Interspecific divergence in foliar nutrient dynamics and stem growth in a temperate forest in response to chronic nitrogen inputs

Abstract

Abstract:We studied the effects of excessive nitrogen (N) fertilization on foliar nutrient dynamics and stem growth in three important tree species in a mixed-deciduous forest. Stem diameter growth, foliar N concentrations, nitrogenphosphorus (N/P) ratios, and nutrient resorption were determined for Acer rubrum L. (ACRU), Liriodendron tulipifera L. (LITU), and Prunus serotina Ehrh. (PRSE) on two 30-year-old watersheds at the Fernow Experimental Forest, West Virginia, USA: WS3, fertilized annually with 35 kg ammonium sulfate·ha -1 since 1989, and WS7, an untreated control watershed. In an earlier (1992) study, foliar N concentrations of all three species averaged 11% higher in WS3 than in WS7. By 2000, that was no longer the case for any species; indeed N in ACRU leaves was 13% lower in WS3 that year. N/P ratios were elevated in WS3 only in PRSE in 1992 and in both ACRU and PRSE in 1997, but by 2001, mean N/P for all three species was lower in WS3. N resorption efficiencies were 30% lower in WS3 in ACRU and PRSE, but not in LITU. Stem diameter growth in WS3 was 55% lower in ACRU and 30% lower in LITU and PRSE compared with that in WS7. Results may indicate declining growth vigor in ACRU and, to a lesser extent, PRSE and LITU in the fertilized watershed. Observed interspecific differences in growth and plant nutrition responses suggest eventual changes in species composition under increasing N saturation.

Vegetation and Acidification

“…Boxman et al (1998) also found that reducing N deposition in throughfall on roofed plots at Ysselsteyn, Netherlands resulted in significantly improved radial growth of Scots pine, suggesting that growth was being suppressed by ambient throughfall. Finally, May et al (2005) also noted reduced diameter growth in black cherry, yellow-poplar, and red maple trees at Fernow from 1999 to 2001, during the period of decline in growth noted by the tree cores. Theories of forest ecosystem acidification discussed in Chapter 1 suggest that a pattern of increased followed by decreased growth can result from prolonged exposure to acidic deposition.…”

“…As indicated in Figure 5-9 increases were significant in yellow-poplar during 3 years and in black cherry during 7 years prior to 1996. May et al (2005) found diameter growth on WS3 reduced by 37% compared to WS7 from 1999-2001 in three each of red maple, yellow-poplar, and black cherry trees. These data were collected late in the treatment period analyzed here and support the tree core analysis showing reduced radial growth had occurred.…”

Acidification and Nutrient Cycling

“…Differences in foliar nutrient concentrations were observed , May et al 2005, which suggests there may have been differences in N uptake by the vegetation. Specifically, N concentrations of foliage collected in 1992 from WS3 were generally higher than from WS7 for four tree species: red maple, black cherry, yellow-poplar, and sweet birch -but were only significantly greater on WS3 relative to WS7 for black cherry and red maple.…”

“…May et al (2005) reported that the acidification treatment decreased nutrient resorption efficiencies on WS3. The resorption of N averaged 30% lower in WS3 for red maple and black cherry than in WS7, but there were no significant differences in N resorption efficiency between watersheds for yellow-poplar.…”

“…A sustained increase in foliar N concentrations would have provided support for the idea of continued high rates of N uptake as availability continued to increase. May et al (2005) also evaluated three of the same tree species in 1992 and 2001. In 1992, foliar N concentrations for red maple, yellow-poplar and black cherry were approximately 11% greater in WS3 relative to WS7.…”