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Many degraded ecosystems have altered nutrient dynamics due to invaders' possessing a suite of traits that allow them to both outcompete native species and alter the environment. In ecosystems where invasive species have increased nutrient turnover rates, it can be difficult to reduce nutrient availability. This study examined whether a functional trait‐based restoration approach involving the planting of species with conservative nutrient‐use traits could slow rates of nutrient cycling and consequently reduce rates of invasion. We examined a functional trait restoration initiative in a heavily invaded lowland wet forest site in Hilo, Hawaiʻi. Native and introduced species were chosen to create four experimental hybrid forest communities, in comparison to the invaded forest, with a factorial design in which communities varied in rates of carbon turnover (slow or moderate [SLOW, MOD]), and in the relationship of species in trait space (redundant or complementary [RED, COMP]). After the first 5 years, we evaluated community‐level outcomes related to nutrient cycling: carbon (C), nitrogen (N), and phosphorus (P) via litterfall, litter decomposition, and outplant productivity and rates of invasion. We found that (1) regardless of treatment, the experimental communities had low rates of nutrient cycling through litterfall relative to the invaded reference forest, (2) the MOD communities had greater nutrient release via litterfall than the SLOW communities, (3) introduced species had greater nutrient release than native species in the two MOD experimental communities, and (4) within treatments, there was a positive relationship between nutrient levels and outplant basal area, but outplant basal area was negatively associated with rates of invasion. The negative relationships among basal area and weed invasion, particularly for the two COMP treatments, suggest species existing in different parts of trait space may help confer some degree of invasion resistance. The diversification of trait space was facilitated by the use of introduced species, a new concept in Hawaiian forest management. Although challenges remain in endeavors to restore this heavily degraded ecosystem, this study provides evidence that functional trait‐based restoration approaches using carefully crafted hybrid communities can reduce rates of nutrient cycling and invasion in order to reach management goals. [ABSTRACT FROM AUTHOR]

The supply of nitrogen (N) constrains primary productivity in many ecosystems, raising the question 'what controls the availability and cycling of N'? As a step toward answering this question, we evaluated N cycling processes and aspects of their regulation on a climate gradient on Kohala Volcano, Hawaii, USA. The gradient extends from sites receiving <300 mm/yr of rain to those receiving >3,000 mm/yr, and the pedology and dynamics of rock-derived nutrients in soils on the gradient are well understood. In particular, there is a soil process domain at intermediate rainfall within which ongoing weathering and biological uplift have enriched total and available pools of rock-derived nutrients substantially; sites at higher rainfall than this domain are acid and infertile as a consequence of depletion of rock-derived nutrients, while sites at lower rainfall are unproductive and subject to wind erosion. We found elevated rates of potential net N mineralization in the domain where rock-derived nutrients are enriched. Higher-rainfall sites have low rates of potential net N mineralization and high rates of microbial N immobilization, despite relatively high rates of gross N mineralization. Lower-rainfall sites have moderately low potential net N mineralization, relatively low rates of gross N mineralization, and rates of microbial N immobilization sufficient to sequester almost all the mineral N produced. Bulk soil δ15N also varied along the gradient, from +4‰ at high rainfall sites to +14‰ at low rainfall sites, indicating differences in the sources and dynamics of soil N. Our analysis shows that there is a strong association between N cycling and soil process domains that are defined using soil characteristics independent of N along this gradient, and that short-term controls of N cycling can be understood in terms of the supply of and demand for N. [ABSTRACT FROM AUTHOR]

Human impacts on biogeochemical cycles are evident around the world, from changes to forest structure and function due to atmospheric deposition, to eutrophication of surface waters from agricultural effluent, and increasing concentrations of carbon dioxide (CO2) in the atmosphere. The National Ecological Observatory Network (NEON) will contribute to understanding human effects on biogeochemical cycles from local to continental scales. The broad NEON biogeochemistry measurement design focuses on measuring atmospheric deposition of reactive mineral compounds and CO2 fluxes, ecosystem carbon (C) and nutrient stocks, and surface water chemistry across 20 eco‐climatic domains within the United States for 30 yr. Herein, we present the rationale and plan for the ground‐based measurements of C and nutrients in soils and plants based on overarching or “high‐level” requirements agreed upon by the National Science Foundation and NEON. The resulting design incorporates early recommendations by expert review teams, as well as recent input from the larger natural sciences community that went into the formation and interpretation of the requirements, respectively. NEON's efforts will focus on a suite of data streams that will enable end‐users to study and predict changes to biogeochemical cycling and transfers within and across air, land, and water systems at regional to continental scales. At each NEON site, there will be an initial, one‐time effort to survey soil properties to 1 m (including soil texture, bulk density, pH, baseline chemistry) and vegetation community structure and diversity. A sampling program will follow, focused on capturing long‐term trends in soil C, nitrogen (N), and sulfur stocks, isotopic composition (of C and N), soil N transformation rates, phosphorus pools, and plant tissue chemistry and isotopic composition (of C and N). To this end, NEON will conduct extensive measurements of soils and plants within stratified random plots distributed across each site. The resulting data will be a new resource for members of the scientific community interested in addressing questions about long‐term changes in continental‐scale biogeochemical cycles, and is predicted to inspire further process‐based research. [ABSTRACT FROM AUTHOR]

The article discusses the procedure used at a restoration project at the Hawaiian lowland wet forests (HLWF) with the use of a plant species with functional trait. Topics discussed include invasion resistance and ecosystem functioning, approaches for functional ecosystem restoration efforts, and ways to choose a functional species from potential species pool that includes native species too.

Question How do canopy disturbance and soil properties structure vascular plant community species composition and resilience to encroachment by exotic species in a tropical montane wet forest? Location Hawai'i Experimental Tropical Forest ( HETF), a tropical montane wet forest, on Mauna Kea, Hawai'i Island, Hawai'i, USA. Methods Previous studies employing airborne Li DAR were used to define three zones across an elevation gradient from 900 to 1500 m. Within each zone, a ~1000-m block transect was selected to cross two different volcanic substrates: one derived from surface lava and one derived from thick ash deposits. Non-metric multidimensional scaling ( NMS) scores of vegetation data were related to independently-derived environmental NMS scores and spatial location with generalized additive models ( GAM). Results Vascular plant species composition in all elevation zones consists of three NMS axes, which are best modelled by one of three possible environmental NMS axes or by location. The first NMS axis of species composition in the lowest elevation zone (40% variance explained ( VE)) is a function of location on volcanic substrates (61% deviance explained ( DE)). The second lowest elevation axis (27% VE) is a function of unexplained spatial heterogeneity (31% DE). The third lowest elevation NMS axis (24% VE) is a function of the spatial mosaic of canopy disturbance (16% DE). In the middle elevation zone, species composition most strongly relates to the interaction between volcanic substrate and the condition of the soil surface for all three NMS axes (41%, 27%, 24% VE; 70%, 16%, 24% DE). The primary axis of species composition in the highest elevation zone (41% VE) corresponds with substrate and soil condition (55% DE) but the second and third axes of species composition (27% and 25% VE) relate to canopy dieback disturbance (36%, 14% DE). Counts of exotic species and 0-2 m height class native tree species respond to the type of volcanic substrate and soil surface condition in all three elevation zones. Lava-derived substrates have a higher incidence of exotic species and less native tree regeneration; whereas ash-derived substrates have higher numbers of native tree species regenerating and many fewer exotic species. Discussion The tropical montane forests on Mauna Kea reflect a native-dominated plant community response to disturbance on both lava- and ash-derived volcanic substrates, and a higher propensity for exotic species to occur on the lava-derived substrate. Native plant communities on ash-derived soils may have higher resilience to exotic invasion than communities on lava-derived substrates. Our results indicate resource managers should explicitly account for variation in soils and substrate type when prioritizing, implementing and monitoring management interventions to foster native plant assemblages and control the spread of exotic and invasive species. [ABSTRACT FROM AUTHOR]

Soils retain large quantities of carbon, thereby slowing its return to the atmosphere. The mechanisms governing organic carbon sequestration in soil remain poorly understood, yet are integral to understanding soil-climate feedbacks. We evaluated the biochemistry of dissolved and solid organic carbon in potential source and sink horizons across a chronosequence of volcanic soils in Hawai'i. The soils are derived from similar basaltic parent material on gently sloping volcanic shield surfaces, support the same vegetation assemblage, and yet exhibit strong shifts in soil mineralogy and soil carbon content as a function of volcanic substrate age. Solid-state13carbon nuclear magnetic resonance spectra indicate that the most persistent mineral-bound carbon is comprised of partially oxidized aromatic compounds with strong chemical resemblance to dissolved organic matter derived from plant litter. A molecular mixing model indicates that protein, lipid, carbohydrate, and char content decreased whereas oxidized lignin and carboxyl/carbonyl content increased with increasing short-range order mineral content. When solutions rich in dissolved organic matter were passed through Bw-horizon mineral cores, aromatic compounds were preferentially sorbed with the greatest retention occurring in horizons containing the greatest amount of short-range ordered minerals. These minerals are reactive metastable nanocrystals that are most common in volcanic soils, but exist in smaller amounts in nearly all major soil classes. Our results indicate that long-term carbon storage in short-range ordered minerals occurs via chemical retention with dissolved aromatic acids derived from plant litter and carried along preferential flow-paths to deeper B horizons. [ABSTRACT FROM AUTHOR]

Black carbon (BC) has long been considered a chemically resistant component of soil organic carbon (SOC). However, there is substantial evidence that the chemistry of most C compounds is less important for long-term storage than is physical protection (e.g., mineral sorption). We explored BC retention in grasslands that lie along a climate gradient that produces strong differences in short range order (SRO) minerals known to drive landscape-scale retention of SOC. We measured soil BC content using 13C nuclear magnetic resonance (NMR) spectroscopy, and used radiocarbon dating on a subset of samples to relate BC content to long-term soil C storage. Black C concentrations in soil ranged from 0.2 to 2.9%, representing 10-30% of SOC and spanning levels found in temperate grasslands around the world. Black C concentrations were significantly correlated with SRO minerals, but the strongest single predictor of BC content was simply SOC. The ratio of BC/OC was fairly insensitive to SRO minerals, suggesting that BC responds similarly to reactive minerals as does OC. Direct links between SOC and BC retention warrant further study. We found no evidence that BC is preferentially retained relative to OC, with soil radiocarbon ages apparently driven primarily by inputs of new OC. These results indicate that physical protection may play a strong role in BC retention, and that BC cycling in soils may be more similar to OC cycling than is generally thought. [ABSTRACT FROM AUTHOR]

Prehistoric Rapa Nui farmers used a variety of rock veneer and mulch gardens to increase crop productivity.These cultural features ranged from small ca. 10 x 10 m gardens, to much larger expanses of continuous rock concentrations covering many hectares. The rock gardens probably served several purposes, including protecting crops and soils from high winds, promoting water penetration, maintaining ground moisture, and reducing temperature fluctuations. In addition, soil nutrient dynamics might have been a factor in the construction of rock gardens. Analysis of soil nutrients within and outside of gardens suggests rainfall leaching significantly altered soil nutrients throughout the island. Furthermore, rock gardens generally have elevated levels of nutrients in relation to non-garden settings. This could have been the result of rock gardens functioning as the physical foci for increased organic mulching, the construction of gardens in natural nutrient rich sweet spots, or the elevation of nutrient levels within gardens via the weathering of relatively soft basaltic rocks. The research presented here documents the elevated soil nutrient levels of gardens and begins to investigate the reasons for this and the impacts it might have had on crop productivity. [ABSTRACT FROM AUTHOR]

The article presents a study on the condition of the nutrient restriction of nitrogen (N) and phosphorus (P) to the biological processes in terrestrial ecosystems. The study examines six mechanics that force P restriction in terrestrial ecosystems, as well as the other mechanisms that serve as soil barriers that control access to P. The results show that soil barriers, depletion, and low-P parent material induce ultimate limitation because they inhibit the P mass balance in ecosystems.

Drought stress in tropical dry forests is thought to result in greater asexual regeneration via vegetative sprouting ( e.g., basal, root, and branch layering) than occurs in moister tropical forests. We tested this hypothesis by examining the prevalence of tree sprouting and seeding in tropical forests located along a rainfall gradient on the island of Hawai'i. Additionally, we examined the potential for novel disturbance, feral pig Sus scrofa rooting and trampling, to alter patterns in tree regeneration mode. We found greater sprouting (in terms of relative density and basal area) in dry forests than in mesic and wet forests, supporting the hypothesis. We also found that feral pig disturbance is negatively correlated with the relative density and basal area of seedlings in wet forests, but is positively correlated with the relative importance of sprouting, and the richness and diversity of sprouting species. Our results suggest rainfall regimes may be an important factor controlling broad-scale patterns in tree regeneration mode, and that exotic ungulates can significantly modify such patterns with potential consequences for the structure and dynamics of tree populations and communities. [ABSTRACT FROM AUTHOR]

We compared forest canopy heights and nitrogen concentrations in long-term research sites and in 2 × 2 km landscapes surrounding these sites along a substrate age gradient in the Hawaiian Islands. Both remote airborne and ground-based measurements were used to characterize processes that control landscape-level variation in canopy properties. We integrated a waveform light detection and ranging (LiDAR) system, a high-resolution imaging spectrometer, and a global positioning system/inertial measurement unit to provide highly resolved images of ground topography, canopy heights, and canopy nitrogen concentrations (1) within a circle 50 m in radius focused on a long-term study site in the center of each landscape; (2) for the entire 2 × 2 km landscape regardless of land cover; and (3) after stratification, for our target cover class, native-dominated vegetation on constructional geomorphic surfaces throughout each landscape. Remote measurements at all scales yielded the same overall patterns as did ground-based measurements in the long-term sites. The two younger landscapes supported taller trees than did older landscapes, while the two intermediate-aged landscapes had higher canopy nitrogen (N) concentrations than did either young or old landscapes. However, aircraft-based analyses detected substantial variability in canopy characteristics on the landscape level, even within the target cover class. Canopy heights were more heterogeneous on the older landscapes, with coefficients of variation increasing from 23-41% to 69-78% with increasing substrate age. This increasing heterogeneity was associated with a larger patch size of canopy turnover and with dominance of most secondary successional stands by the mat-forming fern Dicranopteris linearis in the older landscapes. [ABSTRACT FROM AUTHOR]

The article presents a study which evaluates the sources of nutrients of the irrigated pond field windward system in Kohala, Hawaii. It analyzes soil chemical and stream water materials to assess the presence of minerals such as resin extractable phosphorus (P) and calcium (Ca) and correlates it with the availability of the plants existing in the windward system. It shows that leeward Hawi soil is infertile as manifested by the high volume of remaining P relative to parent material.

The growth-rate hypothesis states that fast-growing organisms need relatively more phosphorus-rich RNA to support rapid rates of protein synthesis, and therefore predicts, within and among taxa, increases in RNA and phosphorus content (relative to protein and nitrogen content) with increased growth rate. Here, we present a test of this hypothesis in vascular plants. We determined nitrogen : phosphorus ratios and protein : RNA ratios in pines growing at different rates due to nutrient conditions. In general, when comparing leaves of the same species at low and high growth rates, the faster-growing plants had higher RNA content, higher %N and %P, and lower protein : RNA ratios, but not consistently lower N : P ratios. We found no link between growth rate and foliar N : P or protein : RNA when comparing multiple species of different inherent growth rates. We conclude that plants adjust the balance of protein and RNA to favour either speed or efficiency of protein synthesis, but this balance does not alone dictate leaf stoichiometry. [ABSTRACT FROM AUTHOR]

We evaluated differences in the rates and correlates of decomposition among 32 fern and angiosperm litter types collected in Hawai'i. Leptosporangiate ferns were separated into groups based on phylogeny: ‘polypod’ ferns, a monophyletic clade of ferns that diversified in the Cretaceous, and all other (‘non-polypod’) ferns that diversified earlier. We measured initial litter chemistry (nutrients and carbon chemistry), and mass loss and nitrogen (N), phosphorus (P), and calcium (Ca) of litter tissue during a 1-yr incubation in a common garden. Nutrient concentrations and carbon (C) chemistry differed significantly among litter types, and litter turnover ( k-values) ranged from 0.29 to 8.31. Decomposition rates were more closely correlated with nutrient concentration than is typically observed. Lignin:N was the best predictor of decomposition across all litter types combined; however, among plant groups different predictors of decomposition were important. Nitrogen and P concentrations best predicted fern decomposition, whereas C chemistry, particularly lignin concentration, was more important for angiosperm (monocot and dicot) decomposition. Among native plants, non-polypod ferns decomposed significantly more slowly than both polypod ferns and angiosperms. Contrary to our hypothesis, fern litter did not decompose more slowly than angiosperm litter overall. Nutrient dynamics in litter were affected by initial litter concentration more than phylogeny; low-nutrient litter immobilized more nutrients than high-nutrient litter. Systematic differences in rates of decomposition, and the importance of nutrients in predicting fern decomposition, imply that changes in species composition within ferns and between ferns and angiosperms could influence the functioning of ecosystems where ferns are important forest components. [ABSTRACT FROM AUTHOR]

The role of terrestrial soil nutrient supply in determining the composition and productivity of epiphyte communities has been little investigated. In a montane Hawaiian rainforest, we documented dramatic increases in the abundance and species richness of canopy epiphytes in a forest that had been fertilized annually with phosphorus (P) for 15 years; there was no response in forest that had been fertilized with nitrogen (N) or other nutrients. The response of N-fixing lichens to P fertilization was particularly strong, although mosses and non-N-fixing lichens also increased in abundance and diversity. We show that enhancement of canopy P availability is the most likely factor driving the bloom in epiphytes. These results provide strong evidence that terrestrial soil fertility may structure epiphyte communities, and in particular that the abundance of N-fixing lichens – a functionally important epiphyte group – may be particularly sensitive to ecosystem P availability. [ABSTRACT FROM AUTHOR]

Nitrogen-fixing epiphytes (especially lichens with a cyanobacterial symbiont—cyanolichens) have the potential to contribute significant amounts of nitrogen (N) to montane tropical forests, which are typically low in N—but the factors controlling the abundance and distribution of epiphytic cyanolichens are poorly understood. In long-term fertilization experiments in montane forests on a 4.l million-yr-old Oxisol on the island of Kauà'i and on a 152-yr-old lava flow on the island of Hawai'i, the epiphytic cyanolichen Pseudocyphellaria crocata increased significantly in abundance in canopies of host trees fertilized with phosphorus (P). There was no response to fertilization with N or other essential elements. Nitrogen-fixation rates were also elevated in lichens in P-fertilized plots at both sites. Phosphorus supply to host trees may be an important factor controlling N inputs to montane tropical forests by N-fixing epiphytes. [ABSTRACT FROM AUTHOR]

1 Tansley's ecosystem concept remains a vital framework for ecological research in part because the approach facilitates interdisciplinary analyses of ecological systems. 2 Features of the Hawaiian Islands – particularly the nearly orthogonal variation in many of the factors that control variation among ecosystems elsewhere – make the archipelago a useful model system for interdisciplinary research designed to understand fundamental controls on the state and dynamics of ecosystems, and their consequences for human societies. 3 Analyses of rain forest sites arrayed on a substrate age gradient from c. 300 years to over 4 million years across the Hawaiian archipelago demonstrate that the sources of calcium and other essential cations shift from > 80% rock-derived in young sites to > 80% derived from marine aerosol on substrates older than 100 000 years. Rock-derived phosphorus is retained longer within ecosystems, but eventually long-distance transport of continental dust from Asia becomes the most important source of phosphorus. 4 A biogeochemical feedback from low nutrient availability to efficient resource use by trees to slow decomposition and nutrient regeneration accentuates the geochemically driven pattern of low phosphorus availability and phosphorus limitation to net primary productivity in the oldest site. 5 Variations in ecosystem biogeochemistry across the archipelago shaped the development and sustainability of Polynesian agricultural systems in the millennium between their discovery of Hawai’i and contact by Europeans. Irrigated pondfields were largely confined to stream valleys on the older islands, while rain-fed dryland systems occupied a narrow zone of fertile, well-watered soils on the younger islands. 6 The ecosystem approach often represents the most appropriate level of organization for analyses of human influences on ecological systems; it can play a central role in the design and analysis of alternative agricultural, industrial and residential systems that could reduce the human footprint on the Earth. [ABSTRACT FROM AUTHOR]

We used strontium isotopes and analysis of foliar and soil nutrients to test whether erosion can rejuvenate the supply of rock-derived nutrients in the lowland tropical rain forest of La Selva, Costa Rica. We expected that these nutrients would be depleted from soils on stable surfaces, a result of over one million years of weathering in situ. In fact, trees and palms in all landscape positions derive a relatively high percentage (≥40%) of their strontium from bedrock, rather than atmospheric, sources. The fraction that is rock-derived increases on slopes, but with no detectable effect on plant macronutrient concentrations. These results differ from those in a similar ecosystem on Kauai, Hawaii, where plants on uneroded surfaces derive almost all of their foliar Sr from atmospheric, rather than bedrock, sources. The results from La Selva challenge the assumption that tropical Oxisols in general have low nutrient inputs from bedrock, and support the hypothesis that erosion can increase the supply of these nutrients in lower landscape positions. [ABSTRACT FROM AUTHOR]

Evergreen broad-leaved tropical forests can have high rates of productivity and large accumulations of carbon in plant biomass and soils. They can therefore play an important role in the global carbon cycle, influencing atmospheric CO2 concentrations if climate warms. We applied meta-analyses to published data to evaluate the apparent effects of temperature on carbon fluxes and storages in mature, moist tropical evergreen forest ecosystems. Among forests, litter production, tree growth, and belowground carbon allocation all increased significantly with site mean annual temperature (MAT); total net primary productivity (NPP) increased by an estimated 0.2–0.7 Mg C·ha-1·yr-1·°C-1. Temperature had no discernible effect on the turnover rate of aboveground forest biomass, which averaged 0.014 yr-1 among sites. Consistent with these findings, forest biomass increased with site MAT at a rate of 5–13 Mg C·ha-1·°C-1. Despite greater productivity in warmer forests, soil organic matter accumulations decreased with site MAT, with a slope of -8 Mg C·ha-1·°C-1, indicating that decomposition rates of soil organic matter increased with MAT faster than did rates of NPP. Turnover rates of surface litter also increased with temperature among forests. We found no detectable effect of temperature on total carbon storage among moist tropical evergreen forests, but rather a shift in ecosystem structure, from low-biomass forests with relatively large accumulations of detritus in cooler sites, to large-biomass forests with relatively smaller detrital stocks in warmer locations. These results imply that, in a warmer climate, conservation of forest biomass will be critical to the maintenance of carbon stocks in moist tropical forests. [ABSTRACT FROM AUTHOR]

Elevated CO2, N deposition and climate change can alter ecosystem-level nutrient cycling both directly and indirectly. We explored the interactive effects of these environmental changes on extracellular enzyme activity and organic matter fractionation in soils of a California annual grassland. The activities of hydrolases (polysaccharide-degrading enzymes and phosphatase) increased significantly in response to nitrate addition, which coincided with an increase in soluble C concentrations under ambient CO2. Water addition and elevated CO2 had negative but nonadditive effects on the activities of these enzymes. In contrast, water addition resulted in an increase in the activities of lignin-degrading enzymes (phenol oxidase and peroxidase), and a decrease in the free light fraction (FLF) of soil organic matter. Independent of treatment effects, lignin content in the FLF was negatively correlated with the quantity of FLF across all samples. Lignin concentrations were lower in the aggregate-occluded light fraction (OLF) than the FLF, and there was no correlation between percent lignin and OLF quantity, which was consistent with the protection of soil organic matter in aggregates. Elevated CO2 decreased the quantity of OLF and increased the OLF lignin concentration, however, which is consistent with increased degradation resulting from increased turnover of soil aggregates. Overall, these results suggest that the effects of N addition on hydrolase activity are offset by the interactive effects of water addition and elevated CO2, whereas water and elevated CO2 may cause an increase in the breakdown of soil organic matter as a result of their effects on lignin-degrading enzymes and soil aggregation, respectively. [ABSTRACT FROM AUTHOR]

Biological, atmospheric, and geochemical processes interact to shape how element cycles and nutrient losses develop within newly formed landscapes. We examined losses of nitrogen (N), phosphorus (P), and base cations across a four-million-year substrate age gradient of Hawaiian montane tropical forests, with the goal of understanding how losses depend on changes in biotic demand weathering, and atmospheric sources. We were particularly interested in whether losses of nutrients that are not subject to traditional mechanisms of biotic availability could influence ecosystem fertility and nutrient limitation over time Over three-year period we sampled nutrient empros in soil solutions below the active plant-soil system and small streams, gaseous N losses (NO, N[sub 2]O, and N[sub 2]), and pools and transformations of N in soils. Weathering was the major determinant of ecosystem losses of P, of base cations and Si, and of ecosystem acid-base status. Sharp reductions in weathering inputs after 20 000 years of forest development caused dramatically lower outputs of P (∼65% reduction), Ca[sup 2+] (∼99%), and Si (∼94%), to rates that matched inputs from dilute sea-salt and dust aerosols. Internal production of organic acids, in combination with low weathering, caused highly acidic soil waters (pH < 5.0) with elevated Al (up to 300 ρg/L) and Ca:Al ratios (<0.3) below values considered critical thresholds for many plant species. Long-term N and P interactions were more complex than predicted by the Walker and Syers model, with important influences of N and P loss pathways that were not subject to direct biotic availability. While losses of available forms of dissolved N and P, and N gases followed (as predicted ecosystem nutrient availability, significant dissolved organic N DON and dissolved organic P (DOP losses occurred independent of ecosystem N or P status. DON losses were not sufficient (relative to external inputs to sustain N limitation beyond 20 000 years, while dissolved P losses remained large enough to maintain P limitation in older forests. Forests developed high N:P loss ratios over time (>300 on mass weight basis) due to efficient P recycling and unexpectedly high N throughputs (4-9 kg N·ha[sup -1]·yr[sup -1]) by either N fixation and/or N deposition. [ABSTRACT FROM AUTHOR]

Dissolved organic nitrogen (DON) is present in soils and streams around the world. We are only now beginning to explore the important roles this chemically heterogeneous mixture of compounds plays in terrestrial nitrogen (N) cycling. Over centuries, DON leaching may represent a significant "leak" of N, which occurs because plants and microbes cannot prevent DON losses, even in times of high N demand. However, in many ecosystems, plants may "short-circuit" the terrestrial N cycle by direct uptake of amino acid DON without microbial mineralization of organic N to ammonium (NH4+). These apparently contradictory roles for DON in N cycling are due to the biological and physical factors that regulate DON loss, and the fact that there are many biochemical forms of organic N in solution. Recognition of these processes complicates the standard conceptual view of terrestrial N cycling. Here we focus on the dual roles of DON as a nutrient-loss pathway and as an N source for plants. [ABSTRACT FROM AUTHOR]

Aim The purposes of this paper are to suggest that a greater use of model systems would advance our understanding of ecology, and to illustrate that oceanic islands are valuable model systems for ecosystem studies in particular. Location The illustrations discussed herein result from studies in the Hawaiian Islands. Methods Sequences of sites that are similar in most respects but differ widely in temperature, precipitation or substrate age have been developed and analysed in the Hawaiian Islands. Process studies, experiments and models arrayed on these gradients are used to determine fundamental controls over ecosystem processes, with a precision that cannot be duplicated in continental ecosystems. Results Increasing temperatures enhance rates of decomposition to a greater extent than plant production, in soil organic matter as well as litter. Ecosystem-level losses of N by fractionating pathways are greater in drier sites. Sea spray and long-distance dust transport play increasing roles in the nutrient economy of ecosystems as soils become progressively older. Main conclusions All of the results describe processes that occur in continental as well as island ecosystems, but a number of features of islands make the processes more amenable to analysis on islands. [ABSTRACT FROM AUTHOR]

The article demonstrates the stand characteristics, nitrogen accumulation, and rates of nitrogen fixation in regenerating stands of Acacia koa. It notes the increase of the tree's breast height, and the decline of stem density, dbh increment, and leaf area index. Results showed that nitrogen fertilization did not affect dbh increment, while measurements of foliar and root phosphorus suggest a decline in phosphorus availability which may have contributed to the decline in nitrogen fixation.

Examines the influence of nutrient availability on the mechanism used by plants to acquire nitrogen and phosphorus from the soil in Hawaii. Increase of extracellular phosphatase activity; Effect of phosphorus additions; Efficiency of plant resource allocation.

Examines the controls of nonsymbiotic nitrogen (N) fixation. Importance of N limitation to primary production and other processes; Fixation of low-lignin litter; Importance of non-N nutrients; Studies on the decomposition of low-lignin litter in adding N.

Assesses whether the same nutrients limit decomposition and aboveground net primary production (ANPP) along a soil chronosequence where nutrients demonstrably and predictably limit ANPP. Fertilization for assessment whether in nitrogen and/or phosphorus limit decomposition; Comparison of limitation by externally supplied nutrients vs limitation by nutrients within litter.

Provides information on a study which evaluated the effects of precipitation on litter quality and surface litter decomposition across a natural rainfall gradient. Materials and methods used in the study; Results and discussion. INSET: 3.

SummaryWe examined interactions between temperature, soil development, and decomposition on three elevational gradients, the upper and lower ends of each being situated on a common lava flow or ash deposit. We used the reciprocal transplant technique to estimate decomposition rates of Metrosideros polymorpha leaf litter during a three-year period at warm and cool ends of each gradient. Litter quality was poorest early in soil development or where soils were most intensely leached and waterlogged. In situ litter decomposition was slowest on the young 1855 flow (k = 0.26 and 0.14 at low and high elevation, respectively). The more fertile Laupahoehoe gradient also supported more rapid in situ decay at the warmer low elevation site (k = 0.90) than at high elevation (k = 0.51). The gradient with the most advanced soil development showed no difference for in situ decay at low and high elevations (k = 0.88 and 0.99, respectively) probably due to low soil nutrient availability at low elevation, which counteracted the effect of warmer temperature. Comparisons of in situ, common litter, and common site experiments indicated that site factors influenced decomposition more than litter quality did. The effect of temperature, however, could be over-ridden by soil fertility or other site factors. Field gradient studies of this sort yield variable estimates of apparent Q10, even under the best conditions, due to interactions among temperature, moisture, nutrient availability, decomposer communities and litter quality. Such interactions may be as likely to occur with changing climate as they are along elevational gradients. [ABSTRACT FROM AUTHOR]

Studies the species composition and biomass of vascular plants in a matrix of 29 sites on the wet eastern slope of Mauna Loa volcano in Hawaii. Increase in biomass with substrate age; Variations in community composition; Succession at low altitude compared to high altitude.

(1) Nitrogen availability (net nitrogen mineralization) was extremely high in a lowland rainforest on volcanic soil at La Selva, Costa Rica, averaging 50–80 μg g-1 month-1 (822 kg ha-1 year-1)- Available phosphorus concentrations were relatively low (2.5μg-1). (2) Nitrogen mineralization did not increase in the crown-fall zone of treefall gaps, although the possibility of a short-lived increase immediately after treefall could not be ruled out. Phosphorus concentrations increased slightly but not significantly (to 3.3μg g=1. (3) The root-throw zone of treefall gaps had significantly lower nitrogen mineralization and phosphorus concentrations than the crown-fall zone or the zone along the fallen trunk. Low nutrient availability in the root-throw zone could select for colonizing species distinct from those establishing in other zones of treefall gaps. [ABSTRACT FROM AUTHOR]

Evaluates the effects of plant functional group richness on seasonal patterns of soil nitrogen and phosphorus cycling using serpentine grassland in south San Jose, California. Available nutrients; Anion exchange resin phosphorus; Bicarbonate extractable P; Water availability; Relative resource use; Leaching losses; Microbial dynamics.

Studies soil organic matter (SOM) dynamics in allophanic soils along independent gradients of temperature and land use on the island of Hawaii. Separation of rapid, intermediate and very slow turnover SOM pools; Estimation of turnover times for the large intermediate pool; Comparison of the estimates to independent estimates.

Determines the consequences of systematic changes in nutrient availability during long-term soil development by measuring foliar nutrient concentrations. Analysis of samples of sun leaves from the dominant tree Metrosideros polymorpha and of eight other species in Hawaiian rain forests with various substrate ages.

Evaluates the patterns of nitrogen trace gas emissions, soil nitrogen flux and nutrient availability at five sites that form a chronosequence in Hawaiian montane rain forest. Soil age as a major factor underlying variation in soils and ecosystems; Age of study sites; Nutrient pools; Nutrient availability and transformation; Nitrogen trace gas emission.

Focuses on ecology and global environmental change. Increase of atmospheric carbon dioxide concentration; Alterations in the biogeochemistry if the nitrogen cycle; Human land use and land cover; Effects on biological diversity; Growth in size and resource use of the human population.

Determines controls on litter decomposition and nutrient release for the widespread native tree Metrosideros polymorpha in 11 sites arrayed on gradients of elevation, precipitation and substrate age on Hawaiian lava flows. Effects of site characteristics; Variation in rates of decomposition in sites and substrates; CENTURY soil organic matter model.

Examines the extent of human alteration on the nitrogen cycle, focusing on the consequences of this process on the functioning of many terrestrial, freshwater and marine ecosystems. Details on what the nitrogen cycle is used for; Benefits of this cycle to human existence; Information on the nitrogen cycle process; Effects this cycle has on the atmosphere.

Summary Dicranopteris linearis (Gleicheniaceae), a native fern common throughout the Old World tropics and Polynesia, forms dense thickets > 3m deep over large areas of open-canopy, oligotrophic, wet Hawaiian rainforests. Our objectives were to identify leaf- and whole plant-level traits that are key to its success and to determine its community-and ecosystem-level consequences in primary successional sites. Along an elevational gradient from 90 to 1660m, mean maximum net assimilation rates of Dicranopteris ranged from 2.9 to 5.0 μmol m-2 s-1 , compared with 3.6–9.5 μmol m-1 s-1 in the codominant tree Metrosideros polymorpha. Gas-exchange characteristics did not explain Dicranopteris' success, nor its trends in production. However, indeterminate, clonal growth form, shallow rhizomes, marcescent leaves with low decomposability, and a mat-forming capacity enabled Dicranopteris to colonize sites and to maintain dominance via high effective leaf area, despte its low biomass. Phosphorus use efficiency, which reached 24 kg g-1 , was exceptionally high, allowing colonization of phosphorus-poor sites. Dicranopteris contributed up to 74% of above-ground net primary productivity in a site where it contained only 14% of live biomass. It accounted for up to 57% and 47% of total nitrogen and phosphorus uptake by plants, respectively, where it contained only 24% and 30% of plant nitrogen and phosphorus. Dicranopteris leaves are short-lived and slow to decompose; thus, fixed carbon is transferred quickly to soil detrital pools where it contributes to aggrading soil organic matter pools and may exacerbate oligotrophic conditions, thereby strongly influencing soil genesis and ecosystem development. The fern therefore influences forest-floor light regimes and directs later community development. An exclusion experiment demonstrated that Dicranopteris competed with Metrosideros, but lack of revegetation in 40% of the exclusion area after 39 months showed that Dicranopteris also colonized microenvironments unavailable to its endemic codominants. Dicranopteris may play an important role in resisting invasions of exotic species into Hawaiian rainforests. [ABSTRACT FROM AUTHOR]