Admixture of alder (Alnus formosana) litter can improve the decomposition of eucalyptus (Eucalyptus grandis) litter

• Alder and eucalyptus mixed litter decomposition were examined every half-month.
• Admixture of alder litter can improve the decomposition of eucalyptus litter.
• A small proportion of eucalyptus litter may promote alder litter decomposition.
• Litter mixture displayed addition effects in initial stage.
• Both positive and negative non-addition effects were observed in later stage.

The slow nutrient turnover of eucalyptus (Eucalyptus grandis) plantations has been well documented. To examine whether the admixture of alder (Alnus formosana) litter could improve the decomposition of eucalyptus litter, a field litterbag experiment was conducted on a new eucalyptus plantation in southwestern China. We investigated the mass loss rate from an alder and eucalyptus foliar litter mixture every half month from May 1st to October 1st, 2009. Five mixture proportions were examined: pure eucalyptus litter (10E), 70% eucalyptus litter mixed with 30% alder litter (7E:3A), 50% eucalyptus litter mixed with 50% alder litter (5E:5A), 30% eucalyptus litter mixed with 70% alder litter (3E:7A) and pure alder litter (10A). Over 169 days of decomposition, approximately 79.22%, 70.23%, 62.82%, 49.95% and 48.59% of mass was lost from the 3E:7A, 10A, 5E:5A, 7E:3A and 10E litter mixtures, respectively. Compared with pure eucalyptus litter, 3E:7A, 10A, 5E:5A and 7E:3A litter mixtures increased 63.04%, 44.54%, 29.29% and 2.80% of accumulated mass loss. The admixture of alder litter can significantly improve eucalyptus litter decomposition, and a small proportion of eucalyptus litter (3E:7A) may also promote alder litter decomposition. As the decomposition proceeded, the litter mixture displayed exactly additive effects in the initial stage and positive non-additive effects in the middle stage. However, negative non-additive effects were detected in the 7E:3A litter mixture in the later stage, although positive non-additive effects were maintained throughout decomposition in the 5E:5A and 3E:7A mixtures. Compared to pure eucalyptus litter, mixtures containing alder litter presented increased microbial biomass carbon and bacterial DGGE (Denaturing Gradient Gel Electrophoresis) bands, but the litter mixture decomposition relied more on microbial biomass than on microbial diversity. The results imply that alder litter can improve material cycling on eucalyptus plantations and that alder could be a potential species for mixed planting with eucalyptus.