Foliage Nitrogen Research Articles

Mid-infrared spectroscopy for planted forest soil and foliage nutrition predictions, New Zealand case study

Soil nutrient supply is one of several environmental and biotic drivers of planted forest productivity and testing the soil and tree foliage can inform nutrient management decisions. For many forest companies and research organisations the collection and analysis of a large number of soil samples for chemical properties has previously been considered expensive if not cost-prohibitive. Consequently, site nutrition status may not be measured or, as is the case with many forestry managers, efforts are directed towards foliar sampling to assess tree health and vigour. Diffuse reflectance infrared spectroscopy has emerged as a quick, cost-effective, and non-destructive method for the analysis of many soil properties. Because of the advances in diffuse reflectance spectroscopy, we see potential advantages to the forest industry and research organisations by utilising this method as a cost-effective means of analysing forest soil and foliage nutrient status. In this study we build a New Zealand planted-forest specific mid-infrared spectral training library for soil and foliage chemical properties. Nationally applicable partial least squares regression models for soil and foliage chemical properties were built from the respective libraries and were applied to an independent national data set to test their robustness. The soil properties with good (R2 >0.8) and fair (R2 0.5–0.8) predictions on the independent data set were soil pH, total carbon, total nitrogen, total phosphorus, available aluminium, available calcium, CEC (cation exchange capacity), base saturation, and the following elemental totals: aluminium, calcium, iron, potassium, magnesium, nickel, and zinc. The foliage properties with fair predictions (R2 0.5–0.8) were total calcium, total potassium and total phosphorus. Total nitrogen had an R2 of 0.47 which was a result of a narrow range in nitrogen values within the test set. The root mean squared error (RMSE) for foliage nitrogen was acceptable. Most of the key planted forest soil and tree foliage nutrient properties were able to be predicted using MIR (mid infrared) spectroscopy. However, some soil available macro-nutrients and all measured soil available micro-nutrients and foliage micro-nutrients predictions were unreliable (R2 <0.5). The high throughput of samples and efficiency of analysis when using MIR spectroscopy will result in cost savings whereby forest companies and research organisations can afford to routinely analyse soil and foliar samples for their nutrient status that will then benefit the industry in their quest for productive and sustainable planted forests.

Chipilín (C. longirostrata Hook. and Arn.) Capacity for Regrowth and Leaf Area Production in Response to Nitrogen and Phosphorus Fertilizer Application

Background: Fertilizer application combined with successive foliage cuttings can positively affect plant growth, yield and quality. The objective of this study was to evaluate the response of chipilín to successive foliage cuttings and nitrogen and phosphate fertilizer application under greenhouse conditions. Methods: During 2018, an experiment was carried out in a greenhouse under a completely randomized design, with six replications of each treatment. The treatments were as follows: control, 100 kg ha-1 N as urea and 60 kg ha-1 P2O5 as triple superphosphate. The fertilizers were applied one month after planting (MAP). Two MAPs, uniform cuttings were performed, followed by three successive cuttings, with one every 30 days. At each cutting, the traits evaluated included the number of new shoots; the length, diameter, leaf area and dry biomass of the new shoots by component (leaves and stems); the relative growth rate (RGR) of the biomass of the shoot leaves, the chlorophyll (a, b and total) and carotenoid content and NDVI. Result: Cutting foliage every 30 days increased (p less than 0.05) the number of new shoots, leaf biomass, total biomass and leaf area, but reduced the length and diameter of the shoots. There was no effect (p greater than 0.05) of cutting on root biomass or nodulation, but there was an effect of fertilizer application, with both variables decreasing with nitrogen addition.

Using hyperspectral plant traits linked to photosynthetic efficiency to assess N and P partition

Spatial prediction of photosynthesis requires an understanding of how foliage nitrogen (N) and phosphorus (P) regulate this process and the relationship between these elements and scalable spectral proxies. Hyperspectral imagery has been used to predict important photosynthetic variables such as the maximum rate of carboxylation (Vcmax) and electron transport (Jmax). However, our understanding of how generally applicable these relationships are for plants that are limited by N and P, characterised by respective mass based ratios of N/P ≤ 10 and N/P > 10, is still incomplete as most studies assume N and P co-limit photosynthesis.Hyperspectral imagery and measurements of photosynthesis were obtained from one-year old Pinus radiata D. Don, grown under a factorial combination of N and P treatments. Using these data, the objectives of this study were to (i) identify whether trees were co-limited or independently limited by N and P, and then use hyperspectral imagery to (ii) partition N and P limited trees, (iii) build models of N and P from a range of hyperspectral indices and (iv) explore links between key plant traits and both Vcmax and Jmax.Compared to the use of all data, which assumes co-limitation, markedly stronger relationships between N and P and photosynthetic capacity were obtained through splitting data at N/P = 10 (independent limitation) for both Vcmax (R2 = 0.40 vs. 0.59) and Jmax (R2 = 0.38 vs. 0.64). A random forest model was used to accurately partition N from P limited trees and the two main variables used within this model were Photochemical Reflectance Index (PRI) and Solar-Induced Chlorophyll Fluorescence (SIF). Using data from the P limiting phase, the most precise models of P were created using PRI (R2 = 0.75) and SIF (R2 = 0.52). Indices that were proxies for chlorophyll were the most precise predictors of N within the N limiting phase but strong positive relationships were also evident between N and both PRI (R2 = 0.83) and SIF (R2 = 0.57). Through their correlations with N and P, there were strong positive relationships between both SIF, PRI and Vcmax (R2 = 0.78 and 0.83, respectively) and Jmax (R2 = 0.80 and 0.83, respectively) that were generalisable across both N and P limiting ranges. These results suggest that quantified SIF and PRI from hyperspectral images may have greater precision and generality for predicting both foliage nutrition and biochemical limitations to photosynthesis than other widely used hyperspectral indices.

Host plant-mediated effects of elevated CO2 and temperature on growth and developmental parameters of Zygogramma bicolorata (Coleoptera: Chrysomelidae).

Mexican beetle, Zygogramma bicolorata Pallister (Coleptera: Chrysomelidae) is a potential weed control biocontrol agent in Australia, India and other countries. Its grubs and adults feed on the leaves of parthenium weed, Parthenium hysterophorus and check the further growth of the plant. Experiments were conducted to understand host plant-mediated effects of elevated temperature and elevated CO2 on biocontrol agent Z. bicolorata. Food consumption, utilization, ecological efficiency and life-table parameters of Z. bicolorata were studied in grubs and adults stage up to diapause. Reduction of leaf nitrogen in parthenium weed foliage with a significant increase in carbon and C:N ratio was recorded at elevated CO2. Elevated CO2 and temperature had no effect on adult longevity before diapausing. Duration of egg's hatching, specific stages of grub and pupa of Z. bicolorata were significantly longer when beetles fed on leaves grown under elevated CO2 but these parameters decreased significantly on leaves grown under elevated temperature. Significantly high consumption rates with low growth and digestion conversions were observed under elevated CO2 and/or in coupled with elevated temperature. Elevated CO2 and temperature-grown parthenium weed foliage also had a significant effect on Z. bicolorata intrinsic rate of increase (R), finite rate of increase (λ), mean generation time (T), and gross reproductive rate. Changed quality of parthenium weed leaves in elevated CO2 and temperature levels resulted in the increase of consumption, slower food conversion rates, increase in developmental period with reduced reproduction efficiency of Z. bicolorata. Our results indicate that the reproduction efficiency of Z. bicolorata is likely to be reduced as the climate changes, despite increased feeding rates exhibited by grubs and adult beetles on parthenium weed foliage.

Organic Farming Sharpens Plant Defenses in the Field.

Plants deploy a variety of chemical and physical defenses to protect themselves against herbivores and pathogens. Organic farming seeks to enhance these responses by improving soil quality, ultimately altering bottom up regulation of plant defenses. While laboratory studies suggest this approach is effective, it remains unclear whether organic agriculture encourages more-active plant defenses under real-world conditions. Working on the farms of cooperating growers, we examined gene expression in the leaves of two potato (Solanum tuberosum) varieties, grown on organic vs. conventional farms. For one variety, Norkotah, we found significantly heightened initiation of genes associated with plant-defense pathways in plants grown in organic vs. conventional fields. Organic Norkotah fields exhibited lower levels of nitrate in soil and of nitrogen in plant foliage, alongside differences in communities of soil bacteria, suggesting possible links between soil management and observed differences in plant defenses. Additionally, numbers of predatory and phloem-feeding insects were higher in organic than conventional fields. A second potato variety, Alturas, which is generally grown using fewer inputs and in poorer-quality soils, exhibited lower overall herbivore and predator numbers, few differences in soil ecology, and no differences in gene-activity in organic and conventional farming systems. Altogether, our results suggest that organic farming has the potential to increase plants' resistance to herbivores, possibly facilitating reduced need for insecticide applications. These benefits appear to be mediated by plant variety and/or farming context.

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.

Physiological changes and growth promotion induced in poplar seedlings by the plant growth-promoting rhizobacteria Bacillus subtilis JS

This study aimed to determine the effects of plant growth-promoting rhizobacteria Bacillus subtilis JS on the growth and physiological changes of Populus euramericana and Populus deltoides × P. nigra. Poplar seedlings were treated with B. subtilis JS and their growth was monitored for up to 120 d. Three different types of treatments [control, B1 (B. subtilis:double-distilled water, 1:100, v/v), and B2 (1:50)] were established. B. subtilis JS enhanced seedling height by 62% and total biomass by 37% after 120 d. Physiologically, the photosynthetic rate increased by 54%, and the total chlorophyll (Chl) content, foliage nitrogen and phosphate content were significantly higher after treatment with B2 than that of the control. These results suggest that the total Chl content is directly related to not only the photosynthetic capacity of the foliage but also to the nitrogen content, indicating that the strain JS may promote the growth of poplar.

Variability in the growth rates and foliage δ15N values of black spruce trees across a slope gradient in the Alaskan Interior

Black spruce (Picea mariana (Mill.) B.S.P.) is a dominant species on north-facing slopes located on the permafrost in the Alaskan Interior, where tree growth rates vary significantly across slope gradients. To better understand the effects of nitrogen (N) and mycorrhizal associations on plant growth, we investigated the relationships between tree growth and isotope ratios of nitrogen (δ15N) in foliage and roots, because plant δ15N values reflect tree dependencies on N uptake by mycorrhizae. We established two transects (one along a slope gradient, and a second on a north-to-east axis at a fixed elevation) and four plots on the slope gradient transect. We measured current shoot growth of saplings on transects and aboveground biomass (AGB) in the plots. We collected foliage and fine root samples and measured their δ15N signatures and N concentrations. The AGB and shoot growth varied widely across the gradient: values were higher at high elevations and at the east–northeast aspect. Foliage δ15N values and N concentrations were positively correlated with tree growth, but growth rate was negatively correlated with the dependency on mycorrhizae for N uptake. Thus, black spruce had a reduced dependency on mycorrhizae for N uptake on the upper slope, where conditions were N-rich. On the lower slope, where the soil active layer was shallow, black spruce growth was limited and had an elevated dependency on mycorrhizae for N uptake.

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.

Examining spectral reflectance features related to foliar nitrogen in forests: Implications for broad-scale nitrogen mapping

Abstract The concentration of nitrogen (N) in foliage often limits photosynthesis and can influence a number of important biogeochemical processes. For this reason, methods for estimating foliar %N over a range of scales are needed to enhance understanding of terrestrial carbon and nitrogen cycles. High spectral resolution aircraft remote sensing has become an increasingly common tool for landscape-scale estimates of canopy %N because reflectance in some portions of the spectrum has been shown to correlate strongly with field-measured %N. These patterns have been observed repeatedly over a wide range of biomes, opening new possibilities for planned Earth observation satellites. Nevertheless, the effects of spectral resolution and other sensor characteristics on %N estimates have not been fully examined, and may have implications for future analyses at landscape, regional and global scales. In this study, we explored the effects of spectral resolution, spatial resolution and sensor fidelity on relationships between forest canopy %N and reflectance measurements from airborne and satellite platforms. We conducted an exercise whereby PLS, simple and multiple regression calibrations to field-measured canopy %N for a series of forested sites were iteratively performed using (1) high resolution data from AVIRIS (Airborne Visible/Infrared Imaging Spectrometer) that were degraded spectrally from 10 nm to 30 nm, 50 nm, 70 nm, and 90 nm bandwidths, and spatially from 18 m to 30 m and 60 m pixels; (2) data representing Landsat and MODIS (Moderate Resolution Imaging Spectroradiometer) spectral bands simulated with data from AVIRIS; and (3) actual data from Landsat and MODIS. We observed virtually no reduction in the strength of relationships between %N and reflectance when using coarser bandwidths from AVIRIS, but instead saw declines with increasing spatial resolution and loss of sensor fidelity. This suggests that past efforts to examine foliar %N using broad-band sensors may have been limited as much by the latter two properties as by their coarser spectral bandwidths. We also found that regression models were driven primarily by reflectance over broad portions of the near infrared (NIR) region, with little contribution from the visible or mid infrared regions. These results suggest that much of the variability in canopy %N is related to broad reflectance properties in the NIR region, indicating promise for broad scale canopy N estimation from a variety of sensors.

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.

Partial shading of lateral branches affects growth, and foliage nitrogen- and water-use efficiencies in the conifer Cunninghamia lanceolata growing in a warm monsoon climate.

The degree to which branches are autonomous in their acclimation responses to alteration in light environment is still poorly understood. We investigated the effects of shading of the sapling crown of Cunninghamia lanceolata (Lamb.) Hook on the whole-tree and mid-crown branch growth and current-year foliage structure and physiology. Four treatments providing 0, 50, 75 and 90% shading compared with full daylight (denoted as Treatment(0), Treatment(50%), Treatment(75%) and Treatment(90%), and Shaded(0), Shaded(50%), Shaded(75%) and Shaded(90%) for the shaded branches and Sunlit(0), Sunlit(50%), Sunlit(75%) and Sunlit(90%) for the opposite sunlit branches under natural light conditions, respectively), were applied over two consecutive growing seasons. Shading treatments decreased the growth of basal stem diameter, leaf dry mass per unit leaf area, stomatal conductance, transpiration rate, the ratio of water-soluble to structural leaf nitrogen content, photosynthetic nitrogen-use efficiency and instantaneous and long-term (estimated from carbon isotope composition) water-use efficiency in shaded branches. Differences between shaded and sunlit branches increased with increasing severity and duration of shading. A non-autonomous, partly compensatory behavior of non-shaded branches was observed for most traits, thus reflecting the dependence between the traits of sunlit branches and the severity of shading of the opposite crown half. The results collectively indicated that tree growth and branch and leaf acclimation responses of C. lanceolata are not only affected by the local light environment, but also by relative within-crown light conditions. We argue that such a non-autonomous branch response to changes in light conditions can improve whole-tree resource optimization. These results contribute to better understanding of tree growth and utilization of water and nitrogen under heterogeneous light conditions within tree canopies.

Estimation of nitrogen vertical distribution by bi-directional canopy reflectance in winter wheat.

Timely measurement of vertical foliage nitrogen distribution is critical for increasing crop yield and reducing environmental impact. In this study, a novel method with partial least square regression (PLSR) and vegetation indices was developed to determine optimal models for extracting vertical foliage nitrogen distribution of winter wheat by using bi-directional reflectance distribution function (BRDF) data. The BRDF data were collected from ground-based hyperspectral reflectance measurements recorded at the Xiaotangshan Precision Agriculture Experimental Base in 2003, 2004 and 2007. The view zenith angles (1) at nadir, 40° and 50°; (2) at nadir, 30° and 40°; and (3) at nadir, 20° and 30° were selected as optical view angles to estimate foliage nitrogen density (FND) at an upper, middle and bottom layer, respectively. For each layer, three optimal PLSR analysis models with FND as a dependent variable and two vegetation indices (nitrogen reflectance index (NRI), normalized pigment chlorophyll index (NPCI) or a combination of NRI and NPCI) at corresponding angles as explanatory variables were established. The experimental results from an independent model verification demonstrated that the PLSR analysis models with the combination of NRI and NPCI as the explanatory variables were the most accurate in estimating FND for each layer. The coefficients of determination (R2) of this model between upper layer-, middle layer- and bottom layer-derived and laboratory-measured foliage nitrogen density were 0.7335, 0.7336, 0.6746, respectively.

Mass- and area-based contents in nitrogen, proteins, and chlorophyll within crowns of balsam fir (Abies balsamea) and black spruce (Picea mariana) trees located along a temperature gradient

The variation in nitrogen, insoluble and soluble proteins, and chlorophyll concentrations (mg·g−1) and contents per unit leaf area (mg·cm−2) as a function of specific leaf area (SLA) was examined in leaves sampled at the bottom, middle, and upper sections of the crowns of balsam fir (Abies balsamea) and black spruce (Picea mariana) trees located along a temperature gradient in Quebec, Canada. Differences in needle dimensions, mass, surface, and SLA among crown sections and needle age were more pronounced for balsam fir than for black spruce. Relationships of foliage nitrogen, insoluble and soluble proteins, and chlorophyll content per unit leaf area as a function of SLA were generally more significant than those based on concentration. However, the different variables varied little along a temperature gradient. The higher significance of area-based relationships in comparison with mass-based relationships was attributed to the change in leaf morphology in response to light availability within the crown. Yet, nitrogen availability most likely restricted light acclimation to changes in morphology, since there was very limited modulation of nitrogen partitioning among the different protein fractions as a function of light environment.

Isotopic composition of carbon (δ13C) and nitrogen (δ15N) in foliage and soil as a function of tree species.

Isotopic composition of carbon (δ13C) and nitrogen (δ15N) in foliage and soil as a function of tree species.

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 Timing of Paddy Field Drainage for Foliage Treatment Herbicide Spraying and Nitrogen Top-dressing on the Growth and Yield of Dry Direct Seeded Rice in Hokkaido, Japan

Effects of Timing of Paddy Field Drainage for Foliage Treatment Herbicide Spraying and Nitrogen Top-dressing on the Growth and Yield of Dry Direct Seeded Rice in Hokkaido, Japan

Which are the most important parameters for modelling carbon assimilation in boreal Norway spruce under elevated [CO2] and temperature conditions?

Photosynthesis is highly responsive to environmental and physiological variables, including phenology, foliage nitrogen (N) content, atmospheric CO2 concentration ([CO2]), irradiation (Q), air temperature (T) and vapour pressure deficit (D). Each of these responses is likely to be modified by long-term changes in climatic conditions such as rising air temperature and [CO2]. When modelling photosynthesis under climatic changes, which parameters are then most important to calibrate for future conditions? To assess this, we used measurements of shoot carbon assimilation rates and microclimate conditions collected at Flakaliden, northern Sweden. Twelve 40-year-old Norway spruce trees were enclosed in whole-tree chambers and exposed to elevated [CO2] and elevated air temperature, separately and in combination. The treatments imposed were elevated temperature, +2.8 °C in July/August and +5.6 °C in December above ambient, and [CO2] (ambient CO2 ∼370 μ mol mol(-1), elevated CO2 ∼700 μ mol mol(-1)). The relative importance of parameterization of Q, T and D responses for effects on the photosynthetic rate, expressed on a projected needle area, and the annual shoot carbon uptake was quantified using an empirical shoot photosynthesis model, which was developed and fitted to the measurements. The functional form of the response curves was established using an artificial neural network. The [CO2] treatment increased annual shoot carbon (C) uptake by 50%. Most important was effects on the light response curve, with a 67% increase in light-saturated photosynthetic rate, and a 52% increase in the initial slope of the light response curve. An interactive effect of light saturated photosynthetic rate was found with foliage N status, but no interactive effect for high temperature and high CO2. The air temperature treatment increased the annual shoot C uptake by 44%. The most important parameter was the seasonality, with an elongation of the growing season by almost 4 weeks. The temperature response curve was almost flat over much of the temperature range. A shift in temperature optimum had thus an insignificant effect on modelled annual shoot C uptake. The combined temperature and [CO2] treatment resulted in a 74% increase in annual shoot C uptake compared with ambient conditions, with no clear interactive effects on parameter values.

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.

The Effect of Latitude on Carbon, Nitrogen and Oxygen Stable Isotope Ratios in Foliage and in Nitric- oxide ions of Aerosols

Cosmic rays in the upper troposphere (9000 meters to 15000 meters) initiate the followingnuclear chemical reaction: 1n + 14N => 14C + 1H. Previous research has shown a strong effect of latitude onthe abundance of neutrons from cosmic rays. However, to date, there has been little exploration of therelationship between the latitude effect for cosmic-ray neutrons and latitudinal variations of stable isotoperatios in aerosols and foliage. In this study, aerosol samples (PM 4.5) and foliage samples were collected inSingapore in November 2009, February and July 2010 and in Fairbanks, Alaska, U.S.A. in January, April andSeptember 2010. The average value of delta 15/14N in foliage in Fairbanks was -1.84 [per mil], whereas theaverage value in Singapore was -1.3 [per mil]. These results show a clear latitude effect on delta 15/14N infoliage. Furthermore, the average value of delta 15/14N in the nitric-oxide substances in the aerosol samples in Fairbanks was -2.70 [per mil], whereas the average value in Singapore was +7.61 [per mil], demonstrating that delta 15/14N in nitric-oxide substances from aerosol samples also experiences a latitude effect. In both Singapore and Fairbanks, it was observed that values of delta 15/14N in nitric-oxide substances from aerosols were correlated with declination. The value of delta 15/14N in nitric-oxide substances from aerosols in Fairbanks increased with increasing declination due to more active conversions from 14N to 14C by neutron bombardment.