plazo en un paradigma de la denominación y dominación.Palabras clave: Aymaras, quechuas, kichwas; paradigma de la denominación y dominación; significante; significación; colonial; postcolonial; deconstrucción; tierra y territorio.Abstract: The article will show how the different denominations: Indian, Indian or indigenous people, peasant, indigenous or native community, ethnicity, nation and nationality, granted to the Aymaras, Quechuas (Bolivia) and Kichwas (Ecuador) are a social historical deconstruction of almost five centuries towards its millenarian and historical identity, which causes three effects: a) domination (guardianship), b) territorial destructuration, therefore, political-administrative, economic and social disarticulation, and c) limitation in its struggle for emancipation.Thus, the different denominations used by the Plurinational States of Bolivia and Ecuador, are a hegemonic-historical deconstructive language by means of signifiers and significations that will impregnate a colonial and postcolonial "sign" to the jaques, runas, ayllus, markas, suyus, señoríos Aymaras, Quechuas, and Kichwas become a paradigm of denomination and domination over the long term.Keywords: Aymaras, Quechuas, Kichwas; paradigm of denomination and domination; significant; significance; colonial; postcolonial; of construction; land and territory.

Decreased carbon limitation of litter respiration in a mortality-affected piñon–juniper woodland

Microbial respiration depends on microclimatic variables and carbon (C) substrate availability, all of which are altered when ecosystems experience major disturbance. Widespread tree mortality, currently affecting piñon–juniper ecosystems in southwestern North America, may affect C substrate availability in several ways, for example, via litterfall pulses and loss of root exudation. To determine piñon mortality effects on C and water limitation of microbial respiration, we applied field amendments (sucrose and water) to two piñon–juniper sites in central New Mexico, USA: one with a recent (< 1 yr), experimentally induced mortality event and a nearby site with live canopy. We monitored the respiration response to water and sucrose applications to the litter surface and to the underlying mineral soil surface, testing the following hypotheses: (1) soil respiration in a piñon–juniper woodland is water- and labile C-limited in both the litter layer and mineral soil; (2) piñon mortality reduces the C limitation of litter respiration; and (3) piñon mortality enhances the C limitation of mineral soil respiration. Litter respiration at both sites responded to increased water availability, yet surprisingly, mineral soil respiration was not limited by water. Consistent with hypothesis 2, C limitation of litter respiration was lower at the recent mortality site compared to the intact canopy site. Applications to the mineral soil showed evidence of reduction in CO2 flux on the girdled site and a non-significant increase on the control. We speculate that the reduction may have been driven by water-induced carbonate dissolution, which serves as a sink for CO2 and would reduce the net flux. Widespread piñon mortality may decrease labile C limitation of litter respiration, at least during the first growing season following mortality.

Decreased carbon limitation of litter respiration in a mortality-affected piñon-juniper woodland

Microbial respiration depends on microclimatic variables and carbon (C) substrate availability, all of which are altered when ecosystems experience major disturbance. Widespread tree mortality, currently affecting piñon-juniper ecosystems in Southwestern North America, may affect C substrate availability in several ways; for example, via litterfall pulses and loss of root exudation. To determine piñon mortality effects on C and water limitation of microbial respiration, we applied field amendments (sucrose and water) to two piñon-juniper sites in central New Mexico, USA: one with a recent (< 1 yr), experimentally-induced mortality event and a nearby site with live canopy. We monitored the respiration response to water and sucrose applications to the litter surface and to the underlying mineral soil surface, testing the following hypotheses: (1) soil respiration in a piñon-juniper woodland is water- and labile C-limited in both the litter layer and mineral soil; (2) water and sucrose applications increase temperature sensitivity of respiration; (3) the mortality-affected site will show a reduction in C limitation in the litter; (4) the mortality-affected site will show an enhancement of C limitation in the mineral soil. Litter respiration at both sites responded to increased water availability, yet surprisingly, mineral soil respiration was not limited by water. Temperature sensitivity was enhanced by some of the sucrose and water treatments. Consistent with hypothesis 3, C limitation of litter respiration was lower at the recent mortality site compared to the intact canopy site. Results following applications to the mineral soil suggest the presence of abiotic effects of increasing water availability, precluding our ability to measure labile C limitation in soil. Widespread piñon mortality may decrease labile C limitation of litter respiration, at least during the first growing season following mortality.