Response of Crops and Weeds to Climate and
CO2: Threats and Opportuni es
Na onal Forum on Climate and Pests, October 4-6, 2016 Lewis H. Ziska, USDA-ARS Weeds represent the greatest bio c constraint to crop yield.
Best es mates within the United States are a ~10% loss of produc on associated with weeds, with herbicide applica on. This increases to ~25% with BMP but no herbicide; 100% if no effort is made to control weeds. Globally, weeds probably represent the greatest bio c restraint to crop produc on, especially in developing countries. More money is spent on controlling weeds than any other pest threat. Climate change: Crop/weed Responses
ABIOTIC: Increasing temperatures, but also increasing varia on in temperature and precipita on, with more frequent extremes.
BIOTIC: The Increase in CO2 represents an increase in a basic resource needed for plant growth*
Bio c Response of weeds and crops. “CO2 is plant food; that will mean fewer weeds” WHY?
• First systema c a empt to evaluate globally the serious or significant weed problems in agriculture. • Based on input from weed scien sts from 100 countries around the world. • Focus is on global agriculture and “worst” weeds.
• Observa ons: Many crops had the C3 photosynthe c pathway, while many weeds had the C4 photosynthe c pathway. Bio c Response “CO2 is plant food; that will mean fewer weeds” WHY?
C3 Crops / C4 Weeds CO2 favors? Environment Reference
Fescue / Sorghum halapense crop glasshouse Carter & Peterson 1983.
Soybean / S. halapense crop chamber Pa erson et al. 1984.
Rice / Echinochloa glabrescens crop phytotron Alberto et al. 1996.
Soybean / Amaranthus retroflexus crop field Ziska 2000.
• Paradigm: Because weeds are less responsive to CO2 than crops, weed compe on will decline as will crop losses as CO2 increases. The Problem with Paradigms: They change.
Holm (1977) Current
Corn Cyperus rotundus (C4) Albu lon theophras (C3) Digitaria sanguinalis (C4) Ipomea spp. (C3) Echinochloa crus-galli (C4) Albu lon theophras (C3) Sorghum halapense (C4) Ambrosia trifida (C3) Portulaca oleracea (C4) Amaranth spp. (C4) Cynodon dactylon (C4) Chenopodium album (C3)
Soybean Turns out, “worst” changes with me. Eleusine indica (C4) Ipomea spp. (C3) Echinochloa colonum (C4) Setaria spp. (C4) Cyperus rotundus (C4) Amaranthus spp. (C4) Echinochloa crus-galli (C4) Albu lon theophras (C3) Chenopodium album (C3)
Wheat Avena fatua (C3) Cirsium arvense (C3) Polygonum convolvulus (C3) Convolvulus arvensis (C3) Chenopodium alba (C3) Avena fatua(C3) Convolvulus arvensis (C3) Bromus tectorum (C3)
Reality: Both C3 and C4 Crops compete with C3 and C4 weeds. On average, a given crop competes with 8-10 weeds.
Weed Paradigm shi s Crop Favored? Environ. Reference
Grasses (C44) Lucerne Crop Field Bunce, 1993
Amaranthus retroflexus (C44) Soybean Crop Field Ziska, 2000
Amaranthus retroflexus (C44) Sorghum Weed Field Ziska, 2003 C3 Crops / C4 Weeds CO2+ Crop or Weed? Reference
Chenopodium album (C33) Soybean Weed Field Ziska, 2000 Rice / Barnyardgrass CO2+temperature Weed Alberto et al. 1996.
Taraxacum officinale (C33) Lucerne Weed Field Bunce 1995 Tomato / Pigweed CO2+drought Weed Valerio et al. 2011.
Albutilon theophrasti (C33) Sorghum Weed Field Ziska, 2003 Rice / Barnyardgrass CO2+ N deficit Weed Zhu et al. 2008.
. Taraxacum and Plantago (C33) Grasses Weed Field Potvin and Vasseur, 1997 Worst? O en the “worst” weed may be a wild, weedy rela ve of the crop.
Rice Yield Loss from Heavy, Season-Long Weed Interference Why Worst? Weed Species Yield Loss, %
1. Pre-adapted to the same abio c condi ons Red rice 82 Barnyardgrass 70 as the crop. Bearded sprangletop 36 Amazon sprangletop 35 2. Difficult to iden fy; may not be recognized Broadleaf signalgrass 32 Ducksalad 21 Hemp sesbania 19 as a weed (and removed)un l damage has Spreading dayflower 18 Northern jointvetch 17 been done. Eclipta 10
R. J. Smith, Jr. 1988. Weed Technology. 2:232-241 Bio c Response Wild vs. cul vated crop A new Paradigm?
a 20 300 µmol mol-1 -1 400 µmol mol-1 300 µmol mol CO2 a ) 5000 -1 500 µmol mol-1
-2 400 µmol mol CO2 15 -1 500 µmol mol CO2 b 4000 b a 300010 c
2000 b c 5 c Seed Yield (g m 1000
0 0 Relative of yield seed, Stuttgart:Clearfield -2 -2 8 Clearfieldplants m 161 Stuttgart-S16 plants "red" m
Weeds, especially “worst” weeds, respond more to a resource change (e.g. CO2) than the crop. As such, crop losses are likely to increase, not decrease with higher [CO2]. Clearfield Rice, Management
Clearfield® rice is a chemical mutant that confers tolerance to imazethapyr herbicides.
Before the advent of this technology, there were no effective options to control red rice in conventional white rice.
There is a small amount of outcrossing (~.3%) between red rice and cultivated rice. Outcrossing is based on floral synchronicity, spatial proximity and genetic compatibility.
HYPOTHESIS: CAN CO2 EFFECT OUTCROSSING RATES AND THE TRANSFER OF HERBICIDE RESISTANCE?
Clearfield 161, planted with Stuttgart red rice at ratio of 7:1 for three CO2 concentrations, 300, 400 and 600 ppm (beginning, end of 20th century, IPCC 21st century prediction), using growth chambers. And?
Resultant seed was planted in Arkansas. As Clearfield rice crosses at low rates with red rice any herbicide-resistant hybrids could be confirmed using DNA fingerprin ng.
300 ppm CO2, CL-161 female 600 ppm CO2, CL-161 female And?
Percent outcrossing and outcrosses per plot for the pollen donor as detected in cul vated and wild rice popula ons in the field plots.
The direc on of outcrossing was from wild to the cul vated popula on; this resulted in a subsequent increase in rice dedomes ca on and a greater number of weedy, herbicide-resistant hybrid progeny Why the difference in bio c response between wild and cul vated? A comparison of wild and cul vated rice lines. Wild biotypes vs. cultivated rice.
8000 100 ~300 ppm CO
Cultivated rice lines ) 2
300 ppm Wild or red rice. -1 ~400 ppm CO2
6000 80
60 4000 40
2000 20 Seed yield (g plant Seed yield per plant) 2 0 0 8000 Clearfield Stuttgart-S 400 ppm
6000 Leaf area (cm 4000 Sugges on that there has been selec on by nature for increased sensi vity to recent 2000 changes in atmospheric carbon dioxide; in
0 contrast to ar ficial selec on. Total biomass at 55 DAS Can recent increases in CO2 be a selection factor in weed biology and competitive performance?
Wild oat (A. fatua) Cultivated oat (A. sativa)
1965, ~319 ppm CO 2 2013, ~395 ppm CO2 WO old WOnew Clintland 64, Cultivated Oat CO2 AND SELECTION
2500 P =0.06 1.4 WO CO 1.4 CO CO (old) CO 15 ) Stem Wt. (g)Stem Wt. 2 * 1.22000 * WO(old) 1.2 WO 1.0 (old) WO(old) 1.0
1500 10 PRY 0.8 0.8 PRY 0.61000 0.6 Leaf Area (cm Leaf Area * 5 0.4 0.4 500 0.2 0.2
0.0 0 0 0.0 WO WO CO (new) 1.4 (new) * 1.4 CO * * * 1.215 * 151.2
CO * WO (g) Wt. Total 1.0 WO(new) (new) CO 1.0 PRY 0.8 0.8 10 10
PRY 0.6 0.6
Leaf Wt Leaf Wt (g) 0.4 0.4 5 5 0.2 0.2
0.0 0.0 0 315 ppm 418 ppm 315 ppm 418 ppm 0 315 418Leaf Area315 418 315Above 418 Ground Biomass315 418
WOold WOnew WOold WOnew Why are weeds adap ng to CO2 and not crops?
300 "4484" "Cl-161" * *
200
100
Breeding 0
300 * "M204" "Stg-S" *
Seed Yield (g per plant) per (g Yield Seed 200 *
100
0 29/21 31/23 33/25 29/21 31/23 33/25
Day/Night (oC) How are weeds adap ng? What characteris cs are associated with greater increases in seed yield as CO2 increases?
"4484" "CL-161" "M204" "Stg-S"
70 70 o o o 29/21 C 29/21 C 29/21oC 29/21 C 60 60 Ambient CO Ambient CO Ambient CO2 Ambient CO2 2 2 50 Elevated CO Elevated CO 50 Elevated CO2 Elevated CO2 2 2 40 40
30 30
20 20
10 10
0 0
70 70 o 31/23oC o 31/23oC 31/23 C 60 31/23 C 60
50 50
40 40
30 30
20 20 Number of tillers 10 10
0 0
70 70 o o o o 60 33/25 C 33/25 C 33/25 C 33/25 C 60
50 50
40 40
30 30
20 20
10 10
0 0 10 20 30 40 10 20 30 40 10 20 30 40 10 20 30 40
Days after sowing (DAS) Let me Sum Up.
There is no basis for assuming that as CO2 rises, or as climate changes, that weeds will be less of a threat for crop production based on photosynthetic pathway. Preliminary evidence suggests that weeds may impose greater limitations on crop production.
The worst weeds, often wild relative of the crop, may be better able to adapt to the increase in CO2 and/or temperature associated with future conditions. This adaptation may include, but is not limited to, increased gene transfer from wild to Cultivated lines, increased herbicide resistance and enhanced adaptation to CO2. ?
However, adaptation among wild, weedy lines may serve as a means to enhance adaptation of cultivated lines, especially cereal lines, to increase production as CO2 increases. We may be able to learn from our weedy “cousins”.