In a detritus food chain, decomposition of detritus depends upon all, except

Options

A. Oxygen non-availability
B. Chemical composition of detritus
C. temperature and soil moisture
D. soil microbes

Answer

To solve the question regarding the detritus food chain and the factors affecting the decomposition of detritus, we will analyze each option provided in the question step by step.

### Step-by-Step Solution:

1. **Understanding Detritus Food Chain**:
- The detritus food chain begins with dead organic matter (detritus) and involves organisms that decompose this matter. Decomposers and detritivores play a crucial role in this process.

2. **Analyzing the Options**:
- We need to determine which option does not affect the decomposition of detritus.

3. **Option 1: Oxygen Non-availability**:
- Decomposition can occur in both aerobic (with oxygen) and anaerobic (without oxygen) conditions. However, the process is significantly slower in anaerobic conditions. Thus, while oxygen availability can influence the rate of decomposition, the absence of oxygen does not prevent decomposition entirely. This suggests that oxygen non-availability is not a critical factor for decomposition in the detritus food chain.

4. **Option 2: Chemical Composition of Detritus**:
- The chemical composition of detritus is vital for decomposition. Different types of organic matter decompose at different rates based on their chemical makeup. Therefore, this option is essential for decomposition.

5. **Option 3: Temperature and Soil Moisture**:
- Temperature and soil moisture are significant factors that influence the rate of decomposition. Higher temperatures generally increase microbial activity, while adequate soil moisture is necessary for the survival of decomposers. Hence, this option is also crucial for decomposition.

6. **Option 4: Soil Microbes**:
- Soil microbes, including bacteria and fungi, are fundamental to the decomposition process. They break down organic matter, making this option critical for decomposition.

7. **Conclusion**:
- Based on the analysis, the only factor that does not critically depend on decomposition in the detritus food chain is **Option 1: Oxygen Non-availability**. Therefore, the correct answer is **Option 1**.

### Final Answer:
**Option 1: Oxygen Non-availability**