Changes in Leaf Area and Nutrient Content of Celtis spp. Across a Precipitation Gradient in Texas
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Nitrogen is a key nutrient for cell and protein function in both plants and animals, and the ratio of carbon to nitrogen in leaves is a good indicator of nutrient quality within an ecosystem. Studies have shown that an increase in precipitation increases leaf size and the C/N ratio, but can decrease leaf nitrogen concentration, thereby increasing the quantity of forage while potentially decreasing quality. I examined whether this prediction held across the longitudinal precipitation gradient of Texas. I also tested whether soil mineral nutrients showed a unimodal relationship across the same gradient, as asserted by Albrecht’s curve. I sampled leaves from three species of Celtis (Family: Cannabaceae) and took soil samples under their canopies along US Interstate 10 from El Paso County to Orange County, spanning a mean annual precipitation range of 24 – 156 cm. I measured leaf area (LA), specific leaf area (SLA) and C/N ratio using a Flash EA 1112 C/N Analyzer. I determined the relative concentrations of soil mineral nutrients using Mehlich-3 analysis. Only two species were common enough to be included in the analysis. Of the three species, Celtis reticulata had the widest distribution and showed a significant change in LA, SLA, and the C/N ratio with changes in precipitation. As predicted, leaf size and C/N ratio increased with precipitation. No significant statistical trends could be attributed to the relative concentrations of the nutrients P, Na, K, Mg, Ca and Mn and heavier elements Fe, Cu, Zn, and Al in soil. My results showed that, in general, leaf characteristics are highly variable but that a large sample size can exhibit significant trends with precipitation, specifically larger but less nutritious foliage with precipitation. The decrease in nutritional quality may be due to the dilution of leaf nitrogen as leaf size increases.