In ecosystem ecology, nutrient cycling, energetic functions, and ecological succession dic… — State PSC Exam

In ecosystem ecology, nutrient cycling, energetic functions, and ecological succession dictate community dynamics over time. Which of the following statements regarding ecological functions, biogeochemical cycles, and ecological succession are correct?

The phosphorus cycle is a sedimentary biogeochemical cycle where rock weathering serves as the primary reservoir pool, lacking a significant atmospheric gaseous phase.Cevap
As ecological succession progresses from pioneer stages to a mature climax ecosystem, the ratio of total community biomass to gross primary productivity ( $\frac{B}{P}$ ) increases while Net Community Productivity ( $NCP$ ) decreases toward zero.Cevap
C
Biological nitrogen fixation by free-living aerobic soil bacteria such as *Azotobacter* converts atmospheric nitrogen ( $N_2$ ) directly into nitrate ions ( $NO_3^-$ ) without producing ammonia ( $NH_3$ ) or ammonium ( $NH_4^+$ ) intermediates.
D
In primary hydrarch succession of an aquatic body, submerged aquatic vegetation is succeeded directly by the terrestrial scrub stage, bypassing the reed-swamp and marsh-meadow seral stages.

Cevap

The statements confirming that the phosphorus cycle is a sedimentary cycle relying on rock weathering without a major atmospheric component, and that ecological succession leads to an increased total biomass to gross productivity ratio (B/P) while net community productivity (NCP) approaches zero, are correct.

The phosphorus cycle is a classic sedimentary cycle driven by rock weathering rather than atmospheric gaseous exchange. Furthermore, Odum's model of ecosystem succession dictates that mature climax communities maximize biomass per unit energy flow (increasing the B/P ratio) while community respiration rises to equal gross primary production, causing net community productivity to approach zero.

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Analyze the nature and reservoir pools of the phosphorus cycle.

Phosphorus is a sedimentary cycle with lithospheric reservoir pools (rocks and minerals) and negligible atmospheric gaseous phase.

Unlike gaseous cycles (carbon, nitrogen) whose main reservoir is the atmosphere or hydrosphere, sedimentary cycles retain their main reservoir in Earth's crust.

Analyze ecosystem energetics and biomass parameters during ecological succession.

As succession moves from pioneer to climax stages, total community biomass (

B

) accumulates relative to gross production (

P

), increasing the

\frac{B}{P}

ratio, while community respiration (

R

) increases to balance

GPP

, lowering

NCP = GPP - R

toward zero.

Mature ecosystems maintain high maintenance structure (biomass) with balanced energy income and energy expenditure.

Evaluate the biochemical pathway of biological nitrogen fixation.

Nitrogenase reduces

N_2

NH_3

NH_4^+

, not directly to

NO_3^-

. Nitrification by *Nitrosomonas* and *Nitrobacter* is required subsequently for nitrate formation.

Direct conversion of atmospheric nitrogen to nitrate in a single biological step by *Azotobacter* is biochemically inaccurate.

Evaluate the sequence of seral stages in hydrarch ecological succession.

The correct sequence requires reed-swamp and marsh-meadow stages between floating/submerged vegetation and scrub/forest stages.

Reed-swamp and marsh-meadow plants accumulate organic matter and silt necessary to transition an aquatic environment into semi-terrestrial land before woody shrubs can establish.

Anahtar Kavram

Biogeochemical cycle classifications, biochemical steps of nitrogen fixation, and bioenergetic changes across ecological succession seral stages.

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