Wiener Index Research Articles

Aggregate Size Mediated the Changes in Soil Microbial Communities After the Afforestation of a Former Dryland in Northwestern China

Although the afforestation of former arable lands is a common global land-use conversion, its impact on soil microbial communities at the aggregate scale has not been adequately addressed. In this study, soil samples were categorized into large macroaggregates (LM, >2 mm), small macroaggregates (SM, 2–0.25 mm), and microaggregates (MI, <0.25 mm) to assess the changes in microbial composition, diversity, network complexity, and network stability within soil aggregates after the afforestation of a former dryland in northwestern China. The results revealed that afforestation enhanced the relative abundance of Actinobacteriota, Chloroflexi, Ascomycota, and Mortierellomycota within the soil aggregates, suggesting that these phyla may have greater advantages in microbial communities post-afforestation. The Shannon–Wiener and Pielou indices for bacterial communities showed no significant differences between land-use types across all aggregate fractions. However, the alpha diversity of fungal communities within the LM and SM significantly increased after afforestation. Bray–Curtis dissimilarity indices showed that afforestation altered bacterial beta diversity within the LM and MI but had a minimal impact on fungal beta diversity across all three aggregate fractions. The topological features of cross-kingdom microbial co-occurrence networks within the soil aggregates generally exhibited a decreasing trend post-afforestation, indicating a simplification of microbial community structure. The reduced robustness of microbial networks within the LM and SM fractions implies that afforestation also destabilized the structure of microbial communities within the macroaggregates. The composition of the soil microbial communities correlated closely with soil carbon and nitrogen contents, especially within the two macroaggregate fractions. The linkages suggests that improved resource conditions could be a key driver behind the shifts in microbial communities within soil aggregates following afforestation. Our findings indicate that the impact of afforestation on soil microbial ecology can be better understood by soil aggregate fractionation.

Exponential Wiener index of some silicate networks

Any graph that depicts a particular molecular structure can be given a topological graph index, also known as a molecular descriptor. This index can be used to examine numerical data and discover more about specific physical properties of molecules. Silicates are hard crystals that can be sliced into little pieces. Therefore, silicon play a vital role in many real time applications. It is the authentic material to make microchips which run in PDA, PC and other game tools. In the current study, we have determined the new topological index for a few silicate structures, including cyclic, single-chain, and Pyro silicates by grouping the vertices of the corresponding molecular graphs based on their distance sums. This index is known as the exponential Wiener index. It is expanded to include their line graphs as well. The numerical values of exponential Wiener index and multiplicative exponential Wiener index for the molecular graphs of cyclic silicates, single chain silicates and their line graphs with n vertices where n = 3, 4, 5 are explored.

Wiener and Harary index of the zero-divisor graph of ℤn

The zero-divisor graph of a ring [Formula: see text] is a graph whose vertex set consists of all the elements of [Formula: see text] and distinct vertices [Formula: see text] and [Formula: see text] are adjacent if and only if [Formula: see text]. We study the zero-divisor graph [Formula: see text], for [Formula: see text], where [Formula: see text] and [Formula: see text] are distinct primes. Topological indices such as Wiener and Harary indices of [Formula: see text] are determined.

Diversity and ethnobotanical study of homegarden plants in Goba district, Oromia region, Ethiopia

Homegardens are one of the most diverse agroforestry systems and make a vital contribution to meeting various household needs, especially for smallholder farmers in developing countries. The aim of this study was to record the diversity and use of homegarden plant species in the Goba District. The households were randomly selected from five kebeles, with the number selected proportionate to the size of each kebele using the probability proportional to size (PPS) calculation. Seventy-one homegarden owners were chosen for the detailed study and data collection. Of the fifteen kebeles in the Goba District, five kebeles were chosen at random. Observations, semi-structured interviews, preference rating, direct matrix rankings, and paired comparisons were the methods used to gather ethno-botanical data. Descriptive statistical approaches, including density, frequency, relative frequency, relative density, and the Shannon and Wiener indices for species diversity were used to analyze the data. A total of 67 plant species belonging to 31 families were identified. Of the 67 plant species, 36 (or 54%) were herbs, 15 (or 22%) were tree species, 22% shrubs, and 2% were climbers. Twenty-eight (20.8%) species collected from homegardens had food and forage value, 17 (25.3%) had fence value, 12 (18%) had shade value, and 23 (34.3%) had medicinal value; moreover, 90% of the homes had home gardens, indicating that farmers value gardening plants that helps improve household food security and revenue generation. The involvement of the local population and government institutions in providing awareness through instruction or training on the sustainable use and management of plant resources is vital to conserve homegarden plants.

On comparison between the distance energies of a connected graph

Let G be a simple connected graph of order n having Wiener index W(G). The distance, distance Laplacian and the distance signless Laplacian energies of G are respectively defined asDE(G)=∑i=1n|υiD|,DLE(G)=∑i=1n|υiL−Tr‾|andDSLE(G)=∑i=1n|υiQ−Tr‾|, where υiD,υiL and υiQ,1≤i≤n are respectively the distance, distance Laplacian and the distance signless Laplacian eigenvalues of G and Tr‾=2W(G)n is the average transmission degree. In this paper, we will study the relation between DE(G), DLE(G) and DSLE(G). We obtain some necessary conditions for the inequalities DLE(G)≥DSLE(G),DLE(G)≤DSLE(G),DLE(G)≥DE(G) and DSLE(G)≥DE(G) to hold. We will show for graphs with one positive distance eigenvalue the inequality DSLE(G)≥DE(G) always holds. Further, we will show for the complete bipartite graphs the inequality DLE(G)≥DSLE(G)≥DE(G) holds. We end this paper by computational results on graphs of order at most 6.

Rapid declines in species diversity and occurrence of common plant species are related to nutrient availability and soil moisture in open habitats

AbstractAimsEnvironmental changes in Europe influence plant community composition, but the literature quantifying these changes often shows inconsistent trends, due mostly to heterogeneous survey methods. Here, we investigated temporal changes in plants over 12 years at the species and community level at a regional scale, using a standardized, plot‐based monitoring scheme.LocationData originated from 1,389 permanent plots of a standardized monitoring scheme targeting plant communities. Plots were distributed in the Burgundy region (France), initially grouped into 175 (2 km × 2 km) grid cells containing eight 10‐m2 plots each, that were surveyed in at least 2 years between 2009 and 2020.MethodsWe characterized changes in vascular plants in 10‐m2 plots by examining the temporal changes in the probability of occurrence of common species, changes in species diversity using species richness, Shannon–Wiener and Pielou's indices and changes in abundance‐weighted mean community ecological preferences using Ellenberg indicator values.ResultsAcross 198 common species, probability of occurrence in the region has shown a decline since 2009. This decline is associated with a general decrease by 13% of both species richness and the Shannon index between 2009 and 2020. This trend was stronger in annual crops and grasslands, whereas forest diversity remained relatively constant over time. Pielou's index diminished on average, except in natural forests. Mean community Ellenberg indicator values suggested slight changes in plant community composition, with an increasing preference for nutrient‐poor soils and Atlantic conditions over time.ConclusionsThe observed biodiversity loss in the Burgundy region is consistent with a widespread shift in community composition in response to environmental change. Existing conservation measures do not seem to compensate for the average losses, indicating that these measures are still inadequate to protect plant communities. Our approach also emphasizes the speed at which plant communities are changing and thus the need for better monitoring of the European flora.

Gastrointestinal parasite prevalence, diversity and association in free-ranging Chacma baboon troops in a semi-arid savanna ecosystem of Zimbabwe

Free-ranging Chacma baboon species are known to harbour a wide range of zoonotic parasites, and their frequent close interactions with humans pose a risk of transmission of zoonotic parasites between the two species. This research study focused on understanding parasite dynamics in free-ranging baboon populations that inhabit human-wildlife interface areas, a case of Gwanda State University's Epoch Mine campus in Filabusi at Insiza district. A descriptive and analytical cross-sectional design was used to investigate the prevalence, diversity and association of gastrointestinal parasites among three baboon troops found at the Epoch Mine campus. One hundred and twenty (120) fresh faecal samples were collected from the three troops between February and September 2023. The centrifugal floatation technique was used to process and analyse faecal samples, and parasite ova and cysts were identified using morphological features like shape and size. The prevalence of the parasite taxa and a chi-squared multiple comparison test was computed. Results showed significant differences among most parasite taxa except Coccidia spp and Entamoeba spp among the three troops. The Shannon–Wiener (H′) index was used to calculate diversity and graphs were utilized to present the association. The Kruskal-Wallis tests showed no significant difference in parasite diversity among the three troops. Although troop-parasite association showed different parasite species for each troop, helminths Strongylid spp. and Schistosoma spp. were highly common across all three troops. Troop 1 and 3 were associated with four parasite taxa, whereas Troop 2 had only three. The study reveals the presence of gastro-intestinal parasites of public health concern, as they are capable of causing diseases in humans and domestic animals. The study, therefore, underscores the importance of understanding parasite-host dynamics in mitigating zoonotic disease transmission and suggests the need to generate baseline data for mitigating zoonotic diseases and maintaining a healthy ecosystem.

Effect of Caragana microphylla Lam. on Desertified Grassland Restoration

Background: The restoration of the degraded sandy grasslands in Hulun Buir is crucial for maintaining the local ecological balance and sustainable development. Caragana microphylla Lam., a shrub species widely employed in the restoration of sandy vegetation. It is essential to understand its impact on the understory vegetation and soil properties during this process. Methods: This study employed ANOVA, Pearson correlation, and redundancy analysis to systematically analyze the impact of C. microphylla on the three critical stages of desertified grassland vegetation recovery: semi-fixed dunes, fixed dunes, and sandy grasslands. It provided strategies for the restoration of desertified grassland vegetation and offered additional theoretical evidence for the role of vegetation in promoting the recovery of sandy lands. Results: (1) As the degree of vegetation recovery in desertified grasslands increases, the species richness of understory vegetation, Shannon–Wiener index, community height, and biomass also increase. Both the community height and biomass within shrublands are higher than outside, with species richness within the shrublands being higher than outside during the semi-fixed and fixed-sand land stages. (2) In both the 0~10 cm and 10~20 cm soil layers, soil water content showed an increasing trend, peaking in the sandy grassland stage (1.2%), and was higher within the shrublands than outside. The soil water content at 10~20 cm was higher than in the 0~10 cm layer. In both layers, clay and silt content gradually increased with the degree of vegetation recovery in the sandy land, and higher within the shrublands than outside, while the opposite was true for sand content. (3) In both soil layers, soil organic carbon gradually increased with the degree of vegetation recovery, peaking in the sandy grassland stage (4.12 g·kg−1), and was higher within the shrublands than outside. Total nitrogen increased from the semi-fixed-sand land stage to the fixed-sand land stage, with higher levels within the shrublands than outside at all stages. Soil pH within the shrublands decreased as the degree of vegetation recovery increased. There was no significant change in the total phosphorus content. (4) In both soil layers, soil physicochemical characteristics accounted for 59.6% and 46.9% of the vegetation changes within and outside the shrublands, respectively, with the main influencing factors being the soil particle size, total nitrogen, soil water content, and soil organic carbon. Conclusions: In the process of sandy grassland restoration, C. microphylla facilitates the growth and development of vegetation by enhancing the underlying soil physicochemical properties, specifically regarding the soil particle size distribution, soil water content, soil organic carbon, and total nitrogen.

Diversity Patterns of Plant Communities along an Elevational Gradient in Arid and Semi-Arid Mountain Ecosystems in China

Quantitative classification and ordination are instrumental in improving our understanding of plant community patterns and facilitating effective conservation efforts in national mountain ecosystems worldwide. However, there has been a lack of relevant research focused on arid and semi-arid mountain ecosystems. This study aims to address this gap by investigating the Ningxia Helan Mountain National Nature Reserve (located in Northwest China). We conducted a comprehensive study on the patterns of plant communities and their association with environmental factors across a broad elevation range from 1200 m a.s.l. to 2600 m a.s.l. Our findings revealed the presence of 121 angiosperm species across 41 families, with vegetation classified into six distinct groups through two-way indicator species analysis (TWINSPAN) along the elevational gradient. Notably, the communities of Ulmus, Prunus, and Stipa in the middle elevation range exhibited the highest Shannon–Wiener (SW) and Simpson (SN) diversity indices, and these indices followed a single-peak pattern with increasing elevation. Canonical correspondence analysis (CCA) further revealed six distinct yet interrelated plant communities, revealing elevation (ELE) and the biological aridity index (BK) as the most influential environmental factors influencing plant communities’ distribution. This understanding is critically important for biodiversity conservation and the management of ecosystems in arid and semi-arid mountain ecosystems.

Molecular Topology Index of a Zero Divisor Graph on a Ring of Integers Modulo Prime Power Order

In chemistry, graph theory has been widely utilized to address molecular problems, with numerous applications in graph theory and ring theory within this field. One of these applications involves topological indices that represent chemical structures with numerical values. Various types of topological indices exist, including the Wiener index, the first Zagreb index, and the hyper-Wiener index. In the context of this research, the values of the Wiener index, the first Zagreb index, and the hyper-Wiener index for zero-divisor graphs on the ring of integers modulo a prime power order will be explored through a literature review and conjecture.

Wiener index of inverse fuzzy mixed graphs with application in education system

Wiener index of inverse fuzzy mixed graphs with application in education system

Molecular descriptors of symmetrically configured carbon nanocones via quotient graph technique

Carbon nanocones, characterized by planar networks primarily consisting of hexagonal carbon faces and a few pentagons in the core, hold significant promise in various fields such as electronics, medicine, and material research due to their exceptional properties. This study exclusively investigates the topological descriptors of symmetrically configured carbon nanocones, specifically nanocones with two and three pentagonal core respectively. By modeling these structures as chemical graphs and employing molecular descriptors, we aim to provide a quantitative analysis of the structures without laboratory experimentation. The quotient graph approach is employed to determine the distance based descriptors, namely wiener, szeged and Padmakar-Ivan indices for these symmetrically configured carbon nanocones. The analytically closed formulas determined could be useful in quantitative structure-property-activity relationship studies, which helps in predicting the physico-chemical properties of the underlying structures. Thus the findings in this work not only deepen our understanding of symmetric carbon nanocones but also pave the way for significant advancements in nanotechnology and materials science.

Response of Species Diversity and Stability of Typical Steppe Plant Communities on the Mongolian Plateau to Different Grazing Patterns

ABSTRACTGrasslands represent a major biome on Earth and play a vital role in ecosystem functioning and dynamics. However, owing to the variations among grassland types, the impact of grazing on plant community diversity and stability remains unclear. This study is based on the typical steppe of the Mongolian Plateau. Field sampling and data analysis were combined to qualitatively and quantitatively investigate the structural characteristics, species diversity, and stability of plant communities under varying grazing intensities, that is, four‐season nomadic, two‐season rotational, and sedentary grazing (FSNG, TSRG, and SG, respectively). The results indicated that FSNG pastures exhibited the largest number of plant species while FSNG and TSRG pastures exhibited relatively high importance values for the primary dominant species. Carex duriuscula, Chenopodium glaucum, and Cleistogenes squarrosa were prominent in SG pastures, with C. duriuscula having the largest importance value. The mean height, cover, and aboveground biomass of plant communities in FSNG were significantly higher than those in SG (p < 0.05), with no significant difference observed between FSNG and TSRG. FSNG also demonstrated the highest Shannon–Wiener, Simpson, and Pielou indexes. The Shannon–Wiener and Simpson indexes between the FSNG, TSRG, and SG pastures showed significant differences (p < 0.05). Nomadic plant communities displayed positive loosely interspecific traits, suggesting independence and positive succession. Conversely, communities in TSRG and SG exhibited negative correlations and higher instability. The stability analysis ranked community stability as FSNG > TSRG > SG, suggesting that judicious grazing practices could enhance grassland stability. The findings reveal that grazing patterns influence plant community composition and function and that FSNG pastures promote higher species diversity, perennial dominance, and overall stability compared with TSRG and SG pastures.

D-Index of Certain Ladder Graphs

For any two distinct vertices , of a connected graph , the -distance , in which the minimum is taken over all paths, and is the length of the path . The -index of is defined as . In this paper, we obtained a formula for -index or Wiener -index , where is the ladder graph, . Also, we obtained the Wiener -index and Wiener index of semi-Ladder graph .

Plant Species Classification and Biodiversity Estimation from UAV Images with Deep Learning

Biodiversity is a characteristic of ecosystems that plays a crucial role in the study of their evolution, and to estimate it, the species of all plants need to be determined. In this study, we used Unmanned Aerial Vehicles to gather RGB images of mid-to-high-altitude ecosystems in the Zao mountains (Japan). All the data-collection missions took place in autumn so the plants present distinctive seasonal coloration. Patches from single trees and bushes were manually extracted from the collected orthomosaics. Subsequently, Deep Learning image-classification networks were used to automatically determine the species of each tree or bush and estimate biodiversity. Both Convolutional Neural Networks (CNNs) and Transformer-based models were considered (ResNet, RegNet, ConvNeXt, and SwinTransformer). To measure and estimate biodiversity, we relied on the Gini–Simpson Index, the Shannon–Wiener Index, and Species Richness. We present two separate scenarios for evaluating the readiness of the technology for practical use: the first scenario uses a subset of the data with five species and a testing set that has a very similar percentage of each species to those present in the training set. The models studied reach very high performances with over 99 Accuracy and 98 F1 Score (the harmonic mean of Precision and Recall) for image classification and biodiversity estimates under 1% error. The second scenario uses the full dataset with nine species and large variations in class balance between the training and testing datasets, which is often the case in practical use situations. The results in this case remained fairly high for Accuracy at 90.64% but dropped to 51.77% for F1 Score. The relatively low F1 Score value is partly due to a small number of misclassifications having a disproportionate impact in the final measure, but still, the large difference between the Accuracy and F1 Score highlights the complexity of finely evaluating the classification results of Deep Learning Networks. Even in this very challenging scenario, the biodiversity estimation remained with relatively small (6–14%) errors for the most detailed indices, showcasing the readiness of the technology for practical use.

Lack of Small-Scale Changes in Breeding Birds after a Fire: Does the Resilience of Cork Oaks Favor Rapid Recolonization in Suburban Wood Patches?

Forest fires are disturbance events that can impact biological assemblages at multiple scales. In this study, the structures of breeding bird communities in cork oak patches located in an agro-mosaic suburban landscape of central Italy (Rome) were compared at the local scale with a fine-grained mapping method before (2018) and after (2023) a fire event occurred in July 2022. The analyses did not reveal any significant changes in the density of territorial pairs or in the diversity metrics, both univariate (Shannon–Wiener index, evenness, Margalef normalized richness) and bivariate (Whittaker and k-dominance plots, abundance/biomass curves) of diversity. Even when the guilds of strictly forest-related species were compared, no differences emerged before and after the fire. This counterintuitive phenomenon may be due to the characteristics of the dominant tree, the cork oak (Quercus suber), a sclerophilous tree that is very resilient to fires and able to recover foliage in the following spring season, thus allowing rapid bird recolonization. However, other small-scale phenomena (e.g., the ‘crowding effect’ and local dispersal of territorial pairs from remnant wood patches not affected by fire) may explain this lack of change in breeding bird density and diversity. Further studies should be carried out at larger spatial and temporal scales and at different levels of fire frequency and intensity to confirm these responses at the guild/community level in suburban cork oak wood patches.

Ecological quality of the Jucusbamaba River, a high Andean urban river in northeastern Peru

The Jucusbamaba River, located in the northeastern region of Peru, flows through two towns that use its waters for agricultural activities. However, these activities generate waste discharged back into the river, which is additionally polluted by untreated domestic wastewater discharges. The main objective was to evaluate the ecological quality of this lotic system, analyzing biotic and abiotic parameters during two seasons. The biotic parameters included microinvertebrates and fecal coliforms, while the abiotic parameters encompassed temperature, pH, dissolved oxygen, electrical conductivity, turbidity, total dissolved solids, and biochemical oxygen demand. Six sampling points were established where physicochemical and microbiological parameters were analyzed. Simultaneously, quantitative sampling of macroinvertebrates was carried out at the same points to evaluate their diversity using Shannon- Wiener, Margalef and Simpson indices. The Andean Biotic Index (ABI) and the Biotic Family Index (FBI) were calculated to determine the ecological quality of the river using macroinvertebrates. Finally, the spatio-temporal variation of macroinvertebrate composition and physicochemical and microbiological parameters were analyzed. Very high concentrations of BOD, total dissolved solids, and electrical conductivity were obtained in the dry season, while in the rainy season, they were pH, dissolved oxygen, and turbidity. 12548 individuals from 6 classes, 11 orders, and 26 families were collected. The greatest richness of macroinvertebrate families was found at points 1 and 2, with Trichoptera, Ephemeroptera and Plecoptera individuals predominating. There was evidence of temporal variation in physicochemical and microbiological parameters, as well as in macroinvertebrate composition. It was concluded that the ecological quality of the Jucusbamba River decreases as it follows its course due to anthropic disturbances. This research can be used to develop management plans, awareness-raising, and sanitation measures to ensure the protection and conservation of the Jucusbamaba River.

Tree diversity drives understory carbon storage rather than overstory carbon storage across forest types

Although numerous studies have proposed explanations for the specific and relative effects of stand structure, plant diversity, and environmental conditions on carbon (C) storage in forest ecosystems, understanding how these factors collectively affect C storage in different community layers (trees, shrubs, and herbs) and forest types (mixed, broad-leaved (E), broad-leaved (M), and coniferous forest) continues to pose challenges. To address this, we used structural equation models to quantify the influence of biotic factors (mean DBH, mean height, maximum height, stem density, and basal area) and abiotic factors (elevation and canopy openness), as well as metrics of species diversity (Shannon–Wiener index, Simpson index, and Pielou’s evenness) in various forest types. Our analysis revealed the critical roles of forest types and elevation in explaining a substantial portion of variability in C storage in the overstory layer, with a moderate influence of stand factors (mean DBH and basal area) and a slightly negative impact of tree species diversity (Shannon–Wiener index). Notably, forest height emerged as the primary predictor of C storage in the herb layer. Regression relationships further highlighted the significant contribution of tree species diversity to mean height, understory C storage, and branch biomass within the forest ecosystem. Our insights into tree species diversity, derived from structural equation modeling of C storage in the overstory, suggest that the effects of tree species diversity may be influenced by stem biomass in statistical reasoning within temperate forests. Further research should also integrate tree species diversity with tree components biomass, forest mean height, understory C, and canopy openness to understand complex relationships and maintain healthy and sustainable ecosystems in the face of global climate challenges.

Forgotten Topological Index and its Properties on Neutrosophic Graphs

Topological indices play a significant role in crisp, fuzzy graphs and their real-life application. But to avoid the vagueness in the final result, these indices should be dealt with in the neutrosophic environment since it consolidates the uncertain quantity or values of an event in the name of "indeterminacy membership". Except for the wiener index, no other indices are introduced under the neutrosophic graphical setting. In this article, we consider the forgotten topological index (ToI) and the Edge forgotten index in the 3-valued logic neutrosophic graph and came up with some important theorem results and applications.

Analysis of Phenotypic Trait Variation in Germplasm Resources of Lycium ruthenicum Murr.

Exploring the phenotypic trait variation and diversity of Lycium ruthenicum germplasm resources can support selection, breeding, and genetic improvement, enhancing agricultural production. This study collected 213 wild Lycium ruthenicum seedlings from a resource nursery in Alxa League, Inner Mongolia. These seedlings originated from eight sources across four provinces. Using 11 pseudo-qualitative traits and 20 quantitative traits, the phenotypic variation of the germplasm was analyzed. The analysis involved the coefficient of variation, Shannon–Wiener index (H), Simpson’s genetic diversity index (D), principal component analysis, correlation analysis, and Q-type cluster analysis. The results showed that the variation range of 31 phenotypic traits across the 213 Lycium ruthenicum germplasm resources was 17.26% to 105.41%, with an average coefficient of variation of 39.85%. The H and D indexes ranged from 0.18 to 1.58 and 0.20 to 0.75, respectively. For the 11 pseudo-qualitative traits, the H and D ranges were 0.18 to 1.58 and 0.07 to 0.74, with average values of 0.77 and 0.42. For the quantitative traits, the H and D ranges were 0.54 to 1.49 and 0.25 to 0.75, with average values of 1.21 and 0.63. This indicates that Lycium ruthenicum germplasm resources exhibit significant phenotypic diversity, with quantitative traits showing higher diversity than pseudo-qualitative traits. Principal component analysis revealed that the cumulative variance contribution rate of the first 10 principal components was 74.03%, comprehensively reflecting the information of the 31 traits. Q-type cluster analysis grouped the 213 Lycium ruthenicum germplasm resources into six clusters, each with distinct phenotypic characteristics. This analysis also identified the trait characteristics and breeding value of each cluster. The results of this study provide valuable information on the genetic improvement, conservation, and evaluation of Lycium ruthenicum germplasm resources.