Patterns Of Nutrient Cycling Research Articles

Insect Herbivore Relationship to the State of the Host Plant: Biotic Regulation of Ecosystem Nutrient Cycling through Ecological Succession

This paper provides a conceptual framework for increasing our understanding of the relationships between plant resistance to insect herbivores and insect herbivore influences on ecosystem nutrient cycling and succession. For a given plant species, adequate nutrient/light availability favors establishment and productivity; small insect herbivore populations regulated by plant biochemistry stimulate primary productivity and short-term nutrient cycling. As biomass and competition for nutrients and light increase during succession, plants become stressed as they approach their tolerance limits. Earlier successional plant species initially dominating the plant community have higher nutrient/light requirements and become stressed sooner than later successional plant species. Abundance and stress make the earlier plant species more apparent and susceptible, than later plant species, to insect herbivores. Insect herbivore populations increasing rapidly on stressed hosts tend to regulate long-term nutrient cycling patterns by accelerating changes in competitive relationships between plant species with different nutrient/light requirements.

Natural Disturbance and the Steady State in High-Altitude Balsam Fir Forests

Wind-induced, cyclic waves of death, regeneration, and maturation constantly move through the high-altitude balsam fir forests in the northeastern United States. Biomass and productivity relations, species diversity, and nutrient cycling patterns are closely tied to this cycle of disturbance. Disturbance is thus an integral part of the long-term maintenance of this ecosystem. Since forests of this type normally include all phases of the disturbance-regeneration cycle, they may constitute a steady-state ecosystem in equilibrium with the surrounding environment.

Influence of Amphibian Larvae on Primary Production, Nutrient Flux, and Competition in a Pond Ecosystem

In a pond ecosystem near St. Louis, Missouri, natural variations in tadpole biomass during 1971—1972 were accompanied by shifts in patterns of nutrient cycling and primary production, particularly when metamorphoses caused abrupt removal of these transient consumers. In the field, increased tadpole biomass was associated with: (1) reduced standing crop of suspended particles, including phytoplankton, the tadpoles' major food source; (2) a shift in the state of nitrogen from largely particulate to largely dissolved; (3) reduced rates of primary production, from both H14CO3 uptake and diurnal oxygen methods; (4) a nonliner effect on phytoplankton specific growth rates; (5) a shift in phytoplankton community structure away from filamentous blue—green algae; and (6) a reduced proportion of active chlorophyll @a in the photosynthetic pigments of phytoplankton. From laboratory experiments, the potential impact of tadpoles on nitrogen flux, through feeding and nutrient release, was estimated. Several conclusions were made: (1) Suspensions feeding by tadpoles reduced concentrations of suspended particles. Under conditions of low particles: high tadpoles, the specific growth rates of tadpoles reduced. Recruitment was absent except under conditions of high particles: low tadpoles; the most diverse community of new tadpole recruits (four species) was observed under such conditions. All four species (three genera) had similarly sized particles in their guts. These field observations are consistent with an hypothesis of competition among the tadpoles. (2) Tadpoles apparently were regulatory consumers; they became a large component with respect to phytoplankton. Nitrogen flux through tadpoles was within the same order of magnitude, and sometimes exceeded the estimated N uptake by phytoplankton. (3) Tadpoles probably regulated primary production by both reducing standing crop and altering specific growth rates of algae. At maximum tadpole biomass, suspended particle concentrations were stabilized near the laboratory—determined threshold concentration for feeding by these Rana tadpoles. When metamorphosis removed these transient consumers, rates of primary production increased dramatically. (4) Interactions within the pond ecosystem apparently determined aquatic—terrestrial nutrient balances for the amphibian communities. Some species deposited more nutrient in their eggs than was assimilated by larvae, but the community as a whole extracted nutrient from the ecosystem. Nutrient input in eggs was much less than that assimilated by autotrophs.

Litter decomposition and Ectomycorrhiza in Amazonian forests. 1. A comparison of litter decomposing and ectomycorrhizal Basidiomycetes in latosol-terra-firme rain forest and white podzol campinarana

Abstract Application of a mycosociological method (adaptation of the Lange method) in Central Amazonia produced the following results: In the white-sand podzol campinarana type of forests the dominant trees are obligatorily ectotrophically mycorrhizal; litter is accumulated as raw humus as a consequence of ectotroph dominance; fewer leaf inhabiting litter fungi occur in the dry as well as the wet seasons than are counted in the latosol terra-firme rain forest, and the fungi of that category are most strongly represented ("F-dominance") by other species here than in the terra-firme stands tested. The ectomycorrhizal trees and fungi are enumerated. On the other hand, in the terra-firme forest, ectotrophically mycorrhizal fungi did not occur in the test plots. The trees are almost all non-ectomycorrhizal in primary terra-firme forest; here, litter does not appreciably accumulate as a deep raw humus layer because the considerably higher number of leaf inhabiting litter fungi (ratios of 4:1 to 4.2:1 in favor cf terra-firme) and greater diversification (a larger number of species) is potentially capable of reducing more than the yearly leaf-fall. In this study, a group of fungi was mainly considered which is not represented in laboratory litter decomposition experiments. However, a comparison with unpublished and published data shows that our results satisfactorily match the experimental and phyto-sociological data obtained both with other classes of microorganisms and with observations in other regions. The quantity of litter decomposing fungi in the foliicolous group depends mainly on the amount of precipitation during the last few days before counting. This does not hold for all lignicolous fungi. The reasons for this as well as the mechanisms by which the ectomycorrhizas may reduce litter decomposition rates and influence the nutrient cycling patterns are discussed. The most important genera of Basidiomycetes involved in litter decomposition in the Lower Rio Negro forest associations are enumerated. Possible economic significance of introducing ectotrophs in the terra-firme forest is indicated.

Organic matter and nutrient dynamics of the forest and forest floor in the Hubbard Brook forest.

The forest floor is a major reservoir of organic matter and nutrients for the ecosystem and as such it influences or regulates most of the functional processes occurring throughout the ecosystem. This study reports on the nutrient and organic matter content of the forest floor of the Hubbard Brook Experimental Forest during different seasons and attempts to correlate results from studies of vegetation, litter, decomposition, stemflow, throughfall, and soil. An organic matter budget is presented for an undisturbed watershed.Average weight of the forest floor on an undisturbed watershed ranged from 25,500 to 85,500 kg/ha. The weighted watershed average was 46,800 kg/ha. Although the F and H horizons did not vary significantly with time, the L horizon increased significantly during the period June to August largely as a result of a severe hail storm. The order of abundance of elements in the forest floor was Nτ;Ca≷Fe>S>P>Mn>K>Mg>Na>Zn>Cu. The concentrations of Ca, K, and Mn decreased with depth in the forest floor while N, P, S, Na, Fe, Zn, and Cu concentrations increased. N:P ratios were similar in decomposing leaf tissue, the forest floor, litterfall, and net stemflow plus throughfall suggesting a similar pattern of cycling. S was proportional to N and P in decomposing leaf tissue, the forest floor, and litterfall. Net stemflow and throughfall were affected by a relatively large input of SO4=-S from the atmosphere. Residence times for elements in the forest floor were affected by inputs other than litterfall (precipitation, stemflow, and throughfall). Calculation of residence times using all inputs caused smaller values than if litterfall alone was used. While all residence times were reduced, the major differences occurred for K, S, and Na. N and P showed relatively long residence times as a result of retranslocation and immobilization by decomposers. The slow turnover rate because of the strong demand and retention by all biota must account for the efficiency of the intrasystem cycling process for N and P. K showed the shortest residence time. A rapid and efficient uptake of K by vegetation seems to account for the efficient cycling of this element. The patterns of nutrient cycling are several depending on the chemical properties of the forest floor, and nutritional requirements of the biota.