cology of C3 and C4 Grasses (Poaceae) in

cology of C3 and C4 Grasses (Poaceae) in

cology of C3 and C4 Grasses (Poaceae) in the United States: a Phylogenetically Controlled Analysi
Patrick J. Alexander, Department of Biology, New Mexico State University, Las Cruces, NM, [email protected]


However, although it is common knowledge that C3 and C4 grasses segregate

Grasses (Poaceae) are the fifth-largest plant family
world-wide, and yet far more important than their
diversity indicates both in structuring ecosystems
and in human nutrition, through direct and indirect
consumption. As a result, grass ecology is of
fundamental importrance. A major factor affecting
grass distribution across climates is photosynthesis
type. The family includes members with both C 3
and C4 photosynthesis, with C4 photosynthesis
arising independently multiple times.

1 Choose sites across the US to represent a
wide array of climates within the constraints
of availability of climatological and
distributional data:

4 Calculate a diversity-weighted annual
mean value of each climatological
variable for each genus ( =( across
sites (# species at each site * climate
value for site)) / total # of occurrences
of the genus ) and a phenologically
corrected mean (since climatic
separation can occur at a single site
through different phenology; p.c. mean
is calculated as for annual mean except
that only climate data from estimated
growth period (each of the 2 months of
greatest collection minus one) are

along climatic gradients, with C4 grasses in hotter, drier habitats, this is based
on phylogenetically-uncorrected analyses. Phylogenetic constraints on
photosynthesis evolution reduce the number of independent data points, since
closely-related taxa will tend to be similar in all traits rather than only
photosynthetic pathway. Unless comparisons are limited to independent
derivations of C4 photosynthesis with their sister groups, confounding
similarities among clade members may be responsible for the observed
pattern. A preliminary analysis (results not shown) using six sites in Arizona
showed no significant relationship between photosynthesis type and either
maximum mean annual temperature or total annual precipitation, so a
nationwide analysis including a wider variety of habitats and representing
more independent derivations of C4 photosynthesis was conducted.

2 Compile a list of grass
species present at each site
from online herbarium
databases (1, 2, 3, 4, 5, 6, 7, 8,
9, 10); check names against
the online Manual of Grasses of
North America (11) and USDA
PLANTS Database (12) for
nomenclatural consistency;
score number of species in
each genus at each site; find
the 2 months of greatest
collection for each site.

3 Compile climatological data-annual mean maximum
temperatue, annual mean
temperature, and total precipitation
--for all sites from Regional Climate
Center data (13, 14, 15).

In addition to the CAIC analysis results shown at left, highly significant (p<.0001) relationships were found in all phylogenetically-uncorrected Students T-Test analyses. Results from CAIC analysis are shown below: These results suggest that C4 photosynthesis does indeed significantly affect the Annual Mean Values p-value r2 distribution of grasses along heat and moisture gradients. Failure to find a relationship Annual maximum mean temperature 0.0530 0.4906 in the preliminary Arizona analysis may be due to either insufficient climatic variation Annual mean temperature 0.0208 0.6174 Precipitation 0.0490 0.5025 among sample areas or to poor representation of the multiple origins of C 4 photosynthesis in Panicoideae. Phenologically-Corrected Values p-value r2 The effect of phenological correction is puzzling. In the Arizona analysis, Annual maximum mean temperature 0.0136 0.6650 Annual mean temperature 0.1079 0.3728 phenological correction increased the strength of all tested relationships (data not Precipitation 0.4463 0.0996 shown), but in the nationwide analysis it rendered associations with both annual mean temperature and precipitation nonsignifcant. Although phenological separation of C 3 and C4 plants is common in warm climates, the tendency for all plants to grow together during brief warm growing seasons in colder climates may tend to erode differences between these predominantly C 3 areas and the warmer sites of the southern US. This may explain the pattern with precipitation and annual mean temperature, although the contrary increase in significance of association of photosynthesis type with annual maximum mean temperature remains anomalous. Results & Discussion: Citations: 1. 2. 3. 6 Test for a relationship between C3/C4 photosynthesis and each of the three climatic variables using Comparative Analysis via Independent Contrasts (CAIC, 22) and by a Students T-Test in Microsoft Excel (23). Pooideae Bambusoideae Oryzoideae Aristidoideae Arundinoideae Danthonioideae Chloridoideae Centothecoideae Andropogoneae Steinchisma Axonopus, Paspalum, Panicum Obtusa Phanopyrum Panicum s Agrostoidea and Tenera Digitaria 5 Compile a phylogeny of the included genera from published Dichanthelium phylogenies (16, 17, 18, 19); at right is a simplified phylogeny, Panicum Verrucosa generated in NONA (20) with Winclada (21), showing major Echinochloa Oplismenus lineages and all independent derivations of C 4 photosynthesis. Branches leading to C4 taxa are in red. Genera not included in published phylogenies were entered as basal polytomies in the least-inclusive higher taxon (usually the tribe) available. { Panicum s Dichotomiflora, Panicum, Bulbosa, and Virgata; Urochloa, Setaria, Stenotaphrum, Cenchrus, and Pennisetum 4. 5. 1. 3. 4. Panicoideae SEINet. Collections Search. (Arizona State University, Tempe AZ, 2006., 2-5 June 2006). Consortium of California Herbaria. Search Pages. (University of California, Berkeley CA, 2006., 2-5 June 2006). CU Museum. Vascular Plants of Colorado Database Search. (University of Colorado, Boulder CO, 2006., 2-5 June 2006). Colorado State University Herbarium. Herbarium Search Page. (Colorado State University, Fort Collins CO, 2006., 2-5 June 2006). University of Michigan Herbarium. University of Michigan Species Database. (University of Michigan, Ann Arbor MI, 2006., 2-5 June 2006). J. F. Bell Museum of Natural History Herbarium. Vascular Plant Collection Database. (University of Minnesota, Minneapolis MN, 2006., 2-5 June 2006). Pullen Herbarium. Specimen Database Search. (University of Mississippi, Oxford MS, 2006., 2-5 June 2006). INRAM. Biodiversity Query Page. (Institute of Natural Resource Analysis and Management, 2002-2006., 2-5 June 2006). Oregon State University Herbarium. Oregon Vascular Plant Database. (Oregon State University, Corvallis OR, 2006., 2-5 June 2006). A.C. Moore Herbarium. South Carolina Plant Atlas. (University of South Carolina, Columbia SC, 2006., 2-5 June 2006). 11. Barkworth, M. E., editor. Grass Manual on the Web. (Utah State University, Logan UT, 2006., 2-5 June 2006). 5. USDA, NRCS. The PLANTS Database (National Plant Data Center, Baton Rouge LA, 2006., 2-5 June 2006). 6. Western Regional Climate Center. Western U.S. Climate Historical Summaries. (Desert Research Institute, Reno NV, 2006., 2-10 June 2006). 7. Southeast Regional Climate Center. Historical Climate Data for the Southeast. (South Carolina Department of Natural Resources, Columbia SC, 2006., 2-10 June 2006). Midwestern Regional Climate Center. Historical Climate Summaries. (Illinois State Water Survey, Champaign IL, 2000-2006., 2-10 June 2006). Aliscioni, S. S., Giussani, L. M., Zuloaga, F. O. & Kellogg, E. A. A molecular phylogeny of Panicum (Poaceae: Paniceae): tests of monophyly and phylogenetic placement within the Panicoideae. American Journal of Botany 90, 796-821 (2003). Catalan, P., Kellogg, E. A. & Olmstead, R. G. Phylogeny of Poaceae Subfamily Pooideae Based on Chloroplast ndhF Gene Sequences. Molecular Phylogenetics and Evolution 8, 150-166 (1997). Hilu, K. W., Alice, L. A. & Liang, H. Phylogeny of Poaceae Inferred from matK Sequences. Annals of the Missouri Botanical Garden 86, 835-651 (1999). Hilu, K. W. & Alice, L. A. A Phylogeny of Chloridoideae (Poaceae) Based on matK Sequences. Systematic Botany 26, 386-405 (2001). Goloboff, P. A. NONA (NO NAME) ver. 2 (Published by the author, Tucuman, Argentina, 2000) Nixon, K. C. WinClada ver. 1.0000 (Published by the author, Ithaca, NY, US, 1999-2002) Purvis, A. & Rambaut, A. Comparative analysis by independent contrasts (CAIC): an Apple Macintosh application for analysing comparative data. CABIOS 11, 247-251 (1995).

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