Foliar Nitrogen Concentration Research Articles

Leaf traits of Central-European beech (Fagus sylvatica) and oaks (Quercus petraea/robur): Effects of severe drought and long-term dynamics

In 2018—2020, Central-European forests suffered from extremely hot and dry summers. We used data from long-term forest monitoring of six stands of European beech (Fagus sylvatica) and two stands of oak (Quercus petraea/Q. robur) growing on different geological substrates in the climatically uniform state of Saarland (south-western Germany) for analyzing leaf traits of the period 2004—2021. We aimed at detecting overall effects of the drought on foliar morphology, nutrient concentrations, and injury, and long-term alterations in these traits. Across sites, drought resulted in a decrease in leaf size and specific leaf area (SLA) and increased fruiting in the beech and a decrease in the foliar nitrogen (N) concentrations in both tree genera. During drought, foliar calcium and manganese concentrations were lower and potassium (K) concentrations higher across the beech stands, whereas in the oak stands, drought led to a reduction in the foliar phosphorus (P) and magnesium (Mg) concentrations. High rates of anthropogenic N deposition during recent decades have resulted in high foliar N concentrations and low to deficient concentrations of P and, in the beech, of Mg. However, a significant (negative) long-term trend in leaf traits across the study sites was only found for the K concentration and necroses of the beech leaves. Foliar N correlated positively with SLA in the beech and with leaf size in the oak but was not related to herbivory. Chlorosis was the only leaf trait that, in the beech, correlated (negatively) with the climatic water balance. We conclude that even severe drought during three consecutive years does not seem to critically affect the nutrient supply to the two most important deciduous forest tree genera of Central Europe. In the beech, a decrease in leaf size and SLA might be used as an early indication of severe drought stress effects in regular monitoring programs.

Ecology of Nepenthes on Mount Talang, West Sumatra, Indonesia

AbstractGunung (Mount) Talang is an active volcano in West Sumatra that has a number of Nepenthes species, including the endemic N. talangensis, but their ecology has been little been studied. This study found five species of Nepenthes growing in the protected forest area of Gunung Talang, namely N. bongso, N. inermis, N. pectinata, N. spathulata and N. talangensis. The population of N. talangensis is very small (23 individuals) and it grows sympatrically with N. bongso and N. inermis forming natural hybrids. Lithocarpus conocarpus, Camellia lanceolata, Syzygium acuminatissimum, Adinandra dumosa and Dehaasia sp. are the five most dominant tree species found in the Nepenthes habitat, while L. conocarpus and Podocarpus neriifolius had strong positive associations with N. talangensis. Growth rates of the five Nepenthes species were not significantly different, neither were foliar nitrogen (mean = 1.14%) or phosphorus concentrations (mean = 0.11%). We suggest that N. talangensis should be considered as Critically Endangered and outline some possible conservation actions.

Fire-modulated fluctuations in nutrient availability stimulate biome-scale floristic turnover in time, and elevated species richness, in low-nutrient fynbos heathland.

In many systems, postfire vegetation recovery is characterized by temporal changes in plant species composition and richness. We attribute this to changes in resource availability with time since fire, with the magnitude of species turnover determined by the degree of resource limitation. Here, we test the hypothesis that postfire species turnover in South African fynbos heathland is powered by fire-modulated changes in nutrient availability, with the magnitude of turnover in nutrient-constrained fynbos being greater than in fertile renosterveld shrubland. We also test the hypothesis that floristic overlaps between fynbos and renosterveld are attributable to nutritional augmentation of fynbos soils immediately after fire. We use vegetation survey data from two sites on the Cape Peninsula to compare changes in species richness and composition with time since fire. Fynbos communities display a clear decline in species richness with time since fire, whereas no such decline is apparent in renosterveld. In fynbos, declining species richness is associated with declines in the richness of plant families having high foliar concentrations of nitrogen, phosphorus and potassium and possessing attributes that are nutritionally costly. In contrast, families that dominate late-succession fynbos possess adaptations for the acquisition and retention of sparse nutrients. At the family level, recently burnt fynbos is compositionally more similar to renosterveld than is mature fynbos. Our data suggest that nutritionally driven species turnover contributes significantly to fynbos community richness. We propose that the extremely low baseline fertility of fynbos soils serves to lengthen the nutritional resource axis along which species can differentiate and coexist, thereby providing the opportunity for low-nutrient extremophiles to coexist spatially with species adapted to more fertile soil. This mechanism has the potential to operate in any resource-constrained system in which episodic disturbance affects resource availability.

Spatial and Temporal Variability of Vegetation Indices with Industrial Tomato Yield

Vegetation indices indicate crop development and help identify areas with potential productivity reduction in the desired crop. Thus, this study aimed to determine the spatial and temporal influence of vegetation indices on industrial tomato (Solanum lycopersicum L.) yield. The research was conducted at Barcelos Farm in Anápolis, GO, covering a 55-hectare area. A sampling grid of 61-point pairs, spaced at 90 x 90 meters, was established using a GPS receiver. Vegetation indices were characterized by measuring the Soil Plant Analysis Development (SPAD) index, foliar nitrogen content through the Kjeldahl method, and Normalized Difference Vegetation Index (NDVI) using both a spectroradiometer and satellite imagery. Industrial tomato yield was assessed during harvest. Through the results, it was observed that temporal variability between vegetation indices and actual foliar nitrogen content exhibited a significant and positive correlation with industrial tomato productivity, particularly during the flowering stage. However, temporal variability between vegetation indices and foliar nitrogen content displayed low correlation across the mapped areas over time. Determining foliar nitrogen content and vegetation indices during the flowering stage is recommended for the industrial tomato crop. The relationship between ground-based remote sensing NDVI and orbital NDVI displayed a 55% positive correlation during the flowering stage.

Foliar Mn and Zn Treatments Improve Apple Tree Nutrition and Help to Maintain Favorable Soil pH

The foliar application of micronutrients can improve primary nutrient uptake. As a result, foliar treatments can reduce fertilizer application rates and help to maintain the natural health of soil. Here, we report on the tentative implementation of this approach in an apple orchard located in a temperate climate (JSC “Dubovoye” 52°36′57.1″ N 40°17′04.1″ E; planted in 2002 according to the 6 × 4 m or 417 trees ha–1 cultivar (cv.) Bogatyr grafted on B118 (Budagovskii 118). Manganese treatments augmented foliar nitrogen content and, in certain seasons, foliar phosphorus, whereas zinc treatments enhanced foliar potassium. Low-rate chemical fertilizers application (once in 5 years) on the background of initial high-rate organic fertilization (60 t ha–1 manure) allowed us to retain the optimal soil pH in the experimental orchard.

Long-term field translocation differentially affects arbuscular mycorrhizal and ectomycorrhizal trees in a sub-tropical forest

Arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) trees are commonly represented in tropical forests, but their response to warming is generally not known. We conducted a long-term (9-year) field experiment in subtropical China by translocating AM tree species (Machilus breviflora and Schima superba) and EcM tree species (Syzygium rehderianum and Castanopsis hystrix) from a cooler high-elevation site (300 m) to a 1 °C warmer low-elevation site (30 m). Here, we report leaf chemical and physiological data from the last three years (Years 7–9) of the translocation experiment. Translocation to warmer site induced higher air (Tair) and soil (Tsoil) temperatures, but lower soil volumetric water content (SVWC). Translocation treatment significantly increased the light-saturated photosynthetic rate (Asat) for AM trees due to higher stomatal conductance (gs) and Rubisco carboxylation capacity (Vcmax), generating increased growth in AM trees. Translocation treatment reduced the maximum efficiency of photosynthetic quantum yield (Fv/Fm) and growth in EcM trees. Translocation treatment increased leaf turgor loss point (TLP) in AM trees, but reduced TLP in EcM trees. Translocation treatment increased foliar nitrogen (N) concentrations and phosphorus (P) concentrations for AM trees. In EcM trees, stable foliar N and P concentrations were related to higher N and P resorption efficiencies. Translocation treatment was more beneficial for the growth of AM trees than EcM trees, while EcM trees were more tolerant of soil water deficit. Differential responses to these co-occurring climate drivers may alter the composition of tree functional groups and ecosystem function in tropical forests in response to future warmer and drier climate conditions.

Silicon supplementation and jasmonate activation synergistically increase phenolic defences against a legume herbivore

Abstract The accumulation of silicon (Si) is widely reported to have anti‐herbivore defensive properties in grasses. There is emerging, but fragmentary, evidence that Si could play a similar role in legumes. Here, we sought to understand the effects of Si supplementation on anti‐herbivore defensive properties in lucerne (Medicago sativa), especially in relation to other potential defences (i.e. phenolics) and the phytohormone that regulates anti‐herbivore defences, jasmonic acid or jasmonate (JA), which is also linked to Si accumulation. We determined how growth, root nodulation and chemistry (carbon, nitrogen and phenolic concentrations) of four genotypes of lucerne responded to Si supplementation, with and without the application of JA, and we used feeding assays to determine the subsequent effects on the feeding success of adult Sitona discoideus weevils. Si supplementation increased plant mass and root nodulation of M. sativa by 61% and 227%, respectively, and reduced relative consumption (RC) and frass production by S. discoideus by 38% and 30% respectively. Si supplementation had no effect on foliar nitrogen concentrations, most likely due to the dilution effects of increased plant growth and foliar carbon. Phenolic concentrations were negatively correlated with leaf RC; RC also decreased by 34% when JA was applied to plants. When Si was combined with JA application, phenolics were significantly enhanced, demonstrating the potential to stimulate multiple anti‐herbivore properties in M. sativa. Overall, the Si‐ and JA‐induced phytochemical and herbivore feeding responses were consistent between the four lucerne genotypes tested. Synthesis. The novel findings suggest that Si accumulation may play a more important role in legume resistance to herbivorous animals than previously thought. The ubiquity of soil Si and its emerging functional role in plant biology, including plant–animal interactions, suggest that these patterns could be common among legumes.

Spatial Distribution of Leymus chinensis Is Not Determined by Its Ecological Stoichiometry

Leymus chinensis is a widely distributed species of Eurasian grasslands that is well adapted to a range of environmental conditions. In this study, we measured soil and plant chemical elements to examine the basis of the ecological adaptations of L. chinensis to temperate steppe. We sampled leaves of L. chinensis and soil layers at different latitudes in temperate steppe for three consecutive years from 2012 to 2014. One-way analysis of variance and linear regression were used to analyze the variation in foliar nitrogen (N) and phosphorus (P) contents and the N:P ratio in L. chinensis. The correlations between the foliar N:P ratio and the variation in soil total nitrogen (TN) and total P contents with latitudinal gradient were measured to explore the homeostasis stoichiometry of foliar N and P in L. chinensis. With increasing latitude, both the foliar N and P contents of L. chinensis showed parabolic trends with significant negative correlations. The population of L. chinensis was limited by N, and the soil TN content showed a significant increasing trend with the increase in the foliar N:P ratio. The variation in the foliar N:P ratio of L. chinensis was determined through the variation in the soil N content. In different latitude intervals, the foliar N, P, and N:P ratio of L. chinensis showed absolute stability and strong internal stability, and the values of HN:P were high and similar in different latitudes. In conclusion, the population of L. chinensis in the temperate steppe is highly adaptable; and, thus, can maintain a dominant position in the variable environment and has a wide distribution range.

Hyperspectral Imaging of Adaxial and Abaxial Leaf Surfaces for Rapid Assessment of Foliar Nutrient Concentrations in Hass Avocado

Rapid assessment tools are required for monitoring crop nutrient status and managing fertiliser applications in real time. Hyperspectral imaging has emerged as a promising assessment tool to manage crop nutrition. This study aimed to determine the potential of hyperspectral imaging for predicting foliar nutrient concentrations in avocado trees and establish whether imaging different sides of the leaves affects prediction accuracy. Hyperspectral images (400–1000 nm) were taken of both surfaces of leaves collected from Hass avocado trees 0, 6, 10 and 28 weeks after peak anthesis. Partial least squares regression (PLSR) models were developed to predict mineral nutrient concentrations using images from (a) abaxial surfaces, (b) adaxial surfaces and (c) combined images of both leaf surfaces. Modelling successfully predicted foliar nitrogen (RP2 = 0.60, RPD = 1.61), phosphorus (RP2 = 0.71, RPD = 1.90), aluminium (RP2 = 0.88, RPD = 2.91), boron (RP2 = 0.63, RPD = 1.67), calcium (RP2 = 0.88, RPD = 2.86), copper (RP2 = 0.86, RPD = 2.76), iron (RP2 = 0.81, RPD = 2.34), magnesium (RP2 = 0.87, RPD = 2.81), manganese (RP2 = 0.87, RPD = 2.76) and zinc (RP2 = 0.79, RPD = 2.21) concentrations from either the abaxial or adaxial surface. Foliar potassium concentrations were predicted successfully only from the adaxial surface (RP2 = 0.56, RPD = 1.54). Foliar sodium concentrations were predicted successfully (RP2 = 0.59, RPD = 1.58) only from the combined images of both surfaces. In conclusion, hyperspectral imaging showed great potential as a rapid assessment tool for monitoring the crop nutrition status of avocado trees, with adaxial surfaces being the most useful for predicting foliar nutrient concentrations.

Beneficial Microorganisms Affect Soil Microbiological Activity and Corn Yield under Deficit Irrigation

Water scarcity is one of the main factors that decrease the growth and productivity of corn, since it negatively affects gas exchange and the general metabolism of the crop. The use of beneficial microorganisms (BM) has been considered a potential attenuator of water stress. This study aimed to evaluate the effect of BM and water deficit on growth, gas exchange, grain yield, and soil microbial activity. A field experiment was carried out, in which the treatments were composed of a 2 × 4 factorial scheme, corresponding to two irrigation levels (100% of ETc and 50% of ETc) and to four treatments (T) referring to the soil inoculation with BM (C: control; T1: Bacillus amyloliquefaciens + Azospirillum brasiliense; T2: B. subtilis; and T3: A. brasiliense). The evaluations were carried out in the flowering phase (plant growth, gas exchange, and foliar nitrogen content) and at the end of the plant cycle (grains yield, mineral nitrogen, and microbiological activity). The 50% reduction in irrigation depth severely restricted corn growth and gas exchange and decreased the grain yield by 38%. The water deficit increased the protein content in the grains and the concentration of mineral nitrogen in the soil when the plants were inoculated with BM. Under water stress, inoculation with BM increased corn productivity by 35% and increased soil microbial activity. The inoculation of plants with BM, either in combination (Bacillus amyloliquefaciens + A. brasiliense) or alone (B. subtilis), attenuated the adverse effects of water deficit in maize.

Co-planting of a fast-growing, nitrogen-fixing host tree facilitates regeneration of the root hemiparasitic ‘iliahi (Hawaiian sandalwood)

Root hemiparasitic trees can photosynthesize yet also acquire resources from host plants, which may benefit the long-term survival and growth of the hemiparasite. Experimental evaluation of planting distance between tree hemiparasites and their hosts can lead to biological insights and contribute to practitioner decision making. On an abandoned pasture site in a historically tropical dry forest in Hawai‘i, we studied the effects of two host species and four planting distances on the survival and growth of ‘iliahi (Hawaiian sandalwood, Santalum paniculatum), an endemic root hemiparasitic tree. Treatments included a control with no host or one of two native host species: ‘aʻaliʻi (Dodonaea viscosa), a fast-growing shrub, or koa (Acacia koa), a fast-growing nitrogen-fixing tree. ‘Iliahi and host seedlings were planted at a distance of <0.2, 0.5, 1.0, or 2.0 m from each other. After three years, survival of ‘iliahi seedlings was greatest for ‘iliahi paired with koa at 1.0 m (88 %) compared to the control with no host (53 %) and when paired with koa at 2.0 m (55 %). Height and ground line diameter of ‘iliahi seedlings were greater when paired with koa at closer distances than with ‘aʻaliʻi at any distance or the control with no host. Specifically, ʻiliahi growth was greatest when paired with koa at <0.2 m distance. Foliar nitrogen concentration was greater for ‘iliahi paired with koa at <0.2, 0.5, and 1.0 m distances, whereas the other foliar nutrient concentrations were typically greater for the ‘iliahi control with no host. For sites with few or no pre-established hosts, such as abandoned pastures, ‘iliahi growth can be greatly improved by co-planting in proximity to koa. As with other Santalum spp., early and abundant parasitic root connections with a host, especially a nitrogen-fixing host, are likely important for ‘iliahi establishment and early growth.

Investigating Foliar Macro- and Micronutrient Variation with Chlorophyll Fluorescence and Reflectance Measurements at the Leaf and Canopy Scales in Potato

Vegetation indices (VIs) related to plant greenness have been studied extensively for the remote detection of foliar nitrogen content. Yet, the potential of chlorophyll fluorescence (ChlF) and photoprotection-based indices such as the photochemical reflectance index (PRI) or the chlorophyll/carotenoid index (CCI) for the detection of a wide range of nutrients remains elusive. We measured the dynamics of foliar macro- and micronutrient contents in potato plants as affected by fertilization and water stress, along with leaf and canopy level observations of spectral reflectance and ChlF (or solar-induced fluorescence). ChlF and photoprotection-related indices were more strongly related to a wide range of foliar nutrient contents compared to greenness-based indices. At the leaf level, relationships were largely mediated by foliar chlorophyll contents (Cab) and leaf morphology, which resulted in two contrasting groupings: a group dominated by macronutrients N, P, K, and Mg that decreased during canopy development and was positively correlated with Cab, and a group including Cu, Mn, Zn, and S that increased and was negatively related to Cab. At the canopy-level, spectral indices were additionally influenced by canopy structure, and so their capacity to detect foliar nutrient contents depends on the spatiotemporal covariation between foliar Cab, morphology, and canopy structure within the observations.

Response of Forest Ecosystems to Decreasing Atmospheric Nitrogen Deposition

Nitrogen deposition has serious consequences to global change. Excessive nitrogen deposition leads to nitrogen saturation in forests, resulting in soil acidification, nitrate leaching, an increase in nitrous oxide emissions, and a decrease in plant species diversity and vegetation productivity. Under the reduction of atmospheric nitrogen deposition in Europe, North America, and China, summarizing the response of forests to decreasing nitrogen deposition can not only improve the knowledge framework of the impact of nitrogen deposition on forests, but also evaluate the effects of emission abatement actions, as well as provide scientific basis for future air pollution control. This study reviewed the response of soil, surface water, nitrogen cycle, and vegetation of temperate forests in Europe and North America and subtropical forests in southwest China to the reduction in atmospheric nitrogen pollution gases and thus nitrogen deposition. The soil water nitrogen concentration responded rapidly to the nitrogen deposition reduction, although the trend was inconsistent. The soil acidification and nitrogen cycles showed a delayed response of recovery from high nitrogen deposition. The nitrogen mineralization and immobilization, soil carbon retention, and net primary production might take decades to respond to the nitrogen deposition reduction. However, the soil inorganic nitrogen pool and nitrogen leaching decreased with the decline in nitrogen deposition, although a one-or two-year lag existed. The surface water nitrogen concentration was closely related to nitrogen status in forests. After the nitrogen deposition decreased, the nitrogen leaching and thus the surface water nitrogen concentration decreased in the areas with historically high nitrogen deposition. However, the low surface water nitrogen concentration in the nitrogen-limited forests was not significantly affected by the nitrogen deposition changes. The recovery of surface water acidification was affected by soil sulfur desorption/mineralization and nitrification/denitrification. The foliar nitrogen concentration decreased with the decline in nitrogen deposition. The nitrogen-saturated forests and regional surface water in southwest China showed a recovery trend from high nitrogen deposition, as a consequence of the implementation of the Total Emissions Control of Air Pollutants and later the Action Plan of Air Pollution Prevention and Control.

Developing Integrated Strategies to Address Emerging Weed Management Challenges in Christmas Tree Production

Weed control is an important aspect during the first few years of Christmas tree establishment, as weed competition directly relates to the rate of Christmas tree growth during this time. The objectives of this study were to evaluate the weed control efficacy of organic mulch and herbicide combinations and to determine their phytotoxic effects on four different species of Christmas trees during the establishment stage: Fraser fir (Abies fraseri (Pursh) Poir), blue spruce (Picea pungens Engelm.), white pine (Pinus strobus L.), and Scotch pine (Pinus sylvestris L.). Twelve weed control treatments were established in a complete randomized block design with four replications in each of five fields. Weed control treatments included cypress bark organic mulch and herbicides applied alone and in combinations as well as an untreated control. Herbicides included clopyralid, oxyfluorfen, and glyphosate. All herbicides were applied at their highest labeled rate. Data collection included visual estimations of weed control and phytotoxicity to trees at 30, 60, and 90 days after treatment (DAT). Tree growth and foliar nitrogen concentration were also measured. Mulch combined with herbicide provided 60%–100% weed control in all cases; at two farms, mulch provided a significant increase in weed control when compared to the same treatments without mulch. Combinations of mulch + clopyralid + glyphosate and clopyralid + oxyfluorfen + glyphosate resulted in the highest phytotoxicity ratings. Tree growth was decreased due to some treatments at Gobles farm, and foliar N did not differ among any of the treatments.

Correlation of the Foliar Nitrogen Content with Yield and Grain Protein Accumulation in Pearl Millet

Correlation of the Foliar Nitrogen Content with Yield and Grain Protein Accumulation in Pearl Millet

An omnivore vigour hypothesis? Nutrient availability strengthens herbivore suppression by omnivores across 48 field sites.

Nutrients regulate herbivore growth from the 'bottom-up' via improved plant vigour and food quality. Nitrogen also affects 'top-down' control of herbivores by moderating attraction of predators and the rates at which they consume herbivorous prey. Tri-trophic consequences of nitrogen availability are more challenging to predict among omnivorous natural enemies who feed on both plants and herbivores, limiting our ability to predict net outcomes of nutrient availability in food webs. In a two-year field survey of insects on zucchini host plants at 48 sites, I predicted that both herbivores and foliar-feeding omnivores would increase with nutrient availability, while predators would not. My results revealed positive relationships between omnivores and foliar nitrogen concentrations, while predators had neutral responses to foliar N. Surprisingly, herbivores declined with increasing foliar N across the field sites. Greenhouse experiments re-enforced these patterns, as herbivore growth inversely correlated with soil N concentrations in communities that included foliar-feeding omnivores. Conversely, herbivore growth was uncorrelated with soil N on plants with predators, nor on predator-free plants. These results suggest that omnivores mount strong and consistent responses to nitrogen in plant tissues in a variety of ecological contexts. In environments where omnivorous arthropods can thrive, their recruitment to nitrogen-rich plants may increase predation and thereby counterbalance and stabilize 'bottom-up' increases in herbivore performance supported by enhanced foliar nutrition.

Hyperspectral Imaging of Adaxial and Abaxial Leaf Surfaces as a Predictor of Macadamia Crop Nutrition.

Tree crop yield is highly dependent on fertiliser inputs, which are often guided by the assessment of foliar nutrient levels. Traditional methods for nutrient analysis are time-consuming but hyperspectral imaging has potential for rapid nutrient assessment. Hyperspectral imaging has generally been performed using the adaxial surface of leaves although the predictive performance of spectral data has rarely been compared between adaxial and abaxial surfaces of tree leaves. We aimed to evaluate the capacity of laboratory-based hyperspectral imaging (400-1000 nm wavelengths) to predict the nutrient concentrations in macadamia leaves. We also aimed to compare the prediction accuracy from adaxial and abaxial leaf surfaces. We sampled leaves from 30 macadamia trees at 0, 6, 10 and 26 weeks after flowering and captured hyperspectral images of their adaxial and abaxial surfaces. Partial least squares regression (PLSR) models were developed to predict foliar nutrient concentrations. Coefficients of determination (R2P) and ratios of prediction to deviation (RPDs) were used to evaluate prediction accuracy. The models reliably predicted foliar nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), copper (Cu), manganese (Mn), sulphur (S) and zinc (Zn) concentrations. The best-fit models generally predicted nutrient concentrations from spectral data of the adaxial surface (e.g., N: R2P = 0.55, RPD = 1.52; P: R2P = 0.77, RPD = 2.11; K: R2P = 0.77, RPD = 2.12; Ca: R2P = 0.75, RPD = 2.04). Hyperspectral imaging showed great potential for predicting nutrient status. Rapid nutrient assessment through hyperspectral imaging could aid growers to increase orchard productivity by managing fertiliser inputs in a more-timely fashion.

Bioplastic (PHBV) addition to soil alters microbial community structure and negatively affects plant-microbial metabolic functioning in maize

Microplastic contamination poses a significant threat to agroecosystem functioning, provoking a move away from the use of conventional oil-based plastics in agriculture, to biodegradable alternatives that may be degraded over a shorter timescale. The impact of these bioplastics on plant and soil health, however, has received relatively little attention. Here, we investigated the effect of soil loading (0.01%, 0.1%, 1% and 10%) of biobased microplastic poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) on soil and plant ( Zea mays L.) health and function. We showed that PHBV caused a dose-dependent reduction in plant growth and foliar nitrogen (N) content while untargeted metabolite analysis revealed significant shifts in foliar metabolic function. These results were also reflected in soil, where PHBV led to reduced plant availability of both ammonium and nitrate. Soil 14 C-isotope tracing and 16 S metabarcoding revealed that PHBV supressed microbial activity, reduced bacterial diversity and shifted microbial community structure, inducing a major shift in soil metabolic pathways, and thus functioning. Overall, our data suggests that the bioplastic PHBV is not environmentally benign and that contamination levels as low as 0.01% (0.01 mg kg -1 ) can induce significant short-term changes in both plant and soil microbial functioning, with potential implications for long term agroecosystem health. • Effect of biopolymer PHBV microplastic on soil and plant health was investigated • PHBV addition caused a dose-dependent negative effect on soil and plant health • PHBV addition altered foliar metabolism and reduced plant growth and foliar N • PHBV reduced soil microbial activity and changed the bacterial community structure • Bioplastics may not be environmentally benign

Whole-tree dormant season nitrogen pools for different species receiving combinations of fertilization and irrigation after one short rotation

Our understanding of the accretion and distribution of tree tissue nitrogen (N) pools across a variety of species and genotypes suitable for short-rotation woody crop (SRWC) production in response to water and N availability remains limited. We measured dormant-season, rotation-length, whole-tree N pools for five tree genotypes from four species (two eastern cottonwood, Populus deltoides Bartr., genotypes; American sycamore, Platanus occidentalis L.; American sweetgum, Liquidambar styraciflua L.; and loblolly pine, Pinus taeda L.) receiving irrigation (I), fertilization (F), their combination (IF), or no resources manipulation (C). Our results demonstrate that foliar nitrogen concentration [N] responded to fertilization but was constrained within genotype-specific ranges and varied temporally. Tree genotypes differed in their composite and component tissue N content (NC), and these differences mostly reflected tissue mass (i.e., larger components and trees resulted in higher NC). Resource amendments (I, F, IF) resulted in up to 3.8-fold increases in NC compared with C, which were most pronounced for sycamore and sweetgum with F and IF treatments, respectively. By the end of the rotation, forest stands accumulated 73 to 452 kg N ha−1 in tree tissues with 40 – 78 % distributed aboveground and 22 – 60 % distributed belowground. A critical difference between genotypes was that all hardwoods exhibited larger belowground N distributions than the evergreen conifer. Our results stress the importance of belowground N pools and highlight differences among genotypes. Our study underscores valuable information about N pools across genotypes suitable for SRWC production, which can be leveraged to inform fertilization plans and devise sustainable nutrient management as production expands across marginal lands.

Will the grass be greener on the other side of climate change? (with corrigendum)

Increasing atmospheric [CO2] is stimulating photosynthesis and plant production, increasing the demand for nitrogen relative to soil supply with declining global foliar nitrogen concentrations as a consequence. The effects of such oligotrophication on the forage quality of sweetveld, mixed veld, and sourveld grasslands in South Africa, which support livestock production and native ungulates, are unknown. Soil characteristics and the herbage quality of an abundant grass are described from baseline historical (mid- 1980s) data collected across a sweet-mixed-sour grassland gradient in KwaZulu-Natal. Sourveld occurred on the most acidic, dystrophic soils and exhibited a pronounced decline in leaf nitrogen, digestibility, and other macronutrients during winter, in sharp contrast to sweetveld, on nutrient-rich soils, where forage quality varied little seasonally. In a carbon-enriched, warmer, and most likely drier future climate, we predict that forage quality will not be substantially altered in sweetveld where soil nutrients and temperature are not limiting but that sourveld could become ‘sourer’ because soil nutrients will be inadequate to match higher plant production promoted by elevated [CO2] and warmer and longer growing seasons. Reassessing historical data and seasonal and spatial monitoring of forage quality will enable assessment of past and future impacts of climate change on grassland forage quality. Significance: Grassland forage quality will likely decline with elevated [CO2] and warming, particularly in sourveld. Climate change could deepen and widen the sourveld winter forage bottleneck, necessitating greater supplementary feeding of livestock.