Short-term effects of crop rotation,residue management,and soil water on carbon mineralization in a tropical cropping system

The purpose of this study was to investigate the short-term effects of maize (Zea mays)-fallow rotation, residue management, and soil water on carbon mineralization in a tropical cropping system in Ghana. After 15 months of the trial, maize–legume rotation treatments had significantly (P?C ₀ (μg CO₂–C g^?1) than maize–elephant grass (Pennisetum purpureum) rotations. The C ₀ for maize–grass rotation treatments was significantly related to the biomass input (r?=?0.95; P?=?0.05), but that for the maize–legume rotation was not. The soil carbon mineralization rate constant, k (per day), was also significantly related to the rotation treatments (P?k values for maize–grass and maize–legume rotation treatments were 0.025 and 0.036 day^?1 respectively. The initial carbon mineralization rate, m ₀ (μg CO₂–C g^?1 day ^?1), was significantly (P?θ. The m ₀ ranged from 3.88 to 18.67 and from 2.30 to 15.35 μg CO₂–C g^?1 day^?1 for maize–legume and maize–grass rotation treatments, respectively, when the soil water varied from 28% to 95% field capacity (FC). A simple soil water content (θ)-based factor, f _w, formulated as: \(f_{\text{w}} = \left[ {\frac{{\theta - \theta _{\text{d}} }}{{\theta _{{\text{FC}}} - \theta _{\text{d}} }}} \right]\), where θ _d and θ _FC were the air-dry and field capacity soil water content, respectively, adequately described the variation of the m ₀ with respect to soil water (R ²?=?0.91; RMSE?=?1.6). Such a simple relationship could be useful for SOC modeling under variable soil water conditions.     

Controlling Soil Factor in Plant Growth and Salt Tolerance of Leguminous Plant <Emphasis Type="Italic">Alhagi sparsifolia</Emphasis> Shap. in Saline Deserts,Northwest China

The understanding of relationships between the plants and environmental variables is important for ecological restoration. The objective of this research was to investigate the controlling soil factor in plant growth and salt tolerance of leguminous plant Alhagi sparsifolia Shap. (A. sparsifolia) in a saline desert ecosystem of western China. Results showed that coverage of A. sparsifolia was positively linked to soil total K. A. sparsifolia accumulated the toxic Na⁺ in either roots or stems and thus reduced their allocation in the leaves to adapt the salt stress. The most important factor that determined Na⁺ uptake of A. sparsifolia was soil total K content, which suggests that total K can alleviate toxic Na⁺ accumulation in A. sparsifolia. In addition, there was a significant negative correlation among toxic Cl^? concentration in A. sparsifolia, soil total K and pH. Overall, soil total K accounted for 18.2% of plant growth and salt tolerance of A. sparsifolia, followed by soil pH 13.1%, and soil total P 11.6%. In order to restore A. sparsifolia in the degraded desert ecosystems on salinized soil, first we need to consider the effects of soil total K, and then synergistically consider the soil pH and total P.     

Tolerance of <Emphasis Type="Italic">Mitragyna parvifolia</Emphasis> (Roxb.) Korth. seedlings to NaCl salinity

Increase in salinity is predicted to affect plant growth and survival in most arid and semiarid regions worldwide. Mitragyna parvifolia (Roxb.) Korth. is an important medicinal tree species distributed throughout the semiarid regions of India; however, it is facing a threat of its extinction in its natural habitat. We examined the effects of increasing NaCl salinity on two-month-old M. parvifolia seedlings grown in an environment-controlled chamber and exposed to soils of different electrical conductivity (EC) caused by NaCl [0–5 (control), 5–10, 10–15, 15–20, and 20–25 dS m^?1)] for 85 days. Seedlings transferred to soil of EC >15 dS m^?1 did not survive beyond 1 week. Increase in the Na⁺ concentration negatively correlated with their height and positively correlated with their water-use efficiency (WUE). However, leaf area, net photosynthetic rate (P _N), stomatal conductance, and transpiration rate showed varying correlations and an overall decrease in these parameters compared with the control. At EC of 10–15 dS m^?1, the seedling height was reduced by 37% and P _N was lowered by 50% compared with those of the control. An increase in the Na⁺/K⁺ ratio was observed with increasing salinity. The maximum quantum efficiency of PSII significantly decreased with increasing salinity compared with the control. Our results suggest that the increase in salinity reduced the overall performance of the M. parvifolia seedlings. However, the maintenance of WUE and maximum quantum efficiency of PSII might help M. parvifolia to tolerate NaCl salinity of 15 dS m^?1.     

Role of perfusion parameters on DCE-MRI and ADC values on DWMRI for invasive ductal carcinoma at 3.0 Tesla

Background

The value of apparent diffusion coefficient (ADC) values and quantitative parameters (Ktrans, Kep, Ve) in detecting prognostic factor at 3.0 Tesla remains unclear, especially in predicting prognosis of breast cancer.

Methods

A total of 151 patients with IDC underwent breast DCE-MRI and DWI-MRI at 3.0 Tesla following surgery. The ADC values were acquired with b values of 0 and 1000?s/mm². The relationship between ADC values or DCE-MRI quantitative parameters and size, histologic grade (HG), lymph node metastasis (LNM), ER, PR, and Ki67 was evaluated. The predictive values of ADC, Ktrans, Kep, and Ve to prognosis of IDC were assessed.

Results

ADC value was positively related to size (P?=?0.04) and HER2 (P?=?0.046) expression and negatively related to ER (P?=?0.012) and PR (P?<?0.001) expression. Ktrans value has positive correlation with size (P?<?0.001), HG (P?<?0.001), LNM (P?<?0.001), HER2 (P?=?0.007), and Ki67 (P?<?0.001) expression and negative correlation with ER (P?<?0.001) and PR (P?<?0.001) expression. Kep value was positively related to size (P?<?0.001) and negatively related to ER (P?<?0.001) and PR (P?<?0.001) expression. Ve value was negatively related to HER2 expression (P?=?0.004). The Cox hazard ratio (HR) of ADC, Ktrans, Kep, and Ve values on survival was 5.26 (P?=?0.093), 1.081 (P?=?0.002), 1.006 (P?=?0.941), and 0.883 (P?=?0.926), respectively.

Conclusions

Ktrans value was a best predictive indicator of HG, LNM, ER, PR, and Ki67 expression, and ADC value was the best predictive indicator of HER2. Preoperative use of the 3.0 Tesla could provide important information to determine the optimal treatment plan.

     

Production,characteristics and applications of phytase from a rhizosphere isolated <Emphasis Type="Italic">Enterobacter</Emphasis> sp. ACSS

Optimization of process parameters for phytase production by Enterobacter sp. ACSS led to a 4.6-fold improvement in submerged fermentation, which was enhanced further in fed-batch fermentation. The purified 62 kDa monomeric phytase was optimally active at pH 2.5 and 60 °C and retained activity over a wide range of temperature (40–80 °C) and pH (2.0–6.0) with a half-life of 11.3 min at 80 °C. The kinetic parameters K _m, V _max, K _cat, and K _cat/K _m of the pure phytase were 0.21 mM, 131.58 nmol mg^?1 s^?1, 1.64 × 10³ s^?1, and 7.81 × 10⁶ M^?1 s^?1, respectively. The enzyme was fairly stable in the presence of pepsin under physiological conditions. It was stimulated by Ca⁺², Mg⁺² and Mn⁺², but inhibited by Zn⁺², Cu⁺², Fe⁺², Pb⁺², Ba⁺² and surfactants. The enzyme can be applied in dephytinizing animal feeds, and the baking industry.     

Effect of long-term different fertilization on bacterial community structures and diversity in citrus orchard soil of volcanic ash

This study was conducted to assess bacterial species richness, diversity and community distribution according to different fertilization regimes for 16 years in citrus orchard soil of volcanic ash. Soil samples were collected and analyzed from Compost (cattle manure, 2,000 kg/10a), 1/2 NPK+compost (14-20-14+2,000 kg/10a), NPK+compost (28-40-28+2,000 kg/10a), NPK (28-40-28 kg/10a), 3 NPK (84-120-84 kg/10a), and Control (no fertilization) plot which have been managed in the same manners with compost and different amount of chemical fertilization. The range of pyrosequencing reads and OTUs were 4,687–7,330 and 1,790–3,695, respectively. Species richness estimates such as Ace, Chao1, and Shannon index were higher in 1/2 NPK+compost than other treatments, which were 15,202, 9,112, 7.7, respectively. Dominant bacterial groups at level of phylum were Proteobacteria, Acidobacteria, and Actinobacteria. Those were occupied at 70.9% in 1/2 NPK+compost. Dominant bacterial groups at level of genus were Pseudolabrys, Bradyrhizobium, and Acidobacteria. Those were distributed at 14.4% of a total of bacteria in Compost. Soil pH displayed significantly closely related to bacterial species richness estimates such as Ace, Chao1 (p<0.05) and Shannon index (p<0.01). However, it showed the negative correlation with exchangeable aluminum contents (p<0.05). In conclusion, diversity of bacterial community in citrus orchard soil was affected by fertilization management, soil pH changes and characteristics of volcanic ash.     

Response of performance and bacterial community to oligotrophic stress in biofilm systems for raw water pretreatment

Understanding the dynamics of performance and bacterial community of biofilm under oligotrophic stress is necessary for the process optimization and risk management in biofilm systems for raw water pretreatment. In this study, biofilm obtained from a pilot-scale biofilm reactor was inoculated into a pilot-scale experimental tank for the treatment of oligotrophic raw water. Results showed that the removal of NH₄ ⁺–N was impaired in biofilm systems when influent NH₄ ⁺–N was less than 0.35 mg L^?1 or NH₄ ⁺–N loading rate of less than 7.51 mg L^?1 day^?1. The dominant bacteria detected in biofilm of different carrier were obvious distinct from phylum to genus level under oligotrophic stress. The dominant bacteria in elastic stereo media carrier changed from Proteobacteria (51.1%) to Firmicutes (32.7%), while Proteobacteria was always dominant in suspended ball carrier after long-term operation under oligotrophic conditions. Oligotrophic stress largely decreased the functional bacteria for the removal of nitrogen and organics including many genera in Proteobacteria and Nitrospirae, but increased several genera with spore forming organisms or potential bacterial pathogens in ESM carrier mainly including Bacillus, Mycobacterium, Pseudomonas, etc.     

Effects of soil fertility on early development of wetland vegetation from soil seed bank: Focusing on biomass production and plant species diversity

To examine the effects of soil fertility on biomass production, plant species diversity, and early vegetation development, we performed a mesocosm experiment using soil seed bank under three soil fertility levels (ombrotrophic, mesotrophic, and eutrophic). Biomass production linearly increased (P < 0.01), whereas plant species diversity significantly decreased (P < 0.001) as soil fertility increased. Soil fertility seemed to play a role as an environmental sieve in early vegetation development, in turn, lead the patterns of biomass production and plant species diversity. Several Poaceae species which are forming tall and dense canopy, such as Phalaris arundinacea, Miscanthus sacchariflorus, and Zizania latifolia, showed higher importance values under fertilized condition, whereas relatively small macrophytes of Eleocharis acicularis, Carex dickinsii, and Isachne globosa mainly survived under ombrotrophic condition. Although plant species richness decreased as soil fertility increased, the percentages of perennials and exotics increased rather than annuals and natives. Predominance of perennials and exotics under eutrophic condition in early vegetation development seemed to lead a continuous decrease in plant species diversity as a result of competitive effect. A significant negative relationship between plant species diversity and biomass production (P < 0.0001) was obtained when all experimental plots are included in correlation analysis.     

Xylem sap chemistry: seasonal changes in timberline conifers <Emphasis Type="Italic">Pinus cembra</Emphasis>, <Emphasis Type="Italic">Picea abies</Emphasis>, and <Emphasis Type="Italic">Larix decidua</Emphasis>

The seasonal course of xylem sap parameters (electrical conductivity EC, potassium concentration [K⁺], and pH) of three conifers (Pinus cembra, Picea abies, and Larix decidua) growing at the alpine timberline was monitored. We also looked into possible effects of [K⁺] and pH on the difference in hydraulic conductivity (Δk_s). In all studied species, EC, [K⁺], and pH varied considerably over the year, with pH ranging between 7.3 (February) and 5.8 (June) and [K⁺] changing between 0.4 (January) and 2.5 mM (June). The Δk_s was overall low with positive values during winter (up to +20 %) and negative values in summer (-15 % in August). Samples perfused with alkaline solutions showed higher Δk_s. Xylem sap parameters in all conifers under study were surprisingly variable over the year thus indicating either effects upon seasonal changes in environmental factors or active adjustments, or both. Although Δk_s values over the year were minor, observed induction of Δk_s by high pH might indicate a role for hydraulic adjustment in harsh winter periods.     

Analysis of applicability of triplet-state emission of molecular hydrogen for spectral diagnostics of a DC discharge

The applicability of emission of the N ³Λ_σ triplet states of molecular hydrogen for spectral diagnostics of the positive column of a dc glow discharge in hydrogen at translational gas temperatures of 360–600 K, specific absorbed powers of 0.8–4.25 W/cm, gas pressures of p = 0.3–15.0 Torr, reduced fields of E/N = 30–130 Td, and electron densities of n _e = 4.0 × 10⁹–6.5 × 10¹⁰ cm^–3 is analyzed by using an advanced level-based semi-empirical collisional?radiative model. It is found that secondary processes make the main contribution to the population and decay of the N ³Λ_σ = a ³Σ⁺ _g , c ³Π _u , g ³Σ⁺ _g , h ³Σ⁺ _g , and i ³Π _g triplet states. The dipole-allowed transitions e ³Σ⁺ _g → a ³Σ⁺ _g , f ³Σ⁺ _g → a ³Σ⁺ _g , g ³Σ⁺ _g and k ³Π _u → a ³Σ⁺ _g can be used for spectral diagnostics of a dc discharge within a simplified coronal model.     

Polymorphism of the genes for antioxidant defense enzymes and their association with the development of chronic obstructive pulmonary disease in the population of Bashkortostan

In this study, frequencies of the polymorphic variants of the genes encoding antioxidant enzymes, GSTM1, GSTT1, GSTP1, CAT, GPX1, NQO1, SOD1, and SOD3 were examined in three ethnic groups of healthy subjects from the Republic of Bashkortostan (Russians, Tatars, and Bashkirs). An association of these markers with the development of chronic obstructive pulmonary disease (COPD) was tested. Interethnic differences relative to the distribution of the polymorphic variants of the GSTP1 locus Ile105Val and the NQO1 locus 609C/T were revealed. Relative to the genotype distribution at the Ile105Val locus of the GSTP1 gene, ethnic group of Bashkirs was found to be statistically significantly different from Tatars (χ² = 8.819; d.f. = 2; P = 0.012). Relative to the genotype frequency distribution pattern at the NQO1 locus 609C/T, the group of Bashkirs differed from Russians (χ² = 8.913; d.f. = 2; P = 0.012). An association of genotype Val/Val of the GSTP1 Ile105Val locus with the risk of COPD in Russians (χ² = 5.25; P = 0.022; P _cor = 0.044; OR = 4.09), and of the GSTP1 haplotype *D in Tatars, was demonstrated (χ² = 11.575; P = 0.0014; P _cor = 0.0042; OR = 3.178). Genotype TT of the CAT ?262C/T locus marked resistance to the COPD development in Russians (χ² = 6.82; P = 0.0098; P _cor = 0.0196; OR = 0.31; 95%CI, 0.119 to 0.77). The risk for COPD in the ethnic group of Tatars was associated with the CAT haplotype (?262)C/(1167)T (χ² = 6.038; P = 0.0147; P _cor = 0.044; OR = 1.71). Analysis of the NQO1 haplotypes at the 465C/T and 609C/T loci showed that haplotype 465C/609T was associated with COPD in Russians (χ² = 4.571; P = 0.0328; P _cor = 0.01; OR = 1.799). It was demonstrated that Gly allele of the Arg213Gly polymorphic locus of the SOD3 gene marked the risk for COPD in the ethnic group of Tatars (OR = 2.23; 95%CI, 1.22 to 4.1). Thus, GSTP1, CAT, NQO1, and SOD3 polymorphisms play an important role in the development of COPD among the population of Bashkortostan.     

Intervention points for community- acquired methicillin–resistant <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> colonization and load in healthy population of lesser Himalayan Belt,South Asia,India

Objectives

To trace the critical practicing, clinical and epidemiological risk factors in bacterial load and points of intervention in spread of community-acquired methicillin resistant Staphylococcus aureus (CA-MRSA) in healthy community.

Study Design

2872 individuals with no prominent clinical features were enrolled and administered a pre-tested questionnaire prepared on the basis of outcome of a prior pilot study in same region. Swab samples from skin, throat and nasal nares were tested for MRSA and molecular identification was done to track the strains moving from hospital to community.

Methods

Swab samples from skin, throat and nasal nares were tested for MRSA culture followed by molecular characterization of isolates and antimicrobial resistance pattern. Bacterial load was estimated to better understand the burden in different categories. Statistical analysis was done using SPSS 16.0 version.

Results

History of prior infection (OR 3.9, 95% CI 1.363 – 5.793), habit of self remedy (OR 3.2, 95% CI 0.991 – 1.473) and incomplete treatment (OR 0.26, 95% CI 0.08 – 0.80) (P < 0.05 for each) were the predominant factors that contributed to spread of CA-MRSA. Increased drug resistance in CA-MRSA was observed for 4 different clones: SCCmec ⁺ IVa/PVL ⁺, SCCmec ⁺ IVa/PVL ^? and SCCmec ⁺ IVc/PVL ⁺, SCCmec ⁺ IVc/PVL ^?. Bacterial load was found significantly high in below poverty line dwellers and drug abusers (P < 0.05).

Conclusion

We identified habit of self remedy, drug abusing and incomplete treatment as practicing risk factors where interventions can be made to manage the dissemination of CA-MRSA in rural population.

     

Acid-base and gas-transfer properties of the blood of newborn infants

The concentration of HCO ₃ ^? , pH, pO₂, sO₂, and pCO₂ were measured in the total umbilical blood of neonates born in January–February (n = 169) and June–July (n = 172). The former group displayed higher values of pH, pO₂, and sO₂, whereas pCO₂ and the concentration of HCO ₃ ^? were higher in the latter group. There was a 70–80% coincidence of the variants in both groups (the regions of statistical transgressions); seasonal factors were responsible for 20–30% of the differences.     

Testing the cost of reproduction with the rotifer <Emphasis Type="Italic">Brachionus</Emphasis><Emphasis Type="Italic">patulus</Emphasis> at different pH levels

In the present work, we tested the hypothesis that the cost of reproduction was evident under stressful conditions with the rotifer Brachionus patulus at different pH levels (5–10 at 1 unit intervals). We used sublethal pH levels (pH 5, 9, and 10) to simulate stressful conditions. We analyzed the correlations between age-specific fecundity (m ₁, m ₂, m ₃, …) versus future survival (l _x + 1, l _x + 2, l _x + 3, … for the entire lifespan) (survival costs) and future expectation of reproduction (\( V_{ 1}^{*} , \, V_{ 2}^{*} , \, V_{ 3}^{*} , \ldots \) for the entire lifespan) (reproductive costs), using the data obtained from life table demographic studies of B. patulus under stressful and favorable (pH 6, 7, and 8) pH levels. The results showed that significant negative correlations were observed between age-specific fecundity and future survival and future expectation of reproduction at all tested pH levels, indicating that costs of reproduction exist in the rotifer B. patulus under stressful and favorable pH conditions. However, the percentage of statistically significant negative correlations from total correlations of survival and reproductive costs differed greatly, depending on the tested pH conditions. The percentage of significant negative correlation of reproductive costs is significantly higher under stressful pH conditions (pH 5, 9, and 10) than favorable pH conditions (pH 6, 7, and 8). For survival costs, the same trends are also observed, suggesting that the costs of reproduction were more obvious under stressful pH than favorable pH.     

<Emphasis Type="Italic">Phenylobacterium terrae</Emphasis> sp. nov., isolated from a soil sample of Khyber-Pakhtun-Khwa,Pakistan

A Gram-stain negative, aerobic, motile, non-spore-forming and rod-shaped bacterial strain, designated YIM 730227^T, was isolated from a soil sample, collected from Karak district, Khyber-Pakhtun-Khwa, Pakistan. The bacterium was characterized using a polyphasic taxonomic approach. Pairwise comparison of the 16S rRNA gene sequences showed that strain YIM 730227^T is closely related to Phenylobacterium lituiforme FaiI3^T (97.5% sequence similarity), Phenylobacterium muchangponense A8^T (97.4%), Phenylobacterium panacis DCY109^T (97.1%), Phenylobacterium immobile E^T (97.1%) and Phenylobacterium composti 4T-6^T (97.0%), while also sharing 98.0% sequence similarity with Phenylobacterium hankyongense HKS-05^T after NCBI blast, showing it represents a member of the family Caulobacteraceae. The major respiratory quinone was Q-10 and the major fatty acids were C_16:0, summed feature 8 (comprising C_18:1ω7c and/or C_18:1ω6c), C_18:1ω7c 11-methyl and C_17:0. The polar lipids were phosphatidylglycerol, unidentified glycolipids, phospholipid and unidentified lipid. The G?+?C content of the genomic DNA was 68.2 mol%. The DNA–DNA relatedness values of strain YIM 730227^T with P. hankyongense HKS-05^T, P. lituiforme FaiI3^T, P. muchangponense A8^T, P. panacis DCY109^T, P. immobile E^T and P. composti 4T-6^T were 31.3?±?0.6, 26.1?±?0.2, 24.3?±?0.1, 21.8?±?0.9, 19.8?±?0.6 and 18.2?±?1.1%, respectively, values lower than 70%. Besides the morphological and chemotaxonomic characteristics, phylogenetic analyses of 16S rRNA gene sequences and the biochemical characteristics indicated that the strain YIM 730227^T represents a novel member of the genus Phenylobacterium, for which the name Phenylobacterium terrae sp. nov. (type strain YIM 730227^T =?KCTC62324^T?=?CGMCC 1.16326^T) is proposed.     

A novel malic enzyme gene, <Emphasis Type="Italic">Mime2</Emphasis>, from <Emphasis Type="Italic">Mortierella isabellina</Emphasis> M6-22 contributes to lipid accumulation

Objective

This study was aimed at cloning and characterizing a novel malic enzyme (ME) gene of Mortierella isabellina M6-22 and identifying its relation with lipid accumulation.

Methods

Mime2 was cloned from strain M6-22. Plasmid pET32aMIME2 was constructed to express ME of MIME2 in Escherichia coli BL21. After purification, the optimal pH and temperature of MIME2, as well as K_m and V_max for NADP⁺ were determined. The effects of EDTA or metal ions (Mn²⁺, Mg²⁺, Co²⁺, Cu²⁺, Ca²⁺, or Zn²⁺) on the enzymatic activity of MIME2 were evaluated. Besides, plasmid pRHMIME2 was created to express MIME2 in Rhodosporidium kratochvilovae YM25235, and its cell lipid content was measured by the acid-heating method. The optimal pH and temperature of MIME2 are 5.8 and 30 °C, respectively.

Results

The act ivity of MIME2 was significantly increased by Mg²⁺, Ca²⁺, or Mn²⁺ at 0.5 mM but inhibited by Cu²⁺ or Zn²⁺ (p?<?0.05). The optimal enzymatic activity of MIME2 is 177.46 U/mg, and the K_m and V_max for NADP⁺ are 0.703 mM and 156.25 μg/min, respectively. Besides, Mime2 transformation significantly increased the cell lipid content in strain YM25235 (3.15?±?0.24 vs. 2.17?±?0.31 g/L, p?<?0.01).

Conclusions

The novel ME gene Mime2 isolated from strain M6-22 contributes to lipid accumulation in strain YM25235.

     

Nutrient concentration in wheat and soil under allelopathy treatments

Allelopathy is related to soil nutrient availability and allelochemicals can change the soil and therefore the plant nutrient status. Wheat is one of the most important crops for the production of human food in the world. Alhagi maurorum and Cardaria draba are the most important weeds in wheat fields. We performed experiments to assess the allelopathic effect of A. maurorum and C. draba shoots on mineral nutrient concentrations in pot-grown wheat plants and soil. The presence of dry powder of A. maurorum and C. draba shoots reduced concentrations of macronutrients (NO₃ ^?, K⁺, Ca²⁺ and P) and micronutrients (Fe²⁺ and Cu²⁺) in roots and shoots of wheat plants, whereas it did not affect concentrations of Mg²⁺, Mn²⁺ and Zn²⁺. Allelopathic effect of A. maurorum was significantly greater than that of C. draba. There was a significantly positive correlation between wheat growth and ion concentration. There was a significantly negative correlation between the soil nutrient concentration and plant nutrient concentration across the treatments. These results suggest that allelopathy increases the nutrient availability in the soil because of the decrease in absorption by plants.