Soil microorganisms are critical to ecosystem functioning and the maintenance of soil fertility. However, despite global increases in the inputs of nitrogen (N) and phosphorus (P) to ecosystems due ...to human activities, we lack a predictive understanding of how microbial communities respond to elevated nutrient inputs across environmental gradients. Here we used high-throughput sequencing of marker genes to elucidate the responses of soil fungal, archaeal, and bacterial communities using an N and P addition experiment replicated at 25 globally distributed grassland sites. We also sequenced metagenomes from a subset of the sites to determine how the functional attributes of bacterial communities change in response to elevated nutrients. Despite strong compositional differences across sites, microbial communities shifted in a consistent manner with N or P additions, and the magnitude of these shifts was related to the magnitude of plant community responses to nutrient inputs. Mycorrhizal fungi and methanogenic archaea decreased in relative abundance with nutrient additions, as did the relative abundances of oligotrophic bacterial taxa. The metagenomic data provided additional evidence for this shift in bacterial life history strategies because nutrient additions decreased the average genome sizes of the bacterial community members and elicited changes in the relative abundances of representative functional genes. Our results suggest that elevated N and P inputs lead to predictable shifts in the taxonomic and functional traits of soil microbial communities, including increases in the relative abundances of faster-growing, copiotrophic bacterial taxa, with these shifts likely to impact belowground ecosystems worldwide.
Enhanced plant biomass accumulation in response to elevated atmospheric CO2 concentration could dampen the future rate of increase in CO2 levels and associated climate warming. However, it is unknown ...whether CO2-induced stimulation of plant growth and biomass accumulation will be sustained or whether limited nitrogen (N) availability constrains greater plant growth in a CO2-enriched world. Here we show, after a six-year field study of perennial grassland species grown under ambient and elevated levels of CO2 and N, that low availability of N progressively suppresses the positive response of plant biomass to elevated CO2. Initially, the stimulation of total plant biomass by elevated CO2 was no greater at enriched than at ambient N supply. After four to six years, however, elevated CO2 stimulated plant biomass much less under ambient than enriched N supply. This response was consistent with the temporally divergent effects of elevated CO2 on soil and plant N dynamics at differing levels of N supply. Our results indicate that variability in availability of soil N and deposition of atmospheric N are both likely to influence the response of plant biomass accumulation to elevated atmospheric CO2. Given that limitations to productivity resulting from the insufficient availability of N are widespread in both unmanaged and managed vegetation, soil N supply is probably an important constraint on global terrestrial responses to elevated CO2.
We used two independent methods to determine the dynamics of soil carbon and nitrogen following abandonment of agricultural fields on a Minnesota sand plain. First, we used a chronosequence of 19 ...fields abandoned from 1927 to 1982 to infer soil carbon and nitrogen dynamics. Second, we directly observed dynamics of carbon and nitrogen over a 12-yr period in 1900 permanent plots in these fields. These observed dynamics were used in a differential equation model to predict soil carbon and nitrogen dynamics. The two methods yielded similar results. Resampling the 1900 plots showed that the rates of accumulation of nitrogen and carbon over 12 yr depended on ambient carbon and nitrogen levels in the soil, with rates of accumulation declining at higher carbon and nitrogen levels. A dynamic model fitted to the observed rates of change predicted logistic dynamics for nitrogen and carbon accumulation. On average, agricultural practices resulted in a 75% loss of soil nitrogen and an 89% loss of soil carbon at the time of abandonment. Recovery to 95% of the preagricultural levels is predicted to require 180 yr for nitrogen and 230 yr for carbon. This model accurately predicted the soil carbon, nitrogen, and carbon: nitrogen ratio patterns observed in the chronosequence of old fields, suggesting that the chronosequence may be indicative of actual changes in soil carbon and nitrogen. Our results suggest that the rate of carbon accumulation was controlled by the rate of nitrogen accumulation, which in turn depended on atmospheric nitrogen deposition and symbiotic nitrogen fixation by legumes. Our data support the hypothesis that these abandoned fields initially retain essentially all nitrogen and have a closed nitrogen cycle. Multiple regression suggests that vegetation composition had a significant influence on the rates of accumulation of both nitrogen and carbon; legumes increased these rates, and C3grasses and forbs decreased them. C4grasses increased the C:N ratio of the soil organic matter and thereby increased the rate of carbon accumulation, but not nitrogen accumulation.
Mammalian herbivores can have pronounced effects on plant diversity but are currently declining in many productive ecosystems through direct extirpation, habitat loss and fragmentation, while being ...simultaneously introduced as livestock in other, often unproductive, ecosystems that lacked such species during recent evolutionary times. The biodiversity consequences of these changes are still poorly understood. We experimentally separated the effects of primary productivity and herbivores of different body size on plant species richness across a 10-fold productivity gradient using a 7-year field experiment at seven grassland sites in North America and Europe. We show that assemblages including large herbivores increased plant diversity at higher productivity but decreased diversity at low productivity, while small herbivores did not have consistent effects along the productivity gradient. The recognition of these large-scale, cross-site patterns in herbivore effects is important for the development of appropriate biodiversity conservation strategies.
In grassland ecosystems, N and P fertilization often increase plant productivity, but there is no concensus if fertilization affects soil C fractions. We tested effects of N, P and N+P fertilization ...at 5, 10, 15 g m-2 yr-1 (N5, N10, N15, P5, P10, P15, N5P5, N10P10, and N15P15) compared to unfertilized control on soil C, soil microbial biomass and functional diversity at the 0-20 cm and 20-40 cm depth in an alpine meadow after 5 years of continuous fertilization. Fertilization increased total aboveground biomass of community and grass but decreased legume and forb biomass compared to no fertilization. All fertilization treatments decreased the C:N ratios of legumes and roots compared to control, however fertilization at rates of 5 and 15 g m-2 yr-1 decreased the C:N ratios of the grasses. Compared to the control, soil microbial biomass C increased in N5, N10, P5, and P10 in 0-20 cm, and increased in N10 and P5 while decreased in other treatments in 20-40 cm. Most of the fertilization treatments decreased the respiratory quotient (qCO2) in 0-20 cm but increased qCO2 in 20-40 cm. Fertilization increased soil microbial functional diversity (except N15) but decreased cumulative C mineralization (except in N15 in 0-20 cm and N5 in 20-40 cm). Soil organic C (SOC) decreased in P5 and P15 in 0-20 cm and for most of the fertilization treatments (except N15P15) in 20-40 cm. Overall, these results suggested that soils will not be a C sink (except N15P15). Nitrogen and phosphorus fertilization may lower the SOC pool by altering the plant biomass composition, especially the C:N ratios of different plant functional groups, and modifying C substrate utilization patterns of soil microbial communities. The N+P fertilization at 15 g m-2 yr-1 may be used in increasing plant aboveground biomass and soil C accumulation under these meadows.
Fiber Reinforced Plastics (FRP) are widely used for the design of load-bearing structures. Life time prediction based on failure analysis is therefore essential for many applications in Aeronautics, ...Automotive and Civil Engineering. Analysis of Failure in Fiber Polymer Laminates presents Alfred Puck´s failure model, which, among several other theories, predicts fracture limits best and describes the failure phenomena in FRP most realistically – as confirmed within the "World-wide Failure Exercise". Using Puck´s model the composite engineer can follow the gradual failure process in a laminate and deduce from the results of the analysis how to improve the laminate design. This capability distinguishes the model from other phenomenological and global models. It thus reduces the number of required component tests and iteration loops in the design process and paves the way to sorely needed software for crash-simulation of FRP-structures.
What drives masting? The phenological synchrony hypothesis Koenig, Walter D; Knops, Johannes M. H; Carmen, William J ...
Ecology (Durham),
2015-January, 2015, 20150101, January 2015, 2015-Jan, 2015-01-00, Letnik:
96, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Annually variable and synchronous seed production, or masting behavior, is a widespread phenomenon with dramatic effects on wildlife populations and their associated communities. Proximally, masting ...is often correlated with environmental factors and most likely involves differential pollination success and resource allocation, but little is known about how these factors interact or how they influence seed production. We studied masting in the valley oak (
Quercus lobata
Née), a California endemic tree, and report evidence that phenological synchrony in flowering driven by microclimatic variability determines the size of the acorn crop through its effects on pollen availability and fertilization success. These findings integrate two of the major factors believed to influence seed production in wind-pollinated species-environmental conditions and pollen limitation-by means of a coherent mechanistic hypothesis for how highly variable and synchronized annual seed production is accomplished. We illustrate how, by means of a simulation based on the mechanism proposed here, climate change may influence masting patterns through its effects on environmental variability.
Masting, the intermittent and synchronized production of seeds, is a common and important phenomenon throughout the plant kingdom. Surprisingly, the proximate mechanisms by which populations of ...masting plants synchronize their seed sets have been relatively unexplored. We examined how temperature influences the acorn crop of the valley oak Quercus lobata, a masting species common in California, USA, over 33 years in order to assess whether temperature acts directly on acorn crop as a cue or whether it acts instead through intermediate steps indicative of a direct mechanistic connection to acorn production. Compared to several alternatives, the difference in temperature during the spring flowering period over the prior two years (Δt) was a good predictor of annual acorn crop in valley oak, as proposed recently by Kelly et al. Significantly, Δt correlates positively with temperatures the previous April, a likely driver of pollination success in valley oak, and negatively with the previous year's acorn crop, which is in turn negatively correlated with the current year's acorn crop, presumably due to resource limitation. Thus, the success of Δt is not as a cue but rather explained by its close relationship to the proximate drivers that have a direct, mechanistic relationship with acorn crop size.
Life-history traits interact in important ways. Relatively few studies, however, have explored the relationships between life-history traits in long-lived taxa such as trees. We examined patterns of ...energy allocation to components of reproduction and growth in three species of California oaks (Quercus spp.) using a combination of annual acorn censuses, dendrometer bands to measure radial increment, and litterfall traps. Our results are generally consistent with the hypothesis that energy invested in reproduction detracts from the amount of energy available for growth in these long-lived taxa; i.e., there are trade-offs between these traits. The relationships between reproduction and growth varied substantially among specific trait combinations and tree species, however, and in some cases were in the direction opposite that expected based on the assumption of trade-offs between them. This latter finding appears to be a consequence of the pattern of resource use across years in these long-lived trees contrasting with the expected partitioning of resource use within years in short-lived taxa. Thus, the existence and magnitude of putative trade-offs varied depending on whether the time scale considered was within or across years. Collectively, our results indicate that negative relationships between fundamental life-history traits can be important at multiple levels of modular organization and that energy invested in reproduction can have measurable consequences in terms of the amount of energy available for future reproduction and both current and future growth.
Soil carbon (C) sequestration rates vary widely in abandoned agricultural lands, and factors determining this variation, beyond climate, soil type, and productivity, are poorly understood. One such ...factor is soil disturbance by burrowing mammals. Despite being ubiquitous in all grasslands, the impact of burrowing mammals on soil C dynamics is not well understood. We quantified the major ecosystem processes that are influenced by one such burrowing mammal, plains pocket gophers (Geomys bursarius), in old field ecosystems located in east‐central Minnesota, USA. We found that pocket gopher abundance varied among old fields and that newly formed gopher mounds covered up to 6% of the soil surface annually. We first measured short‐term C pool and flux changes induced by gopher activities. Soil N mineralization did not differ between the soil in gopher mounds and undisturbed soil. However, for the soil under gopher mounds, N mineralization was 30% lower compared with the undisturbed soil. We developed a process model to simulate the long‐term gopher disturbance impact on old field soil C accumulation. This simulation showed that pocket gophers reduced both the rate of soil C accumulation and the total C pool. This reduction is primarily driven by reduced plant C input due to the time it requires for the vegetation to recolonize gopher mounds. Soil organic matter (SOM) decomposition changes had only a minor impact. The process model showed that the depth from which burrowing mammals redistribute soil to the surface is a key factor in determining the overall impact on SOM. In total, our study indicated that soil disturbance by burrowing animals could significantly reduce C storage in old field ecosystems when the mammals are mostly active at the surface soil and can be a significant factor in decreasing overall C sequestration after land abandonment. However, at our study site, gopher abundance decreased with abandonment age, which was likely to have been cause by successional vegetation changes, therefore the gopher disturbance‐induced reduction in soil C is transient and decreases with abandonment age.
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