Question

1. What is a lotic aquatic system? Describe the conditions (i.e. nutrients, light, etc.) and the microbial communities characteristic of these systems. (5 marks)
2. Describe the interaction between Rhizobium and plants.

Answer 1

Lotic aquatic system is one of the division of fresh water habitat. In different term lotic system contains flowing or running water having flow velocity ranges from 0.1-1 m/s and water residency of 2 weeks.

It is characterised by stream orders depending on the origin and flow as well as on the type of stream pattern (Ractangular , parallele, radial etc) which ultimately determines the flooding and soil erosion hazards of the region.

Conditions:

• Light, Temperature: The penetration of light is strongly influenced by turbidity. If water is clear , adequet light reach to the substrate and photosynthesis can take place. There is no stratification due ti the temperature. temperature follows the air temperatue .
• Dissolved gases: Oxygen is the most abundant and important dissolved gas in lotic water.The concentration is high due to tubulance and mixing of the water. The CO2 content is tend to be scarce due to contact with air and turbulance.
• Microbial community: The plankton community is found same like in lentic system but due to high water current , plankton community is at the mercy of the current. Fishes are highly adopted and are distributed from surface to bottom due to high dissolved oxygen.

Relation between Rhizobium and plant:

Legume plants are able to form symbiotic relation with rhizobia ( a nitrogen fixing soil bacteria). With this relationship plant form nodules where this bacteria found their habitat and live , in turn of this bacteria fixes atmospheric nitrogen into ammonia which is further used by plant .