A novel proxy to examine interspecific phosphorus facilitation between plant species.

Resource complementarity can contribute to enhanced ecosystem functioning in diverse plant communities, but the role of facilitation in the enhanced complementarity is poorly understood. Here, we use leaf manganese concentration ([Mn]) as a proxy for rhizosheath carboxylate concentration to explore novel mechanisms of complementarity mediated by phosphorus (P) facilitation. In pot experiments, we showed that mixtures involving Carex korshinskyi, an efficient P-mobilizing species, exhibited greater biomass and relative complementarity effect than combinations without C. korshinskyi on P-deficient soils. Compared with monocultures, leaf [Mn] and [P] of species that are inefficient at P mobilization increased by 27% and 21% when grown with C. korshinskyi (i.e. interspecific P facilitation via carboxylates) rather than next to another inefficient P-mobilizing species. This experimental result was supported by a meta-analysis including a range of efficient P-mobilizing species. Phosphorus facilitation enhanced the relative complementarity effect in low-P environments, related to a greater change in several facilitated species of their root morphological traits relative to those in monoculture. Using leaf [Mn] as a proxy, we highlight a vital mechanism of interspecific P facilitation via belowground processes and provide evidence for the pivotal role of P facilitation mediated by the plasticity of root traits in biodiversity research.

Plant litter strengthens positive biodiversity-ecosystem functioning relationships over time.

Plant biodiversity-productivity relationships become stronger over time in grasslands, forests, and agroecosystems. Plant shoot and root litter is important in mediating these positive relationships, yet the functional role of plant litter remains overlooked in long-term experiments. We propose that plant litter strengthens biodiversity-ecosystem functioning relationships over time in four ways by providing decomposing detritus that releases nitrogen (N) over time for uptake by existing and succeeding plants, enhancing overall soil fertility, changing soil community composition, and reducing the impact of residue-borne pathogens and pests. We bring new insights into how diversity-productivity relationships may change over time and suggest that the diversification of crop residue retention through increased residue diversity from plant mixtures will improve the sustainability of food production systems.

Belowground facilitation and trait matching: two or three to tango?

High biodiversity increases ecosystem functions; however, belowground facilitation remains poorly understood in this context. Here, we explore mechanisms that operate via 'giving-receiving feedbacks' for belowground facilitation. These include direct effects via root exudates, signals, and root trait plasticity, and indirect biotic facilitation via the effects of root exudates on soil biota and feedback from biota to plants. We then highlight that these two- or three-way mechanisms must affect biodiversity-ecosystem function relationships via specific combinations of matching traits. To tango requires a powerful affinity and harmony between well-matched partners, and such matches link belowground facilitation to the effect of biodiversity on function. Such matching underpins applications in intercropping, forestry, and pasture systems, in which diversity contributes to greater productivity and sustainability.

Phosphorus facilitation and covariation of root traits in steppe species.

Different phosphorus (P)-acquisition strategies may be relevant for species coexistence and plant performance in terrestrial communities on P-deficient soils. However, how interspecific P facilitation functions in natural systems is largely unknown. We investigated the root physiological activities for P mobilization across 19 coexisting plant species in steppe vegetation, and then grew plants with various abilities to mobilize sorbed P in a microcosm in a glasshouse. We show that P facilitation mediated by rhizosphere processes of P-mobilizing species promoted growth and increased P content of neighbors in a species-specific manner. When roots interacted with a facilitating neighbor, Cleistogenes squarrosa and Bromus inermis tended to show greater plasticity of root proliferation or rhizosheath acid phosphatase activity compared with other non-P-mobilizing species. Greater variation in these root traits was strongly correlated with increased performance in the presence of a facilitator. The results also show, for the first time, that P facilitation was an important mechanism underlying a positive complementarity effect. Our study highlights that interspecific P-acquisition facilitation requires that facilitated neighbors exhibit a better match of root traits with a facilitating species. It provides a better understanding of species coexistence in P-limited communities.

Linking shifts in species composition induced by grazing with root traits for phosphorus acquisition in a typical steppe in Inner Mongolia.

Long-term overgrazing tends to cause soil phosphorus (P) deficiency in grasslands. The relationships between grazing-induced shifts in species composition and root traits associated with P acquisition involved in these shifts remain unknown. Species vary in their P-acquisition strategies, and we hypothesize that species that acquire P more efficiently are better adapted to overgrazing. We measured relative biomass, root physiological activities (e.g., rhizosheath acid phosphatase activity (Apase), and leaf manganese concentration ([Mn]) as a proxy for carboxylate concentrations in rhizosheath) and morphological traits (e.g., specific root length) of six common species in a field experiment conducted in a typical steppe of Inner Mongolia. There were two exclosure demonstration plots, i.e. exclosed since 1983 and 1996, and long-term free grazing without exclosure of sheep. Long-term overgrazing caused a reduction in bulk soil Olsen P concentration and increased community-weighted leaf nitrogen: P ratio by 27% and 37%, respectively, indicating more severe P limitation for steppe vegetation. Carex duriuscula exhibited an inherently greater specific root length, proportion of fine roots and rhizosheath Apase than other species did in both exclosure and grazing treatments. Cleistogenes squarrosa showed a greater leaf [Mn] induced by overgrazing. The increased dominance of C. duriuscula and C. squarrosa was positively correlated with finer roots, greater rhizosheath Apase or carboxylate release under long-term overgrazing. Species that had inefficient root traits for P acquisition (e.g., low specific root length and low leaf [Mn]), i.e. Stipa grandis, exhibited a decreased dominance in response to overgrazing. Dominance of species did not change under grazing which may be related to either relatively inefficient inherent morphological (i.e. in Artemisia frigida) or physiological traits (i.e. in Leymus chinensis and Agropyron michnoi) for P acquisition. Our study highlights the importance of acknowledging root traits involved in efficient P acquisition for theories on community succession induced by overgrazing.

[Analysis and comparison of trace elements of herba euphorbiae humifusae in different periods by microwave digestion-atomic absorption spectroscopy].

Herba euphorbiae humifusae is the dried whole plant of Euphorbia humi fusa Willd. that belongs to euphorbiaceae. In the present paper, the microwave digestion procedure was used to digest herba euphorbiae humifusae collected in different periods, and then flame atomic absorption spectrometry (FAAS) was used to determine the contents of eight kinds of trace elements of herba euphorbiae humifusae in different periods, and the change in the contents of trace elements at different times was studied and analysed. The results showed that of all the trace elements of herba euphorbiae humifusae in different periods, element Fe was the highest in June, element K was in August at the highest level, element Mn reached the highest content in September, elements Na and Ca were dividedly at the highest content in October and November, and in December the highest content elements were Zn, Cu and Mg. In one word, the change of Na and Ca was jumping, while the change of Cu and Zn was comparatively mild. The results provide scientific basis for the time of collection of herba euphorbiae humifusae.

[Determination of trace elements in radix Paeoniae alba by microwave digestion-ICP-AES].

Microwave digestion technique was used in the decomposition of radix Paeoniae alba samples of different growing area, different growing time and before and after processing, and the contents of K, Ca, Na, Mg, Zn and Fe were determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES). The results of the determination show that radix Paeoniae alba samples are rich in the trace elements. The RSDs of these elements were lower than 4%, and the recovery ratio ranged between 99% and 113%. The results revealed that the analytic method is sensitive and precise. The pattern recognition based on the principal component analysis (PCA) was applied to the measured trace elements of different radix Paeoniae alba samples. The PCA was useful in the classification of radix Paeoniae alba. This paper provides scientific basis for deeply studying the relation between the trace elements and the drug effect of radix Paeoniae alba.

[Study on the absorption and fluorescence spectra of ethylene glycol and glycerol].

The absorption and fluorescence spectra of ethylene glycol and glycerol solution induced by UV light were studied respectively in the present paper. The most intense absorption wavelength for both of them was located at 198 nm. Moreover, fluorescence was detected when induced by suitable UV light, and the corresponding fluorescence spectra were listed. But there is no obvious relationship found between the fluorescence intensity and the excited wavelength, and a further research should be done. From the first derivative fluorescence spectra of ethylene glycol, it was concluded that under the UV light of 210 nm, the variation speed for relative intensity proved to be the fastest. In contrast, when excited by 225 nm, the speed proved to be the slowest. In addition, based on the quantum calculation and the transition from HOMO to LUMO of electronics in one-dimensional quantum well, the authors attempted to give out the value of absorption wavelength. In consideration of the bond-length variety brought out by the chain processing, the error between the experimental and calculation values should be apprehensible, and the latter can serve as some reference value in theory.

[Determination and comparison of trace elements in four sorts of Bulbus Fritillariae by microwave digestion-atomic absorption spectrometry].

The contents of elements such as Zn, Fe, Mn, Cu, Na, Mg, K, Ca, As, Pb, Cd, Co, Cr, Sr, and Al in four sorts of Bulbus Fritillariae, namaly from Fritillaria thunbergii Miq. (Panan and Ningbo), Fritillaria thunbergii Miq. Var. chekiangensis Hsiao et K. C. Hsia and Fritillaria cirrhosa D. Don, were determined by flame atomic absorption spectrometry (FAAS) and graphite furnace atomic absorption spectrometry (GFAAS) respectively. The effect of different microwave digestion conditions on the analysis results was reviewed, and optimal condition for using atomic absorption spectrophotometry was determined. Principal component analysis (PCA) was applied taking trace elements contents as indexes. The results revealed that microwave digestion was a simple, rapid, digestion complete, and low blank value method, and the measurement result is satisfactory. The experimental results indicated that the linear relationships for different elements within the limits of working curve were good. The RSDs were all smaller than 3.97%. The addition standard rates of the procedure was between 91.0% and 108.7%. Principal component analysis has the application value of reflecting the differences in trace elements contents in various samples.

[Study of fluorescence spectra of starch suspension].

To achieve detection, monitoring and automation of starch graft copolymerzation, the investigation was carried out according to the luminescence of free radical produced in the reaction. The investigation on the fluorescence spectra of starch-water suspension excited by ultraviolet light and its characteristics contributes to the study of the characteristics and mechanisms of free radical coming into being, emitting and disappearing. The experimental results indicate that starch-water suspension can emit fluorescence, whose peak wavelength is about 339 nm. Furthermore, the physical mechanism of fluorescence emission of starch is analyzed. It is considered that this fluorescence comes from the transition from nonbonding electrons in the hetero-atom (O) of the functional group (C--O--C) called ether linkage to the antibonding orbital sigma*.

[Experiment study of alcohol-water mixtures absorption and fluorescence spectra induced by UV-light].

By using equipment of UV-240 ultra-violet spectrophotometer and Sp-2558 multifunctional spectrometer system, the UV-light absorption spectra and the fluorescence spectra of propanol and isopropanol, as well as their comparison were studied. According to the results, propanol and isopropanol can be clearly distinguished with absorption spectra and fluorescence spectra. The reasons for difference spectra of the two liquids were also explained. Moreover, the fluorescence spectra of the four kinds of difference alcohol were compared and the results were discussed. The whole research outcomes will provide a new method for effective measurement of different alcohol, and also produce some valuable theoretical references to the calculation of quantum chemistry.