Aerenchyma formation and radial O2 loss along adventitious roots of wheat with only the apical root portion exposed to O2 deficiency

This study investigated aerenchyma formation and function in adventitious roots of wheat (Triticum aestivum L.) when only a part of the root system was exposed to O₂ deficiency. Two experimental systems were used: (1) plants in soil waterlogged at 200 mm below the surface; or (2) a nutrient solution system with only the apical region of a single root exposed to deoxygenated stagnant agar solution with the remainder of the root system in aerated nutrient solution. Porosity increased two‐ to three‐fold along the entire length of the adventitious roots that grew into the water‐saturated zone 200 mm below the soil surface, and also increased in roots that grew in the aerobic soil above the water‐saturated zone. Likewise, adventitious roots with only the tips growing into deoxygenated stagnant agar solution developed aerenchyma along the entire main axis. Measurements of radial O₂ loss (ROL), taken using root‐sleeving O₂ electrodes, showed this aerenchyma was functional in conducting O_2. The ROL measured near tips of intact roots in deoxygenated stagnant agar solution, while the basal part of the root remained in aerated solution, was sustained when the atmosphere around the shoot was replaced by N₂. This illustrates the importance of O₂ diffusion into the basal regions of roots within an aerobic zone, and the subsequent longitudinal movement of O₂ within the aerenchyma, to supply O₂ to the tip growing in an O₂ deficient zone.     

Growth and Solute Composition in Two Wheat Species Experiencing Combined Influence of Stress Conditions1

The effects of environmental stress combinations on the soluble metabolites were investigated in several cultivars of Triticum aestivum and T. durum. The seedlings grown at optimum (24/16°C), low (5/–5°C) (LT), and high (40/30°C) (HT) day/night temperature conditions were exposed to waterlogging, drought, and salinity (0.7% NaCl, w/w) stresses for six days. Root and shoot fresh weight significantly decreased under waterlogging, drought and salt stresses. Fresh weight was most reduced at severe drought + HT combinations. The lowest relative water content was found under drought stress + HT combination. Soluble carbohydrate (SC) contents increased under LT conditions, but decreased under HT conditions. Under HT + salt combinations, T. aestivum genotypes showed higher SC content thanT. durum genotypes. Proline content significantly increased in the case of water deficit and salt stress. Under drought and salt stresses, T. aestivum genotypes had lower proline contents than T. durum genotypes. These results indicate that biochemical responses to drought, waterlogging, and salt stresses were significantly changed in wheat seedlings under LT and HT conditions.     

Effects of waterlogging on growth and some physiological parameters of four Brassica species

Waterlogging tolerance of four Brassica species, Brassica campestris L., B. carinata A. Br., B. juncea (L.) Czern and Coss., and B. napus L. was assessed after 4 weeks growth in greenhouse at two waterlogging treatments, unflooded control soil, and fully waterlogged soil.Shoot fresh and dry biomass, in both mean and relative terms, was highest in B. juncea and lowest in B. napus at waterlogging treatment. B. carinata was as good as B. juncea in mean shoot fresh and dry matter but it had almost same relative shoot fresh matter as that in B. campestris, but was second highest in relative shoot dry weight.Waterlogging treatment caused a marked reduction in chlorophyll content in all four species but the species difference was not evident. However, B. juncea and B. napus had lower relative total chlorophyll than the other species.A marked increase in soluble protein content of B. juncea and a significant increase in total amino acids in B. carinata was observed under waterlogged conditions as compared to the other species.At the waterlogging regime, an increase in iron content in both shoots and roots was observed in all four species. B. juncea accumulated lower amount of iron in both shoots and roots as compared to the other species, whereas B. carinata had also lower iron in the roots. The species did not differ for shoot manganese content but B. carinata had significantly higher manganese in the roots as compared to the other species.     

Effect of soil waterlogging on below‐ground biomass allometric relations in Norway spruce

Abstract

An increasing importance is assigned to the estimation and verification of carbon stocks in forests. Forestry practice has several long‐established and reliable methods for the assessment of above‐ground biomass; however, we still miss accurate predictors of below‐ground biomass. A major windthrow event exposing the coarse root systems of Norway spruce trees allowed us to assess the effects of contrasting soil stone and water content on below‐ground allocation. Increasing stone content decreases the root/shoot ratio, while soil waterlogging leads to an increase in this ratio. We constructed allometric relationships for below‐ground biomass prediction and were able to show that only soil waterlogging significantly impacts model parameters. We showed that diameter at breast height is a reliable predictor of below‐ground biomass and, once site‐specific parameters have been developed, it is possible to accurately estimate below‐ground biomass in Norway spruce.     

Morphological and phenological strategies for flooding tolerance in Cerrado and Pantanal trees: implications for restoration under new legislation

In 2012, the Native Vegetation Protection Law 12,651 decreased the extent of Areas of Permanent Preservation in Brazil. While previously the distance from water was measured during the rainy season, the new version only considered the extent of the regular watercourse. This change affects conservation and restoration sites, and restoration programs need to be modified based on the new legislation. For instance, more flood-tolerant species need to be planted, given the higher probability that restoration efforts will be lost during flooding. To identify species suitable for the restoration of such areas, we tested if plants that develop morphological structures to tolerate waterlogging stress are more resistant to hypoxia caused by flooding and can recover better afterwards. We experimentally evaluated survival and morphological or phenological strategies (root dry mass, height, basal diameter, adventitious roots, lenticels, and leaf renewal) of 13 tree species from the Cerrado and Pantanal biomes of Brazil. After 56 days of simulated inundation and 56 days of post-inundation recovery, we found that all study species were able to survive on waterlogged soil and to recover after the flood, and they can be used to restore periodically flooded riparian forests within the new legal zone. Our study is particularly relevant, as climate change is expected to increase flooding. As environmental laws change and new areas get restored including those in artificially flooded areas, such as on banks of hydroelectric dams, the experimental approach introduced in this study should be replicated with other species from various phytogeographic domains worldwide.     

Effects of waterlogging on chickpeas I. Influence of timing of waterlogging

The effect of timing of waterlogging on chickpeas was examined in two pot trials. Plants were waterlogged for ten days from 21 days after sowing (DAS), at flowering or at mid-pod fill, plus combinations of these times. Waterlogging at any stage reduced seed yield; waterlogging at 21 DAS had the least effect, reducing yield relative to the non-waterlogged control by 35%. Ability of the plant to survive and regrow following waterlogging decreased with increasing physiological age: mortality rate averaged 0, 30 and 100% after waterlogging at 21 DAS, flowering and pod fill, respectively. Tolerance to waterlogging was not enhanced by previous exposure to waterlogging.In the second experiment, waterlogging was imposed at six different times shortly before or after flowering began. Ability to survive waterlogging declined sharply as flowering commenced: mortality rate increased from 13% when waterlogging was imposed six days before flowering to 65% one day after flowering, and 100% when waterlogging began 7.5 days after flowering. We suggest that survival and recovery after waterlogging may have been inhibited in flowering plants by an inadequate supply of nitrogen or carbohydrates.     

Microtopography‐induced transient waterlogging affects switchgrass (Alamo) growth in the lower coastal plain of North Carolina,USA

Very limited information is currently available on growth responses of switchgrass (lowland cultivars) to transient waterlogging in lowland or poorly drained areas. This study investigated impacts of microtopography‐induced transient waterlogging on switchgrass (Alamo cultivar) growth, represented by leaf‐level gas exchange and biomass yield, in an established experimental field located in the Atlantic coastal plain of North Carolina, USA. Intensive leaf‐level gas exchange measurements were conducted on switchgrass at paired spots with distinct elevations in three sub‐blocks. Aboveground biomass was randomly collected across the study field to explore the potential impacts of the transient waterlogging on biomass yield. The sum of excess water (SEW) was calculated based on measured instantaneous water table depth to generalize the relationship between biomass yield and intensity of transient waterlogging. Results showed significant (P ≤ 0.0001) treatment effects on leaf‐level gas exchange, characterized by evident reduction in both CO₂ assimilation rate and stomatal conductance when water table was at or near the soil surface at low positions. Negative impacts of transient waterlogging on leaf‐level gas exchange became more evident with the increasing of elevation differences between paired subplots. Stomatal closure was found to be the main mechanism responsible for the decline of net assimilation under transient waterlogging. Aboveground biomass yields of switchgrass showed relatively high spatial variability and were positively and linearly correlated with microtopography (represented by elevation in the analysis) (P < 0.03, R² > 0.77). Further analysis showed that biomass yields were negatively correlated with SEW (P < 0.001, R² > 0.6) with an exponential relationship. Results of this study strongly demonstrated transient waterlogging could negatively affect switchgrass growth by suppressing leaf‐level gas exchange rates and ultimately reducing biomass yield. Findings from this study have critical implications for evaluating the economic viability of growing switchgrass on marginal lands that are subject to transient waterlogging stresses.     

Nutrient deficiencies do not contribute to yield loss after waterlogging events in winter wheat (Triticum aestivum)

Frequent waterlogging increases the risk of possible harvest losses in winter wheat. The aim of this study was to analyse which developmental stage of wheat was impaired by waterlogging and whether yield losses can be explained by nutrient deficiences. A large‐scale container experiment was designed to evaluate growth, yield and nutrient status of two wheat cultivars after 14 days of waterlogging at two different developmental stages: DC 31 (first node visible) and DC 51 (beginning of ear emergence). Early waterlogging treatment impaired vegetative growth stages of winter wheat and nutrient uptake, leading to transient nutrient deficiencies, but yield was not significantly reduced. Late waterlogging at the beginning of ear emergence mainly affected generative growth stages and caused yield reductions ranging up to 61%. The main reason for yield loss was the significantly decreased thousand kernel weight in combination with a decreased number of grains per spike. Yield depressions in winter wheat depend on the timing of waterlogging. Early waterlogging transiently reduces vegetative growth through nutrient deficiencies, whereas late waterlogging results in an impaired grain development and associated therewith, yield losses.