The effects of land use and management on belowground carbon and nutrient interactions

Gan, Huei Ying GND

Carbon (C) turnover has been increasingly shown to be linked to the mineralization of other nutrients due to the co-limitation of these elements on microbial processes. Regional factors such as climate and parent materials, land use and management practices are important controls of soil nutrient and availabilities that potentially result in mineral soils with varied carbon-to-nutrient ratios. The main objectives of this thesis were to study the interactions between C and nutrients in the mineral soils using soil incubation and leaching techniques under controlled environments. To study the intensity of soil priming under different land uses and management, substrate-induced soil incubations were performed using 13C-labelled glucose solution. Overall, land use and management types were observed to affect the rates of CO2 production relative to nutrient release. As hypothesized, this was mainly due to the differences in soil C-to-nutrient ratios between these land use types, where higher ratios were observed in forests than grasslands. In contrast to expectations, CO2-to-N- and CO2-to-S-leaching ratios were significantly higher in grasslands than forests in all regions. This was mostly caused by significantly higher CO2 and significantly lower N and S leaching in grasslands than forests which might be due to higher microbial biomass at the grassland sites. When normalized to microbial biomass C, soil C:N positively correlated to C mineralization DOC leaching, showing that low soil N contents increase C losses per microbial biomass as indicated by the nutrient mining theory. Overall, the findings from this thesis confirmed the importance of nutrient stoichiometry on SOM mineralization, and highlight the important interactions between C, N, P and S mineralization under differently managed soils in forests and grasslands. Land use were shown to be important driver for SOM mineralization and soil priming due to differences in microbial biomass and activities.

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