Jianming Xue

Relating nutritional and physiological characteristics to growth of Pinus radiata clones planted on a range of sites in New Zealand

Six clones of radiata pine with known differences in growth rate were examined for clonal nutritional characteristics and for physiological determinants of clonal growth rate. We compared growth, foliar characteristics and nutrient, ¹³C and ¹⁵N concentration data for the six clones in 4- to 6-year-old field trials planted over a range of nutritionally contrasting sites. These data were also compared with growth, nutrient uptake and remobilization, foliar characteristic and gas exchange data from intensive physiological glasshouse experiments using 1- and 2-year-old plants of the same clones. Significant genotype x environment interactions in our field experiments conducted over strong nutritional gradients allowed us to identify radiata pine clones with consistent, superior growth and nutritional characteristics and clones that may be suited to particular site conditions. Our results suggest that the opportunity exists to exploit clone x site variation for site-specific clonal deployment and planting of fast-growing clones could be accompanied by planting of clones able to take relative advantage of site nutritional characteristics. Faster tree growth was not strongly related to any physiological characteristic, and the factors influencing growth rate differed among clones. The fastest-growing clone had consistent, high uptake of all nutrients, high fascicle weights and high water-use efficiency.

Response of Pinus radiata D. Don to Boron Fertilization in a Glasshouse Study

Limited information is available on the effect of slow-release boron (B) fertilizer on Pinus radiata growth and physiological properties and soil microbiological activities. A 7-month-long pot experiment was carried out under glasshouse conditions to investigate the response of Pinus radiata to different rates (0.0222, 0.0446, 0.089, and 0.178 mg B g−1 soil), equivalent to 0, 4, 8 16, and 32 kg B ha−1 of ulexite, a slow-release B fertilizer. Hot 0.02 M calcium chloride (CaCl2)–extractable soil B, soil dehydrogenase activity, plant B concentration, growth, and photosynthesis were measured at the time of harvest. The B concentrations in the soil and plant organs (needles, stem, and roots) significantly increased with increasing rates of B fertilizer. The optimum B fertilizer rates of 4–8 kg B ha−1 produced the greatest plant growth and net photosynthetic rate. However, the B rates of 16 and 32 kg B ha−1 significantly reduced net photosynthetic rate, and the rate of 32 kg B ha−1 significantly reduced stem diameter growth when compared to the optimum B rates. Soil dehydrogenase activity, an indicator of soil microbiological activities, was significantly reduced by B application at the rates of 16 and 32 kg ha−1. This study confirms the narrow range between B deficiency and toxicity in a tree crop and stresses the need for selection of the optimum rate of B fertilizer application.

Host Genotype and Nitrogen Form Shape the Root Microbiome of Pinus radiata.

A central challenge in community ecology is understanding the role that phenotypic variation among genotypes plays in structuring host-associated communities. While recent studies have investigated the relationship between plant genotype and the composition of soil microbial communities, the effect of genotype-by-environment interactions on the plant microbiome remains unclear. In this study, we assessed the influence of tree genetics (G), nitrogen (N) form and genotype-by-environment interaction (G x N) on the composition of the root microbiome. Rhizosphere communities (bacteria and fungi) and root-associated fungi (including ectomycorrhizal and saprotrophic guilds) were characterised in two genotypes of Pinus radiata with contrasting physiological responses to exogenous organic or inorganic N supply. Genotype-specific responses to N form influenced the composition of the root microbiome. Specifically, (1) diversity and composition of rhizosphere bacterial and root-associated fungal communities differed between genotypes that had distinct responses to N form, (2) shifts in the relative abundance of individual taxa were driven by the main effects of N form or host genotype and (3) the root microbiome of the P. radiata genotype with the most divergent growth responses to organic and inorganic N was most sensitive to differences in N form. Our results show that intraspecific variation in tree response to N form has significant consequences for the root microbiome of P. radiata, demonstrating the importance of genotype-by-environment interactions in shaping host-associated communities.

Prediction model for mercury transfer from soil to corn grain and its cross-species extrapolation

Abstract In this study the transfer characteristics of mercury (Hg) from a wide range of Chinese soils to corn grain (cultivar Zhengdan 958) were investigated. Prediction models were developed for determining the Hg bioconcentration factor (BCF) of Zhengdan 958 from soil, including the soil properties, such as pH, organic matter (OM) concentration, cation exchange capacity (CEC), total nitrogen concentration (TN), total phosphorus concentration (TP), total potassium concentration (TK), and total Hg concentration (THg), using multiple stepwise regression analysis. These prediction models were applied to other non-model corn cultivars using a cross-species extrapolation approach. The results indicated that the soil pH was the most important factor associated with the transfer of Hg from soil to corn grain. Hg bioaccumulation in corn grain increased with the decreasing pH. No significant differences were found between two prediction models derived from different rates of Hg applied to the soil as HgCl2. The prediction models established in this study can be applied to other non-model corn cultivars and are useful for predicting Hg bioconcentration in corn grain and assessing the ecological risk of Hg in different soils.

Biodegradation of gentamicin by bacterial consortia AMQD4 in synthetic medium and raw gentamicin sewage

Gentamicin, a broad spectrum antibiotic of the aminoglycoside class, is widely used for disease prevention of human beings as well as animals. Nowadays the environmental issue caused by the disposal of wastes containing gentamicin attracts increasing attention. In this study, a gentamicin degrading bacterial consortia named AMQD4, including Providencia vermicola, Brevundimonas diminuta, Alcaligenes sp. and Acinetobacter, was isolated from biosolids produced during gentamicin production for the removal of gentamicin in the environment. The component and structure of gentamicin have a great influence on its degradation and gentamicin C1a and gentamicin C2a were more prone to being degraded. AMQD4 could maintain relatively high gentamicin removal efficiency under a wide range of pH, especially in an alkaline condition. In addition, AMQD4 could remove 56.8% and 47.7% of gentamicin in unsterilized and sterilized sewage in a lab-scale experiment, respectively. And among the isolates in AMQD4, Brevundimonas diminuta BZC3 performed the highest gentamicin degradation about 50%. It was speculated that aac3iia was the gentamicin degradation gene and the main degradation product was 3′-acetylgentamicin. Our results suggest that AMQD4 and Brevundimonas diminuta BZC3 could be important candidates to the list of superior microbes for bioremediation of antibiotic pollution.

Prediction models for transfer of arsenic from soil to corn grain (Zea mays L.)

In this study, the transfer of arsenic (As) from soil to corn grain was investigated in 18 soils collected from throughout China. The soils were treated with three concentrations of As and the transfer characteristics were investigated in the corn grain cultivar Zhengdan 958 in a greenhouse experiment. Through stepwise multiple-linear regression analysis, prediction models were developed combining the As bioconcentration factor (BCF) of Zhengdan 958 and soil pH, organic matter (OM) content, and cation exchange capacity (CEC). The possibility of applying the Zhengdan 958 model to other cultivars was tested through a cross-cultivar extrapolation approach. The results showed that the As concentration in corn grain was positively correlated with soil pH. When the prediction model was applied to non-model cultivars, the ratio ranges between the predicted and measured BCF values were within a twofold interval between predicted and measured values. The ratios were close to a 1:1 relationship between predicted and measured values. It was also found that the prediction model (Log [BCF]=0.064 pH-2.297) could effectively reduce the measured BCF variability for all non-model corn cultivars. The novel model is firstly developed for As concentration in crop grain from soil, which will be very useful for understanding the As risk in soil environment.

Fate of biuret 15N and its effect on net mineralisation of native soil N in forest soils

Biuret (C 2 H S N 3 O 2 ) priming effect on mineralisation of native soil N has not been precisely quantified in previous studies, although it is a potential microbial activity regulator and slow-release N fertiliser. Following application of biuret at concentrations of 0 (BO) and 100 (B100) mg/kg (oven-dried) soil, we measured the dynamics of biuret-derived 15 N in soil N pools, soil C mineralisation, and microbial biomass C in a sandy loam and a silt loam during a 112-day-long incubation to investigate the fate of biuret 15 N and its effect on net mineralisation of native soil N. Biuret was decomposed faster in the sandy loam soil than the silt loam soil. In the sandy loam soil, the stabilised N pool was a strong sink for the biuret-derived 15 N and accumulated about half of the applied 15 N at the end of incubation. In the silt loam soil, 68% of the 15 N applied was recovered in the NO 3 -N pool and the stabilised N pool accumulated only about 25% of the applied 15 N at the end of incubation. Biuret addition increased the turnover rate constant of soil organic matter and caused a real priming effect on net mineralisation of native soil N in both soils. The additional mineralisation of native soil N was 20.1 mg/kg (equivalent to 27.3kgN/ha) in the sandy loam soil and 20.5 mg/kg (equivalent to 57.3kgN/ha) in the silt loam soil. Biuret priming effect was related to the acceleration of soil organic matter decomposition by increased microbial activity at an early stage and the death/decay of microbes at a later stage of incubation. The native soil N released through the priming effect was partially from soil non-biomass organic matter and partially from soil microbial biomass.

Aquaporin regulaton in roots controls plant hydraulic conductance, stomatal conductance and leaf water potential in Pinus radiata under water stress: Aquaporin activity regulates stomatal conductance

Stomatal regulation is crucial for forest species performance and survival on drought-prone sites. We investigated the regulation of root and shoot hydraulics in three Pinus radiata clones exposed to drought stress and its coordination with stomatal conductance (gs ) and leaf water potential (Ψleaf ). All clones experienced a substantial decrease in root-specific root hydraulic conductance (Kroot-r ) in response to the water stress, but leaf-specific shoot hydraulic conductance (Kshoot-l ) did not change in any of the clones. The reduction in Kroot-r caused a decrease in leaf-specific whole-plant hydraulic conductance (Kplant-l ). Among clones, the larger the decrease in Kplant-l , the more stomata closed in response to drought. Rewatering resulted in a quick recovery of Kroot-r and gs . Our results demonstrated that the reduction in Kplant-l , attributed to a down regulation of aquaporin activity in roots, was linked to the isohydric stomatal behaviour, resulting in a nearly constant Ψleaf as water stress started. We concluded that higher Kplant-l is associated with water stress resistance by sustaining a less negative Ψleaf and delaying stomatal closure.

A Simple, Sensitive, and Reliable Method for the Simultaneous Determination of Multiple Antibiotics in Vegetables through SPE-HPLC-MS/MS

Antibiotics, widely used in livestock breeding, enter the environment through animal manure because of incomplete absorption in animals, especially the farmland ecosystem. Therefore, antibiotics may be adsorbed by plants and even become hazardous to human health through the food chain. In this study, a simple, sensitive, and reliable method was developed for the simultaneous determination of eleven antibiotics, including four sulfonamides, two tetracyclines, three fluoroquinolones, tylosin, and chloramphenicol in different vegetable samples using SPE-HPLC-MS/MS. Vegetable samples were extracted by acetonitrile added with hydrochloric acid (125:4, v/v). The extracts were enriched by circumrotating evaporation, and then cleaned through SPE on a hydrophilic-lipophilic balance (HLB) cartridge. All compounds were determined on a C18 reverse phase column through HPLC-MS/MS. The mean recoveries of 11 antibiotics from spiked samples of vegetables ranged from 71.4% to 104.0%. The limits of detection and quantification were 0.06–1.88 μg/kg and 0.20–6.25 μg/kg, respectively. The applicability of this technique demonstrated its good selectivity, high efficiency, and convenience by the analysis of 35 vegetable samples available from a vegetable greenhouse. Antibiotic residues in vegetables have aroused wide concern from the public. Therefore, standards should be established for antibiotic residues in vegetables to ensure food safety and human health.

Genotypic variation in Pinus radiata responses to nitrogen source are related to changes in the root microbiome

Variation in traits within a plant species contributes to differences in soil physicochemistry and rhizosphere microbial communities. However, how intraspecific variation in plant responses to nitrogen (N) shapes these communities remains unclear. We studied whether plant responses to organic and inorganic N forms vary among genotypes, and if these responses were associated with variation in root-associated communities. We investigated how the root microbiomes of two Pinus radiata D. Don genotypes were altered by two years of N-fertilisation in field conditions. We characterised rhizosphere bacterial and fungal communities, as well as root-associated fungal communities, of trees receiving yearly additions of NH4NO3 or L-arginine, and control trees. We also measured plant traits and rhizosphere soil physicochemical properties. Two main findings emerged: (i) N form and tree genotype affected soil physicochemical properties as well as plant measures, and these responses were associated with variation in microbial communities, and (ii) rhizosphere and root-associated communities differed in their responses to N form and host genotype. Our results suggest that N forms have different influences on N and carbon dynamics at the plant-soil interface by inducing root-mediated responses that are associated with shifts in the root microbiome such that communities more closely associated with roots are more sensitive to genotype-specific responses.