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Subtropical evergreen broadleaved forests (EBLFs) inhabit large areas of East Asia. Although paleovegetation reconstructions have revealed that the subtropical EBLFs existed in Southwest China during the Miocene, the historical construction of these forests remains poorly known. Here, we used the tea family (Theaceae), a characteristic component of the subtropical EBLFs, to gain new insights into the assembly of this important biome. Using a robust phylogenetic framework of Theaceae based on plastome and nuclear ribosomal DNA sequence data, the temporal history of the family was reconstructed. Data from other characteristic components of subtropical EBLFs, including Fagaceae, Lauraceae and Magnoliaceae, were also integrated. Most of the essential elements of the subtropical EBLFs appear to have originated around the Oligocene–Miocene (O–M) boundary. However, small woody lineages (e.g. Camellia, Hartia) from Theaceae were dated to the late Miocene. Accelerated net diversification rates within Theaceae were also detected near the O–M transition period and the late Miocene. Our results suggest that two independent intensifications of the East Asian summer monsoon (EASM) around the O–M boundary and the late Miocene may have facilitated the historical assembly of the subtropical EBLFs in East Asia.

Aims Moso bamboo (Phyllostachys pubescens) is a typical native invasive plant imposing serious threats on ecosystem processes and functions. A primary concern is alterations of litter and soil N mineralization in evergreen broadleaved forests coupled with bamboo population expansion. Methods We conducted a field study to determine the litter production, quality, N resorption efficiency, and soil N mineralization rates in bamboo-dominated forest (BDF) and adjacent uninvaded evergreen broadleaved forest (EBF) in subtropical China. Results The mean annual litter production for BDF was 5.82 Mg ha⁻¹, 36.0 % lower than that for EBF (9.09 Mg ha⁻¹). Litter N concentration was also lower, but C: N was higher after bamboo expansion, coupled with higher N resorption efficiency for Moso bamboo and lower litterfall, resulting in potential N return decreasing as much as 60.41 kg N ha⁻¹ yr⁻¹ to the soil. The soil N net nitrification and mineralization rates exhibited lower values in BDF than in EBF. In addition, annual soil N mineralization rate was positively correlated with litter production but negatively with C: N ratio of litter. Conclusions Expansion of bamboo into neighboring EBF decreased litter production and quality, reduced soil N mineralization rate, and ultimately retarded N cycling. These effects should be carefully considered in the design of restoration strategies for ecosystems impacted by bamboo species.

Aim According to palaeo-biome reconstructions, the subtropical evergreen broadleaved forests (EBLF) in East Asia contracted to a narrow belt south of 24 degrees N during the Last Glacial Maximum (LGM). Yet numerous phylogeographical studies of EBLF plants have inferred glacial refugia north of this area. Here, we aim to further elucidate the Quaternary dynamics of EBLFs using the widespread shrub Lindera aggregata as model. Location Subtropical China. Taxon Lindera aggregata (Sims) Kosterm (angiosperms). Methods Four chloroplast DNA (cpDNA) fragments and 15 low-copy nuclear genes (LCGs) were sequenced in 19 populations. The time to the most recent common ancestor (TMRCA) was estimated using secondary calibrations. Bayesian algorithms were used to infer population clustering, phylogeny and divergence time. Historical gene flow was estimated using a maximum-likelihood algorithm. Potential habitats at present and during the LGM were predicted using ecological niche modelling. Results The TMRCA estimate was 1.78 Myr. We observed a shallow cpDNA network organized around one dominant haplotype. The LCGs revealed three distinct genetic clusters that reflected contrasting historical population dynamics. The most ancient cluster was located south of the Nanling and Wuyi Mountains and indicated long-term population persistence in multiple refugia. The area further north was occupied by two disjunct clusters that dated back to the LGM and showed signatures of a rapid northward expansion from two refugia. We detected noteworthy pollen-mediated secondary admixture between all three clusters including somewhat preferential southward gene flow. Main conclusions Lindera aggregata represents a rare example of extensive post-glacial range expansion across the EBLF biome (expansion-contraction model) that contrasts with its generalized long-term population stability in the southernmost range parts. Our findings also provide rare evidence for noteworthy post-glacial gene flow into long-term refugial populations. They correspond relatively well with palaeo-biome reconstructions and support the hypothesis that the EBLF has undergone extensive post-glacial community reshuffling.

Aims Fine root phenology represents ecological strategy of plants in utilizing soil resources and plays an essential role in carbon and nutrient cycling. Here, we aimed to understand how fine root phenology could change in subtropical broadleaved forests with increasing tree species diversity. Methods Three 37–40 years old Castanopsis carlesii forests with low to high tree species diversity were selected in southern China: a plantation forest (PF), a secondary forest through the assisted regeneration (AR), and a secondary forest through natural regeneration (NR), with a nearby natural C. carlesii forest as a control. Fine root length production in these forests was measured monthly during January 2013 to December 2014 using minirhizotron, and fine root production phenology and its correlations with environmental factors were compared among these forests. Results No significant difference in fine root length production was found among these forests; however, there was distinct fine root phenology. The timing of fine root growth initiation and growth peak was quite stable across the two years in PF, while they were more flexible in AR and NR which were higher in tree species diversity. However, the timing of fine root growth cessation was quite fixed for all the forests. The duration and inter-annual stability of fine root growth both decreased with increasing tree species diversity. Moreover, the correlations of monthly fine root production with monthly air and soil temperature both increased with increasing tree species diversity. Conclusions It is concluded that the timing of fine root growth in higher tree species diversity stand seems more flexible and more synchronous with seasonal and annual fluctuations of soil resources caused by weather variability, which helps our understanding of the relationships between tree diversity and ecosystem carbon and nutrient cycling.

Subtropical evergreen broad-leaved forests (EBF) face great pressure from global climate change. However, little consensus exists related to how coexisting trees in these forests will respond to climatic change. We used tree rings to establish climate-growth relationships of three coexisting dominant canopy tree species in an EBF located in the Gutianshan National Nature Reserve, Zhejiang Province, in eastern China. Our results emphasize highly species-specific radial growth responses to both local and large-scale climate variability. The radial growth of Pinus massoniana was enhanced by high minimum autumn and low winter temperatures as well as La Niña events. Positive growth responses in Castanopsis eyrei were linked to high minimum summer and spring temperatures. Low winter temperatures and summer sunshine also increased the growth of Schima superba . We modeled future tree-ring growth using two climate change scenarios. Under both an intermediate (Representative Concentration Pathway, RCP 4.5) and a high emission climate change scenario (RCP 8.5), we projected further growth acceleration in C. eyrei , but a reduced growth rate in S. superb . Growth of P. massoniana was not predicted to change under the RCP 4.5 scenario, but was predicted to increase significantly under the RCP 8.5 scenario. These results suggest that climate change will have repercussions for the competitive balance among these tree species in subtropical forests, and the diverging responses of individual tree species need to fully considered in any models of the effects of climate change on the EBF and in future management plans.

Soil respiration (Rs) was measured over 2 years in mature, clear-cut, and clear-cut with slash burnt stands of Cunninghamia lanceolata Lamb. (Chinese fir) (CF) and secondary evergreen broadleaved forest (BF) located in Fujian Province, southeastern China from late October 2001 to 2003. Rs was measured as CO₂ evolved in situ using the soda lime absorption method. Soil temperature and moisture content at 10 cm depth were monitored in treatments of clear-cut (CC) and slash burnt (SB) and undisturbed controls. Respiration levels varied seasonally with maximum rates observed from May to July. Both, CC and SB plots showed increase in Rs for the first 3 months after treatments but for the subsequent 2 years the Rs in the CC and SB stands fell below that of controls. There were no significant difference in soil temperature among treatments in each forest, while the CC and SB treatments resulted in reduced soil moisture contents. Relationships between Rs and soil environmental variables were examined via a regression analysis. A combination of soil temperature and soil moisture content proved to be a reliable predictor of CO₂ evolution in control plots, but not in CC and SB plots. We concluded that the effect of forest management on Rs is a combined result of changes in other factors rather than soil temperature and moisture. This study contributes to our understanding of how common forestry management practices might affect soil carbon sequestration, as Rs is a major component of ecosystem respiration.

In southern China, moso bamboo (Phyllostachys pubescens) forests have been expanding into surrounding vegetation such as natural broadleaved forests and coniferous plantation forests. It has been speculated that the expansion of moso bamboo forest could alter soil carbon content and soil environmental condition. Soil samples were taken at 0-20 cm depth from three vegetation types, i.e. evergreen broadleaved forest, moso bamboo forest and mixed forest with broadleaved and moso bamboo. It was found that soil properties, especially soil microbes and nitrogen, contributed significantly to the variations in soil organic carbon. Soil carbon was higher under mixed forest with broadleaved and moso bamboo compared to evergreen broadleaved forest and moso bamboo forest. In soil environment, the direct contribution of bacteria and fungi to soil carbon content was highest. If the microbe indirect effect and nitrogen direct effect were considered, the expansion of moso bamboo could have substantial consequences on soil organic carbon. The finding indicated that the expansion of moso bamboo forest into evergreen broadleaved forest could increase soil carbon content. To better understand the effects of moso bamboo invasion on ecosystem functions, future studies on soil carbon dynamics and carbon cycling is required.

The proliferation of digital cameras co-located with eddy covariance instrumentation provides new opportunities to better understand the relationship between canopy phenology and the seasonality of canopy photosynthesis. In this paper we analyze the abilities and limitations of canopy color metrics measured by digital repeat photography to track seasonal canopy development and photosynthesis, determine phenological transition dates, and estimate intra-annual and interannual variability in canopy photosynthesis. We used 59 site-years of camera imagery and net ecosystem exchange measurements from 17 towers spanning three plant functional types (deciduous broadleaf forest, evergreen needleleaf forest, and grassland/crops) to derive color indices and estimate gross primary productivity (GPP). GPP was strongly correlated with greenness derived from camera imagery in all three plant functional types. Specifically, the beginning of the photosynthetic period in deciduous broadleaf forest and grassland/crops and the end of the photosynthetic period in grassland/crops were both correlated with changes in greenness; changes in redness were correlated with the end of the photosynthetic period in deciduous broadleaf forest. However, it was not possible to accurately identify the beginning or ending of the photosynthetic period using camera greenness in evergreen needleleaf forest. At deciduous broadleaf sites, anomalies in integrated greenness and total GPP were significantly correlated up to 60 days after the mean onset date for the start of spring. More generally, results from this work demonstrate that digital repeat photography can be used to quantify both the duration of the photosynthetically active period as well as total GPP in deciduous broadleaf forest and grassland/crops, but that new and different approaches are required before comparable results can be achieved in evergreen needleleaf forest.

Aim Our aims were to provide new pollen data for establishing a sub-continental surface pollen database (East Asian Pollen Database, EAPD) and to study relationships between vegetation and climate. Location The sample sites covered most regions of East Asia, including China, Mongolia, the Russian Far East, Vietnam, Cambodia and Thailand. Methods Data quality control procedures were applied, including taxonomic standardization, removal of duplicates, and adjustment of geographical coordinates. Vegetation types and climate parameters were assigned to each sample. Modern pollen distribution maps were drawn using circle scattergrams. The plots of pollen percentages versus climate variables allowed quantitative estimates of climate values. The modern analogue technique (MAT) was used to predict modern biomes and climate parameters. Results Pollen assemblages extracted from 2858 sites were used to model the geographical distribution of selected taxa and their relationships with climate. For most taxa, the reconstructed range fitted the observed geographical distribution rather well. Arboreal pollen (AP) and Pinus dominated the transition zone between forest and steppe. Use of the MAT revealed that the predicted and observed biomes matched in 71% of the cases. The warm temperate evergreen broadleaf forest had the best agreement between predictions and observations. Climate values reconstructed using MAT were highly correlated with observed values in January temperature. The correlation coefficient of the temperature variables ranged from 0.799 to 0.930 and was as high as 0.939 for precipitation. Main conclusions This paper documents a new modern pollen database for East Asia and makes the data readily available. The reconstructed biomes and climate variables are significantly correlated with the observed values, thus demonstrating the utility of the pollen database for future multiscale palaeoenvironmental studies.

Nitrogen (N) and phosphorus (P) availability regulate plant productivity throughout the terrestrial biosphere, influencing the patterns and magnitude of net primary production (NPP) by land plants both now and into the future. These nutrients enter ecosystems via geologic and atmospheric pathways and are recycled to varying degrees through the plant–soil–microbe system via organic matter decay processes. However, the proportion of global NPP that can be attributed to new nutrient inputs versus recycled nutrients is unresolved, as are the large-scale patterns of variation across terrestrial ecosystems. Here, we combined satellite imagery, biogeochemical modeling, and empirical observations to identify previously unrecognized patterns of new versus recycled nutrient (N and P) productivity on land. Our analysis points to tropical forests as a hotspot of new NPP fueled by new N (accounting for 45% of total new NPP globally), much higher than previous estimates from temperate and high-latitude regions. The large fraction of tropical forest NPP resulting from new N is driven by the high capacity for N fixation, although this varies considerably within this diverse biome; N deposition explains a much smaller proportion of new NPP. By contrast, the contribution of new N to primary productivity is lower outside the tropics, and worldwide, new P inputs are uniformly low relative to plant demands. These results imply that new N inputs have the greatest capacity to fuel additional NPP by terrestrial plants, whereas low P availability may ultimately constrain NPP across much of the terrestrial biosphere.