Do changes in water levels in wetlands give plants a backbone?

The usual rule whenever a headline asks a silly question is that answer is no, and that’s the same here because plants don’t have backs. However research by Hamann and Puijalon does show that emergence due to falling water levels can cause a biomechanical response.

The stresses for aquatic and terrestrial plants differ, because aquatic plants have the support of water to give them buoyancy. Hamann and Puijalon point out, if a plant can float then the chief stress it will have is tension as it is dragged by the local current. What it needs is an anchor and flexibility to cope with the forces on it. A terrestrial plant in contrast feels gravity much more. It has to support its own weight. Wind can put a plant in tension, but the force of gravity can compress some tissues. So the mechanical needs of a plant out of water are different to those in water.

Diagram of forces on aquatic and terrestrial plants

Schematic overview of the main forces (thick arrows) and stresses (thin arrows) acting on plants in aquatic and terrestrial environments. In the aquatic environment, buoyant plants withstand the drag forces resulting from current flow through tension (σ +). In the terrestrial environment, in addition to the force of gravity, self-supportive plants withstand drag forces induced by wind through bending (a combination of tension σ + and compression σ −). Diagram by Elena Hamann and Sara Puijalon.

This is a problem for a plant that is happily sat in water, until there’s a drought. When the water goes the plants are faced with a major change in environment. Can they change their physical structure to cope? Hamann and Puijalon expected that plants could increase their cross-sectional area and the proportion of strengthening tissue in their stems to increase strength. They also expected the stems to become stiffer.

They looked at a wide variety of species Berula erecta (Hudson) Coville, Hippuris vulgaris L., Juncus articulatus L., Lythrum salicaria L., Mentha aquatica L., Myosotis scorpioides L., Nuphar lutea L. and Sparganium emersum Rehmann. The plants were growing in wetlands along the Ain and the Rhône in eastern France. One set of plants was picked from submerged conditions and the other from close by in emergent conditions, to keep the population and growing conditions as similar as possible. They then tested the plants for strength and flexibility and examined them physically.
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Pollination, flower size variation and floral symmetry

Pollination, flower size variation and floral symmetry

Pollination, flower size variation and floral symmetry

The pollinator-mediated stabilizing selection hypothesis suggests that the specialized pollination system of zygomorphic flowers might cause stabilizing selection, reducing their flower size variation compared to actinomorphic flowers. By using data on 43 species from two contrasting communities, Lázaro and Totland show that zygomorphic species that are highly dependent on pollinators and ecologically specialized are less variable in flower size than ecologically generalist and selfing zygomorphic species. However, these relationships are not found in actinomorphic species. The results suggest that the relationship between flower size variation and floral symmetry may be influenced by population-dependent factors, such as ecological generalization and species’ dependence on pollinators.

Population persistence of a displaced shrub

Population persistence of a displaced shrub

Population persistence of a displaced shrub

Olearia flocktoniae (Asteraceae) is an endangered shrub that was passively translocated from its natural ecosystem where it has since gone extinct. Gross and Mackay use two decades of demographic monitoring and a seed bank study in a sensitivity analysis in order to reveal vulnerabilities in the life cycle. They find that seed production is high but populations are short-term persistent (<5 years) due to transient seed banks and poor survivorship of seedlings. Seedling establishment is promoted by soil disturbance and only populations that have been disturbed annually survived the full 20 years of the study. They conclude that active management is thus required to keep this species from extinction.

Evolution of Old World Salvia in Africa

Evolution of Old World <i>Salvia</i> in Africa

Evolution of Old World Salvia in Africa

Salvia (Lamiaceae) is the largest genus in the mint family, and phenotypic diversity of the genus in Africa is largely the result of repeated colonizations of the continent from different sources. Will and Claßen-Bockhoff produce a phylogenetic reconstruction and suggest that parallel character evolution is the rule rather than the exception in Old World Salvia. Notable examples are given by papery, conspicuously coloured calyces and repeated switches from bee- to bird-pollination. Different staminal lever types also evolved in parallel and should not be used any longer for characterizing major clades.

Bacteria and seed dormancy, nitrogen acquisition in grass species and the cellular basis of salt tolerance in halophytes – what’s new in Annals of Botany this week.

Lolium rigidum A potential role for endogenous microflora in dormancy release, cytokinin metabolism and the response to fluridone in Lolium rigidum seeds
Dormancy in annual ryegrass (Lolium rigidum) can be alleviated by warm stratification in the dark or by application of fluridone, an inhibitor of plant abscisic acid (ABA) biosynthesis via phytoene desaturase. However, germination and absolute ABA concentration are not strongly correlated. The aim of this study was to determine if cytokinins of both plant and bacterial origin are involved in mediating dormancy status and in the response to fluridone. Seeds lacking bacteria were no longer able to lose dormancy in the dark unless supplied with exogenous gibberellin or fluridone. It is probable that resident microflora contribute to dormancy status in L. rigidum seeds via a complex interaction between hormones of both plant and bacterial origin. This interaction needs to be taken into account in studies on endogenous seed hormones or the response of seeds to plant growth regulators.

 

Relationships between functional traits and inorganic nitrogen acquisition among eight contrasting European grass species
Leaf functional traits have been used as a basis to categoize plants across a range of resource-use specialization, from those that conserve available resources to those that exploit them. However, the extent to which the leaf functional traits used to define the resource-use strategies are related to root traits and are good indicators of the ability of the roots to take up nitrogen (N) are poorly known. This is an important question because interspecific differences in N uptake have been proposed as one mechanism by which species’ coexistence may be determined. This study investigated the relationships between functional traits and N uptake ability for grass species across a range of conservative to exploitative resource-use strategies. The results support the use of leaf traits as indicators of the N uptake ability across a broad range of grass species. The difficulties associated with assessing root properties are also highlighted, as root traits were only weakly correlated with leaf traits.

 

Sodium chloride toxicity and the cellular basis of salt tolerance in halophytes
Halophytes are the flora of saline soils. They adjust osmotically to soil salinity by accumulating ions and sequestering the vast majority of these (generally Na+ and Cl) in vacuoles, while in the cytoplasm organic solutes are accumulated to prevent adverse effects on metabolism. At high salinities, however, growth is inhibited. Possible causes are: toxicity to metabolism of Na+ and/or Cl in the cytoplasm; insufficient osmotic adjustment resulting in reduced net photosynthesis because of stomatal closure; reduced turgor for expansion growth; adverse cellular water relations if ions build up in the apoplast (cell walls) of leaves; diversion of energy needed to maintain solute homeostasis; sub-optimal levels of K+ (or other mineral nutrients) required for maintaining enzyme activities; possible damage from reactive oxygen species; or changes in hormonal concentrations. This review discusses the evidence for Na+ and Cl toxicity and the concept of tissue tolerance in relation to halophytes.

 

Plant functional types in Earth system models – application of dynamic vegetation models in high-latitude ecosystems

Plant functional types in Earth System Models

Plant functional types in Earth System Models

Earth system models describe the physical, chemical and biological processes that govern our global climate. While it is difficult to single out one component as being more important than another in these sophisticated models, terrestrial vegetation is a critical player in the biogeochemical and biophysical dynamics of the Earth system. There is much debate, however, as to how plant diversity and function should be represented in these models.

A recent review in Annals of Botany traces the origins of the plant functional types (PFT) concept from its origin in the early 1800s to its current use in regional and global dynamic vegetation models (DVMs). Special attention is given to the representation and parameterization of PFTs and to validation and benchmarking of predicted patterns of vegetation distribution in high-latitude ecosystems. These ecosystems are sensitive to changing climate and thus provide a useful test case for model-based simulations of past, current and future distribution of vegetation.

 

Wullschleger, Stan D., Howard E. Epstein, Elgene O. Box, Eugénie S. Euskirchen, Santonu Goswami, Colleen M. Iversen, Jens Kattge, Richard J. Norby, Peter M. van Bodegom, and Xiaofeng Xu. (2014) Plant functional types in Earth system models: past experiences and future directions for application of dynamic vegetation models in high-latitude ecosystems. Annals of Botany 114 (1): 1-16. doi: 10.1093/aob/mcu077

Laughing gas no laughing matter for climate change

There’s an interesting article published in PLOS One that I like. It’s one of these things that’s very clever, but the basic idea is very simple.

Beech wood and leaves

The future of climate change might lie beneath the soil. Photo by Karl-Ludwig Poggemann / Flickr.

Temperatures are rising, and there’s plenty of research on how that might affect plants. In PLOS One this month Gschwendtner et al. investigate how rising temperatures affect the soil. In fact they look at the microbe community in it. Bacteria and archaea are part of the biological process of putting Nitrogen into usable form for plants. Knowing how they might react to climate change would be useful.

The experiment was very simple. At the Tuttlingen Research Station in southern Germany, Gschwendtner and her team took some beech seedlings, and the soil around them, growing on a northwest facing slope and replanted some of them on a southwest facing slope. They got more sunlight on the soil and so you effectively change the climate for those soil samples. Compare one with the other and you get to see what sort of changes warmer weather might have.

That sounds simple, but there are some obvious problems. If the geology of the new slope is radically different, maybe you’re just measuring the change in geology, not climate. So what they did was core the soil, to make sure the new sites were a close match for the old sites.

That’s fine, but there’s another problem. The moved seedlings will have moved. That might lead to stresses that the other seedlings didn’t have. If that’s the case you’re measuring stress not climate. So to get round that problem they also replanted the control sample in new locations on the northwest slope, so they had the same stresses too.

The target was to see how Nitrogen production in the soil was affected. Measuring the soil and sniffing for outgassing would be a pain, so they used a different technique. They tested the soil for specific genes. Sampling the soil and comparing the relative proportions and quantities of certain genes in the soil would give measure of the kind of activity going on. For example they looked for the genes nirK, nirS, cnor and nosZ as markers of denitrification. These are genes associated with microbes that take nitrates in the soil and convert them to gases. If there are more bacteria and archaea working on denitrification, then they will be more copies of these genes to find.

What they found is that these genes became much more common in soil samples from the seedlings moved to the sunnier position. They also followed up the experiment by simulating drought and flood. They found that the denitrifying microbes did better under those conditions.

This has a double blow for plants. The first is that the plants are competing with these microbes for nitrogen. We think of plants living off carbon dioxide and water, but building proteins needs nitrogen too. The second blow is that the nitrogen is lost from the soil when the microbes emit it as nitrous oxide N2O. It’s known as laughing gas, but it’s also a greenhouse gas, adding to the climate problems the plants are already facing.

I think what appeals to me about the paper is the clever way they’ve looked at denitrification. If I wanted to measure change of nitrogen in a soil, I’d try directly measuring the nitrogen. Looking for DNA markers is simpler, and it also gives an idea of what might be driving that change. I also like the simplicity of the idea let’s move seedlings from here to there, and the fact that the control was replanted too. With hindsight it’s easy to say that should be done, but I bet that wouldn’t have occurred to me until the experiment was near its end.

As it’s in PLOS One you can pick it up now as an Open Access paper.

Gschwendtner S., Tejedor J., Bimueller C., Dannenmann M., Kögel Knabner I. & Schloter M. (2014). Climate Change Induces Shifts in Abundance and Activity Pattern of Bacteria and Archaea Catalyzing Major Transformation Steps in Nitrogen Turnover in a Soil from a Mid-European Beech Forest, PLoS ONE, 9 (12) e114278. DOI: http://dx.doi.org/10.1371/journal.pone.0114278

Wood components and Dutch elm disease tolerance

Wood components and Dutch elm disease tolerance

Wood components and Dutch elm disease tolerance

Changes occurring in the macromolecular traits of wood cell wall components of elm (Ulmus species) following an attack by Ophiostoma novo-ulmi (Dutch elm disease) are poorly understood. Ďurkovič et al. examine two elm hybrids with contrasting survival strategies upon infection with the current prevalent strain of the disease (ssp. americana × novo-ulmi) and find that the syringyl-to-guaiacyl ratio in lignin affects the degradability of cellulose by cellulolytic enzymes. When infected, the hybrids respond to medium-molecular weight cellulose degradation with the biosynthesis of high-molecular weight macromolecules of cellulose, resulting in an increase in values for the degree of polymerization and polydispersity. However, only guaiacyl-rich lignin in the tolerant hybrid is involved in a successful defence against the fungus.

Role of PCD in the reproductive biology of kiwifruit

Role of PCD in the reproductive biology of kiwifruit

Role of PCD in the reproductive biology of kiwifruit

Actinidia chinensis var. deliciosa (kiwifruit) is a functionally dioecious species with a highly successful reproductive performance that is impaired by a short effective pollination period. Ferradás et al. look for features of programmed cell death (PCD) in the stigmatic arms and find that in the secretory tissues cell organelles disintegrate sequentially while progressive vacuolization is detected. At the same time, chromatin condensation, nuclear deformation and DNA fragmentation and degradation are observed. These features are are evident in pollinated flowers by the second day after anthesis, but only by 4 days after anthesis in non-pollinated flowers, which corresponds to the effective pollination period. The results indicate that PCD might be accelerated by pollination, suggesting its involvement during the progamic phase.

Diffuse light and increased yield in tomato

Diffuse light and increased yield in tomato

Diffuse light and increased yield in tomato

Plants use diffuse light more efficiently than direct light, but it is often difficult to quantify this experimentally because of confounding effects such as differences in light intensity. Li et al. combine greenhouse studies with model simulations to examine photosynthesis in tomato (Solanum lycopersicum) crops, and conclude that higher production in diffuse light results primarily from a more homogeneous horizontal and vertical light distribution. In addition, plants acclimate to a high level of diffuseness by gaining a higher photosynthetic capacity of leaves in the middle of the crop and a higher leaf area index. Diffuse light also results in lower leaf temperatures and less photoinhibition at the top of the canopy when global irradiance is high.