Amino acid concentration in sampled soil water: Effects of sampling and storage using lysimeters with small pore-size and sterile pre-evacuated sampling tubes

In order to avoid microbial degradation of amino acids in sampled soil water within the sampling system before analysis, an approach of using lysimeters with a small mean pore size (0.1 mum) connected to preevacuated sterile sampling tubes was tested. The sampling system was also tested for adsorption/release of amino acids. When soil water with added amino acids were incubated in room temperature, amino acids were mineralized to ammonium. After sampling with the described sampling system, the soil water did not show any further mineralization of amino acids even after 138 hours in room temperature. There was no significant adsorption/release of amino acids caused by the sampling system or caused by freezing of the samples within the sampling tubes. It was concluded that the lysimeter system considerably reduces the number of microorganisms in the sampled water and that the sample stays rather unchanged concerning free amino acids for several days after sampling.