Is leaf-level photosynthesis related to plant success in a highly productive grassland?

Abstract

We addressed the question: "Are short-term, leaf-level measurements of photosynthesis correlated with long-term patterns of plant success?" in a productive grassland where interspecific competitive interactions are important. To answer this question, seasonal patterns of leaf-level photosynthesis were measured in 27 tallgrass prairie species growing in sites that differed in species composition and productivity due to differences in fire history. Our specific goals were to assess the relationship between gas exchange under field conditions and success (defined as aerial plant cover) for a wide range of species, as well as for these species grouped as dominant and sub-dominant grasses, forbs, and woody plants. Because fire increases productivity and dominance by grasses in this system, we hypothesized that any relationship between photosynthesis and success would be strongest in annually burned sites. We also predicted that regardless of fire history, the dominant species (primarily C grasses) would have higher photosynthetic rates than the less successful species (primarily C grasses, forbs and woody plants). Because forbs and woody species are less abundant in annually burned sites, we expected that these species would have lower photosynthetic rates in annually burned than in infrequently burned sites. As expected, the dominant C␣grasses had the highest cover on all sites, relative to␣other growth forms, and they had the highest maximum and seasonally averaged photosynthetic rates (17.6 ± 0.42 μmol m s). Woody species had the lowest average cover as well as the lowest average photosynthetic rates, with subdominant grasses and forbs intermediate in both cover and photosynthesis. Also as predicted, the highest overall photosynthetic rates were found on the most productive annually burned site. Perhaps most importantly, a positive relationship was found between leaf-level photosynthesis and cover for a core group of species when data were combined across all sites. These data support the hypothesis that higher instantaneous rates of leaf-level photosynthesis are indicative of long-term plant success in this grassland. However, in contrast to our predictions, the subdominant grasses, forbs and woody species on the annually burned site had higher photosynthetic rates than in the less frequently burned sites, even though their average cover was lower on annually burned sites, and hence they were less successful. The direct negative effect of fire on plant cover and species-specific differences in the availability of resources may explain why photosynthesis was high but cover was low in some growth forms in annually burned sites.

Establishing North American prairie vegetation in urban parks in northern England: Effect of management and soil type on long-term community development

“…C4 prairie grasses are the latest species to come into leaf in prairie communities and lose little new foliage when burnt in spring. This, in combination with their higher leaf level photosynthesis (McAllister et al, 1998) results in them out-competing C3 prairie forbs under a frequent burning regime (Seastedt et al, 1991). Whilst this is the general pattern, in studies conducted over a 20-year period, Tester (1996) found that cover values of prairie forbs increased with fire frequency.…”

Relative effects of precipitation variability and warming on tallgrass prairie ecosystem function

“…We expected interannual variability to have a smaller effect on A CO 2 relative to that of intra-annual rainfall variability, because A CO 2 in these grasses decreases strongly with soil moisture depletion, and recovery is often slow when soil moisture is restored, especially after extended drought (Knapp, 1985;Heckathorn et al, 1997). Leaf level photosynthesis has been associated with long-term plant success in this grassland (McAllister et al, 1998), and the ability to track soil moisture variability is crucial to the success of the grasses (Swemmer et al, 2006;Nippert et al, 2006a). The finding that A CO 2 was strongly correlated with 15 (Table 1) suggests that on average, A CO 2 was strongly coupled to interannual climate variation and associated interannual differences in soil water supply.…”

“…For example, grass ANPP and A CO 2 was more highly correlated with 15 than was forb ANPP and A CO 2 (Table 1). C 4 grasses such as A. gerardii and S. nutans typically have higher photosynthetic rates and experience greater variation in plant water status than forbs (Knapp, 1984;Turner et al, 1995;McAllister et al, 1998;Nippert et al, 2006a). Stable isotope studies of soil water use by C 4 grasses at the Konza site shows that they rely on surface soil water regardless of landscape location, soil water availability, or time of year, while forbs increase their dependence on deeper soil moisture as surface soils dry (Nippert and Knapp, 2007a, b).…”

Photosynthetic characteristics involved in adaptability to Karst soil and alien invasion of paper mulberry (Broussonetia papyrifera (L.) Vent.) in comparison with mulberry (Morus alba L.)

“…Photosynthetic activities can be represented as the growth potentials of the plant (Mooney 1972, Walters et al 1993, McAllister et al 1998, Knee and Thomas 2002. Chlorophyll (Chl) a fluorescence of photosystem 2 plays an important role in the response of leaf photosynthesis to environmental stresses (Baker 1991).…”