Phenolic variation among Chamaecrista nictitans subspecies and varieties revealed through UPLC-ESI(-)-MS/MS chemical fingerprinting.

INTRODUCTION: Comparative analysis of metabolic features of plants has a high potential for determination of quality control of active ingredients, ecological or chemotaxonomic purposes. Specifically, the development of efficient and rapid analytical tools that allow the differentiation among species, subspecies and varieties of plants is a relevant issue. Here we describe a multivariate model based on LC-MS/MS fingerprinting capable of discriminating between subspecies and varieties of the medicinal plant Chamaecrista nictitans, a rare distributed species in Costa Rica. METHODS: Determination of the chemical fingerprint was carried out on a LC-MS (ESI-QTOF) in negative ionization mode, main detected and putatively identified compounds included proanthocyanidin oligomers, several flavonoid C- and O-glycosides, and flavonoid acetates. Principal component analysis (PCA), partial least square-discriminant analysis (PLS-DA) and cluster analysis of chemical profiles were performed. RESULTS: Our method showed a clear discrimination between the subspecies and varieties of Chamaecrista nictitans, separating the samples into four fair differentiated groups: M1 = C. nictitans ssp. patellaria; M2 = C. nictitans ssp. disadena; M3 = C. nictitans ssp. nictitans var. jaliscensis and M4 = C. nictitans ssp. disadena var. pilosa. LC-MS/MS fingerprint data was validated using both morphological characters and DNA barcoding with ITS2 region. The comparison of the morphological characters against the chemical profiles and DNA barcoding shows a 63% coincidence, evidencing the morphological similarity in C. nictitans. On the other hand, genetic data and chemical profiles grouped all samples in a similar pattern, validating the functionality of our metabolomic approach. CONCLUSION: The metabolomic method described in this study allows a reliably differentiation between subspecies and varieties of C. nictitans using a straightforward protocol that lacks extensive purification steps.

Mutualistic rhizobia reduce plant diversity and alter community composition.

Mutualistic interactions can be just as important to community dynamics as antagonistic species interactions like competition and predation. Because of their large effects on both abiotic and biotic environmental variables, resource mutualisms, in particular, have the potential to influence plant communities. Moreover, the effects of resource mutualists such as nitrogen-fixing rhizobia on diversity and community composition may be more pronounced in nutrient-limited environments. I experimentally manipulated the presence of rhizobia across a nitrogen gradient in early assembling mesocosm communities with identical starting species composition to test how the classic mutualism between nitrogen-fixing rhizobia and their legume host influence diversity and community composition. After harvest, I assessed changes in α-diversity, community composition, ß-diversity, and ecosystem properties such as inorganic nitrogen availability and productivity as a result of rhizobia and nitrogen availability. The presence of rhizobia decreased plant community diversity, increased community convergence (reduced ß-diversity), altered plant community composition, and increased total community productivity. These community-level effects resulted from rhizobia increasing the competitive dominance of their legume host Chamaecrista fasciculata. Moreover, different non-leguminous species responded both negatively and positively to the presence of rhizobia, indicating that rhizobia are driving both inhibitory and potentially facilitative effects in communities. These findings expand our understanding of plant communities by incorporating the effects of positive symbiotic interactions on plant diversity and composition. In particular, rhizobia that specialize on dominant plants may serve as keystone mutualists in terrestrial plant communities, reducing diversity by more than 40%.

[Effects of selenium on Chamaecrista rotundifolia growth, nutrient absorption and nitrogen-fixing ability].

In this paper, a field experiment was conducted on a red soil of South China to study the effects of applying selenium fertilizer on the growth, forage quality and nitrogen-fixing ability of Chamaecrista rotundifolia. The results showed that applying 75, 150, 225 and 300 g Se x hm(-2) could increase the plant height, branch number, dry root weight and dry forage yield by 0.3% - 6.2%, 65.1% - 79.5%, 155% - 252% and 30.6% - 54.1%, respectively. The total nitrogen, total phosphorus and total potassium contents of plant were increased by 21.79% - 41.46%, 20.74% - 34.67% and 34.3% - 62.4%, respectively, and the raw protein, raw fat, raw fiber and amino acid contents were increased by 21.79% - 41.46%, 1.4% - 89.6%, 34.1% - 56.6% and 6.33% 63.24%, respectively. Among the 4 doses, 150 g Se x hm(-2) was the most effective and suitable application amount. The selenium content in plant after applying 300 g Se x hm(-2)(S4) was 0.695 mg x kg(-'), with an increase of 0.658 mg x kg(-1) compared to no selenium fertilization. There was a significantly positive correlation between plant selenium content and applied selenium (R2 = 0.9666**). The root nodule weight, number and nitrogenase activity in treatment 150 g Se x hm(-2)(S2) were respectively 131.7%, 114.3% and 1417.9% higher than those of no selenium fertilization. The correlation between applied selenium and nitrogenase activity was also significant (R2 = 0.9606*).