Nodulation and biomass production in Blackbrush Acacia (Acacia rigidula) seedlings.
Teaschner, Terri*,1, Fulbright, Timothy1, 1 Caesar Kleberg Wildlife Research Institute, Kingsville, TX, USA
ABSTRACT- Blackbrush acacia (Acacia rigidula) is an important browse shrub for wildlife in southern Texas and northern Mexico and is common on soils low in fertility. This dominance on low nitrogen soils may be linked to the ability of blackbrush acacia to fix nitrogen. We grew blackbrush acacia in a shade house to determine when nodulation occurs and to test the hypothesis that defoliation reduces root nodulation and biomass production in blackbrush acacia seedlings. Seedlings received one of 2 treatments: removal of topmost leaflet group ('defoliated') or no biomass removal ('control'). Defoliated seedlings had the upper leaflet removed at 2 weeks of age only. Seedlings were measured and harvested at 2-week intervals from 2 weeks of age to 10 weeks of age. Sixteen percent of seedlings harvested at 2 weeks of age had nodules, at 4 weeks of age 53% of control plants and 62% of defoliated seedlings had nodules, and at 6 weeks of age 71% of control and 100% of defoliated seedlings had nodules. While a higher percentage of defoliated seedlings were observed to have nodules, the number of nodules per plant and average nodule weight per plant was higher in control seedlings (p < 0.05). However, root mass and aboveground biomass production was greater in defoliated seedlings (p < 0.05). Competition for water and nutrients is high in southern Texas, so nodule production in response to defoliation may be an anti-herbivore defense mechanism that enables seedlings to produce nitrogen for use in photosynthesis and replacement of lost biomass, and can ultimately increase the seedlings chance of survival and establishment.
Key words: Acacia rigidula, nodulation, southern Texas
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