Effects of understory removal, N fertilization, and litter layer removal on soil N cycling in a 13-year-old white spruce plantation infested with Canada bluejoint grass

Abstract

Canada bluejoint grass [Calamagrostis canadensis (Michx.) Beauv., referred to as bluejoint below] is a competitive understory species widely distributed in the boreal region in North America and builds up a thick litter layer that alters the soil surface microclimate in heavily infested sites. This study examined the effects of understory removal, N fertilization, and litter layer removal on litter decomposition, soil microbial biomass N (MBN), and net N mineralization and nitrification rates in LFH (the sum of organic horizons of litter, partially decomposed litter and humus on the soil surface) and mineral soil (0-10 cm) in a 13-year-old white spruce [Picea glauca (Moench.) Voss] plantation infested with bluejoint in Alberta, Canada. Removal of the understory vegetation and the litter layer together significantly increased soil temperature at 10 cm below the mineral soil surface by 1.7 and 1.3°C in summer 2003 and 2004, respectively, resulting in increased net N mineralization (by 1.09 and 0.14 mg N kg -1 day -1 in LFH and mineral soil, respectively, in 2004) and net nitrification rates (by 0.10 and 0.20 mg N kg -1 day -1 in LFH and mineral soil, respectively, in 2004). When the understory vegetation was intact, nitrification might have been limited by NH 4 + availability due to competition for N from bluejoint and other understory species. Litter layer removal increased litter decomposition rate (percentage mass loss per month) from 2.6 to 3.0% after 15 months of incubation. Nitrogen fertilization did not show consistent effects on soil MBN, but increased net N mineralization and nitrification rates as well as available N concentrations in the soil. Clearly, understory removal combined with N fertilization was most effective in increasing rates of litter decomposition, net N mineralization and nitrification, and soil N availability. The management of understory vegetation dominated by bluejoint in the boreal region should consider the strong effects of understory competition and the accumulated litter layer on soil N cycling and the implications for forest management.

Impacts of litter and understory removal on soil properties in a subtropical Acacia mangium plantation in China

“…Understory functioning as a habitat for animals thus contributing to forest biodiversity has also been reported (Camprodon and Brotons 2006). However, the impact of understory on soil ecosystems has been studied less and focused mainly on soil nitrogen (N) mineralization and N cycling (Tripathi et al 2005;Matsushima and Chang 2007). Due to high turnover rates, understory vegetation has been suggested to contribute substantially to nutrient cycling and soil fertility (Yarie 1980;Chapin III 1983;Nilsson and Wardle 2005).…”

Short-Term vs. Long-Term Effects of Understory Removal on Nitrogen and Mobile Carbohydrates in Overstory Trees

“…Previous experimental studies have found that removal of understory plants led to significant increase in soil N content [49,50] and soil water availability [12,51], and consequently, resulted in increased growth rate of the overstory trees [6,51]. The present study provided insight to explain the functional mechanisms underlying the positive effects of understory-removal on overstory growth.…”

“…Hence, the understory may be most likely to affect the overstory through below ground competition for soil resources [48]. For example, dense understory vegetation can significantly decrease the soil temperature, net N mineralization, net nitrification rates, and soil water availability [12]. Removal experiments showed that understory removal can lead to significant increases in soil N [49,50] and soil water availability [12,51], and consequently, result in increased growth rate of the overstory trees [6,51].…”

“…For example, dense understory vegetation can significantly decrease the soil temperature, net N mineralization, net nitrification rates, and soil water availability [12]. Removal experiments showed that understory removal can lead to significant increases in soil N [49,50] and soil water availability [12,51], and consequently, result in increased growth rate of the overstory trees [6,51]. The higher sensitivity of N and NSC in dry season and their insensitivity in the wet season (Figures 1-3) suggest that the most important effects of understories occur in regions with stressful growth conditions such as dry areas.…”

Drought-induced mortality of Scots pines at the southern limits of its distribution in Europe: causes and consequences

“…The litera ture about the effect of understory vegetation on the water availability of overstory trees is sparse. One study has shown that dense understory vegetation can significantly decrease soil-water availability (Matsushima & Chang 2007). An optimal stand density and removing of shrubs might improve water availability and reduce risks of cavitation for trees and thus have a positive effect on sto matal opening and consequently on carbon uptake.…”