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 CO 2 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 CO 2 release at some stage during the incubation, with eight significant positive and only one significant negative interaction for total CO 2 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.