Climate change will increase drought in many regions of the world. Besides decreasing productivity, drought also decreases the concentration (%) of nitrogen (N) and phosphorous (P) in plants. We investigated if decreases in nutrient status during drought are correlated with decreases in levels of nutrient-uptake proteins in roots, which has not been quantified. Drought-sensitive (Hordeum vulgare, Zea mays) and -tolerant grasses (Andropogon gerardii) were harvested at mid and late drought, when we measured biomass, plant %N and P, root N- and P-uptake rates, and concentrations of major nutrient-uptake proteins in roots (NRT1 for NO3, AMT1 for NH4, and PHT1 for P). Drought reduced %N and P, indicating that it reduced nutrient acquisition more than growth. Decreases in P uptake with drought were correlated with decreases in both concentration and activity of P-uptake proteins, but decreases in N uptake were weakly correlated with levels of N-uptake proteins. Nutrient-uptake proteins per gram root decreased despite increases per gram total protein, because of the larger decreases in total protein per gram. Thus, drought-related decreases in nutrient concentration, especially %P, were likely caused, at least partly, by decreases in the concentration of root nutrient-uptake proteins in both drought-sensitive and -tolerant species.

Atmospheric CO enrichment is expected to often benefit plant growth, despite causing global warming and nitrogen (N) dilution in plants. Most plants primarily procure N as inorganic nitrate (NO ) or ammonium (NH ), using membrane-localized transport proteins in roots, which are key targets for improving N use. Although interactive effects of elevated CO , chronic warming and N form on N relations are expected, these have not been studied. In this study, tomato (Solanum lycopersicum) plants were grown at two levels of CO (400 or 700 ppm) and two temperature regimes (30 or 37°C), with NO or NH as the N source. Elevated CO plus chronic warming severely inhibited plant growth, regardless of N form, while individually they had smaller effects on growth. Although %N in roots was similar among all treatments, elevated CO plus warming decreased (1) N-uptake rate by roots, (2) total protein concentration in roots, indicating an inhibition of N assimilation and (3) shoot %N, indicating a potential inhibition of N translocation from roots to shoots. Under elevated CO plus warming, reduced NO -uptake rate per g root was correlated with a decrease in the concentration of NO -uptake proteins per g root, reduced NH uptake was correlated with decreased activity of NH -uptake proteins and reduced N assimilation was correlated with decreased concentration of N-assimilatory proteins. These results indicate that elevated CO and chronic warming can act synergistically to decrease plant N uptake and assimilation; hence, future global warming may decrease both plant growth and food quality (%N).

Limited evidence indicates that moderate leaf hyponasty can be induced by high temperatures or unnaturally high CO2. Here, we report that the combination of warming plus elevated CO2 (eCO2) induces severe leaf hyponasty in tomato (Solanum lycopersicum L.). To characterize this phenomenon, tomato plants were grown at two levels of CO2 (400 vs. 700 ppm) and two temperature regimes (30 vs. 37°C) for 16–18 days. Leaf hyponasty increased dramatically with warming plus eCO2 but increased only slightly with either factor alone and was slowly reversible upon transfer to control treatments. Increases in leaf angle were not correlated with leaf temperature, leaf water stress, or heat‐related damage to photosynthesis. However, steeper leaf angles were correlated with decreases in leaf area and biomass, which could be explained by decreased light interception and thus in situ photosynthesis, as leaves became more vertical. Petiole hyponasty and leaf‐blade cupping were also observed with warming + eCO2 in marigold and soybean, respectively, which are compound‐leaved species like tomato, but no such hyponasty was observed in sunflower and okra, which have simple leaves. If severe leaf hyponasty is common under eCO2 and warming, then this may have serious consequences for food production in the future.

Atmospheric carbon dioxide (CO 2) concentration is increasing, as is the frequency and duration of drought in some regions. Elevated CO 2 can decrease the effects of drought by further decreasing stomatal opening and, hence, water loss from leaves. Both elevated CO 2 and drought typically decrease plant nutrient concentration, but their interactive effects on nutrient status and uptake are little studied. We investigated whether elevated CO 2 helps negate the decrease in plant nutrient status during drought by upregulating nutrient-uptake proteins in roots. METHODS: Barley (Hordeum vulgare) was subjected to current vs. elevated CO 2 (400 or 700 ppm) and drought vs. well-watered conditions, after which we measured biomass, tissue nitrogen (N) and phosphorus (P) concentrations (%N and P), N-and P-uptake rates, and the concentration of the major N-and P-uptake proteins in roots. RESULTS: Elevated CO 2 decreased the impact of drought on biomass. In contrast, both drought and elevated CO 2 decreased %N and %P in most cases, and their effects were additive for shoots. Root N-and P-uptake rates were strongly decreased by drought, but were not significantly affected by CO 2. Averaged across treatments, both drought and high CO 2 resulted in upregulation of NRT1 (NO 3 − transporter) and AMT1 (NH 4 + transporter) per unit total root protein, while only drought increased PHT1 (P transporter). CONCLUSIONS: Elevated CO 2 exacerbated decreases in %N and %P, and hence food quality, during drought, despite increases in the concentration of nutrient-uptake proteins in roots, indicating other limitations to nutrient uptake.

Growing lignocellulosic crops on marginal lands is a promising solution for sustainable biofuel production. We evaluated the productivity of bioenergy cropping systems (switchgrass [Panicum virgatum L., var. Cave‐In‐Rock], miscanthus [Miscanthus × giganteus, ‘Illinois clone’], hybrid poplar [Populus nigra × P. maximowiczii A. Henry ‘NM6’], native grasses [five species], early successional vegetation, and restored prairie vs. historical vegetation [as reference control]) with and without nitrogen fertilization on low‐fertility former cropland at five sites in the Great Lakes Region, United States. We reported biomass yields for the first 7 years after establishment. Switchgrass was most consistently productive across all sites but miscanthus was more productive at three of the five sites. When averaged across sites, years, and nitrogen (N) treatments, biomass yields followed the order miscanthus > switchgrass > hybrid poplar ≈ native grasses > restored prairie > early successional vegetation ≈ historical vegetation, but varied substantially by crop and site, with a significant crop by site interaction. Yields of miscanthus and switchgrass peaked after four–five growing seasons and declined thereafter, while yields of both native grasses and restored prairie increased throughout 6 years with no sign of follow‐on decline, suggesting that polycultures may outperform monocultures over the long term. Yields of early successional vegetation—similar in composition to historical vegetation at each site—did not improve with time. Nitrogen fertilization increased the yields of all cropping systems at all sites. Our results demonstrate the viability of low‐productivity former cropland for long‐term bioenergy production and suggest there is no single crop best suited for all low fertility soils.