Canada bluejoint foliar δ¹⁵N and δ¹³C indicate changed soil N availability by litter removal and N fertilization in a 13-year-old boreal plantation

Abstract

Canada bluejoint grass [Calamagrostis canadensis (Michx.) P. Beauv., hereafter referred to as bluejoint] outcompetes overstory tree species such as white spruce [Picea glauca (Moench) Voss] by creating a thick litter layer and competing for the available nitrogen (N). This study was conducted to investigate the effects of bluejoint litter layer (with or without litter removal) and N fertilization on soil water and N availabilities using principal component analysis (PCA) and foliar δ 15 N and δ 13C of bluejoint in a plantation in northcentral Alberta, Canada. PCA using soil properties and understory growth data demonstrated that N fertilization was more effective in changing the soil environment and resource availabilities for bluejoint growth than litter layer removal. The increase in soil N availability by N fertilization was linked with increased bluejoint foliar δ 15 N (by around 3‰) in fertilized plots, as a result of greater N isotopic fractionation in the fertilized plots. The more negative δ 13 C (by around 1‰) of bluejoint in litter layerremoved plots suggested that litter layer removal increased soil water availability, indicating that the litter layer reduced soil water availability on the site. Therefore, results from this and previous studies showed that the litter layer decreased both soil water and N availabilities. Although the exact mechanisms of the benefit of the litter layer for bluejoint remains unknown, bluejoint likely adversely impacted tree growth by competing for N due to its strong N acquisition ability under soil resource-limiting conditions.

Nitrogen Subsidies from Hillslope Alder Stands to Streamside Wetlands and Headwater Streams, Kenai Peninsula, Alaska

“…C. canadensis, which has been observed rooting at depths of 50 cm (Chapin et al, 1996), may be assimilating nitrogen from deeper, more highly enriched locations in the soil than those sampled in our study (0-20 cm) or by Michelsen et al (1998) (0-5 cm). The d 15 N values we observed in C. canadensis foliage (5.52 AE 0.56&) are higher than those cited in the JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION literature [e.g., approximately À1.0& (Michelsen et al, 1996), 3.0& (Michelsen et al, 1998), 0.77 AE 0.38& (Miller and Bowman, 2002), À0.7 to 2.3& (Matsushima et al, 2014)], although they approach the high end of the range for C. canadensis foliage reported by Schulze et al (1994) in northern Alaska (approximately À3.0 to +5.0&). Schulze et al (1994) additionally observed an interesting, though nonsignificant, correlation between d 15 N in C. canadensis foliage and concentrations of soil ammonium or of soil nitrate.…”

“…Similarly, Matsushima et al . () noted the δ 15 N of C. canadensis foliage increased 3‰ two years after fertilization despite the relatively low δ 15 N of the applied urea (0.87 ± 0.03‰). They interpret this paradoxical enrichment of foliar nitrogen levels in the presence of 15 N‐depleted fertilizer as evidence of increased isotopic fractionation when the soil is amended with nitrogen.…”

“…() (0‐5 cm). The δ 15 N values we observed in C. canadensis foliage (5.52 ± 0.56‰) are higher than those cited in the literature [ e.g ., approximately −1.0‰ (Michelsen et al ., ), 3.0‰ (Michelsen et al ., ), 0.77 ± 0.38‰ (Miller and Bowman, ), −0.7 to 2.3‰ (Matsushima et al ., )], although they approach the high end of the range for C. canadensis foliage reported by Schulze et al . () in northern Alaska (approximately −3.0 to +5.0‰).…”

“…or Alnus incana. Interspecific differences in foliar d 15 N values have been attributed to differential access to soil nitrogen pools through differences in rooting depth, nitrogen uptake kinetics, nitrogen-fixation ability, and/or mycorrhizal status (Nadelhoffer et al, 1996;H€ ogberg, 1997;Miller and Bowman, 2002;Matsushima et al, 2014). C. canadensis, which has been observed rooting at depths of 50 cm (Chapin et al, 1996), may be assimilating nitrogen from deeper, more highly enriched locations in the soil than those sampled in our study (0-20 cm) or by Michelsen et al (1998) (0-5 cm).…”

“…At the detailed alder-near and no-alder sites, an isotopic analysis of foliage and soil samples was conducted based upon the 15 N "natural abundance" approach (Black and Waring, 1977;Binkley et al, 1985). Naturally occurring variations in abundance of the stable nitrogen isotope, 15 N, have been utilized for decades to study the nitrogen cycle in managed and natural ecosystems (Peterson and Fry, 1987;H€ ogberg, 1997;Matsushima et al, 2014). In particular, the distinctly low d 15 N value characteristic of nitrogen-fixing species, such as legumes and alder, has been used as a tracer to detect transfer of nitrogen originating from nitrogen-fixing species to neighboring species and soils (Peoples et al, 2015).…”