Soil Co2 Efflux, Water and Nutrient Use Efficiencies, and Litter Decomposition Across Diverse Cover Types in Southern Applachian Hardwood Forests
Bilal, Ruba Candiga
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Appalachian mixed hardwood stands along south facing slopes of the Ridge and Valley physiographic province were used to determine fine scale soil respiration (Rs ) and nutrient dynamics among four distinct cover types, white oak (WO, Quercus alba L.), scarlet oak (SO, Quercus coccinea Muech.), chestnut oak (CO, Quercus montana Wild.) and a pine-oak co-dominant cover (PO, Pinus spp. and Quercus spp. (primarily Pinus pungens Lamb. and Q. montana)). Null hypotheses were that: (1) Rs and its relationship to environmental drivers would not differ among the cover types, (2) water and nutrient use efficiencies (WUE and NUE) would not differ among the cover types, and (3) litter decomposition would not differ among the diverse cover types. In 0.02 ha plots, replicated four times, Rs and associated variables (e.g., soil temperature and moisture) were measured. Measurements occurred in three sub-sample locations per plot, from July 2014 - December 2015. In each plot, foliage from two trees of the dominant species were collected to determine WUE using �[BULLET]13C isotope discrimination. Nutrient (N, P and K) content of this fresh foliage was compared with that of litterfall to determine NUE. Litterbags, collected over a one and half year period were used to determine decomposition rate constants for each dominant species. Soil temperature and moisture explained 71% of the variability in Rs. Although only slight, there were statistically significant differences in the Rs models due to cover type. At the same soil temperature, the PO cover type had the highest Rs while the SO, WO cover types had the lowest Rs. WUE, and NUE varied among cover types. SO had significantly greater WUE than the other species, including Table mountain pine, which had the highest NUE. Higher elevation cover types (i.e., PO and CO) ad greater decomposition rate constants. Among the factors driving decomposition, soil C: N ratio had the strongest correlation to decomposition. Correlations between decomposition and productivity variables of total above ground biomass, total stand biomass, and aboveground net primary production also exist. In conclusion, carbon and nutrient cycling varies across the level of cover type within the southern Appalachian hardwood forests. Future efforts to focus on carbon and nutrient dynamics in the context of land use or global change should consider these finer-scale differences.
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