Plant Nutrient Dynamics Research Articles

Relationship between plant nitrogen and phosphorus accumulations in a canola crop as affected by nitrogen management under ample phosphorus supply conditions

The understanding of plant nutrient uptake and dynamics is a necessary step to develop site-specific, economically viable, and environmentally responsible management practices. A field study on canola (Brassica napus L.), treated with preplant and sidedress nitrogen (N) applications under ample phosphorus (P) supply conditions, was conducted to determine seasonal plant dry matter (DM) and N and P uptake patterns. We found that periodic DM measured at 20% flowering (FL), from FL to 50% pods reaching maximum size (FL-RI), and from RI to physiological maturity (RI-PM) contributed to 30%, 57%, and 14% of total DM, respectively. Yields ranged from 111 to 447 g m−2 with a sharp decline in 2012 induced by heat and drought. The crop took up about 58%–71% of total plant N by FL, whereas up to 42% of total plant P was assembled during the RI-PM. Canola seed accounted for 60%–66% of total plant N and 59%–63% of total plant P. Accumulation of DM and N post-FL, and of P during RI-PM could explain 69%, 43%, and 55%, respectively, variations in yield, seed N, and seed P. Our data indicated that plant P uptake under adequate P supply conditions in canola was largely enhanced by N application.

The effect of pre‐industrial charcoal kilns on chemical properties of forest soil of Wallonia, Belgium

SummaryIn Wallonia, Belgium, intensive in situ charcoal production that was linked closely to pre‐industrial smelting and steel‐making affected a large part of the forested area in the late eighteenth century. Charcoal kiln relics can be detected under forest as domes of about 10 m in diameter, with the topsoil greatly enriched with charcoal residues. We sampled 19 charcoal kiln sites and the adjacent reference soil by soil horizon on four different soil types (Arenosols, Luvisols, Cambisols and Podzols). Data were analysed with linear mixed models to assess the effect of the charcoal kiln site on soil properties in relation to depth and soil conditions. We also addressed the evolution of soil properties over time by a comparison of the soil characteristics at a currently active kiln site. The charcoal‐rich topsoil has a larger C:N ratio and cation exchange capacity (CEC) per unit of organic carbon than the reference soil. The largest CECs per unit of carbon were observed on soil with coarser textures. On acidic soil, the increase in base saturation in the subsoil reflects the past liming effect of ash produced by wood charring, whereas the topsoil is re‐acidified. The acidity of carbonate‐rich Cambisols, however, is not reduced. Regardless of soil type, the kiln topsoil is greatly depleted in exchangeable K+ and available P, which may be attributed to the small affinity of the exchange complex of charcoal for K+ and a decrease in P availability with time. Therefore, we recommend further research on the long‐term effects of biochar on the dynamics of plant nutrients.

Herbivory and N2-fixation drive plant and soil nutrient dynamics in a southern African savanna

Herbivory and N2-fixation drive plant and soil nutrient dynamics in a southern African savanna

Cyanobacterial inoculation in rice grown under flooded and SRI modes of cultivation elicits differential effects on plant growth and nutrient dynamics

The influence of microbial inoculants on rice plants grown under two different cultivation methods – conventional (flooded) and SRI (system of rice intensification) – was evaluated in terms of nutrients’ availability in soil and their uptake by plants in a field experiment undertaken at the Indian Agricultural Research Institute, New Delhi. The treatments under conventional management recorded significantly higher values of nitrogen fixation in the soil, with Rhizobium sp. recording the highest values, although the populations of nitrogen fixers, phosphate solubilizers and cyanobacteria exhibited a 10-fold enhancement in the plots under SRI. Methane production was 50–80% lower in SRI plots inoculated with cyanobacterial-biofilmed formulations (T8–T9) and in the plots receiving recommended dose of fertilizers. The novel Anabaena-based biofilmed inoculants – T9 Anabaena–Trichoderma biofilm and T8 Anabaena–Pseudomonas biofilm, were particularly superior under both methods of cultivation ranking highest for microbiological and plant biometric parameters. The availability of P in the soil and its translocation through roots to leaves was significantly increased as a result of cyanobacterial inoculation under both modes of cultivation. The N and P content of grains were significantly higher in most of the microbial treatments in SRI mode. The treatments T5 (BF 1–4; Anabaena–Nostoc consortium), T10 (Trichoderma) and T9 (Anabaena–Trichoderma biofilm) under conventional methods recorded the highest values of grain and straw yield, which were statistically at par with those of plots with recommended dose of fertilizers. This study illustrated the benefits of both types of rice cultivation methods and the promise of cyanobacteria in improving nutrient availability, soil fertility, and crop productivity with a savings of 60kgNha−1season−1.

The hidden Serengeti—Mycorrhizal fungi respond to environmental gradients

Abstract Mycorrhizas influence plant productivity, community composition, nutrient dynamics and soil structure, yet the factors determining the abundance and diversity of these symbioses in natural ecosystems are poorly understood. We studied arbuscular mycorrhizal (AM) fungi (Glomeromycota) in long-term grazed and un-grazed plots at eight sites forming natural gradients of soil properties and rainfall in the Serengeti National Park, Tanzania. Four metrics of AM fungal abundance and diversity were examined: (1) abundance and species composition of spores, (2) standing crop of AM hyphae in the soil, (3) production of new AM hyphae in buried mesh bags and (4) a bioassay of AM fungal inoculum potential. Our first goal was to test the predictions of the Functional Equilibrium Model that AM fungi should be most abundant in grazed plots (because of increased nutrient demands caused by overcompensation) and at sites with the lowest soil phosphorus (P) and rainfall. Our second goal was to use multi-group structural equation models (SEMs) to investigate the interrelated influences of grazing, soil properties, rainfall and root biomass on the abundance and species composition of AM fungal communities. Two multi-group SEMs were generated: one to examine abundance patterns of AM fungi and another to examine patterns in the spores or auxiliary cells of different families of AM fungi. We observed an extremely high abundance and diversity of AM fungal spores. Only one prediction of the Functional Equilibrium Model was supported; production of new hyphae was highest in the lowest P soils. The abundance and species composition of AM fungi varied across sites but the only variable that responded to grazing was the abundance of Glomeraceae spores, with higher abundance in fenced (un-grazed) plots. Multi-group SEMs revealed that rainfall, total soil P, soil organic matter and soil texture were all important predictors, but the relative importance of each factor varied depending upon the AM metric or taxon observed. Our findings suggest niche differentiation among AM fungal taxa and demonstrate that climate and soil properties are important predictors of the abundance and community composition of these important, hidden components in the Serengeti ecosystem.

Dynamics of key plant nutrients (N & P) in hokersar, a typical wetland of Kashmir Himalaya, India

Hokersar wetland suffers highly due by nutrient inputs from the catchment area, internal wetland processes and various types of anthropogenic pressures around. To characterize nutrient dynamics of the wetland, nitrogen (N) and phosphorus (P) samples were collected from six study sites in the Queen wetland of Kashmir Himalaya for a period of one year from Sep. 2012 to Aug. 2013. Clear spatial and temporal variations were observed among the recorded parameters (ammonical nitrogen, nitrate nitrogen, total orthophosphate phosphorus and total phosphorus) throughout the year. Ammonical nitrogen concentration was found to be maximum in winter (242.3±10.1 µg/L). Lower nitrate nitrogen was observed in summer, recording 259.6±35.3 µg/L. Both the forms of phosphorus registered higher values in summer and lower values in winter. Scatter plot showed highly significant values among all the parameters (R²=0.748 and 0.719). Principal component analysis showed highest principle component vector displacement among the sites IV and VI reflecting polluted nature of the sites. Further, higher Eigen-vector displacement values were due to ammonical nitrogen and nitrate nitrogen, registering values 3.36724 and 0.542639 respectively. Similarity matrix was highest between total phosphorus and ammonical nitrogen (92.9666%), followed by ammonical nitrogen and nitrate nitrogen making 58.5729%.

Earthworm Communities in Previously Glaciated and Unglaciated Eastern Deciduous Forests

Native earthworms were removed from forested ecosystems during the last glacial advance and have since been replaced with nonnative earthworm species. Nonnative earthworms can cause major changes in microbial and plant communities and nutrient cycling. In this study, we sought to compare the earthworm communities north and south of the last glacial terminus, and to examine correlations between plant communities and soil characteristics. In summer 2011, we measured the earthworm, herbaceous plant, and woody plant communities in 3 forests in southwestern Ohio and 3 forests in northern Kentucky. We also measured soil characteristics including moisture, pH, organic matter, and nitrate and ammonium content. We found no native earthworm species at any of our study sites; however, previously glaciated forests exhibited more diverse earthworm communities and included all ecological groups. Earthworm species richness increased with increased density of invasive woody plant species and decreased with increased soil ammonium. Scientists and managers should continue to survey the earthworm communities in forests to better understand the ranges of nonnative earthworms and the impacts they have on plant communities and nutrient dynamics.

Biotic interactions in the rhizosphere in relation to plant and soil nutrient dynamics

The rhizosphere is the interface between roots and the soil where nutrient absorption for plant growth in agroecosystems is facilitated. An abundant and diverse rhizosphere biome is involved in biogeochemical processes, including bacteria, fungi and soil fauna, driving soil C, N and P dynamics. Plant carbon photosynthates allocated to the root and rhizosphere are priming microbial activities important for plant nutrition such as organic matter decomposition, P solubilization, N fixation, mycorrhizal nutrient transport and biocontrol of root pests. While substantial information is available on the role of individual groups of the rhizosphere microbiome in biogeochemical processes, less attention has been given to the interactions between different beneficial rhizosphere microorganisms. Also, interactions between soil fauna and rhizosphere microorganisms still remain relatively unexplored. In order to improve our knowledge on the role of the rhizosphere in C, N and P biogeochemical processes a more holistic and functional approach is required. In this review, state of the art information on the role of biotic interactions in the rhizosphere on C, N and P biogeochemical processes relevant for plant nutrition in agroecosystems is presented.

Long-term effect of pulse crops inclusion on soil–plant nutrient dynamics in puddled rice (Oryza sativa L.)-wheat (Triticum aestivum L.) cropping system on an Inceptisol of Indo-Gangetic plain zone of India

Given inherent qualities like N-fixation, P-solublization and nutrient recycling pulses remain the most preferred option for diversification of cereal-based rotations. A long-term experiment was used to assess the effect of including pulses in rice–wheat rotation on soil–plant nutrient dynamics under inorganic and organic nutrient management. Results revealed that pulses were equally responsive to organic and inorganic nutrient management while, growth of cereals especially wheat was restricted severely under organic production system due to low nutrient input. The annual input (kg ha−1) of N (103.6–160.8) and P (25.9–34.7) under organic treatment was almost ½ of the recommended inorganic rate, while organics supplied higher K and S. Under organic management, the apparent balance of all the nutrients was negative whereas, inorganic fertilization resulted in positive balance of N, P and Zn. Long-term inclusion of pulses in rice–wheat rotation significantly increased soil organic C and available nutrients thus, increased the nutrient uptake by cereals. Mungbean inclusion in rice–wheat rotation significantly (P ≤ 0.05) increased uptake of N (23.0 %), P (32.9 %) and K (21.1 %) by rice crop. Continuous inorganic fertilization enriched soil available N, P, Zn and B. While organic management maintained higher SOC, available K and S over inorganic treatment. Thus, the study suggested that under organic management N and P nutrition is limiting factor for cereals and needs inorganic supplementation. The study also indicates the need for including pulses in conventional rice–wheat system for optimum nutrient acquisition and long-term soil health management.

Seasonal and clonal variations of microbial biomass and processes in the rhizosphere of poplar plantations

Plant nutrient acquisition and dynamics are closely coupled with microbial activities and rhizosphere processes. This study was conducted using an in situ rhizobox approach and incubation experiments, with the primary goal to elucidate rhizosphere effects of different poplar clones at different sampling seasons on soil microbial processes and biomass content. Evaluations included pH, inorganic N (NO3−-N and NH4+-N), microbial biomass carbon (MBC) and nitrogen (MBN), enzyme activities related to N cycling, as well as net N mineralization and nitrification rates in rhizosphere soils of three poplar clones (Nanlin-895, NL-80351 and 75) at three periods of the year. The magnitude of rhizosphere effects varied with time and poplar genotypes. Significant variations in microbial biomass content and enzyme activities were observed among the tested three poplar clones; and microbial biomass content was positively correlated with soil NO3−-N concentration. The obtained results suggested that genotypes (clones or cultivars) had profound impacts on the rhizosphere microbial communities; and NO3−-N concentration rather than total inorganic N was the primary determinant of seasonal dynamics of microbial biomass and processes in the rhizosphere soils of poplar trees in a seasonally flooded soil.

Responses of nutrient dynamics in barley seedlings to the interaction of salinity and carbon dioxide enrichment

The effects of elevated CO2 on the content of several nutrients in plants have been well studied, but few studies have investigated plant nutrient dynamics under future environmental conditions, which are expected to include elevated CO2 and elevated soil salt concentrations. This study investigated whether high salt and CO2 conditions, singly or in combination, might affect nutrient dynamics, and the underlying mechanisms. We measured macro- and micronutrient uptake and translocation rates, nutrient content and concentrations in whole seedlings and in each plant organ. We estimated whole-plant nutrient use efficiencies in barley subjected to 0, 80, 160, or 240mM NaCl and grown at either 350 (ambient) or 700 (elevated) μmolmol−1 CO2. Under non-saline conditions, plants grown at elevated CO2 adjusted their root size and activity to change nutrient uptake and transport efficiency in response to the demand for a given nutrient. Under high saline conditions, salt stress reduced K, Ca, N, B, and S uptake rates and concentrations in tissues, which caused growth reduction. Nevertheless, barley had the ability to increase the selectivity of K over Na, and Ca over Na. Under combined conditions of salt stress and elevated CO2, barley seedlings were able to maintain higher uptake and translocation rates of almost all nutrients. This ability allowed the plants to adapt to higher demands under elevated CO2; they could grow more rapidly by allocating more C to root growth and by increasing active nutrient uptake and translocation. Our results indicated that salinity generally increased nutrient use efficiency under both CO2 conditions. However, we found no consistent evidence that nutrient use efficiency was affected by CO2 concentration, either under non-saline or saline conditions.

Selecting a nitrogen availability index for understanding plant nutrient dynamics in rehabilitated bauxite-processing residue sand

Understanding nutrient dynamics in non-typical soil materials such as bauxite-processing residue sand (pH>10; EC>30dSm−1) is critical for developing fertilizer strategies and evaluating ecological restoration performance. Indices relating nitrogen (N) concentration in soil to plant N uptake are well-established for natural soils but their application to non-typical soils has received little attention. This study investigated a range of soil-based methods [i.e. 2M KCl extractable inorganic N (NH4+, NO3−), potentially mineralizable nitrogen (PMN), and 0.01M CaCl2 extractable N] to identify their suitability for describing soil–plant N relations in highly alkaline bauxite-processing residue sand. Nitrogen availability indices were measured under laboratory (pot trial) and field conditions. Pot trial was established using residue sand that had been amended (10%, v/v, basis) with various organic (greenwaste compost, biochar and biosolids) and inorganic (zeolite) materials. Both the field study and pot trial showed that 2M KCl extractable NO3−-N was most highly correlated with plant biomass N compared with the other N availability indices. Findings from this study suggest that 2M KCl extractable NO3−-N can be used as a soil quality indicator in developing fertilizer management strategies and assessing ecological status of the residue storage areas.

Latitudinal Patterns of Herbivory in Mangrove Forests: Consequences of Nutrient Over-Enrichment

Ecosystems in the tropics are predicted to have stronger responses to nutrient enrichment, greater diversity, and more intense biotic interactions than in temperate areas. Mangrove forests, which occur across a broad biogeographic range from warm temperate to tropical, provide a unique opportunity to test these hypotheses by investigating the responses of herbivores to nutrient enrichment in temperate versus tropical latitudes. Mangroves are complex intertidal ecosystems with spatial differences in structure and diversity along tidal gradients and are threatened globally by human activities including nutrient over-enrichment. In this study, we used long-term fertilization experiments at the Indian River Lagoon, FL; Twin Cays, Belize; and Bocas del Toro, Panama to determine how increased nutrients impact herbivore abundance and herbivory of Rhizophora mangle at the tree, forest, and regional scales. At these locations, which span approximately 2185 km and 18.4o of latitude, we fertilized individual trees with one of three treatments (Control, +N, +P) in two zones (fringe, scrub) along transects perpendicular to the shoreline and measured their responses for 4 years. Herbivory was measured as folivory, loss of yield, and tissue mining. Although nutrient enrichment altered plant growth, leaf traits, and nutrient dynamics, these variables had little effect on folivory at any location. Our results did not support the prediction that herbivory and per capita consumption are greatest at the most tropical location. Instead, folivory was highest at the most temperate location and lowest at the intermediate location. Folivory was generally higher in the fringe than in the scrub zone, but the pattern varied by location, herbivore, and nutrient treatment. Folivory by a dominant herbivore, Aratus pisonii, decreased from the highest to the lowest latitude. Our data suggest that factors controlling population dynamics of A. pisonii cascade to the mangrove canopy, linking herbivory to crab densities.

An invasive tree fern alters soil and plant nutrient dynamics in Hawaii

Invasive species that alter ecosystems are often successful competitors due to their effects on nutrient cycling. Sphaeropteris cooperi (Cyatheaceae; Australian tree fern) has been invading intact Hawaiian rainforests for decades and displacing the dominant native tree fern Cibotium glaucum (Cibotiaceae). S. cooperi produces more leaves that grow faster, contain more N and P, and decompose faster than C. glaucum leaves. Our experiment tested the effects of additions of leaf litter from native and non-native tree ferns on the growth and nutrient content of four native angiosperm species in forest (N-rich) and landslide (P-rich) soils. Both litter treatments inhibited growth initially in all species, but subsequent responses were species-specific. Compared to control treatments, the increase in biomass was highest in the fast-growing Carex wahuensis and Hibiscus arnottianus with S. cooperi litter in landslide soil. Leaf N in C. wahuensis was higher with S. cooperi litter and in forest soil, as expected, but other leaf nutrient responses showed some evidence of nutrient immobilization from litter addition. Several growth measures were higher with S. cooperi than C. glaucum litter and in forest than landslide soil, suggesting that N availability is the strongest driver of growth. Our results show that S. cooperi can alter nutrient cycling in Hawaiian plants, sometimes with positive effects on growth. However, under natural conditions, native plants must compete for these additional nutrients with S. cooperi and other invasive species. This study contributes to invasion biology as the first to examine the impact of leaf litter of an invasive fern on native species.

Forest fragment size and nutrient availability: complex responses of mycorrhizal fungi in native–exotic hosts

In the past few decades, it has been widely accepted that forest loss due to human actions alter the interactions between organisms. We studied the relationship between forest fragment size and arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE) colonization, and the AMF spore communities in the rhizosphere of two congeneric Euphorbia species (native and exotic/invasive). We hypothesized that these fungal variables will differ with fragment size and species status, and predicted that (a) AMF and DSE colonization together with AMF spore abundance and diversity would be positively related to forest fragment size; (b) these relationships will differ between the exotic and the native species; and (c) there will be a negative relationship between forest fragment size and the availability of soil nutrients (NH4+, NO3−, and phosphorus). This study was performed in the eight randomly selected forest fragments (0.86–1000 ha), immersed in an agricultural matrix from the Chaquean region in central Argentina. AMF root colonization in the native and exotic species was similar, and was positively related with forest fragment size. Likewise, AMF spore diversity and spore abundance were higher in the larger fragments. While DSE root colonization in the native host was positively related with forest fragment size, DSE colonization in the exotic host showed no relationship. Soil nutrients contents were negatively related with forest fragment size. In addition, NH4+ and NO3− were negatively correlated with AMF spores abundance and root colonization and with DSE colonization in the native species. The results observed in this study show how habitat fragmentation might affect the interaction between key soil components, such as rhizospheric plant-fungal symbiosis and nutrient availability. These environmental changes may have important consequences on plant community composition and nutrient dynamics in this fragmented landscape.

The effect of hydraulic lift on organic matter decomposition, soil nitrogen cycling, and nitrogen acquisition by a grass species

Hydraulic lift (HL) is the passive movement of water through plant roots, driven by gradients in water potential. The greater soil-water availability resulting from HL may in principle lead to higher plant nutrient uptake, but the evidence for this hypothesis is not universally supported by current experiments. We grew a grass species common in North America in two-layer pots with three treatments: (1) the lower layer watered, the upper one unwatered (HL), (2) both layers watered (W), and (3) the lower layer watered, the upper one unwatered, but with continuous light 24 h a day to limit HL (no-HL). We inserted ingrowth cores filled with enriched-nitrogen organic matter ((15)N-OM) in the upper layer and tested whether decomposition, mineralization and uptake of (15)N were higher in plants performing HL than in plants without HL. Soils in the upper layer were significantly wetter in the HL treatment than in the no-HL treatment. Decomposition rates were similar in the W and HL treatments and lower in no-HL. On average, the concentration of NH(4)(+)-N in ingrowth cores was highest in the W treatment, and NO(3)(-)-N concentrations were highest in the no-HL treatment, with HL having intermediate values for both, suggesting differential mineralization of organic N among treatments. Aboveground biomass, leaf (15)N contents and the (15)N uptake in aboveground tissues were higher in W and HL than in no-HL, indicating higher nutrient uptake and improved N status of plants performing HL. However, there were no differences in total root nitrogen content or (15)N uptake by roots, indicating that HL affected plant allocation of acquired N to photosynthetic tissues. Our evidence for the role of HL in organic matter decomposition and nutrient cycling suggests that HL could have positive effects on plant nutrient dynamics and nutrient turnover.

The role of lysimeters in the development of our understanding of soil water and nutrient dynamics in ecosystems

AbstractThis paper considers the development of lysimeters and their role in the evolution of our understanding of the dynamics of water and plant nutrients in ecosystems. Lysimeters are delineated volumes of soil. They can be divided into those filled with repacked soil, and those enclosing an undisturbed monolith. The original repacked lysimeter was developed to investigate the concept that all life stems from water, and is considered to be the first quantitative experiment in history. It focussed on the growth of a willow tree and how much of the increment was derived from the soil solids. From this start some 360 years ago lysimeters quickly contributed to the quantification of the transpiration stream and the differentiation of water loss by evaporation from the soil from loss via the leaves of plants. Chronologically, further development began about 210 years ago with the exploration of whether precipitation could account for all the water moving from the land to the oceans, and was the origin of springs. In part, this required a careful quantification of soil evaporation, runoff and deep drainage. This in turn led to the quantification of the soil water balance. As a result, we are able to predict indices, such as crop water use efficiency, drainage and irrigation requirements, contributions to stream flow, groundwater recharge and nutrient loss by leaching. Recognition that the quantification of drainage and leaching required soils of natural structure and profile integrity resulted in the building of the first monolith lysimeter and the development of ‘pan’ or ‘Ebermayer’ lysimeters. Improved technology allowed a better understanding of the role of soil in the regional water balance through the development of small diameter lysimeters that could be transported to a central location subject to the same climatic variables. In contrast, other technological changes allowed the impact of typical soil management operations carried out using regular machinery to be applied on field‐scale lysimeters. The contribution of the different types of lysimeter to the development of our understanding of soil use and management is considered.

Controls of primary productivity and nutrient cycling in a temperate grassland with year‐round production

Abstract Net primary production (NPP) and nutrient dynamics of grasslands are regulated by different biotic and abiotic factors, which may differentially affect functional plant groups. Most studies have dealt with grasslands that have extremely low or zero production over a significant period of the year. Here we explore the relative importance of a few environmental factors as controls of aerial and below‐ground plant biomass production and nutrient dynamics in a grassland that is active throughout the year. We investigate their effect on the response of three main plant functional groups (warm‐ and cool‐season graminoids and forbs). We conducted a factorial experiment in a continuously grazed site in the Flooding Pampa grassland (Argentina). Factors were seasons (summer, autumn, winter and spring), and environmental agents (mowing, shade, addition of phosphorus [P] and nitrogen [N]). N addition had the largest and most extended impact: it tripled aerial NPP in spring and summer but had no effect on below‐ground biomass. This positive effect was accompanied by higher N acquisition and higher soil N availability. Mowing increased aerial NPP in winter, increased root biomass in the first 10 cm during autumn and winter and promoted N and P uptake by plants. Shading did not affect aerial NPP, but stimulated N and P uptake by plants. P addition had no effect on aerial NPP, but increased shallow root biomass and its N content in spring, and tripled P accumulation in plant biomass. The three plant functional groups differentially accounted for these ecosystem‐level responses. Graminoids explained the greater biomass production of N‐fertilized plots and mowing tended to promote forbs. These results suggest that the environmental controls of aerial NPP in this grassland vary among seasons, differentially impact the major floristic groups, and affect the energy and nutrient transfer to herbivores.

Impact of land clearing methods and cropping systems on labile soil C and N pools in the humid zone Forest of Nigeria

Abstract Labile soil C and N play vital roles in soil–plant nutrient dynamics, especially in the low input cropping system and are vulnerable to perturbation. Surface (0–0.15 m) soils from three land clearing methods (slash and burn, bulldozed non-windrowed and bulldozed windrowed) and each with two cropping systems (5-and 4-year cropping/2-year cassava fallow) were collected in the humid forest ecosystem of Nigeria. The soils were analysed for total C and N, microbial biomass C and N (SMB C and N), particulate organic matter C and N (POM C and N), water-soluble C, potentially mineralizable N (PMN) and mineral N. The size of the labile C and N and their relative contributions to the organic C and total N differed significantly among land clearing methods, irrespective of the cropping system. Soils under slash and burn had a significantly ( p > 0.05) higher particulate organic matter C, N (10.80 and 0.16 g kg −1 , respectively) and microbial biomass C and N (1.07 and 0.12 g kg −1 ) compared to the bulldozed windrow, regardless of the cropping system. Four years cropping/2-year cassava fallow resulted in a significant higher labile C and N, relative to 5-year cropped plots across the land clearing methods. Effect of the treatments on the concentration of PMN and mineral N mirrored the SMB N and POM N. However, the quantity of most of the labile C and N pool and crop yield obtained from the slash and burn and bulldozed non-windrowed treatment did not differ significantly. Hence, bulldozed non-windrowed clearing could be a viable alternative to slash and burn in the case of large-scale farming in ensuring reduced losses of soil organic matter and nutrient during land clearing in the humid tropics.

Nutrient dynamics of reindeer forage species along snowmelt gradients at different ecological scales

Growing season nutrient dynamics of four reindeer forage species (Betula nana, Eriophorum angustifolium, Rumex acetosa and Vaccinium myrtillus) were studied in a mountainous sub-arctic landscape in N Sweden. Changes in nitrogen (N), phosphorus (P) and fibre (ADF) concentrations in leaves and shoots were analysed (from a reindeer foraging perspective) along four ecological gradients significant to regional and local snowmelt regimes: season, oceanicity, altitude, and snow-patch retreat. N and P concentrations showed marked seasonal variations with peaks occurring from the middle of June to the end of July depending on species and snowmelt progression. The seasonal pattern for ADF concentrations, as well as differences between snowmelt regimes, were less consistent and showed large differences between species. N concentrations increased along snowmelt gradients at small (within snow-patches) and medium (along altitude gradients) spatial scales. Furthermore, variations in N concentrations were temporally and spatially scale-dependent, which underlines the importance of scale for understanding plant nutrient dynamics in sub-arctic and alpine systems, as well for plant–animal interactions. The greatest temporal and spatial differences in nutrient quality were observed early in the season, i.e., at the time of highest nutrient requirements for reindeer. Climate-induced changes of the start and the progress of the growing season may result in significant consequences to the development of calves and subsequently to the population demography of reindeer, mediated through spatial and temporal changes in the distribution of high quality food. These results provide basic knowledge for reindeer management in the light of the ongoing global warming. Die Nährstoffdynamiken in der Wachstumsperiode wurden bei vier Arten von Rentierfutterpflanzen (Betula nana, Eriophorum angustifolium, Rumex acetosa, Vaccinium myrtillus) in einer bergigen subarktischen Landschaft N-Schwedens untersucht. Die Veränderungen der Konzentrationen von Stickstoff (N), Phosphor (P) und Fasern (ADF) in den Blättern und Trieben wurden entlang von vier ökologischen Gradienten analysiert, die für regionale und lokale Schneeschmelzeregimes bezeichnend sind: Jahreszeit, Ozeanität, Höhe und Schneefleckenrefugien. Die N- und P-Konzentrationen zeigten deutliche saisonale Variationen mit Spitzen, die zwischen Mitte Juni und Ende Juli auftraten, abhängig von Art und Fortschritt der Schneeschmelze. Das saisonale Muster der ADF-Konzentrationen sowie die Unterschiede zwischen den Schneeschmelzeregimes waren weniger konsistent und zeigten große Unterschiede zwischen den Arten. Die N-Konzentrationen stiegen entlang von Schneeschmelzegradienten auf kleinen (innerhalb von Schneeflecken) und mittleren (entlang von Höhengradienten) räumlichen Skalen an. Darüber hinaus waren die Variationen in den N-Konzentrationen zeitlich und räumlich skalenabhängig. Dies unterstreicht die Wichtigkeit der Skala für das Verständnis der Dynamiken von Pflanzennährstoffen in subarktischen und alpinen Systemen, sowie der Pflanze-Tier-Interaktionen. Die größten zeitlichen und räumlichen Unterschiede in der Nährstoffqualität wurden früh in der Saison beobachtet, d. h. zur Zeit des höchsten Nährstoffbedarfs der Rentiere. Klimainduzierte Veränderungen des Beginns und Verlaufs der Wachstumssaison können signifikante Konsequenzen für die Entwicklung von Kälbern und infolgedessen für die Populationsdemografie der Rentiere zum Ergebnis haben, vermittelt durch räumliche und zeitliche Veränderungen in der Verbreitung von Futter hoher Qualität. Diese Ergebnisse bilden Basiswissen für das Management von Rentieren in Hinsicht auf die stattfindende globale Erwärmung.