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Zorluk: ZorEcological Functions, Nutrient Cycles and Ecological Succession

Consider the following statements regarding ecological succession and biogeochemical nutrient cycles:

1. Hydrarch succession occurs in aquatic environments and progresses from hydric conditions towards mesic conditions.
2. Biological nitrogen fixation by *Rhizobium* directly converts atmospheric nitrogen (N2N_2) into nitrate (NO3−NO_3^-) in a single enzymatic step.
3. In xerarch succession on bare rocks, lichens serve as pioneer species by secreting organic acids that accelerate rock weathering and initiate soil formation.

Which of the statements given above are correct?

  1. A
    1 and 2 only
  2. 1 and 3 onlyCevap
  3. C
    2 and 3 only
  4. D
    1, 2 and 3

Cevap

Statements 1 and 3 are correct
The correct answer includes Statements 1 and 3. Hydrarch succession originates in aquatic habitats and moves towards a balanced mesic state. Lichens initiate xerarch succession on rocks via acid secretion and weathering. Statement 2 is false because biological nitrogen fixation yields ammonia (NH3NH_3/NH4+NH_4^+), which must undergo nitrification by *Nitrosomonas* and *Nitrobacter* to become nitrate (NO3−NO_3^-).

Adım Adım Çözüm

1
Evaluate Statement 1 regarding hydrarch succession
Statement 1 is correct. Ecological succession starting in water bodies (hydrarch) proceeds from hydric conditions (wet environment) to mesic conditions (medium moisture environment), culminating in a climax forest community.
Both hydrarch and xerarch successions naturally lead to medium water (mesic) conditions regardless of the starting environment.
2
Evaluate Statement 2 regarding nitrogen cycle pathways
Statement 2 is incorrect. Nitrogenase enzymes in symbiotic nitrogen fixers like *Rhizobium* convert atmospheric dinitrogen (N2N_2) into ammonia (NH3NH_3) or ammonium (NH4+NH_4^+), not nitrate (NO3−NO_3^-). Nitrification by nitrifying bacteria (*Nitrosomonas* converting ammonia to nitrite, and *Nitrobacter* converting nitrite to nitrate) is required subsequently to form nitrate.
Direct conversion of N2N_2 to NO3−NO_3^- in a single step does not occur during biological nitrogen fixation.
3
Evaluate Statement 3 regarding xerarch pioneer species
Statement 3 is correct. Crustose lichens are pioneer species on bare rock (xerarch succession). They produce carbonic and organic acids that erode rock surfaces, capturing dust particles to build up thin soil layers for bryophytes.
Chemical weathering induced by lichens is essential for soil formation on bare rocky substrates.

Anahtar Kavram

Mechanisms of Ecological Succession (Hydrarch/Xerarch) and Nitrogen Cycle Steps
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Konular

Ecological Functions, Nutrient Cycles and Ecological Succession