Nutrient Content Of Vegetables Research Articles

Nutrient content of vegetation and soil of four conifer species growing under different site and competing vegetation management conditions

In this study we examined the long-term effects of competing vegetation control on the total nutrient content of different ecosystem components of 19-year-old Douglas-fir (DF), western hemlock (WH), western redcedar (WRC), and grand fir (GF) stands growing in Oregon’s central Coast Range (CR) and of DF and WRC growing in Oregon’s Cascade mountain foothills (CF). Nutrient content responses were evaluated under two contrasting vegetation control treatments, including the Control (no herbicide application post-planting), and VM (5 consecutive years of herbicide application post-planting). Both treatments involved a pre-planting herbicide application. The ecosystem components were divided into overstory (planted crop trees), midstory, understory, forest floor, fine roots, and mineral soil. All samples were analyzed for content (mass per unit ground area) of total carbon, nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, boron, copper, iron, manganese, sodium, and zinc. VM effects on total plant derived nutrient masses were more prominent than differences in concentrations. Ca was the only nutrient for which all species showed higher plant derived masses in the VM condition. Plant derived tissue content of C, Cu, P, and B all tended to be higher in VM plots, with the exception of WRC plots at the CR site. This case was an outlier due to the fact that Control plots developed significantly more biomass as a result of high midstory biomass, whereas the VM plots developed relatively little midstory and crop tree biomass. There were few differences in soil nutrients content between species and treatments, and those that were significant were unable to be explained by differences in uptake by plant species. Notably, total soil N of WRC at the CR site was significantly lower for VM plots. This may indicate the potential for VM applied to a slow growing species, such as WRC, to reduce ecosystem retention of N. With the exception of C and N, total soil nutrient reserves were orders of magnitude greater than total plant derived masses. This indicated that there is low probability of an adverse effect of VM on soil nutrient stores.

Application of organic wastes to subsoil materials can provide sustained soil quality in engineered soil covers for mine tailings rehabilitation: A 7 years study

Improper disposal or poor management practices at mine Tailings Storage Facilities (TSF) can give rise to fugitive emissions with risk to both the surrounding environment. Establishing sustainable vegetation covers (rehabilitation) on TSFs is a critical objective and effective management strategy to mitigate pollution risk. Although direct revegetation is a potential strategy, tailings can exhibit properties such as extreme pH, salinity, elevated metal content, deficiency of nutrients and organic matter that inhibit vegetation establishment and necessitate the provision of a cover soil medium (≥ 30 cm). This requires a high amount of topsoil sourcing, which is often in limited supply at mine sites because of degradation, contamination, or previous removal. Moreover, materials often used as a soil cover for tailings may not favour plant establishment and development due to the poor soil structure and the low level of organic matter and nutrient content.Thus, improvement of substrate physiochemical characteristics by using organic and/or inorganic amendments is needed to promote plant establishment and drive soil processes. While several studies have assessed the feasibility of different plant growth media (soils) they are often based on short-term evaluation in greenhouse and lack the longer term implications of field based studies.Soil cover materials were evaluated using 1 m3 plots at a Pb/Zn TSF. Treatments included tailings, subsoil and subsoil amended with Compost like Output (CLO) and Spent Mushroom Compost (SMC). Following 7 years' revegetation, soil samples were taken at two depths (0–10 cm and 10–20 cm) and pH, salinity (EC), structure, nutrient and metal content were determined. Vegetation nutrient content was determined after 1 yrs. growth (2015) and again at 7 yrs. (2021).Bare tailings and subsoil displayed poor physico-chemical properties, whereas SMC or CLO amendment, improved physical characteristics and nutrient content both in soil and in vegetation, showing that the benefits of organic amendment to subsoil materials for rehabilitation are effective in the long-term. Moreover, results showed a higher content of C, N and P in all treatments at the depth 0–10 cm than at 10–20 cm, highlighting the role played by the rhizosphere. While lower vegetation nutrient content was recorded in the in the 2021, in some cases below deficiency criteria, results highlight the need for rehabilitation criteria specific rather than applying standard agronomy guidelines.

Disentangling the effects of phosphorus, nitrogen and species identity on the vegetation reflectance spectrum

AbstractQuestionsEffective and successful restoration of species‐rich semi‐natural grasslands requires knowledge of the soil nutrient status, including soil phosphorus availability. Plants are solid indicators of soil nutrient status, because their growth reflects nutrient availability integrated over a certain period. The use of reflectance spectroscopy to estimate vegetation nutrient content has the potential to offer a fast and efficient approach to provide information about soil nutrient availability for plants. Here, we investigated the effect and relative importance of vegetation phosphorus content compared with vegetation nitrogen content and species identity in explaining variation in vegetation reflectance.LocationPot experiment mimicking Western European grassland communities on a restoration trajectory.MethodsWe combined a pot experiment with a broad range of mesotrophic grassland species growing along a soil phosphorus gradient with a multivariate modelling approach. We measured vegetation spectra and vegetation phosphorus and nitrogen content in monocultures and mixtures.ResultsAlthough vegetation biochemistry explained a considerable part of the variation in vegetation reflectance, we found no pronounced absorption features for vegetation nitrogen and phosphorus content across the reflectance spectrum. The relatively large effect of species and community identity suggest that other drivers, for example vegetation architecture, overruled the effect of vegetation biochemistry on the reflectance spectrum. Our findings indicate that species detection and indirect case‐specific estimation of nutrients is possible, especially in structurally less‐complex canopies such as monospecific grass swards.ConclusionsDisentangling the specific drivers of variation in spectral reflectance is challenging. Many studies confound the effect of species identity on the vegetation reflectance spectrum with the effect of vegetation biochemistry. Here, we showed the importance of explicitly taking species identity into account. Gaining insight into light–vegetation interactions and the in‐depth integration of ecological theory in remote sensing are the way forward.

Retrieval of Nitrogen Content in Apple Canopy Based on Unmanned Aerial Vehicle Hyperspectral Images Using a Modified Correlation Coefficient Method

The accurate retrieval of nitrogen content based on Unmanned Aerial Vehicle (UAV) hyperspectral images is limited due to uncertainties in determining the locations of nitrogen-sensitive wavelengths. This study developed a Modified Correlation Coefficient Method (MCCM) to select wavelengths sensitive to nitrogen content. The Normalized Difference Canopy Shadow Index (NDCSI) was applied to remove the shadows from UAV hyperspectral images, thus yielding the canopy spectral information. The MCCM was then used to screen the bands sensitive to nitrogen content and to construct spectral characteristic parameters. Finally, the optimal model for nitrogen content retrieval was established and selected. As a result, the screened sensitive wavelengths for nitrogen content selected were 470, 474, 490, 514, 582, 634, and 682 nm, respectively. Among the nitrogen content retrieval models, the best model was the Support Vector Machine (SVM) model. In the training set, this model outperformed the other models with an R2 of 0.733, RMSE of 6.00%, an nRMSE of 12.76%, and a MAE of 4.49%. Validated by the ground-measured nitrogen content, this model yielded good performance with an R2 of 0.671, an RMSE of 4.73%, an nRMSE of 14.83%, and a MAE of 3.98%. This study can provide a new method for vegetation nutrient content retrieval based on UAV hyperspectral data.

The effect of different genotype cattle grazing on the nutrient content of saline grasslands vegetation

Maintaining saline grasslands in good condition, preserving their yield and diversity is important not only for the purpose of nature conservation, but also for farming. Therefore, the primary purpose of our study is to analyse the effect of pasture use of the smaller weight extensive and the larger weight intensive beef cattle on the grassland vegetation and nutrient content. In this way, we can answer the question whether grazing for nature conservation can be achieved with more profitable, more economical and more intense varieties.
 The tests were carried out in May 2016 and May 2017, in the Hortobágy National Park (Pap-ere and Zám puszta), where a total of 16 sample areas were analysed. These areas are grazed with extensive beef cattle (Hungarian grey) and mixed genotype of intensive cattle. The associations were selected along a moisture gradient, such as wet salt marsh (Bolboschoenetum maritimi) and drier saline meadow (Beckmannion eruciformis). All the vegetative material collected both years in May was analysed for the following parameters: dry matter, crude protein, crude fibre and life-sustaining net energy content. We compared the effects of medium grazing (0.46 livestock/ha) and abandonment on vegetation and nutrient content.
 We examined the effect of (i) grazing, (ii) different grasslands (salt marsh, saline meadow) and (iii) grazing of different cattle breeds (Hungarian grey, intensive beef) on the nutrient content of the vegetation of grasslands Based on our results, it was found that grazing had an impact on crude protein and life-sustaining net energy content. The highest crude protein content (12.75 m/m%) was obtained in the year 2017 in the area where higher density had been grazed for two years. For the lifesustaining net energy, the highest value (5.05 MJ/kg d.m.) was also obtained in 2017 and the lowest in 2016. Furthermore, it was found that there was no significant difference between the effect of the two cattle breeds on the parameters examined. Significant effects were observed only in the case of life-sustaining net energy: in the area of intensive beef cattle we received a higher value (5.15 MJ/kg body weight) than in the area with extensive beef cattle (4.96 MJ/kg body weight).
 Our results have also shown that cattle grazing is of the utmost importance for the maintenance of both wet and mesophilous habitats. Based on our three-year study, we can say that grazing by both extensive and intensive cattle breeds is suitable for the management of saline habitats.

Variability of environmental factors and the effects on vegetation diversity with different restoration years in a large open-pit phosphorite mine

Open-pit mining activities can cause serious disturbance to the local land and even regional vegetation communities. Vegetation restoration is a crucial approach for maintaining ecological stability in a post-mining area. In this study, the role of the environment factors on vegetation diversity under different restoration years (2a, 5a, 10a and control area) in the largest phosphate mining areas in Southwestern China was evaluated by a multi-model inference (MMI) based on the Akaike information criterion (AIC). Three competing models of environmental factors included vegetation nutrient content (M1), soil heavy metal content (M2) and human disturbance (M3) were constructed to analyze how they impact vegetation diversity. The results revealed the changing effects of different environmental factors under four restoration stages. Heavy metal content in the soil (M2) had the strongest effect on vegetation diversity in the restoration areas at 2 and 10 years, whereas human disturbance (M3) had the strongest effect in the restoration area at 5 years. In the control area, the vegetation nutrient content (M1) had the strongest effect on vegetation diversity. According to the different models, a comprehensive index of environmental factors (CIEF) was established to build the fitting formula with vegetation diversity. The index could be used for assessing the efficiency of vegetation restoration by comparing the theoretical value and the actual value of Shannon's diversity index in the study area and other phosphate mining areas.

Effect of cadmium accumulation on mineral nutrient levels in vegetable crops: potential implications for human health.

Consumption of vegetables is often the predominant route whereby humans are exposed to the toxic metal Cd. Health impacts arising from Cd consumption may be influenced by changes in the mineral nutrient content of vegetables, which may occur when plants are exposed to Cd. Here, we subjected model root (carrot) and leaf (lettuce) vegetables to soil Cd concentrations of 0.3, 1.5, 3.3, and 9.6μgg(-1) for 10weeks to investigate the effect of Cd exposure on Cd accumulation, growth performance, and mineral nutrient homeostasis. The findings demonstrated that Cd accumulation in lettuce (20.1-71.5μgg(-1)) was higher than that in carrot (3.2-27.5μgg(-1)), and accumulation exceeded the maximum permissible Cd concentration in vegetables when soil contained more than 3.3μgg(-1) of Cd. There was a marked hormetic effect on carrot growth at a soil Cd concentration of 3.3μgg(-1), but increasing the Cd concentration to 9.6μgg(-1) caused decreased growth in both crops. Additionally, in most cases, there was a positive correlation between Cd and the mineral nutrient content of vegetables, which was due to physiological changes in the plants causing increased uptake and/or translocation. This may suggest a general mechanism whereby the plant compensated for disrupted mineral nutrient metabolism by increasing nutrient supply to its tissues. Increased nutrient levels could potentially offset some risks posed to humans by increased Cd levels in crops, and we therefore suggest that changes in mineral nutrient levels should be included more widely in the risk assessment of potentially toxic metal contamination. Graphical abstract The Cd concentration (μg g-1 in dry matter) in the root, shoot and translocation factor (TF) of Cd from root to shoot in the carrot and lettuce, and the percentage of root Cd to the gross Cd contents (%) in carrot (C) and lettuce (D) exposed to soil Cd (0 (control), 1, 3, and 9 μg g-1) for 70 days. Values are means ± SD (n = 5).

Mapping of macro and micro nutrients of mixed pastures using airborne AisaFENIX hyperspectral imagery

On-farm assessment of mixed pasture nutrient concentrations is important for animal production and pasture management. Hyperspectral imaging is recognized as a potential tool to quantify the nutrient content of vegetation. However, it is a great challenge to estimate macro and micro nutrients in heterogeneous mixed pastures. In this study, canopy reflectance data was measured by using a high resolution airborne visible-to-shortwave infrared (Vis–SWIR) imaging spectrometer measuring in the wavelength region 380–2500nm to predict nutrient concentrations, nitrogen (N) phosphorus (P), potassium (K), sulfur (S), zinc (Zn), sodium (Na), manganese (Mn) copper (Cu) and magnesium (Mg) in heterogeneous mixed pastures across a sheep and beef farm in hill country, within New Zealand. Prediction models were developed using four different methods which are included partial least squares regression (PLSR), kernel PLSR, support vector regression (SVR), random forest regression (RFR) algorithms and their performance compared using the test data. The results from the study revealed that RFR produced highest accuracy (0.55⩽R2CV⩽0.78; 6.68%⩽nRMSECV⩽26.47%) compared to all other algorithms for the majority of nutrients (N, P, K, Zn, Na, Cu and Mg) described, and the remaining nutrients (S and Mn) were predicted with high accuracy (0.68⩽R2CV⩽0.86; 13.00%⩽nRMSECV⩽14.64%) using SVR. The best training models were used to extrapolate over the whole farm with the purpose of predicting those pasture nutrients and expressed through pixel based spatial maps. These spatially registered nutrient maps demonstrate the range and geographical location of often large differences in pasture nutrient values which are normally not measured and therefore not included in decision making when considering more effective ways to utilized pasture.

Nutrient Density and the Cost of Vegetables from Elementary School Lunches.

Vegetables are the major source of the dietary fiber, magnesium, potassium, and vitamins A and C that are crucial in the diets of children. This study assessed the nutrient content of vegetables offered through the National School Lunch Program and examined the relation between the overall nutrient density of vegetable subgroups and the costs of nutrients offered and wasted before and after the changes in school meal standards. Using data collected from 3 elementary schools before and after the changes in school meal standards, we found that vegetable plate waste increased from 52% to 58%. Plate waste for starchy vegetables, exclusive of potatoes, was relatively high compared with other subgroups; however, plate waste for white potatoes was the lowest among any type of vegetable. Energy density; cost per 100 g, per serving, and per 100 kcal; and percentage daily value were calculated and used to estimate nutrient density value and nutrient density per dollar. Cost per 100 kcal was highest for red/orange vegetables followed by dark green vegetables; however, nutrient density for red/orange vegetables was the highest in the group and provided the most nutrients per dollar compared with other subgroups. Given that many vegetables are less energy dense, measuring vegetable costs per 100 g and per serving by accounting for nutrient density perhaps is a better way of calculating the cost of vegetables in school meals.

Effect of Preservation on Two Different Varieties of <i>Vernonia amygdalina</i> Del. (Bitter) Leaves

Vernonia amygdalina Del. is one of the leafy vegetables that can be used in an attempt to alleviate the problem of micronutrient malnutrition, prominent in tropical Africa. In order to ensure availability in non-growing areas or seasons, the vegetable needs to be preserved. Processing and preservation methods influence the nutrient content of vegetables. The present study was aimed at determining the effects of preservation on two different varieties of V. amygdalina (bitter) leaves (broad and small leaves). To this effect, evaluations were made on the chlorophyll content, phytochemicals, and antioxidant capacity of the two varieties of bitter leaf (V. amygdalina Del.) stored at 4℃ and –20℃ over a period of two weeks. Results showed a significant decrease in all parameters studied for both varieties at –20℃ except for the free radical reducing power (FRAP), DPPH radical scavenging activity (%RSA) and nitric oxide radical scavenging activity (%RSA) of V. amygdalina broad leaves where increase in scavenging activity was observed. Thus, it was concluded that to preserve the chlorophyll, phenol, total soluble proteins and reducing sugar levels, preservation at 4℃ is recommended. The present study finding would be useful during short-term preservation of bitter leaves for soup preparation and/or its aqueous extract for ethnomedicinal purposes, especially the small leaf variety.

Herbaceous Community Structure and Function in the Kluane Region

Our research on the herbaceous understory vegetation in the Kluane region, Yukon, has focused on the structure and function of natural forest understory and grassland communities. The research has involved two long-term projects. The first investigated fertilizer addition and mammalian herbivore exclosure in understory vegetation over a 20-year period and showed that nutrient availability, and not herbivory, controlled herbaceous biomass. Fertilization increased the amount and nutrient content of vegetation, but 13 species were lost, whereas natural levels of mammalian herbivory rarely affected this vegetation or its diversity. The second study investigated how removing plant functional groups from a grassland influences its functioning. Over a seven-year period, we determined that the identity of the functional group was important in determining ecosystem properties and that graminoids were more influential than expected from their proportional biomass. In both of these studies, short-term responses were transient and not indicative of longer-term responses of these communities. This finding reinforces the need for long-term experiments, especially in northern ecosystems. The long-term plots from both projects will continue to be valuable, and they may detect shifts in the plant community due to climate change or unique events in the area.

New Metrics of Affordable Nutrition: Which Vegetables Provide Most Nutrients for Least Cost?

Measuring food prices per gram, rather than per calorie, is one way to make healthful vegetables appear less expensive. However, a better measure of affordability would take the nutrient content of vegetables into account. This study, based on analyses of US Department of Agriculture datasets, aimed to identify which vegetables, including juices and soups, provided the most nutrients per unit cost. Nutrient density was measured using the Nutrient Rich Foods (NRF) index, based on nine nutrients to encourage: protein; fiber; vitamins A, C, and E; calcium; iron; magnesium; and potassium; and on three nutrients to limit: saturated fat, added sugar, and sodium. Food cost in dollars was calculated per 100 g, per 100 kcal, per serving, and per nutrient content. One-way analyses of variance with post hoc tests were used to determine statistical significance. Results showed that tomato juices and tomato soups, dark green leafy and nonleafy vegetables, and deep yellow vegetables, including sweet potatoes, had the highest NRF scores overall. Highest NRF scores per dollar were obtained for sweet potatoes, white potatoes, tomato juices and tomato soups, carrots, and broccoli. Tomato sauces, raw tomatoes, and potato chips were eaten more frequently than were many other vegetables that were both more affordable and more nutrient-rich. These new measures of affordable nutrition can help foodservice and health professionals identify those vegetables that provide the highest nutrient density per unit cost. Processed vegetables, including soups and juices, can contribute to the quality and the affordability of the diet.

Characterizing properties and drivers of long distance movements by elephants (Loxodonta africana) in the Gourma, Mali

Wide-ranging, landscape-level movements by terrestrial herbivores are increasingly threatened globally. Understanding the ecology of spatio-temporal movement patterns is critical for conservation of wide-ranging terrestrial species and the ecosystems on which they rely. The range of the Gourma elephant population inhabiting the Sahelian eco-region near Tombouctou (Timbuktu), Mali encompasses the largest areal extent in this species (29% greater than range sizes reported in other populations). Over the course of a year, the Gourma elephants (Loxodonta africana) move in a coordinated north–south movement pattern that is relatively unique for the species. We apply two new approaches to this system to characterize space use patterns; a time-density algorithm that provides a probability surface of normalized time spent per unit grid cell of GPS tracked animals and a velocity-grid algorithm that summarizes linear movements (directions, speeds and directional similarity) in cartographic form. The derived movement vector raster was analyzed using standard clustering methods to categorize areas by movement properties. Using these techniques we inferred regions of relative ecological importance to the Gourma elephants, protection of which is essential for the preservation of this unique terrestrial movement system. Analysis suggests the observed spatio-temporal pattern is a complex function of availability of surface water, vegetation productivity (as measured using the Normalized Difference Vegetation Index, NDVI) and possibly vegetation nutrient content. The approaches and applications demonstrated here can further our understanding of the movement ecology of other wildlife landscapes and facilitate the identification of crux points for their improved management.

Effects of Liming on Forage Availability and Nutrient Content in a Forest Impacted by Acid Rain

Acidic deposition and subsequent forest soil acidification and nutrient depletion can affect negatively the growth, health and nutrient content of vegetation, potentially limiting the availability and nutrient content of forage for white-tailed deer (Odocoileus virginianus) and other forest herbivores. Liming is a mitigation technique that can be used to restore forest health in acidified areas, but little is known about how it affects the growth or nutrient content of deer forage. We examined the effects of dolomitic limestone application on the growth and chemical composition of understory plants in an acidified forest in central Pennsylvania, with a focus on vegetative groups included as white-tailed deer forage. We used a Before-After-Control-Impact study design with observations 1 year before liming and up to 5 years post-liming on 2 treated and 2 untreated 100-ha sites. Before liming, forage availability and several nutrients were below levels considered optimal for white-tailed deer, and many vegetative characteristics were related to soil chemistry. We observed a positive effect of liming on forb biomass, with a 2.7 fold increase on limed sites, but no biomass response in other vegetation groups. We observed positive effects of liming on calcium and magnesium content and negative effects on aluminum and manganese content of several plant groups. Responses to liming by forbs and plant nutrients show promise for improving vegetation health and forage quality and quantity for deer.

Body size and the division of niche space: food and predation differentially shape the distribution of Serengeti grazers

1. Theory predicts that small grazers are regulated by the digestive quality of grass, while large grazers extract sufficient nutrients from low-quality forage and are regulated by its abundance instead. In addition, predation potentially affects populations of small grazers more than large grazers, because predators have difficulty capturing and handling large prey. 2. We analyse the spatial distribution of five grazer species of different body size in relation to gradients of food availability and predation risk. Specifically, we investigate how the quality of grass, the abundance of grass biomass and the associated risks of predation affect the habitat use of small, intermediate and large savanna grazers at a landscape level. 3. Resource selection functions of five mammalian grazer species surveyed over a 21-year period in Serengeti are calculated using logistic regressions. Variables included in the analyses are grass nitrogen, rainfall, topographic wetness index, woody cover, drainage lines, landscape curvature, water and human habitation. Structural equation modelling (SEM) is used to aggregate predictor variables into 'composites' representing food quality, food abundance and predation risk. Subsequently, SEM is used to investigate species' habitat use, defined as their recurrence in 5 × 5 km cells across repeated censuses. 4. The distribution of small grazers is constrained by predation and food quality, whereas the distribution of large grazers is relatively unconstrained. The distribution of the largest grazer (African buffalo) is primarily associated with forage abundance but not predation risk, while the distributions of the smallest grazers (Thomson's gazelle and Grant's gazelle) are associated with high grass quality and negatively with the risk of predation. The distributions of intermediate sized grazers (Coke's hartebeest and topi) suggest they optimize access to grass biomass of sufficient quality in relatively predator-safe areas. 5. The results illustrate how top-down (vegetation-mediated predation risk) and bottom-up factors (biomass and nutrient content of vegetation) predictably contribute to the division of niche space for herbivores that vary in body size. Furthermore, diverse grazing assemblages are composed of herbivores of many body sizes (rather than similar body sizes), because these herbivores best exploit the resources of different habitat types.

Handling Practices to Control Ascorbic Acid and β-Carotene Lossess in Collards (Brassica oleracea)

Knowledge of the alterations in the nutrient content of vegetables after harvest and during preparation is still limited although studies have been reported. The objective of this study was to select handling practices to control losses of vitamin C (ascorbic acid (AA) and dehydroascorbic acid) and β-carotene in collards during storage, sanitization, slicing, and time after preparation. Determination of carotenoids was carried out by HPLC. β-carotene retention was greater at 10°C than 23°C after 24-h storage. Sanitization for a period longer than 15 min negatively affected AA retention in the sample stored under refrigeration. Increased waiting time between frying and consumption of stir-fried collards increased AA losses both in sliced and torn collards. Storage under refrigeration, sanitization time control, and reduced time between preparation and consumption are therefore recommended.

Short-term changes in soil nutrients and vegetation biomass and nutrient content following the introduction of extensive management in upland sown swards in Scotland, UK

Agri-environmental policy changes promote more extensive grazing management but the temporal responses of soil nutrients and vegetation biomass and quality to reductions in grazing intensity are still unresolved. We measured soil nutrients and the biomass and nutrient content of vegetation over 5 years following the introduction of extensive management treatments at three sites in Scotland, UK. Five unfertilised treatments, representing different levels of extensive management, were established on existing sown perennial ryegrass/white clover swards. One treatment was ungrazed (UN) and the others had sward surface height treatments of 4 or 8 cm during two grazing season treatments, summer and autumn, within each year in a factorial combination (4/4, 4/8, 8/8, 8/4 cm). A further treatment, representative of current more intensive systems, received an annual total of 140 kg N ha−1 plus maintenance P and K and was grazed by sheep to maintain a sward surface height of 4 cm (4F). When compared with more intensive management, there was little effect of 5 years of extensive management on soil nutrients at any of the three sites. The extensive treatments created swards with different above-ground biomass during the season, thus changing the balance between the litter and excretal routes for the recycling of plant nutrients. When expressed relative to treatment 4F, the proportion of live dry mass and N, P and K contents in sown species was on average higher in swards maintained at 4 cm in summer than at 8 cm, and there was evidence of a decline over time in the latter treatments. The proportion of unsown species in live mass increased over time in the unfertilised treatments, and the increase was most rapid in the ungrazed treatment. Nutrient contents of the vegetation in unfertilised swards were lower than those in fertilised swards, and changes over 5 years in the different management treatments differed between sites. However nutrient contents remained above levels that could adversely affect sheep performance throughout this period. Agri-environment schemes that promote extensive grazing management will change vegetation biomass and nutrients but are unlikely to reduce soil nutrients in the short term.

Vernal nitrogen and phosphorus retention by forest understory vegetation and soil microbes

Northern hardwood forests experience annual maximal loss of nutrients during spring. The vernal dam hypothesis predicts that spring ephemeral herbs in northern hardwood forests serve as sinks for nutrients during this season and reduce the loss of nutrients from the terrestrial ecosystem. Soil microbes of northern hardwood forests also sequester nutrients during spring. We compared the vernal nutrient acquisition ability of a soil microbial community and an understory plant community with species of mixed leaf phenology. We monitored nitrogen and phosphorus pool sizes in understory vegetation and soil microbes during spring from 1999 through 2001 in a northern hardwood forest in the Catskill Mountains, New York. Vegetation nutrient content increased during two spring seasons by an average of 3.07 g N m−2 and 0.19 g P m−2 and decreased during one spring by 0.81 g N m−2 and 0.10 g P m−2. Evergreen, wintergreen, and deciduous plant species were able to sequester nutrients during spring. Soil microbial nutrient content decreased during one spring by 1.29 g N m−2 and remained constant during the other two springs. Streamwater nitrogen losses were not correlated with biotic nutrient uptake suggesting a temporal disconnect between the two processes. We conclude that understory vegetation is a larger potential sink for vernal nutrients than are soil microbes in this northern hardwood forest and understory and species representing multiple phenologies are capable of vernal nutrient uptake.

BIOMASS AND CO2FLUX IN WET SEDGE TUNDRAS: RESPONSES TO NUTRIENTS, TEMPERATURE, AND LIGHT

The aim of this research was to analyze the effects of increased N or P availability, increased air temperature, and decreased light intensity on wet sedge tundra in northern Alaska. Nutrient availability was increased for 6–9 growing seasons, using N and P fertilizers in factorial experiments at three separate field sites. Air temperature was increased for six growing seasons, using plastic greenhouses at two sites, both with and without N + P fertilizer. Light intensity (photosynthetically active photon flux) was reduced by 50% for six growing seasons at the same two sites, using optically neutral shade cloth. Responses of wet sedge tundra to these treatments were documented as changes in vegetation biomass, N mass, and P mass, changes in whole-system CO2 fluxes, and changes in species composition and leaf-level photosynthesis. Biomass, N mass, and P mass accumulation were all strongly P limited, and biomass and N mass accumulation also responded significantly to N addition with a small N × P interaction. Greenhouse warming alone had no significant effect on biomass, N mass, or P mass, although there was a consistent trend toward increased mass in the greenhouse treatments. There was a significant negative interaction between the greenhouse treatment and the N + P fertilizer treatment, i.e., the effect of the two treatments combined was to reduce biomass and N mass significantly below that of the fertilizer treatment only. Six years of shading had no significant effect on biomass, N mass, or P mass. Ecosystem CO2 fluxes included net ecosystem production (NEP; net CO2 flux), ecosystem respiration (RE, including both plant and soil respiration), and gross ecosystem production (GEP; gross ecosystem photosynthesis). All three fluxes responded to the fertilizer treatments in a pattern similar to the responses of biomass, N mass, and P mass, i.e., with a strong P response and a small, but significant, N response and N × P interaction. The greenhouse treatment also increased all three fluxes, but the greenhouse plus N + P treatment caused a significant decrease in NEP because RE increased more than GEP in this treatment. The shade treatment increased both GEP and RE, but had no effect on NEP. Most of the changes in CO2 fluxes per unit area of ground were due to changes in plant biomass, although there were additional, smaller treatment effects on CO2 fluxes per unit biomass, per unit N mass, and per unit P mass. The vegetation was composed mainly of rhizomatous sedges and rushes, but changes in species composition may have contributed to the changes in vegetation nutrient content and ecosystem-level CO2 fluxes. Carex cordorrhiza, the species with the highest nutrient concentrations in its tissues in control plots, was also the species with the greatest increase in abundance in the fertilized plots. In comparison with Eriophorum angustifolium, another species that was abundant in control plots, C. cordorrhiza had higher photosynthetic rates per unit leaf mass. Leaf photosynthesis and respiration of C. cordorrhiza also increased with fertilizer treatment, whereas they decreased or remained constant in E. angustifolium. The responses of these wet sedge tundras were similar to those of a nearby moist tussock tundra site that received an identical series of experiments. The main difference was the dominant P limitation in wet sedge tundra vs. N limitation in moist tussock tundra. Both tundras were relatively unresponsive to the increased air temperatures in the greenhouses but showed a strong negative interaction between the greenhouse and fertilizer treatments. New data from this study suggest that the negative interaction may be driven by a large increase in respiration in warmed fertilized plots, perhaps in relation to large increases in P concentration.

Vehicle Perturbation Effects upon a Tundra Soil‐Plant System: I. Effects on Morphological and Physical Environmental Properties of the Soils

AbstractChanges obtaining in the soil abiotic physical environment due to tracked‐vehicle disturbance were determined in Tundra soils near Barrow, Alaska. The study was a contribution of the U.S.I.B.P., Tundra Biome Program.Six years following the scarring of the tundra surface by several years of infrequent passage by tracked‐vehicles (Weasel), the soils within the track had higher bulk densities and temperatures, accelerated and deeper thaw, and lower moisture percentages than undisturbed soil. Soil morphology was little altered except for direct physical alteration of surface organic horizons and a slight increase in mottling of mineral horizons in all but the wetter portions of the track. The intensity of alteration and associated environmental changes were related to the degree of evident disturbance (the amount of visible damage to the vegetative cover and soil surface) which, in turn, were related to differences in the natural drainage of the soils along the tracks; disturbance being greater, the poorer the natural drainage.The study indicated that a slight amount of disturbance to the tundra surface may be beneficial in terms of increased productivity and nutrient content of vegetation (see Part II of this paper). On the other hand, heavy disturbance can result in severe damage to the tundra system due to subsidence and erosion preventing the revegetation of the disturbed areas.