Foliar Calcium Oxalate Crystals and Radial Growth in Balsam Fir Tricia McCarthy pmc27@unh.edu

Current Year 5th Year 4Y 4th Year 3Y 3 Y 3rd Year 2Y 2Y CY 2nd Year CY

Study Site: USFS Hubbard Brook Experimental Forest, Thornton, NH

Site Description 3160 hectares (137,649,600 acres) reserved by the USFS in the White Mountain National Forest, established in 1955 northern hardwood forests on lower slopes and spruce-fir on upper reaches coarse, acidic, glacially-derived soils study plots are on south-facing slopes with an elevation of approximately 2600 feet.

The Hubbard Brook Experimental Forest

Hubbard Brook Watersheds 1-6

In October 1999 the Ca content of the soil in Watershed 1 was increased through the application of Wollastonite (CaSiO3).

Why is calcium important? Prevailing weather conditions bring acidic clouds and air masses from the west. NH’s bedrock and soils provide poor buffering for acidic deposition. Soil calcium depletion is a problem in the northeast. Calcium is an important nutrient for plant growth. Membrane calcium is needed for nutrient absorption and transport in foliar and root tissue. Calcium pectate in the middle lamella acts as a glue to bind cells together.

Hypothesis: Watershed 1, the calcium-amended watershed, will have more Calcium-Oxalate crystals and enhanced tree growth than Watershed 6, the reference watershed.

Research Methods: Bough and core samples were collected from 15 trees in Watershed 1 and 18 trees in Watershed 6. A sub-sample of needles were cross-sectioned and analyzed using a Scanning Electron Microscope (SEM) and Energy Dispersive X-Ray (EDX) analysis, to look for trends in the concentration of CaOx crystals. Cores were examined using a dissecting microscope and a mm ruler to measure annual growth. A radial growth index was established for each tree in order to reduce the natural variance in growth rates of individual trees.

Collecting cores at Hubbard Brook

Procedure used to establish a radial growth index: The mean annual increment width was calculated for the entire core. This value was then subtracted from each increment measurement. An index value greater than 0 indicates above average growth. Negative numbers represent below average growth.

Calcium Oxalate Crystals (SEM)

Why do plants form calcium oxalate crystals? Some hypotheses include: Calcium regulation in environments where soluble Ca is abundant Protection as a defense against herbivores Detoxification (e.g. oxalic acid) Calcium Sequestration for future fertilization? Ion balance? Tissue support/plant rigidity? Light gathering and reflection?

SEM EDX Spectrum Comparing Tree #461 CY needles (green) to 5Y needles (red). In general, we see increased Ca concentrations in older needles, regardless of the watershed. The inverse relationship between potassium and calcium is an interesting phenomenon that has also been seen in spruce needles using a different analysis.

Comparisons between the two study plots: Growth Index: more radial growth is shown in the Ca amended watershed in 2007 (CY) than in the reference watershed; however, the reference watershed shows more growth in 2003 (5Y) than the Ca amended watershed. Percent Calcium: a higher percentage of calcium oxalate crystals were measured in needles from the Ca amended watershed in both CY and 5Y needles. There doesn’t appear to be a correlation between % Ca and growth in these samples. Other factors may have affected the growth of the reference watershed trees in 2003 (less competition due to ice storm damage in 1998?).

Conclusions: Current year and 5 year needles from the calcium-amended watershed have a higher concentration of CaOx crystals than needles from the reference watershed. More radial (wood) growth was seen in the calcium-amended watershed in 2007. The reference watershed shows more radial growth in 2003. Radial growth in watershed 1 increased consistently after the Ca amendment; growth in Watershed 6 was variable, peaking in 2004 and declining over the past three years. More research is needed to determine if increased concentrations of CaOx crystals are associated with increased radial growth.

References: Hawley, G.J., Schaberg, P.G., Eager, C., Borer, C.H., 2006. Calcium addition at the Hubbard Brook Experimental Forest reduced winter injury to red spruce in a high-injury year. Can. J. For. Res. 36:1-6. Hudgins, J.W., Krekling, T., Franceschi, V.R. (2003). Distribution of calcium oxalate crystals in the secondary phloem of conifers: a constitutive defense mechanism? New Phytologist 159:677-690. Schaberg, P.G., DeHayes D.H., Hawley G.J., 2001. Anthropogenic Calcium Depletion: A Unique Threat to Forest Ecosystem Health? Ecosystem Health 7:214–228. Smith, K.T. and Shortle, W.C. (2003) Radial Growth of hardwood following the 1998 ice storm in New Hampshire and Maine. Can. J. For. Res. 33:3325-329. http://www.hubbardbrook.org