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1.
The objective of this study was to investigate the influence of mopane canopy cover on litter decomposition in a semi‐arid African savannah. We used a randomized block design with five blocks of 100 × 100 m demarcated in a 10‐ha pocket of open mopane woodland. Litterbags were placed beneath large (8.3 m crown diameter) and small mopane trees (2.7 m crown diameter) and in the intercanopy area. Decomposition was fastest in the intercanopy area exposed to solar radiation (k = 0.35 year?1), intermediate beneath small trees (k = 0.28 year?1) and slowest beneath large trees (k = 0.23 year?1). Soil temperatures beneath small and large trees were 3–5 and 6–9°C lower than in the intercanopy area, respectively. Bacterial and fungal counts were significantly higher (P < 0.05) beneath large than small trees and in the intercanopy area. The amount of N and P released did not vary significantly among sampling sites. Soil moisture in the dry season was similar among sampling sites but rainy‐season soil moisture was significantly greater (P < 0.05) beneath large than small trees and in the intecanopy area. Mopane canopy cover retarded litter decomposition suggesting that photodegradation could be an important factor controlling carbon turnover in semi‐arid African savannahs. 相似文献
2.
Conversion of secondary broadleaved forest into Chinese fir plantation alters litter production and potential nutrient returns 总被引:2,自引:0,他引:2
Litter production, litter standing crop, and potential nutrient return via litterfall to soil were studied during a 4-year
period (January 2004–December 2007) in a Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantation and a secondary broadleaved forest in Hunan Province in subtropical China. Mean annual litterfall
in the sampling sites varied from 358 g m−2 in the pure plantation to 669 g m−2 in the secondary broadleaved forest. Total litterfall followed a bimodal distribution pattern for both forests. Amount of
litterfall was also related to the air temperature in both forests. During the period under this study, annual variation in
the total litterfall in the pure plantation was significantly higher than that in the secondary broadleaved forest. Litterfall
was markedly seasonal in the both forests. Leaf proportions of litterfall in the pure plantation and secondary broadleaved
forest were 58.1 and 61.7%, respectively. Total potential nutrient returns to the soil through litterfall in the pure plantation
were only 46.2% of those in the secondary broadleaved forest. Total litter standing crop was 913 and 807 g m−2 in the pure plantation and secondary broadleaved forest, respectively. Our results confirm that conversion from a secondary
broadleaved forest into a pure coniferous plantation changes the functioning of the litter system. 相似文献
3.
Litterfall dynamics in carbonate and deltaic mangrove ecosystems in the Gulf of Mexico 总被引:1,自引:0,他引:1
Carlos Coronado-Molina H. Alvarez-Guillen J. W. DayJr. E. Reyes B. C. Perez F. Vera-Herrera R. Twilley 《Wetlands Ecology and Management》2012,20(2):123-136
From 1996 to 2002, we measured litterfall, standing litter crop, and litter turnover rates in scrub, basin, fringe and riverine
forests in two contrasting mangrove ecosystems: a carbonate-dominated system in the Southeastern Everglades and a terrigenous-dominated
system in Laguna de Terminos (LT), Mexico. We hypothesized that litter dynamics is driven by latitude, geomorphology, hydrology,
soil fertility and soil salinity stress. There were significant temporal patterns in LT with litterfall rates higher during
the rainy season (2.4 g m−2 day−1) than during the dry season (1.8 g m−2 day−1). Total annual litterfall was significantly higher in the riverine forest (12.8 Mg ha−2 year−1) than in the fringe and basin forests (9.7 and 5.2 Mg ha−2 year−1, respectively). In Southeastern Everglades, total annual litterfall was also significantly higher during the rainy season
than during the dry season. Spatially, the scrub forest had the lowest annual litterfall (2.5 Mg ha−2 year−1), while the fringe and basin had the highest (9.1 and 6.5 Mg ha−2 year−1, respectively). In LT, annual standing litter crop was 3.3 Mg ha−1 in the fringe and 2.2 Mg ha−1 in the basin. Litter turnover rates were significantly higher in the fringe mangrove forest (4.1 year−1) relative to the basin forests (2.2 year−1). At Southeastern Everglades there were significant differences in annual standing litter crop: 1.9, 3.3 and 4.5 Mg ha−1 at scrub, basin and fringe mangrove sites, respectively. Furthermore, turnover rates were similar at both basin and fringe
mangrove types (2.1 and 2.0 year−1, respectively) but significantly higher than scrub mangrove forest (1.3 year−1). These findings suggest that litter export is important in regulating litter turnover rates in frequently flooded riverine
and fringe forests, while in infrequently flooded basin forests, in situ litter decomposition controls litter turnover rates. 相似文献
4.
Min B. Rayamajhi Thai K. Van Paul D. Pratt Ted D. Center 《Wetlands Ecology and Management》2006,14(4):303-316
Melaleuca quinquenervia dominates large areas of the Florida Everglades in the southeastern USA where it has transformed sedge-dominated marshes
into melaleuca forests. Despite its prevalence, very little is known about the ecology and stand dynamics of this invasive
tree. We delineated large-, intermediate-, and small-tree stands in non-flooded, seasonally flooded and permanently flooded
areas of Florida in 1997, measured their biological attributes, and then quantified litterfall components for 3–4 year periods.
Melaleuca wood components and mature seed-capsules comprised the largest and the smallest portions of aboveground biomass,
respectively, while leaves, fine stems, mature fruits, bud scales, floral structures, and residues represented decreasingly
smaller fractions of the litter during the succeeding year. Dry weight proportion of leaves in litter was greatest (80.9%)
in non-flooded and least (69.1%) in permanently flooded habitats. It was also greatest in small (85.6%) and least in large
(64.7%) tree stands. Reproductive structures and mature-fruit fractions in litter were highest in large-tree stands whereas
the bud-scale fraction showed no relationship to tree size. Seasonally flooded habitats had the most litterfall, wherein small-,
intermediate-, and large-tree stands generated 0.662, 0.882, and 1.128 kg m−2 yr−1, respectively. Dry weight of stems, leaves, bud–scales, floral structures, and mature fruit fractions in litter increased
as the predominant size of the trees in the stand increased. Total annual litter production was highest during 1999–2000.
Leaf fall occurred year-round with maximal amount during April, July, and October. Highest amounts of bud scales and floral
structures fell during October–January, which corresponded with flushes of vegetative growth and major flowering events. Overall,
melaleuca alone accounted for nearly 99% of the total litterfall dry weight in all habitats and months sampled. The amount
of non-melaleuca litter was greater in small-tree stands than in intermediate- or large-tree stands. Litterfall data of this
nature will be helpful in detecting changes occurring in melaleuca canopies in response to biological control impact and in
prescribing site-specific management strategies. 相似文献
5.
Tropical upper montane forests usually comprise trees of small stature with a relatively low aboveground productivity. In
contrast to this rule, in the Cordillera de Talamanca (Costa Rica), tall trees (>35 m in height and more than 60 cm in diameter)
are characteristic for the upper montane old-growth oak forests which are growing at an altitude of almost 3,000 m close to
the alpine timberline. For these exceptional forests, productivity data are not yet available. In this study, we analyzed
litterfall and its components (tree leaves, litter of epiphytic vascular and non-vascular plants, mistletoes, twigs and other
canopy debris) in three forest stands belonging to different successional stages and related seasonal changes in litterfall
to micrometeorological variables. The studied stands were early-successional forest (10–15-year-old), mid-successional forest
(40-year-old), and old-growth forest. The stands are dominated by Quercus copeyensis and are located at 2,900-m altitude. Total litterfall was highest in the mid-successional forest (1,720 g m−2 y−1), and reached 1,288 g m−2 y−1 in the old-growth forest and 934 g m−2 y−1 in the early-successional forest. Litter mass was dominated by leaves in all stages (56–84% of total litterfall). In the old-growth
forest, however, twigs and small canopy debris particles (33%), epiphytes (6%), and mistletoes (5%) also contributed substantially
to litter mass. Leaf litterfall showed a clear seasonal pattern with a negative correlation to monthly precipitation and highest
values in the dry season (January–April). However, the strongest correlation existed with minimum air temperature (negative),
probably because temperatures already dropped at the end of the rainy season, when precipitation had not yet declined and
leaf shedding already increased. In contrast, litterfall of epiphyte mass, and twigs and other debris was mostly dependent
on occasional strong winds. We conclude that the upper montane oak forests of the Cordillera de Talamanca are exceptional
with respect to the large tree size and the relatively high productivity as indicated by litterfall. Litter mass was especially
high in the mid-successional and old-growth forests, where the observed annual totals are among the highest recorded for tropical
forests so far. 相似文献
6.
Sparse Ulmus pumila woodlands play an important role in contributing to ecosystem function in semi-arid grassland of northern China. To understand
the key attributes of soil carbon cycling in U. pumila woodland, we studied dynamics of soil respiration in the canopy field (i.e., the projected crown cover area) and the open
field at locations differing in distance (i.e., at 1–1.5, 3–4, 10, and >15 m) to tree stems from July through September of
2005, and measured soil biotic factors (e.g., fine root mass, soil microbial biomass, and activity) and abiotic factors [e.g.,
soil water content (SWC) and organic carbon] in mid-August. Soil respiration was further separated into root component and
microbial component at the end of the field measurement in September. Results showed that soil respiration had a significant
exponent relationship with soil temperature at 10-cm depth. The temperature sensitivity index of soil respiration, Q
10, was lower than the global average of 2.0, and declined significantly (P < 0.05) with distance. The rate of soil respiration was generally greater in the canopy field than in the open field; monthly
mean of soil respiration was 305.5–730.8 mg CO2 m−2 h−1 in the canopy field and 299.6–443.1 mg CO2 m−2 h−1 in the open field from July through September; basal soil respiration at 10°C declined with distance, and varied from ~250 mg
CO2 m−2 h−1 near tree stems to <200 mg CO2 m−2 h−1 in the open field. Variations in soil respiration with distance were consistent with patterns of SWC, fine root mass, microbial
biomass and activities. Regression analysis indicated that soil respiration was tightly coupled with microbial respiration
and only weakly related to root respiration. Overall, variations in SWC, soil nutrients, microbial biomass, and microbial
activity are largely responsible for the spatial heterogeneity of soil respiration in this semi-arid U. pumila woodland. 相似文献
7.
H. González-Rodríguez T. G. Domínguez-Gómez I. Cantú-Silva M. V. Gómez-Meza R. G. Ramírez-Lozano M. Pando-Moreno C. J. Fernández 《Plant Ecology》2011,212(10):1747-1757
The aim of this study was to determine the litterfall production and macronutrient (Ca, K, Mg, N, and P) deposition through
leaf litter in four sites with different types of vegetation. Site one (Bosque Escuela) was located at 1600 m a.s.l. in a
pine forest mixed with deciduous trees, second site (Crucitas at 550 m a.s.l.) in the ecotone of a Quercus spp. forest and the Tamaulipan thornscrub and third and fourth sites (Campus at 350 m a.s.l. and Cascajoso at 300 m a.s.l.,
respectively) were in the Tamaulipan thornscrub. Litter constituents (leaves, reproductive structures, twigs, and miscellaneous
residues) were collected at 15-day intervals from December 21, 2006, throughout December 20, 2007. Collections were carried
out in ten litter traps (1.0 × 1.0 m) randomly situated at each site of approximately 2,500 m2. Total annual litterfall deposition was 4407, 7397, 6304, and 6527 kg ha−1 y−1 for Bosque Escuela, Crucitas, Campus and Cascajoso, respectively. Of total annual litter production, leaves were higher varying
from 74 (Bosque Escuela) to 86% (Cascajoso) followed by twigs from 4 (Cascajoso) to 14% (Crucitas), reproductive structures
from 6 (Bosque Escuela) to 10% (Crucitas), and miscellaneous litterfall from <1 (Campus) to 12% (Bosque Escuela). The Ca annual
deposition was significantly higher in Cascajoso (232.7 kg ha−1 y−1), followed by Campus (182.3), Crucitas (130.5) and Bosque Escuela (30.3). The K (37.5, 32.5, 24.8, 7.2, respectively), Mg
(22.6, 17.7, 13.7, 4.5, respectively) followed the same pattern as Ca. However, N was higher in Campus (85.8) followed by
Crucitas (85.1), Cascajoso (68.3), and Bosque Escuela (18.3). The P was higher in Campus and Crucitas (4.0) followed by Cascajoso
(3.4) and Bosque Escuela (1.4). On an annual basis for all sites, the order of nutrient deposition through leaf litter was
Ca > N> K > Mg > P, whereas on site basis of total nutrient deposition (Ca + N + K + Mg + P), the order was Cascajoso > Campus > Crucitas > Bosque
Escuela. Ca, K, Mg, N, and P nutrient use efficiency values in leaf litter were higher in Bosque Escuela, while lower figures
were acquired in Cascajoso and Crucitas sites. It seems that the highest litterfall deposition was found in the ecotone of
a Quercus spp. forest and the Tamaulipan thornscrub; however, the Tamaulipan thornscrub vegetation alone had better leaf litter nutrient
return. 相似文献
8.
Total Belowground Carbon Allocation in a Fast-growing Eucalyptus Plantation Estimated Using a Carbon Balance Approach 总被引:4,自引:0,他引:4
Trees allocate a large portion of gross primary production belowground for the production and maintenance of roots and mycorrhizae.
The difficulty of directly measuring total belowground carbon allocation (TBCA) has limited our understanding of belowground
carbon (C) cycling and the factors that control this important flux. We measured TBCA over 4 years using a conservation of
mass, C balance approach in replicate stands of fast growing Eucalyptus saligna Smith with different nutrition management and tree density treatments. We measured TBCA as surface carbon dioxide (CO2) efflux (“soil” respiration) minus C inputs from aboveground litter plus the change in C stored in roots, litter, and soil.
We evaluated this C balance approach to measuring TBCA by examining (a) the variance in TBCA across replicate plots; (b) cumulative
error associated with summing components to arrive at our estimates of TBCA; (c) potential sources of error in the techniques
and assumptions; (d) the magnitude of changes in C stored in soil, litter, and roots compared to TBCA; and (e) the sensitivity
of our measures of TBCA to differences in nutrient availability, tree density, and forest age. The C balance method gave precise
estimates of TBCA and reflected differences in belowground allocation expected with manipulations of fertility and tree density.
Across treatments, TBCA averaged 1.88 kg C m−2 y−1 and was 18% higher in plots planted with 104 trees/ha compared to plots planted with 1111 trees/ha. TBCA was 12% lower (but not significantly so) in fertilized plots.
For all treatments, TBCA declined linearly with stand age. The coefficient of variation (CV) for TBCA for replicate plots
averaged 17%. Averaged across treatments and years, annual changes in C stored in soil, the litter layer, and coarse roots
(−0.01, 0.06, and 0.21 kg C m−2 y−1, respectively) were small compared with surface CO2 efflux (2.03 kg C m−2 y−1), aboveground litterfall (0.42 kg C m−2 y−1), and our estimated TBCA (1.88 kg C m−2 y−1). Based on studies from similar sites, estimates of losses of C through leaching, erosion, or storage of C in deep soil were
less than 1% of annual TBCA.
Received 6 March 2001; accepted 7 January 2002. 相似文献
9.
Parasitic plants are increasingly becoming the focus of research in many ecosystems. They have been shown to alter litterfall properties and decomposition rates in environments where they occur. Despite this recognition, the role of mistletoes in nutrient cycling in semi-arid savanna remains poorly understood. We investigated the litter input, element returns, and associated below-canopy soil nutrient concentrations of three mistletoe species (Erianthemum ngamicum, Plicosepalus kalachariensis, and Viscum verrucosum) that parasitize Acacia karroo trees in a semi-arid savanna, southwest Zimbabwe. Element concentrations in mistletoe leaf litter were enriched relative to the host. Litterfall from mistletoes significantly increased overall litterfall by up to 173 %, with E. ngamicum and P. kalachariensis having greater litterfall than their host trees. Associated with these changes in litterfall was an increase in element returns and the below-canopy soil nutrient concentrations. The increase in nutrient returns was due to both the effect of enriched mistletoe litter and increased volumes of litterfall beneath host trees. Litterfall, element returns, and the below-canopy soil nutrient concentrations were significantly influenced by mistletoe density, with higher values at high mistletoe density. Overall, E. ngamicum and P. kalachariensis had greater influence on litterfall, element returns, and soil nutrient concentrations than V. verrucosum. These findings are consistent with current understanding of enhanced nutrient cycling in the presence of parasitic plants particularly in nutrient-poor ecosystems. We conclude that the introduction of nutrients and associated increase in resource heterogeneity play an important role in determining ecosystem structure and function in semi-arid savannas. 相似文献
10.
Soil Nutrients Limit Fine Litter Production and Tree Growth in Mature Lowland Forest of Southwestern Borneo 总被引:1,自引:0,他引:1
Efforts to improve models of terrestrial productivity and to understand the function of tropical forests in global carbon
cycles require a mechanistic understanding of spatial variation in aboveground net primary productivity (ANPP) across tropical
landscapes. To help derive such an understanding for Borneo, we monitored aboveground fine litterfall, woody biomass increment
and ANPP (their sum) in mature forest over 29 months across a soil nutrient gradient in southwestern Kalimantan. In 30 (0.07 ha)
plots stratified throughout the watershed (∼340 ha, 8–190 m a.s.l.), we measured productivity and tested its relationship
with 27 soil parameters. ANPP across the study area was among the highest reported for mature lowland tropical forests. Aboveground
fine litterfall ranged from 5.1 to 11.0 Mg ha−1 year−1 and averaged 7.7 ± 0.4 (mean ± 95 C.I.). Woody biomass increment ranged from 5.8 to 23.6 Mg ha−1 year−1 and averaged 12.0 ± 2.0. Growth of large trees (≥60 cm dbh) contributed 38–82% of plot-wide biomass increment and explained
92% of variation among plots. ANPP, the sum of these parameters, ranged from 11.1 to 32.3 Mg ha−1 year−1 and averaged 19.7 ± 2.2. ANPP was weakly related to fine litterfall (r
2 = 0.176), but strongly related to growth of large trees at least 60 cm dbh (r
2 = 0.848). Adjusted ANPP after accounting for apparent “mature forest bias” in our sampling method was 17.5 ± 1.2 Mg ha−1 year−1.Relating productivity measures to soil parameters showed that spatial patterning in productivity was significantly related
to soil nutrients, especially phosphorus (P). Fine litterfall increased strongly with extractable P (r
2 = 0.646), but reached an asymptote at moderate P levels, whereas biomass increment (r
2 = 0.473) and ANPP (r
2 = 0.603) increased linearly across the gradient. Biomass increment of large trees was more frequently and strongly related to
nutrients than small trees, suggesting size dependency of tree growth on nutrients. Multiple linear regression confirmed the
leading importance of soil P, and identified Ca as a potential co-limiting factor. Our findings strongly suggest that (1)
soil nutrients, especially P, limit aboveground productivity in lowland Bornean forests, and (2) these forests play an important,
but changing role in carbon cycles, as canopy tree logging alters these terrestrial carbon sinks.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
11.
We compared the abundance of litter categories (coarse particulate organic matter 1–16 mm, leaves >16 mm, and small woody
detritus 16–100 mm) and macroinvertebrate assemblages between natural litter patches in pools and riffles in a headwater stream.
Litter patches in pools were formed under conditions of almost no current (<6 cm s−1), but in riffles they were formed under variable current velocities (13–89 cm s−1). Although the abundance of each litter category exhibited seasonal change, leaves were more abundant in riffles, and coarse
particulate organic matter and small woody detritus were more abundant in pools throughout the study period. Macroinvertebrate
assemblages in pools and riffles also changed seasonally but distinctly differed from each other. Shredders, collector-gatherers,
and predators were the dominant functional groups in abundance in both pools and riffles, but the dominant shredders were
caddisflies in pools and stoneflies in riffles. It is considered that the hydraulic conditions affected macroinvertebrate
assemblages directly and indirectly through influences on the characteristics of litter retained in the patches. Our results
suggest that the relative abundance of litter patches in pools and riffles largely affects the macroinvertebrate community
structure of the headwater stream.
Received: July 19, 2001 / Accepted: December 19, 2001 相似文献
12.
Culm recruitment, standing crop biomass, net production and carbon flux were estimated in mature (5 years after last harvest)
and recently harvested bamboo (Dendrocalamus strictus (Roxb.) Nees) savanna sites in the dry tropics. During the 2 study years bamboo shoot recruitment was 1711–3182 and 1432–1510
shoots ha−1 in harvested and mature sites, respectively. Corresponding shoot mortality was 66–93% and 62–69%, respectively. Total biomass
was 34.9 t ha−1 at the harvested site and 47.4 t ha−1 at the mature site. Harvesting increased the relative contribution of belowground bamboo biomass. Annual litter input to
soil was 2.7 and 5.9 t ha−1 year−1 at the harvested and mature sites, respectively. The bulk of the annual litterfall (78–88%) occurred in the cool dry season
(November to February). The mean litter mass on the savanna floor ranged from 3.1 to 3.3 t ha−1; at the harvested site wood litter contributed 70% of the litter mass and at the mature site leaves formed 77% of the litter
mass. The mean total net production (TNP) for the two annual cycles was 15.8 t ha−1 year−1 at the harvested site and 19.3 t ha−1 year−1 at the mature site. Nearly half (46–57%) of the TNP was allocated to the belowground parts. Short lived components (leaves
and fine roots) contributed about four-fifths of the net production of bamboo. Total carbon storage in the system was 64.4
t ha−1 at the harvested site and 75.4 t ha−1 at the mature site, of which 23–28% was distributed in vegetation, 2% in litter and 70–75% in soil. Annual net carbon deposition
was 6.3 and 8.7 t ha−1 year−1 at harvested and mature sites, respectively. 相似文献
13.
Invasion by a Perennial Herb Increases Decomposition Rate and Alters Nutrient Availability in Warm Temperate Lowland Forest Remnants 总被引:3,自引:0,他引:3
Rachel J. Standish Peter A. Williams Alastair W. Robertson Neal A. Scott Duncan I. Hedderley 《Biological invasions》2004,6(1):71-81
We determined the impact of the invasive herb, Tradescantia fluminensis Vell., on litter decomposition and nutrient availability in a remnant of New Zealand lowland podocarp–broadleaf forest. Using
litter bags, we found that litter beneath mats of Tradescantia decomposed at almost twice the rate of litter placed outside the mat. Values of k (decomposition quotient) were 9.44±0.42 yrs for litter placed beneath Tradescantia and 5.42±0.42 yrs for litter placed in native, non-Tradescantia plots. The impact of Tradescantia on decomposition was evident through the smaller forest floor mass in Tradescantia plots (2.65±1.05 t ha−1) compared with non-Tradescantia plots (5.05±1.05 t ha−1), despite similar quantities of annual leaf litterfall into Tradescantia plots (6.85±0.85 t ha−1 yr−1) and non-Tradescantia plots (7.45±1.05 t ha−1 yr−1). Moreover, there was increased plant nitrate available, as captured on resin bags, in Tradescantia plots (25.77 ± 8.32 cmol(−)/kg resin) compared with non-Tradescantia plots (9.55±3.72 cmol(−)/kg resin). Finally, the annual nutrient uptake by Tradescantia represented a large proportion of nutrients in litterfall (41% N, 61% P, 23% Ca, 46% Mg and 83% K), exceeded the nutrient
content of the forest floor (except Ca), but was a small proportion of the topsoil nutrient pools. Taken together, our results
show that Tradescantia increases litter decomposition and alters nutrient availability, effects that could influence the long-term viability of
the majority of podocarp–broadleaf forest remnants affected with Tradescantia in New Zealand. These impacts are likely mostly due to Tradescantia's vegetation structure (i.e., tall, dense mats) and associated microclimate, compared with native ground covers.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
Checo Colón-Gaud Scot Peterson Matt R. Whiles Susan S. Kilham Karen R. Lips Cathy M. Pringle 《Hydrobiologia》2008,603(1):301-312
Allochthonous inputs of detritus represent an important energy source for streams in forested regions, but dynamics of these
materials are not well studied in neotropical headwater streams. As part of the tropical amphibian declines in streams (TADS)
project, we quantified benthic organic matter standing stocks and organic seston dynamics in four Panamanian headwater streams,
two with (pre-amphibian decline) and two without (post-decline) healthy amphibian assemblages. We also measured direct litterfall
and lateral litter inputs in two of these streams. Continuous litterfall and monthly benthic samples were collected for 1 year,
and seston was collected 1–3 times/month for 1 year at or near baseflow. Direct litterfall was similar between the two streams
examined, ranging from 934–1,137 g DM m−2 y−1. Lateral inputs were lower, ranging from 140–187 g DM m−1 y−1. Dead leaves (57–60%), wood (24–29%), and green leaves (8–9%) contributed most to inputs, and total inputs were generally
higher during the rainy season. Annual habitat-weighted benthic organic matter standing stocks ranged from 101–171 g AFDM
m−2 across the four study reaches, with ∼4 × higher values in pools compared to erosional habitats. Total benthic organic matter
(BOM) values did not change appreciably with season, but coarse particulate organic matter (CPOM, >1 mm) generally decreased
and very fine particulate organic matter (VFPOM, 1.6–250 μm) generally increased during the dry season. Average annual seston
concentrations ranged from 0.2–0.6 mg AFDM l−1 (fine seston, <754 μm >250 μm) and 2.0–4.7 mg AFDM l−1 (very fine, <250 μm >1.6 μm), with very fine particles composing 85–92% of total seston. Quality of fine seston particles
in the two reaches where tadpoles were present was significantly higher (lower C/N) than the two where tadpoles had been severely
reduced (P = 0.0028), suggesting that ongoing amphibian declines in this region are negatively influencing the quality of particles
exported from headwaters. Compared to forested streams in other regions, these systems receive relatively high amounts of
allochthonous litter inputs but have low in-stream storage.
Handling editor: J. Padisak 相似文献
15.
Past studies have focused primarily on the effects of invasive plants on litter decomposition at soil surfaces. In natural
ecosystems, however, considerable amounts of litter may be at aerial and belowground positions. This study was designed to
examine the effects of Spartina
alterniflora invasion on the pool sizes and decomposition of aerial, surficial, and belowground litter in coastal marshlands, the Yangtze
Estuary, which were originally occupied by two native species, Scirpus mariqueter and Phragmites australis. We collected aerial and surficial litter of the three species once a month and belowground litter once every 2 months. We
used the litterbag method to quantify litter decomposition at the aerial, surficial and belowground positions for the three
species. Yearly averaged litter mass in the Spartina stands was 1.99 kg m−2; this was 250 and 22.8% higher than that in the Scirpus (0.57 kg m−2) and Phragmites (1.62 kg m−2) stands, respectively. The litter in the Spartina stands was primarily distributed in the air (45%) and belowground (48%), while Scirpus and Phragmites litter was mainly allocated to belowground positions (85 and 59%, respectively). The averaged decomposition rates of aerial,
surficial, and belowground litter were 0.82, 1.83, and 1.27 year−1 for Spartina, respectively; these were 52, 62 and 69% of those for Scirpus litter at corresponding positions and 158, 144 and 78% of those for Phragmites litter, respectively. The differences in decomposition rates between Spartina and the two native species were largely due to differences in litter quality among the three species, particularly for the
belowground litter. The absolute amount of nitrogen increased during the decomposition of Spartina stem, sheath and root litter, while the amount of nitrogen in Scirpus and Phragmites litter declined during decomposition for all tissue types. Our results suggest that Spartina invasion altered the carbon and nitrogen cycling in the coastal marshlands of China. 相似文献
16.
We investigated the influence of the exotic nitrogen-fixing black locust (Robinia pseudoacacia) on nitrogen cycling in a pitch pine (Pinus rigida) −scrub oak (Quercus ilicifolia, Q. prinoides) ecosystem. Within paired pine-oak and adjacent black locust stands that were the result of a 20-35 year-old invasion, we
evaluated soil nutrient contents, soil nitrogen transformation rates, and annual litterfall biomass and nitrogen concentrations.
In the A horizon, black locust soils had 1.3-3.2 times greater nitrogen concentration relative to soils within pine-oak stands.
Black locust soils also had elevated levels of P and Ca, net nitrification rates and total net N-mineralization rates. Net
nitrification rates were 25-120 times greater in black locust than in pine-oak stands. Elevated net N-mineralization rates
in black locust stands were associated with an abundance of high nitrogen, low lignin leaf litter, with 86 kg N ha–1 yr–1 in leaf litter returned compared with 19 kg N ha–1 yr–1 in pine-oak stands. This difference resulted from a two-fold greater litterfall mass combined with increased litter nitrogen
concentration in black locust stands (1.1% and 2.6% N for scrub oak and black locust litter, respectively). Thus, black locust
supplements soil nitrogen pools, increases nitrogen return in litterfall, and enhances soil nitrogen mineralization rates
when it invades nutrient poor, pine-oak ecosystems.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
17.
In a declining sugar maple (SM) stand, we tested the hypothesis that an increasing relative abundance of American beech (AB)
and yellow birch (YB) would improve litter quality by providing a higher proportion of litterfall richer in base cations and
lower in acidity. From 1989 to 2006, SM leaf fall diminished from 59% (1,718 kg ha−1 year−1) to 36% (915 kg ha−1 year−1) of the total leaf fall biomass. Overall, the increase in AB and YB litterfall compensated for the SM decrease, resulting
in constant annual leaf litterfall fluxes (2,803 kg ha−1 year−1) over the period studied. However, because the leaf litter for AB and YB had Ca and Mg concentrations 2–3 times higher than
did SM, Ca and Mg concentrations and fluxes in leaf litterfall significantly increased between 1989 and 2006. Leaf litterfall
of AB and YB also has a higher base/acid ratio than SM. Consequently, changes in forest composition following SM decline led
to a clear improvement in litterfall quality in terms of base cations content and fluxes and acid–base properties. 相似文献
18.
The role of phytophagous insects in ecosystem nutrient cycling remains poorly understood. By altering the flow of litterfall nutrients from the canopy to the forest floor, herbivores may influence key ecosystem processes. We manipulated levels of herbivory in a lower montane tropical rainforest of Puerto Rico using the common herbivore, Lamponius portoricensis (Phasmatidea), on a prevalent understory plant, Piper glabrescens (Piperaceae), and measured the effects on nutrient input to the forest floor and on rates of litter decomposition. Four treatment levels of herbivory generated a full range of leaf area removal, from plants experiencing no herbivory to plants that were completely defoliated (>4,000 cm2 leaf area removed during the 76-day study duration). A significant (P<0.05) positive regression was found between all measures of herbivory (total leaf area removed, greenfall production, and frass-related inputs) and the concentration of NO
3
−
in ion exchange resin bags located in the litter layer. No significant relationship was found between any of the herbivory components and resin bag concentrations of NH
4
+
or PO
4
−
. Rates of litter decay were significantly affected by frass-related herbivore inputs. A marginally significant negative relationship was also found between the litter mass remaining at 47 days and total leaf area removed. This study demonstrated a modest, but direct relationship between herbivory and both litter decomposition and NO
3
−
transfer to the forest floor. These results suggest that insect herbivores can influence forest floor nutrient dynamics and thus merit further consideration in discussions on ecosystem nutrient dynamics. 相似文献
19.
Salix gracilistyla is one of the dominant plants in the riparian vegetation of the upper-middle reaches of rivers in western Japan. This species
colonizes mainly sandy habitats, where soil nutrient levels are low, but shows high potential for production. We hypothesized
that S.␣gracilistyla uses nutrients conservatively within stands, showing a high resorption efficiency during leaf senescence. To test this hypothesis,
we examined seasonal changes in nitrogen (N) and phosphorus (P) concentrations in aboveground organs of S. gracilistyla stands on a fluvial bar in the Ohtagawa River, western Japan. The concentrations in leaves decreased from April to May as
leaves expanded. Thereafter, the concentrations showed little fluctuation until September. They declined considerably in autumn,
possibly owing to nutrient resorption. We converted the nutrient concentrations in each organ to nutrient amounts per stand
area on the basis of the biomass of each organ. The resorption efficiency of N and P in leaves during senescence were estimated
to be 44 and 46%, respectively. Annual net increments of N and P in aboveground organs, calculated by adding the amounts in
inflorescences and leaf litter to the annual increments in perennial organs, were estimated to be 9.9 g and 0.83 g m−2 year−1, respectively. The amounts released in leaf litter were 6.7 g N and 0.44 g P m−2. These values are comparable to or larger than those of other deciduous trees. We conclude that S. gracilistyla stands acquire large amounts of nutrients and release a large proportion in leaf litter. 相似文献
20.
Pools and fluxes of carbon in three Norway spruce ecosystems along a climatic gradient in Sweden 总被引:1,自引:0,他引:1
Dan Berggren Kleja Magnus Svensson Hooshang Majdi Per-Erik Jansson Ola Langvall Bo Bergkvist Maj-Britt Johansson Per Weslien Laimi Truus Anders Lindroth Göran I. Ågren 《Biogeochemistry》2008,89(1):7-25
This paper presents an integrated analysis of organic carbon (C) pools in soils and vegetation, within-ecosystem fluxes and
net ecosystem exchange (NEE) in three 40-year old Norway spruce stands along a north-south climatic gradient in Sweden, measured
2001–2004. A process-orientated ecosystem model (CoupModel), previously parameterised on a regional dataset, was used for
the analysis. Pools of soil organic carbon (SOC) and tree growth rates were highest at the southernmost site (1.6 and 2.0-fold,
respectively). Tree litter production (litterfall and root litter) was also highest in the south, with about half coming from
fine roots (<1 mm) at all sites. However, when the litter input from the forest floor vegetation was included, the difference
in total litter input rate between the sites almost disappeared (190–233 g C m−2 year−1). We propose that a higher N deposition and N availability in the south result in a slower turnover of soil organic matter
than in the north. This effect seems to overshadow the effect of temperature. At the southern site, 19% of the total litter
input to the O horizon was leached to the mineral soil as dissolved organic carbon, while at the two northern sites the corresponding
figure was approx. 9%. The CoupModel accurately described general C cycling behaviour in these ecosystems, reproducing the
differences between north and south. The simulated changes in SOC pools during the measurement period were small, ranging
from −8 g C m−2 year−1 in the north to +9 g C m−2 year−1 in the south. In contrast, NEE and tree growth measurements at the northernmost site suggest that the soil lost about 90 g C m−2 year−1.
An erratum to this article can be found at 相似文献