دانلود رایگان مقاله اثرات منفی نیتروژن و آب اضافی بر خاک باکتریایی و جوامع قارچی

Abstract

Grasslands are important ecosystems and make up 40% of the terrestrial ecosystems worldwide. The Inner Mongolia steppe is the main grassland region of China, and nitrogen (N) and water availability are two importantfactors that limitthe productivity of these grasslands. We tested how N and water addition influence the composition of the microbial community in the soil using PLFA, and soil physical and chemical properties in two semiarid grassland sites in Inner Mongolia during two consecutive years. In both sites, a split-plot design was employed with two water treatments (natural precipitation, stimulated wet year precipitation) and three N treatments (0 kg N ha
1 , 25 kg N ha
1 , 50 kg N ha
1 ). Water addition greatly increased soil fungi and decreased bacteria while N had opposite effects. Water addition resulted in a significant increase in soil pH and electric conductivity. N addition did not lead to consistent changes in soil characteristics. Multivariate analysis showed that PLFA composition varied between all treatments but was mainly influenced by water addition. This study provides insight into how climatic changes such as alternations in rainfall and N deposition shape the soil microbial communities in Inner Mongolia steppes.

4. Discussion

This study shows that N and water addition can have opposite effects on soil bacterial and fungal communities. N addition significantly decreased the relative abundance of soil fungal PLFA, while water addition caused an increase. The opposite was true for bacterial PLFA that increased after N addition and decreased after long-term water addition. Water addition also caused an increase in soil pH and EC. Our study clearly shows that the effects of water and N addition are not simply additive. Moreover, an important result of this study is that the effects of water and N addition differed between the two sites, even though the experimental design was exactly the same and the sites were located only three kilometers apart. The multivariate analysis of the PLFA community showed that PLFA composition was explained mainly by soil pH and by the water treatment and not consistently by the N addition treatment.