RESPIRATION AND NUTRIENT RELEASE FROM TREE LEAF-LITTER MIXTURES

The effect of mixing litters on decomposition rates was investigated b y incubating seven tree leaf litter types in all possible two-litter c ombinations under controlled laboratory conditions for 26 weeks. Inorg anic N and CO2 release were monitored during the course of the incubat ion and final litter concentrations of N, P, Ca, Mg and K were determi ned. Initial Ca content provided the best correlation (r(2) = 0.458, P < 0.001) between total respiration of the pure and mixed units and in itial 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 t he calculation the remaining litters gave a strong correlation (r(2) = 0.720, P < 0.001). The majority of litter combinations showed interac tion effects for CO2 release at some stage during the incubation, with eight significant positive and only one significant negative interact ion for total CO2 release. All mixtures showed interaction effects for inorganic N, with release from mixtures generally occurring later tha n expected. Total N loss was significantly lower in four mixtures, and significantly higher in one. It is suggested that the 'mixtures effec t' could be a useful management tool for modifying the timing and rate of release of N from decomposing plant residues to improve the synchr ony between mineralisation and plant uptake. Increased rates of decomp osition appear to have been a result of a 'sharing' of resources betwe en the component litters of a mixture. Elemental translocation by fung al hyphae, along with diffusion, is proposed as a means by which the d egradation of one litter was facilitated by the presence of another.