Effect functional traits of litter decomposition rates and plant available inorganic N, of nine bunchgrasses native to the Blue Ash-Oak Savanna of the Inner Bluegrass Region of Kentucky

Background/Question/Methods

As part of a restoration ecology study, a monoculture experiment was conducted from 2009 to 2011 to study the functional traits of nine bunchgrasses native to the Blue Ash-Oak Savanna of the Inner Bluegrass Region of Kentucky.  One goal of this monoculture experiment was to quantify the effect traits of nutrient cycling, and litter decomposition of these bunchgrasses.  My hypothesis is that there will be species differences in effect traits that will affect the community assembly of these nine grasses.  Nine monocultures, plus a species mixture treatment replicated 10 times created 100-2 m² plots in a completely randomized design at Griffith Woods WMA in Harrison County, KY.  The nine grasses in this study include, six C₃ species and three C₄ species.  The C₃ species include four Elymus species that are well documented in historical records, Dicanthelium clandestinum, and Chasmanthium latifolium.  The C₄ species are Tridens flavus, Panicum anceps, and Andropogon virginicus. 

Litter decomposition rates for each species were measured using 5 grams of dried litter in 10 x 10 cm² fiberglass-nylon mesh bag.  Four replicates (one of each species) were picked up ~two months for a total of 6 pick-up times.  At each pick-up, dry biomass was recorded, and total %C and %N were analyzed.  To measure plant available NO₃-N and NH₄-N, nylon mesh resin bags were filled with 15 mls of cation and anion exchange resins.  One bag per plot placed five centimeters below the soil surface was collected and replaced monthly during the growing season (April to October) of 2010.  Samples were analyzed using the KCl extraction technique. 

Results/Conclusions

No significant differences in decomposition rates (k) were found between C₃ and C₄ species.  There were significant differences in C:N ratios.  The C₄ species had higher C:N ratios than the C₃ species and the four Elymus species had the lowest C:N ratios.  C:N declined the fastest in the four Elymus species as well.  This implies that the four Elymus species had a faster turnover rate than the other species.  C₄ species has significantly more total plant available inorganic N (F_1,87=7.41, p=0.0078), NO₃-N (F_1,88=4.70 p=0.033), and NH₄-N (F_1,87=4.22 p=0.043) than the C₃ species.  This implies that the C₃ species were better at capturing inorganic nitrogen which would give them a selective advantage.  These results suggest that the C₃ species (in particular the Elymus) may be better adapted to this savanna landscape.