Home-field advantage accelerates leaf litter decomposition in forests

Several leaf litter decay studies have indicated that decomposition occurs more rapidly when litter is placed beneath the plant species from which it had been derived than beneath a different plant species (i.e. home-field advantage, HFA), although support for this notion has not been universal. We provide the first quantification of HFA in relation to leaf litter decomposition using published litter mass loss data from forest ecosystems in North America, South America, and Europe. Our findings indicate that HFA is widespread in forest ecosystems; on average litter mass loss was 8% faster at home than away. We hypothesize that HFA results from specialization of the soil biotic community in decomposing litter derived from the plant above it. Climate and initial litter quality data can be used to explain about 70% of the variability in litter decomposition at a global scale, leaving about 30% unexplained. We suggest that HFA be recognized as a factor that explains some of this remaining variability.     

No ‘home’ versus ‘away’ effects of decomposition found in a grassland-forest reciprocal litter transplant study

Plant litter often decomposes faster in the habitat from which it was derived (i.e. home) than when placed in foreign habitats (i.e. away), which has been called the home-field advantage (HFA) of litter decomposition. We tested whether the HFA of litter decomposition is driven by decomposer communities being specialized at decomposing litter in their home habitat, by reciprocally transplanting litter from grassland to early-successional forest. Unexpectedly, we found an overall disadvantage for at-home decomposition despite large differences in litter quality (lignin:N) between the two habitats. We found more evidence for habitat specialization among secondary decomposers (mites) than the primary decomposers (bacteria and fungi), suggesting that soil animals may be important in driving HFA patterns where they do exist. Grass litter decomposition in forest slowed down and became more fungal-based, while tree litter decomposition in grassland increased yet showed no shift to being bacterially-based, relative to ‘at home’ decomposition. This suggests a biological explanation for why a positive HFA was not observed. Our results highlight that both environmental context and soil biology can play an important and sometimes counter-intuitive role in modifying decomposition. A better understanding of the interaction between all three primary drivers of decomposition (the environment, litter quality and soil organisms) is necessary for reliable prediction of decomposition at global scales.     

Nitrogen addition enhances home-field advantage during litter decomposition in subtropical forest plantations

Nitrogen (N) exerts strong effects on litter decomposition through altering microbial abundance and community composition. However, the effect of N addition on plant–soil interactions such as home-field advantage (HFA: enhanced decomposition at a home environment compared to a guest environment) in relation to litter decomposition remains unclear. To fill this knowledge gap, we conducted a reciprocal litter transplant plus N addition experiment in Mytilaria laosensis and Cunninghamia lanceolata plantations for two years in subtropical China where anthropogenic N input is amongst the highest in the world. We found positive HFA effects (in which the calculation incorporates litter of both species) with litter mass loss 11.2% faster at home than in the guest environment in the N addition (50 kg N ha⁻¹ yr⁻¹) treatment, but no significant HFA effects were found in the control treatment. The magnitude of the HFA effect on carbon (C) release increased with N addition, while that on N release decreased. The HFA effects on phosphorus, potassium, calcium, sodium, and magnesium release were positive overall, but varied through time and the magnitude of the effects were different among elements. The greater HFA effects in the N addition treatment were associated with greater differences in microbial biomass and community composition between home and guest environments than in the control treatment. Our results indicate that anthropogenic N enrichment could lead to enhanced HFA effects, through modification of microbial communities, and thereby affect C sequestration and N cycling in subtropical forests.     

Home-field advantage of litter decomposition and nitrogen release in forest ecosystems

Litter decomposition is a major fundamental ecological process that regulates nutrient cycling, thereby affecting net ecosystem carbon (C) storage as well as primary productivity in forest ecosystems. Litter decomposes in its home environment faster than in any other environment. However, evidence for this phenomenon, which is called the home-field advantage (HFA), has not been universal. We provide the first HFA quantification of litter decomposition and nutrient release through meta-analysis of published data in global forest ecosystems. Litter mass loss was 4.2 % faster on average, whereas nitrogen (N) release was 1.7 % lower at the home environment than in another environment. However, no HFA of phosphorus (P) release was observed. Broadleaf litter (4.4 %) had a higher litter mass loss HFA than coniferous litter (1.0 %). The positive HFA of N release was found in the coniferous litter. Mass loss HFA was significantly and negatively correlated with the initial lignin:N litter ratio. The litter decomposition and N release HFAs were obtained when mesh size ranged from 0.15 mm to 2.0 mm. The HFA of litter decomposition increased with decomposition duration during the early decomposition stage. The HFA of N release was well correlated with mass loss, and the greatest HFA was at mass loss less than 20 %. Our results suggest that the litter decomposition and N release HFAs are widespread in forest ecosystems. Furthermore, soil mesofauna is significantly involved in the HFA of litter decomposition.     

Decomposition and macroinvertebrates in experimental litter along a secondary chronosequence of tropical montane forest

This paper presents the results of a decomposition experiment performed in a secondary chronosequence of tropical montane cloud forest in Mexico. The experiment was designed to explore whether the age of the forest influences the decomposition process and macroinvertebrate community independently of the quality of the decomposition resources. Fresh Pinus chiapensis needles and Persea americana leaves were set to decompose in each of four successional stages (15, 45, 75 and 100 years old). Results do not support the hypothesis that decomposition rate declines with increasing nutrient deficiency as forest succession proceeds. However, the chemical composition in decomposing leaves differed between successional stages. Higher availability of Ca in the 15-year-old forest appears to promote a positive feedback in the release of this nutrient from Persea americana leaves. Additionally, in old forests, a soil community that is more capable of breaking down recalcitrant material (acid detergent lignin) appears to have developed compared to early successional stages. The diversity of macroinvertebrates and abundance of predatory (Aranea and Diplura), detrivorous (Diplopoda) and geophagous (Enchytaeidae) taxa were different between boxes placed in different successional stages. We conclude that the decomposition and associated biota differ between successional stages. Apart from differences in litter quality, other factors associated with the age of the forest, such as small differences in soil temperature and long-lasting effects of disturbance, may also play influential roles.     

Multiple effects of reindeer grazing on the soil processes in nutrient-poor northern boreal forests

Reindeer grazing has a great influence on the ground vegetation of nutrient-poor northern boreal forests dominated by Cladonia lichens in Fennoscandia. Grazing may influence the soil processes in these systems either by influencing the quality of plant litter, or by indirect effects through the soil microclimate. In order to investigate the mechanisms underlying the effects of reindeer on boreal forest soils, we analyzed litter decomposition, soil and microbial C and N, microbial community composition, and soil organic matter quality in three forest sites with old reindeer exclosures adjacent to grazed areas. There was no effect of grazing on soil C/N ratio, inorganic N concentrations, microbial biomass C, microbial community structure analyzed by phospholipid fatty acid (PLFA) analysis, and organic matter quality analyzed by sequential fractionation, in the soil organic layer. However, microbial N was enhanced by grazing at some of the sampling dates and was negatively correlated with soil moisture, which indicates that increased microbial N could be a stress response to drought. The effect of grazing on litter decomposition varied among the decomposition stages: during the first 1.5 months, the litter C loss was significantly higher in the grazed than the ungrazed areas, but the difference rapidly levelled out and, after one year, the accumulated litter C loss was higher in the ungrazed than the grazed areas. Litter N loss was, however, higher in the grazed areas. Our study demonstrates that herbivores may influence soil processes through several mechanisms at the same time, and to a varying extent in the different stages of decomposition.     

Decreases in soil moisture and organic matter quality suppress microbial decomposition following a boreal forest fire

Climate warming is projected to increase the frequency and severity of wildfires in boreal forests, and increased wildfire activity may alter the large soil carbon (C) stocks in boreal forests. Changes in boreal soil C stocks that result from increased wildfire activity will be regulated in part by the response of microbial decomposition to fire, but post-fire changes in microbial decomposition are poorly understood. Here, we investigate the response of microbial decomposition to a boreal forest fire in interior Alaska and test the mechanisms that control post-fire changes in microbial decomposition. We used a reciprocal transplant between a recently burned boreal forest stand and a late successional boreal forest stand to test how post-fire changes in abiotic conditions, soil organic matter (SOM) composition, and soil microbial communities influence microbial decomposition. We found that SOM decomposing at the burned site lost 30.9% less mass over two years than SOM decomposing at the unburned site, indicating that post-fire changes in abiotic conditions suppress microbial decomposition. Our results suggest that moisture availability is one abiotic factor that constrains microbial decomposition in recently burned forests. In addition, we observed that burned SOM decomposed more slowly than unburned SOM, but the exact nature of SOM changes in the recently burned stand are unclear. Finally, we found no evidence that post-fire changes in soil microbial community composition significantly affect decomposition. Taken together, our study has demonstrated that boreal forest fires can suppress microbial decomposition due to post-fire changes in abiotic factors and the composition of SOM. Models that predict the consequences of increased wildfires for C storage in boreal forests may increase their predictive power by incorporating the observed negative response of microbial decomposition to boreal wildfires.     

Temporal dynamics of microbial communities on decomposing leaf litter of 10 plant species in relation to decomposition rate

Few empirical studies have examined how microbial communities on decomposing litters change in relation to litter chemistry or how microbial community composition is related to the rate of decomposition. We examined the relationships among microbial community composition, litter chemistry, and decomposition rates in a common garden experiment of the decomposition of leaf litters of 10 plant species. Microbial community composition, as measured by phospholipid fatty acids (PLFA), and 7 litter chemistry variables (%N, C:N, four carbon fractions, and lignin:N) were examined at 1, 2, and 8 months into decomposition. Both microbial and litter chemistry variables were reduced to a single axis each through nonmetric multidimensional scaling (NMS) to examine the relationship between microbes, litter chemistry, and decomposition rates. Although microbial communities were separated according initial litter chemistry and lability, individual measures of litter chemistry had limited ability to predict microbial community composition during decomposition. Decomposition rate constants were explained by litter chemistry of initial, 1-, 2- and, 8-month old litters (60–72% of the variance), and by microbial community composition at the 8-month collection date (67%). The results suggest that initial litter chemistry determines the rate of decomposition and microbial community composition early in decomposition while the composition of the microbial community plays a more important role in determining decomposition rate later in decomposition.     

Effect of litter quality on its decomposition in broadleaf and coniferous forest

Recently there has been much interest in the effect of litter mixing as well as the effect of different forest habitats on the decomposition process. Our aim was to test two hypotheses: high quality litter promotes decomposition of poor quality litter, and litter decomposes faster in broadleaf than in coniferous forest. We conducted a litter mixing experiment using litterbags placed in two forest floors, in which treatments consisted of litter monocultures of each of two campy species (Castanopsis eyrei and Pinus massoniana), as well as mixtures of these two species. The results showed that C. eyrei leaves decomposed significantly faster in the coniferous habitat than in their native habitat. On the other hand, P. massoniana needles decomposed significantly faster in their native coniferous habitat than in the broadleaf habitat. In our experiment we found that the mixture had different effect on different quality litter. P. massoniana needles (poor quality) had a positive effect on the decomposition of C. eyrei leaves (high quality), while C. eyrei leaves had a negative effect on the decomposition of P. massoniana needles in the mixture case in both broadleaf and coniferous habitats. The diversity of the fungi identified from different litters varied among treatments and the mass loss was positively correlated with the Shannon–Weaver diversity index of fungi. It is suggested that fungi may be one of the major drivers to control the decomposition process.     

Tree species effects on microbial respiration from decomposing leaf and fine root litter

Tree species have an impact on decomposition processes of woody litter, but the effects of different tree species on microbial heterotrophic respiration derived from decomposing litter are still unclear. Here we used leaf and fine root litter of six tree species differing in chemical and morphological traits in a temperate forest and elucidated the effects of tree species on the relationships between litter-derived microbial respiration rates and decomposition rates and morphological traits, including specific leaf area (cm² g⁻¹) and specific root length (m g⁻¹) of litter at the same site. Litterbags set in forest soil were sequentially collected five times over the course of 18 months. During litter decomposition, microbial respiration from leaf and fine root litter differed among the six tree species. Temporal changes in the remaining mass and morphology (specific leaf area and specific root length) were observed, and the magnitude of these changes differed among species. Positive correlations were observed between respiration and mass loss or morphology across species. These results revealed that litter mass loss and morphological dynamics during decomposition jointly enhanced microbial respiration, and these carbon-based litter traits explained species differences in decomposition of leaves and fine roots. In conclusion, tree species influenced the magnitude and direction of microbial respiration during leaf/fine root litter decomposition. Tree species also affected the relationship between microbial respiration and litter decomposition through direct effects of litter traits and indirect effects mediated by regulation of heterotroph requirements.     

Litter-type specific microbial responses to the transformation of leaf litter into millipede feces

The transformation of leaf litter into fecal pellets by saprophagous macroarthropods has long been suggested to play an important role in litter decomposition by altering microbial processes. However, conflicting results are reported in the literature, and it is currently not clear to what extent varying initial litter quality contributes to distinct microbial responses to the transformation of litter into feces. Here we performed a screening test using a wide range of distinct leaf litter from 26 tree species. We fed these litters to the macroarthropod species Glomeris marginata during one week under controlled conditions, and compared microbial responses in uningested leaf litter with that of feces produced from the 26 different leaf litter types. We assessed substrate induced respiration (SIR) as an integrative measure of microbial responses. We found that litter SIR was highly variable across species and well related to initial litter quality. However, variability in feces SIR was strongly reduced and only weakly related to initial litter quality. Moreover, the difference between feces and litter SIR decreased with increasing litter SIR as a result of higher microbial stimulation in litter with low associated litter SIR. Our data clearly showed that the direction and magnitude of microbial stimulation in feces depend strongly on the litter type. Therefore, the consequence of litter transformation into macroarthropod fecal pellets for microbial decomposers and possibly for subsequent decomposition of feces is specific to litter species.     

Nutrient limitation of litter decomposition with long-term secondary succession: evidence from controlled laboratory experiments

Purpose

Understanding ecosystem processes such as litter decomposition in response to dramatic land-use change is critical for modeling and predicting carbon (C) cycles. However, the patterns of litter decomposition along with long-term secondary succession (over 100 years) are not well reported, especially concerning nutrient limitations on litter decomposition.

Materials and methods

To clarify the response of litter decomposition to changes in soil nutrient availability, we conducted four incubation experiments involving soil and litter and nutrient addition from different successional stages and investigated the changes in microbial respiration and litter mass loss.

Results and discussion

Our results revealed that microbial respiration increased with succession without any litter addition (1.19~1.73 mg C g^?1 soil), and litter addition significantly promoted microbial respiration (16.5~72.9%), especially in the early successional stage (grassland and shrubland). The decomposition rate of the same litter decreased with succession. In addition, nitrogen (N) and phosphorus (P) addition showed significant effects on litter decomposition and microbial respiration; P addition promoted litter decomposition (2.4~15.3%) and microbial respiration (10.1~34.5%) in all successional stages, while N addition promoted litter decomposition (4.0~10.3%) and microbial respiration (5.4~27.2%) in all except the last stage of succession, which showed a negative effect on litter decomposition (??7.5%) and microbial respiration (??6.1%), indicating possible N saturation of litter decomposition and microbial respiration.

Conclusions

This work highlights that soil nutrient availability and successional stages need to be taken into account to predict the changes to litter decomposition in response to global changes.

     

Microbial function in adjacent subtropical forest and agricultural soil

Soil microbial communities and their activities are altered by land use change; however impacts and extent of these alterations are often unclear. We investigated the functional responses of soil microbes in agricultural soil under sugarcane and corresponding native soil under Eucalyptus forest to additions of contrasting plant litter derived from soybean, sugarcane and Eucalyptus in a microcosm system, using a suite of complimentary techniques including enzyme assays and community level physiological profiles (CLPP). Initially agricultural soil had 50% less microbial biomass and lower enzyme activities than forest soil, but significantly higher nitrification rates. In response to litter addition, microbial biomass increased up to 11-fold in agricultural soil, but only 1.8-fold in forest soil, suggesting a prevalence of rapidly proliferating ‘r’ and slower growing ‘K’ strategists in the respective soils. Litter-driven change in microbial biomass and activities were short lived, largely returning to pre-litter addition levels by day 150. Decomposition rates of sugarcane and soybean litter as estimated via CO₂ production were lower in agricultural than in forest soil, but decomposition of more recalcitrant Eucalyptus litter was similar in both soils, contradicting the notion that microbial communities specialise in decomposing litter of the dominant local plant species. Enzyme activities and community level physiological profiles (CLPP) were closely correlated to microbial biomass and overall CO₂ production in the agricultural soil but not the forest soil, suggesting contrasting relationships between microbial population dynamics and activity in the two soils. Activities of enzymes that break down complex biopolymers, such as protease, cellulase and phenol oxidase were similar or higher in the agricultural soil, which suggests that the production of extracellular biopolymer-degrading enzymes was not a factor limiting litter decomposition. Enzyme and CLPP analyses produced contrasting profiles of microbial activity in the two soils; however the combination of both analyses offers additional insights into the changes in microbial function and community dynamics that occur after conversion of forest to agricultural land.     

Herpetofauna diversity and microenvironment correlates across a pasture-edge-interior ecotone in tropical rainforest fragments in the Los Tuxtlas Biosphere Reserve of Veracruz, Mexico

We evaluated the relationship between amphibian and reptile diversity and microhabitat dynamics along pasture-edge-interior ecotones in a tropical rainforest in Veracruz, Mexico. To evaluate the main correlation patterns among microhabitat variables and species composition and richness, 14 ecotones were each divided into three habitats (pasture, forest edge and forest interior) with three transects per habitat, and sampled four times between June 2003 and May 2004 using equal day and night efforts. We measured 12 environmental variables describing the microclimate, vegetation structure, topography and distance to forest edge and streams.After sampling 126 transects (672 man-hours effort) we recorded 1256 amphibians belonging to 21 species (pasture: 12, edge: 14, and interior: 13 species), and 623 reptiles belonging to 33 species (pasture: 11, edge: 25, and interior: 22 species). There was a difference in species composition between pasture and both forest edge and interior habitats. A high correlation between distance to forest edge and temperature, understorey density, canopy cover, leaf litter cover, and leaf litter depth was found. There was also a strong relationship between the composition of amphibian and reptile ensembles and the measured environmental variables. The most important variables related to amphibian and reptile ensembles were canopy cover, understorey density, leaf litter cover and temperature.Based on amphibian and reptile affinity for the habitats along the ecotone, species were classified into five ensembles (generalist, pasture, forest, forest edge and forest interior species). We detected six species that could indicate good habitat quality of forest interior and their disappearance may be an indication of habitat degradation within a fragment, or that a fragment is not large enough to exclude edge effects. Different responses to spatial and environmental gradients and different degrees of tolerance to microclimatic changes indicated that each ensemble requires a different conservation strategy. We propose to maintain in the Los Tuxtlas Biosphere Reserve the forest remnants in the lowlands that have gentler slopes and a deep cover of leaf litter, a dense understorey, and high relative humidity and low temperature, to buffer the effects of edge related environmental changes and the invasion of species from the matrix.     

Functional diversity of microbial communities in the mixed boreal plain forest of central Canada

This study was designed to examine whether or not specific tree species (Picea glauca, Picea mariana, Pinus banksiana, Populus tremuloides), their post-fire stand age, or their position in a successional pathway had any significant effect on the functional diversity of associated soil microbial communities in a typical mixed boreal forest ecosystem (Duck Mountain Provincial Forest, Manitoba, Canada). Multivariate analyses designed to identify significant biotic and/or abiotic variables associated with patterns of organic substrate utilization (assessed using the BIOLOG™ System) revealed the overall similarity in substrate utilization by the soil microbial communities. The five clusters identified differed mainly by their substrate-utilization value rather than by specific substrate utilization. Variability in community functional diversity was not strongly associated to tree species or post-fire stand age; however, redundancy analysis indicated a stronger association between substrate utilization and successional pathway and soil pH. For example, microbial communities associated with the relatively high pH soils of the P. tremuloides-P. glauca successional pathway, exhibited a greater degree of substrate utilization than those associated with the P. banksiana-P. mariana successional pathway and more acidic soils. Differences in functional diversity specific to tree species were not observed and this may have reflected the mixed nature of the forest stands and of their heterogeneous forest floor. In a densely treed, mixed boreal forest ecosystem, great overlap in tree and understory species occur making it difficult to assign a definitive microbial community to any particular tree species. The presence of P. tremuloides in all stand types and post fire stand ages has probably contributed to the large amount of overlap in utilization profiles among soil samples.     

Experimental evidence for the interacting effects of forest edge,moisture and soil macrofauna on leaf litter decomposition

Forest ecosystems have been widely fragmented by human land use. Fragmentation induces significant microclimatic and biological differences at the forest edge relative to the forest interior. Increased exposure to solar radiation and wind at forest edges reduces soil moisture, which in turn affects leaf litter decomposition. We investigate the effect of forest fragmentation, soil moisture, soil macrofauna and litter quality on leaf litter decomposition to test the hypothesis that decomposition will be slower at a forest edge relative to the interior and that this effect is driven by lower soil moisture at the forest edge. Experimental plots were established at Wytham Woods, UK, and an experimental watering treatment was applied in plots at the forest edge and interior. Decomposition rate was measured using litter bags of two different mesh sizes, to include or exclude invertebrate macrofauna, and containing leaf litter of two tree species: easily decomposing ash (Fraxinus excelsior L.) and recalcitrant oak (Quercus robur L.). The decomposition rate was moisture-limited at both sites. However, the soil was moister and decomposition for both species was faster in the forest interior than at the edge. The presence of macrofauna accelerated the decomposition rate regardless of moisture conditions, and was particularly important in the decomposition of the recalcitrant oak. However, there was no effect of the watering treatment on macrofauna species richness and abundance. This study demonstrates the effect of forest fragmentation on an important ecosystem process, providing new insights into the interacting effects of moisture conditions, litter quality, forest edge and soil macrofauna.     

The feeding habits of collembola along decomposition gradients using stable carbon and nitrogen isotope analyses

We measured the natural stable carbon (C) and nitrogen (N) isotope ratio patterns of collembola and the organic substrates of their habitats and potential food sources in a warm temperate coniferous forest. Based on previous studies, we classified collembola into successional classes along litter decomposition gradients: early colonizers, late colonizers, and dominants-throughout. The stable C and N isotope ratios of late colonizers exceeded those of early colonizers, and those of the dominants-throughout were intermediate between early and late colonizers, which is consistent with previous studies on two macro-invertebrates, earthworms and termites. The C and N isotopic signature differences in collembola may reflect food resource partitioning along decomposition gradients.     

Direct and indirect effects of tree diversity drive soil microbial diversity in temperate deciduous forest

We investigated the link between aboveground and belowground diversity in temperate deciduous forest ecosystems. To this end, we determined the effects of the tree species composition on the biomass and composition of the soil microbial community using phospholipid fatty acid (PLFA) profiles in the Hainich National Park, a deciduous mixed forest on loess over limestone in Central-Germany. We investigated the effects of the leaf litter composition on the microbial community, hypothesizing that distinctive leaf litter compositions increase signature PLFAs. In addition, we studied the impact of clay content, pH and nutrient status of the soil on the microbial community in different surface soil layers. Consequently, soil was sampled from depths of 0-5 cm, 5-10 cm and 10-20 cm. Plots with highest leaf litter diversity had the largest total amounts of fatty acids, but only PLFA 16:1ω5, which is a common marker for arbuscular mycorrhizal fungi, was significantly increased. In the uppermost soil layer, the pH explained most of the variance in microbial composition. In the deeper surface soil layers, nutrients such as carbon, nitrogen and phosphorus determined the microbial abundances and composition. Our results suggest that the soil microbial community is mainly indirectly influenced by aboveground diversity. Changes in soil pH or the soil nutrient status that are driven by specific plant traits like leave litter quality drive these indirect changes. Specific direct interactions are most reasonable for mycorrhizal fungi.     

Plant species richness leaves a legacy of enhanced root litter-induced decomposition in soil

Increasing plant species richness generally enhances plant biomass production, which may enhance accumulation of carbon (C) in soil. However, the net change in soil C also depends on the effect of plant diversity on C loss through decomposition of organic matter. Plant diversity can affect organic matter decomposition via changes in litter species diversity and composition, and via alteration of abiotic and/or biotic attributes of the soil (soil legacy effect). Previous studies examined the two effects on decomposition rates separately, and do therefore not elucidate the relative importance of the two effects, and their potential interaction. Here we separated the effects of litter mixing and litter identity from the soil legacy effect by conducting a factorial laboratory experiment where two fresh single root litters and their mixture were mixed with soils previously cultivated with single plant species or mixtures of two or four species. We found no evidence for litter-mixing effects. In contrast, root litter-induced CO₂ production was greater in soils from high diversity plots than in soils from monocultures, regardless of the type of root litter added. Soil microbial PLFA biomass and composition at the onset of the experiment was unaffected by plant species richness, whereas soil potential nitrogen (N) mineralization rate increased with plant species richness. Our results indicate that the soil legacy effect may be explained by changes in soil N availability. There was no effect of plant species richness on decomposition of a recalcitrant substrate (compost). This suggests that the soil legacy effect predominantly acted on the decomposition of labile organic matter. We thus demonstrated that plant species richness enhances root litter-induced soil respiration via a soil legacy effect but not via a litter-mixing effect. This implies that the positive impacts of species richness on soil C sequestration may be weakened by accelerated organic matter decomposition.     

Plant litter quality influences the contribution of soil fauna to litter decomposition in humid tropical forests, southwestern China

The aim of this field experiment was to quantify the contribution of soil fauna to plant litter decomposition in three forest sites differing in C/N ratio under natural conditions in Xishuangbanna, southwestern China. We conducted a survey of soil fauna communities, the forest floor litter and investigated mass loss of mixed tree species leaf litter for two years in a tropical secondary forest, an evergreen broad-leaf forest and a tropical rain forest. Exclusion treatments of different sized soil fauna from the leaf litter by using varying mesh size litter bags (2 mm and 0.15 mm) were also performed. Mass loss and C and N concentrations in litter bag leaf materials were determined at monthly intervals. We found that: (1) the three forests differed in floor litter biomass and nutrient contents but not in soil fauna richness and abundance; (2) litter mass loss and decomposition rate were slower when soil macrofauna and most of mesofauna were excluded; and (3) greatest soil fauna contribution to plant litter decomposition occurred in the rain forest, where leaf litter C/N ratio was also highest (41.5% contribution: 54.8 C/N ratio), in comparison to 8.69% in the broad-leaf forest and 19.52% in the secondary forest, both with low leaf litter C/N ratios (<32). Our results suggested that, soil fauna played a more pronounced role in the decomposition of mixed leaf litter in tropical rain forest, and significantly bigger effects from fauna were ascribed to the enhancement of N concentration and decrease of C concentration of the initially high C/N ratio litter in this forest site.