دانلود رایگان مقاله رشد باکتری و قارچ در بسترهای گیاهی در خاک مدیترانه

Abstract

Plant litter represents an important source of nutrients and energy for soil microorganisms, but will also selectively affect which organism group, fungi or bacteria, that will be favoured during decomposition. The balance of fungal to bacterial growth will furthermore be affected by soil chemistry like pH. A laboratory experiment was carried out using two different Mediterranean forest soils differing in pH, adding five types of litter varying in C/N ratio from 15 to 75, including the major litter type from the two soils. Growth of bacteria (using the leucine incorporation technique) and fungi (using the acetate into ergosterol incorporation technique) was then followed during 6 weeks. The balance of fungal to bacterial growth was positively affected by litter with increasing C/N ratio, while the C availability, as judged by evolved CO2, did not have any influence. Furthermore, low pH in the soil further favoured fungal growth, irrespective of the litter type. Despite differences in fungal to bacterial growth this appeared to have little influence on respiration rates from the added litter, suggesting functional redundancy. Our results highlight how both initial soil conditions (pH) and litter composition (C/N ratio) independently affects fungal and bacterial growth during decomposition.

4.3. Concluding remarks

Our research used tracer based techniques to study soil microbial growth during microbial utilization of forest litters added to soil. By combining different litters and different soils it was possible to entangle the effect of soil pH and the effect of C/N ratio on the balance of fungal to bacterial growth, suggesting that the variation in carbon availability between litter types appeared negligible in this respect. The approach has earlier also shown the importance of the concentration of substrate added to soil on the balance of fungal to bacterial growth, both easily available (glucose; Reischke et al., 2014) and more difficult to decompose (high C/N rich plant material; Barreiro et al., 2016). It can easily be adapted to include other factors of presumed importance for litter decomposition in soil, like mineral nutrients and redox state, as well as litter effects, like degree of fragmentation. For example, the especially high fungal to bacterial growth ratio for turkey oak litter in the beech forest could not be explained by C/N ratio of litter and soil pH, but this may be due to the low pH of turkey oak litter that additionally disfavouring bacterial growth, especially in a low pH soil. Thus, the specific effect of pH of litter types, and its interaction with soil pH, on the balance of fungal to bacterial growth could be worth pursuing.