Soybean Root Morphological and Anatomical Traits Associated with Acclimation to Flooding

Abstract

Soybean [Glycine max (L.) Merr.] acclimation to flooding has been investigated at biochemical and physiological levels, but longterm acclimation to flooding may be associated with morphological changes. Supplementing legumes with nitrate ameliorates flooding stress, compared with plants dependent on N2 fixation. Two experiments evaluated morphological and anatomical changes induced by flooding for plants relying on N2 fixation or supplemented with nitrate. An additional experiment assessed the role of aerenchyma in flooding acclimation by blocking aerenchyma formation with silver. Flooding soybean for 21 d with nutrient solution without N increased biomass allocation to roots. No aerenchyma was observed in roots of nonflooded plants; however, it was abundant in roots of flooded plants. Porosity measurements of root and stem‐base tissues indicated that 10 to 15% of the volume was gas filled in flooded plants, while gasfilled volume was negligible in the nonflooded controls. Flooding in the presence of nitrate decreased aerenchyma and increased adventitious roots, compared with plants flooded with nutrient solution without N. Increased growth under flooding of nitrate‐supplemented plants, therefore, was not directly associated with increased root porosity. For flooded plants dependent on N2 fixation, silver prevented aerenchyma and adventitious root development and decreased biomass accumulation and N2 fixation by approximately one‐half compared with plants flooded in the absence of silver. These results indicate that acclimation to flooding in soybean involves preferential allocation of photosynthates to development of porous adventitious roots and that aerenchyma formation for soybean relying on N2 fixation is critical for acclimation to flooding.

Tolerance to flooding in five Brachiaria brizantha accessions

“…In the flooding-tolerant tropical grass Hymenachne amplexicaulis, the capacity to form adventitious root is considered one of its major adaptation attributes to flooding (Kibbler & Bahnisch, 1999). The same condition has also been proposed for the herbaceous flood-tolerant legume Lotus glaber (Vignolio et al, 1999) and for soybean (Bacanamwo & Purcell, 1999).…”

Amino acid and ureide transport in the xylem of symbiotic soybean plants during short-term flooding of the root system in the presence of different sources of nitrogen

“…Tolerance to flooding can arise in the long-term with the formation of aerenchyma, an important morphological adaptation resulting in increased availability of oxygen to submerged roots (Drew et al, 2000). However, in soybean at least, nitrate must exert its beneficial effect on flooding tolerance by other mechanisms since it was found to diminish the amount of aerenchyma formed (Bacanamwo and Purcell, 1999a). On the other hand, the effect of NH 4 + (the predominant form of N in flooded soils) on the metabolism and development of legumes under hypoxia has received little attention, although it is known that the exclusive feeding of NH 4 + , even under aerobic conditions, can be harmful to many plant species (Howitt and Udvardi, 2000;Wirén et al, 2000;Brito et al, 2001).…”

Effects of Short-Term Waterlogging on Soybean Nodule Nitrogen Fixation at Different Soil Reductions and Temperatures

“…Long-term waterlogging has been shown to promote acclimatization to the waterlogging conditions in soybean plants and result in plant adaptation (development of lateral roots and adventitious roots, thickening of stems, and formation of aerenchyma in roots and nodules) to relieve the damage (Bacanamwo and Purcell, 1999b;Shimamura et al, 2002). However, in the present experiment, the development of lateral roots and thickening of stems were slight in the W and WR treatments and obvious plant adaptation was not observed because the waterlogging, as the waterlogging treatment period was less than one week.…”

“…Under long-term waterlogging (i.e., for several weeks), soybean adapts to waterlogging stress, by forming adventitious roots (Bacanamwo and Purcell, 1999b). The aerenchyma formed in stem, roots and nodules improves gas exchange between the shoots and root system (Bacanamwo and Purcell, 1999b;Shimamura et al, 2003;Shimamura et al, 2010); the nodule nitrogen fixation is restored by the formed aerenchyma to some extent (Bacanamwo and Purcell, 1999b;Shimamura et al, 2002;Thomas et al, 2005).…”

“…The aerenchyma formed in stem, roots and nodules improves gas exchange between the shoots and root system (Bacanamwo and Purcell, 1999b;Shimamura et al, 2003;Shimamura et al, 2010); the nodule nitrogen fixation is restored by the formed aerenchyma to some extent (Bacanamwo and Purcell, 1999b;Shimamura et al, 2002;Thomas et al, 2005). However, short-term waterlogging for several days (i.e., less than a week) in farm fi elds, did not lead to the development of adventitious roots or the formation of aerenchyma.…”