The carbon fertilization effect over a century of anthropogenic CO2 emissions: higher intracellular CO2 and more drought resistance among invasive and native grass species contrasts with increased water use efficiency for woody plants in the US Southwest.

From 1890 to 2015, anthropogenic carbon dioxide emissions have increased atmospheric CO2 concentrations from 270 to 400 mol mol-1 . The effect of increased carbon emissions on plant growth and reproduction has been the subject of study of free-air CO2 enrichment (FACE) experiments. These experiments have found (i) an increase in internal CO2 partial pressure (ci ) alongside acclimation of photosynthetic capacity, (ii) variable decreases in stomatal conductance, and (iii) that increases in yield do not increase commensurate with CO2 concentrations. Our data set, which includes a 115-year-long selection of grasses collected in New Mexico since 1892, is consistent with an increased ci as a response to historical CO2 increase in the atmosphere, with invasive species showing the largest increase. Comparison with Palmer Drought Sensitivity Index (PDSI) for New Mexico indicates a moderate correlation with Δ13 C (r2  = 0.32, P < 0.01) before 1950, with no correlation (r2  = 0.00, P = 0.91) after 1950. These results indicate that increased ci may have conferred some drought resistance to these grasses through increased availability of CO2 in the event of reduced stomatal conductance in response to short-term water shortage. Comparison with C3 trees from arid environments (Pinus longaeva and Pinus edulis in the US Southwest) as well as from wetter environments (Bromus and Poa grasses in New Mexico) suggests differing responses based on environment; arid environments in New Mexico see increased intrinsic water use efficiency (WUE) in response to historic elevated CO2 while wetter environments see increased ci . This study suggests that (i) the observed increases in ci in FACE experiments are consistent with historical CO2 increases and (ii) the CO2 increase influences plant sensitivity to water shortage, through either increased WUE or ci in arid and wet environments, respectively.

Evolutionary optimization of material properties of a tropical seed.

Here, we show how the mechanical properties of a thick-shelled tropical seed are adapted to permit them to germinate while preventing their predation. The seed has evolved a complex heterogeneous microstructure resulting in hardness, stiffness and fracture toughness values that place the structure at the intersection of these competing selective constraints. Analyses of different damage mechanisms inflicted by beetles, squirrels and orangutans illustrate that cellular shapes and orientations ensure damage resistance to predation forces imposed across a broad range of length scales. This resistance is shown to be around the upper limit that allows cracking the shell via internal turgor pressure (i.e. germination). Thus, the seed appears to strike an exquisitely delicate adaptive balance between multiple selection pressures.

Comparison of methods for rooting phylogenetic trees: a case study using Orcuttieae (Poaceae: Chloridoideae).

DNA sequence data (cpDNA trnL intron and nrDNA ITS1 and ITS2) were analyzed to identify relationships within Orcuttieae, a small tribe of endangered grasses endemic to vernal pools in California and Baja California. The tribe includes three genera: Orcuttia, Tuctoria, and Neostapfia. All three genera carry out C(4) photosynthesis but aquatic taxa of Orcuttia lack Kranz anatomy. The unusual habitat preference of the tribe is coupled with the atypical development of C(4) photosynthesis without Kranz anatomy. Furthermore, the tribe has no known close relatives and has been noted to be phylogenetically isolated within the subfamily Chloridoideae. In this study we examine the problem of inferring the root of the tribe in the absence of an identified outgroup, analyze the phylogenetic relationships of the constituent taxa, and evaluate the evolutionary development of C(4) photosynthesis. We compare four methods for inferring the root of the tree: (1) the outgroup method, (2) midpoint rooting, the imposition of a molecular clock for both (3) maximum likelihood (ML) and (4) Bayesian analysis. We examine the consequences of each method for the inferred phylogenetic relationships. Three of the methods (outgroup rooting and the ML and Bayesian molecular clock analyses) suggest that the root of Orcuttieae is between Neostapfia and the Tuctoria/Orcuttia lineage, while midpoint rooting gives a different root. The Bayesian method additionally provides information about probabilities associated with other possible root locations. Assuming that the true root of Orcuttieae is between Neostapfia and the Tuctoria/Orcuttia lineage, our data indicate Neostapfia and Orcuttia are both monophyletic, while Tuctoria is paraphyletic (with no synapomorphies in either dataset) and forming a grade between the other two genera and needs taxonomic revision. Our data support the hypothesis that Orcuttieae was derived from a terrestrial ancestor and evolved specializations to an aquatic environment, including C(4) photosynthesis without Kranz anatomy.

Evaluation of aqueous extracts of Taraxacum officinale on growth and invasion of breast and prostate cancer cells.

Ethnotraditional use of plant-derived natural products plays a significant role in the discovery and development of potential medicinal agents. Plants of the genus Taraxacum, commonly known as dandelions, have a history of use in Chinese, Arabian and Native American traditional medicine, to treat a variety of diseases including cancer. To date, however, very few studies have been reported on the anti-carcinogenic activity of Taraxacum officinale (TO). In the present study, three aqueous extracts were prepared from the mature leaves, flowers and roots, and investigated on tumor progression related processes such as proliferation and invasion. Our results show that the crude extract of dandelion leaf (DLE) decreased the growth of MCF-7/AZ breast cancer cells in an ERK-dependent manner, whereas the aqueous extracts of dandelion flower (DFE) and root (DRE) had no effect on the growth of either cell line. Furthermore, DRE was found to block invasion of MCF-7/AZ breast cancer cells while DLE blocked the invasion of LNCaP prostate cancer cells, into collagen type I. Inhibition of invasion was further evidenced by decreased phosphorylation levels of FAK and src as well as reduced activities of matrix metalloproteinases, MMP-2 and MMP-9. This study provides new scientific data on TO and suggests that TO extracts or individual components present in the extracts may be of value as novel anti-cancer agents.

Genetic diversity in Chihuahuan Desert populations of creosotebush (Zygophyllaceae: Larrea tridentata).

We examined isozyme variation in the dominant Chihuahuan Desert shrub, Larrea tridentata (creosotebush), to determine the genetic variation within and among populations, the biogeographic relationships of populations, and the potential inbreeding in the species. We surveyed 17 populations consisting of 20 to 50 individuals per population along a 1600-km north-south transect across the Chihuahuan Desert. The southernmost population was near Villa Hidalgo, Mexico, and the northernmost near Isleta Pueblo, New Mexico. All 12 isozyme loci examined were polymorphic (H(t) = 0.416), with up to nine alleles per locus. Despite high levels of variation, we detected moderate inbreeding in L. tridentata populations. Most variation was found within rather than among populations (G(ST) = 0.118). Furthermore, recently established populations in the northern limits of the Chihuahuan Desert did not show decreased levels of genetic variation (H(o) = 0.336). A significant correlation was found between pairwise genetic and geographic distances (r = 0.305). Larrea tridentata showed and continues to show a massive range expansion into the arid and semi-arid regions of the American Southwest, but as shown by the high genetic variation, this expansion took place as a wave, rather than a series of founder events.