Flooding constraints on tree (Taxodium distichum) and herb growth responses to elevated CO2

Abstract

Elevated CO 2 generally stimulates C 3 -type photosynthesis, but it is unclear how an increase in CO 2 assimilation will interact with other factors that influence plant growth. In wetlands, the response of plants to elevated CO 2 will interact with soil saturation, particularly in forested wetlands where soil saturation is a strong regulator of plant productivity. We performed a four-month experiment to determine whether elevated CO 2 and flooding interact to influence the growth of a flood-tolerant tree (Taxodium distichum) and a flood-tolerant herbaceous emergent macrophyte (Orontium aquaticum). Seedlings were grown in glasshouses at two CO 2 levels (350 and 700 L L Ϫ1 ) crossed with two water depths (5 cm above and Ն5 cm below the soil surface). We hypothesized that elevated CO 2 would increase photosynthesis regardless of water depth and species; however, we also expected flooding to prevent elevated CO 2 from increasing the growth of the tree species due to O 2 limitation or other physiological stresses associated with reduced soil environments. We found that elevated CO 2 increased whole-plant photosynthesis in both species regardless of the flooding treatment. For T. distichum, this higher photosynthetic rate resulted in greater biomass only in the non-flooded treatment. This result suggests that some factor related to flooding constrained the biomass response of the flooded woody plants to elevated CO 2 . In contrast, elevated CO 2 increased O. aquaticum biomass regardless of the flooding regime, perhaps because it occurs in wetter landscape positions than T. distichum and is less sensitive to flooding. We conclude that flooding may limit plant growth responses to elevated CO 2 , particularly in woody plant species.

Can elevated CO2 modify regeneration from seed banks of floating freshwater marshes subjected to rising sea-level?

“…Ethylene synthesis is increased in the seeds of Helianthus annuus in higher CO 2 levels (Corbineau et al, 1990). Our findings showed some effect on seed germination, but generally support the broader pattern that CO 2 primarily influences seedling growth, rather than germination, similar to findings of other freshwater wetlands studies (e.g., Megonigal et al, 2005).…”

“…In other studies, C 4 species did not increase growth in enhanced CO 2 in any water regime or salinity level (Rozema et al, 1991;Lenssen et al, 1993). In elevated CO 2 , the seedlings of Taxodium distichum (C 3 ), a freshwater swamp species, did not have a higher biomass in flooded conditions, but seedlings of Orontium aquaticum (C 3 ) had higher biomass when exposed to elevated CO 2 in both flooded and unflooded conditions (Megonigal et al, 2005).…”

An oxygen‐mediated positive feedback between elevated carbon dioxide and soil organic matter decomposition in a simulated anaerobic wetland

“…Data were analyzed for statistical differences between the main effects (planting and CO 2 treatment) by two-way ANOVA using the SAS generalized linear model (GLM) procedure (e.g. Megonigal et al, 2005). Data with heterogeneous variance were log transformed and outliers were removed using Grubbs' outlier test.…”

Comparative studies on physiological and biochemical adaptation of Taxodium distichum and Taxodium ascendens seedlings to different soil water regimes

“…All of the tests were conducted between 9:00 am-11:00 am at a temperature of 25°C, with 400 µmol L −1 CO 2 and 1,000 µmol photons m −2 s −1 Megonigal 2002, 2003). Leaf area was determined according to Megonigal et al (2005), by tracing the portion of the leaf enclosed by the Li-Cor LI-6400 cuvette onto paper, then passing it through a Li-Cor 3100 leaf area meter. The paper area was divided by two to correct for spaces between the individual needles on the leaf.…”