Orchids are one of the largest groups of flowering plants, with over 22,000 species worldwide. All orchids form symbiotic mycorrhizal associations with fungi. Some species begin this association at seed germination, when fungal enzymes break down the cell walls of the seed. In many species the fungal partner goes on to provide all the nutrients required by the plant during the seedling phase, and in some a lifelong association ensues. In these partnerships, the plant gains access to nutrients released as the fungal hyphae break down otherwise inaccessible soil organic matter. The distribution of orchid mycorrhizal fungi in the soil determines orchid distribution, and understanding the growth and survival of these fungi is an important consideration in orchid conservation.

In a recent study of four orchid species, Nurfadilah et al. (2013) examined the breakdown and uptake of a range of nutrients by their fungal partners. The study site was in the Southwest Australian Floristic Region, characterised by nutrient-poor, organic-deficient soils. Fungi were isolated from each orchid species and grown on media containing more than 25 different nutrient types. These contained a wide “menu” of carbon, phosphorous and nitrogen sources. The authors found that the mycorrhizal fungus Ceratobasidium, associated with the more abundant and widespread of the orchid species, Pterostylis recurva (pictured), grew faster on almost every nutrient source compared with the other fungal species. It could also utilise galactose and nitrate from the growth medium (which the others did not, or did so very slowly). The rarer orchid species studied, Drakaea elastica, found exclusively on nutrient-poor sandy soils, had the slowest-growing fungal partner. It is assumed that in richer soils, this fungus would be out-competed by other species.

The authors conclude that, in a nutrient-limited area, the ability of an orchid’s fungal partner to make use of a wide range of nutrients can provide both parties access to inhabiting a broader range of environmental conditions. Additionally, different species making use of distinct nutrient sources can occur side-by-side without competing directly for the same resource.

Original article: Nurfadilah, S., Swarts, N. D., Dixon, K. W., Lambers, H. and Merritt, D. J. (2013) Variation in nutrient-acquisition patterns by mycorrhizal fungi of rare and common orchids explains diversification in a global biodiversity hotspot. Annals of Botany 111: 1233–1241. DOI:10.1093/aob/mct064

Image of Pterostylis recurva is from the book Australian Orchids by R. D. Fitzgerald (1877). Courtesy of the Swiss Orchid Foundation website www.orchid.unibas.ch

Google Reader closes at the end of the month, and it’s going to make a few things around the web break. Here, we use it to power the Other Botany Blogs widget on the right. There are plenty of options for people to move their personal feeds (see below), but is there value in a public aggregation of RSS feeds?

I’ve looked at how to put together a site that pulls in headlines from various (~100) botany/plant blogs and then makes a combined feed that anyone can re-use. So far I’ve not found a good free way to do this, but the problem can be solved if I hand over some money. The answer would be to set up a new server and install something like Pligg.

The advantage Pligg has over many Digg/Reddit clones is that it can automatically pull in RSS feeds from blogs. It should be possible to set it up to check a site twice a day and then mix the feeds together in roughly date order. It gets complicated when some people’s feeds don’t have dates. I have a couple of questions.

Would you use this?

I expect the answer is no. Personal solutions tend to be better. Alan Cann is using The Old Reader, I’m also using NewsBlur and a lot of people are using Feedly. The appeal of a site following 100 feeds picked by someone else is limited, but it might be useful for some people. If I’m wrong and a lot of people are interested I can make more time to work on it.

Would you object to this?

There are different ways of doing this. The way I want to do it is automatically pull in a headline and a brief snippet of a blog post. I have looked at Planet, but that tends to pull in full feeds. That means it make visiting the source site unnecessary. If people are reading your blog, I think it would at least be nice to add to the page views of the site. The best way of adding sites would be if people actively consented, but a few of the feeds in the file are from dormant sites. Their authors might not be taking much of an interest in what they’re doing right now, but they could spring back to life. It’s useful to track these sites, but you’re not likely to get active consent for that. If you’re wary of having your feed compiled with sites then let me know in the comments. I’d rather know before I set this up than remove lots of feeds from the site after I’ve set it up.

It’s not certain the feed aggregator will happen, or will happen soon. The new version of WordPress will mean a few changes on this site. I’ve been tracking that too and we have a new theme, layout and a few other changes ready for when WP3.6 is released. It might be that its launch will clash with the closing of Reader, and the blog is the priority.

If there’s no interest then I’m happy to let the aggregator idea go. It has its positive side, but it’s also one more thing to go wrong and one more place to get spam too.

Plants must compete for space, light and other resources with the same and with other species. The shade-avoidance syndrome (SAS) is a strategy of major adaptive significance to plants. The SAS is highly widespread in most species growing in open habitats and depends on the ability of the plant to perceive the presence of neighbours to anticipate competition for scarce resources such as light in crowded stands. A plant canopy reduces the ratio of red to far-red light (R/FR) by the efficient absorption of red light by photosynthetic pigments and the relative increase of FR photons. Plants perceive this light quality change through the phytochrome system and respond very rapidly, enhancing SAS, including via vegetative structure elongation, hyponastic response and acceleration of flowering.

A recent paper in Annals of Botany examines the SAS genetic architecture of hypocotyl elongation to an end-of-day FR signal (EOD) – a light treatment that simulates shade conditions in nature – in Arabidopsis thaliana. The authors found that the ERECTA gene is implicated in the SAS in a background-dependent manner. ERECTA polymorphic effects in EOD responses were detected for other SAS traits, suggesting that its role in shaded environments is relevant for some populations in different phases of plant development.

The receptor-like kinase ERECTA contributes to the shade-avoidance syndrome in a background-dependent manner. (2013) Annals of Botany 111 (5): 811-819. doi: 10.1093/aob/mct038
Abstract
Plants growing at high densities perceive a decrease in the red to far-red (R/FR) ratio of incoming light. These changes in light quality trigger a suite of responses collectively known as the shade-avoidance syndrome (SAS) including hypocotyl and stem elongation, inhibition of branching and acceleration of flowering. Quantitative trait loci (QTLs) were mapped for hypocotyl length to end-of-day far-red (EOD), a simulated shade-avoidance response, in recombinant inbred line (RIL) populations of Arabidopsis thaliana seedlings, derived from Landsberg erecta (Ler) and three accessions (Columbia, Col; Nossen, No-0; and Cape Verde Islands, Cvi-0).
Five loci were identified as being responsible for the EOD response, with a positive contribution of Ler alleles on the phenotype independently of the RIL population. Quantitative complementation analysis and transgenic lines showed that PHYB is the candidate gene for EODRATIO5 in the Ler × Cvi-0 RIL population, but not for two co-localized QTLs, EODRATIO1 and EODRATIO2 mapped in the Ler × No-0 and Ler × Col RIL populations, respectively. The ERECTA gene was also implicated in the SAS in a background-dependent manner. For hypocotyl length EOD response, a positive contribution of erecta alleles was found in Col and Van-0, but not in Ler, Cvi-0, Hir-1 or Ws. Furthermore, pleiotropic effects of ERECTA in the EOD response were also detected for petiole and lamina elongation, hyponastic growth, and flowering time.
The results show that the analysis of multiple mapping populations leads to a better understanding of the SAS genetic architecture. Moreover, the background- and trait-dependent contribution of ERECTA in the SAS suggest that its function in shaded natural environments may be relevant for some populations in different phases of plant development. It is proposed that ERECTA is involved in canalization processes buffering the genetic variation of the SAS against environmental light fluctuations.

The Australian legume Viminaria juncea forms both cluster roots and mycorrhizal associations. de Campos et al. manipulate P supply over a range of 0 to 50 mg P kg^–1 dry soil in order to investigate if these root specializations are expressed at different shoot P concentrations [P]. Remarkably, they find that shoot [P] over the entire range of supplies is constant. They conclude that to maintain stable shoot [P] values, V. juncea must down-regulate its growth rate when very little P is supplied; conversely, it down-regulates its P-uptake capacity very tightly at higher P supply, when its maximum growth rate has been reached. The persistence of cluster roots and mycorrhizal colonization up to the highest P treatments is probably a consequence of tightly controlled shoot [P].

Gloxinia (Sinningia speciosa) is a popular ornamental plant with attractive, colourful flowers, but the genetic mechanisms that regulate flowering are largely unknown. Li et al. generate transgenic gloxinia plants that over-express or supress miR159, and determine that this leads to late and early flowering, respectively. miR159-mediated SsGAMYB expression affects the expression levels of SsLEAFY (SsLFY) and three MADS-box genes (SsAP1, SsAP3 and SsAG), which regulated floral transition downstream of GAMYB. They conclude that transgenic manipulation of miR159 has the potential to be used to regulate flowering time in commercial ornamental plants.

Agroforestry has been replaced by monocultures in farms across Europe, but could a drive to sustainable agriculture herald its return? The English version of this post follows the French.

Longtemps considérée comme une méthode culturale réservée aux pays du Sud, l’agroforesterie connaît depuis peu une certaine expansion en Europe. L’agroforesterie définit toute association d’arbres et de cultures, ou d’activités d’élevage, sur une même parcelle agricole.^[1] Autrefois traditionnellement et massivement présente, elle a peu à peu disparu de nos paysages après la seconde guerre mondiale ; dans un besoin urgent de développer une agriculture productiviste, on arracha en masse les arbres pour laisser place à de plus grandes parcelles, destinées à la monoculture, et ainsi mieux adaptées à de forts rendements. Mais cette course aux rendements a entraîné, au fil du temps, diverses répercussions malheureusement néfastes, notamment sur la biodiversité et les écosystèmes, que nous ne mesurons qu’aujourd’hui. Afin de répondre aux défis posés à l’agriculture moderne, de nombreuses recherches ont été menées pour essayer de concilier rendements, biodiversité et respect de l’environnement, et il semblerait que l’agroforesterie constitue en soi une réponse en termes d’agriculture durable.
Read more on “Et si l’agroforesterie remplaçait les monocultures en Europe… / Do you believe agroforestry may replace monoculture in Europe?” »

There are numerous examples in nature of distantly-related organisms converging on similar shapes that have proved useful to each. This convergent evolution can generate strikingly similar but independently evolved forms such as the streamlined bodies of dolphins and ichthyosaurs (a group of extinct marine reptiles); the wing shapes of birds and bats and the similar body shapes of the placental wolf and the thylacine (a recently extinct wolf-like marsupial). Such similarities have long been assumed to result from exposure to similar environmental conditions and selection pressures.

A recent AoB paper considered the similarities between the habitats of American and African succulent plants. The spurges, milkweeds and iceplants of Africa and the ancestrally distant cacti of America are outwardly very similar in appearance, and these resemblances have been explained by similarities in local climate. This study aimed to quantify the environmental spaces in which the two groups of plants exist, and therefore show whether similarity in form is indeed a corollary of similarity in habitat.

The selected study sites were hotspots of succulent abundance and diversity on each continent. In these dry, warm areas, storage of water and prevention of water loss are priorities for plants and so spherical or globular growth forms have evolved in each group. The authors analysed local climate data and employed GIS and niche equivalence modelling to compare the American and African succulent hotspot sites. What they found were surprisingly many differences in variables such as rainfall and temperature between the sites, and these differences outnumbered any similarities.

The authors concluded that the resemblance between the succulents on each continent may be explained by factors that were not included in their climate analyses, such as soil type, distance from the sea, and possibly important contributions of water to the plants by fog and dew. They also point out that the “similarities” (to the human eye) between these groups may be quite subjective, and that more robust measurements of similarity may be required when claiming convergence of growth forms.

Original Paper:
Alvarado-Cárdenas, L. O., Martínez-Meyer, E., Feria, T. P., Eguiarte, L. E., Hernández, H. M., Midgley, G., & Olson, M. E. (2013). “To converge or not to converge in environmental space: testing for similar environments between analogous succulent plants of North America and Africa”. Annals of Botany, 111(6), 1125-1138. DOI:10.1093/aob/mct078