Throughfall chemistry and soil nutrient effects of the invasive shrub Lonicera maackii in deciduous forests.
|Abstract:||Invasive species usurp habitat space at the expense of natives, reducing biodiversity and altering ecosystem function. The non-native invasive shrub Amur honeysuckle (Lonicera maackii) is known to have substantial effects on forest structure and biodiversity in Midwestern North America; however, its influence on nutrient cycling is relatively unexplored. We investigated throughfall volume and chemistry, and soil nutrients, under and away from L. maackii shrubs in random locations along transects in three patchily invaded second-growth forests. Significantly lower volumes of throughfall were found under L. maackii canopies than in sites located away from L. maackii. Cation concentrations in throughfall were significantly higher, and in some instances 3 x higher, under L. maackii than in "away" locations. Despite lower throughfall volumes under L. maackii compared to "away" locations, total deposition of cations in throughfall under L. maackii was also consistently higher than in adjacent areas of native forest canopy. In contrast, [NH.sub.4.sup.+]-N concentrations in throughfall were significantly lower under L. maackii than away, suggesting N transformation and assimilation as rainwater passed through the canopy. No differences were found in soil properties between "under" and "away" locations. In summary, L. maackii significantly reduced the volume of rainwater arriving at the forest floor and altered the chemistry of that rainwater causing an increase in cation concentrations and a reduction in [NH.sub.4.sup.+]-N. These results suggest that L. maackii invasion has the potential to cause significant alterations to nutrient cycling in forests.|
Soil quality (Research)
Deciduous forests (Environmental aspects)
Honeysuckle (Environmental aspects)
Honeysuckle (Nutritional aspects)
Plants (Food and nutrition)
McEwan, Ryan W.
Arthur, Mary A.
Alverson, Sarah E.
|Publication:||Name: The American Midland Naturalist Publisher: University of Notre Dame, Department of Biological Sciences Audience: Academic Format: Magazine/Journal Subject: Biological sciences; Earth sciences Copyright: COPYRIGHT 2012 University of Notre Dame, Department of Biological Sciences ISSN: 0003-0031|
|Issue:||Date: July, 2012 Source Volume: 168 Source Issue: 1|
|Topic:||Event Code: 310 Science & research|
|Geographic:||Geographic Scope: United States Geographic Code: 1USA United States|
The invasion of forests by non-native species can substantially influence ecosystem composition and function (Evans et al., 2001; Mack et al., 2000). Invasive species rapidly expand into habitat space, forming virtual monocultures in some instances (Mack et al., 2000). These invasions can suppress native species and are extremely costly to control (Pimental et al., 2000; Webster et al., 2006). In forests of eastern North America, invasive plants are considered one of the most important threats to biodiversity (Miller and Gorchov, 2004; Hartman and McCarthy, 2007). A number of studies provide strong evidence that invasive species also have the capacity to elicit fundamental changes in ecosystem function. A literature review by Ehrenfeld (2003) uncovered myriad examples of changes to nutrient cycling caused by invasive plants. Heneghan et al. (2004) found that soil N, C, and pH were significantly higher under the invasive shrub Rhamnus cathartica than in control areas. The problematic invasive herb Alliaria petiolata was found by Rodgers et al. (2008) to increase nutrient availability in mixed conifer forests and Rothstein et al. (2004) found that an invasive tree (Fraxinus uhdei) had much faster leaf decomposition than native species. These studies, among others (e.g., Vitousek, 1990; Evans et al., 2001; Rout and Callaway, 2009), suggest that non-native plant invasion can result in alterations of ecosystem-level processes; an important task for science is identifying specific nutrient cycling effects of particularly problematic species.
The deciduous shrub Amur honeysuckle (Lonicera maackii) is a non-native invasive plant that was introduced to North America ca. 1900 from China (Luken and Thieret, 1996; Hutchinson and Vankat, 1997; Miller and Gorchov, 2004). Once established, this species can grow rapidly, forming a virtual monoculture shrub layer (Luken and Thieret, 1996). This species has longer leaf duration than native species (McEwan et al., 2009b) and may have chemical resistance against insect herbivores (McEwan et al., 2009a). A series of studies have indicated that this species has the potential to chemically suppress potential competitors through allelopathic effects (Dorning and Cipollini, 2006; Cipollini et al., 2008; McEwan et al., 2010). Lonicera maachii invasion has been clearly linked to substantial alterations in ecological community attributes (e.g., Luken and Thieret, 1996; Gorchov and Trisel, 2003; Hartman and McCarthy, 2004). Native trees, shrubs, and herbaceous species are negatively influenced by L. maackii (Gould and Gorchov, 2000; Collier et al., 2002; Gorchov and Trisel, 2003) and Hartman and McCarthy (2007) have demonstrated a negative effect of this shrub on the growth of overstory trees.
We assessed the consequences of Lonicera maackii invasion for nutrient cycling in forests of central Kentucky. In particular, we analyzed the influence of L. maackii on nutrient flux into ecosystems associated with rainwater passing through the leafy canopy (throughfall). Soil nutrients were also measured under and away from L. maackii shrubs to assess potential alterations in soil nutrient availability. We hypothesized that ([H.sub.1]) the presence of L. maackii in the forest understory would alter the volume and chemistry of throughfall arriving on the forest floor, and ([H.sub.2]) that L. maackii would significantly influence soil nutrient availability under its canopy.
Study Site Descriptions.--This work was conducted in forested portions of three central Kentucky natural areas: the University of Kentucky Arboretum woods (UKA; Fayette County; ca. 6.5 ha in size), Griffith Woods (GRW; Harrison County; ca. 303.5 ha), and Lower Howard's Creek (LHC; Clark County; ca. 92.3 ha). These forests were all located in the Inner Bluegrass Region (IBR), which is defined by its limestone geological substrate and karst topography (Wharton and Barbour, 1991). The IBR is a patchwork landscape dominated by agriculture and development interspersed with infrequent forest fragments which are subject to invasions by a suite of species including L. maackii, Rosa multiflora, Alliaria petiolata, and Ailanthus altissima. The soils of the IBR are deep and well-drained silt loams, elevation ranges from ca. 330 to 180 m ASL, and climate is continental with a mean annual temperature of 12.8 C and mean precipitation of 111.8 cm (Wharton and Barbour, 1991). The forests in all three sites were similar in species composition and structure. They were secondary mixed deciduous, approximately 60-80 y old, and composed of hickories (e.g., Carya laciniosa, C. ovata), ash (Fraxinus americana, F. quadrangulata), oaks (e.g., Quercus macrocarpa, Q. muehlenbergii), and a mix of other species including Acer saccharum and Celtis occidentalis. The native shrub layer in these forests is sparse. These sites were ideal for our work because (1) the forest canopy in each site was relatively uniform with an understory that was patchily invaded by Lonicera maackii yet relatively absent of other species in the shrub stratum, and (2) the management structure of each location allowed for protection of the field gear. Botanical nomenclature follows Jones (2005).
Field methods.--In each site, one 50 m transect was established in a section of the forest that was qualitatively representative of the stand and away from features such as streams, forest edges, and canopy gaps. Along these transects, throughfall was collected in 6 cm diameter funnels attached to 300 ml polyethylene bottles in 10 locations under, and 10 locations away from, Lonicera maackii shrubs (n = 10 for each treatment within each site, summing to 60 total funnels). The method for establishing sampling funnels was identical for each site. First, 20 random distances along each transect were chosen and each of these distances was randomly assigned a direction away from the transect (perpendicular, left, or right) and treatment (under or away from L. maackii). For "under" locations, the funnels were located near the canopy center of a L. maachii shrub, which we required to be [greater than or equal to] 1.5 m tall, with a crown that was [greater than or equal to] 1.5 m wide. We sought the closest possible location, perpendicular to the transect, where those conditions were met. For "away" sites, funnels were located in the nearest location perpendicular to the transect with [greater than or equal to] 3 m clearance from the canopy of any L. maackii shrubs. Distances from the central 50 m transect to the sampling location were generally short and no sample collection locations were >20 m from the central transect. Therefore, the under and away sites were relatively near each other in the forest and were qualitatively similar in terms of overhead forest canopy. No other invasive species were present that could have influenced throughfall coming into our sample collectors and the areas were devoid of native shrubs. Glass wool was placed in the mouth of each funnel to prevent debris from entering the bottles, and we never found significant debris accumulation in the funnels.
Water was collected after three separate precipitation events. The collection funnels were installed just prior to the forecasted rain event, and removed just after the conclusion of each event. The first sampling was made on 6 Jun. 2007 and collected precipitation from a rain event that occurred on 4 and 5 Jun. The second sampling was made on 31 Aug. 2007, from a rain event that occurred on 28 and 30 Aug. The third sampling was made on 15 Nov. 2007, from a rain event that occurred on 13 and 14 Nov. None of the collection bottles ever overflowed.
Soil chemistry was assessed in all three study sites along the same transects described above. Soil was collected using a 2.54 cm diameter soil probe starting just below the Oa horizon to a depth of 10 cm. Soils were collected on 29 May 2007 for analysis ([K.sup.+], [Ca.sup.2+], [P.sup.+], pH, total C, total N, [NH.sub.4.sup.+]-N, N[O.sub.3.sup.-]-N). Soil samples were collected in the same locations on 16 Jul. 2007 to reassess [NH.sub.4.sup.+]-N and N[O.sub.3.sup.-]-N.
Laboratory methods.--Throughfall samples were returned to the laboratory on ice and stored in the dark at 4 C until analysis. Within 24 h, throughfall volume was measured and inorganic N ([NH.sub.4.sup.+]-N and N[O.sub.3.sup.-] + N[O.sub.2.sup.-]-N) was analyzed colorimetrically with an automated continuous-flow analyzer (Bran + Luebbe Autoanalyzer III, Bran-Luebbe, Chicago, IL). Within 72 h, [Ca.sup.2+], [Mg.sup.2+] and [K.sup.+] were measured using an atomic absorption spectrophotometer (Avanta AAS, GBC Scientific Equipment, Hampshire, IL). Measurement of pH was accomplished using an Orion[R] benchtop pH meter following standard procedures. Deposition estimates were calculated as content (concentration*volume) divided by the collecting area (diameter) of the funnel.
Soil was processed in the laboratory and analyzed for nutrient concentrations and pH. Mineral soils were sieved through a 2-mm mesh screen to homogenize the sample and remove extraneous debris. For available nitrogen, 10 g subsamples were placed in extraction cups with 50 ml of 1 mol [L.sup.-1] KCl and shaken for 1 h. The solution was filtered through No. 40 Whatman paper, and the supernatant analyzed colorimetrically for inorganic N ([NH.sub.4.sup.+]-N and N[O.sub.3.sup.-]-N) with a Bran + Luebbe Autoanalyzer III. Mehlich III-extractable [Ca.sup.2+], [Mg.sup.2+], [K.sup.+] and [P.sup.+] were analyzed on an inductively coupled plasma spectrometer. Soil pH was measured using a 5 g sub-sample of mineral soil mixed in a 1:2 soil:water slurry (Hendershot et al., 1993).
Data analysis.--Data were first scanned for outliers. Individual values were removed if they exceeded 3 x the interquartile range (IQR) for the data collected from a given treatment environment (under or away), for a single sample date, at an individual site (<2% of values were removed as outliers). Analysis of pH was conducted using measured values (Yang et al., 2004). All data were screened for normality and homogeneity of variance using the D'Agostino omnibus test (D'Agostino et al., 1990). For all soil and throughfall variables, comparisons were made within date using ANOVA in which site was treated as a block effect and funnel location (under vs. away) as a fixed (treatment) effect. This analysis approach assumes variation among sites and rain events and focuses specifically on differences associated with the treatment within each site. In instances where a significant overall treatment effect was detected via ANOVA, post-hoc t-tests were conducted to assess differences caused by the treatments within site on [NH.sub.4.sup.+]-N. Analysis procedures were conducted within NCSS, and differences were considered significant at P < 0.05 (Hintze 2001).
Rainfall input to the forest floor was reduced by Lonicera maackii canopy interception. Throughfall volume was significantly influenced by the presence of L. maackii for all sites and events (Fig. 1; all P < 0.03), and in each case the volume was lower in the under locations. For all three precipitation events there was a significant site effect on throughfall volume (all P < 0.001; Fig. 1) suggesting non-uniformity in inputs across the region during the rain event. Post-hoc comparisons of treatments within site revealed significant differences in two of the sites in Jun. and Aug. and one site in Nov. (all P < 0.01; Fig. 1).
Cation concentrations in throughfall were also influenced by Lonicera maackii presence (Table 1). In Jun., concentrations of all cations, in all sites, were significantly influenced by the presence of a L. maackii canopy (Table 1; ANOVA results: P < 0.001 for all three tests). In some cases, cation concentrations were more than 3 X higher under L. maackii and post-tests indicated significant difference within site among treatments in many instances (Table 1). In Aug., [Ca.sup.2+] concentrations were not statistically different among treatments, but K+ and Mg2+ concentrations were significantly influenced by the L. maackii canopy (Table 1; ANOVA results: P < 0.001 for both tests). In fact, post-tests revealed statistically higher [K.sup.+] and [Mg.sup.2+] concentration from under L. maackii for the Aug. sampling from all sites (P < 0.05 for all tests). This pattern was repeated in the Nov. sampling; cation concentrations were significantly influenced by location of funnels, with higher cation concentrations found in samples collected from under L. maackii (Table 1). Throughfall pH was significantly influenced by the canopy of L. maackii in Aug. (F = 6.25; P = 0.015), but there was not a statistically significant difference in pH among treatments in Jun, and Nov. (Table 1).
Cation deposition (mg [m.sup.-2]) in throughfall was significantly influenced by the presence of Lonicera maackii shrubs, with higher concentrations of cations (Table 1) often overriding lower throughfall volumes (Fig. 1), leading to higher cation deposition on most dates (Fig. 2). For instance, [K.sup.+] deposition was significantly influenced by the presence of L. maackii in Jun. and Aug. (ANOVA results: P < 0.05; Fig. 2). In Jun., [K.sup.+] deposition was apparently higher under L. maackii in all three locations, and post-tests revealed a statistically significant difference in LHC (P = 0.039; Fig. 2). In Aug., [K.sup.+] deposition was statistically higher in the "under" treatment in all three sites (post-test results, P < 0.05 for all sites; Fig. 2). In Nov., there was no significant effect of treatment for [K.sup.+] (P = 0.42). Results for [Ca.sup.2+] in Jun. were similar to that for [K.sup.+], with significant overall treatment effects and post-tests revealing that deposition values were higher in the under treatments (Fig. 2). In contrast, Aug. [Ca.sup.2+] was significantly higher away from the canopy of L. maackii in GRW and LHC, and there was no discernible treatment effect for [Ca.sup.2+] in Nov. (Fig. 2). For [Mg.sup.2+] there was no significant effect of treatment in Jun., but there were significant differences in Aug. (F = 4.34; P < 0.04) and Nov. (F = 6.23; P = 0.016). In both of those samplings, in all locations, [Mg.sup.2+] deposition values were apparently higher in samples collected under L. maackii canopy; however, the only statistically significant difference identified by post-tests was in LHC in Nov.
[FIGURE 1 OMITTED]
Concentration of [NH.sub.4.sup.+]-N in throughfall was influenced by the presence of Lonicera maackii shrubs. In Aug. and Nov., samples collected away from L. maackii had higher concentrations of [NH.sub.4.sup.+]-N (mg [L.sup.-1]) than those collected under the shrub's canopy (ANOVA results, P < 0.01 for both tests; Table 2). This is the opposite of the pattern seen for cations (Table 1 vs. Table 2). Generally higher [NH.sub.4.sup.+]-N concentrations in "away" locations, coupled with higher throughfall volume in these locations, led to consistently and substantially higher deposition of [NH.sub.4.sup.+]-N in samples collected away from L. maackii (Fig. 3). On all three sample dates there was a significant overall treatment effect (ANOVA results, P < 0.001 for all samplings), and post-tests revealed within-site treatment effects for most sites and dates (Fig. 3). There were no statistically significant differences between under and away locations for N[O.sub.3.sup.-]-N concentration or deposition (Table 2; Fig. 3).
[FIGURE 2 OMITTED]
Soil properties were not significantly different under Lonicera maackii shrubs compared to away sites. Soil pH, cation concentrations, and total carbon (C) and N were not statistically distinguishable among treatments in May (Table 3). [NH.sub.4.sup.+]-N and N[O.sub.3.sup.-]-N concentrations also were not different among treatments in May or Jul. (Table 3).
Lonicera maackii is an aggressive invader of deciduous forests that has been shown to negatively impact biodiversity (e.g., Luken and Thieret, 1996; Hutchinson and Vankat, 1997; Gould and Gorchov, 2000; Hartman and McCarthy, 2004). This species may also be strongly influencing nutrient cycling in these forests. Trammell et al. (2012) found that forests invaded by L. maackii had 1.5 x higher total foliar biomass and that litter decomposition rate in these forests was substantially higher. In fact, several studies have shown that L. maackii leaf material decays much more rapidly than native species (Poulette and Arthur, 2012; Blair and Stowasser, 2009; Trammell et al., 2012). Trammell et al. (2012) found that native species decomposition was more rapid in forests where L. maackii was dominant. Poulette and Arthur (2012) provide evidence that the effect of L. maackii on litter decomposition may be variable depending on the composition of native litter present at the site. Working in an aquatic system, McNeish et al. (In press) found that L. maackii decomposition in headwater streams was much faster than native species. These findings are indicative of an emerging literature which supports the concept that L. maackii invasion has the potential to substantially alter ecosystem function.
[FIGURE 3 OMITTED]
Our data supported the hypothesis (H1) that the presence of Lonicera maackii in the forest understory would alter the volume and chemistry of throughfall arriving on the forest floor. A rich scientific literature has focused on the general importance of throughfall in nutrient cycling (e.g., Cronan and Reiners, 1983; Arthur and Fahey, 1993; Liu et al., 2008; Gielis et al., 2009). Throughfall chemistry is influenced by stand age and the species identity of canopy trees (Van der Salm et al., 2006; Alexander and Arthur, 2010; Pelster et al., 2010; Talkner et al., 2010). The volume and chemistry of throughfall changes across forest edge-to-interior gradients (Draaijers et al., 1988; Weathers et al., 2001; Wuyts et al., 2008) and is influenced by tree phenology over the growing season (Staelens et al., 2007). We found that the L. maackii canopy, which can be extensive and dense, intercepts a significant amount of rainwater, causing areas under the shrub to receive less water than sites without the shrub. Our data also suggest both higher cation concentration, and higher total deposition, under the L. maackii canopy.
A forest canopy can influence the concentration of cations in throughfall chemistry in several ways. First, a plant canopy can be impacted by dry deposition (DD) of particles that are subsequently washed off by rainwater. Second, the plant canopy can serve as an evaporation surface (EVS) for rainwater and this evaporation can leave behind increased concentrations of chemical nutrients which eventually fall to the soil surface. Finally, rainwater passing through the canopy may result in chemical leaching from plant materials, i.e., canopy leaching (CL). Our study was not designed to delineate which of these processes were most responsible for changes in throughfall cations, and it is likely that each plays some role. For instance, the Lonicera maackii shrub canopy provides an extensive surface for DD that is absent in the native forest. It is well known that DD is a significant contributor to throughfall (Lovett & Lindberg, 1984; Lovett et al., 2000); however, it is unclear whether a subcanopy shrub like L. maackii can perform as a novel collection surface for DD in invaded habitats. The extensive shrub canopy may also be influencing throughfall by acting as an EVS. In regional second-growth forests, the native shrub layer is sparse and native shrubs such as Lindera benzoin and Asimina triloba are much less frequent with much lower cover than that of L. maackii (Wilson et al., in review). Therefore, the ecosystem effects of L. maackii may be a simple case of vastly increased biomass and a dense shrub canopy in forests where shrubs are sparse and infrequent, creating the opportunity for nutrient additions to throughfall through DD and/or chemical concentration associated with the extensive canopy acting as an EVS.
Lonicera maackii may also be influencing throughfall chemistry by introducing unique leaf traits (e.g., leaf cuticle thinness, or leaf chemistry) which facilitate the leaching of these compounds. Differences in leaf morphology and chemistry can significantly influence CL (Alexander and Arthur, 2010). Lovett and Lindberg (1984), for example, pointed to differences in cuticle wax, leaf tricomes, and leaf chemistry as partial explanations of variation in cation leaching between Quercus alba and Q. prinus. It is known that [K.sup.+] and [Mg.sup.2+] are readily leached from plant material by rainfall and that there is variation among species in throughfall contribution of these elemental ions (e.g., Stachurski and Zimka, 2002; Staelens et al., 2007). Leaching of [Ca.sup.2+] from plant material is also known to occur, although it is more tightly bound in plant structures than [K.sup.+] and [Mg.sup.2+] (e.g., Berger et al., 2001). Research that specifically assesses leaf morphology, chemistry, and cation leaching of native species vs. L. maackii is needed to address this issue.
We found that Lonicera maackii had a significant influence on nitrogen in throughfall. In particular, significantly higher deposition of [NH.sub.4.sup.+]-N was found under a native forest canopy than under L. maackii shrubs. Throughfall concentration of nitrogen is thought to be primarily governed by DD of N to the canopy, which is washed off by rainfall. Biotic transformations of organic N (ammonification to produce [NH.sub.4.sup.+], followed by nitrification to N[O.sub.3.sup.-]) may also occur on leaf surfaces, and assimilation of these ions to bacterial and plant biomass can occur within the plant canopy (Schwarz et al., 2011). One hypothesis that could explain our finding of significantly lower [NH.sub.4.sup.+]-N in "under" samples is assimilation into the plant itself or into microbial biomass residing on surface of L. maackii leaves. Future work focused specifically on leaf-level processes is needed to confirm the patterns detected in our study and to work toward a mechanistic explanation.
Our analyses of soil chemistry did not reveal statistically significant differences based on the presence of Lonicera maackii (refuting [H.sub.2]). This lack of effect on soil chemistry could be explained by the fact that the sites were only recently invaded. To test our hypotheses, this study was intentionally conducted in forests where the distribution of L. maackii was patchy. This allowed us to sample both under, and away from, L. maackii within the same forest stand. Lonicera maackii can form dense quasi-monocultures in the shrub layer; therefore, the patchy distribution in our stand may be an indication that the invasion was in a relatively early phase of development. Under more intense conditions of invasion, L. maackii could be significantly altering soil chemistry.
In summary, our data provide evidence that Lonicera maackii influences the volume and chemistry of rainfall as it passes through the forest canopy. If the patterns indicated by our data are generally representative of processes in L. maackii invaded sites, this change in throughfall chemistry could have a substantial influence on ecosystem processes. Lonicera maackii has significantly longer leaf duration than native species, which could magnify this effect (McEwan et al., 2009b). It is unknown if the effects we detected were associated with the dense leaf canopy created by L. maackii invasion, or if this species has novel leaf traits that create the effect. Further work is needed to verify our findings and examine more closely the influence L. maackii invasion may be having on other aspects of nutrient cycling in forests where it has proliferated aggressively.
Acknowledgments.--We thank Laura Baird for assistance with installing and collecting funnels in the field. We thank Jim Lempke at the University of Kentucky Arboretum for providing access to Walnut Woods. Thanks also to Clare Sipple and the Kentucky State Nature Preserves Commission for providing access to a forested portion of Lower Howard's Creek. This study (# 11-09-098) was connected with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director.
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SUBMITTED 23 AUGUST 2011
ACCEPTED 26 JANUARY 2012
RYAN W. MCEWAN (1)
Department of Biology, University of Dayton, 300 College Park, Dayton, Ohio 45459
MARY A. ARTHUR
Department of Forestry, University of Kentucky, T.P. Cooper Building, Lexington 40546
SARAH E. ALVERSON
Aullwood Audubon Center and Farm, 1000 Aullwood Road, Dayton, Ohio 45414
(1) Corresponding author: e-mail: firstname.lastname@example.org
Table 1.--Mean concentrations (and SE) of [K.sup.+], [Ca.sup.2+] [Mg.sup.2+] (mg [L.sup.-1]) and pH in throughfall collected under, and away from, the canopy of Lonicera maackii shrubs in three second- growth forests of central Kentucky, USA GRW Away Under Jun. [K.sup.+] *** 15.87 [+ or -] 2.22## 32.34 [+ or -] 4.12## [Ca.sub.2+] *** 03.06 [+ or -] 0.52### 11.74 [+ or -] 1.63### [Mg.sub.2+] *** 01.98 [+ or -] 0.17## 03.56 [+ or -] 0.41## pH 07.49 [+ or -] 0.13 07.75 [+ or -] 0.08 Aug. [K.sup.+] *** 00.41 [+ or -] 0.11## 02.48 [+ or -] 0.64## [Ca.sub.2+] 02.67 [+ or -] 0.26 01.24 [+ or -] 0.28 [Mg.sub.2+] *** 00.61 [+ or -] 0.11# 01.00 [+ or -] 0.09# pH * 06.27 [+ or -] 0.11 06.43 [+ or -] 0.06 Nov. [K.sup.+] * 03.57 [+ or -] 0.58## 10.04 [+ or -] 2.09## [Ca.sub.2+] *** 02.80 [+ or -] 0.32## 05.03 [+ or -] 0.66## [Mg.sub.2+] *** 02.56 [+ or -] 0.16### 03.94 [+ or -] 0.29### pH 06.99 [+ or -] 0.02 06.91 [+ or -] 0.10 UKA Away Under Jun. [K.sup.+] *** 11.99 [+ or -] 1.21 18.34 [+ or -] 3.60 [Ca.sub.2+] *** 03.60 [+ or -] 0.64 05.14 [+ or -] 1.01 [Mg.sub.2+] *** 01.80 [+ or -] 0.37 02.20 [+ or -] 0.28 pH 07.46 [+ or -] 0.42 06.96 [+ or -] 0.15 Aug. [K.sup.+] *** 03.60 [+ or -] 1.13## 17.40 [+ or -] 3.70## [Ca.sub.2+] 01.52 [+ or -] 0.28 03.38 [+ or -] 0.47 [Mg.sub.2+] *** 00.88 [+ or -] 0.13# 01.40 [+ or -] 0.12# pH * 06.55 [+ or -] 0.11 06.70 [+ or -] 0.07 Nov. [K.sup.+] * 09.60 [+ or -] 2.95 10.25 [+ or -] 1.90 [Ca.sub.2+] *** 05.31 [+ or -] 1.61 04.24 [+ or -] 0.57 [Mg.sub.2+] *** 01.97 [+ or -] 0.17 02.55 [+ or -] 0.24 pH 06.58 [+ or -] 0.10 06.56 [+ or -] 0.09 LHC Away Under Jun. [K.sup.+] *** 4.88 [+ or -] 0.81## 15.43 [+ or -] 3.74## [Ca.sub.2+] *** 1.05 [+ or -] 0.21## 03.60 [+ or -] 0.75## [Mg.sub.2+] *** 0.64 [+ or -] 0.19## 01.97 [+ or -] 0.32## pH 6.50 [+ or -] 0.09 07.19 [+ or -] 0.14 Aug. [K.sup.+] *** 1.51 [+ or -] 0.60## 06.02 [+ or -] 1.22## [Ca.sub.2+] 3.10 [+ or -] 0.40 01.95 [+ or -] 0.24 [Mg.sub.2+] *** 0.59 [+ or -] 0.06## 00.93 [+ or -] 0.10## pH * 6.59 [+ or -] 0.06 06.75 [+ or -] 0.05 Nov. [K.sup.+] * 2.20 [+ or -] 0.34### 05.28 [+ or -] 0.71### [Ca.sub.2+] *** 0.94 [+ or -] 0.14## 04.89 [+ or -] 1.35## [Mg.sub.2+] *** 0.84 [+ or -] 0.09## 01.82 [+ or -] 0.24## pH 5.80 [+ or -] 0.14 06.30 [+ or -] 0.14 Overall Treatment effect: * P < 0.05; ** P < 0.01; *** P < 0.001 Post-tests- differences within site: bold P < 0.05; bold italic P < 0.01; bold italic underline P < 0.001 Post-tests- differences within site: bold P < 0.05 is indicated with #; bold italic P < 0.01 is indicated with ##; bold italic underline P < 0.001 is indicated with ###. Table 2.--Concentration of N[0.sub.3.sup.-]-N and N[H.sub.4.sup.+]-N (mg [L.sup.-1]) in throughfall collected under, and away from, the canopy of Lonicera maackii shrubs in three second-growth forests of central Kentucky, USA GRW Away Under Jun. N[O.sub.3.sup.-]-N 0.36 [+ or -] 0.13 0.47 [+ or -] 0.22 N[H.sub.4.sup.+]-N 7.58 [+ or -] 0.40 6.45 [+ or -] 0.87 Aug. N[0.sub.3.sup.-]-N 0.27 [+ or -] 0.02 0.24 [+ or -] 0.03 N[H.sub.4.sup.+]-N ** 0.37 [+ or -] 0.05 0.26 [+ or -] 0.04 Nov. N[O.sub.3.sup.-]-N 0.60 [+ or -] 0.05 0.40 [+ or -] 0.10 N[H.sub.4.sup.+]-N *** 0.82 [+ or -] 0.06### 0.46 [+ or -] 0.06### UKA Away Under Jun. N[O.sub.3.sup.-]-N 0.24 [+ or -] 0.12 0.32 [+ or -] 0.12 N[H.sub.4.sup.+]-N 7.06 [+ or -] 0.69 4.87 [+ or -] 0.80 Aug. N[O.sub.3.sup.-]-N 0.34 [+ or -] 0.08 0.41 [+ or -] 0.09 N[H.sub.4.sup.+]-N ** 0.20 [+ or -] 0.06# 0.04 [+ or -] 0.01# Nov. N[O.sub.3.sup.-]-N 0.43 [+ or -] 0.13 0.52 [+ or -] 0.15 N[H.sub.4.sup.+]-N *** 0.35 [+ or -] 0.06 0.23 [+ or -] 0.04 LHC Away Under Jun. N[O.sub.3.sup.-]-N 0.34 [+ or -] 0.05 0.28 [+ or -] 0.05 N[H.sub.4.sup.+]-N 1.17 [+ or -] 0.14 1.95 [+ or -] 0.30 Aug. N[O.sub.3.sup.-]-N 0.44 [+ or -] 0.03 0.53 [+ or -] 0.05 N[H.sub.4.sup.+]-N ** 0.47 [+ or -] 0.03 0.41 [+ or -] 0.05 Nov. N[O.sub.3.sup.-]-N 0.26 [+ or -] 0.05 0.14 [+ or -] 0.05 N[H.sub.4.sup.+]-N *** 0.56 [+ or -] 0.03# 0.37 [+ or -] 0.06# Overall Treatment effect: * P < 0.05; ** P < 0.01; *** P < 0.001 Post-test- differences within site: bold P < 0.05; bold italic P < 0.01; bold italic underline P < 0.001 Note: Post-test- differences within site: bold P < 0.05 is indicated with #; bold italic P < 0.01 is indicated with ##; bold italic underline P < 0.001 is indicated with ###. Table 3.--Concentrations of K+, [Ca.sup.2+], [P.sup.+ ], N[O.sub.3.sup.-]-N and N[H.sub.4.sup.+]-N (mg per g dry soil) and total N and C (%), in soils collected under, and away from, the canopy of Lonicera maackii shrubs in three second growth forests of central Kentucky, USA GRW Away Under May [K.sup.+] 0.14 [+ or -] 0.01 0.17 [+ or -] 0.01 [Ca.sup.2+] 2.12 [+ or -] 0.16 2.14 [+ or -] 0.12 [P.sup.+] 0.03 [+ or -] 0.01 0.03 [+ or -] 0.00 pH 6.15 [+ or -] 0.08 6.19 [+ or -] 0.07 C(%) 3.87 [+ or -] 0.21 4.01 [+ or -] 0.16 N (%) 0.33 [+ or -] 0.02 0.33 [+ or -] 0.01 N[H.sub.4.sup.+]-N 3.26 [+ or -] 0.15 3.41 [+ or -] 0.18 N[O.sub.3.sup.-]-N 0.16 [+ or -] 0.04 0.12 [+ or -] 0.06 Jul. N[H.sub.4.sup.+]-N 3.13 [+ or -] 0.20 3.64 [+ or -] 0.20 N[O.sub.3.sup.-]-N 5.71 [+ or -] 0.49 1.83 [+ or -] 0.22 UKA Away Under May [K.sup.+] 0.30 [+ or -] 0.02 0.30 [+ or -] 0.02 [Ca.sup.2+] 2.69 [+ or -] 0.11 3.02 [+ or -] 0.20 [P.sup.+] 0.11 [+ or -] 0.01 0.09 [+ or -] 0.00 pH 6.41 [+ or -] 0.11 6.46 [+ or -] 0.11 C(%) 4.06 [+ or -] 0.17 4.46 [+ or -] 0.31 N (%) 0.36 [+ or -] 0.01 0.40 [+ or -] 0.02 N[H.sub.4.sup.+]-N 3.12 [+ or -] 0.27 2.88 [+ or -] 0.21 N[O.sub.3.sup.-]-N 1.22 [+ or -] 0.55 1.53 [+ or -] 0.48 Jul. N[H.sub.4.sup.+]-N 3.09 [+ or -] 0.15 3.53 [+ or -] 0.20 N[O.sub.3.sup.-]-N 5.50 [+ or -] 0.32 0.16 [+ or -] 0.05 LHC Away Under May [K.sup.+] 00.32 [+ or -] 0.03 00.35 [+ or -] 0.07 [Ca.sup.2+] 04.88 [+ or -] 0.31 05.44 [+ or -] 0.50 [P.sup.+] 00.17 [+ or -] 0.01 00.14 [+ or -] 0.01 pH 06.43 [+ or -] 0.13 06.80 [+ or -] 0.06 C(%) 7.76 [+ or -] 0.49 7.68 [+ or -] 0.48 N (%) 00.56 [+ or -] 0.03 00.60 [+ or -] 0.03 N[H.sub.4.sup.+]-N 05.08 [+ or -] 0.41 05.03 [+ or -] 0.58 N[O.sub.3.sup.-]-N 00.66 [+ or -] 0.14 00.94 [+ or -] 0.15 Jul. N[H.sub.4.sup.+]-N 05.09 [+ or -] 0.31 04.70 [+ or -] 0.40 N[O.sub.3.sup.-]-N 00.81 [+ or -] 0.19 01.37 [+ or -] 0.14 Overall Treatment effect: * P < 0.05; ** P < 0.01; *** P < 0.001 Post-test- differences within site: bold P < 0.05; bold italic P < 0.01; bold italic underline P < 0.001
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