DOI: 10.25338/b8g34c
title: Wheat grain yield decreased over the past 35 years, but protein content did not change

description: The extent to which rising atmospheric CO2 concentration has already
 influenced food production and quality is uncertain. Here, we analyzed
 annual field trials of fall-planted common wheat in California from 1985
 to 2019, a period during which global atmospheric CO2 concentration
 increased 19%. Even after accounting for other major factors (cultivar,
 location, degree-days, soil temperature, total water applied, nitrogen
 fertilization, and pathogen infestation), wheat grain yield and protein
 yield declined 13% over this period, but grain protein content did not
 change. These results suggest that wheat, when exposed to gradual CO2
 enrichment, sacrifices grain yield and protein yield for stable grain
 protein content.
description: The dataset of fall-planted, common wheat cultivars from field
 trials conducted at multiple locations throughout central California
 (Lundy and Dubcovsky, 2021) has 6,508 records with values for
 (<i>a</i>) year; (<i>b</i>) cultivar name;
 (<i>c</i>) location; (<i>d</i>) grain protein
 content (%); (<i>e</i>) grain yield (kg);
 (<em>f</em>) total water supplied (mm);
 (<em>g</em>) air degrees days; (<em>h</em>) total
 N fertilizer applied (kg/ha); (<em>i</em>) years from
 introduction of the cultivar into field trials; (<em>j</em>)
 quantitative scores for stripe rust, leaf rust, Septoria leaf blotch, and
 Yellow dwarf virus (area of flag-1 leaf affected at soft dough stage: 1 =
 0 – 3%, 2 = 4 – 14%, 3 = 15 – 29%, 4 = 30 – 49%, 5 = 50 – 69%, 6 = 70 –
 84%, 7 = 85 – 95%, 8 = 96 – 100%); (<em>k</em>) soil
 temperature (°C); and (<i>l</i>) Vapor Pressure Deficit (VPD,
 Pa). Soil temperatures, air degree-days, and Vapor Pressure Deficit (VPD)
 were derived from hourly data collected at the closest California
 Irrigation Management Information System (CIMIS) station (California
 Department of Water Resources, 2021); degree-days were calculated based on
 temperatures measured during January, February, and March via the single
 sine method with a horizontal upper cutoff with a maximum temperature for
 common wheat of 30°C and a minimum temperature of 7°C (Statewide
 Integrated Pest Management Program, 2021); and VPD was calculated from
 average air temperatures (Huang, 2018) and vapor pressures during January,
 February, and March at the closest California Irrigation Management
 Information System (CIMIS) station. Protein yield is the product of grain
 protein percentage and yield, and total water addition is the sum of
 rainfall and irrigation. California fall-planted wheat
 field trials provided at least 16 years of data for each of five
 <i>locations</i>: Sacramento Delta (“Delta”), Imperial County
 (“Imperial”), Kern County (“Kern”), Kings County (“Kings”), and Yolo
 County at the University of California Davis (“UCD”). We merged the data
 for Butte County and Colusa County, two adjacent counties that had very
 little temporal overlap, to form a sixth <i>location</i>
 (“North”) with more than 16 years of data. The six locations extend
 between latitudes 32.8°N and 39.8°N, from deserts near the Mexican border
 (Imperial and Kern) where plants received nearly all of their water from
 irrigation to the Sacramento River flood plain (Delta and North) where
 plants received much of their water from precipitation and ground water.
 The trials also provided at least 18 years of data for each of six check
 <i>cultivars</i> (Anza, Blanca Grande, Express, Klasic, Serra,
 and Yecora Rojo). Data for the cultivars Blanca Grande, Patwin, and Summit
 were merged with data for derivatives in which stripe rust resistance
 genes Yr5 and Yr15 were introduced by four backcross generations into the
 susceptible parent cultivar (Jackson, 2011).