Responses of stomatal density and carbon isotope composition of sugar maple and yellow birch foliage to N, P and CaSiO₃ fertilization.

This article focuses on the effects of nitrogen (N), phosphorus (P), and calcium silicate (CaSiO₃) addition on stomatal density, stomatal length, and carbon isotope composition (δ¹³C) in sugar maple (Acer saccharum Marsh.) and yellow birch (Betula alleghaniensis Britton) within the Multiple Element Limitation in Northern Hardwood Ecosystems (MELNHE) experiment in New Hampshire, USA. The study found a modest increase (8%) in stomatal density with phosphorus addition and increased δ¹³C with nitrogen and calcium silicate addition in sugar maple, while no consistent nutrient effects were observed in yellow birch. Variance partitioning revealed that most variability in stomatal density occurred within leaves and among trees, suggesting that future sampling protocols should increase sampling intensity at these levels to better detect treatment effects. The findings imply that phosphorus availability may influence stomatal traits in sugar maple, potentially affecting photosynthesis and transpiration, whereas nitrogen and calcium silicate additions may enhance intrinsic water-use efficiency as indicated by δ¹³C changes.