Respiration and nutrient release from tree leaf litter mixtures

The effect of mixing litters on decomposition rates was investigated by incubating seven tree leaf litter types in all possible two-litter combinations under controlled laboratory conditions for 26 weeks. Inorganic N and CO2 release were monitored during the course of the incubation and final litter concentrations of N, P, Ca, Mg and K were determined. Initial Ca content provided the best correlation (r(2) = 0.458, P < 0.001) between total respiration of the pure and mixed units and initial litter quality. There was a very poor correlation (r(2) = 0.046, P = 0.272) between total respiration and initial N content across all litters, but when alder, and mixtures with alder, were removed from the calculation the remaining litters gave a strong correlation (r(2) = 0.720, P < 0.001). The majority of litter combinations showed interaction effects for CO2 release at some stage during the incubation, with eight significant positive and only one significant negative interaction for total CO2 release. All mixtures showed interaction effects for inorganic N, with release from mixtures generally occurring later than expected. Total N loss was significantly lower in four mixtures, and significantly higher in one. It is suggested that the 'mixtures effect' could be a useful management tool for modifying the timing and rate of release of N from decomposing plant residues to improve the synchrony between mineralisation and plant uptake. Increased rates of decomposition appear to have been a result of a 'sharing' of resources between the component litters of a mixture. Elemental translocation by fungal hyphae, along with diffusion, is proposed as a means by which the degradation of one litter was facilitated by the presence of another.