Weeds in a Changing Climate

Abstract

Current and projected increases in the concentrations of CO2and other radiatively-active gases in the Earth's atmosphere lead to concern over possible impacts on agricultural pests. All pests would be affected by the global warming and consequent changes in precipitation, wind patterns, and frequencies of extreme weather events which may accompany the “greenhouse effect.” However, only weeds are likely to respond directly to the increasing CO2concentration. Higher CO2will stimulate photosynthesis and growth in C3weeds and reduce stomatal aperture and increase water use efficiency in both C3and C4weeds. Respiration, and photosynthate composition, concentration, and translocation may be affected. Perennial weeds may become more difficult to control, if increased photosynthesis stimulates greater production of rhizomes and other storage organs. Changes in leaf surface characteristics and excess starch accumulation in the leaves of C3weeds may interfere with herbicidal control. Global warming and other climatic changes will affect the growth, phenology, and geographical distribution of weeds. Aggressive species of tropical and subtropical origins, currently restricted to the southern U.S., may expand northward. Any direct or indirect consequences of the CO2increase that differentially affect the growth or fitness of weeds and crops will alter weed-crop competitive interactions, sometimes to the detriment of the crop and sometimes to its benefit.

Alien plant species favoured over congeneric natives under experimental climate warming in temperate Belgian climate

“…Many prior studies of invasiveness have focused on the traits associated with the capacity of alien plant species to successfully invade new habitats Richardson and Pysek 2006) and apart from a broad native range, especially traits related to high growth rate under varying environmental conditions seem important (Durand and Goldstein 2001;Lake and Leishman 2004). Photosynthesis is such a trait and since increases in temperature can affect photosynthesis, warming could potentially lead to changes in invasiveness through this pathway (Patterson 1995). The results of the current study are thus in agreement with the hypothesis that climate warming might favour alien species over natives and enhance their invasion success (Dukes and Mooney 1999;Hellmann et al 2008).…”

Is leaf-level photosynthesis related to plant success in a highly productive grassland?

“…Implicit in these studies is the assumption that short-term, leaf-level photosynthetic rates are related to various attributes of plant success ± productivity, competitiveness, resistance to herbivores or pathogens, seed production ± i.e., ®tness (McGraw 1987;Jackson et al 1994;Pell et al 1994;Burton and Bazzaz 1995;Patterson 1995;Van Der Kooij and De Kok 1996). Thus, the measurement of instantaneous, leaf-level photosynthetic rates is assumed to be of predictive value for assessing the longer-term consequences of abiotic/biotic factors affecting plant performance.…”

Responses of Invasive Species to a Changing Climate and Atmosphere

“…On the other hand, many studies have shown that the outcome of competition can depend on environmental conditions (see, for example, Patterson 1995 ). For instance, in the Rocky Mountains of North America, native bull trout ( Salvelinus confl uentus ) outcompete non -native brook trout ( Salvelinus fontinalis ) in cooler streams, but warmer water would favour the brook trout (Rieman et al 1997 ).…”

“…It has long been recognized that the increasing atmospheric CO 2 concentration could alter the balance of competition among plants (with implications for the effects of weed species on crop yield, for instance (Patterson 1995 ), or for competition between C 3 and C 4 plants). Many experiments have examined responses of single plants or single species growing in pots to elevated CO 2 .…”