Urban grasslands span climates and topography in soils with variable water infiltration and drainage rates that result in occasional waterlogging stress, while data on grass species tolerance to waterlogging stress is scant. Whole plant responses to waterlogging stress among cool-season grass species were quantified in a controlled environment. The following grasses were grown in well-drained vs. waterlogged soil for 55 d: strong creeping red fescue (Festuca rubra ssp. rubra), slender creeping red fescue (F. rubra ssp. littoralis), Chewings fescue (F. rubra ssp. commutata), hard fescue (F. brevipila), tall fescue (F. arundinacea syn. Schedonorus arundinaceus), Kentucky bluegrasses (Poa pratensis), annual bluegrass (P. annua), rough bluegrass (P. trivialis), creeping bentgrass (Agrostis stolonifera), perennial ryegrass (Lolium perenne), and alkaligrass (Puccinellia distans). Five cultivars of each fine fescue (Festuca spp.) taxon were included for comparison. When grown in waterlogged soil compared to well-drained conditions, relative differences generally ranged from -3% to -26% (shoots) and -13% to -33% (roots) for creeping bentgrass, tall fescue, and Kentucky bluegrass indicating higher waterlogging stress tolerance. The relative differences ranged from -18% to -43% in shoots and -3% to -34% in roots for annual bluegrass and perennial ryegrass indicating fair performance under waterlogging stress. Fine fescues, rough bluegrass, and alkaligrass exhibited the poorest performance during waterlogging stress with plant responses ranging from -12% to -64% (shoots) and -17% to -73% (roots). Negative whole plant responses among cultivars of four fine fescue taxa were similar. The selection of grasses tolerant to waterlogging stress will be important in developing resilient landscapes.

Flooding stress is an increasingly serious problem in wetlands, often affecting large areas of crops and timber production areas. The current study aimed to explore the species differences in responses to flooding stress between Q. nuttallii and Q. palustris in an outdoor environment. All the tested plants survived after a 60-day flooding treatment that left 5 cm of water above the soil surface. This suggests that the two species are flood-tolerant, so they can be applied in the construction of riparian protection forests and wetland restoration. Compared with control conditions, flooding treatment significantly decreased seedling height and diameter and the P-n, G(s), T-r, F-v/F-m, ABS/CSm, TR0/CSm, ET0/CSm, RE0/CSm, IAA, and GA(3) content and significantly increased the content of MDA, H2O2, soluble sugars, SOD, POD, ADH, ABA, and JA. Under control conditions, Q. nuttallii showed significantly greater growth and photosynthetic capability than Q. palustris. In contrast, Q. palustris exhibited less inhibition of growth and photosynthesis, oxidative stress levels, and antioxidant enzyme activities than Q. nuttallii under flooding conditions. The findings indicate that Q. palustris has better defense mechanisms against the damage caused by flooding stress than Q. nuttallii. Q. nuttallii was more sensitive and responsive to flooding than Q. palustris.

It is well-known that relative growth rate (RGR) is closely related to C:N:P stoichiometry at the whole-plant level, yet it remains a misgiving to determine whether the growth-rate hypothesis is consistent between plant organs. Here, we examined RGR, C, N, P concentrations and their ratios of N:C, P:C, and N:P for four marsh herbaceous species (two gramineous species, Deyeuxia angustifolia and Glyceria spiculosa; two sedge species, Carex pseudocuraica and Carex lasiocarpa) grown in an increasing water level gradient (-5, 0, +5, and +15 cm relative to the soil surface) in the Sanjiang Plain of Northeast China. The applicability of the growth-rate hypothesis to leaf, stem, root, and total biomass was subsequently tested. With the increase of flooding stress, RGR and root mass ratio decreased to a certain degree for all species, whereas the above-ground biomass allocation was increased. The variation of N was much greater than that of P; hence the change in N:P ratios was determined mainly by N concentration. RGR was positively correlated with N concentration, N:C, and N:P for stem and total biomass when the data were pooled for all species but was negatively correlated with those for leaf and root organs. Furthermore, the theoretical predictions regarding the relationship between RGR and nutrient ratios were not always the case for each of the marsh herbs. Therefore, our results indicated that the organ-specific and species-specific for vascular plants should be carefully considered when using the theoretical association of growth rate with C:N:P stoichiometry. (c) 2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).