Microsite Influences on Productivity and Nutrient Circulation Within Two Southeastern Floodplain Forests
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At broad spatial scales, floodplain forests of the southeastern USA are often perceived as either nutrient poor or nutrient rich. Perceived differences in nutrient availabilities between oligotrophic blackwater and eutrophic redwater floodplain forests suggest rates of aboveground net primary production (ANPP) are lower on the former. However, for these floodplain types, microsite variation may influence relationships between nutrient circulation and ANPP to a greater extent than landscape position and geomorphology of their associated watershed. Therefore, our objectives were to compare ANPP, nutrient circulation through litterfall and decomposition, and the microbial biomass among microsites that differed in terms of soils and hydrology within two riverine floodplain forests. The two floodplains used in this study were located along the Satilla River, a Coastal Plain blackwater system, and the Altamaha River, a Piedmont redwater system, both of which are located in southeastern Georgia. Microsite influences on ANPP were not significantly different during 1999 and 2000 for the Satilla (SAT) and Altamaha (ALT) floodplains. Litterfall production and patterns of P and Ca circulation on the SAT floodplain were significantly lower for the driest microsite type during both years. Microbial biomass N and P were also lowest for the driest microsite, especially in 2000. Overall, microsites on the SAT displayed greater variation in P and Ca cycling than did those of the ALT. Litterfall production, nutrient circulation in litterfall and decomposition, and the microbial biomass were similar among microsites of the ALT floodplain during both years. These findings suggest that spatial variability in nutrient cycling may be greater for oligotrophic floodplain forests.Keywords:
Microsite
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Nutrient cycle
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The knowledge on nutrient cycling through litter is important for the management of the species in agroforestry systems (SAFs), since the litter is an important way of making plant nutrients available to soil. The aim of this work was to evaluate the litterfall production and nutrient cycling of woody species in an agroforestry system of Caatinga. The study was developed in SAF belonging to Embrapa Goats and Sheep, located in the county of Sobral-CE, Brazil. The evaluated species were four native leguminous from Caatinga: Mimosa caesalpiniifolia (sabia), Mimosa tenuiflora (jurema-preta), Libidibia ferrea (juca) and Poncianella piramydalis (catingueira). To collect the litter, collectors were installed under the tree canopy, using six replicates for each species evaluated.
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The analysis of litter quantity, litter decomposition and its pattern of nutrient release is important for understanding nutrient cycling in forest ecosystems. Plant growth and maintenance are partly met through nutrient cycling (O'Connell & Sankaran 1997) which is dominated by litter production and decomposition. Litter fall is a major process for transferring nutrients from above-ground vegetation to soils (Vitousek & Sanford 1986), while decomposition of litter releases nutrients (Maclean & Wein 1978). The rate at which nutrients are recycled influences the net primary productivity of a forest. Knowledge of these processes from tropical rain forests is relatively poor (O'Connell & Sankaran 1997), and in particular there are no known published studies on nutrient cycling from lowland tropical forests in Papua New Guinea. The few studies from Papua New Guinea are confined to the mid-montane forest zone (Edwards 1977, Edwards & Grubb 1982, Enright 1979, Lawong et al. 1993).
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1. Natural conditions of floodplain forests. 2. Basic environmental factors. 3. Primary Production. 4. Some physiological processes in the ecosystem of a floodplain forest. 5. Secondary Production. 6. Decomposition. 7. Cycling of mineral nutrients. Plates. Index.
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Plant litter
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Floodplain forest species diversity is driven, in part, by variation in disturbance regime. Flood patterns create heterogeneity in microsite quality from small differences in elevation across a floodplain which, in turn, influence flood timing and duration. Differences in species’ regeneration niches in relation to hydrologic patterns can account for long-term coexistence of various species. In the past century floodplain forests have exhibited a wide range of changes in stand development and species composition as a result of altered hydrology in rivers and floodplains. I evaluated the role of regeneration in floodplain forest systems of the Lower Mississippi River Alluvial Valley to gain insight into the mechanisms behind compositional transitions. Specifically, I focused on how flood timing related to species-specific germination and first-year seedling survival patterns and processes.
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Abstract Litterfall is an important cause of damage and mortality to seedlings in many forest ecosystems. This study is the first to investigate the contribution of variable risk of litterfall damage to microsite heterogeneity. Two hundred artificial seedlings were ‘planted’ in the ground at 2‐m intervals along transects in each of two New Zealand forests, and all plant species with foliage directly above each artificial seedling were recorded. Additional artificial seedlings were planted on the ground underneath treeferns and on their trunks (epiphytically). The artificial seedlings were monitored monthly for damage over 2 years. Three overtopping species that cause litterfall damage, along with one species that impedes litterfall, produced different microsites with a hierarchy of litterfall damage risk to seedlings (2–30% per year). This risk differed significantly among microsites ( P < 0.0005). Seedlings differ in resilience to litterfall and, therefore, microsites with different litterfall risks provided the potential for regeneration niche differentiation. More seedlings were damaged beneath Cyathea dealbata (Cyatheaceae), which drops whole fronds, than on its trunks. The reverse was found for Dicksonia fibrosa (Dicksoniaceae) , which retains dead fronds as a ‘skirt’. We suggest that shedding whole fronds, or producing a skirt of fronds, are alternative ‘strategies’ that can reduce competition from terrestrial and epiphytic seedlings, respectively.
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Functional traits are useful for characterizing variation in community and ecosystem dynamics. Most advances in trait-based ecology to date centre on plant functional traits, although there is an increasing recognition that animal traits are also key contributors to processes operating at the community or ecosystem scale. Terrestrial invertebrates are incredibly diverse and ubiquitous animals with important roles in nutrient cycling. Despite their widespread influence on ecosystem processes, we currently lack a synthetic understanding of how invertebrate functional traits affect terrestrial nutrient cycling. We present a meta-analysis of 511 paired observations from 122 papers that examined how invertebrate functional traits affected litter decomposition rates, nitrogen pools and litter C:N ratios. Based on the available data, we specifically assessed the effects of feeding mode (bioturbation, detritus shredding, detritus grazing, leaf chewing, leaf piercing, ambush predators, active hunting predators) and body size (macro- and micro-invertebrates) on nutrient cycling. The effects of invertebrates on terrestrial nutrient cycling varied according to functional trait. The inclusion of both macro- (≥2 mm) and micro-invertebrates (<2 mm) increased litter decomposition by 20% and 19%, respectively. All detritivorous feeding modes enhanced litter decomposition rates, with bioturbators, detritus shredders and detritus grazers increasing decomposition by 28%, 22% and 15%, respectively. Neither herbivore feeding mode (e.g. leaf chewers and leaf piercers) nor predator hunting mode (ambush and active hunting) affected decomposition. We also revealed that bioturbators and detritus grazers increased soil nitrogen availability by 99% and 70%, respectively, and that leaf-chewing herbivores had a weak effect on litterfall stoichiometry via reducing C:N ratios by 11%. Although functional traits might be useful predictors of ecosystem processes, our findings suggest context-dependent effects of invertebrate traits on terrestrial nutrient cycling. Detritivore functional traits (i.e. bioturbators, detritus shredders and detritus grazers) are more consistent with increased rates of nutrient cycling, whereas our currently characterized predator and herbivore traits are less predictive. Future research is needed to identify, standardize and deliberately study the impacts of invertebrate functional traits on nutrient cycling in hopes of revealing the key functional traits governing ecosystem functioning worldwide.
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Biogeochemical cycling study of ecosystems and their functioning are fundamental for planning conservation practices and management of forest remnants in Brazil. The objective of the study was to characterize the leaf litterfall production rate and the nutrients release via decomposition in a fragment of Seasonal Semideciduous Forest, in Southern Brazil, in advanced stage of regeneration. For two years, evaluations of litterfall and leaf litter decomposition (using the mass loss method with litterbags) were performed monthly, as well as their nutrient content analysis. Annual input of leaf litterfall was 4,532.7 kg ha-1 of dry matter, which promoted, for the two-year period, a supply of 195.5, 9.2 and 55.3 kg ha-1 of N, P and K, respectively. The litter nutrients use efficiency followed the decreasing order P > K > N. The annual decomposition constant for leaf litter was 1.16, reaching a half-life at 215 days, making 84.4% N, 72.7% P and 92.9% K available at the decomposition end of two years. In the two years of collection, the largest deposition rate of litter occurred in the spring, with the highest peak in October, indicating a seasonal deposition behavior. The forest fragment presents high production of leaf litter (66% leaves) and input of N. The rapid decomposition of leaf litter contributes to the release of nutrients over time, N and K initially, and P in the long run. P is limited due to the high efficiency of its use.
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Abstract Studies were conducted near Manaus, Brazil in cooperation with INPA to try to establish how nutrient cycling influences the formation of black water and white water. The studies measured the rate of decay of Caryocar villosum leaves on spodosol and oxisol terrestrial and aquatic sites when the leaves were untreated, and treated with a bacteriostat, or insecticide or fungicide. It also measured litter, animal populations, and the elemental content of ten biologically important elements in soils and decomposing litter. Results show considerable differences in the rates of decay and the agents and end products of decay which indicate that black water and white water formation are closely tied to the rate and type of decay and to basic soil types and their associated vegetation, except for the rediments in white water.
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