The Effects of Inorganic Nitrogen form and CO2CO_2 Concentration on Wheat Yield and Nutrient Accumulation and Distribution

Inorganic N is available to plants from the soil as ammonium ($NH^+_4$) and nitrate ($NO^-_3$). We studied how wheat grown hydroponically to senescence in controlled environmental chambers is affected by N form ($NH^+_4$ vs. $NO^-_3$) and $CO_2$ concentration (“subambient,” “ambient,” and “elevated”) in terms of biomass, yield, and nutrient accumulation and partitioning. Wheat supplied with $NH^+_4$ as a sole N source had the strongest response to $CO_2$ concentration. Plants exposed to subambient and ambient $CO_2$ concentrations typically had the greatest biomass and nutrient accumulation under both N forms. In general $NH^+_4$-supplied plants had higher concentrations of total N, P, K, S, Ca, Zn, Fe, and Cu, while $NO^-_3$-supplied plants had higher concentrations of Mg, B, Mn, and $NO^-_3$ - N. $NH^+_4$-supplied plants contained amounts of phytate similar to $NO^-_3$-supplied plants but had higher bioavailable Zn, which could have consequences for human health. $NH^+_4$-supplied plants allocated more nutrients and biomass to aboveground tissues whereas $NO^+_3$-supplied plants allocated more nutrients to the roots. The two inorganic nitrogen forms influenced plant growth and nutrient status so distinctly that they should be treated as separate nutrients. Moreover, plant growth and nutrient status varied in a non-linear manner with atmospheric $CO_2$ concentration

Nitrate reductase 15N discrimination in Arabidopsis thaliana, Zea mays, Aspergillus niger, Pichea angusta, and Escherichia coli

Stable 15N isotopes have been used to examine movement of nitrogen (N) through various pools of the global N cycle. A central reaction in the cycle involves nitrate (NO3–) reduction to nitrite (NO2–) catalyzed via nitrate reductase (NR). Discrimination against 15N by NR is a major determinant of isotopic differences among N pools. Here, we measured in vitro 15N discrimination by several NRs purified from plants, fungi, and a bacterium to determine the intrinsic 15N discrimination by the enzyme and to evaluate the validity of measurements made using 15N-enriched NO3–. Observed NR isotope discrimination ranged from 22‰ to 32‰ (kinetic isotope effects of 1.022 to 1.032) among the different isozymes at natural abundance 15N (0.37%). As the fractional 15N content of substrate NO3– increased from natural abundance, the product 15N fraction deviated significantly from that expected based on substrate enrichment and 15N discrimination measured at natural abundance. Additionally, isotopic discrimination by denitrifying bacteria used to reduce NO3– and NO2– in some protocols became a greater source of error as 15N enrichment increased. We briefly discuss potential causes of artifactual results with enriched 15N and recommend against the use of highly enriched 15N tracers to study N discrimination in plants or soils

Impacts of elevated atmospheric CO₂ on nutrient content of important food crops.

One of the many ways that climate change may affect human health is by altering the nutrient content of food crops. However, previous attempts to study the effects of increased atmospheric CO2 on crop nutrition have been limited by small sample sizes and/or artificial growing conditions. Here we present data from a meta-analysis of the nutritional contents of the edible portions of 41 cultivars of six major crop species grown using free-air CO2 enrichment (FACE) technology to expose crops to ambient and elevated CO2 concentrations in otherwise normal field cultivation conditions. This data, collected across three continents, represents over ten times more data on the nutrient content of crops grown in FACE experiments than was previously available. We expect it to be deeply useful to future studies, such as efforts to understand the impacts of elevated atmospheric CO2 on crop macro- and micronutrient concentrations, or attempts to alleviate harmful effects of these changes for the billions of people who depend on these crops for essential nutrients

Impacts of elevated atmospheric CO2 on nutrient content of important food crops

One of the many ways that climate change may affect human health is by altering the nutrient content of food crops. However, previous attempts to study the effects of increased atmospheric CO2 on crop nutrition have been limited by small sample sizes and/or artificial growing conditions. Here we present data from a meta-analysis of the nutritional contents of the edible portions of 41 cultivars of six major crop species grown using free-air CO2 enrichment (FACE) technology to expose crops to ambient and elevated CO2 concentrations in otherwise normal field cultivation conditions. This data, collected across three continents, represents over ten times more data on the nutrient content of crops grown in FACE experiments than was previously available. We expect it to be deeply useful to future studies, such as efforts to understand the impacts of elevated atmospheric CO2 on crop macro- and micronutrient concentrations, or attempts to alleviate harmful effects of these changes for the billions of people who depend on these crops for essential nutrients

The effects of land-use change on soil carbon in oak woodlands and vineyards

Land-use change influences soil carbon (C) transformations and characteristics as well as soil physical properties. We examined the effects of the land-use change in oak woodlands and adjacent vineyards converted approximately 35-40 years ago in the Oakville region of Napa Valley, California. All experimental sites were located on the same soil type and on similar slopes. Field experiments found that annual soil CO2 efflux was greatest at the oak woodland sites, although during the summer drought the rates of soil CO2 efflux measured from oak sites were generally similar to those measured from the vineyards. Soil profile CO2 concentrations at the oak woodland sites were lower below 15 cm despite higher CO2 efflux rates than those observed from vineyard sites. Soil gas diffusion coefficients for oak soils were larger than for vineyard soils. Soil profile CO2 concentration ([CO2]) and δ13C values showed substantial temporal changes over the course of a year. Vineyard soil CO 2 was more depleted in 13CO2 below 25 cm in the soil profile during the active growing season as indicated by more negative δ 13C ratios. It is likely that different C sources were being oxidized in vineyard soils as compared to oak soils. Annual C losses were less from vineyard soils (7.02 ± 0.58 Mg C ha-1 yr-1) than oak soils (15.67 ± 1.44 Mg C ha-1 yr-1). Long-term 810 day laboratory incubations were used to further address soil organic C (SOC) decomposition and microbial substrate utilization. Greater NO3- and microbial biomass C accumulations in the oak soils, combined with lower DOC, total soil C, and lower respiration rates in the vineyard soils, indicated that vineyard soils were C limited relative to the oak soils. Normalized respiration rates (respiration g-1 C) demonstrated that C quantity rather than other factors such as quality had a stronger impact on microbial activity. Respiration δ 13CO2 values decreased over time with the oak soil respiration having the most depleted δ13C values. Vineyard berms, which were managed to remove weed biomass under the vines, showed the most enriched δ13C values, suggesting that root and rhizosphere deposition make a greater relative contribution to total soil organic matter composition than in oak soils. The δ13C data indicated that microbes utilized different substrates in the vineyard and oak soils. Increasing microbial biomass and decreasing metabolic quotient (qCO2 ) measurements suggested that a shift in microbial community to one better suited to utilize a more highly degraded substrate occurred during the incubation for the oak and vineyard soils. In the Mediterranean climate of California, water has been found to be the primary limiting resource to soil microbial activity during the hot summer months. Furthermore, season (i.e. wet or dry season) has been found to have differing impacts on soil C transformations in oak woodlands and vineyards that have been converted from oak woodland systems. Conversion of oak woodlands has resulted in changes in profile C characteristics including particulate organic matter (POM) C, bulk soil C, DOC, microbial activity, and soil atmosphere [CO2]. POM C fractions, particularly those associated with the mineral soil (<53 μm) was greater in oak than vineyard soils. This fraction is thought to be the most stable of the POM fractions, and demonstrates that the loss of C from the soil profile during the conversion process was primarily of the most stable POM C pool. Water additions were found to have different impacts on soil C in the oak and vineyard sites, primarily with regard to microbial responses to the increased soil moisture

Evaluation of hyperspectral reflectance indexes to detect gravepine water status in vineyards

P. 302-317Irrigation scheduling is critical as it affects both fruit yield and composition. We examined the potential to use field-measured hyperspectral remote sensing data to stimate leaf water content, equivalent water thickness, and leaf water potential in a commercial vineyard of Vitis vinifera cv. Pinot noirS