Search

1. All bark beetles are in symbiosis with fungi. Although obligate mutualisms with fungi are common with tree‐killing bark beetles (primaries), fungi associated with non‐tree‐killing bark beetles (secondaries) are usually dismissed as commensals. 2. Using an ecological stoichiometric approach, we show secondaries are also involved in nutrition‐based mutualisms, some of which appear obligate, and that differences in symbiont provisioning efficiency have a potent effect on beetle carbon (C): nitrogen (N): phosphorus (P) ratios. 3. Some secondary beetles have high P contents and require efficient P provisioning via fungi, while others have low P contents that may allow them to exploit less efficient fungi or a broader range of species with variable efficiencies. A co‐occurring scavenger that feeds on nutrient‐poor bark beetle frass (excrement/boring residues) exhibited the lowest phosphorus content yet recorded for an invertebrate. 4. Our results generally support the growth‐rate hypothesis that posits differences in C:P and N:P ratios in consumers are due to differential allocation of P to P‐rich RNA to support growth. However, while the beetle species that accumulated the most biomass was considerably enriched in P and that with the least biomass was P‐poor, one beetle species that was P‐rich was also small possibly due to limitation by an element other than P. 5. Our results indicate that fungi are important to a broader range of bark beetles than previously recognised. Additional research is needed to describe how these various symbioses influence forest ecosystems via differential effects of fungi on host beetle fitness. [ABSTRACT FROM AUTHOR]

1. Ecological stoichiometry theory was applied to investigate how a consumer contends with an extreme elemental mismatch between its food and its body via symbiotic facilitation. 2. The beetle Dendroctonus brevicomis LeConte develops in bark, a substrate extremely low in nitrogen (N) and phosphorus (P). Its survival there depends on interactions with mutualist and antagonist fungi. 3. This study found that mutualists transfer N and P from sapwood and phloem into bark, where beetles feed, whereas the antagonist moves these elements only to phloem, resulting in starvation of the insect. However, even with mutualists, N and P concentrations remained low in bark, resulting in low N and extremely low P concentrations in the beetle. 4. The N:P ratios found in D. brevicomis larvae were the highest thus far reported for beetles and among the highest for insects and invertebrates. This suggests that the beetle has evolved additional, nutrient‐sparing adaptations. [ABSTRACT FROM AUTHOR]

Abstract Global nitrogen (N) deposition can change the contents and stoichiometry of soil resources and thus of microbial communities, which can drive the flow of carbon (C) and nutrients in food webs in forest ecosystems. It is critical to understand the status of soil elements required for microbial growth, the elements of microbial growth, and how soil microorganisms would reallocate resources and release extracellular enzymes for adjusting the imbalance between resources and microorganisms due to N deposition. We chose a plantation of Pinus tabuliformis where N had been added across a gradient (0–9 g N m−2 y−1) for two years to reveal how matters flow and soil resources were reallocated by microbes to cope N addition. Our results showed that although two years of N inputs only significantly affect the ratio between the activities of β-1,4- N ‑acetylglucosaminidase and alkaline phosphatase in the 0–20 cm soil layer, activities for both organic N and organic phosphorus (P) acquisition enzymes scale with C acquisition with slope of about 1, following the global ecoenzymatic patterns. Contents and elemental ratios of soil organic carbon (SOC), total N (TN) and total phosphorus (TP) were changed after this short-term N addition. Ratios of SMBC, SMBN and SMBP were concentrated from soil and lower than ratios of soil resources. Soil microbial communities under N addition were limited by N and co-limited by P at 3 and 6 g N m−2 y−1. Although imbalance between soil and microbes caused by N addition, in the 0–20 and 20–40 cm layers, C: N relationship between soil and the microbial community indicated microbial community maintained homeostasis. However, C:P relationship between soil and the microbial community indicated no microbial community homeostasis. In addition, both soil resources elemental stoichiometry and contents can affect soil microbial communities. Further study of the structure of soil microbial communities, identifying the microbes that are more adaptive to high N concentrations and N deposition, is needed for a better understanding of the mechanisms of nutrient flow in the food web and how to maintain microbial homeostasis in response to N deposition in forest ecosystems. Highlights • Enzymatic activities, microbial coping with N addition, maintain no change. • Microbial communities are limited by N and co-limited by P at N3 and N6. • Soil microbes generally maintain community-level elemental homeostasis. • Contents and stoichiometry of soil resources influence microbial communities. [ABSTRACT FROM AUTHOR]

Abstract: Quantitative approaches to predator–prey interactions are central to understanding the structure of food webs and their dynamics. Different predatory strategies may influence the occurrence and strength of trophic interactions likely affecting the rates and magnitudes of energy and nutrient transfer between trophic levels and stoichiometry of predator–prey interactions. Here, we used spider–prey interactions as a model system to investigate whether different spider web architectures—orb, tangle, and sheet‐tangle—affect the composition and diet breadth of spiders and whether these, in turn, influence stoichiometric relationships between spiders and their prey. Our results showed that web architecture partially affects the richness and composition of the prey captured by spiders. Tangle‐web spiders were specialists, capturing a restricted subset of the prey community (primarily Diptera), whereas orb and sheet‐tangle web spiders were generalists, capturing a broader range of prey types. We also observed elemental imbalances between spiders and their prey. In general, spiders had higher requirements for both nitrogen (N) and phosphorus (P) than those provided by their prey even after accounting for prey biomass. Larger P imbalances for tangle‐web spiders than for orb and sheet‐tangle web spiders suggest that trophic specialization may impose strong elemental constraints for these predators unless they display behavioral or physiological mechanisms to cope with nutrient limitation. Our findings suggest that integrating quantitative analysis of species interactions with elemental stoichiometry can help to better understand the occurrence of stoichiometric imbalances in predator–prey interactions. [ABSTRACT FROM AUTHOR]

Arid ecosystems are characterized by stressful conditions of low energy and nutrient availability for soil microorganisms. It has been observed that the ecoenzymes needed for the transformation of organic compounds into assimilable products show similar scaling relationships in different habitats (logarithmic C:N:P scaling ratios ~1:1:1). In this study in Cuatro Ciénegas Basin (CCB) in the Chihuahuan desert of México, we report among the lowest ecoenzymatic activities yet quantified in soil. Nevertheless, activities for both organic N and organic P acquisition enzymes scale with C acquisition with a slope of ∼1.0, indicating that the soil microbial communities of this ultra-oligotrophic desert ecosystem follow the global ecoenzymatic stoichiometry patterns. CCB soil microbial communities were co-limited by C and either by N or P but this co-limitation played out differently in different parts of the CCB as indicated by microbial ecoenzymatic shift to allocate more resources to acquire and immobilize the scarcer nutrient. By extending ecoenzymatic analyses to these ultra-oligotrophic soils, our findings support the broad utility of the approach in illuminating how microbes acquire limiting resources in arid ecosystems. [ABSTRACT FROM AUTHOR]

1. Ecological stoichiometry expresses ecological interactions as the balance between multiple elements. It relates the ecological function of organisms to their elemental composition, or their organismal stoichiometry. Organismal stoichiometry is thought to reflect elemental investments in life history and morphology acting in concert with variability in abiotic or environmental conditions, but the relative contribution of these factors to natural variability in organismal stoichiometry is poorly understood. 2. We assessed the relative contribution of stream identity, predation, body size and sex to the organismal stoichiometry of guppies ( Poecilia reticulata) in six streams in Trinidad. In this system, guppy life-history phenotype evolves in response to predation. Guppies adapted to high-predation (HP) pressure grow faster, mature earlier, produce fewer and smaller offspring and eat a higher-quality diet than guppies adapted to low-predation (LP) pressure. This pattern of life-history evolution is repeated in many rivers encompassing a wide range of abiotic conditions. 3. Organismal stoichiometry of guppies was widely variable, spanning up to ∼70% of the range of variability reported across freshwater fish taxa. Streams from where guppies were sampled were the most important predictor of organismal stoichiometry. In many cases, guppy populations from sites within the same stream varied as much as from sites in different streams. 4. Surprisingly, predation regime was a minor predictor of % C, C : P and C : N in female guppies, despite its strong correlation with life-history phenotype and other organismal traits in this species. Body size and sex were not significant predictors of organismal stoichiometry. 5. Guppies from HP sites were more stoichiometrically balanced with their diets than guppies from LP sites. The latter appeared to be more vulnerable to phosphorus limitation than the former, suggesting that dietary specialization associated with guppy life-history phenotype may have stoichiometric consequences that can affect guppy physiology and nutrient recycling. 6. Our findings suggest that local environmental conditions are a stronger predictor of organismal stoichiometry than organismal traits. We recommend that future work should explicitly consider correlations between organismal traits and organismal stoichiometry in the context of environmental heterogeneity. [ABSTRACT FROM AUTHOR]

• Soil EES indicate microbial nutritional status and resource limitations. • Thinning and seasonal changes affect ecoenzymes and microbial metabolism in the soil. • Differences in soil EEA and EES may be related to the variations in soil properties, especially soil nutrients and microbial biomass. • Soil microbial metabolism was limited by N in Larix principis-rupprechtii plantations. The extracellular ecoenzymatic stoichiometry (EES) of the soil are key indicators of the nutritional status and relative resource limitations of microbes that play important roles in biogeochemical cycling and ecosystem functions. However, our knowledge of the effects of forest thinning and the seasons on the variability of extracellular ecoenzymatic activities (EEA) and EES in the soil is limited. We examined the soils from Larix principis-rupprechtii plantations after nine years of treatments with four different thinning intensities (i.e., control (CK), low thinning (LT), moderate thinning (MT), and high thinning (HT)) in four different seasons. We measured the activities of one carbon (C) acquiring enzyme (β-1,4-glucosidase (BG)), two nitrogen (N) acquiring enzymes (β-1,4-N-acetylglucosaminidase (NAG), leucine aminopeptidase (LAP)), and one phosphorus (P) acquiring enzyme (acid phosphatase (AP)), and examined potential factors (soil environment, nutrients, and microbial biomass) that may influence the activities of these enzymes. Our results showed that thinning significantly (p < 0.05) enhanced the activities of the BG, NAG + LAP, and AP. The EEA were higher in summer and autumn than those in spring and winter. Further, MT and HT stands exhibited lower BG:(NAG + LAP) and higher (NAG + LAP):AP ratios than the CK and LT stands, demonstrating that MT and HT caused a greater N limitation for soil microbes. The higher (NAG + LAP):AP ratio during winter indicated that the microbial N limitation was increased in this season. The variations in the EEA, EES, environment, nutrients, and microbial biomass in the soil among different thinning treatments demonstrated that thinning could markedly promote microbial activities and metabolism and improve nutrient cycling. Based on analyses of the BG:(NAG + LAP) ratio, (NAG + LAP):AP ratio, and the threshold element ratio, we found that the metabolism of soil microbes was limited by N in L. principis-rupprechtii plantations in North China. A redundancy analysis and a variation partitioning analysis revealed that variations in the EEA and EES of soils could attributed to the alterations in soil properties, especially soil nutrient and microbial biomass. Overall, the ecoenzymatic C:N:P stoichiometry was dependent on the resource availability in the soils rather than on homeostatic mechanisms. Our research highlights the importance of the effects of thinning practices and season types on ecoenzymes and microbial metabolism, and provides insights into the microbial resource limitation, nutrient cycling, and ecological processes in plantation forests after thinning. [ABSTRACT FROM AUTHOR]

• Microbial processes during secondary succession were studied on the Loess Plateau. • Microbial communities showed stoichiometric homeostasis during plant secondary succession. • Microbial metabolisms were co-limited by C and P during plant secondary succession. • Microbial activities were strongly affected by soil nutrient status. Soil microbial metabolism is vital for nutrient cycling and ecosystem stability. To quantify microbial metabolism and nutrient limitation during plant secondary succession, we measured soil physicochemical properties, microbial biomass, and four enzyme activities (β-1,4-glucosidase (BG), β-1,4- N -acetylglucosaminidase (NAG), L -leucine aminopeptidase (LAP), and alkaline phosphatase (AP)) and identified the changes of soil ecoenzymatic stoichiometry and microbial nutrient limitation along a secondary succession series in typical arid and semi-arid ecosystems on the Loess Plateau, China. Soil enzyme activities increased in the first 17a succession and then decreased with plant secondary succession. The ln(BG):ln(NAG + LAP) ratio and ln(BG):ln(AP) ratio showed a decreasing trend in the first 22a succession and then increased. Most soil nutrient contents and nutrient stoichiometry were significantly correlated with enzyme activities and enzymatic stoichiometry. Moreover, vector analysis of soil enzymes indicated that microbial community were co-limited by C and P during secondary succession. Linear regression of C:N and C:P between the soil nutrient and microbial community showed that soil microbial community maintained stoichiometry homeostasis during plant secondary succession. The threshold elemental ratio revealed that the microbial nutrient metabolisms were co-limited by N and P, particularly P during plant secondary succession. Therefore, microbial communities were co-limited by C, N, and P, particularly C and P during plant secondary succession, and the limitation was mainly associated with soil nutrient status. [ABSTRACT FROM AUTHOR]

• Forest management practices were conducted in this Pinus tabuliformis to maintain ecological environment. • Soil microbial communities of the artificial plantation are limited by N and P. • Enzymatic activities and ecoenzymatic stoichiometries differed significantly among the five forest management practices. • Forest management practices did not interfere with soil microbial homeostasis. Forest management practices are commonly used in plantation forestry to obtain renewable energy and harvest biomass, in addition to maintaining the ecological environment, by changing the flow of carbon (C) and nutrients in the food webs of terrestrial ecosystems. To identify which forest management practices, alleviate soil nutrient limitation and impact stoichiometric homeostasis in relation to microbes, we used a Pinus tabuliformis plantation in the Loess Plateau where forest management practices were conducted since 1999. Five forest management practices were implemented: two at the forest level (P. tabuliformis with and without ground litter, CK, LRL) and three of different vegetation restorations after clear-cutting (P. tabuliformis seedlings (SPL), grass land (GL), and shrub land (SL)). Generally, the threshold elemental ratios for carbon:nitrogen (TER C:N ; 7.77) and carbon:phosphorus (TER C:P ; 44.37) were lower than the ratios influenced by forest management practices. The forest management practices significantly influenced ecoenzymatic activity and the ratios of ecoenzymes; however, the scale of the ecoenzyme activities for acquiring both organic N and organic P to that for acquiring C still follow the global pattern. The regression coefficients of C:N and C:P between the soil and microbial community at 0–20 cm and 20–40 cm depths were also influenced by these practices. Thus, the influence of forest management practices on the soil microbial community was limited by N and P in the Loess Plateau. The soil microbial community changed ecoenzymatic activities and ratios of ecoenzymes and even changed microbial community in order to balance elemental limitations in the soil. Finally, forest management practices have a minimal impact on the stoichiometric homeostasis of the microbial community at our study site. [ABSTRACT FROM AUTHOR]