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Improving the water use efficiency (WUE) of crop plants without trade-offs in growth and yield is considered a utopic goal. However, recent studies on model plants show that partial restriction of transpiration can occur without a reduction in CO₂ uptake and photosynthesis. In this study, we analyzed the potentials and constraints of improving WUE in Arabidopsis (Arabidopsis thaliana) and in wheat (Triticum aestivum). We show that the analyzed Arabidopsis wild-type plants consume more water than is required for unrestricted growth. WUE was enhanced without a growth penalty by modulating abscisic acid (ABA) responses either by using overexpression of specific ABA receptors or deficiency of ABA coreceptors. Hence, the plants showed higher water productivity compared with the wild-type plants; that is, equal growth with less water. The high WUE trait was resilient to changes in light intensity and water availability, but it was sensitive to the ambient temperature. ABA application to plants generated a partial phenocopy of the water-productivity trait. ABA application, however, was never as effective as genetic modification in enhancing water productivity, probably because ABA indiscriminately targets all ABA receptors. ABA agonists selective for individual ABA receptors might offer an approach to phenocopy the water-productivity trait of the high WUE lines. ABA application to wheat grown under near-field conditions improved WUE without detectable growth trade-offs. Wheat yields are heavily impacted by water deficit, and our identification of this crop as a promising target for WUE improvement may help contribute to greater food security.

Background The anthropogenic increase of atmospheric CO 2 concentration ( c a ) is impacting carbon (C), water, and nitrogen (N) cycles in grassland and other terrestrial biomes. Plant canopy stomatal conductance is a key player in these coupled cycles: it is a physiological control of vegetation water use efficiency (the ratio of C gain by photosynthesis to water loss by transpiration), and it responds to photosynthetic activity, which is influenced by vegetation N status. It is unknown if the c a -increase and climate change over the last century have already affected canopy stomatal conductance and its links with C and N processes in grassland. Results Here, we assessed two independent proxies of (growing season-integrating canopy-scale) stomatal conductance changes over the last century: trends of δ 18 O in cellulose (δ 18 O cellulose ) in archived herbage from a wide range of grassland communities on the Park Grass Experiment at Rothamsted (U.K.) and changes of the ratio of yields to the CO 2 concentration gradient between the atmosphere and the leaf internal gas space ( c a – c i ). The two proxies correlated closely ( R 2  = 0.70), in agreement with the hypothesis. In addition, the sensitivity of δ 18 O cellulose changes to estimated stomatal conductance changes agreed broadly with published sensitivities across a range of contemporary field and controlled environment studies, further supporting the utility of δ 18 O cellulose changes for historical reconstruction of stomatal conductance changes at Park Grass. Trends of δ 18 O cellulose differed strongly between plots and indicated much greater reductions of stomatal conductance in grass-rich than dicot-rich communities. Reductions of stomatal conductance were connected with reductions of yield trends, nitrogen acquisition, and nitrogen nutrition index. Although all plots were nitrogen-limited or phosphorus- and nitrogen-co-limited to different degrees, long-term reductions of stomatal conductance were largely independent of fertilizer regimes and soil pH, except for nitrogen fertilizer supply which promoted the abundance of grasses. Conclusions Our data indicate that some types of temperate grassland may have attained saturation of C sink activity more than one century ago. Increasing N fertilizer supply may not be an effective climate change mitigation strategy in many grasslands, as it promotes the expansion of grasses at the disadvantage of the more CO 2 responsive forbs and N-fixing legumes.

Quantification of leaf respiration is important for understanding plant physiology and ecosystem biogeochemical processes. Leaf respiration continues in the light (R L) but supposedly at a lower rate than in the dark (R Dk). However, there is no method for direct measurement of R L and the available methods require nonphysiological measurement conditions. A method based on isotopic disequilibrium quantified R L (R L 13C) and mesophyll conductance of young and old fully expanded leaves of six species. R L 13C was compared to R L determined by the Laisk method (R L Laisk) on the very same leaves with a minimum time lag. R L 13C and R L Laisk were generally lower than R Dk, and were not significantly affected by leaf ageing. R L Laisk and R L 13C were positively correlated (r 2 = 0.35), and both were positively correlated with R Dk (r 2 ≥ 0.6). R L Laisk was systematically lower than R L 13C by 0.4 μmol m−2 s−1. Using A/C c instead of A/C i curves, a higher photocompensation point Γ* (by 5 μmol mol−1) was found but no influence on R L Laisk estimates was observed. The results imply that the Laisk method underestimates actual R L significantly, probably related to the measurement condition of low CO2 and irradiance. The isotopic disequilibrium method is useful for assessing responses of R L to irradiance and CO2, improving our mechanistic understanding of R L.

Accurate sound source localization in three-dimensional space is essential for an animal's orientation and survival. While the horizontal position can be determined by interaural time and intensity differences, localization in elevation was thought to require external structures that modify sound before it reaches the tympanum. Here we show that in birds even without external structures like pinnae or feather ruffs, the simple shape of their head induces sound modifications that depend on the elevation of the source. Based on a model of localization errors, we show that these cues are sufficient to locate sounds in the vertical plane. These results suggest that the head of all birds induces acoustic cues for sound localization in the vertical plane, even in the absence of external ears.

Background Quantitative understanding of plant carbon (C) metabolism by 13 CO 2 / 12 CO 2 -labelling studies requires absence (or knowledge) of C-isotopic contamination artefacts during tracer application and sample processing. Surprisingly, this concern has not been addressed systematically and comprehensively yet is especially crucial in experiments at different atmospheric CO 2 concentrations ([CO 2 ]), when experimental protocols require frequent access to the labelling chambers. Here, we used a plant growth chamber-based 13 CO 2 / 12 CO 2 gas exchange-facility to address this topic. The facility comprised four independent units, with two chambers routinely operated in parallel under identical conditions except for the isotopic composition of CO 2 supplied to them (δ 13 C CO2 −43.5‰ versus −5.6‰). In this setup, d δ 13 C X (the measurements-based δ 13 C-difference between matching samples X collected from the parallel chambers) is expected to equal d δ 13 C Ref (the predictable, non-contaminated δ 13 C-difference ), if sample-C is completely derived from the contrasting CO 2 sources. Accordingly, contamination ( f contam ) was determined as f contam = 1– d δ 13 C X / d δ 13 C Ref in this experimental setup. Determinations were made for biomass fractions, water-soluble carbohydrate (WSC) components and dark respiration of Lolium perenne (perennial ryegrass) stands following growth for ∼9 weeks at 200, 400 or 800 µmol mol − 1 CO 2 , with a terminal two weeks-long period of extensive experimental disturbance of the chambers. Results Contamination was small and similar (average 3.3% ±0.9% SD, n  = 18) for shoot and root biomass and WSC fractions (fructan, sucrose, glucose, fructose) at every [CO 2 ] level. [CO 2 ] had no significant effect on contamination of these samples. There was no evidence for any contamination of WSC components during extraction, separation and analysis. At 200 and 400 µmol mol − 1 CO 2 , contamination of respiratory CO 2 was close to that of biomass- and WSC-C, suggesting it originated primarily from in vivo-contaminated respiratory substrate. Surprisingly, we found no evidence of contamination of respiratory CO 2 at 800 µmol mol − 1 CO 2 . Overall, contamination likely resulted overwhelmingly from photosynthetic fixation of extraneous contaminating CO 2 which entered chambers primarily during daytime experimental activities. Conclusions The labelling facility enables months-long, quantitative 13 CO 2 / 12 CO 2 -labelling of large numbers of plants with accuracy and precision across contrasts of [CO 2 ], empowering eco-physiological study of climate change scenarios. Effective protocols for contamination avoidance are discussed.

The effect of nitrogen (N) stress on the pool system supplying currently assimilated and (re)mobilized N for leaf growth of a grass was explored by dynamic 15 N labeling, assessment of total and labeled N import into leaf growth zones, and compartmental analysis of the label import data. Perennial ryegrass (Lolium perenne) plants, grown with low or high levels of N fertilization, were labeled with 15 NO 3 - / 14 NO 3 - from 2 h to more than 20 d. In both treatments, the tracer time course in N imported into the growth zones fitted a two-pool model (r 2 > 0.99). This consisted of a \"substrate pool,\" which received N from current uptake and supplied the growth zone, and a recycling/mobilizing \"store,\" which exchanged with the substrate pool. N deficiency halved the leaf elongation rate, decreased N import into the growth zone, lengthened the delay between tracer uptake and its arrival in the growth zone (2.2 h versus 0.9 h), slowed the turnover of the substrate pool (half-life of 3.2 h versus 0.6 h), and increased its size (12.4 μg versus 5.9 μg). The store contained the equivalent of approximately 10 times (low N) and approximately five times (high N) the total daily N import into the growth zone. Its turnover agreed with that of protein turnover. Remarkably, the relative contribution of mobilization to leaf growth was large and similar (approximately 45%) in both treatments. We conclude that turnover and size of the substrate pool are related to the sink strength of the growth zone, whereas the contribution of the store is influenced by partitioning between sinks.

Oxygen isotopes (δ 18 O) in animal and human tissues are expected to be good recorders of geographical origin and migration histories. However, seasonal variation of δ 18 O may diminish the origin information in the tissues. Here the seasonality of δ 18 O in tail hair was investigated in a domestic suckler cow ( Bos taurus ) that underwent different ambient conditions, physiological states, keeping and feeding during five years. A detailed mechanistic model was built to explain this variation. The measured δ 18 O in hair significantly related (p < 0.05) to the δ 18 O in meteoric water in a regression analysis. Modelling suggested that this relation was only partly derived from the direct influence of feed moisture. Ambient conditions (temperature, moisture) also affected the animal itself (drinking water demand, transcutaneous vapor etc.). The clear temporal variation thus resulted from complex interactions with multiple influences. The twofold influence of ambient conditions via the feed and via the animal itself is advantageous for tracing the geographic origin because δ 18 O is then less influenced by variations in moisture uptake; however, it is unfavorable for indicating the production system, e.g. to distinguish between milk produced from fresh grass or from silage. The model is versatile but needs testing under a wider range of conditions.

In water-limited environments, photosynthetic carbon gain and loss of water by transpiration are in a permanent tradeoff as both are contrarily regulated by stomata conductance. In semiarid steppe grasslands water limitation may covary with nitrogen limitation. Steppe grassland species are capable of optimizing their use of limiting resources, water and nitrogen, but regulation is still poorly understood. In a two-year experiment with addition of water (irrigation simulating a wet year) and nitrogen (0, 25, and 50 kg urea-N ha⁻¹) we assessed intrinsic water use efficiency (WUEi), nitrogen use efficiency (NUE), and related plant functional traits (PFTs) of four dominant C₃ species (Leymus chinensis, Agropyron cristatum, Stipa grandis, and Artemisia frigida). Water and N fertilizer supplementation significantly increased plant primary production, and N effect was more pronounced under irrigated conditions. Parallel with the responses of plant production, a strong tradeoff between WUEi and NUE was detected: water supply increased NUE but decreased WUEi, whereas N addition slightly increased WUEi at the expense of NUE. This tradeoff occurred at the leaf level, and involved the responses of leaf N concentration and specific leaf area. WUEi of species changed among treatments in a predictable manner by the parameter of leaf N content per area. Dominant plant species commonly achieved a higher utilization efficiency of the more limiting resource via altering PFTs, which was an important mechanism of adaptation to variable resource limitation in semiarid grasslands.

Excreta deposition redistributes, separates and concentrates nutrients and thus affects sward heterogeneity and environment. Concentration occurs within excrement patches, but also at a larger scale when excreta are not randomly deposited. Thus, detecting excrement patterns and their underlying rules is essential to understand nutrient heterogeneity within a pasture. Two urine and six dung-patch distributions from six grazing periods were mapped on a 0.6 ha rotationally grazed cattle pasture. Excreta density was determined by creating Thiessen polygons. The Thiessen method was preferred to previously used predefined grids, because the resulting pattern is not obscured by the layout and resolution of such a grid. GIS, geostatistical simulation and geostatistical analysis were then applied to detect patterns. All urine and dung distributions had a similar dominant pattern with only small (<5%) random variation. Excreta density increased with distance to the fence, decreasing slope gradient and towards the crest. The pattern evolved preferably during night at preferred resting areas when the animals rarely moved while urination and defecation were still served. Feed-back mechanisms attenuated some of the nocturnal pattern because resting places with high excrement density were avoided during grazing despite their high productivity. Validation with data from two independent studies showed that excrement patterns are common and governed by similar principles where site conditions are similar. Excrement pattern may be enhanced or attenuated by deliberate adjustment of pasture properties relative to terrain properties and the placement of installations such as fences. Placing watering or feeding stations close to preferred resting places and fences at a large distance to them will increase heterogeneity while night shedding would reduce it.