Competitive interactions in mixtures of broccoli and Chenopodium album grown at two UV‐B radiation levels under glasshouse conditions

Abstract

Ultraviolet-B radiation effects on intra-and interspecific competition in broccoli (Brassica oleracea) and Chenopodium album were studied using bivariate factorial experiments. A randomized block design was used in which three monoculture densities for each species [144 (low), 256 (medium), and 400 (high) plants m )2 ] and all binary combinations were grown in a glasshouse at two (4 and 7 kJ m )2 day )1 ) UV-B BE radiation levels for 4 weeks in 1999 and 5 weeks in 2000. Inverse yield-density relationships were more discernible at 4, compared with 7 kJ m )2 day )1 UV-B BE radiation. Substitution rates, indicating the balance of intra-to interspecific competitive effects, declined for broccoli at 7, compared with 4 kJ m )2 day )1 UV-B BE radiation, largely because of reduced interspecific competitive influences. Conversely, substitution rates increased for C. album grown at 7 kJ m )2 day )1 UV-B BE radiation, as a result of both decreased intraspecific and increased interspecific competition. Interspecific competitive effects were influenced more than intraspecific competitive effects by UV-B radiation. Based on relative magnitude of substitution rates, C. album was a stronger competitor than broccoli at 4 kJ m )2 day )1 UV-B BE radiation in both years, and at 7 kJ m )2 day )1 UV-B BE radiation in 1999. In 2000, broccoli was the stronger competitor at 7 kJ m )2 day )1 UV-B BE radiation. Overall, the relative competitiveness of broccoli was enhanced, while that of C. album diminished at 7, compared with 4 kJ m )2 day )1 UV-B BE radiation. These findings indicate that above-ambient UV-B radiation has the potential to alter crop-weed competitive interactions, which could change acceptable weed threshold levels.

Re‐interpreting plant morphological responses to UV‐B radiation

“…Jansen ; Furness et al . ). It is likely that these aboveground effects will also affect the root:shoot ratio.…”

“…For example, UV‐B‐induced shifts in competitive interactions were found in a greenhouse study with broccoli ( Brassica oleracea ) and Chenopodium album (Furness et al . ). Broccoli gained in competitiveness relative to C. album in response to above ambient UV‐B exposure conditions.…”

“…The most frequently reported UV‐B‐induced morphological changes are a decrease in leaf area and/or an increase in leaf thickness (Jansen ; Furness et al . ; Hectors et al . ; Yang et al .…”

“…UV‐induced architectural changes include, among others, thicker leaves, shorter petioles, leaf curling and alterations in leaf shape and width, decreases in stem elongation, increased axillary branching or tillering, and altered root:shoot ratio and structure of the inflorescence (Jansen ; Furness et al . ; Hectors et al . ; Yang et al .…”

Variations in Growth, Photosynthesis and Defense System Among Four Weed Species Under Increased UV‐B Radiation

“…Some previous studies showed that weed species differed significantly in their susceptibility to UV-B radiation (Furness et al 1999;Furness and Upadhyaya 2002;Dai et al 2004). Increased UV-B radiation also changed the competition balance between wheat and wild oat (Li et al 1999;Furness et al 2005). However, little information is available on the growth response to increased UV-B radiation in most of the important weeds.…”