Water stress and warming impact nutrient use efficiency of Mombasa grass (Megathyrsus maximus) in tropical conditions

Temperature and other abiotic factors, such water and nutrient availability, play an important role for plants in response to the changing environments. At this regard, both warming and drought might affect the nutrient use efficiency (NUE) and growth of Megathyrsus maximus a C4 forage grass of high interest for cattle feeding. However, the nutrient requirements of this species under climate change are unknown. Therefore, we aimed to evaluate the individual and combined effects of two levels of temperature: ambient and elevated temperature (2°C above ambient temperature), and two levels of soil water availability: irrigated plants and non‐irrigated plants on accumulation of leaf nutrients, NUE and biomass production of M. maximus. Temperature control was performed by a temperature free‐air‐controlled enhancement (T‐FACE) system under field conditions. In general, we observed that warming under well‐irrigated conditions increased the leaf accumulation of most nutrients, improving the NUE of N, P, K, Ca, Mg, Cu, Mn and Zn. Plant growth was also enhanced under warming effects, with higher leaf dry mass accumulation and root development. Meanwhile, drought decreased NUE of K, Ca, B and leaf dry biomass, while root growth was stimulated. The combined effects of warming and drought on nutrient accumulation, NUE and plant growth tended to be greater than the individual effects expected from a single factor; thus, warming mitigated the negative impacts of individual drought. In summary, our findings suggest that warming and drought, both as individual and combined factors, will change the nutrient requirements of M. maximus in tropical ecosystems.     

自由大气CO2浓度升高对夏大豆光合色素含量和光合作用的影响

研究大气CO2浓度升高对大豆光合指标的影响,有助于了解未来气候变化后大豆光合生理的变化。利用开放式自由大气CO2浓度富集系统(Free Air CO2 Enrichment)在高CO2浓度（550±60 μmol/mol左右）和对照大气CO2浓度（平均389±40 μmol/mol左右）及2种施氮水平下种植‘中黄35’和‘中黄13’大豆品种,测定了2个大豆品种的叶绿素、类胡萝卜素含量及光合作用的变化。结果表明：CO2浓度升高对大豆功能叶光合色素含量的影响存在品种差异,初花期‘中黄13’光合色素含量变化不显著,但在盛荚期光合色素显著下降,且在低肥处理下更明显,对‘中黄35’没有影响。大气CO2浓度升高后,2个品种大豆净光合速率均明显升高,气孔导度下降。大豆净光合速率提高将促使作物积累更多的有机物,有利于作物生物量和产量的提高。气孔导度下降可能会使作物蒸腾作用减弱,有利于作物水分利用率的提高。     

Effects of Single and Multifactor Treatments with Elevated Temperature,CO2 and Ozone on Oilseed Rape and Barley

We investigated the effect of elevated [CO₂], [O₃] and temperature on plant productivity and if these climate factors interacted with each other in multifactor treatments. The climate effects were studied in 14 different cultivars/lines of European spring oilseed rape (Brassica napus L.) and spring barley (Hordeum vulgare L.). Seven genotypes of each species were cultivated in six single‐ and multifactor treatments with ambient or elevated CO₂ (385 ppm and 700 ppm), O₃ (20 ppb and 60 ppb) and temperature (12/19 °C and 17/24 °C). Growth and production parameters were measured. Elevated CO₂ increased yield and biomass. Seed number increased by about 47 % in barley and by 26 % in oilseed rape, but in oilseed rape, the TSW was significantly decreased, possibly because of shortening of the seed filling period. Higher temperatures decreased yield and biomass significantly in both species. A significantly decreased yield and thousand grain weight was also seen in barley due to elevated O₃. The multifactor combination of elevated CO₂, O₃ and temperature showed a decrease in growth and production in the two species, though not statistically significant for all parameters. This trend suggests that the expected increase in the plant production in northern Europe, indicated by Intergovernmental Panel on Climate Change (IPCC) as a consequence of increased [CO₂] and temperature, may not hold, due to interactions between these abiotic factors.     

Sorghum bicolor prioritizes the recovery of its photosynthetic activity when re-watered after severe drought stress,while manages to preserve it under elevated CO2 and drought

Understanding plant response and resilience to drought under a high CO₂ environment will be crucial to ensure crop production in the future. Sorghum bicolor is a C₄ plant that resists drought better than other crops, which could make it a good alternative to be grown under future climatic conditions. Here, we analyse the physiological response of sorghum under 350 ppm CO₂ (aCO₂) or 700 ppm CO₂ (eCO₂) with drought (D) or without drought (WW) for 9, 13 and 16 days; as well as its resilience under long (R1: 9D + 7R) or short (R2: 13D + 3R) recovery treatments. Sorghum showed elevated rates of gs under aCO₂ and WW, which resulted in a significant decrease in Ψ_w, gs, E, Φ_PSII, F_v’/F_m′ when exposed to drought. Consequently, A was greatly decreased. When re-watered, both re-watering treatments prioritized A recovery by restoring photosynthetic machinery under aCO₂, whereas under eCO₂ plants required little recovery since plant were hardly affected by drought. However, sorghum growth rate for aboveground organs did not reach control values, indicating a slower long-term recovery. Overall, these results provide information about the resilience of sorghum and its utility as a suitable candidate for the drought episodes of the future.     

The phenotypic characterisation of R2 generation transgenic rice plants under field and glasshouse conditions

Summary The phenotypes of seed progeny (R₂ generation) of Oryza sativa L. cv. Taipei 309, which carried the neomycin phosphotransferase II (npt II) gene, were compared with those of non-transformed, protoplast-derived plants of the same generation and non-transformed, seed-derived plants under field and glasshouse conditions. Under both conditions the transgenic plants were generally smaller, took longer to flower and had reduced fertility. Significant differences were observed between individuals within the group of transgenic plants. The npt II gene was present in most of the transgenic plants, but NPT II activity was only detected in a minority of individuals.     

Varietal differences in perennial ryegrass for nitrogen use efficiency in leaf growth following defoliation: performance in flowing solution culture and its relationship to yield under simulated grazing in the field

Varietal differences in rates of NO₃ uptake and remobilization of nitrogen (N) during a cycle of severe defoliation and regrowth were assessed in perennial ryegrass (Lolium perenne L.) varieties Ba11778, Aberelan, Talbot and Gator. Plants were grown in flowing solution culture for 34 days, prior to a 30 d treatment period, including 21 d of regrowth. Net uptake of NO₃ was measured continuously from solutions maintained automatically at 10 mmol m^-3NO₃.¹⁵ N-labelled NO_{3 3} was supplied to the plants in situ for either 21 h immediately prior to defoliation, or for 7-11 days afterwards, to measure remobilization of N from roots and stubble into the regrowing leaves. The four varieties differed only slightly in total dry matter production over 30 d, but varied substantially in post-defoliation specific growth rate by the leaf fraction. Gator was the lowest ( 0.11 g g^-1 d^-1), Ba11778 the highest ( 0.15 g g^-1 d^-1) and Aberelan and Talbot intermediate in leaf regrowth rate. Varieties did not vary significantly in shoot: root dry weight ratio, but the rate of NO₃ uptake per unit of leaf fresh weight during regrowth was 27% lower in Ba11778 than in Gator. Leaves of Ba11778 and Aberelan had a lower organic N concentration in the dry matter at the end of the regrowth period than Talbot, which, in turn, had a lower concentration than Gator. Varieties differed in amount of leaf dry matter produced per unit of N absorbed by the plants after defoliation, the values (g g^-1 N) being Ba11778 (22.6 ), Aberelan (20.7), Talbot (18.3) and Gator (16.7). More N was remobilized from the roots than from the stubble after defoliation. There were no significant differences among varieties in the amount and rate of N remobilization following defoliation. In earlier field experiments employing frequent cutting to simulate grazing, Ba11778 and Aberelan yielded at least 10% more dry matter annually than Talbot which, in turn, outyielded the amenity variety Gator by a similar amount. Thus the present results are consistent with the hypothesis that the efficiency of N use in leaf growth is an important factor determining genetic variation in productivity under frequent defoliation in the field when the herbage produced consists primarily of leaf. This revised version was published online in July 2006 with corrections to the Cover Date.