Increased Nitrogen Availability Research Articles

Increased Nitrogen Availability in the Soil Under Mature Picea abies Trees Exposed to Elevated CO2 Concentrations

The response of trees to increasing atmospheric CO2 concentrations is often mediated by the availability of nutrients. However, little is known about the influence of CO2 enrichment on nutrient availability in forests with mature trees. We studied processes in the soil under five 35-m-tall Norway spruce trees (Picea abies) in NW Switzerland that were exposed to a mean CO2 concentration of 550 ppm for 5 growing seasons using free air CO2 enrichment (FACE). We compared them with values from the soil under five control trees. Ceramic suction cups were installed in the soil under each tree to collect soil solution, and ion-exchange resin bags were buried in the soil to absorb ammonium and nitrate. Soil cores taken at the end of the experiment were used to measure the gross production of ammonium and nitrate by the 15N dilution technique. Although temporally and spatially variable, the nitrate concentration was higher in the soil solution under CO2-enriched trees. This effect was reflected in the resin bag extracts, which additionally indicated a trend of increased ammonium availability. Dissolved reduced N concentration (mainly dissolved organic N), however, was lower in the soil solution under CO2-enriched trees. K and Mg, and to a lesser extent Na and sulfate concentrations increased in the soil solution. P concentrations mostly remained below the detection limit. In spite of the higher concentrations of nitrate in soil extracts, gross N mineralization and nitrification rates were not affected by FACE. Needles from CO2-enriched trees contained slightly more N. No difference was observed for other nutrients. Overall, these results support the hypothesis of a priming effect, i. e. that FACE led to the production of more root exudates, which in turn stimulated soil biological activity, including mineralisation, over a time-span of at least several years. However, these tall trees showed no growth response to elevated CO2; hence, they gained no advantage from increased nitrate in the soil solution, presumably owing to other growth constraints including P and Mg availability.

Nitrogen effect on gas exchange characteristics, dry matter production and nitrate accumulation of Amaranthus cruentus L.

Among the mineral nutrients, nitrogen stands out as an essential constituent of amino acids, nucleic acids and proteins, as well as being part of the photosynthetic apparatus. The present study aimed to evaluate the responses of Amaranthus cruentus L. cv. BRS Alegria to nitrogen availability in terms of biomass production, photosynthetic characteristics, content of photosynthetic pigments, total nitrogen, ammonium and nitrate in the leaves. Plants of A. cruentus were cultivated in plastic pots filled with vermiculite and kept in a greenhouse under natural photo-periodic conditions. The plants were watered with 70% of full strength nitrogen-free Long Ashton solution, containing 1.97, 4.94 or 9.88 kg N ha−1 as ammonium nitrate, three times a week. Increased nitrogen availability resulted in higher shoot dry matter, specific leaf mass, total leaf nitrogen, chlorophyll and carotenoids as well as in higher photosynthetic rates. There was a positive correlation between photosynthesis and leaf nitrogen. Higher nitrogen availability resulted in greater stomatal conductance and transpiration, but the CO2 concentration in the sub-stomatal cavity was not significantly altered. In addition, an increase in ammonium and nitrate content of leaves was observed. The nitrate content reached 176, 193 and 288 mg kg−1 of dry matter in low, medium and high nitrogen supply, respectively. The data show that A. cruentus plants are sensitive to changes in nitrogen availability during the vegetative phase. The limitation of photosynthesis under conditions of low nitrogen supply cannot be fully explained by the reduction in stomatal conductance; non-stomatic limitations are also involved. In addition, the maximum nitrate content observed in leaves was far below the risk level for human health.

Coating of sepiolite-chitosan nanocomposites onto urea increases nitrogen availability and its use efficiency in maize

ABSTRACTTo improve the use efficiency of fertilizer and to reduce the rate of nitrogen release, a coated urea was prepared using clay-polymer nanocomposites (CPU). Sepiolite and chitosan were used to form nanocomposites with different clay mineral/polymer ratios. The nanocomposites and CPUs were characterized using several techniques including Fourier Transform Infrared (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Brunauer-Emmett-Teller (BET) specific surface area measurement. The FTIR examination revealed functional groups related to chitosan that interacted with sepiolite. The nitrogen release of CPUs was examined in the sand column showing that 75% of nitrogen content of CPU samples released in about 25 d, much longer than that of urea (3 d) and the rate of release of nitrogen was reduced by increasing the proportion of sepiolite in the clay/polymer nanocomposites. The release mechanism of CPUs was evaluated and the results showed the mechanism was not Fickian diffusion but anomalous diffusion. The nutrient use efficiency of CPUs was studied under greenhouse conditions using Zea mays (corn) as the test plant and a significant efficiency improvement was observed. The results showed that the CPUs with slow-release properties could be considered as efficient N fertilizers in agricultural and horticultural applications.

A pH shift induces high-titer liamocin production in Aureobasidium pullulans.

Liamocins are biosurfactants produced by the fungus Aureobasidium pullulans. A. pullulans belongs to the black yeasts and is known for its ability to produce pullulan and melanin. However, the production of liamocins has not been investigated intensively. Initially, HPLC methods for the quantification of liamocin and the identification of liamocin congeners were established. Eleven congeners could be detected, differing in the polyol head groups arabitol or mannitol. In addition, headless molecules, so-called exophilins, were also identified. The HPLC method reported here allows quick and reliable quantification of all identified congeners, an often-overlooked prerequisite for the investigation of valuable product formation. Liamocin synthesis was optimized during cultivation in lab-scale fermenters. While the pH can be kept constant, the best strategy for liamocin synthesis consists of a growth phase at neutral pH and a subsequent production phase induced by a manual pH shift to pH 3.5. Finally, combining increased nitrogen availability with a pulsed fed-batch fermentation, cell growth, and liamocin titers could be enhanced. Here, the maximal titers of above 10 g/L that were reached are the highest reported to date for liamocin synthesis using A. pullulans in lab-scale fermenters.

Green manure and phosphorus fertilization affect weed community composition and crop/weed competition in organic maize

AbstractGreen manure and compost-enriched in phosphorus can promote the sustainability of cropping systems by increasing soil fertility over the long term. They can also be used to manage crop/weed interactions, a key element in guaranteeing an appropriate level of satisfactory crop yields. We studied how green manuring with hairy vetch (Vicia villosaRoth.) and the application of different types of phosphorous-enriched compost affect weed/maize (Zea maysL.) interactions in an organic stockless Mediterranean agroecosystem for two consecutive dry years. Green manure stimulated the expression of maize traits related to a higher competitive ability against weeds, such as early growth, height and leaf area index, while the effect of compost was less clear. Regarding crop/weed competition, both green manuring and a phosphorus-enriched compost application gave a significant advantage to maize. Neither green manure nor compost increased total weed density and biomass compared to the control. Green manuring significantly affected the weed community composition. The relative density of ruderal and competitive-ruderal species (according to Grime's classification) was higher in plots where the green manure was applied. The use of green manure, together with novel composting techniques, significantly affected crop/weed competitive interactions, favoring maize, but also creating favorable conditions for unwanted weed species such as competitive-ruderals. Increasing nitrogen availability in the early growth stages of maize through green manuring can increase crop competitive ability. However, this may not suffice to preserve the system from future weed problems, should potentially detrimental species be selected. Dedicated strategies for the control of emerging weed species may thus be needed.

Effect of rice straw on chemical properties and heavy metals residues in the bottom sediment of fish pond

The neuromuscular and cardiovascular effects of three different doses of pipecuronium were studied in 60 adult patients. Neuromuscular blockade was measured using electromyographic activity of the adductor pollicis muscle after supramaximal stimulation of the ulnar nerve at 0.1 Hz and 2 Hz. Three subgroups (A, B, C) of 20 patients received pipecuronium doses of 60, 80 and 100 micrograms kg-1, respectively, as an intubating dose and, when necessary, maintenance doses were administered at 25% single twitch recovery in a dose of one-quarter of the initial one. The onset time was 5.4 +/- 2.0 min for 60 micrograms kg-1 and similar for 80 and 100 micrograms kg-1 (3.9 +/- 1.1 and 3.6 +/- 1.1 min). The duration of action was 45 +/- 10 min for 60 micrograms kg-1, 74 +/- 25 and 94 +/- 21 for 80 and 100 micrograms kg-1, respectively. The recovery indices were measured in all patients after neostigmine administration (Groups B and C) and after neostigmine and edrophonium (Subgroup A, 10 patients each). TOF ratio was significant only 2 min after edrophonium administration in Group A patients. Variations of heart rate and blood pressure were not significant.

Leaf temperatures mediate alpine plant communities' response to a simulated extended summer.

We use a quantitative model of photosynthesis to explore leaf‐level limitations to plant growth in an alpine tundra ecosystem that is expected to have longer, warmer, and drier growing seasons. The model is parameterized with abiotic and leaf trait data that is characteristic of two dominant plant communities in the alpine tundra and specifically at the Niwot Ridge Long Term Ecological Research Site: the dry and wet meadows. Model results produce realistic estimates of photosynthesis, nitrogen‐use efficiency, water‐use efficiency, and other gas exchange processes in the alpine tundra. Model simulations suggest that dry and wet meadow plant species do not significantly respond to changes in the volumetric soil moisture content but are sensitive to variation in foliar nitrogen content. In addition, model simulations indicate that dry and wet meadow species have different maximum rates of assimilation (normalized for leaf nitrogen content) because of differences in leaf temperature. These differences arise from the interaction of plant height and the abiotic environment characteristic of each plant community. The leaf temperature of dry meadow species is higher than wet meadow species and close to the optimal temperature for photosynthesis under current conditions. As a result, 2°C higher air temperatures in the future will likely lead to declines in dry meadow species’ carbon assimilation. On the other hand, a longer and warmer growing season could increase nitrogen availability and assimilation rates in both plant communities. Nonetheless, a temperature increase of 4°C may lower rates of assimilation in both dry and wet meadow plant communities because of higher, and suboptimal, leaf temperatures.

Multiple strategies for heat adaptation to prevent chalkiness in the rice endosperm.

Heat-induced chalkiness of rice grains is a major concern for rice production, particularly with respect to climate change. Although the formation of chalkiness in the endosperm is suppressed by nitrogen, little is known about the cell-specific dynamics of this process. Here, using picolitre pressure-probe electrospray-ionization mass spectrometry together with transmission electron microscopy and turgor measurements, we examine heat-induced chalkiness in single endosperm cells of intact rice seeds produced under controlled environmental conditions. Exposure to heat stress decreased turgor pressure and increased the cytosolic accumulation of sugars, glutathione, and amino acids, particularly cysteine. Heat stress also led to a significant enlargement of the protein storage vacuoles but with little accumulation of storage proteins. Crucially, this heat-induced partial arrest of amyloplast development led to formation of chalkiness. Whilst increased nitrogen availability also resulted in increased accumulation of amino acids, there was no decrease in turgor pressure. The heat-induced accumulation of cysteine and glutathione was much less marked in the presence of nitrogen, and storage proteins were produced without chalkiness. These data provide important information on the cell dynamics of heat acclimation that underpin the formation of chalkiness in the rice endosperm. We conclude that rice seeds employ multiple strategies to mitigate the adverse effects of heat stress in a manner that is dependent on nitrogen availability, and that the regulation of protein synthesis may play a crucial role in optimizing organelle compartmentation during heat adaption.

Museum Collections Yield Information on Nitrogen Sources for Coastal Gulf of Mexico, North Carolina, and Caribbean Sea Invertebrates, 1850 to 2004

Aconsequence of land-use change and increasing human population in the United States and Central America has been an increase in nitrogen availability to coastal systems. Whereas many studies evaluate the influence of anthropogenically derived nutrients in modern oceans, fewer studies evaluate nutrient sources in coastal environments before the 1960s. This study used stable C and N isotope values of 35 big-claw snapping shrimps (Alpheus heterochaelis) and 48 ivory barnacles (Balanus eburneus) across the Gulf of Mexico, southeast coast of the United States, and the Caribbean over 121 y to examine whether human-derived nitrogen was used by coastal invertebrates. Gulf of Mexico and southeast U.S. collections were divided into preand post-1960 groups for analysis, roughly coinciding with the increase in fertilizer use associated with the “Green Revolution” and large coastal population increases. For B. eburneus, δ15N decreased in the coastal United States after 1960, but that was not the case for A. heterochaelis. 15N-depleted fertilizer would be quickly incorporated by filter-feeding B. eburneus (via plankton). By contrast, the scavenging, omnivorous, A. heterochaelis would obtain more N from heterotrophic organic matter more isolated from the 15N-depleted fertilizer signal. The Caribbean A. heterochaelis incorporated seagrass C and N. Local variation in N sources from the different collection areas was clearly observed. Although anthropogenic N has been making its way into the filter-feeding barnacles, it is not as apparent in the scavengers.

The fate of monsoonal atmospheric nitrate deposition in two forest catchments in Soyang lake watershed, South Korea: a mass balance and stable isotope approach

Over 60% of South Korea is covered by forests. Nitrate deposition plays an important role as nitrogen source in these forests. Nitrate input from deposition increases nitrogen availability leading initially to increases in productivity. However, later forests may become nitrogen saturated with nitrate leaching, denitrification and forest decline. Using a mass balance approach, we compared the atmospheric nitrate input and output by stream runoff in two forest sub-catchments, a deciduous and a mixed catchment, within the Soyang lake watershed, the main drinking water reservoir for the 20-million-person metropolis Seoul. A dual stable isotope approach was used to identify the origin of nitrate in stream discharge of the two sub-catchments. Extremely different monsoon seasons in 2013 and 2014 drove the nitrate discharge. Total nitrate-N export was closely related with rainfall events and intensities. Nitrate-N discharge at the deciduous forest was lower than nitrate-N deposition, thus sink conditions prevailed. Nitrate-N discharge at the mixed forest was consistently higher. During the heavy monsoon season of 2013 the mixed forest turned from a sink for atmospheric nitrate towards a source, i.e. nitrate amounts in the discharge were higher than atmospheric inputs. Nitrate isotopic compositions of stream water from both forests revealed soil nitrification as main nitrate source. However, under conditions of heavy monsoon rainfall direct runoff of atmospheric deposition nitrate was identified in the mixed forest. Lower nitrate assimilation capacities of conifers compared to broadleaf trees are probably the driver for a lower nitrate retention capacity making coniferous forests more prone to nitrate leaching.

Catchment soils supply ammonium to the coastal zone - Flood impacts on nutrient flux in estuaries

Erosion of soil from catchments during floods can deliver large quantities of sediment to the coastal zone. The transformations and processes of nutrient release from catchment soils during flooding are not well understood. To test the hypothesis that catchment soils supply nutrients to the coastal zone, we examined nutrient release and transformation following wetting of soils formed from three distinct rock types (basalt, granite and sandstone) with fresh and marine water. The soil samples were collected from eroding areas of a subtropical river catchment. We simulated runoff, transport and deposition by tumbling the fine fraction of the soils in freshwater for three days and settling in seawater for four weeks. We also collected and incubated cores from an adjacent coastal bay and added a layer of catchment soil to simulate deposition of new sediment following flood plume settling. Dissolved nutrients were measured in both simulations. Basalt soils were relatively nutrient rich and released substantial quantities of organic and inorganic dissolved nutrients, particularly phosphate. However when soils were added to estuarine sediment cores and incubated, there was a net influx of phosphate from the overlying water. All soils continually released ammonium in both experiments, indicating that catchment soils may be an important source of ammonium to fuel productivity within the coastal zone. This study provides new insights into increased nitrogen availability in a nitrogen-depauperate coastal zone and identifies catchment geology as an important influence in coastal productivity through delivery of soil nitrogen to downstream estuaries.

Drought-Induced Accumulation of Root Exudates Supports Post-drought Recovery of Microbes in Mountain Grassland.

Droughts strongly affect carbon and nitrogen cycling in grasslands, with consequences for ecosystem productivity. Therefore, we investigated how experimental grassland communities interact with groups of soil microorganisms. In particular, we explored the mechanisms of the drought-induced decoupling of plant photosynthesis and microbial carbon cycling and its recovery after rewetting. Our aim was to better understand how root exudation during drought is linked to pulses of soil microbial activity and changes in plant nitrogen uptake after rewetting. We set up a mesocosm experiment on a meadow site and used shelters to simulate drought. We performed two 13C-CO2 pulse labelings, the first at peak drought and the second in the recovery phase, and traced the flow of assimilates into the carbohydrates of plants and the water extractable organic carbon and microorganisms from the soil. Total microbial tracer uptake in the main metabolism was estimated by chloroform fumigation extraction, whereas the lipid biomarkers were used to assess differences between the microbial groups. Drought led to a reduction of aboveground versus belowground plant growth and to an increase of 13C tracer contents in the carbohydrates, particularly in the roots. Newly assimilated 13C tracer unexpectedly accumulated in the water-extractable soil organic carbon, indicating that root exudation continued during the drought. In contrast, drought strongly reduced the amount of 13C tracer assimilated into the soil microorganisms. This reduction was more severe in the growth-related lipid biomarkers than in the metabolic compounds, suggesting a slowdown of microbial processes at peak drought. Shortly after rewetting, the tracer accumulation in the belowground plant carbohydrates and in the water-extractable soil organic carbon disappeared. Interestingly, this disappearance was paralleled by a quick recovery of the carbon uptake into metabolic and growth-related compounds from the rhizospheric microorganisms, which was probably related to the higher nitrogen supply to the plant shoots. We conclude that the decoupling of plant photosynthesis and soil microbial carbon cycling during drought is due to reduced carbon uptake and metabolic turnover of rhizospheric soil microorganisms. Moreover, our study suggests that the maintenance of root exudation during drought is connected to a fast reinitiation of soil microbial activity after rewetting, supporting plant recovery through increased nitrogen availability.

Increasing nitrogen depositions can reduce lichen viability and limit winter food for an endangered Chinese monkey

Increasing economic growth and industrial development in China is starting to impact even remote areas such as the Shennongjia nature reserve, where nitrogen pollution is becoming a major environmental threat. The epiphytic lichen flora is particularly rich in this area and is one of the components of this habitat most sensitive to nitrogen pollution. Since lichens represent an important food resource for the endangered monkey species Rhinopithecus roxellana, a reduction in lichen availability would have harmful consequences for the conservation of its habitat in the Shennongjia Mountains. To investigate the effects of increased nitrogen availability on the local lichen communities, so far scarcely considered, we conducted a one-year field experiment measuring growth, survival, and phosphomonoesterase activity of the widespread species Usnea luridorufa in response to nitrogen (up to 50kgNha−1year−1 deposition) and phosphorus supply. Growth and survival of thalli and propagules of U. luridorufa decreased when treated with N deposition >12.05kgNha−1year−1 and >2.14kgNha−1year−1, respectively. The important role of phosphorus availability in relation to nitrogen supply was demonstrated by the increase in phosphomonoesterase activity with increasing nitrogen availability until a nitrogen toxicity threshold was reached. However, the high concentration of phosphorus in rainwater showed that phosphorus is not a limiting nutrient in the area.The results make a contribution to the knowledge of the negative effects of increased N deposition in the Shennongjia forest ecosystem.

Changes in the abundance and community composition of different nitrogen cycling groups in response to fumigation with 1,3-dichloropropene

The fumigant 1,3-dichloropropene (1,3-D) is widely-used to control pathogenic bacteria, fungi, nematodes and insects in soil before a crop is planted. Although fumigants in general have been reported to have a ‘fertilizer effect’ in the soil by increasing nitrogen availability, little is known of how a specific fumigant such as 1,3-D affects available nitrogen. This study used real-time quantitative PCR (qPCR) and 16S rRNA gene amplicon sequencing techniques to investigate the effects of 1,3-D on microorganisms involved in nitrogen cycling that were present in 2 soils: Jiangxi lateritic red soil and Beijing fluvo-aquic soil. The fumigant 1,3-D temporarily decreased the abundance of 11 functional genes involved in nitrogen-fixing, nitrification and denitrification in both soil types. Different nitrogen cycling groups recovered to the unfumigated level in various incubation phases. Microorganisms containing nifH, nxrB, napA and qnorB genes were most vulnerable to 1,3-D fumigation. However, a stronger and longer inhibition effect of 1,3-D on these 11 functional genes was observed in Jiangxi soil than in Beijing soil. At the same time, the abundance of nifH, AOBamoA, nirS, qnorB and cnorB genes was significantly increased 59 days after 1,3-D fumigation. Fumigation with 1,3-D significantly reduced the nitrogen-fixing bacteria Azospirillum and Paenibacillus; the nitrifiers Nitrosomonas and Nitrospira; and the denitrifiers Pseudomonas, Paracoccus and Sphingomonas. Conversely, fumigation with 1,3-D increased the nitrogen-fixing bacteria Bradyrhizobium and Rhizobium; the nitrification bacteria Nitrosospira and Nitrolancea; and the denitrification bacteria Sphingobium, Alcanivorax, Bacillus, Streptomyces and Aeromonas. Fumigation with 1,3-D therefore caused significant shifts in the species composition and number of microbes directly involved in nitrogen cycling in the short-term. These results contribute toward a better understanding of the impact of 1,3-D fumigation on various types of soil nitrogen-cycling groups.

Microorganisms facilitate uptake of dissolved organic nitrogen by seagrass leaves.

Microorganisms play a critical role in nitrogen cycling by mineralising dissolved organic nitrogen (DON) compounds into bioavailable inorganic forms (DIN). Although DIN is crucial for seagrass growth, the hypothesis that seagrass leaf associated-microorganisms could convert DON to forms available for plant uptake has never been tested. We conducted a laboratory-based experiment in which seagrass (Posidonia sinuosa) leaves were incubated with 15N-amino acids (aa), with and without associated microorganisms. Samples were collected after 0.5, 2, 6 and 12 h. Both bulk stable isotope and nanoscale secondary ion mass spectrometry (NanoSIMS) analysis showed high accumulation of 15N within seagrass leaf tissues with an associated microbiota, but not in plants devoid of microorganisms. These results significantly change our understanding of the mechanisms of seagrass nitrogen use and provide evidence that seagrass microbiota increase nitrogen availability for uptake by seagrass leaves by mineralising aa, thus enhancing growth and productivity of these important coastal ecosystems.

Controlled-release urea reduced nitrogen leaching and improved nitrogen use efficiency and yield of direct-seeded rice

The use of controlled-release urea (CRU) has become one of best management practices for increasing crop yield and improving nitrogen (N) use efficiency (NUE). However, the effects of CRU on direct-seeded rice are not well understood while direct-seeding has gradually replaced transplanting due to increasing labor cost and lack of irrigation water. The objective of this two-year field experiment was to compare the effects of the CRU at four rates (120, 180, 240 and 360 kg N ha−1, CRU1, CRU2, CRU3 and CRU4, respectively) with a conventional urea fertilizer (360 kg N ha−1; U) and a control (no N fertilizer applied; CK) on yield, biomass, NUE of direct-seeded rice and soil nutrients. The results indicated that the successive release rates of N from CRU corresponded well to the N requirements of rice. The use of CRU3 and CRU4 increased rice grain yields by 20.8 and 28.7%, respectively, compared with U. In addition, the NUEs were improved by all CRU treatments compared to the U treatment. Concentrations of NO3−-N and NH4+-N in the soil were increased, especially during the later growth stages of the rice, and the leaching of N was reduced with CRU treatments. In conclusion, applying CRU on direct-seeded rice increased the crops yields and NUE, increased nitrogen availability at the late growth stages, and reduced N leaching.

Water and nitrogen supply effects on four desert shrubs with potential use for rehabilitation activities

Desert evergreen shrubs, which are adapted to low-fertility ecosystems, generally exhibit limited responses to increased nutrient availability and tend to absorb and store nutrients rather than synthesize new tissues. The objective of this work was to analyze the effect of nitrogen fertilization combined with soil water availability on growth, nitrogen content, and nitrogen use efficiency on four shrubs (Atriplex lampa, Capparis atamisquea, Larrea cuneifolia, and Senecio subulatus) from the Monte Desert. In a 120-day glasshouse experiment in Mendoza, Argentina, we compared the effects of three levels of nitrogen fertilization combined with two levels of water availability on seedling biomass, nitrogen content, water potential, and nitrogen use efficiency. Fertilization induced a higher biomass on A. lampa under high water availability and on C. atamisquea regardless of water level. Shoot:root ratios of these two species were lower under water stress without fertilization. On the other hand, L. cuneifolia presented lower root biomass and lower water potential with N fertilization. All species when fertilized exhibited higher nitrogen content and lower nitrogen use efficiency. Also, A. lampa and L. cuneifolia presented higher nitrogen content under water stress conditions. In conclusion, some desert shrubs (A. lampa and C. atamisquea) were able to take advantage of increased nitrogen availability producing more biomass. Understanding seedlings response to nitrogen and water availability on arid lands is critically important to develop adequate revegetation techniques of degraded areas.

Predicting local-scale impact of climate change on rice yield and soil organic carbon sequestration: A case study in Roi Et Province, Northeast Thailand

Climate change poses a serious threat to rice production and soil quality in tropical monsoon areas where it is the lifeline of regional food security. In this study, the Environmental Policy Integrated Climate (EPIC) model was evaluated for the reliability of model calibration and validation procedures using local-scale data. The model was then employed to evaluate the possible impact of climate change on rice yield and soil organic carbon (SOC) sequestration in Roi Et Province, Northeast Thailand. The dominant factors that influence the changes in rice yield and SOC sequestration were identified. Four Representative Concentration Pathway (RCP) scenarios (RCPs 2.6, 4.5, 6.0, and 8.5) and Sixteen General Circulation Models under four future time periods; near future (2020–2039), mid future (2040–2059), far future (2060–2079), and very far future (2080–2099) from the Coupled Model Intercomparison Project Phase 5 (CMIP5) were used as future climate projections. The findings revealed that climate change will impact rice yields positively, which will benefit farmers, especially in rain-fed areas, by +2.6% (RCP8.5: 2080–2099) to +22.7% (RCP6.0: 2080–2099). Rice yields in all case tend to increase significantly by +0.7% (RCP8.5: 2060–2079) to +18.8% (RCP6.0: 2080–2099), with the exception of 2080–2099 under RCP8.5, which results in a decline of rice yield by −8.4%. The precipitation is the most important factor for rice yield in this area. Although rising temperatures will bring a slight rice yield reduction, its impact will be negated by large amounts of increased CO2 concentration and precipitation. Conversely, SOC decreased significantly in all time periods. The highest decreased SOC was a -32.0% decline under RCP8.5 in the very far future. This is because rises in temperature and precipitation, with precipitation being the most important driver, negated the enrichment of CO2 fertilization, resulting in accelerated SOC decomposition rates, which may increase nitrogen availability to the soil and increase yield.

Benefits from Below: Silicon Supplementation Maintains Legume Productivity under Predicted Climate Change Scenarios.

Many studies demonstrate that elevated atmospheric carbon dioxide concentrations (eCO2) can promote root nodulation and biological nitrogen fixation (BNF) in legumes such as lucerne (Medicago sativa). But when elevated temperature (eT) conditions are applied in tandem with eCO2, a more realistic scenario for future climate change, the positive effects of eCO2 on nodulation and BNF in M. sativa are often much reduced. Silicon (Si) supplementation of M. sativa has also been reported to promote root nodulation and BNF, so could potentially restore the positive effects of eCO2 under eT. Increased nitrogen availability, however, could also increase host suitability for aphid pests, potentially negating any benefit. We applied eCO2 (+240 ppm) and eT (+4°C), separately and in combination, to M. sativa growing in Si supplemented (Si+) and un-supplemented soil (Si-) to determine whether Si moderated the effects of eCO2 and eT. Plants were either inoculated with the aphid Acyrthosiphon pisum or insect-free. In Si- soils, eCO2 stimulated plant growth by 67% and nodulation by 42%, respectively, whereas eT reduced these parameters by 26 and 48%, respectively. Aphids broadly mirrored these effects on Si- plants, increasing colonization rates under eCO2 and performing much worse (reduced abundance and colonization) under eT when compared to ambient conditions, confirming our hypothesized link between root nodulation, plant growth, and pest performance. Examined across all CO2 and temperature regimes, Si supplementation promoted plant growth (+93%), and root nodulation (+50%). A. pisum abundance declined sharply under eT conditions and was largely unaffected by Si supplementation. In conclusion, supplementing M. sativa with Si had consistent positive effects on plant growth and nodulation under different CO2 and temperature scenarios. These findings offer potential for using Si supplementation to maintain legume productivity under predicted climate change scenarios without making legumes more susceptible to insect pests.

Linkage of root morphology to anatomy with increasing nitrogen availability in six temperate tree species

Fine root morphological traits are generally changed under soil nitrogen (N) enrichment, however, the underlying mechanism and functional significance are still not well understood. Our aims were to investigate the linkage of root morphology to anatomy, and its implication for root function at elevated soil N availability. Ingrowth cores were used to sample root tips (0–20 cm soil depth) from six temperate tree species growing in monoculture plantations at a common site in northeastern China. Root morphological and anatomical traits were concurrently measured, and their relationships were determined within and among species in both control and N fertilization (10 g N m−2y−1) plots. Root diameter generally increased in all six species (non-significant for Phellodendron amurense) following N fertilization, which was caused by the increased root stele radius rather than cortical thickness. Congruently, N fertilization significantly decreased the ratio of cortical thickness to stele radius, but increased the ratio of total cross-sectional area of conduits to stele area in root tips across all species. The observed anatomical changes of root tips contributed to the alternations of morphological root traits following N fertilization, with potentially important impacts on root physiological functions, like increased water and nutrient transport.