Differences In Soil Nutrient Availability Research Articles

Aridity differentially alters the stability of soil bacterial and fungal networks in coastal and inland areas of Australia.

Despite the importance of soil bacterial and fungal communities for ecosystem services and human welfare, how their ecological networks respond to climatic aridity have yet been evaluated. Here, we collected soil samples from 47 sites across 2500 km in coastal and inland areas of eastern Australia with contrasting status of aridity. We found that the diversity of both bacteria and fungi significantly differed between inland and coastal soils. Despite the significant differences in soil nutrient availability and stoichiometry between the inland and coastal regions, aridity was the most important predictor of bacterial and fungal community compositions. Aridity has altered the potential microbial migration rates and further impacted the microbial assembly processes by increasing the importance of stochasticity in bacterial and fungal communities. More importantly, ecological network analysis indicated that aridity enhanced the complexity and stability of the bacterial network but reduced that of the fungal network, possibly due to the contrasting impacts of aridity on the community-level habitat niche breadth and overlaps. Our work paves the way towards a more comprehensive understanding of how climate changes will alter soil microbial communities, which is integral to predicting their long-term consequences for ecosystem sustainability and resilience to future disturbances.

Geologic Soil Parent Material Influence on Forest Surface Soil Chemical Characteristics in the Inland Northwest, USA

Successful fertilization treatments targeted to improve stand productivity while reducing operational complexities and cost depend on a clear understanding of soil nutrient availability under varying environmental conditions. Soil nutrient data collected from 154 forest sites throughout the Inland Northwest, USA were analyzed to examine soil nutrient characteristics on different geologic soil parent materials and to rank soil fertility. Results show that soil parent material explains significant differences in soil nutrient availability. Soils developed from volcanic rocks have the highest cation exchange capacity (CEC) and are relatively high in phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), boron (B), and copper (Cu), but generally poor in mineralizable nitrogen (MinN). Forest soils developed from plutonic rocks exhibit the lowest CEC and are low in MinN, K, Ca, Mg, S, and Cu, but higher in P. Some soils located on mixed glacially derived soils are low only in K, Ca, Mg, and Cu, but many mixed glacial soils are relatively rich in other nutrients, albeit the second lowest CEC. Soils developed from metasedimentary and sedimentary rocks are among those with lowest soil nutrient availability for P and B. Sulfur was found to have the highest concentrations in metasedimentary influenced soils and the least in sedimentary derived soils. Our results should be useful in designing site-specific fertilizer and nutrient management prescriptions for forest stands growing on soils developed from these major geologies within the Inland Northwest region of the United States.

Patterns of Plumericin Concentration in Leaves of Himatanthus tarapotensis (Apocynaceae) and Its Interactions with Herbivory in the Peruvian Amazon.

We explored the concentration patterns of the bioactive metabolite plumericin produced by Himatanthus tarapotensis (Apocynaceae) under different edaphic conditions and variations in rainfall intensity, as well as its potential role in the chemical defense against insect herbivores. Values of plumericin concentration from leaves were obtained by High-Performance Liquid Chromatography, and evaluated as a function of differences in soil types, variation of precipitation, and variation of the abundance of insect herbivores, using first a Repeated Measures Correlation (rmcorr) and then a Generalized Linear Mixed Model (GLMM) analysis. Plumericin concentration is highly variable among plants, but with a significantly higher concentration in plants growing on clay soil compared to that of the white-sand soil habitat (p < 0.001). Plumericin concentration is not affected by precipitation. The caterpillar of Isognathus leachii (Lepidoptera: Sphingidae) is the most conspicuous herbivore of H. tarapotensis, and its presence is continuous but not related to plumericin concentration, probably because of its capacity to elude the chemical defense of this plant. Nevertheless, our multivariate model revealed that plumericin concentration is related to the abundance of Hymenoptera (Formicidae), and this relationship is significantly influenced by the soil parameters of carbon percentage, clay percentage, and phosphorous percentage (p < 0.001). Plumericin is a mediating agent in the interaction between H. tarapotensis and its natural environment. Variation in plumericin concentration would be induced by the abundance of Hymenoptera (Formicidae), probably as a chemical response against these insects, and by differences in soil nutrient availability.

Long term effects of intensive biomass harvesting and compaction on the forest soil ecosystem

Forest soil ecosystems can be negatively affected by intensive biomass harvesting due to losses of organic inputs and soil compaction, ultimately leading to reduced forest productivity. In this research, we revisited a site from the North American Long-Term Soil Productivity study located on a sandy Spodosol within the Huron National Forest in Michigan, USA, to measure the effects of aboveground organic matter removal of different intensities (three levels: bole only; whole tree harvest; or whole tree harvest and forest floor removal) and soil compaction (2 levels: no or moderate compaction) nearly 20 years following the initial treatments. The effects of harvesting on the soil microbial community in surface and subsurface soils and on soil nutrient availability in surface soils were evaluated. Additionally, patterns of carbon and nitrogen distribution among soil organic matter pools in surface and subsurface soils were compared using a physical fractionation approach to isolate a free – light fraction of particulate organic matter external to aggregates, an occluded – light fraction, which represents particulate organic matter released from the disruption of soil aggregates, and a heavy or mineral-associated fraction. Whole-tree harvests had significantly different microbial community compositions than bole-only harvests (P = 0.02), a result driven by significantly lower abundance of arbuscular mycorrhizae and greater gram positive bacterial abundance in the whole-tree harvest relative to bole-only harvest conditions. Few differences in soil nutrient availability were apparent 20 years after organic matter manipulations, with the exception of reduced calcium availability where organic matter was removed. Soil compaction resulted in greater microbial biomass (0.19 versus 0.14 μmol g−1 soil), which may have also led to a reduced C:N ratio in the heaviest and oldest soil component and increased P availability as well. Nitrogen concentrations and stocks were greatest at the surface (0–10 cm depth) for the free and light soil fractions in bole-only removal treatments, in contrast to whole-tree harvest treatments where C and N concentrations and C stocks were greater in the subsurface soil (free - light fraction at 20–30 cm depth). The soil microbial community, soil fraction size, and soil C and N stocks differed between surface and subsurface soils, highlighting the soil forming processes at work in this Spodosol, and the importance of sampling multiple depths to address research questions. These results demonstrate the long-term effects of forest management on soil biological, physical, and chemical properties and are useful in evaluating sustainable biomass harvesting practices for comparable forests.

Plasticity in root symbioses following shifts in soil nutrient availability during long‐term ecosystem development

Abstract The vast majority of terrestrial plants form root symbioses with arbuscular mycorrhizal (AM) fungi to enhance nutrient (particularly phosphorus, P) acquisition. However, some plant species also form dual symbioses involving ectomycorrhizal (ECM) fungi, with a subset of those also forming triple symbioses also involving dinitrogen (N2)‐fixing bacteria. It has been suggested that these plants show plasticity in root symbioses to optimise nutrient acquisition depending on the type and strength of soil nutrient limitation (e.g., N vs. P), yet empirical evidence remains limited. Alternatively, the degree of investment or “preference” in particular root symbioses might simply reflect differences in inoculum potential among soils of contrasting nutrient availability, reflecting adaptations of root symbionts to different edaphic conditions. Here, we grew two co‐occurring plant species forming triple (AM/ECM/N2‐fixing; Acacia rostellifera) or dual (AM/ECM; Melaleuca systena) symbioses in soils of increasing age and contrasting nutrient availability from an Australian long‐term soil chronosequence to disentangle the relative importance of abiotic factors (e.g., soil nutrient availability and stoichiometry) and biotic factors (e.g., soil inoculum potential) in determining root colonisation patterns and functional outcomes of these multiple root symbioses. For both plant species, we found clear hump‐shaped plant growth patterns along the pedogenesis‐driven gradient in soil nutrient availability, with peak growth in intermediate‐aged soils, while high levels of mycorrhizal colonisation by the “preferred” root symbionts were maintained across all soils. We found large increases (540%) in foliar manganese concentrations with increasing soil age and declining P availability, suggesting that plants may be relying on the release of carboxylates to help acquire P in the most P‐impoverished soils. Finally, we found that soil abiotic properties, such as strong differences in soil nutrient availability, are generally more important than soil inoculum potential in explaining these shifts in our plant and root responses. Synthesis. Our study suggests that plants capable of forming multiple root symbioses show plasticity in their nutrient‐acquisition strategies following shifts in soil nutrients during long‐term ecosystem development, yet maintain a preference for certain root symbionts despite changes in soil microbial inoculum.

Nutrient limitation of soil microbial activity during the earliest stages of ecosystem development.

A dominant paradigm in ecology is that plants are limited by nitrogen (N) during primary succession. Whether generalizable patterns of nutrient limitation are also applicable to metabolically and phylogenetically diverse soil microbial communities, however, is not well understood. We investigated if measures of N and phosphorus (P) pools inform our understanding of the nutrient(s) most limiting to soil microbial community activities during primary succession. We evaluated soil biogeochemical properties and microbial processes using two complementary methodological approaches-a nutrient addition microcosm experiment and extracellular enzyme assays-to assess microbial nutrient limitation across three actively retreating glacial chronosequences. Microbial respiratory responses in the microcosm experiment provided evidence for N, P and N/P co-limitation at Easton Glacier, Washington, USA, Puca Glacier, Peru, and Mendenhall Glacier, Alaska, USA, respectively, and patterns of nutrient limitation generally reflected site-level differences in soil nutrient availability. The activities of three key extracellular enzymes known to vary with soil N and P availability developed in broadly similar ways among sites, increasing with succession and consistently correlating with changes in soil total N pools. Together, our findings demonstrate that during the earliest stages of soil development, microbial nutrient limitation and activity generally reflect soil nutrient supply, a result that is broadly consistent with biogeochemical theory.

Assessing habitat requirements and genetic status of a rare ephemeral wetland plant species, Isoëtes butleri Engelm

Isoëtes butleri Engelm. (Butler’s Quillwort) is a lycopod endemic to the central and southeastern United States. It inhabits sparsely vegetated moist depressions within dolomite prairies that become ephemeral wetlands in the spring. Classified as endangered in portions of its range (Illinois and Kentucky), little is known about the ecology and genetics of I. butleri. In Illinois, the five known populations are disjunct from all other known populations, and there is concern that these populations could be vulnerable to a number of threats, including a lack of suitable microhabitats, displacement by other plant species, accumulation of plant litter, and low genetic diversity and limited gene flow. We evaluated these putative threats by analyzing demographic data collected by Plants of Concern, a citizen-science rare-plant monitoring program; performing experimental litter removals; and assessing population genetic structure. There were no significant differences in soil nutrient availability in topographically similar depressions with and without I. butleri; however, areas inhabited by I. butleri had lower abundance of woody species and higher abundance of conservative (habitat specialist) species than uninhabited areas. Following experimental litter removal, I. butleri exhibited lower size but higher density and recruitment. We found that all populations had high genetic diversity. However, there was also evidence of high inbreeding, which may be due to spatially fine-scale genetic structure and poor dispersal ability. Our findings suggest that reductions of woody plant growth and accumulated litter—both of which can be achieved through prescribed fire—should be management priorities for I. butleri conservation.

Relationship between soil nutrients and mycorrhizal associations of two Bipinnula species (Orchidaceae) from central Chile.

Mycorrhizal associations are influenced by abiotic and biotic factors, including climate, soil conditions and the identity of host plants. However, the effect of environmental conditions on orchid mycorrhizal associations remains poorly understood. The present study examined how differences in soil nutrient availability are related to the diversity and composition of mycorrhizal fungi associated with two terrestrial orchid species from central Chile. For 12 populations of Bipinnula fimbriata and B. plumosa, OTU (operational taxonomic unit) richness, phylogenetic diversity and community composition of mycorrhizal fungi in root samples were estimated using internal transcribed spacer (ITS) sequences. Then, these mycorrhizal diversity variables were related to soil nutrients and host species using generalized linear models and non-metric multidimensional scaling. Variation in OTU composition of mycorrhizal fungi among sites was explained mainly by orchid host species. Fungi in Tulasnellaceae and Ceratobasidiaceae were isolated from both orchid species, but the former were more frequent in B. fimbriata and the latter in B. plumosa. Soil nutrients and orchid host species had significant effects on OTU richness and phylogenetic diversity. Mycorrhizal diversity decreased in habitats with higher N in both species and increased with P availability only in B. fimbriata The results suggest that soil nutrient availability modulates orchid mycorrhizal associations and provide support for the hypothesis that specialization is favoured by higher soil nutrient availability. Inter-specific differences in mycorrhizal composition can arise due to a geographical pattern of distribution of orchid mycorrhizal fungi, host preferences for fungal partners or differential performance of mycorrhizal fungi under different nutrient availabilities. Further experiments are needed to evaluate these hypotheses.

STRUCTURE OF NATURAL REGENERATION IN RELATION TO SOIL PROPERTIES AND DISTURBANCE IN TWO SWAMP FORESTS

ABSTRACT Veredas (palm swamps) is a type of vegetation associated with watercourses, characterized by the presence of Mauritia flexuosa palm trees. These systems are not well understood and suffer from high anthropogenic pressure. The aims of this study were to describe the natural regeneration of two swamp forests in vereda systems with different anthropogenic impacts and investigate if the variation in these plant communities are associated to edaphic conditions. The study was performed in preserved and impacted sites located in the Environmental Protection Area of the Pandeiros River in northern Minas Gerais. At each site, one hundred 25 m2 plots were established for surveying regenerating shrubs and trees (≥1 cm diameter at the base of the stem and &lt; 3 cm diameter at breast height). Vegetation structure was evaluated by phytosociological parameters, similarity index, and size distribution of individuals. Regenerating strata was correlated with chemical and physical soil analyses. The vegetation at the preserved site was characterized by a higher number of individuals and a lower diversity but contained species that were typical of flooded areas. The results also showed differences in soil nutrient availability between sites that influenced the distribution of species at the two study sites.

Cover Crops and Tillage in a Mature Merlot Vineyard Show Few Effects on Grapevines

Permanent cover crops are commonly used in vineyard floor management because of their beneficial effects to soil and vine health, but studies evaluating their competitive effects on vines have been conducted primarily in nonirrigated vineyards. Future air quality regulations could mandate the use of no-till floor management practices in California’s Central Valley. We evaluated the combined effects of cover crop type (oats alone or oats grown with legumes) and tillage on soil nutrient availability, vine nutrition, growth, and yield characteristics of Vitis vinifera cv. Merlot grown under regulated deficit irrigation in a commercial vineyard from 2008 to 2010. Five treatments were used: Resident Vegetation (RV) + Till, Oats + Till, Oats/Legumes +Till, Oats + NoTill, and Oats/Legumes + NoTill. No differences in soil nutrient availability were found among the treatments. Of the numerous nutritional constituents analyzed on leaf petioles and blades, only NO3-Npetiole was affected by floor management. At nearly all growth stages among all years, NO3-Npetiole of tilled treatments was twice the no-till treatments. At harvest, yield, mean cluster weight, cluster number per vine, and aboveground cover crop biomass differed among treatments in 2009 and/or 2010 but not in the first year (2008); however, responses were not consistent among treatments within each respective year. Importantly, yields were similar from all four cover crop treatments compared to the typical management (RV + Till), suggesting that use of cover crops and/or no-till practices may be implemented in an irrigated vineyard with little immediate effect on grape productivity in mature vineyards.

Decorative values and the nutritional status of some Magnolia species under the climatic conditions of Lublin (Poland). Part II. Evaluation of the nutritional status of the plants

The present study was conducted on six &lt;em&gt;Magnolia &lt;/em&gt;species in the period 2006-2008 in the Botanical Garden of the Maria Curie-Skłodowska University in Lublin. The soil and leaves from the locations of the following species of &lt;em&gt;Magnolia &lt;/em&gt;were subjected to evaluation: cucumber tree (&lt;em&gt;Magnolia acuminata &lt;/em&gt;L.), Kobushi magnolia (&lt;em&gt;Magnolia kobus &lt;/em&gt;DC), purple lily magnolia (&lt;em&gt;Magnolia liliiflora &lt;/em&gt;L.), Japanese willow-leaf magnolia (&lt;em&gt;Magnolia salicifolia &lt;/em&gt;Siebold et Zucc. Maxim.), saucer magnolia (&lt;em&gt;Magnolia x soulangiana &lt;/em&gt;Soul.-Bod.), and umbrella magnolia (&lt;em&gt;Magnolia tripetala &lt;/em&gt;L.). The studied plants were planted during the period 1968-1989 on grey-brown podzolic soil derived from loess. The significantly lowest content of phosphorus, potassium and magnesium as well as the lowest pH were recorded in the soil from the location occupied by the purple lily magnolia (&lt;em&gt;M. liliiflora&lt;/em&gt;). The other sites were characterized by an optimal range of pH, high soil phosphorus and magnesium availability as well as medium potassium availability. An optimal content of nitrogen and calcium was found in the leaves of the cucumber tree (&lt;em&gt;M. acuminata&lt;/em&gt;), of phosphorus and magnesium in the leaves of the Kobushi magnolia (&lt;em&gt;M. kobus&lt;/em&gt;), and of potassium in the leaves of the Japanese willow-leaf magnolia (&lt;em&gt;M. salicifolia&lt;/em&gt;). A low content of nitrogen and calcium was shown in the leaves of the purple lily magnolia (&lt;em&gt;M. liliiflora&lt;/em&gt;), of phosphorus in the leaves of the saucer magnolia (&lt;em&gt;M. x soulangiana&lt;/em&gt;), and of potassium in the indicator parts of the cucumber tree (&lt;em&gt;M. acuminata&lt;/em&gt;). The study found that among the studied species the cucumber tree (&lt;em&gt;M. acuminata&lt;/em&gt;) could be a good biostabilizer of nitrogen, while the Kobushi magnolia (&lt;em&gt;M. kobus&lt;/em&gt;) a good biostabilizer of phosphorus and magnesium. In spite of significant differences in soil nutrient availability and clear variations in macronutrient contents in the indicator parts of the investigated plants, no visual symptoms of nutrient deficit were found in the &lt;em&gt;Magnolia &lt;/em&gt;species under study.

Impacts of soil fertility on species and phylogenetic turnover in the high - rainfall zone of the Southwest Australian global biodiversity hotspot

The ancient landscape of the South - West Australian Floristic Region (SWAFR) is characterized by exceptional floristic diversity, attributed to a complex mosaic of nutrient - impoverished soils. Between - soil type differences in nutrient availability are expected to affect floristic assemblage patterns in the SWAFR. We compared patterns of floristic diversity between open - forest samples from three soil types in the high - rainfall zone of the SWAFR. The importance of environmental and spatial factors for species compositional turnover within soil types were evaluated within canonical correspondence analyses using variation partitioning. Patterns of phylogenetic diversity and dispersion were contrasted between soil types and related to differences in soil nutrient availability. Between - quadrat shared phylogenetic branch length for individual life form categories was correlated with explanatory variables using Mantel tests. Species and phylogenetic diversity increased with a decline in soil nutrients and basal area. Nutrient - poorer soils were differentiated by higher species density and phylogenetic diversity, and larger phylogenetic distances between species. Species turnover was best explained by environmental factors when soil nutrient concentrations and basal area were low. Coastal and inland quadrats from the most fertile soil type were distinguished by significantly differing patterns of phylogenetic diversity. Inland quadrats were characterized by strong relationships between phylogenetic diversity and environment, while phylogenetic patterns remained largely unaccounted for by explanatory variables within coastal quadrats. Phylogenetic diversity was more strongly related with environment within upland landform types for nutrient-poor soils. We highlight the complex relationships between climatic and edaphic factors within the SWAFR, and propose that the occurrence of refugial habitat for plant phylogenetic diversity is dynamically linked with these interactions. Climate change susceptibility was estimated to be especially high for inland locations within the high - rainfall zone. Despite the strong relationship between floristic diversity and soil fertility, holistic conservation approaches are required to conserve the mosaic of soil types regardless of soil nutrient status.

Controls of Bedrock Geochemistry on Soil and Plant Nutrients in Southeastern Utah

The cold deserts of the Colorado Plateau contain numerous geologically and geochemically distinct sedimentary bedrock types. In the area near Canyonlands National Park in Southeastern Utah, geochemical variation in geologic substrates is related to the depositional environment with higher concentrations of Fe, Al, P, K, and Mg in sediments deposited in alluvial or marine environments and lower concentrations in bedrock derived from eolian sand dunes. Availability of soil nutrients to vegetation is also controlled by the formation of secondary minerals, particularly for P and Ca availability, which, in some geologic settings, appears closely related to variation of CaCO3 and Ca-phosphates in soils. However, the results of this study also indicate that P content is related to bedrock and soil Fe and Al content suggesting that the deposition history of the bedrock and the presence of P-bearing Fe and Al minerals, is important to contemporary P cycling in this region. The relation between bedrock type and exchangeable Mg and K is less clear-cut, despite large variation in bedrock concentrations of these elements. We examined soil nutrient concentrations and foliar nutrient concentration of grasses, shrubs, conifers, and forbs in four geochemically distinct field sites. All four of the functional plant groups had similar proportional responses to variation in soil nutrient availability despite large absolute differences in foliar nutrient concentrations and stoichiometry across species. Foliar P concentration (normalized to N) in particular showed relatively small variation across different geochemical settings despite large variation in soil P availability in these study sites. The limited foliar variation in bedrock-derived nutrients suggests that the dominant plant species in this dryland setting have a remarkably strong capacity to maintain foliar chemistry ratios despite large underlying differences in soil nutrient availability.

Recruitment and growth decline in Pinus halepensis populations after recurrent wildfires in Catalonia (NE Iberian Peninsula)

Despite many Mediterranean species show efficient mechanisms to withstand fires, they are currently submitted to fire regimes characterized by anthropogenically increased levels of fire recurrence, which may overpass their recovery capacity. We studied fire recurrence effects on Pinus halepensis populations at a regional level in Catalonia (NE Iberian Peninsula), by comparing post-fire populations in paired areas once-burnt (1994) and twice-burnt (once from 1978 to 1991, and again in 1994). Survey was conducted 10 years after fire in 14 study sites: density, height, and diameter were recorded, and dendrochronological analyses were conducted to deal with time of recruitment and radial growth. In both types of areas, post-fire recruitment took place mainly just after the summer fire, in 1994 (87% of individuals), and also in 1995 (12%). Density was significantly lower in twice-burnt areas than in once-burnt ones, which is attributed to fire intervals shorter than 15 years, the minimum time-length required by P. halepensis populations to recover pre-fire density levels. Height and diameter records evidenced a growth decline in twice-burnt areas. Dendrochronological analyses revealed that radial pine growth was lower in twice-burnt areas along the first post-fire years (from 1994 to 1999), thus resulting in lower total radial growth than in once-burnt areas. Such radial growth differences are attributed to differences in soil nutrient availability along the first post-fire years (post-fire nutrient boom), resulting from differences in pre-fire fuel loads between once- and twice-burnt areas. According to our results, drastic changes in P. halepensis forests in the western Mediterranean Basin are likely to be expected under fire regimes characterized by high levels of fire recurrence.

Acclimation of shoot and needle morphology and photosynthesis of two Picea species to differences in soil nutrient availability.

To investigate morphological acclimation to differences in nutrient availability, we compared shoot and needle morphology of Picea glehnii (Friedr. Schmidt) M. T. Mast. and Picea jezoensis (Siebold & Zucc.) Carrière trees growing on nutrient-poor volcanic ash and nutrient-rich, brown forest soil. Trees of both species were shorter and had more open canopies when growing on volcanic ash than when growing on brown forest soil. Nutrient-poor conditions limited height growth less in P. glehnii than in P. jezoensis. In both species, trees growing on volcanic ash had shorter annual increments in the previous year and more needles per shoot length and, hence, a smaller shoot silhouette area (SSA) relative to needle dry mass (NDM) than trees growing on brown forest soil. Soil type had less effect on shoot projected needle area (PNA). Total needle area (TNA) of P. glehnii shoots was similar between soil types, whereas TNA of P. jezoensis was lower in trees growing on volcanic ash than in trees growing on brown forest soil. For both species, low SSA in response to nutrient-poor conditions resulted in low shoot SSA/PNA ratios, indicating high within-shoot self-shading. Shoot SSA/TNA of P. glehnii was lower in trees growing on volcanic ash than in trees growing on brown forest soil, indicating that needles were sun-acclimated. In contrast, shoot SSA/TNA of P. jezoensis was higher in trees growing on volcanic ash than in trees growing on brown forest soil. The contrasting response of TNA to low nutrient availability was associated with species-specific differences in needle morphology. Needles of P. glehnii growing on volcanic ash were slightly shorter, wider, thicker and heavier than those of trees growing on brown forest soil, indicating morphological acclimation to high irradiance. Needles of P. jezoensis growing on volcanic ash were shorter than those of trees growing on brown forest soil, but did not show morphological acclimation to high irradiance in width, thickness or mass. For both species, nutrient-poor conditions decreased maximum photosynthetic rate (Amax) per NDM. However, when expressed per PNA, the decrease in Amax was reduced, and when expressed per SSA, Amax was higher in trees growing on volcanic ash than in trees growing on brown forest soil. On volcanic ash, Amax per NDM was lower for P. glehnii than for P. jezoensis. However, morphological changes at the shoot and needle levels reversed this trend when Amax was expressed per SSA or per PNA. The species-specific differences in morphological response to differences in soil nutrient availability suggest that P. glehnii is more tolerant of nutrient-poor conditions, whereas P. jezoensis is better at exploiting nutrient-rich soils.

Foliar and soil nutrients in tundra on glacial landscapes of contrasting ages in northern Alaska.

We compared foliar and soil nutrients in tundra between two different landscapes in the foothills of the Brooks Range, Alaska, that were deglaciated >50,000 and >11,500years ago, respectively. Our goal was to determine whether foliar nutrients reflect differences in soil nutrient availability, or whether species and/or growth forms have characteristic foliar nutrient concentrations regardless of soil nutrient availability. Sites are located less than 2km from one another, and both are dominated by moist tussock tundra. However, forbs are less common and deciduous and evergreen shrubs more common at the older site. Soils at the older site had higher net nitrogen (N) mineralization rates, but lower pH, cation exchange capacity, percent base saturation, exchangeable calcium (Ca) and magnesium, total Ca, and inorganic N and phosphorus than the younger site. Foliar nutrients generally reflected differences in soil net N mineralization rates and exchangeable base cations, with higher foliar N at the older site, and higher foliar Ca at the younger site. However, large differences in foliar nutrients also occurred among growth forms, and the magnitude of the site differences in foliar nutrients between sites was growth form-dependent. In general, species with short leaf lifespans (deciduous shrubs, sedges, and forbs) had higher foliar nutrient concentrations than evergreen species. Thus, foliar nutrients were a function both of underlying variation in soil nutrient availability and of species and growth form composition.

Mechanisms inhibiting the forest development of historic charcoal hearths in southeastern Pennsylvania

Charcoal production associated with the iron industry had a pervasive influence on forests during the 17th and 18th centuries in the mid-Atlantic region of the eastern United States. In a recent study we reported the altered forest composition and soil properties on historic charcoal hearths in southeastern Pennsylvania. In this study, additional experimental results describe potential past and present mechanisms that may inhibit forest development. Nyssasylvatica Marsh, wood samples taken from the first 15 years of growth on hearth sites contained roughly half the amount of P and Mn and nearly double the amount of K and Na relative to wood produced on nonhearth sites in the same period, consistent with initial pH elevation following hearth abandonment in 1883. In the greenhouse, Quercusalba L. and Quercusrubra L. showed a significant growth depression in hearth soil. When the proportion of charcoal soil varied from 0 to 100%, several growth parameters of Q. rubra declined significantly with increasing charcoal soil content. In situ foliar nutrient concentrations of Vacciniumcorymbosum L. and Quercusvelutina Lam. were significantly different in P, K, Ca, Mg, Mn, Fe, Na, and Cu on hearth versus nonhearth plots. The present inhibition of hearth regeneration appears to be the result of persistent differences in soil nutrient availability after more than a century.

Nutrient status of Thymelaea hirsuta (L.) Endl. in Egypt

The nutrient status of Thymelaea hirsuta, an evergreen desert shrub, was evaluated in six different habitats in the western Mediterranean region of Egypt. It has a relatively low nutrient content compared with many of the Egyptian desert plants. The general trend in the tissue concentration of most nutrients was leaf > stem > root. Estimates of the nutrients in spring is significantly higher than those during summer. This was related to differences in soil nutrient availability and/or differing season requirements. Soil salinity and the amount of exposed rocks seem to be the most important factors that affect both the phytomass and mineral content of the plant. The correlations among the estimated nutrients in its leaves are presented and explained.

Effect of Fire on Growth and Allocation Strategies of Mikania micrantha Under Early Successional Environments

(1) The effect of fire on growth and allocation of biomass and nutrients in Mikania micrantha, an early successional exotic weed, was studied in seral communities developed after slash-and-burn agriculture (jhum) in north-eastern India. (2) In successional fallows, plant vigour was stable in burnt plots, but declined with age in unburnt plots. Biomass and nutrient allocation to seeds was higher in burnt than unburnt 8-year old plots. (3) Nutrient uptake efficiency was higher after burning and increased with age, but decreased with age in unburnt fallows, probably reflecting differences in soil nutrient availability and competition. (4) Nutrient-use efficiency was inversely related to uptake efficiency and may be a compensatory mechanism for survival. (5) It is concluded that M. micrantha is adapted to survival after fire.