Elsevier

Soil Biology and Biochemistry

Volume 73, June 2014, Pages 115-121
Soil Biology and Biochemistry

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

https://doi.org/10.1016/j.soilbio.2014.02.018Get rights and content

Highlights

  • 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.

Abstract

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.

Introduction

The development of eucalyptus (normally Eucalyptus grandis) plantations has been increasing in the global commercial timber industry (Forrester et al., 2006, Forrester et al., 2013, Zhang et al., 2010, Leslie et al., 2012). Because of the plant's short rotation (fast growth) and high consumption of water and soil nutrients, nutrient cycling is one of the limitations to establishing sustainable eucalyptus plantation ecosystems (Lemma et al., 2007). Unfortunately, a thick leaf litter layer often accumulates on the floor of eucalyptus plantations, indicating a slow litter decomposition rate because of low litter quality (Guo and Sims, 2001, Forrester et al., 2006). Several previous studies have reported that mixed-species plantations of eucalyptus with a dinitrogen (N2) fixation species have the potential to increase productivity while maintaining soil fertility, enhancing soil organic carbon sequestration and accelerating nutrient cycling (Forrester et al., 2006, Forrester et al., 2013, le Maire et al., 2013). It is therefore important to select N2 fixation species with readily decomposable litter and high rates of nutrient cycling. However, both synergistic and antagonistic interactions (review from Gartner and Cardon, 2004) and even non-significant effects (Perez-Harguindeguy et al., 2008) have been observed in litter mixture decomposition.

Climate, litter quality and the decomposer community are known to be the main controllers of organic matter decomposition (Couteaux et al., 1995). The non-additive effects on the decomposition of litter mixtures compared to that of monoculture litter can be mainly attributed to the changes of the chemical environment and the physical alteration of the total litter surface where decomposition occurs (Hansen and Coleman, 1998, Kaneko and Salamanca, 1999, Hector et al., 2000). In general, higher-quality litter can stimulate decomposition in adjacent, more recalcitrant litters, and conversely, leaf litter decomposition can be slowed by an admixture of lower-quality litter (Fyles and Fyles, 1993, McTiernan et al., 1997, Salamanca et al., 1998). The transfer of nitrogen between the litters has been documented as a key mechanism in the interaction between decomposing litters (Berglund and Ågren, 2012, Berglund et al., 2013). Moreover, an increase in microhabitats may also be correlated with increased mass loss because of the creation of a more diverse and abundant decomposer community (Hansen and Coleman, 1998, Gartner and Cardon, 2004). Thus, chemical and physical changes in the leaf mixture can influence decomposition rates both directly (physically) and indirectly (through the decomposer community and its activities).

However, this superior chemical and physical diversity disappears as decomposition proceeds because the liable components are lost and the litter shape is destroyed after early rapid decomposition (Berg and McClaugherty, 2008). The remaining substrate is rich in water-soluble defenses or inhibitory compounds (such as lignin and tannin), leading to co-limits with each other in the litter mixture (Ostrofsky, 2007). Therefore, trends in the rates of decomposition and nutrient loss from mixtures of litter from different species are complex and inconsistent when compared to those of monoculture litter. Moreover, litter in mixtures with N2 fixation species does not necessarily decay faster than monoculture litters of non-N2 fixation species (Rothe and Binkley, 2001, Binkley et al., 2003). As a result, additional research is required on the decomposition of litter mixtures of eucalyptus and N2 fixation species with the goal of providing effective information for mixed-species plantations of eucalyptus.

Alder (Alnus spp.) is an N2 fixation tree with a wide distribution from the boreal zone to the subtropical zone, and its leaf litter has been well documented as possessing desirable decomposition characteristics (Chapman et al., 1988, Gartner and Cardon, 2004). The available information indicates that the admixture of alder litter can improve the decomposition of other litter, such as that of Populus tremuloides (Taylor et al., 1989) and Pseudotsuga menziesii (Fyles and Fyles, 1993). Alder's ability to improve the nutrient cycling of litter mixture decomposition makes it a candidate tree species for mixed planting with eucalyptus, but little information on this particular combination is available. Therefore, it is hypothesized that the admixture of alder litter can improve the decomposition of eucalyptus litter, which is potentially beneficial for eucalyptus plantations.

To test this hypothesis, a field litterbag experiment was conducted on a new eucalyptus plantation in southwestern China, where eucalyptus plantations cover more than 200 000 ha (Zhang et al., 2010, Zhang et al., 2012). We measured the accumulated mass loss from alder (Alnus formosana) and eucalyptus (E. grandis) foliar litter mixtures every half month. Five mixed 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). The objectives were (1) to determine whether the admixture of alder litter could improve eucalyptus litter decomposition and (2) to identify the aspects of the litter mixture decomposition. The results will be useful in determining the practicality of alder as a candidate species for mixed planting with eucalyptus.

Section snippets

Study site

The study was conducted in the Leshan region (E103°36′, N29°37′, 413 m a.s.l) in western Sichuan Province, southwestern China. The climate is subtropical, with an annual mean temperature of 18.0 °C and precipitation of 1137 mm. From a local weather station near the sample site, the monthly average air temperature was higher than 20 °C from May to October 2009, with the highest average of 28.2 °C in August. The majority of precipitation falls between June and August, whereas only 48.1 mm and

Mass loss

Over 169 days of decomposition, the accumulated mass loss was significantly different in the pattern 3E:7A > 10A > 5E:5A > 7E:3A > 10E. 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 (Fig. 1). 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. Few differences in the accumulated mass loss were

Discussion

The hypothesis that the admixture of alder litter can improve eucalyptus litter decomposition was confirmed by this study. Both the present study and previous results have demonstrated that mixing eucalyptus litter with more readily decomposable litter can enhance the decomposition of eucalyptus litter (Briones and Ineson, 1996). From a quantitative perspective, this study hypothesized that the litter mixture would decompose more slowly as the amount of slowly decomposing eucalyptus litter

Acknowledgments

The authors are very grateful to their colleagues from Ecological Modelling and Carbon Science (ECO-MCS), Institute of Environment Sciences, University of Quebec at Montreal (UQAM) for providing helpful suggestions in manuscript preparation. This research was financially supported by the National Natural Science Foundation of China (31170423 & 31270498), the National Key Technologies R&D of China (2011BAC09B05), and the Sichuan Youth Sci-tech Foundation (2012JQ0008 & 2012JQ0059).

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