Litter Microbial Biomass Research Articles

Effects of seasonal precipitation regimes on microbial biomass and extracellular enzyme activity during shrub foliar litter decomposition in a subtropical forest

Elucidating the mechanisms underlying microbial biomass and extracellular enzyme activity responses to the seasonal precipitation regime during foliar litter decomposition is highly important for understanding the material cycle of forest ecosystems in the context of global climate change; however, the specific underlying mechanisms remain unclear. Hence, a precipitation manipulation experiment involving a control (CK) and treatments with decreased precipitation in the dry season and extremely increased precipitation in the wet season (IE) and decreased precipitation in the dry season and proportionally increased precipitation in the wet season (IP) was conducted in a subtropical evergreen broad-leaved forest in China from October 2020 to October 2021. The moisture, microbial biomass, and extracellular enzyme activities of foliar litter from two dominant shrub species, Phyllostachys violascens and Alangium chinense, were measured at six stages during the dry and wet seasons. The results showed that (1) both IE and IP significantly decreased the microbial biomass carbon and microbial biomass nitrogen content and the activities of β-1,4-glucosidase, β-1,4-N-acetylglucosaminidase, acid phosphatase and cellulase in the dry season, while the opposite effects were observed in the wet season. (2) Compared with those of IE, the effects of IP on foliar litter microbial biomass and extracellular enzyme activity were more significant. (3) The results from the partial least squares model indicated that extracellular enzyme activity during foliar litter decomposition was strongly controlled by the foliar litter water content, microbial biomass nitrogen, the ratio of total carbon to total phosphorus, foliar litter total carbon, and foliar litter total nitrogen. These results provide an important theoretical basis for elucidating the microbial mechanisms driving litter decomposition in a subtropical forest under global climate change scenarios.

Decreased snow depth inhibits litter decomposition via changes in litter microbial biomass and enzyme activity

Decreased snow depth resulting from global warming has the potential to significantly impact biogeochemical cycles in cold forests. However, the specific mechanisms of how snow reduction affects litter decomposition and the underlying microbial processes remain unclear, this knowledge gap limits our ability to precisely predict ecological processes within cold forest ecosystems under climate change. Hence, a field experiment was conducted in a subalpine forest in southwestern China, involving a gradient of snow reduction levels (control, 50 %, 100 %) to investigate the effects of decreased snow on litter decomposition, as well as microbial biomass and activity, specifically focused on two common species: red birch (Betula albosinensis) and masters larch (Larix mastersiana). After one year of incubation, the decomposition rate (k-value) of the two types of litter ranged from 0.12 to 0.24 across three snow treatments. A significant lower litter mass loss, microbial biomass and enzyme activity were observed under decreased snow depth in winter. Furthermore, a hysteresis inhibitory effect of snow reduction on hydrolase activity was observed in the following growing season. Additionally, the high initial quality (lower C/N ratio) of red birch litter facilitated the colonization by a greater quantity of microorganisms, making it more susceptible to snow reduction compared to the low-quality masters larch litter. Structural equation models indicated that decreased snow depth hindered litter decomposition by altering the biological characterization of litter (e.g., microbial biomass and enzyme activity) and environmental variables (e.g., mean temperature and moisture content). The findings suggest that the potential decline in snow depth could inhibit litter decomposition by reducing microbial biomass and activity, implying that the future climate change may alter the material cycling processes in subalpine forest ecosystems.

The amounts and ratio of nitrogen and phosphorus addition drive the rate of litter decomposition in a subtropical forest

Nitrogen (N) and phosphorus (P) control biogeochemical cycling in terrestrial ecosystems. However, N and P addition effects on litter decomposition, especially biological pathways in subtropical forests, remain unclear. Here, a two-year field litterbag experiment was employed in a subtropical forest in southwestern China to examine N and P addition effects on litter biological decomposition with nine treatments: low and high N- and P-only addition (LN, HN, LP, and HP), NP coaddition (LNLP, LNHP, HNLP, and HNHP), and a control (CK). The results showed that the decomposition coefficient (k) was higher in NP coaddition treatments (P < 0.05), and lower in N- and P-only addition treatments than in CK (P < 0.05). The highest k was observed with LNLP (P < 0.05). The N- and P-only addition treatments decreased the losses of litter mass, lignin, cellulose, and condensed tannins, litter microbial biomass carbon (MBC), litter cellulase, and soil pH (P < 0.05). The NP coaddition treatments increased the losses of litter mass, lignin, and cellulose, MBC concentration, litter invertase, urease, cellulase, and catalase activities, soil arthropod diversity (S) in litterbags, and soil pH (P < 0.05). Litter acid phosphatase activity and N:P ratio were lower in N-only addition treatments but higher in P-only addition and NP coaddition treatments than in CK (P < 0.05). Structural equation model showed that litter MBC, S, cellulase, acid phosphatase, and polyphenol oxidase contributed to the loss of litter mass (P < 0.05). The litter N:P ratio was negatively logarithmically correlated with mass loss (P < 0.01). In conclusion, the negative effect of N addition on litter decomposition was reversed when P was added by increasing decomposed litter soil arthropod diversity, MBC concentration, and invertase and cellulase activities. Finally, the results highlighted the important role of the N:P ratio in litter decomposition.

Phosphorus addition reverses the negative effect of nitrogen addition on soil arthropods during litter decomposition in a subtropical forest

The increase in the nitrogen/phosphorus (N/P) ratio with rising N deposition is changing the biodiversity and function of terrestrial ecosystems at an unprecedented speed. However, the specific effects of P addition and its interaction with N on soil arthropods during litter decomposition in forests are unclear. A two-year experiment was carried out in western China to examine the effects of N and P addition on soil arthropods during litter decomposition. We applied a factorial design in a litterbag experiment combining two levels of low and high N and P alone addition (LN, HN, LP, and HP) and their coaddition (LNLP, LNHP, HNLP, and HNHP), including a no-addition control treatment (CK). The results show that soil pH, litter microbial biomass carbon (MBC), soil arthropod group number (G), individual number (I), diversity index (S), and richness index (M) were lower in the LN and HN treatments than in CK. Compared with CK, the LP and HP treatments reduced I but did not alter G, S, and M. The MBC, soil pH, and G, I, S, and M were higher and the cellulose and lignin concentrations and soil arthropod dominance index values were lower in the LNLP, LNHP, HNLP, and HNHP treatments than in CK. The positive effects of the LNLP, LNHP, HNLP, and HNHP treatments on the soil arthropods were related to the increased MBC and soil pH and decreased cellulose and lignin concentrations and litter N/P ratio. The litter N/P ratio was inversely related to the soil arthropod diversity. In conclusion, the negative effect of N addition on soil arthropod diversity during litter decomposition was reversed when P was added by shifting the MBC, cellulose and lignin concentrations, soil pH, and litter N/P ratio. Thus, increased P availability under rising N deposition scenarios may enhance soil arthropod diversity in this forest.

Long-Term Fire Regime Modifies Carbon and Nutrient Dynamics in Decomposing Eucalyptus pilularis Leaf Litter

The changes in fire regimes expected under climate change are likely to disrupt the biogeochemical cycling of carbon (C) and nutrients in forest ecosystems. Plant litter decomposition is a critical step in the terrestrial biogeochemical cycle, and is an important determinant of fire fuel load and forest C balance. We conducted a 277-day leaf litter decomposition experiment in an Australian eucalypt forest to test whether three contrasting, long-term fire regimes (no burning [NB], 4-yearly burning, and 2-yearly burning) were associated with different C and nutrient dynamics during litter decomposition. Fire regime had strong effects on many litter properties, including overall rates of decomposition and C loss, which were greatest in the NB treatment, suggesting that fire regime can modify the rate at which C is returned from litter to soil or the atmosphere. This has potentially important implications for soil C storage and atmospheric CO2 concentrations under a changing climate. High-frequency fire was associated with litter nutrient depletion and high microbial nutrient demand, but did not affect nutrient loss rates from decomposing litter, suggesting conservative use and retention of nutrients by the litter microbial biomass. These effects differed qualitatively between 2- and 4-yearly burning regimes, and they show how decadal-scale increases in fire frequency might contribute to soil nutrient depletion by disrupting decomposition. Many effects of fire regime on litter properties throughout decomposition were sensitive to litter bag re-collection date, suggesting that seasonal factors moderate the effects of fire regime, and that the role of fire regime-altered litter chemistry in shaping decomposition may be secondary to that of fire regime-altered environmental variables. Together, our findings highlight the potential consequences of long-term increases in prescribed fire frequency for litter decomposition and the storage and cycling of C and nutrients in eucalypt forests, and reveal the specific importance of average burn frequency in this context.

Altered leaf litter quality exacerbates the negative impact of climate change on decomposition

Abstract Leaf litter decomposition is a key component of global biogeochemical cycles that influence soil carbon storage, nutrient availability and plant productivity. Ongoing climate change will lead to warmer and drier conditions in many dryland regions, potentially affecting litter decomposition and nutrient dynamics. Climate change effects can be direct and/or indirect, for example, through changes in litter quality, yet their relative importance on litter decomposition remains unclear. We conducted a manipulative study in a semi‐arid shrubland to assess the effects of leaf litter quality, forecasted climate change, that is, +2.5°C warming (W), 30% rainfall reduction (RR) as well as their interaction (W + RR) to elucidate their relative effects on litter decomposition. Climatic effects alone reduced decomposition of a homogeneous Control leaf litter collected from Helianthemum squamatum shrubs growing in unmanipulated plots by 23.4%, 18.1% and 29.8% in the W, RR and W + RR treatments respectively. Leaf litter quality was lower in shrubs that had been growing in warmed plots (W and W + RR), as they had lower nutrient concentrations (P, Fe) and higher C:N and C:P ratios than leaf litter produced under ambient (Control) conditions. Lignin concentration was significantly lower in litter from W + RR plots, yet when both climate and litter quality were considered simultaneously, decomposition rates were 32.0%, 26.3% and 39.9% lower in W, RR and W + RR plots compared to Controls. In addition, we found greater microbial N immobilization in leaf litter incubated within warmed (W and W + RR) than within non‐warmed plots (Control and RR). Structural equation modelling showed that higher litter moisture and microbial biomass contents stimulated decomposition. Simulated climate change (W, RR and W + RR) reduced decomposition indirectly by negatively affecting litter moisture contents and litter microbial biomass. Microbial nitrogen immobilization was stimulated by the lower quality (i.e. high C:N ratios) of the leaf litter collected in shrubs from warmed plots (W and W + RR). Synthesis. Our findings indicate that forecasted climate change conditions slow down C and N cycling in a dryland ecosystem, an effect that is further exacerbated by climate change‐induced reductions in litter quality and related reductions in bacterial and fungal biomass in litter.

Effects of snow depth on acid-unhydrolyzable residue and acid-hydrolyzable carbohydrates degradation rates during foliar litter decomposition of Pinus koraiensis and Quercus mongolica

Differences in snow depth induced by climate change alter the microenvironments under snowpack, which affect litter decomposition. The degradation of acid-unhydrolyzable residue (AUR) and acid-hydrolyzable carbohydrates (ACID) is a key factor controlling soil organic matter formation. However, how snow depth affects the degradation is poorly understood. A snow depth manipulation experiment with snow-addition, snow-removal, and control treatments was conducted in Northeast China. Foliar litter of Pinus koraiensis and Quercus mongolica was placed on top of the ground in each treatment and sampled for six times from November 2014 to October 2015. AUR and ACID degradation rates decreased with the reduction of snow depth during the snow-covered season because of the insulating effect provided by snowpack; this relationship was reversed during the snow-free season due to more labile carbon remaining after the snowmelt. During the snow-covered season, AUR and ACID degradation rates were positively correlated to the sum of degree days above 0 °C. In contrast, AUR and ACID degradation rates were positively correlated with litter microbial biomass carbon during the snow-free season. Snow depth plays an important role in determining litter AUR and ACID degradation rates, but the effects on degradation rates differed between the snow-covered and snow-free seasons.

The influence of litter composition across the litter–soil interface on mass loss, nitrogen dynamics and the decomposer community

Many studies have investigated the influence of plant litter species composition on decomposition, but results have been context-dependent. Litter and soil are considered to constitute a decomposition continuum, but whether litter and soil ecosystems respond to litter identity and mixing in the same manner is unsure. In a field experiment utilizing 5 litter species and their mixture, we investigated whether the effects of litter identity and mixing on mass loss, nutrient dynamics, and decomposer communities are consistent across the litter–soil interface. In monoculture, mass loss and nitrogen (N) dynamics in the litter layer corresponded to the underlying soil N availability, demonstrating the continuum of resources from litter to soil. Litter microbial biomass and mesofauna abundance tended to be greater on litter with a faster decay rate and greater N release. However, soil decomposer abundance and diversity were not greater with higher soil N, causing litter and soil communities to respond differently to litter identity. Non-additive mass loss and N dynamics were observed after 6 months, and were correlated with non-additive litter microbial community composition and litter mesofauna communities, but all other aspects of the litter community and all measures of the soil community were additive. Decomposer communities and N dynamics did not respond similarly to the litter mixture across the litter–soil interface. This study is one of the few to comprehensively examine how a litter mixture influences decomposition dynamics and communities across the soil–litter interface, including multiple taxa and trophic levels. Our results demonstrate that processes associated with decomposition are decoupled for litter and soil, particularly in that litter showed non-additivity in mass loss, N release and decomposer community, but soil responses were largely additive.

The relationships between microbiological attributes and soil and litter quality in pure and mixed stands of native tree species in southeastern Bahia, Brazil

This study was conducted to link soil and litter microbial biomass and activity with soil and litter quality in the surface layer for different pure and mixed stands of native tree species in southeastern Bahia, Brazil. The purpose of the study was to see how strongly the differences among species and stands affect the microbiological attributes of the soil and to identify how microbial processes can be influenced by soil and litter quality. Soil and litter samples were collected from six pure and mixed stands of six hardwood species (Peltogyne angustifolia, Centrolobium robustum, Arapatiella psilophylla, Sclerolobium chrysophyllum, Cordia trichotoma, Macrolobium latifolium) native to the southeastern region of Bahia, Brazil. In plantations of native tree species in humid tropical regions, the immobilization efficiency of C and N by soil microbial biomass was strongly related to the chemical quality of the litter and to the organic matter quality of the soil. According to the variables analyzed, the mixed stand was similar to the natural forest and dissimilar to the pure stands. Litter microbial biomass represented a greater sink of C and N than soil microbial biomass and is an important contributor of resources to tropical soils having low C and N availability.

Relationships between bacterial diversity, microbial biomass, and litter quality in soils under different plant covers in northern Rio de Janeiro State, Brazil

Microbial populations are primarily responsible for the decomposition of organic residues, the nutrients cycle, and the flow of energy inside of soil. The present study was undertaken to link soil microbiological and soil biochemical parameters with soil- and litter-quality conditions in the surface layer from 5 sites differing in plant cover, in stand age, and in land-use history. The aim was to see how strongly these differences affect the soil microbial attributes and to identify how microbiological processes and structures can be influenced by soil and litter quality. Soil and litter samples were collected from 5 sites according to different land use: preserved forest, nonpreserved forest, secondary forest, pasture, and eucalyptus plantation. Soil and litter microbial biomass and activity were analysed and DNA was extracted from soil. The DNA concentrations and soil microbial C and N correlated positively and significantly, suggesting that these are decisive nutrients for microbial growth and time required for microbial biomass renewal. The litter microbial biomass represented a source of C and N higher than soil microbial biomass and can be an important layer to contribute to tropical soil with low C and N availability. The litter quality influenced the litter and soil microbial biomass and activity and the soil bacterial diversity. The chemical and nutritional quality of the litter influenced the structure and microbial community composition in the eucalyptus plantation.

Effects of fire frequency on oak litter decomposition and nitrogen dynamics

Fire can alter a multitude of ecosystem properties that have the potential to affect rates of litter decomposition and nitrogen dynamics. In this study, we examined the effect of long-term variation in fire frequency in Minnesota oak savanna on rates of litter mass loss of a common tree species (Quercus ellipsoidalis) to determine how site and intraspecific litter characteristics impacted by variation in fire frequency affect rates of decomposition, litter N dynamics, and litter microbial biomass. Although an increase in fire frequency resulted in higher litter temperatures, lower litter moisture, and decreased soil N and P availability, site characteristics had no net effect on rates of mass loss. Rather, litter C:N ratio, which increased with increased fire frequency, was the dominant predictor of rates of decomposition and litter N dynamics. Increased litter C:N led to decreased rates of decomposition and N immobilization, regardless of the characteristics of the site of decomposition. Therefore, it is the indirect effects of long-term variation in fire frequency on litter characteristics rather than fire's direct effects on site characteristics that determine fire effects on decomposition and N dynamics in this system. Slower rates of decomposition and increased N immobilization of litter produced in frequently burned sites may enhance fire-induced N losses, further decelerating rates of N cycling in frequently burned sites.

Alterações na biomassa e na atividade microbiana da serapilheira e do solo, em decorrência da substituição de cobertura florestal nativa por plantações de eucalipto, em diferentes sítios da Região Sudeste do Brasil

O eucalipto é a principal espécie florestal utilizada nos programas de reflorestamento no Brasil. Questiona-se quais as mudanças que essa espécie pode promover no solo. O impacto da substituição de uma cobertura vegetal por outra pode variar com as condições de clima e de solo, e os resultados obtidos numa região podem não ser extrapoláveis numa avaliação supra-regional. A biomassa e a atividade microbiana têm sido sugeridas como indicadores adequados de alterações provocadas por mudanças no uso da terra. Neste trabalho, essas características foram utilizadas para avaliar alterações na serapilheira e no solo em decorrência da substituição de cobertura florestal nativa por plantações de eucalipto em quatro sítios da Região Sudeste brasileira. A quantidade de serapilheira foi maior nas plantações de eucalipto do que nas formações nativas, o que foi explicado pela maior relação C:N na serapilheira do eucalipto. O impacto da conversão da vegetação nativa em eucalipto nos atributos microbiológicos da serapilheira e do solo variou conforme as características específicas analisadas de cada sítio florestal. Diferenças entre os teores de C e de N na biomassa microbiana de eucalipto e vegetação natural foram mais freqüentemente observadas no solo do que na serapilheira. A biomassa microbiana da serapilheira representou uma reserva de C e N maior do que a biomassa microbiana do solo, constituindo-se num compartimento de relevante contribuição a solos com baixos teores desses nutrientes.

Atividade microbiana, carbono e nitrogênio da biomassa microbiana em plantações de eucalipto, em seqüência de idades

Em plantações florestais, a atividade microbiana tem grande relevância para a ciclagem de nutrientes e a fertilidade do solo, uma vez que esses ecossistemas, devido a seus característicos longos períodos de rotação, proporcionam um contínuo aporte de serapilheira e morte de raízes, que contribuem para a manutenção e elevação do teor de matéria orgânica do solo. O objetivo deste trabalho foi caracterizar a atividade e a biomassa microbiana em solos sob plantações de eucalipto em distintas idades de cultivo. Foram avaliadas alterações na biomassa e atividade microbiana em solo e serapilheira de plantações de eucalipto com 1, 3, 5 e 13 anos de idade crescendo sob condições edafoclimáticas semelhantes. Encontraram-se maiores teores de C e N microbiano da serapilheira do que no solo, sugerindo que a serapilheira seria uma importante reserva de C e N microbiano em povoamentos de eucalipto. Não se verificou tendência de aumento ou diminuição da biomassa e da atividade microbiana com as idades das plantações, o que, provavelmente, decorreu do fato dos povoamentos estudados corresponderem a áreas de reforma. A qualidade orgânica da serapilheira influenciou diretamente a atividade, o C e N da biomassa microbiana da serapilheira. Os indicadores mais sensíveis para aferir variações dos solos das plantações de eucalipto foram os teores de C orgânico e N total, e na serapilheira foram os atributos microbianos, os teores de celulose, lignina e N.

Effects of alleviation of ecological stresses on an alpine tundra community over an eight‐year period

Alpine tundra ecosystems such as those which are dominated by ericaceous dwarf shrubs in northern Scandinavia are characterised by low productivity, and this is due in part to low availability of nutrients and retardation of those microbial processes required for nutrient cycling. We conducted an eight‐year field experiment in an alpine tundra in northern Sweden, in which eleven treatments aimed at alleviating possible stresses were applied to field plots; these included addition of various forms of nitrogen and other nutrients, addition of lime, addition of available carbon, and reduction of possible adverse effects of secondary metabolites produced by the dwarf shrub Empetrum hermaphroditum. Nearly all of the treatments had statistically significant effects on at least some of the plant species present in the experiment. Addition of nitrogen and liming both had important effects in reducing E. hermaphroditum cover and in these treatments Deschampsia flexuosa rapidly became dominant. Manipulations that reduced E. hermaphroditum or its effects frequently also stimulated Vaccinium myrtillus and V. vitis‐idaea. Fertilisation and liming treatments also often caused decreases in the mosses Dicranum sp. and Pleurozium schreberi, and the lichen Cladina spp. Ordination analysis revealed that vascular plant community structure was most significantly altered by treatments involving mineral nitrogen addition and liming, moss community structure by treatments involving addition of available carbon and lichen community structure by treatments involving addition of some forms of nitrogen, lime and reduction of effects of E. hermaphroditum. Nearly all treatments significantly reduced total plant diversity (species richness) and several treatments reduced diversity of each of the vascular plant, lichen and moss groups. This reduction in diversity was frequently associated with monopolisation of plots by D. flexuosa. Decomposition rates of litter added to the plots were generally only weakly influenced by treatments, but several treatments (most notably those involving nitrogen addition) induced litter nitrogen immobilisation and increased litter microbial biomass levels. Humus nitrogen and microbial levels were also sometimes enhanced by the nitrogen addition treatments. This suggests that those plots dominated by D. flexuosa were likely to result in greater conservation of nitrogen in the litter relative to those dominated by E. hermaphroditum. An important exception to this pattern was the effects of the liming treatment which, although responsible for an increase in D. flexuosa, caused net losses of nitrogen and reduced microbial biomass both in the litter and the humus. Our data therefore suggest that treatments which have vastly differing consequences for humus properties and the decomposer subsystem (and ultimately conservation of nitrogen in the soil), but which alleviate an inherent stress, have similar consequences above‐ground, e.g. E. hermaphroditum decline, D. flexuosa enhancement, and associated reductions of plant diversity.

Effects of three rates of atmospheric nitrogen deposition enriched with 15N on litter decomposition in a heathland

The decomposition and nitrogen dynamics of litter were investigated at three rates of N deposition, using 15N enriched (NH4)2SO4 applied in artificial rain (0.5, 2.0 and 8.0 g N m−2 in 11 months). The experiment was done in the field under transparent roofs, on leaf litter from Calluna vulgaris (L.) Hull, Molinia caerulea (L.) Moench and Deschampsia flexuosa (L.) Trin. These leaf litters differed in their contents of nitrogen, carbon and recalcitrant carbon compounds.All the litters increased in their δ 15N value markedly, the increases being greater as the rate of N deposition increased. However, the rates at which Molinia or Calluna leaves decomposed remained unaffected. The decomposition rate of Deschampsia leaved increased only temporarily at the highest rate of N deposition. Deschampsia leaves decomposed fastest; this suggests that the amount of carbon usuable by micro-organisms determines whether an additional amount of N will accelerate the decomposition process.The changes in the δ 15N values and total N contents of the litter indicated that Calluna and Deschampsia litter simultaneously retain and release N. The N released originated at least partly from the initial litter. In contrast, all the N (including the N that was retained from the rain) seemed to remain bound in the litter-microbial biomass complex of Molinia.