Leaf elongation response to blue light is mediated by stomatal-induced variations in transpiration in Festuca arundinacea.

Reduced blue light irradiance is known to enhance leaf elongation rate (LER) in grasses, but the mechanisms involved have not yet been elucidated. We investigated whether leaf elongation response to reduced blue light could be mediated by stomata-induced variations of plant transpiration. Two experiments were carried out on tall fescue in order to monitor LER and transpiration under reduced blue light irradiance. Additionally, LER dynamics were compared with those observed in the response to vapour pressure deficit (VPD)-induced variations of transpiration. Finally, we developed a model of water flow within a tiller to simulate the observed short-term response of LER to various transpiration regimes. LER dramatically increased in response to blue light reduction and then reached new steady states, which remained higher than the control. Reduced blue light triggered a simultaneous stomatal closure which induced an immediate decrease of leaf transpiration. The hydraulic model of leaf elongation accurately predicted the LER response to blue light and VPD, resulting from an increase in the growth-induced water potential gradient in the leaf growth zone. Our results suggest that the blue light signal is sensed by stomata of expanded leaves and transduced to the leaf growth zone through the hydraulic architecture of the tiller.

Temperature increase reduces global yields of major crops in four independent estimates.

Wheat, rice, maize, and soybean provide two-thirds of human caloric intake. Assessing the impact of global temperature increase on production of these crops is therefore critical to maintaining global food supply, but different studies have yielded different results. Here, we investigated the impacts of temperature on yields of the four crops by compiling extensive published results from four analytical methods: global grid-based and local point-based models, statistical regressions, and field-warming experiments. Results from the different methods consistently showed negative temperature impacts on crop yield at the global scale, generally underpinned by similar impacts at country and site scales. Without CO2 fertilization, effective adaptation, and genetic improvement, each degree-Celsius increase in global mean temperature would, on average, reduce global yields of wheat by 6.0%, rice by 3.2%, maize by 7.4%, and soybean by 3.1%. Results are highly heterogeneous across crops and geographical areas, with some positive impact estimates. Multimethod analyses improved the confidence in assessments of future climate impacts on global major crops and suggest crop- and region-specific adaptation strategies to ensure food security for an increasing world population.

Increasing the benefits of species diversity in multispecies temporary grasslands by increasing within-species diversity.

BACKGROUND AND AIMS: The positive effects of species diversity on the functioning and production of ecosystems have been discussed widely in the literature. In agriculture, these effects are increasingly being applied to mixed-species crops and particularly to temporary grasslands. However, the effects of increases in genetic diversity (i.e. within-species diversity) on productivity in multispecies crops have not been much studied. Nevertheless, genetic diversity may have strong positive effects on agricultural ecosystems and positively influence production and species abundances in multispecies covers. We examine here the effects of genetic diversity on temporary multispecies grasslands. METHODS: From a real situation, a breeder's field trial, we describe a study with five seed mixtures, each containing seven species (three grasses and four legumes) but with three different levels of genetic diversity (low, medium and high) created by using different numbers of cultivars per species. From the perspective of a plant breeder, we analyse measurements of biomass production over a 5-year period. KEY RESULTS: We show a positive effect of genetic diversity on production, on production stability and on the equilibrium of species abundances in the mixtures over the 5-year period of the experiment. The legume/grass proportions were best balanced, having the highest within-species diversity. CONCLUSIONS: For the first time in a field-plot study, we demonstrate the major role played by within-species genetic diversity on the production, stability and species composition of temporary grasslands. Our key results seem to find their explanation in terms of shifts in the peaks of species biomass production during the season, these shifts likely leading to temporal species complementarity. Our study suggests major benefits will arise with increases in the genetic diversity of multispecies crops. Genetic diversity may be useful in helping to meet new crop-diversification challenges, particularly with multispecies grasslands. Genetic and species diversity will likely provide additional levers for improving crops in diversified systems.

How do various maize crop models vary in their responses to climate change factors?

Potential consequences of climate change on crop production can be studied using mechanistic crop simulation models. While a broad variety of maize simulation models exist, it is not known whether different models diverge on grain yield responses to changes in climatic factors, or whether they agree in their general trends related to phenology, growth, and yield. With the goal of analyzing the sensitivity of simulated yields to changes in temperature and atmospheric carbon dioxide concentrations [CO2 ], we present the largest maize crop model intercomparison to date, including 23 different models. These models were evaluated for four locations representing a wide range of maize production conditions in the world: Lusignan (France), Ames (USA), Rio Verde (Brazil) and Morogoro (Tanzania). While individual models differed considerably in absolute yield simulation at the four sites, an ensemble of a minimum number of models was able to simulate absolute yields accurately at the four sites even with low data for calibration, thus suggesting that using an ensemble of models has merit. Temperature increase had strong negative influence on modeled yield response of roughly -0.5 Mg ha(-1) per °C. Doubling [CO2 ] from 360 to 720 µmol mol(-1) increased grain yield by 7.5% on average across models and the sites. That would therefore make temperature the main factor altering maize yields at the end of this century. Furthermore, there was a large uncertainty in the yield response to [CO2 ] among models. Model responses to temperature and [CO2 ] did not differ whether models were simulated with low calibration information or, simulated with high level of calibration information.

Interactions Between Environment and Genetic Diversity in Perennial Grass Phenology: A Review of Processes at Plant Scale and Modeling.

In perennial grasses, the reproductive development consists of major phenological stages which highly determine the seasonal variations of grassland biomass production in terms of quantity and quality. The reproductive development is regulated by climatic conditions through complex interactions subjected to high genetic diversity. Understanding these interactions and their impact on plant development and growth is essential to optimize grassland management and identify the potential consequences of climate change. Here, we review the main stages of reproductive development, from floral induction to heading, i.e., spike emergence, considering the effect of the environmental conditions and the genetic diversity observed in perennial grasses. We first describe the determinants and consequences of reproductive development at individual tiller scale before examining the interactions between plant tillers and their impact on grassland perenniality. Then, we review the available grassland models through their ability to account for the complexity of reproductive development and genetic × environmental interactions. This review shows that (1) The reproductive development of perennial grasses is characterized by a large intraspecific diversity which has the same order of magnitude as the diversity observed between species or environmental conditions. (2) The reproductive development is determined by complex interactions between the processes of floral induction and morphogenesis of the tiller. (3) The perenniality of a plant is dependent on the reproductive behavior of each tiller. (4) Published models only partly explain the complex interactions between morphogenesis and climate on reproductive development. (5) Introducing more explicitly the underlying processes involved in reproductive development in models would improve our ability to anticipate grassland behavior in future growth conditions.

What determines the complex kinetics of stomatal conductance under blueless PAR in Festuca arundinacea? Subsequent effects on leaf transpiration.

Light quality and, in particular, its content of blue light is involved in plant functioning and morphogenesis. Blue light variation frequently occurs within a stand as shaded zones are characterized by a simultaneous decrease of PAR and blue light levels which both affect plant functioning, for example, gas exchange. However, little is known about the effects of low blue light itself on gas exchange. The aims of the present study were (i) to characterize stomatal behaviour in Festuca arundinacea leaves through leaf gas exchange measurements in response to a sudden reduction in blue light, and (ii) to test the putative role of Ci on blue light gas exchange responses. An infrared gas analyser (IRGA) was used with light transmission filters to study stomatal conductance (gs), transpiration (Tr), assimilation (A), and intercellular concentration of CO(2) (Ci) responses to blueless PAR (1.80 mumol m(-2) s(-1)). The results were compared with those obtained under a neutral filter supplying a similar photosynthetic efficiency to the blueless PAR filter. It was shown that the reduction of blue light triggered a drastic and instantaneous decrease of gs by 43.2% and of Tr by 40.0%, but a gradual stomatal reopening began 20 min after the start of the low blue light treatment, thus leading to new steady-states. This new stomatal equilibrium was supposed to be related to Ci. The results were confirmed in more developed plants although they exhibited delayed and less marked responses. It is concluded that stomatal responses to blue light could play a key role in photomorphogenetic mechanisms through their effect on transpiration.

Narrowing uncertainties in the effects of elevated CO2 on crops.

Plant responses to rising atmospheric carbon dioxide (CO2) concentrations, together with projected variations in temperature and precipitation will determine future agricultural production. Estimates of the impacts of climate change on agriculture provide essential information to design effective adaptation strategies, and develop sustainable food systems. Here, we review the current experimental evidence and crop models on the effects of elevated CO2 concentrations. Recent concerted efforts have narrowed the uncertainties in CO2-induced crop responses so that climate change impact simulations omitting CO2 can now be eliminated. To address remaining knowledge gaps and uncertainties in estimating the effects of elevated CO2 and climate change on crops, future research should expand experiments on more crop species under a wider range of growing conditions, improve the representation of responses to climate extremes in crop models, and simulate additional crop physiological processes related to nutritional quality.

Complementary effects of species and genetic diversity on productivity and stability of sown grasslands.

Plant species diversity regulates the productivity(1-3) and stability(2,4) of natural ecosystems, along with their resilience to disturbance(5,6). The influence of species diversity on the productivity of agronomic systems is less clear(7-10). Plant genetic diversity is also suspected to influence ecosystem function(3,11-14), although empirical evidence is scarce. Given the large range of genotypes that can be generated per species through artificial selection, genetic diversity is a potentially important leverage of productivity in cultivated systems. Here we assess the effect of species and genetic diversity on the production and sustainable supply of livestock fodder in sown grasslands, comprising single and multispecies assemblages characterized by different levels of genetic diversity, exposed to drought and non-drought conditions. Multispecies assemblages proved more productive than monocultures when subject to drought, regardless of the number of genotypes per species present. Conversely, the temporal stability of production increased only with the number of genotypes present under both drought and non-drought conditions, and was unaffected by the number of species. We conclude that taxonomic and genetic diversity can play complementary roles when it comes to optimizing livestock fodder production in managed grasslands, and suggest that both levels of diversity should be considered in plant breeding programmes designed to boost the productivity and resilience of managed grasslands in the face of increasing environmental hazards.

Changes in axial hydraulic conductivity along elongating leaf blades in relation to xylem maturation in tall fescue.

Xylem maturation in elongating leaf blades of tall fescue (Festuca arundinacea) was studied using staining and microcasting. Three distinctive regions were identified in the blade: (1) a basal region, in which elongation was occurring and protoxylem (PX) vessels were functioning throughout; (2) a maturation region, in which elongation had stopped and narrow (NMX) and large (LMX) metaxylem vessels were beginning to function; (3) a distal, mature region in which most of the longitudinal water movements occurred in the LMX. The axial hydraulic conductivity (Kh ) was measured in leaf sections from all these regions and compared with the theoretical axial hydraulic conductivity (Kt ) computed from the diameter of individual inner vessels. Kt was proportional to Kh throughout the leaf, but Kt was about three times Kh . The changes in Kh and Kt along the leaf reflected the different stages of xylem maturation. In the basal 60 mm region, Kh was about 0.30±0.07 mmol s-1 mm MPa-1 . Beyond that region, Kh rapidly increased with metaxylem element maturation to a maximum value of 5.0±0.3 mmol s-1 mm MPa-1 , 105 mm from the leaf base. It then decreased to 3.5±0.2 mmol s-1 mm MPa-1 near the leaf tip. The basal expanding region was observed to restrict longitudinal water movement. There was a close relationship between the water deposition rate in the elongation zone and the sum of the perimeters of PX vessels. The implications of this longitudinal vasculature on the partitioning of water between growth and transpiration is discussed.