The sensitivity of XRD profiles to the amount, coordination, and position of high-Z interlayer scatterers, and to the number of vacant layer sites is illustrated next.Except for one sample obtained by metal sorption on poorly crystalline Mn oxides , the new Zn-rich phyllomanganate contains higher amounts of vacant layer sites and transition elements than any other natural and synthetic variety described so far . The constant Zn:Mn ratio of Mn-Zn precipitate suggests that Zn co-precipitated with Mn by a yet unknown mechanism to form a chemically well-defined phase as natural solids formed by metal sorption on preexisting mineral surfaces are chemically heterogeneous . Birnessite and vernadite minerals were given different names because the basal reflections of birnessite at 7.2-7.0 Å and 3.6-3.5 Å were not observed originally in the diffraction pattern of vernadite. However, recent studies have shown that natural vernadite and its biogenic and chemical analogs most often display a 001 reflection when their XRD pattern is recorded on modern diffractometers , thus confirming the view of Arrhenius et al. and Giovanoli that this mineral is a c-disordered variety of birnessite. Villalobos et al. showed that basal reflections are present when the diffracting crystallites have only 2-3 layers, on average. Here, this number is as low as 1.2 layers,vertical grow rack system meaning that Mn-Zn precipitate is essentially an assemblage of isolated layers.
Measurements of the Mn edge jumps on different Mn-Zn precipitates provide an inkling of how the constitutive nanoparticles are joined at particle or so-called grain boundaries. The Mn edge jump was typically between 0.2 and 0.3 for aggregates ~15-25 µm in diameter, which indicates that the phyllomanganate represents only a small fraction of the black precipitates, thus revealing a high micro-porosity. This porosity is possibly filled, at least partly, by organics that may help disrupt the parallelism of the layers, but also to tie them together.Since biological oxidation of Mn is generally faster than abiotic oxidation, most natural Mn oxides are considered to be biogenic. Manganese oxidation and the subsequent precipitation of Mn bioxides by microscopic fungi is also well documented . Here, we showed that Mn can be biomineralized also in higher living organisms, such as plants. Except for its atypical high Zn content and the structural consequences thereof, this new manganese biomineral is no exception to the intrinsic nanocrystalline nature of biogenic phyllomanganates. Although the mechanism of Mn to Mn oxidation is presently unknown, the constant Zn:Mn ratio of the new Mn biooxide suggests the existence of a well-defined bioactive process, likely in response to metal toxicity. The occurrence of Zn-Mn precipitate only in the root epidermis and the absence in the roots of any Zn-rich species from the soil matrix suggest that Mn oxidation did not occur in the rhizosphere, and thus does not result from bacterial activity or abiotic reaction.
Divalent manganese may have been complexed and transported to the roots by phytosiderophores , and then oxidized by the plant itself or by endomycorrhizal fungi, as shown for wheat and soybean .Knowing how to stimulate the formation of this new phase in biological systems, or how to synthesize it abiotically, would be a significant progress towards Zn immobilization in contaminated environments and their remediation. Formation of this new phase could in particular facilitate the growth of plants in highly contaminated environments in lowering the concentration of bio-available Zn in the rhizosphere. Rice is the primary staple food source for over half the world’s population. The crop is cultivated in at least 114 countries and is the primary source of income and employment for more than 100 million households in Asia and Africa. In recent years, especially in developing countries, rice production has not matched the food demands of an increasing population. To meet this growing demand, rice production has to be raised by at least 70% over the next three decades. The land area devoted to rice cultivation is limited and production cannot be increased by more acreage, so additional, applied research is needed to find other ways of increasing productivity. With limited land resources and increased demand for enhanced production attention is turning towards intensification through higher fertilizer inputs, which is predicted to result in higher yields. Despite a sound logic base supporting increased fertilizer inputs in some rice cropping systems, possible indirect adverse effects of increased fertilizer inputs were highlighted by Heong. In the last decade, plant hopper outbreaks in rice fields have intensified across Asia resulting in heavy yield losses. Over the past decade yield losses substantially increased due to a widespread outbreak of the brown plant hopper.
For example, the Central Plains of Thailand suffered from persistent Plant hopper outbreaks for 10 consecutive growing seasons from 2008 to 2012 and caused losses worth $52 million or equivalent to about 173,000 tons in 2010. The same pest was responsible for losses of around 1 million tons in Vietnam in 2007, and resulted in a government freeze on rice exports. Relationships among fertilizer applications and insect pest outbreaks are widely described in the scientific literature, especially in response to nitrogen fertilization. Specifically regarding rice-based cropping systems, there is a considerable body of research highlighting the indirect effects of fertilizer applications on crop susceptibility to pests. As an example, BPH prefer to feed and oviposit on rice plants supplied with nitrogen. BPH reared on plants with high nitrogen content had high feeding rates and honeydew excretion, less probing behavior, higher survival rates and population build-ups, higher fecundity and oöcyte production, and higher risk of economically important BPH outbreaks. Nitrogen fertilization has also significantly increased the populations of white-backed plant hoppers , green leaf hoppers, and small brown plant hoppers. Finally, Pandey reported higher incidence of rice leaf rollers damage at higher levels of nitrogen fertilization. Phosphorus fertilization has been reported to markedly increase population growth of BPH. Phosphorus alone or combinations with nitrogen and nitrogen-phosphorus-potassium treatments are reported to support moderate leaf hopper populations. Treatments with phosphorus alone and phosphorus in combination with nitrogen also increased populations of ear head bugs and associated grain damage. It has been suggested that phosphorus tends to increase abundance of yellow stem borers in rice, but to a lesser degree than nitrogen. High fertilization levels of both nitrogen and phosphorus caused higher levels of damage by blue beetles in rice crops. Regarding potassium fertilization, there are reports of negative associations between application rates and prevalence of insect pests in rice. As an example, Kulagold et al. reported that higher potassium fertilization of rice plants led to reduced densities of green leaf hoppers, yellow stem borers, blue beetles, rice leaf rollers and ear head bugs. The rate of rice stem borer infestation was greatest when there was no supply of potassium, but decreased in response to increased potassium concentration in rice plants. Silicon content in rice is reported several folds higher than N, P, and K, also promoting a beneficial effect in rice. Recently Guntzer et al. reported that Si increases resistance against insect pests,vertical farming companies pathogens and abiotic stresses including salinity, drought and storms. In this research, N*P*K interactions in a factorial experiments upon Si content of rice is one of the measured attributes. Ample evidence supports a general hypothesis that excessive crop fertilization regimes affects both risk of infestation and severity of economically insect-induced crop losses. However, there are few studies where the combined effects of nitrogen, phosphorous, and potassium fertilizers are studied in detail regarding BPH infestations and its life history characteristics on rice, and also as collectively altered by varying Si content of rice plant tissues. Our previous study showed that biochemical constituents of BPH varied with nutrient levels at different growth stages, and changes in relative water content of rice plants. Moreover, concentrations of N and P were found much higher in the BPH body than in its host rice plants, and this elemental mismatch is an inherent constraint on meeting nutritional requirements of BPH. In this study, rice plants were grown in pots under factorial combinations of fertilizer regimes and subsequently assessed as host plants for BPH. The following specific objectives were to explore direct effects of NPK fertilizer regimes on physiological characteristics of rice plants, and indirect effects of these regimes on fitness traits of BPH.The principal component analysis of fertilizer regimes, nutritional elements of rice plants, and BPH fitness trait responses showed that 78% of the total variance could be explained by the two principal axes, PCA1 and PCA2 . To improve visualization, four variables were not included in Fig. 1, but they were located within the space denoted “cluster 1”.
Due to the high level of variance explained in the two-dimensional space defined by the principal axes, we could make fairly strong inferences about the relative associations of the explanatory variables to show that: 1) there were very close associations between fertilizer regimes and the corresponding content of the same macro elements in rice plants; 2) all agronomic rice plant traits were positively associated with nitrogen fertilization ; 3) nitrogen fertilization was strongly associated with PCA1 explaining most of the variance in the data set; 4) the PCA2 axes was clearly associated with a negative relationship between free soluble sugar and potassium in rice plants.Nitrogen fertilization significantly increased BPH survival from egg to nymph or to adult and all other fitness traits were positively correlated, which indicated these traits improved significantly with the increase of nitrogen inputs . Fitness responses by BPH to phosphorus showed the same trend as nitrogen, but the level of association was more modest. There was a negative association between potassium and soluble sugar , and these two plant nutrition traits were orthogonal to the BPH fitness traits located along the principal axis, PCA1. This suggested that potassium and soluble sugar had only a minor influence on BPH fitness traits. Very interestingly, BPH nymphal development time was positively associated with silicon plant content and negatively correlated with all other principal BPH fitness traits.BPH is one of the most important insect pests of rice in Asia, and it has been an extremely severe pest of rice for decades. However, BPH was a relatively minor rice pest prior to the advent of high-input rice farming which became major after the development and widespread adoption of new high yielding varieties that required increased inputs of fertilizers and pesticides. These practices altered the crop microclimate and accentuated the pest problem such as shifting of the BPH from a minor to a major insect pest. Our data demonstrate that variation of fertilizer inputs to rice plants significantly affected fitness traits of BPH. Firstly, higher nitrogen input increased the survival rate from egg to nymph or adult stages. Secondly, nitrogen excess increased fresh body weight and enhanced the development of BPH. Thus, higher nitrogen input increased the all fitness traits of BPH. Phosphorus and potassium fertilizers had no significant effect BPH. But if phosphorus is supplied with higher nitrogen input , phosphorus significantly influenced several fitness traits including fecundity , fresh body weight and total number of adult BPH developed from one pair of BPH . Potassium has no significant effect on any fitness traits of BPH either alone or combined with higher nitrogen input , but may as shown by MANOVA and stylized 3D plots , exhibit subtle effects that merit further experiments. These results corroborate the first aim of this study by making it clear that altered fertilizer inputs to rice plants can trigger a bottom-up effect on the fitness traits of BPH. Thus, three questions remain to be answered. What are the physiological changes in the host plants that could explain the effects on the fitness traits of BPH? Do our findings support or refute the “Plant vigor hypothesis” which suggests that herbivorous insects prefer and perform better on rapidly-growing plants? Do our findings support or refute the “Plant stress hypothesis”and what can learn from this study to better manage rice production by fertilizer by pest relationships? Different fertilizer treatment combinations influenced rice plant physiology and in turn affected the fitness traits of BPH. When higher doses of nitrogen fertilizer were applied, plants accumulated higher amounts of nitrogen and soluble protein content in their plant tissue, which ultimately influenced herbivore growth and development . Egg hatch ability also increased with nitrogen content, resulting in more BPH produced with higher dry body weights.