Explore the vast range of titles available.

Several studies have previously reported that nanomaterial uptake and toxicity in plants are species dependent. However, the differences between photosynthetic pathways, C3 and C4, following nanomaterial exposure are poorly understood. In the current work, wheat and rice, two C3 pathway species are compared to amaranth and maize, which utilize the C4 photosynthetic mechanism. These plants were cultured in soils which were spiked with CuO, Ag, TiO 2 , MWCNT, and FLG nanomaterials. Overall, the C4 plant exhibited higher resilience to NM stress than C3 plants. In particular, significant differences were observed in chlorophyll contents with rice returning a 40.9–54.2% decrease compared to 3.5–15.1% for maize. Fv/Fm levels were significantly reduced by up to 51% in rice whereas no significant reductions were observed in amaranth and maize. Furthermore, NM uptake in the C3 species was greater than that in C4 plants, a trend that was also seen in metal concentration. TEM results showed that CuO NPs altered the chloroplast thylakoid structure in rice leaves and a large number of CuO NPs were observed in the vascular sheath cells. In contrast, there were no significant changes in the chloroplasts in the vascular sheath and no significant CuO NPs were found in maize leaves. This study was the first to systematically characterize the effect of metal and carbon-based nanomaterials in soil on C3 and C4 plants, providing a new perspective for understanding the impact of nanomaterials on plants. Graphical abstract

Key message An efficient and improved transformation method for functional genetics studies in S. italica , being a boon for the Setaria scientific community and for crop improvement. Foxtail millet ( Setaria italica ) is a short life cycle C4 plant, with sequenced genome, and a potential model plant for C4 species. S. italica is also important on a global food security and healthiness context due to its importance in arid and semi-arid areas. However, despite its importance, there are just few transformation protocols directed to this species. The current protocols reached about 5.5–9% of efficiency, which do not make it a valuable model organism. Different types of explants were used in the above mentioned methods, such as immature and mature inflorescence and shoot apex. However, these techniques have many limitations, such as unavailability of explants throughout the year and a crucial, laborious and considerable time-consuming selection. Aiming a simplified and efficient methodology, we adopted dry mature seeds as explants, which are available in abundance, are constant along the year and well responsive to tissue culture, in addition to a differentiated approach that reaches on an average 19.2% transformation efficiency of S. italica. Thus, we propose a protocol that optimizes the transformation efficiency of this cereal crop allowing a high increase on transformation and regeneration rates. Our transformation protocol provides an interesting tool for Setaria community research as well as enables new strategies for breeding enhanced productivity in the species.

1. Grasses using the C₄ photosynthetic pathway dominate today's savanna ecosystems and account for ~20% of terrestrial carbon fixation. However, this dominant status was reached only recently, during a period of C₄ grassland expansion in the Late Miocene and Early Pliocene (4-8 Myr ago). Declining atmospheric CO₂ has long been considered the key driver of this event, but new geological evidence casts doubt on the idea, forcing a reconsideration of the environmental cues for C₄ plant success. 2. Here, I evaluate the current hypotheses and debate in this field, beginning with a discussion of the role of CO₂ in the evolutionary origins, rather than expansion, of C₄ grasses. Atmospheric CO₂ starvation is a plausible selection agent for the C₄ pathway, but a time gap of around 10 Myr remains between major decreases in CO₂ during the Oligocene, and the earliest current evidence of C₄ plants. 3. An emerging ecological perspective explains the Miocene expansion of C₄ grasslands via changes in climatic seasonality and the occurrence of fire. However, the climatic drivers of this event are debated and may vary among geographical regions. 4. Uncertainty in these areas could be reduced significantly by new directions in ecological research, especially the discovery that grass species richness along rainfall gradients shows contrasting patterns in different C₄ clades. By re-evaluating a published data set, I show that increasing seasonality of rainfall is linked to changes in the relative abundance of the major C₄ grass clades Paniceae and Andropogoneae. I propose that the explicit inclusion of these ecological patterns would significantly strengthen climate change hypotheses of Miocene C₄ grassland expansion. Critically, they allow a new series of testable predictions to be made about the fossil record. 5. Synthesis. This paper offers a novel framework for integrating modern ecological patterns into theories about the geological history of C₄ plants.

In natural grasslands, C₄ plant dominance increases with growing season temperatures and reflects distinct differences in plant growth rates and water use efficiencies of C₃ vs. C₄ photosynthetic pathways. However, in lawns, management decisions influence interactions between planted turfgrass and weed species, leading to some uncertainty about the degree of human vs. climatic controls on lawn species distributions. We measured herbaceous plant carbon isotope ratios (δ13C, index of C₃/C₄ relative abundance) and C₄ cover in residential lawns across seven U.S. cities to determine how climate, lawn plant management, or interactions between climate and plant management influenced C₄ lawn cover. We also calculated theoretical C₄ carbon gain predicted by a plant physiological model as an index of expected C₄ cover due to growing season climatic conditions in each city. Contrary to theoretical predictions, plant δ13C and C₄ cover in urban lawns were more strongly related to mean annual temperature than to growing season temperature. Wintertime temperatures influenced the distribution of C₄ lawn turf plants, contrary to natural ecosystems where growing season temperatures primarily drive C₄ distributions. C₄ cover in lawns was greatest in the three warmest cities, due to an interaction between climate and homeowner plant management (e.g., planting C₄ turf species) in these cities. The proportion of C₄ lawn species was similar to the proportion of C₄ species in the regional grass flora. However, the majority of C₄ species were nonnative turf grasses, and not of regional origin. While temperature was a strong control on lawn species composition across the United States, cities differed as to whether these patterns were driven by cultivated lawn grasses vs. weedy species. In some cities, biotic interactions with weedy plants appeared to dominate, while in other cities, C₄ plants were predominantly imported and cultivated. Elevated CO₂ and temperature in cities can influence C₃/C₄ competitive outcomes; however, this study provides evidence that climate and plant management dynamics influence biogeography and ecology of C₃/C₄ plants in lawns. Their differing water and nutrient use efficiency may have substantial impacts on carbon, water, energy, and nutrient budgets across cities.

Soil labile and recalcitrant carbon (C) and nitrogen (N) are strongly controlled by plant inputs and climatic conditions. However, the interrelation of labile and recalcitrant pools with changes in plant functional groups (i.e., C3 and C4) along precipitation gradients is not fully understood. Here, we investigated the soil organic C and N (SOC and SON), labile C and N (LC and LN), recalcitrant C and N (RC and RN), and their isotopes (δ 13 C, and δ 15 N) in relation to C3 and C4 plant inputs from 20 sites across a 600-km precipitation gradient in secondary grasslands of South China. The SOC content decreased first slightly and then increased along precipitation gradients, largely due to the increase in C4 plant C inputs in the lower precipitation regions. In contrast, the SON content increased with increasing N inputs from C3 plant at higher precipitation regions. The LC and LN contents increased with increasing precipitation, whereas RC and RN did not change with precipitation. The LC and LN were correlated with plant C and N contents, as well as the mean annual precipitation, respectively. Increases in LC and LN stocks were tightly related to enhanced plant C and N inputs influenced by precipitation, suggesting stronger sensitivity of labile pools to both plant functional groups inputs and precipitation compared to the recalcitrant pool. Moreover, the δ 13 C values in RC declined with precipitation, while the δ 15 N values of both labile and recalcitrant N increased with increasing precipitation, further revealing that soil labile and recalcitrant C and N pools closely related to the shift in the C3 and C4 plant along precipitation gradients. Overall, our findings indicated that soil labile and recalcitrant fractions should be considered in context of precipitation under which plant inputs takes place in predicting soil C and N dynamics.

In this paper, we report for the first time the δ 13 C and δ 15 N data for PM 2.5 and PM 10 aerosols collected in Tanzania during May-August 2011 together with total carbon (TC) and nitrogen (TN) contents. Mean TC concentrations were 6.5±2.1 µg m −3 in PM 2.5 and 9.2±3.5 µg m −3 in PM 10 . δ 13 C of TC ranged from −26.1 to −20.6‰ with a mean of −23.6‰ in PM 2.5 and from −24.4 to −22.4‰ with a mean of −23.6‰ in PM 10 . We found substantially greater δ 13 C values in PM 2.5 samples during dry season as well as strong positive correlation between levoglucosan (and nss-K + ) and TC in PM 2.5 . These results suggest a significant contribution from burning of C 4 plants to fine organic aerosol formation. TN contents showed a mean of 0.7±0.3 µg m −3 in PM 2.5 and 0.8±0.2 µg m −3 in PM 10 . δ 15 N ranged from +13.4 to +22.1‰ with a mean of +16.2±2.7‰ in PM 2.5 and +10.4 to +18.7‰ with a mean of +13.7±2.2‰ in PM 10 . δ 15 N showed higher ratios in fine particles than coarse particles in both wet and dry season. The relatively high δ 15 N values suggest isotopic enrichment of 15 N in aerosols via exchange reaction between NH 3 (gas) and (particle). We found a strong correlation between TN and (r 2 =0.94 in PM 2.5 and r 2 =0.86 in PM 10 ) and (r 2 =0.48 in PM 2.5 and r 2 =0.55 in PM 10 ). We also found that organic nitrogen is less significant than inorganic nitrogen in the Morogoro aerosols. Based on stable carbon isotopic composition, contributions of burning C 3 plants to TC were estimated to range from 42 to 74% in PM 2.5 and from 39 to 64% in PM 10, whereas those of C 4 ranged from 26 to 58% in PM 2.5 and from 36 to 61% in PM 10 . These results suggest that burning activities of C 3 and C 4 plants contribute to organic aerosol formation in Tanzania.

Mesophyll (M) chloroplasts in finger millet are known to aggregate to the bundle sheath side when leaves are constantly irradiated with extremely high-intensity light. This aggregative movement of M chloroplasts is also observed in natural environment, but whether a natural light regime is effective in inducing the response remains unclear. Abscisic acid is reported to trigger not only the aggregative movement but also stomatal closure, but photosynthetic responses accompanying the aggregative movement also remain unknown.We investigated changes in chloroplast positioning and photosynthetic traits under diurnal patterns of light, mimicking the natural light environment. M chloroplasts showed the aggregative movement with increasing light intensity whether it frequently fluctuated or not, and kept their aggregative positions in the midday. With decreasing light intensity, M chloroplasts returned to the random position in the evening. These results suggest that M chloroplasts often rearrange their intracellular positions during the daytime and that the chloroplast aggregative movement can be induced by a natural regime of light. The chloroplast aggregative movement was observed with increasing stomatal conductance, suggesting that stomatal closure is not crucial to trigger the chloroplast response.

In C 3 plants, part of the CO 2 fixed during photosynthesis in chloroplasts is released from mitochondria during photorespiration by decarboxylation of glycine via glycine decarboxylase (GDC), thereby reducing photosynthetic efficiency. The apparent positioning of most mitochondria in the interior (vacuole side of chloroplasts) of mesophyll cells in C 3 grasses would increase the efficiency of refixation of CO 2 released from mitochondria by ribulose 1,5-bisphosphate carboxylase/​oxygenase (Rubisco) in chloroplasts. Therefore, in mesophyll cells of C 4 grasses, which lack both GDC and Rubisco, the mitochondria ought not to be positioned the same way as in C 3 mesophyll cells. To test this hypothesis, we investigated the intracellular position of mitochondria in mesophyll cells of 14 C 4 grasses of different C 4 subtypes and subfamilies (Chloridoideae, Micrairoideae, and Panicoideae) and a C 3 –C 4 intermediate grass, Steinchisma hians , under an electron microscope. In C 4 mesophyll cells, most mitochondria were positioned adjacent to the cell wall, which clearly differs from the positioning in C 3 mesophyll cells. In S. hians mesophyll cells, the positioning was similar to that in C 3 cells. These results suggest that the mitochondrial positioning in C 4 mesophyll cells reflects the absence of both GDC and Rubisco in the mesophyll cells and the high activity of phospho enol pyruvate carboxylase. In contrast, the relationship between the mitochondrial positioning and enzyme distribution in S. hians is complex, but the positioning may be related to the capture of respiratory CO 2 by Rubisco. Our study provides new possible insight into the physiological role of mitochondrial positioning in photosynthetic cells.

Biomass burning is one of the major emitters of airborne particulate matter (PM) and gaseous mercury. In order to apply the isotopic fingerprinting method to process identification and source apportionment studies, isotopic characterizations of targeted substances at emission are indispensable. Here, we report the stable isotopic composition of total gaseous mercury (TGM) and the stable and radiocarbon isotopic composition of low-volatile water-soluble nitrogen (LV-WSN) and organic carbon (LV-WSOC) in PM emitted from open grass field burning in the Aso region of Japan. The measurement results showed that TGM concentrations in the air increased during the open field burning events, indicating the presence of TGM emissions. The results of LV-WSN analysis showed very low concentrations; therefore, the stable nitrogen isotope ratios could not be measured. The stable mercury isotope ratios exhibited lighter composition than those observed during non-biomass-burning days. The analysis of LV-WSOC revealed heavy stable carbon isotope ratios (average ± SD, −18 ± 2‰), suggesting a substantial contribution from C4 plant carbon. The 14C analysis showed that more than 98% of the LV-WSOC was modern carbon, indicating the contribution of plant carbon to PM emitted from biomass burning. The findings here provide reference isotope compositions of TGM and particulate LV-WSOC from biomass burning in this region.

Biochar is a carbon (C)‐rich solid produced from the thermochemical pyrolysis of biomass. Its amendment to soils has been proposed as a promising mean to mitigate greenhouse gas emissions and simultaneously benefit agricultural crops. However, how biochar amendment affects plant photosynthesis and growth remains unclear, especially on a global scale. In this study, we conducted a global synthesis of 74 publications with 347 paired comparisons to acquire an overall tendency of plant photosynthesis and growth following biochar amendment. Overall, we found that biochar amendment significantly increased photosynthetic rate by 27.1%, and improved stomatal conductance, transpiration rate, water use efficiency, and chlorophyll concentration by 19.6%, 26.9%, 26.8%, and 16.1%, respectively. Meanwhile, plant total biomass, shoot biomass, and root biomass increased by 25.4%, 22.1%, and 34.4%, respectively. Interestingly, plant types (C3 and C4 plants) showed greater control over plant photosynthesis and biomass than a broad suite of soil and biochar factors. Biochar amendment largely boosted photosynthesis and biomass on C3 plants, but had a limited effect on C4 plants. Our results highlight the importance of the differential response of plant types to biochar amendment with respect to plant growth and photosynthesis, providing a scientific foundation for making reasonable strategies towards an extensive application of biochar for agricultural production management. How biochar amendment affects plant photosynthesis and growth remains unclear, especially on a global scale. We conducted a global synthesis and found that biochar amendment largely boosted photosynthesis and biomass on C3 plants, but had a limited effect on C4 plants. Our results highlight the importance of the differential response of plant types to biochar amendment with respect to plant growth and photosynthesis, providing a scientific foundation for making reasonable strategies towards an extensive application of biochar for agricultural production management.