Nitrogen Content Of Foliage Research Articles

Investigation of hybrid Freeman maple resistance to Chrysobothris flatheaded borers (Coleoptera: Buprestidae).

Red maples (Acer rubrum L.; Sapindales: Sapindaceae) are common shade trees well known for their stunning autumn foliage and fast growth. They are a popular choice for landscapes, parks, and public places across the United States. Flatheaded borer species in the genus Chrysobothris (Coleoptera: Buprestidae) are some of the most damaging insects in red maple production, with attacks being most common on stressed and newly transplanted trees. In nurseries, red maples routinely experience flatheaded borer attacks, while the Freeman maple hybrid 'Autumn Blaze' has been reported as potentially resistant to flatheaded borers. In this study, traits of three borer susceptible red maple cultivars ('Brandywine', 'Sun Valley', and 'October Glory') were compared against a potentially resistant Freeman maple hybrid cultivar for baseline differences as well as differences under the stress of a foliar herbicide application Scythe (pelargonic acid 57%). Morphological, physiological, and biochemical traits of the red maple cultivars were evaluated and contrasted with the hybrid to identify traits related with borer resistance. Under normal conditions, the hybrid maple exhibited faster growth, greater concentrations of sulfur, and lower concentrations of zinc and flavonoids in leaf tissues compared to red maples. The herbicide stress treatment resulted in greater nitrogen and sulfur concentrations in hybrid foliage, but less chlorophyll, flavonoid, and zinc concentrations compared to the red maple cultivars. Field trials validated borer preference for red maples over the hybrid. Traits associated with the hybrid warrant additional study if an understanding of the causal relationship with borer resistance is to be achieved.

Bio agent added organomineral nitrogen fertilizer for heavy metal contaminated paddy field treatment

Industrial waste in paddy field leads to accumulation of heavy metals in the soils. The availability of heavy metal on the soil can affect soil quality and plant growth. The objectives of this research were to obtain the best dosage of bio agent-added organomineral nitrogen fertilizer (ONF+BA) for the improvement of soil quality and paddy rice grown in industrial-waste contaminated soil. Randomized block design were applied with six single treatments: 150 kg ONF+BA (A), 200 kg ONF+BA (B), 250 kg ONF+BA (C), 300 kg ONF+BA (D), 350 kg ONF+BA (E), 250 kg urea (F), each treatment was replicated five times. The result showed that the application of ONF+BA reduced lead (Pb) and chrome (Cr) solubility and foliar accumulation, improved plant growth, and increase foliage nitrogen content. The doses of 300 kg ONF+BA shown highest lead and chrome solubility reduction, while 350 kg ONF+BA decrease foliar accumulation of lead and chrome.

Foliar Nutritional Quality Explains Patchy Browsing Damage Caused by an Invasive Mammal.

Introduced herbivores frequently inflict significant, yet patchy damage on native ecosystems through selective browsing. However, there are few instances where the underlying cause of this patchy damage has been revealed. We aimed to determine if the nutritional quality of foliage could predict the browsing preferences of an invasive mammalian herbivore, the common brushtail possum (Trichosurus vulpecula), in a temperate forest in New Zealand. We quantified the spatial and temporal variation in four key aspects of the foliar chemistry (total nitrogen, available nitrogen, in vitro dry matter digestibility and tannin effect) of 275 trees representing five native tree species. Simultaneously, we assessed the severity of browsing damage caused by possums on those trees in order to relate selective browsing to foliar nutritional quality. We found significant spatial and temporal variation in nutritional quality among individuals of each tree species examined, as well as among tree species. There was a positive relationship between the available nitrogen concentration of foliage (a measure of in vitro digestible protein) and the severity of damage caused by browsing by possums. This study highlights the importance of nutritional quality, specifically, the foliar available nitrogen concentration of individual trees, in predicting the impact of an invasive mammal. Revealing the underlying cause of patchy browsing by an invasive mammal provides new insights for conservation of native forests and targeted control of invasive herbivores in forest ecosystems.

Growth, biomass allocation and photosynthetic responses are related to intensity of root severance and soil moisture conditions in the plantation tree Cunninghamia lanceolata.

We employed the warm temperate conifer Cunninghamia lanceolata (Lamb.) Hook. as a model of plantation forest species to investigate ecophysiological responses to root treatments (control (0%), and ∼25, 50 or 75% of the initial root mass) under well-watered and water-limited conditions. Our results indicated that total root dry mass accumulation was negatively associated with the severity of root pruning, but there was evidence of multiple compensatory responses. The plants exhibited higher instantaneous and long-term (assessed by carbon isotope composition, δ(13)C) water-use efficiency in pruning treatments, especially under low water availability. Root pruning also increased the fine root/total root mass ratio, specific root length and fine root vitality in both water availability treatments. As a result of the compensatory responses, under well-watered conditions, height, stem dry mass accumulation, leaf/fine root biomass ratio (L/FR), transpiration rate, photosynthetic capacity and photosynthetic nitrogen-use efficiency (EN) were the highest under 25% pruning. Yet, all these traits except L/FR and foliage nitrogen content were severely reduced under 75% pruning. Drought negatively affected growth and leaf gas exchange rates, and there was a greater negative effect on growth, water potential, gas exchange and EN when >25% of total root biomass was removed. The stem/aboveground mass ratio was the highest under 25% pruning in both watering conditions. These results indicate that the responses to root severance are related to the excision intensity and soil moisture content. A moderate root pruning proved to be an effective means to improve stem dry mass accumulation.

Effect of redistributing windrowed topsoil on growth and development of ponderosa pine plantations

Windrowing site preparation often displaces significant amounts of topsoil including nutrients and carbon into the strip-piles. Although short-term growth may increase due to the early control of competing vegetation, this practice can reduce long-term plantation productivity. Here, we report an experiment established in 1989 in a 28-year-old ponderosa pine (Pinus ponderosa) plantation to determine if redistributing topsoil, along with several shrub control measures, have influenced soil fertility and tree growth. Five treatments from a partial factorial design with three levels of shrub treatment and two levels of soil manipulation were applied in each of five blocks and consisted of: Control (C, do nothing); understory hydroaxed (masticated) to chips and left in the plot (H); windrows redistributed over brush (S); understory hydroaxed and windrows redistributed over chips (SH); and understory manually removed off-site and windrows redistributed (SM). Over the next 21year period total windrowed topsoil volume and mass were determined, soil nutrient concentrations in and between windrows including soil mineralizable N, total N and C were determined, understory biomass measured, tree diameter, basal area, and volume measured in 1989, 1994, 2005 and 2010, and nitrogen concentration of tree foliage was measured in 1989, 1991 and 1994. Results showed that about 18cm of topsoil had been displaced into windrows, including 1.98 (±0.13) MgN ha−1 and 41.04 (±2.46) Mg carbon ha−1. In general, redistributing windrowed topsoil (S, SH, and SM) yielded a consistently positive effect on quadratic mean diameter, basal area (BA), and volume compared to C and H. No difference in growth was found between SH and SM. These results were supported by higher soil nitrogen and mineralizable nitrogen contents in the three topsoil redistribution treatments. Higher foliage nitrogen concentrations in the redistribution treatments further supported these higher tree growth rates. The positive effects of shrub removal were evidenced only on the treatments without topsoil redistribution (C versus H); the difference in BA and volume between C and H was only significant in 1994. Redistributing topsoil reduced woody plant biomass but significantly enhanced herbaceous biomass six years after treatment. This shows that windrowing site preparation reduces plantation growth and stand development through displacement of topsoil and its nutrients. These negative effects can be mitigated by carefully redistributing windrowed topsoil, even in an established plantation.

Growth of Containerized Chamaecyparis obtusa Seedlings as Affected by Fertilizer and Container Volume

This study was carried out to evaluate the growth characteristics, carbon and nitrogen content of containerized 1-0 Chamaecyparis obtusa seedlings at various levels of fertilizer (2 g/L, 1 g/L, control) and three container volumes (500 mL, 400 mL, 320 mL). The growth of root collar diameter was highest in the 2 g/L (3.14 mm), followed by the 1 g/L (2.75 mm) and control (2.41 mm) treatments, while the height of seedling was significantly higher in the 1 g/L (21.88 cm) than other treatments (2 g/L: 20.92 cm; control: 19.06 cm). The growth of root collar diameter by container volume was better in the 500 mL than in the 320 mL. Dry weight of seedling was the highest in the 1 g/L (), followed by the control () and the 2 g/L () treatments. The dry weight of seedlings by container volume was significantly higher in the 500 mL than in the 320 mL. Nitrogen concentration in foliage was ranged from 1.51% in the control to 2.45-2.60% in the fertilizer treatments. However, carbon concentration of seedlings was not affected by the fertilizer or the container volume treatments. The growth of seedlings following planting in mountain area was better in the fertilized seedlings compared with in the unfertilized seedlings. The results indicate that the 1 g/L fertilization was an optimum rate for growth following planting of Chamaecyparis obtusa seedlings.

Nitrogen vertical distribution by canopy reflectance spectrum in winter wheat

Nitrogen is a key factor for plant photosynthesis, ecosystem productivity and leaf respiration. Under the condition of nitrogen deficiency, the crop shows the nitrogen deficiency symptoms in the bottom leaves, while excessive nitrogen will affect the upper layer leaves first. Thus, timely measurement of vertical distribution of foliage nitrogen content is critical for growth diagnosis, crop management and reducing environmental impact. This study presents a method using bi-directional reflectance difference function (BRDF) data to invert foliage nitrogen vertical distribution. We developed upper-layer nitrogen inversion index (ULNI), middle-layer nitrogen inversion index (MLNI) and bottom-layer nitrogen inversion index (BLNI) to reflect foliage nitrogen inversion at upper layer, middle layer and bottom layer, respectively. Both ULNI and MLNI were made by the value of the ratio of Modified Chlorophyll Absorption Ration Index to the second Modified Triangular Vegetation Index (MCARI/MTVI2) referred to as canopy nitrogen inversion index (CNII) in this study at ±40° and ±50°, and at ±30° and ±40° view angles, respectively. The BLNI was composed by the value of nitrogen reflectance index (NRI) at ±20° and ±30° view angles. These results suggest that it is feasible to measure foliage nitrogen vertical-layer distribution in a large scale by remote sensing.

Effects of Fertilizer on Growth, Carbon and Nitrogen Responses of Foliage in a Red Pine Stand

This study was to examine growth, carbon and nitrogen responses in foliage following forest fertilization in a red pine stand. Two types of fertilizer (N:P:K=113:150:37 kg <TEX>$ha^{-1}$</TEX>; P:K=150:37 kg <TEX>$ha^{-1}$</TEX>) were applied on late April 2011. Growth, carbon and nitrogen responses of foliage were monitored 3 times (July, September, November) after fertilization. Morphological growth responses (dry mass, leaf area, specific leaf area) with foliage age were not significantly (P > 0.05) affected by fertilizer application, while needle dry mass and leaf area of July were significantly lower in current-year-old than in one-year-old or two-year-old needles of September or November. Carbon concentration and content in foliage was little affected by fertilizer application compared with sampling month or needle age, while the NPK fertilizer produced high nitrogen concentration and content of foliage. The results indicate that nitrogen concentration and content in foliage may serve as an indicator of the nitrogen status by fertilization in a red pine stand.

Foliar nitrogen in relation to plant traits and reflectance properties of New Hampshire forests

Several recent studies have shown that the mass-based concentration of nitrogen in foliage (%N) is positively correlated with canopy near-infrared reflectance (NIRr) and midsummer shortwave albedo across North American forests. Understanding the mechanisms behind this relationship would aid in interpretation of remote sensing imagery and improve our ability to predict changes in reflectance under future environmental conditions. The purpose of this study was to investigate the extent to which foliar nitrogen at leaf and canopy scales covary with leaf- and canopy-scale structural traits that are known to influence NIR scattering and reflectance. To accomplish this, we compared leaf and canopy traits with reflectance spectra at 17 mixed temperate forest stands. We found significant positive associations among %N and NIRr at both the leaf and canopy scale. At the canopy scale, both %N and NIRr were correlated with a number of structural traits as well as with the proportional abundance of deciduous and evergreen foliage. Identifying specific causal factors for observed reflectance patterns was complicated by interrelations among multiple traits across scales. Among simple metrics of canopy structure, we saw no relationship between NIRr and leaf area index, but we observed a strong, inverse relationship with the number of leaves per unit canopy volume.

Resource pulses of dead periodical cicadas increase the growth of American bellflower rosettes under competitive and non-competitive conditions

This experiment investigates how pulsed nutrient resources interact with intraspecific competition to influence biomass production and nutrient use efficiency in the American bellflower (Campanulastrum americanum). The competitive environment of these plants was manipulated by growing plants alone or with neighboring conspecifics, and the occurrence of pulsed nutrient resources was manipulated through the addition of 17-year periodical cicada (Magicicada septendecim) carcasses in order to simulate naturally occurring pulsed resources in this system. The addition of cicada carcasses increased mean plant biomass by 61 % compared to non-supplemented plants, while competition decreased mean plant biomass by 44 % compared to plants grown without competition; these effects were additive. In comparison, nutrient use efficiency decreased in fertilized plants (cicada-supplemented plants showed 20 % greater foliage nitrogen concentrations compared to non-supplemented plants), but was not significantly affected by the plant’s competitive environment. In addition, cicada supplementation did not significantly increase the biomass asymmetry in competing pairs of plants. These results suggest that these plants increased their total nutrient uptake at a timescale commensurate with the pulsed increase in nutrient availability due to cicada carcass decomposition.

Measures of light in studies on light-driven plant plasticity in artificial environments.

Within-canopy variation in light results in profound canopy profiles in foliage structural, chemical, and physiological traits. Studies on within-canopy variations in key foliage traits are often conducted in artificial environments, including growth chambers with only artificial light, and greenhouses with and without supplemental light. Canopy patterns in these systems are considered to be representative to outdoor conditions, but in experiments with artificial and supplemental lighting, the intensity of artificial light strongly deceases with the distance from the light source, and natural light intensity in greenhouses is less than outdoors due to limited transmittance of enclosure walls. The implications of such changes in radiation conditions on canopy patterns of foliage traits have not yet been analyzed. We developed model-based methods for retrospective estimation of distance vs. light intensity relationships, for separation of the share of artificial and natural light in experiments with combined light and for estimation of average enclosure transmittance, and estimated daily integrated light at the time of sampling (Qint,C), at foliage formation (Qint,G), and during foliage lifetime (Qint,av). The implications of artificial light environments were analyzed for altogether 25 studies providing information on within-canopy gradients of key foliage traits for 70 species × treatment combinations. Across the studies with artificial light, Qint,G for leaves formed at different heights in the canopy varied from 1.8- to 6.4-fold due to changing the distance between light source and growing plants. In experiments with combined lighting, the share of natural light at the top of the plants varied threefold, and the share of natural light strongly increased with increasing depth in the canopy. Foliage nitrogen content was most strongly associated with Qint,G, but photosynthetic capacity with Qint,C, emphasizing the importance of explicit description of light environment during foliage lifetime. The reported and estimated transmittances of enclosures varied between 0.27 and 0.85, and lack of consideration of the reduction of light compared with outdoor conditions resulted in major underestimation of foliage plasticity to light. The study emphasizes that plant trait vs. light relationships in artificial systems are not directly comparable to natural environments unless modifications in lighting conditions in artificial environments are taken into account.

Effect of Altitude on Photosynthetic and Biochemical Characteristics of Podophyllum hexandrum: An Alpine Endangered Medicinal Herb from Central Himalayas

Podophyllum hexandrum is a high value endangered medicinal plant from alpines of Central Himalaya. This study was conducted to explore its conservation and cultivation possibilities at comparatively lower altitudes. Seedlings of the same age, were selected from alpine medicinal crop nursery, Tungnath (3600m) and were planted at the nurseries located at 3600 and 550m altitudes. After well acclimatization at both the altitudes, plants were examined for gas exchange and biochemical characteristics during their active growth period. Our data shows that the foliage nitrogen content was higher and, P, K and C content were found lower in the plants grown at higher elevation as compared to lower altitude; however, these altitudinal variations were not found statistically significant. Chlorophyll a, Chl b, total Chl and Carotenoids were higher and Chl a/b ratio was lower at lower altitude as compared to plant grown at higher altitude. Level of protein and RUBP Carboxylase activity was higher and level of PEP Carboxylase activity was observed lower in the plants grown at high elevation as compared to their counterparts at lower altitude. Light optima for photosynthesis (PARopt) was observed around 2000µmolm–2s–1 at both the elevations in this species. A shift in optimum temperature for photosynthesis (Topt) was observed towards higher temperature in plants grown at lower altitude as compared to higher elevation, which indicates their potential to survive in the comparatively warmer environment. Topt was observed at 20°C in plants grown at higher altitude whereas, at lower altitude Topt was observed at 25°C for the plants of P. hexandrum. Conductance and transpiration was found slightly higher at high altitude as compared to plants grown at lower altitude. In view of these results, it can be concluded that these species can be cultivated at lower altitudes to meet their ever-increasing industrial demand.

Albedo estimates for land surface models and support for a new paradigm based on foliage nitrogen concentration

AbstractVegetation albedo is a critical component of the Earth's climate system, yet efforts to evaluate and improve albedo parameterizations in climate models have lagged relative to other aspects of model development. Here, we calculated growing season albedos for deciduous and evergreen forests, crops, and grasslands based on over 40 site‐years of data from the AmeriFlux network and compared them with estimates presently used in the land surface formulations of a variety of climate models. Generally, the albedo estimates used in land surface models agreed well with this data compilation. However, a variety of models using fixed seasonal estimates of albedo overestimated the growing season albedo of northerly evergreen trees. In contrast, climate models that rely on a common two‐stream albedo submodel provided accurate predictions of boreal needle‐leaf evergreen albedo but overestimated grassland albedos. Inverse analysis showed that parameters of the two‐stream model were highly correlated. Consistent with recent observations based on remotely sensed albedo, the AmeriFlux dataset demonstrated a tight linear relationship between canopy albedo and foliage nitrogen concentration (for forest vegetation: albedo=0.01+0.071%N, r2=0.91; forests, grassland, and maize: albedo=0.02+0.067%N, r2=0.80). However, this relationship saturated at the higher nitrogen concentrations displayed by soybean foliage. We developed similar relationships between a foliar parameter used in the two‐stream albedo model and foliage nitrogen concentration. These nitrogen‐based relationships can serve as the basis for a new approach to land surface albedo modeling that simplifies albedo estimation while providing a link to other important ecosystem processes.

Nitrogen status of conifer needles at the alpine treeline

Background and Aims: High elevation treelines occur worldwide at similar mean growing season temperatures. Does this result from direct impact of low temperature on growth or carbon metabolism, or does nutrient limitation, induced by low soil temperature, play a role? Similar treeline elevations at contrasting soil fertility argue against the latter, but the actual nutritional status of treeline trees (here addressed as foliage nitrogen concentration) has never been assessed systematically. Although needle nitrogen (N) concentration does not necessarily indicate growth limitation by N, the relative abundance of N would indicate obvious depletions at the treeline. Methods: A central problem with any foliage nutrient assay is that the units for describing the element concentration are dependent on elevation themselves. Here we separate changes in N per unit tissue from changes in reference units. Results: Needles of Pinus cembra and Picea abies in the Alps do not show elevational differences in N concentration per dry weight, water content, area or volume, thus, there is no N depletion near the elevational tree limit. Hence, nutrient supply is either unaltered, or growth is adjusted so that nutrient depletion in needle tissue does not occur. Conclusions: Chronic N shortage at needle level is not an explanation for low tree vigour at the treeline.

Environmental basis of soil–site productivity relationships in ponderosa pine

Understanding the environmental basis for soil–site quality relationships requires that we connect the environmental factors important to resource availability to the physiological processes influencing tree productivity. The nitrogen productivity concept provides this link by relating nitrogen uptake rate to plant growth, although the concept has been verified almost exclusively by laboratory experiments on tree seedlings. We tested the nitrogen productivity concept in a field setting by relating foliage production to nitrogen mineralization rate in 19 mature ponderosa pine (Pinus ponderosa) stands across a moisture gradient in central Oregon, USA. Models developed following the nitrogen productivity concept predicted annual foliage production precisely and adequately represented the different influences of nitrogen and water stress. Current‐year foliage production was proportional to older foliage nitrogen content (R2 = 0.82), and a model including a water stress index (stable carbon isotope ratio, δ13C) further explained 95% of the variability.A direct link between soil nitrogen availability and canopy nutrition was less clear. Annual foliage production was positively, but weakly, correlated with soil‐estimated N‐uptake (estimated in situ), likely because annual nitrogen uptake was small relative to nitrogen retained in the canopy. Foliage nitrogen was highly conserved with a mean retention time of 10.5 yr, which was 2.2 times longer than foliage retention. Annual nitrogen uptake amounted to 0–11% of total canopy N. Multiyear estimates of cumulative N fluxes are needed to adequately assess N availability. Soil nutrient pools were poorly correlated with nutrient uptake and were not useful for predicting stand productivity.

Specific bottom-up effects of arbuscular mycorrhizal fungi across a plant-herbivore-parasitoid system.

The majority of plants are involved in symbioses with arbuscular mycorrhizal fungi (AMF), and these associations are known to have a strong influence on the performance of both plants and insect herbivores. Little is known about the impact of AMF on complex trophic chains, although such effects are conceivable. In a greenhouse study we examined the effects of two AMF species, Glomus intraradices and G. mosseae on trophic interactions between the grass Phleum pratense, the aphid Rhopalosiphum padi, and the parasitic wasp Aphidius rhopalosiphi. Inoculation with AMF in our study system generally enhanced plant biomass (+5.2%) and decreased aphid population growth (−47%), but there were no fungal species-specific effects. When plants were infested with G. intraradices, the rate of parasitism in aphids increased by 140% relative to the G. mosseae and control treatment. When plants were associated with AMF, the developmental time of the parasitoids decreased by 4.3% and weight at eclosion increased by 23.8%. There were no clear effects of AMF on the concentration of nitrogen and phosphorus in plant foliage. Our study demonstrates that the effects of AMF go beyond a simple amelioration of the plants’ nutritional status and involve rather more complex species-specific cascading effects of AMF in the food chain that have a strong impact not only on the performance of plants but also on higher trophic levels, such as herbivores and parasitoids.

Induced accumulation of phenolics and sawfly performance in Scots pine in response to previous defoliation

Phenolic compounds often accumulate in foliar tissues of deciduous woody plants in response to previous insect defoliation, but similar responses have been observed infrequently in evergreen conifers. We studied the effects of defoliation on the foliar chemistry of Scots pine (Pinus sylvestris L.) and cocoon mass, and survival of the pine sawfly (Diprion pini L.). In two successive years, needles were excised early in the season leaving only the current-year shoot intact (defoliated trees); untreated entire shoots served as controls (control trees). A year after the second defoliation, pine sawfly larvae were transferred to the trees. Delayed induced resistance in Scots pine in response to defoliation was indicated by (1) reduced cocoon mass in defoliated trees and (2) increased concentrations of phenolics and soluble condensed tannins in the foliage of defoliated trees compared with controls. Myricetin-3-galactoside, which showed the strongest induced response (104% and 71% increase in current-year (C) and previous-year (C+1) needles) of the compounds analyzed, also entered the regression model explaining variation in sawfly performance. Other compounds that entered the model, e.g., (+)-catechin, showed weaker responses to defoliation than myricetin-3-galactoside. Hyperin, condensed tannins and quercitrin showed strong induced responses in C or C+1 needles, or both, but these compounds did not explain the variation in sawfly performance. Accumulation of phenolics is sometimes associated with the reduced foliage nitrogen (N) concentrations in deciduous trees, and our results suggest that this may also be the case in evergreen conifers. Based on the earlier findings that defoliation reduces needle N concentration and N deficiency results in the accumulation of the same phenolic compounds, i.e., myricetin and quercetin glycosides, and soluble condensed tannins, we suggest that the accumulation of phenolics in defoliated trees occurred in response to the reduced foliar N concentration.

Carbon assimilation, 𝛅13C and water relations of Elaeagnus angustifolia grown at two groundwater depths in the Minqin desert, China

We investigated the physiological responses of Elaeagnus angustifolia to variation in groundwater depth. Elaeagnus angustifolia seedlings were grown in the Minqin desert in lysimeters supplied with underground water at the soil depth of 1.40 m and 3.40 m. Results showed that constant access to groundwater allowed plants supplied with water at the lower soil layer to meet their water requirement and, consequently, they were not affected by water stress. There were no differences in A max (the net CO2 assimilation rate under conditions of photosynthetically photon flux density and CO2 saturation), J max (maximum rate of electron transport) and stomatal conductance between the two underground water treatments. However, plants with deeper groundwater had a significantly higher V cmax (i.e. a higher carboxylation efficiency of Rubisco) and mesophyll conductance resulting in increased photosynthesis measured at the CO2 growth condition (A) and, consequently higher intrinsic water-use efficiency (WUE). However, respiration was also increased in plants grown with deeper groundwater. This may have offset the increased A and led to a similar long-term WUE, as expressed by carbon isotope discrimination (δ13C), between the two ground water treatments. In the present study, we also found a high foliage nitrogen concentration in the E. angustifolia plants (3.75% on average), that may be very significant ecologically in improving soil properties. The physiological traits of E. angustifolia found in this study confirm that the use of perennial phreatophytic, nitrogen fixing species has significant potential to positively impact soil fertility and carbon sequestration under environmental conditions found in the Minqin desert.

Interacting controls by light availability and nutrient supply on biomass allocation and growth of Betula pendula and B. pubescens seedlings

Interactions among environmental drivers commonly occur in natural environments, but their influence on plant performance is not fully understood. We tested for significant interactive effects of light and nutrient availabilities on foliage architecture, chemistry, biomass allocation and growth in shade intolerant temperate deciduous trees Betula pendula Roth. and B. pubescens Ehrh. First-year seedlings were grown at four irradiance and four N and P availability combinations, and the experiment was repeated in two consecutive years. In both species, increases in light availability resulted in larger net assimilation rate (NAR, total plant biomass production rate per unit leaf area), root mass fraction ( F R) and leaf mass per unit area ( M A), but reductions in leaf area ratio (LAR, foliage area per total plant dry mass), stem mass fraction ( F S) and leaf mass fraction ( F L). The strong decrease in LAR (LAR = F L/ M A) with light mainly resulted from increases in M A. The light-dependent increase in NAR was larger than the decline in LAR such that plant relative growth rate (RGR = NAR × LAR) scaled positively with light in both species. Nutrient availability mainly enhanced LAR, and moderately NAR, further improving RGR. The increase in LAR was primarily associated with increases in F L and decreases in F R. Significant interactions between light and nutrients were found for most of the studied variables, overall indicating that plant allocation and growth were more responsive to nutrients at higher light availability. Several significant species and year-to-year differences were observed among the allocation and growth characteristics that were driven by plant size, climate and seedling source. Greater RGR of B. pubescens that is a species colonizing habitats with lower nutrient availability was linked to its greater foliage nitrogen concentrations. Overall, the study highlights a significant light × nutrient interaction that can modify seedling performance along natural gap-understory gradients.

Shifts in depth of water extraction and photosynthetic capacity inferred from stable isotope proxies across an ecotone of Juniperus osteosperma (Utah juniper) and Artemisia tridentata (big sagebrush)

Summary 1 In western North America, juniper trees (Juniperus spp.) are apparently encroaching into numerous communities including sagebrush-dominated (Artemisia tridentata) valleys, where, as density of juniper increases, the density and condition of sagebrush decline but juniper condition appears unaffected. 2 We examined stable isotope proxies of plant gas exchange and relative depth of soil water extraction of Juniperus osteosperma and Artemisia tridentata as their relative densities changed across a transition zone in northern Utah, USA. Measurement of 13C and 18O of foliage allowed separation of the contributions of stomatal and biochemical factors to differences in mean intercellular CO2 concentration, while deuterium composition of stem water served as an indicator of the relative depth of water extraction. 3 Leaf δ13C of juniper and, to a lesser extent, of sagebrush increased with decreasing density of juniper. Foliage 18O did not vary significantly with juniper density, indicating that this was primarily caused by an increase in photosynthetic capacity rather than decreased supply of CO2. Increased foliage nitrogen concentration of both species with decreasing juniper density is also consistent with increased photosynthetic capacity. 4 The much greater mean age of juniper trees in the high juniper density plots may explain their lower photosynthetic capacity. 5 Averaged across densities, juniper always extracted water deeper in the profile than did sagebrush, but in June and August, only the high juniper density plots showed an effect. Sagebrush is either restricted from using water at greater depth in the presence of juniper at high density or was in such poor condition that deep-water sources were not necessary to maintain their reduced function. 6 Ecotones can serve as useful, spatially constrained stages for examining resource partitioning and relationships among plant species. We observed spatial and temporal variation in resource use and partitioning of limited resources that will enable better design of manipulative experiments to explicitly examine competition.