Decomposition patterns of leaf litter of seven common canopy species in a subtropical forest: N and P dynamics

Litter decomposition, governing nutrient and C cycling, is strongly influenced by the chemical litter quality. In order to determine the interspecific variation in leaf decomposition rates and to understand the chemical basis for such variation, decomposition dynamics of seven common canopy species was investigated over 2year using the litterbag technique in a subtropical evergreen broad-leaved forest on Okinawa Island, Japan. The species studied are representatives of the vegetation in the study area and differed significantly in their chemical litter quality. Dry mass loss at the end of study varied in the order: Distylium racemosum< Quercus miyagii< Rapanea neriifolia< Symplocos confusa< Castanopsis sieboldii< Schima wallichii< Daphniphyllum glaucescens. All species showed a pattern characterized by a rapid initial decomposition followed by lower rates except for D. glaucescenswhich decomposition rate appeared to be rather constant. In the late phase, decomposition rates were correlated positively to initial N and ash contents and negatively to lignin content, lignin:N, C:N, and C:P ratios. The effects of N and lignin content or lignin:N ratio were stronger than other quality parameters. There was a wide range in patterns of N and P concentrations, from a net accumulation to a rapid loss in decomposition. The correlation between N and P release suggests that N and P dynamics may have influenced each other during litter decomposition. Analysis of initial quality for species showed that the C:P ratios were extremely high (range 1639–3811) but the N:P ratios were from 28 to 56, indicating a likely P-limitation for this forest. Our results suggest that P is an important control of litter decomposition and N and P dynamics.     

Impacts of Falcataria moluccana Invasion on Decomposition in Hawaiian Lowland Wet Forests: The Importance of Stand-level Controls

Invasive species have the capacity to substantially alter soil processes, including rates of litter decomposition. Currently, the few remaining native-dominated lowland wet forests in Hawai’i are being invaded by Falcataria moluccana, a large, fast-growing, N₂-fixing tree. In this study, we sought to determine the extent to which Falcataria invasion alters decomposition in these lowland wet forests, and whether changes resulted from differences in litter substrate type, lava flow age and type, forest stand type and associated soil biota, or some combination of these factors. We measured decomposition rates and nitrogen (N) and phosphorus (P) dynamics of Metrosideros polymorpha and Falcataria leaf litter in native-dominated and Falcataria-invaded stands on 48- and 300-year-old a’a lava flows and a 213-year-old pāhoehoe flow in the Puna district of eastern Hawai’i. Despite significant differences in the initial quality of Metrosideros and Falcataria litter, in nearly all cases mass remaining of the two litter types did not differ within a given forest stand, whether native-dominated or invaded. Instead, stand type accounted for large differences in the decomposition of both litter types, and litter decomposed two to 10 times faster in Falcataria-invaded stands than it did in their native-dominated counterparts on each lava flow. Dynamics of N (that is, immobilization or release) during decomposition were affected by stand, litter, and lava flow type; P dynamics were affected by stand and flow type, but not litter type. Although not definitive proof of causality, the decay rates of both species were positively correlated to previously measured inputs of N mass and P mass via litterfall as well as availability of soil N and P, characteristics that all increased substantially with Falcataria invasion. Given the degree of change to a host of ecosystem processes, including decomposition, after invasion by Falcataria, these transformed forest ecosystems may best be viewed as fundamentally new and different, in both structure and function, from the native ecosystems they have replaced.     

Insect biological control accelerates leaf litter decomposition and alters short‐term nutrient dynamics in a Tamarix‐invaded riparian ecosystem

Insect herbivory can strongly influence ecosystem nutrient dynamics, yet the indirect effects of herbivore‐altered litter quality on subsequent decomposition remain poorly understood. The northern tamarisk beetle Diorhabda carinulata was released across several western states as a biological control agent to reduce the extent of the invasive tree Tamarix spp. in highly‐valued riparian ecosystems; however, very little is currently known about the effects of this biocontrol effort on ecosystem nutrient cycling. In this study, we examined alterations to nutrient dynamics resulting from beetle herbivory in a Tamarix‐invaded riparian ecosystem in the Great Basin Desert in northern Nevada, USA, by measuring changes in litter quality and decomposition, as well as changes in litter quantity. Generally, herbivory resulted in improved leaf litter chemical quality, including significantly increased nitrogen (N) and phosphorus (P) concentrations and decreased carbon (C) to nitrogen (C:N), C:P, N:P, and lignin:N ratios. Beetle‐affected litter decomposed 23% faster than control litter, and released 16% more N and 60% more P during six months of decomposition, as compared to control litter. Both litter types showed a net release of N and P during decomposition. In addition, herbivory resulted in significant increases in annual rates of total aboveground litter and leaf litter production of 82% and 71%, respectively, under the Tamarix canopy. Our finding that increased rates of N and P release linked with an increased rate of mass loss during decomposition resulting from herbivore‐induced increases in litter quality provides new support to the nutrient acceleration hypothesis. Moreover, results of this study demonstrate that the introduction of the northern tamarisk beetle as biological control to a Tamarix‐invaded riparian ecosystem has lead to short‐term stimulation of nutrient cycling. Alterations to nutrient dynamics could have implications for future plant community composition, and thus the potential for restoration of Tamarix‐invaded ecosystems.     

Effects of exotic invasive trees on nitrogen cycling: a case study in Central Spain

We assess the hypothesis that rates of nitrogen transformations in the soil are altered upon replacement of native by exotic trees, differing in litter properties. Ailanthus altissima and Robinia pseudoacacia, two common exotic trees naturalized in the Iberian Peninsula, were compared with the native trees Ulmus minor and Fraxinus angustifolia, respectively. Naturally senesced leaves of each species were collected and C:N ratio, N and lignin content assessed. We prepared 64 litter bags per species and left them to decompose, below the canopy of the same species and below the canopy of the paired species. Dry mass, N concentration and N pool of the remaining litter were assessed after 5 and 7 months. Soil samples were collected three times during the experiment to assess soil moisture, organic matter, pH, potential mineralization rates and mineral N pools. Mineral N availability was assessed three times in the field by using ion-exchange resin-impregnated membranes. Ailanthus litter decomposed faster than Ulmus litter, probably due to the higher toughness of the latter. In spite of its high N content, Robinia litter decomposed slower than Fraxinus one, probably due to its high lignin content. In both cases, litter decomposition was faster below the exotic than the native canopies. The release of N per unit of initial litter mass was higher under both invaded situations (Ailanthus below Ailanthus and Robinia below Robinia) than under the native ones. However, soils collected below native and exotic trees neither differed in potential N mineralization rate nor in mineral N. This may be attributed to a quick plant uptake of released N and/or to a high organic matter accumulation in the soil previous to invasion that can exert a tighter control on soil N transformations than the current exotic litter.     

Effects of sediment-borne nutrient and litter quality on macrophyte decomposition and nutrient release

Macrophyte decomposition is a critical process that affects carbon and nutrient cycling, and energy flow, although the majority of the details involved in the process remain unclear. For the present study, a litter bag experiment was conducted to investigate the effects of sediment-borne nutrient and litter quality on the decomposition rates and nutrient release of four macrophyte life forms (emergent macrophyte: Phragmites australis, free-floating macrophyte: Hydrocharis dubia, floating-leaved macrophyte: Nymphoides peltata, submerged macrophyte: Ceratophyllum demersum), and a species mixture. Our results indicated that litter quality significantly influenced macrophyte decomposition and nutrient release. High-quality litter species (high initial nitrogen and phosphorus contents, as well as low C:N, C:P, and N:P ratios) decomposed more rapidly than low-quality litter species, and the initial C:N and C:P ratios, rather than the initial N and P contents, were effective indicators of the decomposition rate of macrophytes. Sediment-borne nutrients had little effect on the decomposition rate, yet a strong effect on the release of N and P, although the interactions between litter quality and sediment-borne nutrients significantly affected the decomposition rate. Three-way ANOVA analysis revealed that the litter quality imparted a more potent effect on the macrophyte decomposition rate and release of N and P than sediment-borne nutrients. These results implied that litter quality interacts with sediment-borne nutrients and may control macrophyte decomposition in shallow lakes.     

Tree-microbial biomass competition for nutrients in a temperate deciduous forest,central Germany

Aims

Our goals were (1) to determine whether tree species diversity affects nutrient (N, P and K) cycling, and (2) to assess whether there is competition for these nutrients between microbial biomass and trees.

Methods

We measured nutrient resorption efficiency by trees, nutrient contents in leaf litterfall, decomposition rates of leaf litter, nutrient turnover in decomposing leaf litter, and plant-available nutrients in the soil in mono-species stands of beech, oak, hornbeam and lime and in mixed-species stands, each consisting of three of these species.

Results

Cycling of nutrients through leaf litter input and decomposition were influenced by the types of tree species and not simply by tree species diversity. Trees and microbial biomass were competing strongly for P, less for K and only marginally for N. Such competition was most pronounced in mono-species stands of beech and oak, which had low nutrient turnover in their slow decomposing leaf litter, and less in mono-species stands of hornbeam and lime, which had high nutrient turnover in their fast decomposing leaf litter.

Conclusions

The low soil P and K availability in beech stands, which limit the growth of beech at Hainich, Germany, were alleviated by mixing beech with hornbeam and lime. These species-specific effects on nutrient cycling and soil nutrient availability can aid forest management in improving productivity and soil fertility.

     

Effects of heterogeneous habitat use by cattle on nutrient availability and litter decomposition in soils of an Alpine pasture

Grazing by free-ranging cattle on Alpine pastures in southern Switzerland creates sharp contrasts in plant species composition between small camp areas, which are grazed intensely and receive most cattle excreta, and surrounding pasture dominated by Nardus stricta, which is only lightly grazed. We hypothesised that these contrasts are maintained by positive feedbacks related to nutrient availability in soil, in that (a) plant material with rapid decomposition and nutrient release decomposes in camp areas and (b) litter decomposition is further stimulated by enhanced nutrient availability in soil. We compared nutrient availability at three camp areas with that in surrounding Nardus vegetation and investigated how the decomposition of plant material from both vegetation types responds to nutrient availability in soil, both in the field (during 14 weeks) and in the laboratory (during 4, 10, and 16 weeks). At all three field sites P availability was significantly enhanced in camp areas, whereas differences in N availability were inconsistent among the three sites. Laboratory incubations indicated that microbial activity after the addition of labile C (cellulose) was limited by P availability in the Nardus vegetation but not in camp areas. The camp-area plant substrate decomposed much faster (81.5% vs. 27.1% ash-free dry mass loss in the field) and released more N and P than the Nardus substrate, which tended to immobilise soil nutrients. However, the decomposition rate of neither substrate was influenced by nutrient availability in soil, both in the field (comparing camp areas and Nardus vegetation) and in the laboratory (comparing incubations with and without N or P fertilisation). We conclude that the contrasting quality of plant substrates contributes to the greater nutrient availability in camp areas (feedback a) but that the latter does not influence the decomposition of in situ plant material (feedback b) because the latter is not nutrient-limited.     

Grazing history effects on above- and below-ground litter decomposition and nutrient cycling in two co-occurring grasses

Large herbivores may alter carbon and nutrient cycling in soil by changing above- and below-ground litter decomposition dynamics. Grazing effects may reflect changes in plant allocation patterns, and thus litter quality, or the site conditions for decomposition, but the relative roles of these broad mechanisms have rarely been tested. We examined plant and soil mediated effects of grazing history on litter mass loss and nutrient release in two grazing-tolerant grasses, Lolium multiflorum and Paspalum dilatatum, in a humid pampa grassland, Argentina. Shoot and root litters produced in a common garden by conspecific plants collected from grazed and ungrazed sites were incubated under both grazing conditions. We found that grazing history effects on litter decomposition were stronger for shoot than for root material. Root mass loss was neither affected by litter origin nor incubation site, although roots from the grazed origin immobilised more nutrients. Plants from the grazed site produced shoots with higher cell soluble contents and lower lignin:N ratios. Grazing effects mediated by shoot litter origin depended on the species, and were less apparent than incubation site effects. Lolium shoots from the grazed site decomposed and released nutrients faster, whereas Paspalum shoots from the grazed site retained more nutrient than their respective counterparts from the ungrazed site. Such divergent, species-specific dynamics did not translate into consistent differences in soil mineral N beneath decomposing litters. Indeed, shoot mass loss and nutrient release were generally faster in the grazed grassland, where soil N availability was higher. Our results show that grazing influenced nutrient cycling by modifying litter breakdown within species as well as the soil environment for decomposition. They also indicate that grazing effects on decomposition are likely to involve aerial litter pools rather than the more recalcitrant root compartment.     

Asymbiotic Nitrogen Fixation and Litter Decomposition on a Long Soil-Age Gradient in Hawaiian Montane Rain Forest1

We determined rates of decomposition and asymbiotic nitrogen fixation in the leaf litter of Cheirodendron spp. on the Hawaiian Islands. Leaf litter was collected from four sites on a long soil-age gradient (300 yr to 4.1 M yr) and decomposed at two sites that differed widely in substrate age and nutrient availability. Rates of decomposition were higher in litter decomposed at the older site, where nutrient availability was greater. A substantial amount of nitrogen and phosphorus immobilization occurred in litter decomposed at the older site, with more immobilization occurring in litter with lower initial nitrogen and phosphorus concentrations, suggesting both supply and demand controls on nutrient immobilization. Potential rates of nitrogen fixation were very low in the first 25 d (0–5 nmol acetylene/gdw/h), rose to much higher rates by 70 d (20–45 nmol), and then declined by 140 d. We found no significant difference in rates of potential nitrogen fixation between sites of decomposition, but there was a strong substrate effect, with higher rates in litter with low lignin, low nitrogen, and high phosphorus. Where significant immobilization of nitrogen occurred for decomposing Cheirodendron, nitrogen fixation could have comprised no more than 10 percent of immobilized nitrogen. Overall, rates of nitrogen fixation were dependent on the source of the decomposing substrate but not on the site of decomposition, while short-term decomposition and nutrient immobilization were strongly dependent on the site of decomposition but not as much on the source of the decomposing substrate.     

Leaf litter decomposition of canopy trees, bamboo and moss in a montane moist evergreen broad-leaved forest on Ailao Mountain, Yunnan, south-west China

Litter decomposition and nutrient release of selected dominant synusiae in an old-growth, evergreen, broad-leaved mossy forest on Ailao Mountain, Yunnan, south-west China, were studied over a 22-month period. The species studied were three dominant tall tree species, Lithocarpus xylocarpus Markg., Lithocarpus chintungensis Hsu et Qian and Castanopsis wattii A. Camus; one dominant understory species (the bamboo Sinarundinaria nitida Nakai); and a mixture of dominant mosses (including Homaliodendron scalpellifolium Fleisch, Symphyodon perrottetti Mont., Herberta longifolissa Steph. and Bazzania albicans Horik.). Fast initial litter decomposition was followed by lower rates. Decomposition rates of canopy species and bamboo leaf litter appear to be controlled by the initial concentration of lignin, nitrogen (N) and phosphorus (P) more than by morphological features of the leaves. The decay rate of moss litter was less correlated with nutrient composition and lignin concentration in initial mass. The order of decomposition rates was Castanopsis wattii > L. xylocarpus > L. chintungensis > bamboo > moss. The decomposition rate constants (k) of the leaf litter for the canopy species L. xylocarpus, L. chintungensis and Castanopsis wattii were 0.62, 0.50 and 0.64, respectively, and 0.40 and 0.22 for bamboo and moss, respectively. Turnover time (1/k) for the three canopy species was 1.61 years, 2.0 years and 1.55 years, respectively, and 2.50 years and 4.55 years for bamboo and moss, respectively. The N and P concentration in the decomposing leaf litter increased in the first 6 months and then decreased over the remaining period. There was a relatively rapid initial loss of potassium (K), followed by a slight increase. Each of calcium (Ca) and magnesium (Mg) decreased with time whereas iron (Fe) and manganese (Mn) increased with time to some extent. Nutrient release from decomposing leaf litter was in the order of K > Mg > Ca > N > P > Mn > Fe, except for bamboo (Sinarundinaria nitida) K > Ca > P > N > Mg > Mn > Fe.     

Response of nutrient dynamics of decomposing pine (Pinus massoniana) needles to simulated N deposition in a disturbed and a rehabilitated forest in tropical China

The effects of simulated N deposition on changes in mass, C, N and P of decomposing pine (Pinus massoniana) needles in a disturbed and a rehabilitated forest in tropical China were studied during a 24-month period. The objective of the study was to test the hypothesis that litter decomposition in a disturbed forest is more sensitive to N deposition rate than litter decomposition in a rehabilitated forest due to the relatively low nutrient status in the former as a result of constant human disturbance (harvesting understory and litter). The litterbag method and N treatments (control, no N addition; low-N, 5 g N m⁻² year⁻¹; medium-N, 10 g N m⁻² year⁻¹) were employed to evaluate decomposition. The results revealed that N addition increased (positive effect) mass loss rate and C release rate but suppressed (negative effect) the release rate of N and P from decomposing needles in both disturbed and rehabilitated forests. The enhanced needle decomposition rate by N addition was significantly related to the reduction in the C/N ratio in decomposing needles. However, N availability is not the sole factor limiting needle decomposition in both disturbed and rehabilitated forests. The positive effect was more sensitive to the N addition rate in the rehabilitated forest than in the disturbed forest, however the reverse was true for the negative effect. These results suggest that nutrient status could be one of the important factors in controlling the response of litter decomposition and its nutrient release to elevated N deposition in reforested ecosystems in the study region.     

模拟干旱和磷添加对热带低地雨林叶凋落物分解的影响

凋落物是植物在其生长发育过程中新陈代谢的产物,是土壤有机质输入的重要途径,凋落物分解是生态系统养分循环的关键过程之一。在全球气候变化背景下,热带地区干旱事件发生的频率和强度均在增加,同时,普遍认为热带地区受磷(P)限制,所以探讨干旱胁迫和土壤磷可用性对热带地区叶凋落物分解的影响及两者是否存在交互效应十分必要,有助于了解干旱对该区叶凋落物分解的影响机制以及是否受土壤磷调控。依据植物多度、碳固持类型、叶质地,以海南三亚甘什岭热带低地雨林的4个树种叶凋落物(铁凌 Hopea exalata、白茶树 Koilodepas bainanense、黑叶谷木 Memecylon nigrescens、山油柑 Acronychia pedunculata)为实验材料,依托2019年在该区建成的热带低地雨林模拟穿透雨减少、磷(P)添加双因素交互控制实验平台,包括干旱(D -50%穿透雨)、P添加(P +50Kg P hm^-2a^-1)、模拟干旱×P添加(DP -50%穿透雨×+50Kg P hm^-2a^-1)、对照(CK)4个处理,且4种处理随机分布于3个区组,即设置了3个重复。使用常规的凋落物分解袋法探究实验处理对4个树种叶凋落物的分解系数、碳(C)、氮(N)元素动态变化的影响。结果表明:不同树种的叶凋落物因基质质量不同分解存在差异。模拟干旱处理对叶凋落物C、N损失产生抑制作用,但是对不同树种叶凋落物的抑制作用不同,原因是干旱处理通过抑制土壤分解者活动、减弱凋落物的物理破碎作用,间接抑制凋落物分解,并且由于高质量(含N量高)凋落物受微生物分解者影响较大,所以该凋落物分解受干旱抑制程度较大;P添加处理对叶凋落物C损失存在促进作用、N损失存在抑制作用,原因是土壤中P含量的升高,提高了微生物分解高C物质的能力,以及当土壤中P含量较高时,间接抑制微生物通过分解凋落物获取养分或者促进微生物优先完成自身生长代谢需要而不是合成分解凋落物所需要的酶,导致叶凋落物N损失下降;模拟干旱与P添加处理存在显著交互效应,P添加处理缓解或反转了干旱胁迫对叶凋落物分解的抑制作用。以上结果表明,不同基质质量的凋落物分解存在差异,对干旱胁迫的响应不同;在叶凋落物分解过程中,P添加促进C损失、抑制N损失;此外,在热带低地雨林,土壤中P可用性变化可调节干旱对凋落物分解的影响。     

Endogenous versus exogenous nutrient affects C, N, and P dynamics in decomposing litters in mid-subtropical forests of China

The effect of nutrient availability on litter decomposition has been a major focus of global change ecology. The relative impacts of endogenous (litter) and exogenous (soil) nutrient availability remain unclear. We studied the nutrient dynamics of decomposition in litter from two species with contrasting litter nutrient contents and stoichiometry: Pinus massoniana and Castanopsis sclerophylla. During a 540-day field incubation, we manipulated exogenous nutrient levels by adding microbially available C (+C), N (+N), P (+P), and all three (+CNP) at 90-day intervals. Relative to the no-nutrient control (CK), nutrient additions decreased organic C retention in C. sclerophylla, with the greatest effect observed in +CNP. Nitrogen content in P. massoniana litter similarly increased with nutrient addition, particularly +P and +CNP. The P addition treatments also increased P content in the litter of both species. Nitrogen content in C. sclerophylla and organic C content in P. massoniana were unaffected by nutrient additions. The C/N and C/P ratios in decomposing C. sclerophylla litter were significantly lower in the CK treatment, while those of P. massoniana litter were influenced by the interaction of nutrient addition and decomposition time. Increased availability of C, N, and P individually and collectively alters nutrient release dynamics in decomposing foliar litter. Litter quality, as determined by source species, is a key determinant of the impact of exogenous nutrient inputs. A stronger effect of P addition than N addition indicates a relatively N-rich and P-poor ecosystem.     

Polyphenols in litter from tropical montane forests across a wide range in soil fertility

In nutrient-poor ecosystems high polyphenol concentrations in plant litter have been proposed to influence soil nutrient availability in benefit of the plants. We addressed the question whether litter polyphenol concentrations vary across a soil chronosequence of almost identical geology, climate and plant species composition, but of a wide range in nitrogen (N) and phosphorus (P) availability in the Hawaiian Islands. Concentrations of total phenolics (TPh) and proanthocyanidins (PA) in leaf litter of the dominant tree species Metrosideros polymorpha were higher at the oldest, P-limited site compared to the youngest, N-limited site, with intermediate values at the two relatively fertile sites co-limited by N and P. Polyphenol concentrations in fine root litter differed considerably from those observed in leaf litter and varied differently across the soil age gradient. Long-term fertilization did not significantly alter polyphenol concentrations in Metrosideros litter at either site. Moreover, green leaves and leaf litter of Metrosideros showed similar relative differences among sites when compared between natural populations and plants from the same populations but grown in a common garden. These results suggest that polyphenol concentrations inherently vary among populations of the dominant tree species in Hawaiian montane forests possibly indicating an adaptation to ecosystem properties such as substrate age related differences in soil fertility. The combined above- and below-ground input rate of TPh ranged from 62.4 to 170.8 g/m²/yr and was significantly higher at the P-limited than at the N-limited site. Root-derived polyphenols contributed a much higher absolute and relative amount of phenolic input at the N-limited than at the P-limited site. The differences in amount, quality, and pathways of input might suggest specific interactions with soil processes and nutrient cycling among the Hawaiian rainforests studied here.     

Effects of litter types, microsite and root diameters on litter decomposition in Pinus sylvestris plantations of northern China

Background and aims

Litter decomposition is a major process in the carbon (C) flow and nutrient cycling of terrestrial ecosystems, but the effects of litter type, microsite, and root diameter on decomposition are poorly understood.

Methods

Litterbags were used to examine the decomposition rate of leaf litter and roots at three soil depths (5, 10 and 20 cm) over a 470-day period in Pinus sylvestris plantations in northern China.

Results

Leaves and the finest roots decomposed more quickly at 5 cm depth and coarser roots (>1-mm) decomposed more quickly at 10 and 20 cm depth. Roots generally decomposed more quickly than leaf litter, except at 5 cm deep; leaves decomposed more quickly than the coarsest roots (>5-mm). Root decomposition was strongly influenced by root diameter. Leaves experienced net nitrogen (N) immobilization and coarse roots (>2-mm) experienced more N release than fine roots. Significant heterogeneity was seen in N release for fine-roots (<2-mm) with N immobilization occurring in smaller (0.5–2-mm) roots and N release in the finest roots (<0.5-mm).

Conclusions

Soil depth of litter placement significantly influenced the relative contribution of the decomposition of leaves and roots of different diameters to carbon and nutrient cycling.     

Nitrogen availability affects saprotrophic basidiomycetes decomposing pine needles in a long term laboratory study

Fungi, especially basidiomycetous litter decomposers, are pivotal to the turnover of soil organic matter in forest soils. Many litter decomposing fungi have a well-developed capacity to translocate resources in their mycelia, a feature that may significantly affect carbon (C) and nitrogen (N) dynamics in decomposing litter. In an eight-month long laboratory study we investigated how the external availability of N affected the decomposition of Scots pine needles, fungal biomass production, N retention and N-mineralization by two litter decomposing fungi – Marasmius androsaceus and Mycena epipterygia. Glycine additions had a general, positive effect on fungal biomass production and increased accumulated needle mass loss after 8 months, suggesting that low N availability may limit fungal growth and activity in decomposing pine litter. Changes in the needle N pool reflected the dynamics of the fungal mycelium. During late decomposition stages, redistribution of mycelium and N out from the decomposed needles was observed for M. epipterygia, suggesting autophagous self degradation.     

The direct effects of UV-B radiation on Betula pubescens litter decomposing at four European field sites

A co-ordinated series of field experiments were conducted to consider the effects of elevated UV-B radiation applied directly to decomposing plant litter. Betula pubescens was decomposed under ambient and elevated UV-B (simulating a 15% ozone depletion) using outdoor irradiation facilities at Adventdalen, Norway (78° N), Abisko, Sweden (68° N), Amsterdam, The Netherlands (52° N,) and Patras, Greece (38° N). There was no significant effect of treatment on mass loss for samples collected after 2, 12 and 14 months decomposition at Amsterdam, or after 4 months decomposition at Adventdalen. Significant reductions in the mass loss of litter decomposing under elevated UV-B compared to ambient were found at the other 2 sites. The only effect of treatment on litter chemistry during decomposition was a significant reduction in the N concentration of material at Abisko and a significant increase in C:N at Patras for litter decomposing under elevated UV-B. Significant differences were found in the structure of the fungal community decomposing litter in Sweden, the only site to be tested. These data, and the few published studies of the response of decomposition to UV-B incident on litter suggest that, in the ecosystems and climates that have been studied, such direct effects are typically confined to the initial stages of decomposition, and are rather small in magnitude.     

Litter decomposition of a pine plantation is affected by species evenness and soil nitrogen availability

Background and aims

Litter decomposition is a key process controlling flows of energy and nutrients in ecosystems. Altered biodiversity and nutrient availability may affect litter decomposition. However, little is known about the response of litter decomposition to co-occurring changes in species evenness and soil nutrient availability.

Methods

We used a microcosm experiment to evaluate the simultaneous effects of species evenness (two levels), identity of the dominant species (three species) and soil N availability (control and N addition) on litter decomposition in a Mongolian pine (Pinus sylvestris var. mongolica) plantation in Northeast China. Mongolian pine needles and senesced aboveground materials of two dominant understory species (Setaria viridis and Artemisia scoparia) were used for incubation.

Results

Litter evenness, dominant species identity and N addition significantly affected species interaction and litter decomposition. Higher level of species evenness increased the decomposition rate of litter mixtures and decreased the incidence of antagonistic effects. A. scoparia-dominated litter mixtures decomposed faster than P. sylvestris var. mongolica- and S. viridis-dominated litter mixtures. Notably, N addition increased decomposition rate of both single-species litters and litter mixtures, and meanwhile altered the incidence and direction of non-additive effects during decomposition of litter mixtures. The presence of understory species litters stimulated the decomposition rate of pine litters irrespective of N addition, whereas the presence of pine litters suppressed the mass loss of A. scoparia litters. Moreover, N addition weakened the promoting effects of understory species litters on decomposition of pine litters.

Conclusions

Pine litter retarded the decomposition of understory species litters whereas its own decomposition was accelerated in mixtures. Nitrogen addition and understory species evenness altered species interaction through species-specific responses in litter mixtures and thus affected litter decomposition in Mongolian pine forests, which could produce a potential influence on ecosystem C budget and nutrient cycling.     

Responses of litter decomposition and nutrient release rate to water and nitrogen addition differed among three plant species dominated in a semi-arid grassland

Background and aims

Precipitation and nitrogen (N) deposition are predicted to increase in northern China. The present paper aimed to better understand how different dominant species in semi-arid grasslands in this region vary in their litter decomposition and nutrient release responses to increases in precipitation and N deposition.

Methods

Above-ground litter of three dominant species (two grasses, Agropyron cristatum and Stipa krylovii, and one forb, Artemisia frigida) was collected from areas without experimental treatments in a semi-arid grassland in Inner Mongolia. Litter decomposition was studied over three years to determine the effects of water and N addition on litter decomposition rate and nutrient dynamics.

Results

Litter mass loss and nutrient release were faster for the forb species than for the two grasses during decomposition. Both water and N addition increased litter mass loss of the grass A. cristatum, while the treatments showed no impacts on that of the forb A. frigida. Supplemental N had time-dependent, positive effects on litter mass loss of the grass S. krylovii. During the three-year decomposition study, the release of N from litter was inhibited by N addition for the three species, and it was promoted by water addition for the two grasses. Across all treatments, N and potassium (K) were released from the litter of all three species, whereas calcium (Ca) was accumulated. Phosphorus (P) and magnesium (Mg) were released from the forb litter but accumulated in the grass litter after three years of decomposition.

Conclusions

Our findings revealed that the litter decomposition response to water and N supplementation differed among dominant plant species in a semi-arid grassland, indicating that changes in dominant plant species induced by projected increases in precipitation and N deposition are likely to affect litter decomposition, nutrient cycling, and further biogeochemical cycles in this grassland. The asynchronous nutrient release of different species’ litter found in the present study highlights the complexity of nutrient replenishment from litter decomposition in the temperate steppe under scenarios of enhancing precipitation and N deposition.

     

Solar UV-B decreases decomposition in herbaceous plant litter in Tierra del Fuego, Argentina: potential role of an altered decomposer community

Tierra del Fuego, Argentina (55°S), receives increased solar ultraviolet‐B radiation (UV‐B) as a result of Antarctic stratospheric ozone depletion. We conducted a field study to examine direct and indirect effects of solar UV‐B radiation on decomposition of Gunnera magellanica, a native perennial herb, and on the native community of decomposer organisms. In general, indirect effects of UV‐B mostly occur due to changes in the chemical composition of litter, whereas direct effects during decomposition result from changes in decomposer organisms and/or differences in the photochemical breakdown of litter. We designed a full‐factorial experiment using senescent leaves that had received either near‐ambient or attenuated UV‐B during growth. The leaves were distributed in litterbags and allowed to decompose under near‐ambient or reduced solar UV‐B during the growing season. We evaluated initial litter quality, mass loss, and nutrient release of decomposing litter, and microbial colonization of both initial litter and decomposed litter. We found that litter that decomposed under near‐ambient UV‐B had significantly less mass loss than litter that decomposed under reduced UV‐B. The UV‐B conditions received by plants during growth, which did not affect mass loss and nutrient composition of litter, affected fungal species composition but in different ways throughout the decomposition period. Before the decomposition trial, Beauveria bassiana and Penicillium frequentans were higher under reduced UV‐B, whereas Cladosporium herbarum and pigmented bacteria were more common under the near‐ambient compared to the reduced UV‐B treatment. After the decomposition period, leaves that had grown under reduced UV‐B showed higher frequency of Penicillium thomii and lower frequency of Trichoderma polysporum than leaves that had grown under near‐ambient conditions. The UV‐B condition received during decomposition also affected fungal colonization, with Penicillium chrysogenum being more frequent in leaves that had decomposed under reduced UV‐B, while the other species were not affected. Our results demonstrate that, in this ecosystem, the effects of UV‐B radiation on decomposition apparently occurred mostly through changes in the fungal community, while changes in photochemical breakdown appeared to be less important.