Nutrient Cycling In Ecosystems Research Articles

Dynamics of litterfall production in a forest damaged by oak wilt disease: a case study in a warm-temperate secondary forest

ABSTRACT Quantification of litterfall production is crucial for evaluating net primary productivity and nutrient cycling in forest ecosystems. High mortality among trees in the family Fagaceae due to Japanese oak wilt disease (JOW) might affect litterfall production in secondary forests; however, few studies have quantified these effects. We investigated litterfall production and forest structure in warm-temperate secondary forests in the Kaisho Forest over 6 and 12 years, respectively, and compared the dynamics among different phases of a JOW outbreak to assess the impacts of JOW on litterfall production. We found that total annual litterfall and leaf fall showed little change in peak to post-JOW periods and that changes in basal area were unrelated to total litterfall and leaf fall. The observed fluctuation in BA in the Kaisho Forest may not have been large enough to clearly reveal the effect of JOW during these periods. Canopy gaps formed by JOW may enhance the recruitment and growth rates of sub-canopy and understory trees. Our results may only be applicable to warm secondary forests where evergreen trees are replacing deciduous trees. Additional information on litterfall production in JOW-disturbed secondary forests is needed.

Drivers of soil nitrogen availability and carbon exchange processes in a High Arctic wetland

Increased soil nutrient availability, and associated increases in vegetation productivity, could create a negative feedback between Arctic ecosystems and the climate system, thereby reducing the contribution of Arctic ecosystems to future climate change. To predict whether this feedback will develop, it is important to understand the environmental controls over nutrient cycling in High Arctic ecosystems and their impact on carbon cycling processes. Here, we examined the environmental controls over soil nitrogen availability in a High Arctic wet sedge meadow and how abiotic factors and soil nitrogen influenced carbon dioxide exchange processes. The importance of environmental variables was consistent over the 3 years, but the magnitudes of their effect varied depending on climate conditions. Ammonium availability was higher in warmer years and wetter conditions, while drier areas within the wetland had higher nitrate availability. Carbon uptake was driven by soil moisture, active layer depth, and variability between sampling sites and years ( R2 = 0.753), while ecosystem respiration was influenced by nitrogen availability, soil temperature, active layer depth, and sampling year ( R2 = 0.848). Considered together, the future carbon dioxide source or sink potential of high latitude wetlands will largely depend on climate-induced changes in moisture and subsequent impacts on nutrient availability.

Effects of moderate drought extension on bacterial network structure in the rhizosphere soil of Leymus chinensis in semi-arid grasslands.

Grasslands are home to complex bacterial communities whose dynamic interactions play a crucial role in organic matter and nutrient cycling. However, there is limited understanding regarding the impact of changes in rainfall amount and the duration of dry intervals on bacterial interactions. To assess the impact of changes in precipitation volume and dry intervals on bacterial co-occurrence networks, we carried out precipitation manipulation experiments in the Eastern Eurasian Steppe of China. We found that alterations in precipitation and dry intervals did not significantly affect bacterial alpha and beta diversity. However, we observed significant changes in the co-occurrence network structure of bacteria in the rhizosphere ecosystem, with the 12-day dry interval showing the most notable reduction in the number of degrees, edges, and clustering coefficient. Additionally, the study identified putative keystone taxa and observed that the moderately prolonged dry intervals between precipitation events had a major effect on the robustness of bacterial networks. The complexity and stability of the network were found to be positively correlated, and were primarily influenced by soil water content, phosphorous, and aboveground biomass, followed by available phosphorus (AP) and total biomass. These findings have the potential to enhance our comprehension of how bacterial co-occurrence pattern react to variations in dry intervals, by regulating their interactions in water-limited ecosystems. This, in turn, could aid in predicting the impact of precipitation regime alterations on ecosystem nutrient cycling, as well as the feedback between ecosystem processes and global climate change.

Responses of Soil Enzyme Activity to Long-Term Nitrogen Enrichment and Water Addition in a Typical Steppe

Enzyme activity plays an important role in soil biochemical processes and is a key factor driving nutrient cycling. Although a great number of studies examined the effects of nitrogen (N) enrichment and water (W) addition on soil enzyme activity, most of them focused on the effect of only one resource and are based on short-term investigations. The separate and interactive effects of long-term changes in nitrogen and water on soil enzyme activity remain largely unexplored. In this study, we demonstrated the responses of two types of soil enzyme, β-1,4-glucosidase (BG) and acid phosphatase (APA), to increased nitrogen and water based on a 16-year experiment conducted in a typical grassland in northern China. The results show that: (1) nitrogen addition inhibited BG and APA in 2019 and 2020; (2) water addition had no significant effect on BG activity, but significantly reduced APA activity in 2020; and (3) redundancy analysis (RDA) showed that nitrogen and water addition affected soil enzyme activity mainly by affecting soil microbial biomass carbon (MBC). The present research offers a comprehensive explanation of how atmospheric nitrogen deposition and precipitation patterns affect the characteristics of microorganisms and the cycling of nutrients in grassland ecosystems.

Exploring the determinants of organic matter bioavailability through substrate-explicit thermodynamic modeling

Microbial decomposition of organic matter (OM) in river corridors is a major driver of nutrient and energy cycles in natural ecosystems. Recent advances in omics technologies enabled high-throughput generation of molecular data that could be used to inform biogeochemical models. With ultrahigh-resolution OM data becoming more readily available, in particular, the substrate-explicit thermodynamic modeling (SXTM) has emerged as a promising approach due to its ability to predict OM degradation and respiration rates from chemical formulae of compounds. This model implicitly assumes that all detected organic compounds are bioavailable, and that aerobic respiration is driven solely by thermodynamics. Despite promising demonstrations in previous studies, these assumptions may not be universally valid because OM degradation is a complex process governed by multiple factors. To identify key drivers of OM respiration, we performed a comprehensive analysis of diverse river systems using Fourier-transform ion cyclotron resonance mass spectrometry OM data and associated respiration measurements collected by the Worldwide Hydrobiogeochemistry Observation Network for Dynamic River Systems (WHONDRS) consortium. In support of our argument, we found that the incorporation of all compounds detected in the samples into the SXTM resulted in a poor correlation between the predicted and measured respiration rates. The data-model consistency was significantly improved by the selective use of a small subset (i.e., only about 5%) of organic compounds identified using an optimization method. Through a subsequent comparative analysis of the subset of compounds (which we presume as bioavailable) against the full set of compounds, we identified three major traits that potentially determine OM bioavailability, including: (1) thermodynamic favorability of aerobic respiration, (2) the number of C atoms contained in compounds, and (2) carbon/nitrogen (C/N) ratio. We found that all three factors serve as “filters” in that the compounds with undesirable properties in any of these traits are strictly excluded from the bioavailable fraction. This work highlights the importance of accounting for the complex interplay among multiple key traits to increase the predictive power of biogeochemical and ecosystem models.

Effects of bacteria on early-stage litter decomposition in Wudalianchi volcanic forest.

To understand the role of microorganisms in litter decomposition and nutrient cycling in volcanic forest ecosystem, we conducted in-situ litterbag decomposition experiment and used Illumina MiSeq high-throughput sequencing to analyze the response of bacterial community structure and diversity during the decomposition of litters from Larix gmelinii, Betula platyphylla and Populus davidiana, the dominant tree species in volcanic lava plateau of Wudalianchi. The results showed that mass remaining percentage of litters of three species after 18-month decomposition was 63.9%-68.1%. Litter of B. platyphylla decomposed the fastest, with significant difference in N, C:N, and N:P before and after decomposition. The richness of bacterial species and diversity index differed significantly among the three litters. Proteobacteria, Actinomycetes, and Bacteroidetes were the dominant bacterial groups at the phylum level, while Rhizobium, Sphingomonas, and Pseudomonas were the dominant groups at the genus level, with significant difference among the three litters. After 18 months, the dominant bacterial groups in litter tended to be consistent with those in volcanic lava platform soil. In the volcanic forest ecosystem, bacterial diversity and community structure were mainly affected by P, C:N, and N:P in the litter.

Chemical Stoichiometry and Enzyme Activity Changes during Mixed Decomposition of Camellia sinensis Pruning Residues and Companion Tree Species Litter

(1) Background: In managing ecological tea gardens, litter composed of pruned and fallen tea leaves from companion tree species is an important component of tea garden soil. The decomposition of litter plays a crucial role in regulating nutrient cycling in tea garden ecosystems. (2) Methods: This study employed the litterbag method to investigate chemical stoichiometry characteristics and enzyme activity changes during the decomposition process of pruned and fallen Camellia sinensis leaves from companion tree species in an ecological tea garden located in central Guizhou Province. (3) Results: With decomposition duration, the general trend of changes in the C/N and C/P ratios showed a decrease in the activity of UE (urease), AP (acid phosphatase), and PPO (polyphenol oxidase) followed by an increase, while CAT (catalase) and CEL (cellulase) activity decreased, then increased, and then decreased again. On the other hand, the N/P and the activity of SC (sucrase) first increased and then decreased. The C/N and the activities of UE, PPO, and AP generally reached their maximum values during the late decomposition stage (366–428 d), while the N/P and the CAT activity peaked during the mid-decomposition stage (305 d). In contrast, the activity of SC and CEL reached its maximum value during the early decomposition stage (123 d). The N/P ratios were significantly higher than those of the CS (C. sinensis) litter in the mixed treatment, while C/N and C/P ratios were significantly lower than those in the CS during decomposition for 184–366 days. The UE, CAT, AP, and SC activities of CBL (C. sinensis + B. luminifera) litter were significantly higher than those of the CS litter during decomposition. During the experiment, antagonistic effects were observed in the C/N and C/P ratios of the different litter types. Most mixed litter exhibited additive effects on enzyme activity, while a few showed nonadditive effects. For the nonadditive effects, most were antagonistic effects, mainly in the CPM (C. sinensis + C. glanduliferum) litter. A small portion, mainly observed in the CBL and CCG (C. sinensis + C. glanduliferum) litter, showed synergistic effects. (4) Conclusions: Selecting B. luminifera and C. glanduliferum to be part of the tree species composition in ecological tea gardens can produce positive mixed effects on enzyme activity during litter decomposition, increase nutrient return capacity, maintain tea garden fertility, and achieve the ecological development of tea gardens.

Warmer temperature promotes the contribution of invertebrate fauna to litter components release in an alpine meadow on the Qinghai-Tibetan Plateau

How warming and invertebrate fauna concurrently influence litter carbon and nutrient turnover in alpine meadow is still poorly known. Using a litterbag technique, we evaluated the effects of temperature (ambient temperature vs. warming temperature) × mesh (fine mesh without invertebrate fauna access vs. coarse mesh with invertebrate fauna access) on litter decay (i.e., carbon and nitrogen release, lignin and cellulose degradation) across two typical seasons (cold season vs. warm season) in an alpine meadow ecosystem on the Qinghai-Tibetan Plateau. Our results showed that the whole-soil-profile warming significantly increased litter cellulose degradation (+47%), but less affected the decay of other litter components (i.e., carbon, nitrogen, and lignin: + 7–18% increase). The loss of nitrogen and lignin from litter significantly increased by ca. 2 times in the presence of invertebrate fauna. Moreover, the release of all litter chemical components was significantly faster (by 1.5–5.2 times) in warm season than in cold season. Further, litter carbon release and lignin degradation rates were markedly influenced by the interacting effects of mesh × season, and mesh × temperature, respectively. Overall, these findings highlight the importance of invertebrate fauna as a commonly overlooked co-determinant of the warming effect on litter decay patterns in cold biomes; the changed release rates of litter components in the context of on-going warming may have far-reaching effects on carbon and nutrient cycling in alpine ecosystems.

Effect of changes in soil moisture on agriculture soils: response of microbial community, enzymatic and physiological diversity

Global warming-induced drought stress and the duration of changes in soil moisture content may reshape or complicate these ecological relations. Biological activity could be affected severely by the impact of drought on agricultural ecosystems. In this study, 4 agricultural different soils were collected, and analyzed at each time gradient (0, 1, 2, 4, 8th week) to determine the physicochemical parameters, microbial abundance, enzyme activities (dehydrogenases (DH), phosphatases (acid ACP and alkaline ALP) and urease (UR)), and physiological diversity. We found that soil physicochemical properties fluctuated within the time gradient in all sites, but significantly decreased in total organic carbon, available phosphorus (P2O5 Olsena), nitrate (NO3-), ammonium (NH4+) (except for S site) and calcium carbonate (CaCO3) content (except for L site). Overall, ALP activity was higher compared to ACP activity. The DH activity was highest at sampling day (high moisture content) in G and N sites, and at 2nd week for L and S sites, but significantly decreased at the end of the experiment. The UR activity decreased significantly in G, L and N sites but increased in S site at the end of our experiment compared to the sampling day. Overall, the physiological diversity of the microbial community was strongly affected by water stress in the utilization of carbohydrates, carboxylic and acetic acids, amino acids, polymers, and amines, in all sites. Our findings highlighted that the short-term duration of drought stress had a significant influence on soil biological activity. This may improve the understanding of impact of soil moisture changes on soil nutrient cycling and biological activities in agricultural ecosystems.

Litter mixing promoted decomposition and altered microbial community in common bean root litter

BackgroundDecomposition of plant litter is a key driver of carbon and nutrient cycling in terrestrial ecosystems. Mixing litters of different plant species may alter the decomposition rate, but its effect on the microbial decomposer community in plant litter is not fully understood. Here, we tested the effects of mixing with maize (Zea mays L.) and soybean [Glycine max (Linn.) Merr.] stalk litters on the decomposition and microbial decomposer communities of common bean (Phaseolus vulgaris L.) root litter at the early decomposition stage in a litterbag experiment.ResultsMixing with maize stalk litter, soybean stalk litter, and both of these litters increased the decomposition rate of common bean root litter at 56 day but not 14 day after incubation. Litter mixing also increased the decomposition rate of the whole liter mixture at 56 day after incubation. Amplicon sequencing found that litter mixing altered the composition of bacterial (at 56 day after incubation) and fungal communities (at both 14 and 56 day after incubation) in common bean root litter. Litter mixing increased the abundance and alpha diversity of fungal communities in common bean root litter at 56 day after incubation. Particularly, litter mixing stimulated certain microbial taxa, such as Fusarium, Aspergillus and Stachybotrys spp. In addition, a pot experiment with adding litters in the soil showed that litter mixing promoted growth of common bean seedlings and increased soil nitrogen and phosphorus contents.ConclusionsThis study showed that litter mixing can promote the decomposition rate and cause shifts in microbial decomposer communities, which may positively affect crop growth.

Temperature rather than N availability determines root exudation of alpine coniferous forests on the eastern Tibetan Plateau along elevation gradients.

Root exudation fulfills fundamental roles in regulating carbon (C)-nutrient cycling in forest ecosystems, yet the main ecological drivers of root exudation and underlying mechanisms in forests under natural gradients remain poorly understood. Here, we investigated the intraspecific variation of root exudation rates in two alpine coniferous forests (Abies faxoniana and Abies georgei) along two elevation gradients on the eastern Tibetan Plateau. Meanwhile, the fine root traits and associated climate and soil parameters were assessed to examine the effects of elevation-dependent changes in climatic and soil nutrient conditions on root exudation. Results showed that root exudation rates decreased with increasing elevation and were positively correlated with mean air temperature. However, the relationships of root exudation with soil moisture and soil N availability were not significant. The structural equation model (SEM) further revealed that air temperature affected root exudation both directly and indirectly through the effects on fine root morphology and biomass, implying that the adaption of root C allocation and fine root morphological traits to low temperatures primarily resulted in declined root exudation at higher elevations. These results highlight the perceived importance of temperature in determining the elevational variation of root exudation in alpine coniferous forests, which has foreseeably great implications for the exudate-mediated ecosystem C and nutrient processes in the face of drastic warming on the eastern Tibetan Plateau.

Leaf litter chemistry and its effects on soil microorganisms in different ages of Zanthoxylum planispinum var. Dintanensis

BackgroundLeaf litter is the products of metabolism during the growth and development of plantation, and it is also an important component of nutrient cycling in plantation ecosystems. However, leaf litter chemistry and its effects on soil microorganisms in different ages, as well as the interactions between chemical components in leaf litter have been rarely reported. Based on this, this paper took Zanthoxylum planispinum var. dintanensis (hereafter Z. planispinum) plantations of 5–7, 10–12, 20–22, and 28–32 years old as the objects. By using one-way ANOVA, Pearson correlation analysis and redundancy analysis, we investigated leaf litter chemistry and its effects on soil microorganisms in different ages, and to reveal internal correlation of various chemical components in leaf litter, which can provide a scientific basis for the regulation of soil microbial activity in plantations.ResultsThe variation of organic carbon with plantation age was more stable compared to total nitrogen and phosphorus of leaf litter. Nitrogen resorption was stronger than phosphorus resorption efficiency in Z. planispinum, and resorption efficiencies of leaf nitrogen and phosphorus for different ages were lower than the global average. Total nitrogen was highly significantly positively correlated with lignin, and total potassium was significantly positively correlated with tannin, suggesting the increase of inorganic substances in leaf litter would promote the accumulation of secondary metabolites. The leaf litter chemical traits explained up to 72% of soil microorganisms, where lignin was positively correlated with fungi and negatively correlated with bacteria, indicating that fungi are able to decompose lower quality litter and can break down complex and stable organic compounds more rapidly than bacteria. The nutrient elements carbon and nitrogen in the leaf litter and their interrelationship also have a great impact on soil microorganisms, because carbon is not only the element that provides energy, but also the element with the largest content in the microbiota.ConclusionsThe sustained increase in inorganic nutrients of leaf litter did not favor the decomposition of secondary metabolites, but rather inhibited the degradation of leaf litter. The significant positive effect of the leaf litter chemistry on soil microorganisms indicates the important role of leaf litter in promoting nutrient cycling in Z. planispinum plantations.

Shifts of understory vegetation induced by thinning drive the expansion of soil rare fungi

The gap formation due to forest thinning regulates the understorey microclimate, ground vegetation, and soil biodiversity. However, little is known about abundant and rare taxa's various patterns and assemblage mechanisms under thinning gaps. Thinning gaps with increasing sizes (0, 74, 109, and 196 m2) were established 12 years ago in a 36-year-old spruce plantation in a temperate mountain climate. Soil fungal and bacterial communities were analyzed by MiSeq sequencing and related to soil physicochemical properties and aboveground vegetation. The functional microbial taxa were sorted by FAPROTAX and Fungi Functional Guild database. The bacterial community stabilized under varied thinning intensities and was not different from the control plots, whereas the richness of the rare fungal taxa was at least 1.5-fold higher in the large gaps than in the small ones. Total phosphorus and dissolved organic carbon were the main factors influencing microbial communities in soil under various thinning gaps. The diversity and richness of the entire fungal community and rare fungal taxa increased with the understorey vegetation coverage and shrub biomass after thinning. Gap formation by thinning stimulated the understorey vegetation, the rare saprotroph (Undefined Saprotroph), and mycorrhizal fungi (Ectomycorrhizal-Endophyte-Ericoid Mycorrhizal-Litter Saprotroph-Orchid Mycorrhizal and Bryophyte Parasite-Lichen Parasite-Ectomycorrhizal-Ericoid Mycorrhizal-Undefined Saprotroph), which may accelerate nutrient cycling in forest ecosystems. However, the abundance of Endophyte-Plant Pathogens increased by eight times, which showed the potential risk for the artificial spruce forests. Thus, fungi may be the driving force of forest restoration and nutrient cycling under the increasing intensity of thinning and may induce plant diseases. Therefore, vegetation coverage and microbial functional diversity should be considered to evaluate the sustainability of the artificial forest ecosystem and forest restoration.

Precipitation Drives Soil Protist Diversity and Community Structure in Dry Grasslands.

Protists are essential components of soil microbial communities, mediating nutrient cycling and ecosystem functions in terrestrial ecosystems. However, their distribution patterns and driving factors, particularly, the relative importance of climate, plant and soil factors, remain largely unknown. This limits our understanding of soil protist roles in ecosystem functions and their responses to climate change. This is particularly a concern in dryland ecosystems where soil microbiomes are more important for ecosystem functions because plant diversity and growth are heavily constrained by environmental stresses. Here, we explored protist diversity and their driving factors in grassland soils on the Tibetan Plateau, which is a typical dryland region with yearly low temperatures. Soil protist diversity significantly decreased along the gradient of meadow, steppe, and desert. Soil protist diversity positively correlated with precipitation, plant biomass and soil nutrients, but these correlations were changed by grazing. Structural equation and random forest models demonstrated that precipitation dominated soil protist diversity directly and indirectly by influencing plant and soil factors. Soil protist community structure gradually shifted along meadow, steppe and desert, and was driven more by precipitation than by plant and soil factors. Soil protist community compositions were dominated by Cercozoa, Ciliophora and Chlorophyta. In particular, Ciliophora increased but Chlorophyta decreased in relative abundance along the gradient of meadow, steppe and desert. These results demonstrate that precipitation plays more important roles in driving soil protist diversity and community structure than plant and soil factors, suggesting that future precipitation change profoundly alters soil protist community and functions in dry grasslands.

Root exudation patterns of Chinese fir after thinning relating to root characteristics and soil conditions

Root exudates are crucial to belowground carbon allocation and nutrient cycling in forest ecosystems. Few studies have focused on the effects of forest management activities, such as thinning, on root exudation rates of mature woody species in subtropical regions. In this study, we aimed to determine three kinds of root exudation rates (i.e., per mass, length, and area) in situ under three thinning intensities: Control (unthinned), light thinning intensity (LIT, felled 30% of individual trees), and heavy thinning intensity (HIT, felled 70% of individual trees), in a 29-year-old Chinese fir plantation. We found that root exudation rates increased after thinning and showed significant seasonal dynamics, with the highest and lowest rates being in summer and winter, respectively. The root exudation rates increased with microbial biomass C and N. Positive relationships between the root exudation rates, number of root tips, and root vitalities were observed. The root exudation rates increased with root diameter and decreasing specific root area, suggesting that resource-conservative roots of Chinese fir were biased toward accelerating root exudation rate for nutrient acquisition, instead of optimizing root morphology. In addition, thinning reduced overall soil total carbon content in a Chinese fir plantation. The soil total C content was higher in HIT than in LIT, indicating that HIT could reduce soil C loss by root exudation rates. These findings elucidate how thinning affects fine root exudation rates by altering soil conditions and root characteristics while contributing to our ability to predict belowground C allocation and nutrient cycling in response to silvicultural treatments.

High Sensitivity of the Antarctic Rotifer Adineta editae to Metals and Ecological Relevance in Contaminated Site Risk Assessments.

Anthropogenic activities in Antarctica have led to contamination of terrestrial sites, and soils in ice-free areas have elevated concentrations of metals, particularly around current and historic research stations. Effective management of Antarctic contaminated sites depends on the assessment of risks to a representative range of native terrestrial species. Bdelloid rotifers are an abundant and biodiverse component of Antarctic limnoterrestrial communities and play a key role in nutrient cycling in Antarctic ecosystems. The present study investigates the toxicity of five metals (cadmium, copper, nickel, lead, and zinc) to the endemic bdelloid rotifer Adineta editae, both singly and in metal mixtures. Based on the concentrations tested, zinc was the most toxic metal to survival with a 7-day median lethal concentration (LC50) of 344 µg Zn/L, followed by cadmium with a 7-day LC50 of 1542 µg Cd/L. Rotifers showed high sensitivity using cryptobiosis (chemobiosis) as a sublethal behavioral endpoint. Chemobiosis was triggered in A. editae at low metal concentrations (e.g., 6 µg/L Pb) and is likely a protective mechanism and survival strategy to minimize exposure to stressful conditions. Lead and copper were most toxic to rotifer behavior, with 4-day median effect concentrations (EC50s) of 18 and 27 µg/L, respectively, followed by zinc and cadmium (4-day EC50 values of 52 and 245 µg/L, respectively). The response of rotifers to the metal mixtures was antagonistic, with less toxicity observed than was predicted by the model developed from the single-metal exposure data. The present study provides evidence that this bdelloid rotifer represents a relatively sensitive microinvertebrate species to metals and is recommended for use in contaminant risk assessments in Antarctica. Environ Toxicol Chem 2023;42:1409-1419. © 2023 SETAC.

Altitudinal variations and seasonal dynamics of near-surface and soil temperatures in subtropical forests of Mt. Guanshan, Jiangxi Province, China.

Temperature lapse rate (TLR), measured as the degree of temperature change along an altitudinal gradient, is a key indicator of multiple ecological processes of mountain systems. Although many studies have examined temperature changes of open air or near-surface along altitudes, we know little about altitudinal variations of soil temperature, which play an important role in regulating growth and reproduction of organisms, as well as ecosystem nutrient cycling. Based on temperature data of near-surface (15 cm above ground) and soil layers (8 cm below ground) from 12 sampling sites of subtropical forest along an altitudinal gradient (300-1300 m) in Jiangxi Guan-shan National Nature Reserve from September 2018 to August 2021, we calculated the lapse rates of mean, maximum, and minimum temperatures, as well as accumulated temperatures by using simple linear regression for both near-surface and soil temperature. The seasonal dynamics of aforementioned variables were also evaluated. The results showed that there were large differences among mean, maximum, and minimum lapse rates for annual near-surface temperature, which were 0.38, 0.31 and 0.51 ℃·(100 m)-1, respectively. But little variation was documented for soil temperature which were 0.40, 0.38 and 0.42 ℃·(100 m)-1, respectively. The seasonal variations of temperature lapse rates for near-surface and soil layers were minor except for minimum temperature. The lapse rates of minimum temperature were deeper in spring and winter for near-surface and in spring and autumn for soil layers. For growing degree days (GDD), the accumulated temperature under both layers were negatively correlated with altitude, and the lapse rates of ≥5 ℃ were 163 ℃·d·(100 m)-1 for near-surface and 179 ℃·d·(100 m)-1 for soil. The ≥5 ℃ GDD in soil were about 15 days longer than that in near-surface at the same altitude. The results showed inconsistent patterns of altitudinal variations between near-surface and soil temperature. Soil temperature and its lapse rates had minor seasonal variations compared with the near-surface counterparts, which was related to the strong buffering capacity of soil.

Let sleeping logs lie: Beta diversity increases in deadwood beetle communities over time.

Research Highlight: Seibold, S., Weisser, W., Ambarli, D., Gossner, M. M., Mori, A., Cadotte, M., Hagge, J., Bässler, C. & Thorn, S. (2022). Drivers of community assembly change during succession in wood-decomposing beetle communities. Journal of Animal Ecology, https://doi.org/10.1111/1365-2656.13843. Paradigms of succession and its drivers have largely developed from systems relying on living plants. A substantial portion of terrestrial biodiversity and biomass exists in detrital systems that rely on dead organic matter, yet successional patterns in detrital systems have received far less attention. In particular, deadwood significantly contributes to forest ecosystem nutrient cycling and storage and represents a relatively long-lived detrital system in which to study patterns of succession. Seibold et al. examined successional patterns of deadwood beetle communities over 8 years in a large-scale experiment that included 379 logs from 13 different tree species in 30 forest stands in three regions of Germany. They predicted that deadwood beetle communities would initially differ among deadwood tree species, across space, and with climatic differences but would become more similar over time as deadwood decomposed and characteristics of remaining habitat become more homogeneous. However, Seibold et al. predicted that beetle communities would become increasingly different across space along deadwood succession if late successional species were weaker dispersers than early successional species. Surprisingly, beetle communities became more dissimilar over time contrary to predictions. But, as predicted, increasing phylogenetic distance among tree species led to increasingly dissimilar deadwood beetle communities. Lastly, differences across space, forest structure and climate led to different deadwood beetle communities, but these effects remained constant over time. These results suggest that deadwood succession is influenced by both deterministic and stochastic processes and that stochastic processes may be increasingly important in late successional stages. Seibold et al. reveal important drivers of detrital successional patterns in deadwood that indicate that deadwood beetle biodiversity can be promoted via maintaining a diversity of deadwood decay stages across a large phylogenetic diversity of trees species and structurally diverse forests. Future studies that test the mechanisms driving these patterns and whether these results hold for other saproxylic organisms will help inform forest conservation and management strategies.

Short-term effects of forest gap size on soil enzyme activity in a Platycladus orientalis plantation

IntroductionSoil enzymes play a critical role in organic matter decomposition and nutrient cycling in forest ecosystems. However, the effects of forest gaps on soil enzyme activities remain uncertain.MethodsThis study aims to investigate the short-term effects of forest gap size on soil enzyme activities in Platycladus orientalis plantations. We conducted a study in a 50-year Platycladus orientalis plantation in Xuzhou, sampling soils from three levels of forest gap size (4 m radius, S; 8 m radius, M and 12 m radius, L) at different positions (within gap, edge, and outside the gap) and control plots (CK, no gaps) 2a after the creation of gaps. Soil peroxidase, dehydrogenase, urease, and invertase activities were measured.ResultsSpecifically, we found that M and S gaps had significantly (p < 0.05) higher soil peroxidase activity at the outside position in April and October, respectively, than CK. Additionally, L gaps had significantly (p < 0.05) higher soil dehydrogenase activity at the outside position in April than CK. Furthermore, L and S gaps had significantly (p < 0.05) higher soil urease activity at the outside position in October and July, respectively, than CK. Lastly, L and S gaps had significantly (p < 0.05) higher soil urease activity at the outside position in July than CK.ConclusionOur findings highlight the significant impact of canopy gaps on soil enzyme activities, which has important implications for forest management and conservation.

Distribution of six phenolic acids and soil nutrient relationships during litter decomposition in Rhododendron forests

Litter decomposition is an essential process in nutrient cycling in terrestrial ecosystems. Phenolic acids have an allelopathic effect on the natural regeneration of rhododendron forests, which was recently observed in rhododendron forests in Southwest China. We investigated the distribution of phenolic acids and their relationship with soil nutrients during litter decomposition to provide a reference for the subsequent artificial management of rhododendron forests. High-performance liquid chromatography (HPLC) was used to analyze the contents of six phenolic acids in the litter layer, humus layer, and soil layer during litter decomposition. During the first 3 three months, the rapid decomposition of the litter from two early flowering rhododendron species released large amounts of phenolic acids, and the lower litter layer decomposed rapidly. In addition, the total phenolic acid content in the litter decreased by 257.60 μg/g (Rhododendron siderophyllum) and 53.12 μg/g (Rhododendron annae) in the first three 3 months. During subsequent litter decomposition, the protocatechuic acid content in the litters of Rhododendron siderophyllum ranged from 20.15 μg/g to 39.12 μg/g, and the ferulic acid content was 10.70 μg/g to –33.79 μg/g. The protocatechuic acid and ferulic acid contents in the litter of Rhododendron annae were in the ranges of 10.88—19.68 μg/g and 10.75—18.00 μg/g, respectively. The contents of these two phenolic acids and the trend of decomposition were different from those of gallic acid, chlorogenic acid, caffeic acid and syringic acid. The distribution of phenolic acids was influenced by soil organic matter (SOM), soil ammonium nitrogen (NH4+), soil nitrate nitrogen (NO3–) and soil available phosphorus (AP). The results indicate seasonal variations in phenolic acid release during litter decomposition. The amount of phenolic acid in the litter decreased after 18 months of decomposition, but it returned to the previous level in the soil and the humus after different trends. More research into the metabolism of phenolic acids is needed.