Subtropical Broad-leaved Trees Research Articles

Northward migration of the maximum Indian summer monsoon precipitation during the early–mid-Holocene: Evidence from sporopollen in the Andaman Sea

The Indian summer monsoon (ISM) significantly influences the evolution of the natural environment and the development of human societies in South Asia, however, the spatiotemporal nature of the maximum ISM precipitation remains uncertain. We present the first sedimentary sporopollen record from core ADM-C1 in the southern Andaman Sea, covering the past 11.2 ka to better understand the evolutionary history of the ISM. We use the percentage values of tropical–subtropical broad-leaved tree pollen to indicate regional precipitation. These pollens reached their highest abundances during ∼11–9 cal ka BP, indicating warmest and wettest climatic conditions in the southern Andaman Sea region. The subsequent retreat of the tropical–subtropical broad-leaved forest could reflect a gradual decline in ISM. By comparing numerous ISM precipitation records, we divided these records into two patterns: the timing of maximum ISM precipitation of Pattern 1 records during the early-Holocene (11–9 cal ka BP) and that of Pattern 2 records after 9 cal ka BP. The shift in the maximum ISM precipitation from Pattern 1 to Pattern 2 reflects a northward migration during the early–mid-Holocene, probably induced by the northward migration of the mean position of the Intertropical Convergence Zone (ITCZ). Furthermore, the ∼1.8 ka temporal lag between Patterns 1 and 2 could have resulted from the relatively weak Atlantic Meridional Overturning Circulation, which might have hindered the ITCZ from migrating northward before 9 cal ka BP.

A continuous paleorecord of vegetation and environmental change from Erxianyan Wetland over the past 60,000 years in central China

Reconstructing environmental changes for the last glacial-interglacial cycles in central China plays a key role in deciphering vegetation history and the evolution of the East Asia summer monsoon (EASM). Previous studies have documented climate changes since the Last Glacial Maximum (LGM), but climate dynamics associated with orbital and millennial time-scales is yet to be fully described and understood. In this study, pollen, charcoal, geochemistry and AMS14C dating were performed on a 290 cm long sediment core obtained from the Erxianyan Wetland in central China to reconstruct the environmental history in central China. It covers the past 60,000 years. The region was dominated by Quercus during the Marine Isotope Stage (MIS) 3, and this, together with fire and geochemistry records, indicates that climate was then warm and humid. A cooling and drying trend occurred between MIS 2 and the late Holocene when subtropical broad-leaved trees decreased, along with an increase in herb taxa and ferns, and more frequent fires occurred. On millennial time scales, the abrupt changes of geochemistry parameters corresponded to Heinrich events, resulting from weaker EASM intensities. In addition, orbital timescale changes may be related to precipitation delivery caused by the strength of the EASM, which was driven by the Northern Hemisphere solar radiation budget.

A transient south subtropical forest ecosystem in central China driven by rapid global warming during the Paleocene-Eocene Thermal Maximum

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.

Palynological evidence indicates the paleoclimate evolution in southeast China since late marine isotope stage 5

Four coastal cores collected from Fujian province in southeast China revealed new palynological evidence of vegetation, sea level, and climate changes since the late marine isotope stage (MIS) 5. A comparison between modern and fossil pollen assemblages, using scanning electron microscopy and 45 dating samples ensured an accurate interpretation of pollen data. The evergreen Quercus-dominated pollen assemblage indicated that a relatively warm subtropical climate prevailed during the last glaciation, whereas large amounts of Tsuga pollen indicated distinct cooling during early MIS2. Marine dinocysts revealed three transgressional intervals in the Holocene, early MIS3, and late MIS5, which corresponded to a globally sea-level rising. Richer pollen from tropical and subtropical broad-leaved trees and higher sand content in grain-size components confirmed a warm climate during the early MIS1 and early MIS3, and strong river flow associated with heavy precipitation during late MIS5, reflecting the sensitive response of the land climate to high summer insolation. During the early MIS3 period, the reconstructed optimum climate was consistent with the sea surface temperature records in the west Pacific and northern South China Sea and summer monsoon signal from terrestrial records, implying that high summer insolation strongly affected the climate of East Asia.

Trade-off relationship between light interception and leaf water shedding at different canopy positions of 73 broad-leaved trees of Yangji Mountain in Jiangxi Province, China

<p indent=0mm>As light interception and leaf water shedding may require different leaf traits, trade-offs may exist between the leaves’ abilities in light interception and leaf water shedding. Moreover, such trade-offs may vary with the vertical canopy position as leaf traits vary with tree height. We studied the variations in leaf traits at different canopy positions to study how canopy positions would affect the trade-off between the traits related to light interception and leaf water shedding in subtropical broad-leaved trees. We used the standardized major axis regression method to analyze the relationships among leaf morphological traits (leaf thickness and leaf length/width ratio), configuration traits (leaf angle and leaf drip tip length), and physiological traits (photosynthesis-light saturation point and photosynthesis-light compensation point) between sun and shade leaves. The results are as follows: (i) There was no significant difference in the leaf thickness and leaf length/width ratio at different canopy positions (<italic>P</italic>>0.05). The leaf angle (34.92°±1.15°), light saturation point ((954.89±27.86) µmol/(m²·s)), and light compensation point ((29.45±1.02) µmol/(m²·s)) at the upper canopy were significantly higher than those at the lower canopy (leaf angle: 16.66°±0.50°, light saturation point: (520.74±15.47) µmol/(m²·s), and light compensation point: (12.54±0.38) µmol/(m²·s); <italic>P<</italic>0.05). However, the leaf drip tip length was significantly shorter at the upper canopy position ((4.26±0.15) mm) than at the lower canopy position ((7.18±0.22) mm; <italic>P</italic><0.05). (ii) There were significant correlations among leaf angle, leaf drip tip length, light saturation point, and light compensation point at different canopy positions (<italic>P</italic><0.05), but the leaf drip tip length and leaf length/width ratio were only weakly correlated at the upper canopy leaves (<italic>P</italic><0.05). (iii) Common slope (<italic>P</italic>>0.05) and isometric scaling existed among the leaf angle, light saturation point, and light compensation point at different canopy positions, but there was no common constant (<italic>P</italic><0.05). These results indicated that the canopy position does not alter the trade-off strategy between light interception and leaf water shedding. The leaf drip tip length and inclination were mainly affected by the light saturation point and light compensation point.

Effects of Elevated Ozone Levels on Photosynthesis, Biomass and Non-structural Carbohydrates of Phoebe bournei and Phoebe zhennan in Subtropical China.

To assess the impacts of ozone (O3) on carbon metabolism of subtropical broadleaved tree species, seedlings of Phoebe bournei and Phoebe zhennan were exposed to elevated O3 levels in open-top chambers (OTCs) from June to November 2014. Three treatments were conducted in nine total OTCs, including charcoal-filter air (CF) as a control treatment, low O3 treatment ‘O3-1’ (∼100 nl l-1), and high O3 treatment ‘O3-2’ (∼150 nl l-1). Our findings demonstrated that elevated O3 levels significantly decreased the net photosynthesis rates (Pn) and leaf, root, and total biomass of both species, while it did not significantly affect the root/shoot ratio in P. bournei and P. zhennan. O3-1 treatments significantly increased water soluble carbohydrates (WSC) in leaves of both tree species, while only increased the total non-structural carbohydrates (TNC) and starch in leaves of P. bournei; effects on P. zhennan were equivalent in comparison to the control treatment (CF). Likewise, there was no effect of treatment on the polysaccharide content of both tree species. The contents of polysaccharide, starch contents in fine roots of both species, and TNC in fine roots of P. bournei increased significantly in O3-1 compared to CF. O3-2 treatment significantly decreased starch and TNC in the fine roots of P. bournei, and significantly decreased polysaccharide, starch, WSC, and TNC in the fine roots of P. zhennan. Elevated O3 had no effects on leaf polysaccharide in both species, but O3-1 significantly increased polysaccharide in the fine roots of both species, and O3-1 significantly increased WSC in the leaves while decreased that in the fine roots of both species. These results suggested that elevated O3 levels have significant impacts on the carbon metabolism of both tree species in our study, with differential responses between tree species and among leaves and roots.

Response of litter carbon, nitrogen and phosphorus to simulated leaching

Leaf litter is the main input of organic carbon and nutrients to terrestrial and freshwater ecosystems. The decomposition of leaf litter is crucial to the regulation of ecosystem carbon and nutrient dynamics. Abiotic leaching, i.e., water extraction of soluble elements from litter, is an important mechanism for release of carbon and nutrients from litter, providing easily accessible energy and nutrient source for microbes. However, relatively few studies have quantified the response of different litter species to leaching. In addition, it remains largely unclear that whether different elements in litter differ in solubility and whether the response of elements to leaching can be predicted by initial litter traits. In order to fill these knowledge gaps, recently senesced leaf litter of 15 subtropical broad-leaved tree species were leached in de-ionized water over 6 h in lab. Litter mass loss, carbon, nitrogen and phosphorus release after leaching were quantified. In addition, for each litter species, we measured 11 litter traits, including leaf thickness and toughness, maximum and standardized water holding capacity, contents of carbon, nitrogen, phosphorus, lignin and cellulose, specific leaf area and leaf dry matter content, and tested the influence of these litter traits on elements release patterns. After leaching, there were significant variation in litter mass loss, carbon, nitrogen and phosphorus release among different litter species ( P P P <0.001). The response of elements to leaching could be predicted by initial litter traits. The maximum water holding capacity of litter was the best predictor of carbon release, while the specific leaf area was the best predictor for both nitrogen and phosphorus release after leaching. We concluded that, despite the short duration of leaching, a considerable amount of nutrient release can occur, which influence litter chemistry and then probably affect subsequent microbial decomposition process. However, elements in litter have differential solubility so that different elements cannot be treated equally. Like microbe-mediated decomposition, trait-based approach can be used to predict the response of litter to leaching.

Early Pliocene paleo-altimetry of the Zanda Basin indicated by a sporopollen record

Whether the uplift of the Tibetan Plateau (TP) led to the origin and development of the Indian monsoon is still in dispute. A helpful indicator would be greater knowledge about the chronological development of paleo-altimetry. The Zanda Basin, located on the SW margin of the TP, forms one of the most extensive Cenozoic sedimentary basins in Tibet. The modern climate of this area is controlled by the Indian Monsoon circulation system. It is thus an appropriate region for the study of paleo-altimetry, in addition to research into the relation between the TP and the Indian Monsoon. Sporopollen analyses of early Pliocene lacustrine strata in the Zanda Basin show that gymnosperm pollen is dominant (av. 77%) and mainly composed of Picea (av. 27.2%) and Abies (av. 24.2%); fern spores occupy a lesser proportion (av. 17.6%), while angiosperm pollen including temperate, sub-tropical broadleaved trees, shrubs and herbs, accounts for only a small proportion of the assemblage. This sporopollen assemblage suggests that sub-alpine dark coniferous forests were distributed around the basin and grow in a cool and wet climate, rather than in a modern alpine steppe environment. These characteristics indicate that the Zanda Basin's altitude throughout the early Pliocene was most probably lower than it is at present.

Assessment of spatial and vertical structure of subtropical broadleaved trees in Yambaru areas

Assessment of spatial and vertical structure of subtropical broadleaved trees in Yambaru areas

Transpiration and stomatal control: a cross-species study of leaf traits in 39 evergreen and deciduous broadleaved subtropical tree species

Key message Using an extensive dataset for 39 subtropical broadleaved tree species, we found traits of the leaf economics spectrum to be linked to mean stomatal conductance but not to stomatal regulation.

Modern pollen distribution in marine sediments from the northern part of the South China Sea

We analyzed the pollen and spore distributions in sediments from the northern South China Sea to support reconstruction of the region's paleoenvironment. 1) Based on PCA analysis in the two areas with water depths of < 200 m and > 200 m, pollen and spores found at water depths of < 200 m are transported by rivers and ocean currents, while in samples from water depths of > 200 m, wind transport is dominant. 2) Tree pollen was abundant on the continental shelves near Guangdong and southeastern Hainan Island, the center of the study area, and deep basins in the south. Pinus pollen was abundant, with the highest levels on the continental shelf near Guangdong and in the marine area south of 15°N. Pollen from tropical and subtropical broad-leaved trees (e.g., Castanopsis, Quercus) had low abundances. Castanopsis pollen appeared to originate near Hainan Island, Guangdong, and the Indochina Peninsula. Herbaceous pollen was less abundant, with pollen from the Poaceae and Artemisia scattered among the northern and southern regions, with the highest levels near Guangdong and a distribution that followed the rivers or sea surface circulation. Poaceae pollen was most abundant along the Guangdong and Vietnam coasts due to their proximity to tropical and subtropical grasslands and crops. Monolete spores and Cyperaceae pollen were most abundant near the Pearl River Estuary, southern Hainan Island, and southwestern Taiwan, probably originating from fluvial river discharge. Trilete spores (mostly Dicranopteris) were most abundant on the continental shelf of southeastern Hainan Island and the continental slope far from Guangdong. 3) Pollen and spore assemblages from airborne, sea surface water and sediment samples were compared. From August to September, airborne pollen and spores mainly belong to trees (Ulmaceae, Pinus) and herbaceous pollen, and have seasonal characteristics. Ocean surface waters in August–September mainly contain D. dichotoma, Rhizoma polypodiodis nipponicae and other trilete spores, but no Pinus pollen, with clear seasonality characteristic. Pollen and spore assemblages in surface sediments are dominated by trilete spores, Pinus and herbaceous pollen, and appear to integrate the pollen characteristics of the four seasons.

Responses of native broadleaved woody species to elevated ozone in subtropical China

To assess ozone sensitivity of subtropical broadleaved tree species and explore possible underlying mechanisms, six evergreen and two deciduous native species were exposed to either charcoal-filtered air or elevated O3 (E-O3, ∼150ppb) for one growing season. Initial visible symptoms in deciduous species appeared much earlier than those in evergreen species. The species which first showed visible symptoms also had the largest reductions in biomass. E-O3 induced significant decreases in photosynthesis rate, chlorophyll content and antioxidant capacity but a significant increase in malondialdehyde content in two deciduous species and two evergreen species (Cinnamomum camphora and Cyclobalanopsis glauca). Except C. glauca, however, E-O3 had no significant effects on stomatal conductance (gs), total phenols and ascorbate contents. Difference in O3 sensitivity among all species was strongly attributed to specific leaf mass rather than gs. It suggests that some subtropical tree species will be threatened by rising O3 concentrations in the near future.

Effects of moderate high-temperature stress on photosynthesis in three saplings of the constructive tree species of subtropical forest

During the exposition to moderate high-temperature stress, photosynthetic rates and fluorescence of chlorophyll a were measured with a photosynthetic measurement system (Li-Cor 6400) and leaf chamber fluorometer (Li-Cor6400 LCF), respectively, in leaves of saplings, sun-adapted species ( Schima superba), shade-adapted species ( Cryptocarya concinna), and in mesophytic plant ( Castanopsis hystrix) (42°C). The results showed that moderate high-temperature stress led to a decrease in F v/ F m, namely the primary photochemical quantum efficiency, indicating that moderate high-temperature stress causes a partial inhibition of PSII. It also showed that such an effect was more severe in the shade-adapted plant C. concinna than in the sun-adapted species S. superba. However, except for the sun-grown leaves of C. concinna, the moderate high-temperature stress increased the photosynthetic rate of leaves at high light intensity. Simultaneously, less photoinhibition was found to occur under high-light intensity, suggesting that the capacity of resistant-photoinhibition was stimulated by moderate high-temperature stress. The quantum yield of PSII (ϕ PSII) decreased in the sun-grown leaves of S. superba and C. hystrix but did not show any significant change in leaves of the shade plant C. concinna and shade-grown leaves of sun plant S. superba or the mesophytic plant C. hystrix because they already had a very low ϕ PSII under this condition. Moderate high-temperature stress led to a decrease in ϕ PSII/ϕ CO 2 ratios, an estimate of the quantum requirement for CO 2 assimilation, in the sun plant S. superba and the mesophytic plant C. hystrix because they were associated with the dissipation of a lower fraction of excitation energy. However, no significant changes were found in shade plant C. concinna and in shade-grown leaves of the other examined plants. The effect of moderate high-temperature (42°C) on photosynthesis depends on species and leaf type (sun and shade leaves) in the saplings of subtropical broad-leaved trees.

Pollen distribution in hemipelagic surface sediments of the South China Sea and its relation to modern vegetation distribution

This paper analyses the distribution of pollen in the surface sediments of the South China Sea as recorded in 28 samples from the area 6°09′–20°07′N and 112°05′–119°45′E, at water depths of 329–4307 m. Pollen concentrations range from 444 kgrains/g (dry wt) on the lower part of the continental slope in the northeast to zero in the central basin below 4000 m water depth. Pollen distribution patterns in the concentration and percentage isopolls (incorporating data from the literature) reflect the routes and mechanisms of pollen transport, pollen source areas and considerable systematic differences between north and south. The northern SCS is distinguished by very high concentrations due to the high production and effective long-distance transport of pine pollen and fern spores. The maximum of their concentration occurs in the north, adjacent to the convergence of the Bashi and Taiwan Straits, rather than near the estuaries of big rivers, and stretches as a saddle from NE to SW, consistent with the direction of the NE winter monsoon and sea current. This pattern implies that pine pollen and fern spores, adapted to wind transport and water flotation, come from the northeast through the straits borne on the winter monsoon and sea current forced by it. Their source areas should cover large regions, probably including south and southeast China. Most pollen of tropical and subtropical broad-leaved trees found in the northern part of the SCS occur in low concentrations, however, these concentrations decrease uniformly offshore, implying a fluvial discharge from nearby lowlands in South China. In the southern part of the SCS, pollen of tropical and subtropical broad-leaved trees predominate. Total pollen concentrations, however, are much lower, only 1/10 of those of the northern part. The greatest concentrations occur offshore north Borneo and decrease toward deep water, suggesting fluvial input from relatively local sources on the adjacent islands (e.g. Borneo).

Foliar nutrient levels of broad-leaved tropical trees: A tabular review

Foliar nutrient levels (N, P, S, K, Ca, Mg, Al, Fe, Mn, Zn, Cu, Mo, B), of about 40 tropical and subtropical broad-leaved trees, are listed and classified as deficient, low, intermediate, high, and toxic in each case according to the interpretation and evaluation of the reviewed author(s).