Growth, reproductive and potential competition between rice (Oryza sativa L.) and its associated weeds under elevated carbondioxide and high temperature

Date

10-1995

Abstract

The continuing increase in atmospheric CO2 concentration is expected to lead to a significant increase in global mean temperature. Because CO2and temperature are expected to increase together, their synergistic effects have an impact on photosynthesis, respiration, phenology , growth of crop plants as well as on their competitive interactions between their associated weeds.

Studies were conducted over a two (2) year period to investigate changes in rice/weed growth and potential competition with increasing CO2 and/or temperature. In examining competition three (3) specific areas were investigated: (1) Germination/emergence and early stand establishment of rice (Oryza sativa L. cvIR72) , Echinochloa glabrescens Munro ex Hook.f. and Ludwigia octovalvis (Jacq.) Raven; (2) Characterization of growth and reproductive parameters among E.glabrescens, L. octovalvis and rice; and (3) Changes in potential competition as simulated by variation in planting density between rice and a C4 weed, E. glabrescens.

Studies were made to investigate the effect of elevated CO2 (700ppm) on germination/emergence of E. glabrescens and L. octovalvis, a C4 and C3 weedy species, respectively. In addition, effects of increasing CO2 (Ambient+200ppm) and temperature (37/29°C) on germination/emergence of rice and E. glabrescens were also determined. Exposure to increased CO2 resulted in a significant increase in the percent emergence of E. glabrescens.

In a separate field experiment, elevated CO2 (Ambient+300 ppm) stimulated the emergence and number of weed seedings particularly Fimbristylis miliacea (L) Vahl ( C4 weed). Total dry weight of all the weed seedlings that emerged in the open-top field chambers increased with increasing CO2 (Ambient+300 ppm) and temperature (29/21°C; 37/29°C). Elevated CO2 at the optimal temperature of 29/21°C increased the total dry weight, leaf area and plant height for all three species at maturity. However, interaction between high CO2 and temperature also promoted greater total dry weight, tiller number and leaf area for all the three species.

Grain yield and percent filled spikelets increased with increasing CO2 concentration for the two species (rice and E. glabrescens ). Overall, rice produced more grain yield than the other two species. Differences in reproductive characteristics were also observed among the three species with high CO2 and temperature. The grain yield and grain filling were negative for rice and L. octovalvis but were reduced for E. glabrescens.

Rice and L. octovalvis were more responsive to increasing CO2 and temperature than E. glabrescens. Overall, L. octovalvis showed greater growth than rice and E. glabrescens with increasing CO2 and temperature.

In the third experiment, potential competition between rice and E. glabrescens in terms of their vegetative and reproductive characteristics were examined at different planting densities at different CO2 levels (Ambient; Ambient+200) and temperature regimes (27/21 °C; 37/29°C). Increased CO2 concentration promoted greater biomass, tiller number, grain yield, panicle weight and percent filled spikelets for rice relative to E. glabrescens. Comparison between the two species showed that the ratio of rice/E. glabrescens for total above ground biomass, leaf area, tiller number and grain yield increased with increasing CO2 concentration indicating a potential competitive advantage for rice under elevated CO2.

However, if CO2 and temperature increased simultaneously the increase in rice biomass declined relative to the elevated CO2condition alone. It was also observed that with increasing CO2 and temperature weeds become taller than rice. Interestingly, no grain yield was produced at the higher growth temperature for rice either CO2 concentrations. In contrast, grain yield for E. glabrescens while reduced was still significant at either CO2 concentrations.

Overall, these experiments suggest that increasing atmospheric CO2 could potentially increase the growth of C3 plants with differential growth anticipated for C3 crops such as rice and C3 weeds such as L. octovalvis. While competition was not directly measured between these two (2) C3 species, it appears based on relative enhancement of growth that at least in some circumstances C3 weed could outcompete a C3 crop such as rice. With respect to C3/C4 interactions as CO2 increases, both growth characteristics and competitive interactions suggest that in these experiments C3 crops or weeds (e.g. rice, L. octovalvis) could be favored in comparison to a C4 weed such as E. glabrescens.

But if increasing atmospherics CO2 also results in increasing temperature (i.e global warming) then changes in the response to CO2 between C3 and C4 species may be possible. For example, in the current experiments, no reproductive yield was observed in either L. octovalvis or rice at the higher growth temperature. In addition, in the planting density experiment between rice (C3) and E. glabrescens (C4) the relative simulation of plant biomass of rice with increasing CO2 was reduced at high temperatures. Therefore, although increasing CO2 may enhance C3 relative to C4 growth and C3 (rice) relative to C3 (weed) (consistent with the known effects of photosynthetic biochemistry), the relative effect of high temperature on reproduction could still favor C4 over C3 with global climate change.

Document Type

Dissertation

Degree

Doctor of Philosophy in Botany

College

Graduate School (GS)

Adviser/Committee Chair

Cleofas R. Cervancia

Co-adviser

Lewis H. Ziska

Committee Member

Zenaida N. Sierra, Norma A. Aguilar, Enrique P. Pacardo

Language

English

LC Subject

Rice--Weed control

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

LG 996 1995 B62 A42

Notes

Doctor of Philosophy (Botany)

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