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Predicting species abundance is one of the most fundamental pursuits of ecology. Combining the information encoded in functional traits and metacommunities provides a new perspective to predict the abundance of species in communities. We applied a community assembly via trait selection model to predict quadrat-scale species abundances using functional trait variation on ontogenetic stages and metacommunity information for over 490 plant species in a subtropical forest and a lowland tropical forest in Yunnan, China. The relative importance of trait-based selection, mass effects, and stochasticity in shaping local species abundances is evaluated using different null models. We found both mass effects and trait selection contribute to local abundance patterns. Trait selection was detectable at all studied spatial scales (0.04–1 ha), with its strength stronger at larger scales and in the subtropical forest. In contrast, the importance of stochasticity decreased with spatial scale. A significant mass effect of the metacommunity was observed at small spatial scales. Our results indicate that tree community assembly is primarily driven by ontogenetic traits and metacommunity effects. Our findings also demonstrate that including ontogenetic trait variation into predictive frameworks allows ecologists to infer ecological mechanisms operating in community assembly at the individual level.

Rapid global warming during the Paleocene-Eocene Thermal Maximum (PETM) profoundly affected the marine and terrestrial environments. However, details of the climate and vegetation of subtropical and arid regions of central China during the hyperthermal event are poorly understood. Here, we report a palynological record from the black shale of the lowermost Yangxi Formation exposed in Songzi city, western Jianghan Basin, central China. Biostratigraphy, magnetostratigraphy and isotope stratigraphy indicate a PETM age for the sedimentary succession. The palynological assemblage was characterized by high abundances of diverse tropical and subtropical broadleaved tree pollen, providing strong evidence of a dense south subtropical forest ecosystem that once existed in the arid belt of central China during the PETM. The reconstructed climatic parameters indicate an extremely warm and humid south subtropical climate, with mean annual temperatures (MAT) ranging from 21 to 24 °C and mean annual precipitation (MAP) ranging from 1396 to 1997 mm. The reconstructed precipitation was surprisingly high for such an arid setting that widespread arid climate prevailed in central China at that time. These findings demonstrate that rapid global warming during the PETM significantly increased precipitation, leading to the growth of dense forest ecosystems as well as increasing lake eutrophication in central China. The changes to precipitation and terrestrial ecosystems during this warming event are considerably more significant than previously reported in other mid-latitude regions, and highlighting the need to consider regional geographic characteristics to fully understand how the environment responds to rapid global warming.

The standard litterbag method isolates soil or litter from decomposing roots by a dense nylon mesh that is likely to underestimate root decomposition rate. Thus, we evaluated the effect of direct contact between roots and soil or litter during root decomposition. Schima superba and Cleyera japonica order 1–3, 4–5, and 6 roots were decomposed using two types of litterbags at two soil horizons: standard litterbags (R_O, pure root in O horizon; R_A, pure root in A horizon) and mixed litterbags (R + L_O, mixed root with semi-decomposed litter in O horizon; and R + HS_A, mixed root with humus soil in A horizon). The mass and nutrient dynamics were measured in one year of decomposition. After one year of decomposition, litterbag types and soil horizons significantly affected root mass and nutrient dynamics. Litterbags mixed with humus soil and litter increased 1–3 order root decomposition rate by 139–143% and 42–89%, respectively. Furthermore, 1–3 order roots had a significantly different decomposition rate than higher-order roots, but standard and mixed litterbags showed the opposite effect. The decomposition rate of 1–3 order roots appears to be more sensitive to litterbag type than higher-order roots. Directly contact between root and soil or litter was important for root decomposition in corresponding soil layers. Standard litterbags significantly underestimate the decomposition rate of lower-order roots in the early stages of decomposition.

Few biodiversity indicators are available that reflect the state of broad-sense biodiversity—rather than of particular taxa—at fine spatial and temporal resolution. The Biodiversity Intactness Index (BII) estimates how the average abundance of native terrestrial species in a region compares with their abundances before pronounced human impacts. BII is designed for use with data from a wide range of taxa and functional groups and for estimation at any resolution for which data on land use and related pressures are available. For each year from 2001 to 2012, we combined models of how land use and related pressures in tropical and subtropical forested biomes affect overall abundance and compositional similarity of plants, fungi, invertebrates and vertebrates, with data on anthropogenic pressures to produce annual maps of modelled BII at a spatial resolution of 30 arc seconds (roughly 1 km at the equator) across tropical and subtropical forested biomes. This is the first time temporal change in BII has been estimated across such a large region. The approach we have used to model compositional similarity uses data more efficiently than that used previously when estimating BII. Across tropical and subtropical biomes, BII fell by an average of 1.9 percentage points between 2001 and 2012, with 81 countries seeing an average reduction and 43 an average increase; the extent of primary forest fell by 3.9% over the same period. Changes are not strongly related to countries’ rates of economic growth over the same period.

Subtropical forests are important ecosystems globally due to their extensive role in carbon sequestration. Extreme climate events are known to introduce disturbances in the ecosystem that cause long-term changes in carbon balance and radiation reflectance. However, how these ecosystem function changes contribute to global warming in terms of radiative forcing (RF), especially in the years following a disturbance, still needs to be investigated. We studied an extreme snow event that occurred in a subtropical evergreen broadleaved forest in south-western China in 2015 and used 9 years (2011-2019) of net ecosystem CO2 exchange (NEE) and surface albedo (α) data to investigate the effect of the event on the ecosystem RF changes. In the year of the disturbance, leaf area index (LAI) declined by 40% and α by 32%. The annual NEE was -718 ± 128 g C m-2 as a sink in the pre-disturbance years (2011-2014), but after the event, the sink strength dropped significantly by 76% (2015). Both the vegetation, indicated by LAI, and α recovered to pre-disturbance levels in the fourth post-disturbance year (2018). However, the NEE recovery lagged and occurred a year later in 2019, suggesting a more severe and lasting impact on the ecosystem carbon balance. Overall, the extreme event caused a positive (warming effect) net RF which was predominantly caused by changes in α (90%-93%) rather than those in NEE. This result suggests that, compared to the climate effect caused by forest carbon sequestration changes, the climate effect of α alterations can be more sensitive to vegetation damage induced by natural disturbances. Moreover, this study demonstrates the important role of vegetation recovery in driving canopy reflectance and ecosystem carbon balance during the post-disturbance period, which determines the ecosystem feedbacks to the climate change.

Tree-cavities are considered as key components that support multiple species, including endemic ones, in subtropical forests in Yambaru, the northern area of Okinawa Island, Japan. Here, we establi...

The selection of reforestation species that promote rapid forest establishment has now become more challenging as a result of global climate change. This is because a recent increase in droughts associated with the El Nino Southern Oscillation is presenting a critical challenge to forest seedling survival and growth, thus threatening biodiversity and ecosystem services supply. The severe drought associated with the 2014–2016 El Nino Southern Oscillation event presented an opportunity to assess its impact on the reforestation success of a subtropical forest in Durban, South Africa. We assess how microtopographic positions (specifically, dry and moist microhabitats) influenced seedling/sapling survival and growth performance (stem diameter and height, and canopy width) of four dominant planted tree species (Bridelia micrantha, Erythrina lysistemon, Millettia grandis, and Vachellia natalitia) under a severe drought, measured a month after transplanting and 13 months post-transplanting, after the drought began. Survival ranged from 73% to 93%, but seedlings/saplings in the moist microhabitat had higher survival rates and higher growth rates than species in the dry microhabitat. A higher survival rate exhibited by M. grandis followed by V. natalitia and E. lysistemon in both the dry and moist microhabitats suggests these three species are good pioneers for reforestation in areas that are predicted to experience frequent and intense droughts. Results from this study highlight the importance of considering microtopographic positions, as well as understanding species-specific habitat requirements when selecting reforestation species under the current and future climatic conditions.

Tree growth is the most important factor in determining the carbon sequestration processes of forest ecosystems. However, the growth phenology (seasonal growth pattern) and responses of tree growth to climatic variables vary considerably among different species, especially between deciduous and evergreen species. Thus, it is crucial to explore the seasonal growth patterns of different tree species in relation to climate to better understand the responses of tree physiology to climate changes, especially in mixed-species forest stands. In this study, we monitored the daily basal area increments of 220 individuals belonging to 15 common broadleaved tree species, nine deciduous and six evergreen species, in mixed-species experimental stands in subtropical China and analysed the relationships between radial stem growth and seasonal climate at a high-temporal resolution. We fitted daily increments of stem diameters with four frequently used nonlinear models and chose the best model for each species. The results showed that the evergreen trees grew faster than the deciduous trees, both annually and within the growing season. The tested nonlinear models (Korf, Weibull, logistic and Gompertz) produced good fits for the growth patterns of all species. Overall, the evergreen species began stem growth earlier and finished later during the growing season than that of the deciduous species. Within the growing season, the radial growth of trees in mixed stands containing both types of species was strongly positively correlated with humidity. In spring, increases in both temperature and moisture increased the daily relative basal area increment of all species. Maximum growth rates occurred when the soil water content reached its highest level and gradually decreased when the soil water content decreased. In summer, high temperatures combined with low amounts of precipitation led to heat-induced summer drought, to which the evergreen trees appeared to be more tolerant than the deciduous trees, which was reflected in the reduced stem growth of the latter. These results indicate the different climate-dependent seasonal growth strategies of evergreen and deciduous trees related to the trade-off described by the leaf economics spectrum, i.e., short-lived leaves with higher assimilation rates in deciduous and longer-lived leaves with a greater drought tolerance in evergreen species.

Biodiversity experiments have shown that high species richness increases productivity in forests. However, forests are diverse regarding community composition. It is unclear how species identity and species composition could contribute to the variation of productivity and how their effects interact with species richness. Here we used data from a 9-year-old planted forest experiment with 40 species to test the effects of species identity and species composition on productivity. The plots in the experiment were designed with various compositions across richness levels. We found that for the top 25 species compositions with the highest volume increment there were six monocultures (24%), eight 2-species mixtures (32%) and eleven 4-species mixtures (44%). Schima superba monoculture had the highest volume in the last study year and highest volume increment over five years, while 2-species and 4-species mixtures with Nyssa sinensis or Liquidambar formosana resulted in high average above-ground volume accumulation. Most of the high-productivity species were deciduous with arbuscular mycorrhizal (AM) associations. In addition, the percentage of AM species in plots had a positive significant effect on both above-ground volume in 2018 and increment from 2013 to 2018. While the percentage of evergreen species showed no significant effect on above-ground volume increment, it did significantly decrease the above-ground volume in 2018. Overall, our results encourage reforestation management to consider species identity and species compositions of deciduous and/or AM species, such as Schima superba, Nyssa sinensis or Liquidambar formosana in the studied subtropical area, if the purpose is to enhance ecosystem productivity.

The forests of South Africa and the neighbouring countries, including Lesotho, eSwatini, Namibia, Botswana, Zimbabwe, and Mozambique (south of the Zambezi River), were mapped and classified according to the global system of biomes. The new four-tier hierarchical biome system suggested in this paper includes zonobiome, global biome, continental biome (all recognised earlier), and regional biome – a novel biome category. The existing spatial coverages of the forests were revised and considerably improved, both in terms of forest-patch coverage and mapping precision. Southern Africa is home to three zonal forest types, namely Subtropical Forests (Zonobiome I), Tropical Dry Forest (TDF; Zonobiome II) and Afrotemperate Forests (Zonobiome X). These three biomes are characterised by unique bioclimatic envelopes. Five, two, and eight regional biomes, respectively, have been recognised within these zonal biomes. Recognition of the Zonobiome I and the global biome Tropical Dry Forests in southern Africa is novel and expands our knowledge of the biome structure of African biotic communities. The system of the azonal regional biomes is also new and comprehensively covers the variability of the azonal helobiomes (riparian woodlands and swamp forests), mangroves, and azonal coastal forests. In total, 11 azonal regional biomes have been recognised in the study area. The forest biomes in southern Africa were captured in our electronic map in the form of more than 60 000 polygons, covering 42 416 km2 (1.27% of the study area). No less than 83% of these forests occur in the territory of southern Mozambique.

As extreme climate events are predicted to become more frequent because of global climate change, understanding their impacts on natural systems is crucial. Tropical forests are vulnerable to droughts associated with extreme El Niño events. However, little is known about how tropical seedling communities respond to El Niño-related droughts, even though patterns of seedling survival shape future forest structure and diversity. Using long-term data from eight tropical moist forests spanning a rainfall gradient in central Panama, we show that community-wide seedling mortality increased by 11% during the extreme 2015-16 El Niño, with mortality increasing most in drought-sensitive species and in wetter forests. These results indicate that severe El Niño-related droughts influence understory dynamics in tropical forests, with effects varying both within and across sites. Our findings suggest that predicted increases in the frequency of extreme El Niño events will alter tropical plant communities through their effects on early life stages.

Subtropical and tropical forests account for over 50% of soil CO2 production, 47% of N2O fluxes of natural ecosystems, and act as both significant sources and sinks of atmospheric CH4. However, ecosystem-scale estimates of these fluxes typically do not account for uncertainty that arises from environmental heterogeneity over small spatial scales. To assess the effects of small-scale environmental heterogeneity on GHG fluxes in a tropical forest ecosystem, we measured fluxes of CO2, CH4, and N2O across a topographic gradient and at the base of different tree species. We then used Bayesian linear models together with maps of trees and topography to quantify spatial heterogeneity in ecosystem-scale estimates of GHG emissions. The relationship between GHG fluxes and species and topography varied for each gas type. CO2 varied strongly by species but was only weakly related to topographic variation. In contrast, CH4 and N2O, which are more strongly regulated by soil oxygen, had strong relationships with topography but did not vary across species. Assuming spatial homogeneity and average rainfall conditions, we estimated ecosystem soil CO2 emissions to be 28.91 kg CO2-C/ha/day, net CH4 consumption of − 5.15 g CH4-C/ha/day, and net N2O emissions of 1.78 g N2O-N/ha/day. Including variation caused by tree species decreased ecosystem-level estimates of CO2 emissions by 8.03%, whereas including topographic variation decreased net CH4 consumption by 12.98% and increased net N2O emissions by 1.05%. This translates to a net decrease of 8.32% in estimated CO2-equivalent emissions. Our findings show that ignoring small-scale environmental heterogeneity has implications for bottom-up estimates of GHG fluxes in tropical forests. Given the increasing availability of fine-scale topographic models, incorporating this source of variation in estimates of ecosystem soil GHG emissions could improve our understanding of the role tropical forests play in global GHG cycles.

Vertical root segregation and the resulting niche partitioning can be a key underpinning of species coexistence. This could result from substantial interspecific variations in root profiles and rooting plasticity in response to soil heterogeneity and neighbours, but they remain largely untested in forest communities. In a diverse forest in subtropical China, we randomly sampled > 4000 root samples from 625 0-30 cm soil profiles. Using morphological and DNA-based methods, we identified 109 woody plant species, determined the degree of vertical fine-root segregation, and examined rooting plasticity in response to soil heterogeneity and neighbour structure. We found no evidence of vertical fine-root segregation among cooccurring species. By contrast, root abundance of different species tended to be positively correlated within soil zones. Underlying these findings was a lack of interspecific variation in fine-root profiles with over 90% of species concentrated in the 0-10 cm soil zone with only one species dominating in the 10-20 cm soil zone. Root profiles exhibited low responsiveness to root neighbours but tended to be shallow in soils with low phosphorus and copper content. These findings suggest that if there is niche differentiation leading to coexistence in this diverse forest, it would be occurring by mechanisms other than vertical fine-root segregation.

Quantification of carbon stocks is critical to evaluate the potential of an ecosystem to mitigate the impact of global climate change in the REDD + scenario. Present research project was designed t...

Canopy Chlorophyll Content (CCC) is the most important biophysical parameter in a forest eco-system, since it determines plant production, stress, and photosynthetic capability. Plant adaptation monitoring in a changing environment necessitates analyzing long-term changes in CCC. Present study computes CCC using the PROSAIL Radiative Transfer Model Inversion (RTM) with Artificial Neural Networking (ANN). The data from the Sentinel 2A satellite was utilized for this purpose. The various vegetation indices (VIs) were derived from Landsat and Sentinel data. The Infrared Percentage vegetation index (IPVI) from Landsat 8 demonstrated a strong connection with CC (R2 = 0.8). Green vegetation index (GVI), Normalized difference index (NDI), and Pigment specific simple ratio index (PSSRa) exhibited good correlations with CCC. From 1997 to 2017, the correlation of IPVI with CCC was utilized to model the spatio-temporal variation of CCC. The negative trend and decrease of CCC was detected at a rate of − 1.2 g cm−2 year−1 throughout this 20-year period with 33% fall in chlorophyll concentration, indicating a substantial reduction in forest health. The primary differences observed in dense forest area CCC and change in agricultural CCC were minor. This dramatic drop in chlorophyll concentration creates a variety of photosynthetic vulnerabilities in the forest ecosystem, resulting in forest degradation that may have unintended consequences for humans and wildlife.

Aims Plant–soil feedback (PSF) is a key mechanism that can facilitate tree species coexistence and diversity. Substantial evidence suggests that species-specific soil-borne pathogens around adult trees limit the performance of home (conspecific) seedlings relative to foreign (heterospecific) seedlings. However, the underlying mechanism remains largely elusive. Methods Here, we conducted a reciprocal transplant pot experiment using seedlings and from two tree species, Pinus massoniana and Lithocarpus glaber that are dominant and coexist in a subtropical, evergreen, broad-leaf forest in Gutianshan, Zhejiang Province of eastern China. We examined how seedlings from the two tree species responded to soils originating from underneath their own versus the other tree species, using a full-factorial design. Additionally, we added a fungicide (benomyl) to half of the pots to evaluate the role of soil-borne fungi on seedling growth. Important Findings We found that the seedlings from L. glaber grew better in soils that were collected from beneath the canopy of P. massoniana, while seedling growth of P. massioniana was not affected by soil origin. The addition of fungicide benomyl resulted in a shift towards more positive PSF effects for L. glaber, indicating that L. glaber seedlings performed better in their own soils than in soils from P. massoniana in the absence of fungi. Our findings highlight the importance of soil-borne pathogenic and ectomycorrhizal fungi in driving PSF, and indicate that PSF may promote the coexistence of two subtropical tree species by reducing the performance of L. glaber in own soils.

Tree species composition and diversity were assessed in six forest communities at an altitudinal gradient (i.e. from 247 to 1478 m) by laying four plots of 0.1 ha in each site within sub-tropical forest belt in Mokokchung, Nagaland. A total of 777 individuals belonging to 118 species, 84 genera and 43 families were recorded. The most dominant families from these sites were: Fagaceae, Moraceae, Anacardiaceae and Malvaceae. The tree density (individuals ha−1) in the present study ranged from 313 in Dillenia-Duabanga-Macaranga community to 330 in Morus-Vernonia-Hovenia community. The total basal area (m2 ha−1) ranged between 22.95 and 38.03 in Morus-Vernonia-Hovenia and Bombax-Melia-Gmelina community, respectively. The dominance-diversity curve showed high equitability and low dominance in forest communities (i.e. Trema-Kydia-Callicarpa, Morus-Vernonia-Hovenia and Alnus-Duabanga-Morus) occupied higher altitudes (1145–1478 m) and followed a log-normal distribution pattern. Whereas, the dominance-diversity curve showed low equitability and high dominance in communities (i.e. Bombax-Melia-Gmelina, Dillenia-Duabang-Macaranga and Albizia-Sapium-Gmelina) occupied lower altitudes (247–674 m) and followed a short hooked curve pattern. The Shannon diversity index ranged from 2.95 to 3.88 indicating high tree species diversity in forest communities studied. The Simpson dominance index ranged from 0.03 to 0.09. Over all this study provides useful information on tree species composition and diversity of subtropical forest of Nagaland which can be used as baseline data by the forest department to develop plans for the conservation of forest in subtropical forest, Northeast India.

Nitrogen enrichment is pervasive in forest ecosystems, but its influence on understory plant communities and their stoichiometric characteristics is poorly understood. We hypothesize that when forest is enriched with nitrogen (N), the stoichiometric characteristics of plant species explain changes in understory plant diversity. A 13‐year field experiment was conducted to explore the effects of N addition on foliar carbon (C): N: phosphorus (P) stoichiometry, understory plant species richness, and intrinsic water use efficiency (iWUE) in a subtropical Chinese fir forest. Four levels of N addition were applied: 0, 6, 12, and 24 g m−2 year−1. Individual plant species were categorized into resistant plants, intermediate resistant plants, and sensitive plants based on their response to nitrogen addition. Results showed that N addition significantly decreased the number of species, genera, and families of herbaceous plants. Foliar N:P ratios were greater in sensitive plants than resistant or intermediate resistant plants, while iWUE showed an opposite trend. However, no relationship was detected between soil available N and foliar N, and soil N:P and foliar N:P ratios. Our results indicated that long‐term N addition decreased the diversity of understory plants in a subtropical forest. Through regulating water use efficiency with N addition, sensitive plants change their N:P stoichiometry and have a higher risk of mortality, while resistant plants maintain a stable N:P stoichiometry, which contributes to their survival. These findings suggest that plant N:P stoichiometry plays an important role in understory plant performance in response to environmental change of N., We found the N:P stoichiometric traits of understory plants regulate their loss or presence, in which sensitive plants have flexible N:P stoichiometry and higher risk of extinction than resistant plants that have stable N:P stoichiometry to facilitate them living in the N enrichment environments.

Two new species of Cyphoderus are described; full body chaetotaxy is given. Cyphoderus pataxo sp. nov. and Cyphoderus palaciosi sp. nov. were originally found in metalogenic areas covered with transitional vegetation of savanna and subtropical forest from Minas Gerais, Southeastern Brazil. Both new species are part of the "bidenticulati-group," with mucronal formula 'Aa' and show remarkable plurichaetosis on posterior manubrium and dens.

Soil arbuscular mycorrhizal (AM) fungi were monitored in a 4-year experiment of nitrogen (N) and phosphorus (P) fertilization in three growing seasons (April, August, and November) under two successional stages (young and mature) in a subtropical forest of China. AM fungal extra-radical hyphal density was significantly affected by fertilization, season, and interactions between fertilization and season and between forest stage and season, but not by forest stage. The spore density of AM fungi was significantly affected by forest stage and season, but not by fertilization. Totally, 160 operational taxonomic units (OTUs) of AM fungi have been identified at a 97% sequence similarity level using Illumina MiSeq sequencing of the V4 region of the 18S rDNA. AM fungal Shannon diversity index, but not OTU richness, showed a positive response to P fertilization. The community composition of AM fungi was significantly influenced by P fertilization, but not by N fertilization, season, and forest stage. Phosphorus fertilization exhibited a negative impact on the relative abundance of the dominant Glomeraceae. This finding highlights that P availability has a strong effect on the community of AM fungi in the subtropical forest ecosystem.

The species composition of plant communities is determined by a number of factors, including current environmental conditions as well as biogeographical and evolutionary history. Despite evidence that plant diversity decreases and species relatedness increases along latitudinal and environmental gradients (e.g., low temperatures), it remains unclear whether these same patterns occur along elevational gradients, especially in the subtropical mountainous areas harboring rich biodiversity. In this study, we explored the pattern of phylogenetic relatedness of woody angiosperm assemblages and examined the effects of temperature variables on the phylogenetic relatedness among angiosperm woody plants using generalized linear model in subtropical forest communities along a broad elevational gradient in the Dulong Valley of Yunnan Province, China. Our results showed that woody angiosperm species in local forest plots tend to be more phylogenetically related at higher elevations and in areas with lower temperatures. Additionally, winter average temperature, rather than mean annual temperature, is a major predictor of the pattern of increasing phylogenetic relatedness with increasing elevation. This finding is consistent with the prediction of ‘Tropical Niche Conservatism’ hypothesis, which highlights the role of niche constraints in driving phylogenetic community assembly along an elevational gradient.

Plant diversity affects multi-trophic communities, but in young regrowth forests, where forest insects are in the process of re-establishment, other biotic and also abiotic factors might be more important. We studied cavity-nesting bees, wasps and their natural enemies along an experimental tree diversity gradient in subtropical South-East China. We compared insect communities of experimental young forests with communities of established natural forests nearby the experiment and tested for direct and indirect effects of tree diversity, tree basal area (a proxy of tree biomass), canopy cover and microclimate on bee and wasp community composition, abundance and species richness. Finally, we tested if the trophic levels of bees, herbivore-hunting wasps, spider-hunting wasps and their natural enemies respond similarly. Forest bee and wasp community composition re-established towards communities of the natural forest with increasing tree biomass and canopy cover. These factors directly and indirectly, via microclimatic conditions, increased the abundance of bees, wasps and their natural enemies. While bee and wasp species richness increased with abundance and both were not related to tree diversity, abundance increased directly with canopy cover, mediated by tree biomass. Abundance of natural enemies increased with host (bee and wasp) abundance irrespective of their trophic position. In conclusion, although maximizing tree diversity is an important goal of reforestation and forest conservation, rapid closure of canopies is also important for re-establishing communities of forest bees, wasps and their natural enemies. Supplementary Information The online version contains supplementary material available at 10.1007/s00442-021-04921-y.

In the high-light environment, young leaves accumulate anthocyanins as a photoprotection strategy. However, anthocyanin biosynthesis-related enzymes gene sequence is still unknown in the leaves of subtropical forest plants. There are thus few reports on the relationship between the expression level of these genes and photoprotection. In this study, Machilus chinensis and Castanopsis chinensis were taken as plant material in a subtropical forest. Non-full-length nucleotide sequences of chalcone synthase, dihydroflavonol 4-reductase, anthocyanin synthase, and β-tubulin gene were obtained by homologous and electronic cloning. The expression of those genes was verified and analyzed, and some physiological indicators were measured. The anthocyanin content and anthocyanin synthesis-related gene expression in the young leaves of C. chinensis were significantly higher than that of M. chinensis. Although young leaves of M. chinensis did not accumulate anthocyanins, they showed higher antioxidants and nonphotochemical quenching (NPQ). This study indicates that anthocyanins, antioxidants, and NPQ together mediate the positive effects on photoadaptation in young leaves.

Forest soils play an important role in controlling global warming by reducing atmospheric methane (CH4) concentrations. However, little attention has been paid to how nitrogen (N) deposition may alter microorganism communities that are related to the CH4 cycle or CH4 oxidation in subtropical forest soils. We investigated the effects of N addition (0, 30, 60, or 90 kg N ha−1 yr−1) on soil CH4 flux and methanotroph and methanogen abundance, diversity, and community structure in a Moso bamboo (Phyllostachys edulis) forest in subtropical China. N addition significantly increased methanogen abundance but reduced both methanotroph and methanogen diversity. Methanotroph and methanogen community structures under the N deposition treatments were significantly different from those of the control. In N deposition treatments, the relative abundance of Methanoculleus was significantly lower than that in the control. Soil pH was the key factor regulating the changes in methanotroph and methanogen diversity and community structure. The CH4 emission rate increased with N addition and was negatively correlated with both methanotroph and methanogen diversity but positively correlated with methanogen abundance. Overall, our results suggested that N deposition can suppress CH4 uptake by altering methanotroph and methanogen abundance, diversity, and community structure in subtropical Moso bamboo forest soils.

Pathogenic and mutualistic fungi have contrasting effects on seedling establishment, but it remains unclear whether density-dependent survival and growth are regulated by access to different types of mycorrhizal fungal networks supported by neighbouring adult trees. Here, we conducted an extensive field survey to test how mycorrhizal and pathogenic fungal colonization of arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) seedlings in a subtropical forest respond to density of neighbouring adult trees. In addition, we undertook a hyphal exclusion experiment to explicitly test the role of soil fungal networks in driving density-dependent effects on seedling growth and survival. Conspecific adult density was a strong predictor for the relative abundance of putative pathogens, which was greater in roots of AM than of ECM seedlings, while mycorrhizal fungal abundance and colonization were not consistently affected by conspecific adult density. Both ECM and AM fungal networks counteracted conspecific density-dependent mortality, but ECM fungi were more effective at weakening the negative effects of high seedling density than AM fungi. Our findings reveal a critical role of common fungal networks in mitigating negative density-dependent effects of pathogenic fungi on seedling establishment, which provides mechanistic insights into how soil fungal diversity shapes plant community structure in subtropical forests.

Differences in plant shade tolerance constitute a major mechanism driving the succession of forest communities in subtropical forests. However, the indirect effects of differences in light requirements on the growth of mid- and late-successional tree species are unclear, and this potential growth effect has not been explained at the transcriptome level. Here, a typical mid-successional dominant tree species, Schima superba Gardn. et Champ, and a typical late-successional dominant tree species, Cryptocarya concinna Hance were used as materials and planted under 100% full light (FL) and 30% FL (low light, LL) to explore the responses of tree species in different successional stages of subtropical forests to different light environments. Transcriptome sequencing was used to analyze the expression changes in genes related to growth and photoprotection under different light environments. The young leaves of S. superba accumulated more malondialdehyde (MDA) and superoxide radicals (${\mathrm{O}}_2^{{{}^{\bullet}}^{-}}$) under LL. A lower hormone content (auxin, cytokinin, gibberellin) in the young leaves, a weaker photosynthetic capacity in the mature leaves and significant downregulation of related gene expression were also found under LL, which resulted in the total biomass of S. superba under LL being lower than that under FL. The young leaves of C. concinna had less MDA and ${\mathrm{O}}_2^{{{}^{\bullet}}^{-}}$, and a higher hormone contents under LL than those under FL. There was no significant difference in photosynthetic capacity between mature leaves in contrasting light environments. Although the biomass of C. concinna under LL was less than that under FL, the height of C. concinna under LL was higher than that under FL, indicating that C. concinna could grow well under the two light environments. Our results describing the acclimatization of light at the physiological, molecular and transcriptome levels are important for a complete understanding of successional mechanisms.

Decomposition of forest litter plays a major role in nitrogen (N) dynamics in soil. But to which extent that forest litter affects soil N and how much soil N is derived from the new litter remains unknown. An in-situ soil column experiment with 14-month litter decomposition was conducted to examine the effect of litter retention on soil N dynamics in a typical forest of subtropical China in 2018. Litter removal in the soil column was used as a control treatment, while natural litter or identical amount of 15N labeled litter was added to soil columns as litter retention treatment. The results showed that litter removal caused a continuous decrease in concentration of soil soluble organic nitrogen (SON) in the first 5 months, and then SON began to accumulate and its concentration went up in spring showing obvious seasonal change. Litter retention accelerated the reduction of soil SON concentration in the first 2 months, while maintained a high concentration after that period. Soil NH4+-N derived from litter was nitrified rapidly, and newly formed NO3–N was quickly immobilized or lost. Only 1.8% of soil SON came from litter N and 98.2% from indigenous soil N under the decomposition of labeled litter. Litter provided supplementation N to form new soil SON continuously, however, only a small part of SON was relatively stable, and SON played the role of reserve and regulatory pool. Soil SON and TN were formed after long-term litter accumulation and decomposition.

Temporal dynamics of plant-pollinator interactions inform the mechanisms of community assembly and stability. However, most studies on the dynamics of pollination networks do not consider plant reproductive traits thus offering poor understanding of the mechanism of how networks maintain stable structure under seasonal changes in flower community. We studied seasonal dynamics of pollination networks in a subtropical monsoon forest in China with a clear rainy season (April–September) and dry season (October–March) over 2 consecutive years. We constructed dioecy-ignored networks (combining visitations to dioecious male and female plants by ignoring the difference between dioecious and hermaphroditic plants) and dioecy-considered networks (excluding those visitations that only occurred either on dioecious male or female plants) for eight sampling sessions for each season. Although flower richness and flower abundance were higher in the rainy season than in the dry season, no pronounced seasonal difference was found in network specialization, nestedness and modularity for both networks. There were only significant differences in plant community robustness and pollinator specialization between seasons for dioecy-considered networks but not for dioecy-ignored networks. Furthermore, we found the flower abundance of dioecious and hermaphrodite plants mostly showed trade-off variation between rainy and dry seasons. Our results suggest various plant reproductive traits affect the temporal dynamics of pollination networks, which should be considered for conservation of plant-pollinator interactions in forest communities.

Volatile organic compounds (VOCs) are important pollutants that affect air quality and atmosphere–ecosystem interactions. Atmospheric sampling onboard a multicopter unmanned aerial vehicle (UAV), s...

Aims The factors affecting species abundance are a subject of ongoing debates in community ecology. Empirical studies have demonstrated that tree abundance is affected by plant functional traits and negative density dependence (NDD). However, few studies have focused on the combined effects of NDD and plant functional traits on species abundance. Methods In this study, we used tree functional traits and two census data from a 50-ha forest dynamic plot in the Heishiding (HSD) Nature Reserve to explore the combined effects of functional traits and NDD on species abundance. Using hierarchical Bayesian models, we analyzed how neighbor densities affected the survival of saplings from 130 species and extracted posterior means of the coefficients to represent NDD. The structural equation modeling (SEM) analysis was then applied to investigate the causal relationships among species functional traits, NDD and species abundance. Important Findings SEM showed that tree functional traits, including specific leaf area (SLA), leaf area (LA), leaf dry matter content (LDMC), leaf N content (LNC), maximum electron transport rate (ETRmax) and conspecific adult negative density dependence (CNDDadult), together explained 20% of the total variation in tree abundance. Specifically, SLA affected tree abundance both directly and indirectly via CNDDadult, with a totally negative influence on abundance. LDMC and LNC had only indirect effects mediated by CNDDadult on tree abundance. ETRmax and LA had directly negative effects on abundance, but their direct connections with CNDDadult were not observed. In addition, CNDDadult was negatively correlated with species abundance, indicating that abundant species are under stronger NDD. Among these investigated traits, SLA contributed the most to the variation in CNDDadult and abundance. We argued that our findings of trait–CNDDadult–abundance relationships can improve our understanding of the determinants of species commonness and rarity in forests.

Humic acid (HA) plays vital roles in controlling the conservation of soil and water in the forest soils. The structure of HA is closely related to its stability. A clear understanding of the structural difference of HA will facilitate the rational assessment and efficient regulation of forest soils. This study aimed to investigate the structural difference of HA in the forest soils, and the difference in the stability of HA was evaluated according to HA structure. Soils were collected from different elevations and profile depths of Jiugong Mountain (Hubei, China). Soil HA was then extracted and purified. The structure of HA was analyzed by elemental analysis, fluorescence spectroscopy, and solid-state 13C nuclear magnetic resonance (13C NMR). The stability of soil HA was comprehensively accessed by structural complexity, alkyl C/O-alkyl C ratio, and hydrophobicity of HA. The complexity of HA structure was the greatest in soils in middle elevation (1200 m a.s.l.); it tended to decrease with soil depth in all examined soils. Alkyl C (25.1–40.1%) and O-alkyl C (21.2–44.3%) were the main structural fractions in HA samples. The percentage of alkyl C was the greatest in the HA from middle elevation while the O-alkyl C proportion was the highest in the HA from lower elevation (600 m a.s.l.). Alkyl C percentage tended to decrease with soil depth while O-alkyl C showed an opposite trend. The HA aromaticity increased with soil elevation but decreased with soil depth. The hydrophobicity and alkyl C/O-alkyl C ratio of HA was the greatest in middle elevation, and these indexes tended to decrease with soil depth. The HA structure in the subtropical forest soils showed clear spatial variability. The structural features of HA implied that the stability of soil HA was the greatest in the middle elevation and it tended to decrease with soil depth in the examined subtropical forest.

Tropical forests are the largest contributors to global emissions of carbon dioxide (CO2) to the atmosphere via soil respiration (R s). As such, identifying the main controls on R s in tropical forests is essential for accurately projecting the consequences of ongoing and future global environmental changes to the global C cycle. We measured hourly R s in a secondary tropical moist forest in Puerto Rico over a 3‐year period to (a) quantify the magnitude of R s and (b) identify the role of climatic, substrate, and nutrient controls on the seasonality of R s. Across 3 years of measurements, mean R s was 7.16 ± 0.02 μmol CO2 m‐2 s‐1 (or 2,710 g C m‐2 year‐1) and showed significant seasonal variation. Despite small month‐to‐month variation in temperature (~4°C), we found significant positive relationships between daily and monthly R s with both air and soil temperature, highlighting the importance of temperature as a driver of R s even in warm ecosystems, such as tropical forests. We also found a significant parabolic relationship between mean daily volumetric soil moisture and mean daily R s, with an optimal moisture value of 0.34 m3 m‐3. Given the relatively consistent climate at this site, the large range in mean monthly R s (~7 μmol CO2 m‐2 s‐1) was surprising and suggests that even small changes in climate can have large implications for ecosystem respiration. The strong positive relationship of R s with temperature at monthly timescales particularly stands out, as moisture is usually considered a stronger control of R s in tropical forests that already experience warm temperatures year‐round. Moreover, our results revealed the strong seasonality of R s in tropical moist forests, which given its high magnitude, can represent a significant contribution to the seasonal patterns of atmospheric (CO2) globally., We measured hourly soil respiration in a tropical moist forest in Puerto Rico over a 3‐year period to (a) quantify the magnitude of R s and (b) identify the role of climatic, substrate, and nutrient controls on the seasonality of R s. Across 3 years of measurements, mean R s was 7.08 ± 0.02 μmol CO2 m‐2 s‐1 (2,728 g C m‐2 year‐1) and showed significant seasonal variation at daily and monthly timescales. Despite small month‐to‐month variation in temperature (~4 C), seasonal patterns of daily and monthly R s were strongly correlated with air temperature (R 2 ranged from 0.49 to 0.70 depending on the timescale), highlighting the importance of temperature as a driver of R s even in warm ecosystems, such as tropical forests.

In the subtropics, the influence of water on the net ecosystem carbon exchange (NEE) is critical, subsequently determining net primary productivity (NPP). Water also contributes the majority of int...

Evasion from soil is the largest source of mercury (Hg) to the atmosphere from terrestrial ecosystems. To improve our understanding of controls and in estimates of forest soil–atmosphere fluxes of total gaseous Hg (TGM), measurements were made using dynamic flux chambers (DFCs) over 130 and 96 d for each of five plots at a subtropical forest and a temperate forest, respectively. At the subtropical forest, the highest net soil Hg emissions were observed for an open field (24 ± 33 ng m−2 h−1), followed by two coniferous forest plots (2.8 ± 3.9 and 3.5 ± 4.2 ng m−2 h−1), a broad-leaved forest plot (0.18 ± 4.3 ng m−2 h−1) and the remaining wetland site showing net deposition (−0.80 ± 5.1 ng m−2 h−1). At the temperate forest, the highest fluxes and net soil Hg emissions were observed for a wetland (3.81 ± 0.52 ng m−2 h−1) and an open field (1.82 ± 0.79 ng m−2 h−1), with lesser emission rates in the deciduous broad-leaved forest (0.68 ± 1.01 ng m−2 h−1) and deciduous needle-leaved forest (0.32 ± 0.96 ng m−2 h−1) plots, and net deposition at an evergreen pine forest (−0.04 ± 0.81 ng m−2 h−1). High solar radiation and temperature during summer resulted in the high Hg emissions in the subtropical forest and the open field and evergreen pine forest at the temperate forest. At the temperate deciduous plots, the highest Hg emission occurred in spring during the leaf-off period due to direct solar radiation exposure to soils. Fluxes showed strong positive relationships with solar radiation and soil temperature and negative correlations with ambient air TGM concentration in both the subtropical and temperate forests, with area-weighted compensation points of 6.82 and 3.42 ng m−3, respectively. The values of the compensation points suggest that the atmospheric TGM concentration can play a critical role in limiting TGM emissions from the forest floor. Climate change and land use disturbance may increase the compensation points in both temperate and subtropical forests. Future research should focus on the role of legacy soil Hg in reemissions to the atmosphere as decreases in primary emissions drive decreases in TGM concentrations and disturbances of climate change and land use.

Gap areas create heterogeneity in the spatial environment, which is important to plant regeneration and diversity. Soil physical properties (SPP) are factors that affect plant growth. This study aims to assess the spatial variability of SPP in different gap sizes and to determine the effect of gap size on SPP. We used geostatistical analysis to illustrate the spatial patterns of SPP variability within 9 gaps, classified into three sizes (small, medium, and large) and under the canopy at the Castanopsis kawakamii natural reserve forest, the soil samples were collected entire gap area at 20 cm depth with the grid system (resolution: 3 m × 3 m). The following SPPs were determined using soil cores: soil bulk density (SBD), soil water mass content (SWMC), soil volumetric moisture content (SVMC), maximum moisture capacity (MMC), capillary water capacity (CWC), minimum water-holding capacity (MWHC), soil capillary porosity (SCP), and soil total porosity (STP). We found that every SPP, except SCP and STP, significantly differed with gap size. Gap sizes generally improved the SPPs, especially in the small and large gaps, indicating that the soil there was more suitable for plant growth than the soil under the canopy. The highest spatial variability of SPPs was observed in the large gaps. Gap size affected SPP and its spatial variability. The results from this study will be useful for work on forest gap regeneration and conservation, especially around the study site.

The community species abundance and diversity declined with bamboo invasion had been widely reported worldwide. However, the physiological strategies used during root competition between native species and invasive bamboo are poorly understood. To clarify the mechanisms underlying such strategies, the stoichiometric dynamics and homeostasis of nitrogen, phosphorus, organic carbon in root orders of Phyllostachys edulis (I du [=I-Pe, years 1 and 2]; II du [=II-Pe, years 3 and 4]), Cunninghamia lanceolata in transition and pure forests were analyzed. With increasing intensity of bamboo invasion, N, P, and C content of C. lanceolata root orders declined, N and P content in P. edulis rhizome orders declined, while C increased, the stoichiometric ratios in mixed forest interface mainly increased, and the stoichiometric differences within native and invasive species root orders narrowed. Meanwhile, the stoichiometric homeostasis index (H) of elements in the same root order and even the same elements in different root orders were not consistent. H of most root orders (except some HP) was greater than 4, the H ranked order was I-Pe > Cl > II-Pe in mixed interfaces, and the N:P ratio of most species root orders was greater than 16, despite being affected by invasion. Our research concluded that the bamboo invasion narrows stoichiometric differences within root orders, and the juvenile bamboo rhizome has a stronger capacity for homeostatic regulation than in adult bamboo and C. lanceolata, which is a key determinant of bamboo invasion success.

That functional traits should affect individual performance and, in turn, determine fitness and population growth, is a foundational assumption of trait-based ecology. This assumption is, however, not supported by a strong empirical base. Here, we measured simultaneously two individual performance metrics (survival and growth), seven traits and 10 environmental properties for each of 3981 individuals of 205 species in a 50-ha stem-mapped subtropical forest. We then modelled survival/growth as a function of traits, environments and trait × environment interactions, and quantified their relative importance at both the species and individual levels. We found evidence of alternative functional designs and multiple performance peaks along environmental gradients, indicating the presence of complicated trait × environment interactions. However, such interactions were relatively unimportant in our site, which had relatively low environmental variations. Moreover, individual performance was not better predicted, and trait × environment interactions were not more likely detected, at the individual level than at the species level. Although the trait × environment interactions might be safely ignored in relatively homogeneous environments, we encourage future studies to test the interactive effects of traits and environments on individual performances and lifelong fitness at larger spatial scales or along experimentally manipulated environmental gradients.

Monoterpenes (MTs) play crucial roles not only in atmospheric chemistry and global climate change but also in soil processes and soil ecology. Elevated nitrogen (N) deposition can influence soil microbial community and litter decomposition, and consequently alters MT fluxes from forest floors and litter. Yet, the responses of soil and litter MT to increased N deposition remain poorly understood and the influences of N addition are sometimes contradictory. In the present study, static chambers were placed in masson pine forest (PF) and in monsoon evergreen broad-leaf forest (BF) at Dinghushan, subtropical China. The preconcentrator-GC-MS was used to analyze the effect of N addition on MT fluxes from the forest floors and litter. The results showed that under control treatment (without N addition), the total MT emission rates were 279.90±137.17 and 102.70±45.36 pmol m−2 s−1 in the PF and BF floors, respectively, with a-pinene being the largest MT species in the PF and limonene in the BF. α-pinene and β-pinene emission rates decreased significantly in both forest floors after N addition, whereas a diverse trend was found for limonene and camphene in the PF floor. Furthermore, some MT fluxes showed significant negative correlations with soil respiration and soil temperature. Litter was important in MT fluxes from forest floors and its emission rates were enhanced by N addition. Moreover, different MT response to elevated N was found between the forest floor and litter. This study indicated that the elevated N deposition in the future would inhibit the MT emissions from the subtropical forest floor.

To understand its source, distribution, storage, and translocation in the subtropical forest ecosystems, mercury (Hg) concentrations and stable isotopes in forest biomass tissues (foliage, branch, bark, and trunk) were investigated at Ailao Mountain National Nature Reserve, Southwest China. The total Hg (THg) concentrations in the samples show the following trend: mature foliage (57 ± 19 ng g−1) > bark (11 ± 4.0 ng g−1) > branch (5.4 ± 2.5 ng g−1) > trunk (1.6 ± 0.7 ng g−1). Using the measured THg concentrations and the quantity of respective biomasses, the Hg pools in the forest are: wood (60 ± 26 μg m−2) > bark (51 ± 18 μg m−2) > foliage (41 ± 11 μg m−2) > branch (26 ± 8.3 μg m−2). The tree biomasses displayed negative δ202Hg (− 1.83‰ to − 3.84‰) and ∆199Hg (− 0.18‰ to − 0.62‰). The observed ∆200Hg (− 0.08‰ to 0.04‰) is not significantly from zero. A ∆199Hg/∆201Hg ratio of 1.05 was found in tree biomasses, suggesting that mercury has undergone Hg(II) photoreduction processes. A Hg-isotope based binary mixing model suggests that Hg in the tree biomasses mainly originated from foliage uptake of atmospheric Hg0, constituting 67%, 80%, and 77% of Hg in wood, branch, and bark, respectively. Our study sheds new light on the transportation and sources of Hg in the subtropical forest ecosystems.

Tropical and subtropical ecosystems are widely affected by the expansion of agriculture over pristine lands. Despite research efforts, knowledge of the impact of land-use change on soil is still limited by intrinsic variability, inconsistent results and inadequate replication. This study aimed to better understand the consequences of land-use change by focusing on long-term effects on both soil biotic and abiotic parameters. For this purpose, we selected three productive farms under similar management, each of them with pristine forest sites and agricultural sites that had been deforested for ~15 and ~30 years. In each site, we analysed soil microbiological (phospholipid fatty acids [PLFAs], biomass and activity) and physicochemical parameters. Long-term land-use change caused a detriment in soil microbial biomass, activity and fungal abundance, but only small changes in PLFA composition. In fact, PLFA composition was more affected by soil physicochemical properties such as carbon-to-nutrient ratios and labile carbon than by land use. Some physicochemical parameters (e.g., organic carbon and nutrients) were also negatively affected by land-use change and were more sensitive to time under agricultural use than microbiological parameters. The lower sensitivity of microbiological parameters could be the result of severe drought conditions at sampling, which may have affected soil microbial communities in both land uses. We were also able to detect associations between specific microbiological and physicochemical parameters. Among these, we identified some that seemed to result from their co-variation in response to land-use change and others that seemed to be independent of land use. Overall, our results show that soils can suffer further deterioration several years after deforestation. In order to restore soil health in these degraded lands, we need to keep on investigating the physical, chemical and biological mechanisms responsible for this deterioration. Highlights: Land-use change affected soil microbiological and physicochemical parameters. Microbiological parameters seemed to stabilize after continuous agriculture. Soil organic C, total N and fine particles were still reduced after long-term cultivation. Microbiological parameters were mostly associated with C-to-nutrient ratios and labile C. Drought conditions may have affected microbial response to land-use change. Fil: Tosi, Micaela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales; Argentina Fil: Chludil, Hugo Daniel. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Biología Aplicada y Alimentos; Argentina Fil: Correa, Olga Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales; Argentina Fil: Vogrig, Jimena Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales; Argentina Fil: Montecchia, Marcela Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales; Argentina

Worldwide tree cover increase (TCI) is one the most important climate change mitigation strategies, given the role of the ecosystems as carbon (C) reservoirs. Reforestation could be key to achieving TCI. However, there is still a knowledge gap about its real mitigation effects when it is applied through its replacement approach (REP-app). We evaluate the REP-app effects (replace native forest cover—NFC—by forestry plantation cover—FPC) on magnitude and direction of ecosystem C stock changes. By means of a field study, we quantified the C stock through a space-for-time substitution method, using eight paired sites (NFC/FPC) in a northern Argentinian subtropical forest (SAY). We studied C in saplings, lianas, above and belowground biomass, dead organic biomass, and soil. Through a metaanalysis, we evaluated the reliableness within the response of C sequestration (gain or loss) in international study cases and, therefore, the robustness of outcomes analyzing some main moderator variables that may influence the result. A significant effect of C loss was revealed by both, the field study (− 50%) and the metaanalysis (− 20.4%), and this response was consistent through stands of ages and species different. SAY sequestered 285 MgC ha−1. Only 35-year-old Eucalyptus stand reached similar values, but they are reservoirs of doubtful permanence with functional attributes that could affect long-term ecosystem functioning. Given that the TCI strategy seek to achieve interconnected efforts in relation to climate, biodiversity, and sustainable development, the REP-app must not be considered a mitigation strategy in subtropical ecosystems. Global programs promoting TCI must be redirected urgently.

Climate change has increased the frequency and intensity of droughts, with potential impacts on carbon (C) release from soil (i.e. soil respiration, Rs). Although numerous studies have investigated drought-induced changes in Rs, how roots and the soil microbial community regulate responses of Rs to drought remains unclear. We conducted a 4-year field experiment (2014–2017) with three treatments (i.e. 70% rainfall reduction, control and ambient) in a subtropical forest to examine effects of drought on Rs and its components [i.e. autotrophic (Ra) and heterotrophic respiration (Rh)] and explore the mechanisms underlying these effects. Drought significantly decreased Rs by 17% averaged over the 4 years, but it had no significant effect in the first experimental year. The decrease in Rs was mediated by soil fungi and fine root biomass. Fine root biomass was correlated negatively with Ra and Rs under drought, but positively in the control treatment. Furthermore, drought treatments increased physiological stress in the bacterial community. Structural equation model (SEM) analysis suggested that under drought conditions, microclimate affected Rs via its impact on fine root biomass and fungal biomass. Our results highlight the complex interactions between microclimate, roots and soil microbes in regulating Rs under drought in subtropical forest ecosystems. Incorporating these interactions into land surface models may improve predictions of climate change impacts on forest ecosystems. A free Plain Language Summary can be found within the Supporting Information of this article.