Large herbivores suppress liana infestation in an African savanna.

African savannas are the last stronghold of diverse large-mammal communities, and a major focus of savanna ecology is to understand how these animals affect the relative abundance of trees and grasses. However, savannas support diverse plant life-forms, and human-induced changes in large-herbivore assemblages-declining wildlife populations and their displacement by livestock-may cause unexpected shifts in plant community composition. We investigated how herbivory affects the prevalence of lianas (woody vines) and their impact on trees in an East African savanna. Although scarce (<2% of tree canopy area) and defended by toxic latex, the dominant liana, Cynanchum viminale (Apocynaceae), was eaten by 15 wild large-herbivore species and was consumed in bulk by native browsers during experimental cafeteria trials. In contrast, domesticated ungulates rarely ate lianas. When we experimentally excluded all large herbivores for periods of 8 to 17 y (simulating extirpation), liana abundance increased dramatically, with up to 75% of trees infested. Piecewise exclusion of different-sized herbivores revealed functional complementarity among size classes in suppressing lianas. Liana infestation reduced tree growth and reproduction, but herbivores quickly cleared lianas from trees after the removal of 18-y-old exclosure fences (simulating rewilding). A simple model of liana contagion showed that, without herbivores, the long-term equilibrium could be either endemic (liana-tree coexistence) or an all-liana alternative stable state. We conclude that ongoing declines of wild large-herbivore populations will disrupt the structure and functioning of many African savannas in ways that have received little attention and that may not be mitigated by replacing wildlife with livestock.

De novo transcriptome sequencing and comprehensive analysis of the drought-responsive genes in the desert plant Cynanchum komarovii.

BACKGROUND: Cynanchum komarovii Al Iljinski is a xerophytic plant species widely distributing in the severely adverse environment of the deserts in northwest China. At present, the detailed transcriptomic and genomic data for C. komarovii are still insufficient in public databases. RESULTS: To investigate changes of drought-responsive genes and explore the mechanisms of drought tolerance in C. komarovii, approximately 27.5 GB sequencing data were obtained using Illumina sequencing technology. After de novo assembly 148,715 unigenes were generated with an average length of 604 bp. Among these unigenes, 85,106 were annotated with gene descriptions, conserved domains, gene ontology terms, and metabolic pathways. The results showed that a great number of unigenes were significantly affected by drought stress. We identified 3134 unigenes as reliable differentially expressed genes (DEGs). During drought stress, the regulatory genes were involved in signaling transduction pathways and in controlling the expression of functional genes. Moreover, C. komarovii activated many functional genes that directly protected against stress and improved tolerance to adapt drought condition. Importantly, the DEGs were involved in biosynthesis, export, and regulation of plant cuticle, suggesting that plant cuticle may play a vital role in response to drought stress and the accumulation of cuticle may allow C. komarovii to improve the tolerance to drought stress. CONCLUSION: This is the first large-scale reference sequence data of C. komarovii, which enlarge the genomic resources of this species. Our comprehensive transcriptome analysis will provide a valuable resource for further investigation into the molecular adaptation of desert plants under drought condition and facilitate the exploration of drought-tolerant candidate genes.

Antidiabetic and antioxidant activities of major flavonoids of Cynanchum acutum L. (Asclepiadaceae) growing in Egypt.

Seven flavonoids were isolated from the butanol fraction of the methanolic extract of the aerial parts of Cynanchum acutum L. (Asclepiadaceae). All of which have been isolated for the first time from the genus Cynanchum. Their structures were established as quercetin 3-O-beta-galacturonopyranoside (1), quercetin 7-O-beta-glucopyranoside (2), tamarixtin 3-O-beta-galacturonopyranoside (3), kaempferol 3-O-beta-galacturonopyranoside (4), 8-hydroxyquercetin 3-O-beta-galactopyranoside (5), tamarixtin 3-O-alpha-rhamnopyranoside (6), and tamarixtin 7-O-alpha-arabinopyranoside (7) on the basis of their chromatographic properties, chemical and spectroscopic data. The major isolated flavonoids 1, 2 and 3 were found to exhibit significant antioxidant and antidiabetic activities (by measuring blood glucose and insulin levels). This is the first report about the antioxidant and antidiabetic activities of compounds 1-3.

[Effect of source-sink ratio changing on yield formation of Cynanchum bungei].

OBJECTIVE: To study the effect of changing source-sink ratio on dry matter accumulation yield, distribution and interrelated physiological index of Cynanchum bungei. METHOD: Bud, fruit or side tress of C. bungei were picked artificially in the development stage. LAI, chlorophyll content, photosynthesis of single leaf, accumulation and distribution of dry matter at different and treatments were measured. The untreated plant was used as the control. RESULT: Although leaf decrease can be compensated by the increasing photosynthesis rate of single leaf, the LAI was small, chlorophyll decomposes quickly and these leaves showed the signs of early ageing. The matter accumulation was lower than that of control. Picking bud and fruit made photosynthesis rate of single leaf descend, chlorophyll decomposes slowly and its content keeps high, that inhibited ageing of the plant obviously. The LAI keeps larger, photosynthate was abundant. Dry matter accumulation and distribution to the root were higher than that of control and that of side tress picked. So, the yield with this treatment increased. CONCLUSION: Picking bud can increase LAI, postpone the decomposition of chlorophyll, and protract the functional leaves. Consequently, picking bud can add the accumulation of dry matter, increase proportion to radix and improve the yield and economy benefit.

Interactive effects of mechanical stress, sand burial and defoliation on growth and mechanical properties in Cynanchum komarovii.

In drylands, wind, sand burial and grazing are three important factors affecting growth and mechanical properties of plants, but their interactive effects have not yet been investigated. Plants of the semi-shrub Cynanchum komarovii, common in semi-arid parts of NE Asia, were subjected to brushing, burial and defoliation. We measured biomass allocation and relative increment rates of dry mass (RGR(m)), height (RGR(h)) and basal diameter (RGR(d)). We also measured the stem mechanical properties, Young's modulus (E), second moment of area (I), flexural stiffness (EI) and breaking stress (σ(b)), and scaled these traits to the whole-plant level to determine the maximum lateral force (F(lateral)) and the buckling safety factor (BSF). Brushing increased RGR(m); neither burial nor defoliation independently affected RGR(m), but together they reduced it. Among buried plants, brushing positively affected stem rigidity and strength through increasing RGR(d), E, I and EI, and at whole plant level this resulted in a larger BSF and F(lateral). However, among unburied plants this pattern was not observed. Our results thus show that effects of mechanical stress and grazing on plants can be strongly modified by burial, and these interactions should be taken into account when considering adaptive significance of plant mechanical traits in drylands.