Subtropical Forests In Southern China Research Articles

Plant hydraulics and photosynthesis of 34 woody species from different successional stages of subtropical forests

It is important to understand the ecophysiological characters of plants when exploring mechanisms underlying species substitution in the process of plant succession. In the present study, we selected 34 woody species from different stages of secondary succession in subtropical forests of southern China, and measured their hydraulic conductivity, gas exchange rates, leaf nutrients and drought-tolerance traits such as xylem resistance to cavitation, turgor loss point and carbon isotope ratio. Principal component analysis revealed that early-, mid- and late-successional species were significantly separated along axis 1, which was strongly associated with hydraulic-photosynthetic coordination. In contrast to species distributed in late-successional forest, early-successional species had the highest hydraulic conductivity, net photosynthetic rates, photosynthetic nitrogen and phosphorus use efficiencies, but had the lowest photosynthetic water-use efficiency. However, changes of the measured drought-tolerance traits of the 34 species along the succession did not demonstrate a clear trend - no significant correlations between these traits and plant successional stages were found. Moreover, the trade-off between hydraulic efficiency and safety was not identified. Taken together, our results suggested that hydraulic efficiency and photosynthetic function, rather than drought tolerance, play an important role in species distributions along plant succession in subtropical forests.

Tree species effects on fine root decomposition and nitrogen release in subtropical forests in southern China

Background: Root decomposition is an important process that contributes to forest ecosystem carbon (C) flux and nutrient cycling. Aims: To determine how tree species affected fine root (≤ 2 mm) decomposition rates and nitrogen (N) release. Methods: Fine root samples of the coniferous Pinus massoniana, the deciduous Choerospondias axillaris and the broadleaved evergreen Cyclobalanopsis glauca tree species were collected from three secondary successional subtropical forests (P. massoniana–Lithocarpus glaber mixed forest, C. axillaris forest and C. glauca–L. glaber mixed forest) in southern China. Samples were incubated in situ, using the litterbag method for a period of 500 days to measure mass loss and changes in fine root C and N concentrations. Results: C. axillaris exhibited the fastest decomposition rate (k) during the 500 day decomposition period, followed by P. massoniana and C. glauca. Fine root mass loss was positively correlated with initial N concentrations and negatively correlated with initial C:N ratios. Initial fine root C concentrations had a significant effect on N release, but the effect varied over time. Annual fine root production released ca. 16.2–44.2 kg N ha−1 through decomposition. Conclusions: Fine root mass loss during decomposition differed considerably among tree species. The chemical quality of fine roots was a key driver in the rates of decomposition. Soil properties partly accounted for the differences in decomposition rates.

The 15N natural abundance of the N lost from an N‐saturated subtropical forest in southern China

The 15N‐enrichment of plants and soils is believed to indicate characteristics of the open nitrogen (N) cycle in terrestrial ecosystems because N lost from an ecosystem is presumably 15N‐depleted through isotopic fractionation. However, because of a lack of an appropriate analytical methodology to confirm that supposition, the δ15N value for total dissolved nitrogen (TDN, the sum of ammonium, nitrate, and dissolved organic N) in stream water from forests has been measured only rarely. This report describes the δ15N values for TDN, ammonium, and nitrate in precipitation and stream water, together with those for soil‐emitted nitrous oxide (N2O; measured once) in an N‐saturated subtropical forest in southern China. Concentration‐weighted δ15N values of TDN were −0.7‰ in precipitation and +1.2‰ in stream water. The difference in δ15N between soil (+3.9‰) and TDN in the stream water was 2.7‰. In contrast, soil‐emitted N2O was strongly 15N‐depleted (−14.3‰): 18‰ lower than that of the soil. Our results demonstrate that the discharged N loss is 15N‐depleted only slightly compared with soil N, and gaseous N losses can be a strong driver for raising the terrestrial ecosystem δ15N. Our findings suggest that the relation between ecosystem δ15N and the open N cycle can be interpreted better by considering the net discrimination against 15N determined by the balance between gaseous and discharge N losses. Steady state 15N budget calculations proposed by Houlton and Bai (2009) can provide important information about the gaseous N fluxes, which are difficult to measure directly. The steady state calculation for the relationships among gaseous N loss, apparent isotopic fractionation during gaseous N loss, and isotopic signature of N inputs suggests that precise measurements of unmeasured components (e.g., dry deposition, NO and N2 emission) are quite important for better estimation of gaseous N losses from the ecosystem.

Three new species of Sporidesmiella from southern China

Sporidesmiella rosae sp. nov., S. machili sp. nov., and S. archidendri sp. nov., occurring, respectively, on dead branches of Rosa chinensis, Machilus grijsii, and Archidendron clypearia, were collected from subtropical forests in southern China. They are described, illustrated, and compared with similar taxa. A dichotomous key to Sporidesmiella species is provided.

New species and records of Heteroconium (anamorphic fungi) from southern China

Four anamorphic fungal species of Heteroconium were collected from tropical and subtropical forests in southern China. Among them, Heteroconium tsoongiodendronis sp. nov. and Heteroconium fici sp. nov. are described from specimens collected on dead branches of Tsoongiodendron odorum and Ficus gibbosa, respectively. Two species of Heteroconium, H. decorosum and H. ponapense, are recorded for the first time in China. A key to Heteroconium and related genera is also provided.

New species and a new record of Solicorynespora from southern China

Four species of Solicorynespora were collected on dead branches from tropical or subtropical forests in southern China. The new species S . ligustri on Ligustrum quihoui, S. machili on Machilus chinensis, and S. cryptocaryae on Cryptocarya chinensis are described, illustrated, and compared with closely related taxa. Solicorynespora pseudolmediae is recorded for the first time from China.

New species and record of Sporidesmium from southern China

Four species of Sporidesmium were collected from decaying twigs in tropical and subtropical forests in southern China. Sporidesmium liquidambaris sp. nov. on Liquidambar formosana, S. antidesmatis sp. nov. on Antidesma ghaesembilla, and S. machili sp. nov. on Machilus chinensis, are described, illustrated, and compared with closely related taxa. Sporidesmium takashii is recorded as new for the Chinese mycota.

High abundance of ammonia-oxidizing archaea in acidified subtropical forest soils in southern China after long-term N deposition

Nitrification has been believed to be performed only by autotrophic ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) until the recent discovery of ammonia-oxidizing archaea (AOA). Meanwhile, it has been questioned whether AOB are significantly responsible for NH(3) oxidation in acidic forest soils. Here, we investigated nitrifying communities and their activity in highly acidified soils of three subtropical forests in southern China that had received chronic high atmospheric N deposition. Nitrifying communities were analyzed using PCR- and culture (most probable number)-based approaches. Nitrification activity was analyzed by measuring gross soil nitrification rates using a (15) N isotope dilution technique. AOB were not detected in the three forest soils: neither via PCR of 16S rRNA and ammonia monooxygenase (amoA) genes nor via culture-based approaches. In contrast, an extraordinary abundance of the putative archaeal amoA was detected (3.2×10(8) -1.2×10(9) gsoil(-1) ). Moreover, this abundance was correlated with gross soil nitrification rates. This indicates that amoA-possessing archaea rather than bacteria were predominantly responsible for nitrification of the soils. Furthermore, sequences of the genus Nitrospira, a dominant group of soil NOB, were detected. Thus, nitrification of acidified subtropical forest soils in southern China could be performed by a combination of AOA and NOB.

Three new species of <i>Sporidesmiella</i> from southern China

Sporidesmiella rosae sp. nov., S. machili sp. nov., and S. archidendri sp. nov., occurring, respectively, on dead branches of Rosa chinensis, Machilus grijsii, and Archidendron clypearia, were collected from subtropical forests in southern China. They are described, illustrated, and compared with similar taxa. A dichotomous key to Sporidesmiella species is provided.

New species and records of Heteroconium (anamorphic fungi) from southern China

Four anamorphic fungal species of Heteroconium were collected from tropical and subtropical forests in southern China. Among them, Heteroconium tsoongio-dendronis sp. nov. and Heteroconium fici sp. nov. are described from specimens collected on dead branches of Tsoongiodendron odorum and Ficus gibbosa, respectively. Two species of Heteroconium, H. decorosum and H ponapense, are recorded for the first time in China. A key to Heteroconium and related genera is also provided.

Taxonomic studies of Endophragmiella from southern China

Two new species, Endophragmiella clausenae from dead branches of Clausena lansium and E. pentaphylacis from dead branches of Pentaphylax euryoides, are described and illustrated. Endophragmiella corticola is a new record for China. These three species were collected from tropical and subtropical forests in southern China.

Three new hyphomycetes from southern China

Three new hyphomycetes were collected from dead branches from tropical and subtropical forests in southern China: Ellisembia schimae from Schima superba, Linkosia hibisci from Hibiscus mutabilis, and Stanjehughesia micheliae from Michelia skinneriana. The new species are described, illustrated, and compared with similar species.

Craspedodidymum and Corynespora spp. nov. and a new anamorph recorded from southern China

Two new species are described and illustrated: Craspedodidymum fujianense from dead branches of Acacia confuse and Corynespora fujianensis from dead branches of Myrioneuron faberi . Craspedodidymum proliferans is a new record for China. These three species were collected from tropical and subtropical forests in southern China.

Estimated Soil Respiration Rates Decreased with Long-Term Soil Microclimate Changes in Successional Forests in Southern China

The response of soil respiration to short-term environmental factors changes has been well studied, whereas the influences of long-term soil microclimate changes on soil respiration are still highly unclear, especially in tropical ecosystems. We hypothesized that soil carbon accumulation in southern China, especially in mature forest during recent years, partly resulted from reducing soil respiration rates. To test this hypothesis, we analyzed the temporal trends and variations of air temperature, soil temperature and soil water content (hereafter referred to as SWC), and then estimated soil respiration rates in the 1980s and 2000s with soil temperature and SWC by regression model in three subtropical forests which are at early-, mid-, and advanced-successional stages, respectively, in Dinghushan Nature Reserve (hereafter referred to as DNR) in southern China. The annual mean ambient air temperature increased by 1.03±0.15°C in the last 50years (1954-2007) in DNR. Rainfall amount in the corresponding period did not change significantly, but rainfall pattern changed remarkably in the last three decades (1978-2007). Soil temperature is correlated with ambient air temperature. The average SWC was 36.8±8.4%, 34.7±8.1% and 29.6±8.1% in the 1980s, and then dropped sharply to 23.6±2.9%, 20.5±4.2% and 17.6±3.9% in the 2000s, for the advanced, mid- and early-successional forests, respectively. Concurrent changes of soil temperature and SWC may have a negative effect on soil respiration rates for all three forests, implicated that soil respiration may have a negative feedback to regional climate change and carbon could be sequestered in subtropical forests in southern China.

Responses of Soil CO2 Efflux to Precipitation Pulses in Two Subtropical Forests in Southern China

This study was designed to examine the responses of soil CO(2) efflux to precipitation pulses of varying intensities using precipitation simulations in two subtropical forests [i.e., mixed and broadleaf forests (MF and BF)] in southern China. The artificial precipitation event was achieved by spraying a known amount of water evenly in a plot (50×50cm(2)) over a 30min period, with intensities ranging from 10, 20, 50 and 100mm within the 30min. The various intensities were simulated in both dry season (in December 2007) and wet (in May 2008) season. We characterized the dynamic patterns of soil CO(2) efflux rate and environmental factors over the 5h experimental period. Results showed that both soil moisture and soil CO(2) efflux rate increased to peak values for most of the simulated precipitation treatments, and gradually returned to the pre-irrigation levels after irrigation in two forests. The maximum peak of soil CO(2) efflux rate occurred at the 10mm precipitation event in the dry season in BF and was about 3.5 times that of the pre-irrigation value. The change in cumulative soil CO(2) efflux following precipitation pulses ranged from -0.68 to 1.72g CO(2)m(-2) over 5h compared to the pre-irrigation levels and was generally larger in the dry season than in the wet season. The positive responses of soil CO(2) efflux to precipitation pulses declined with the increases in precipitation intensity, and surprisingly turned to negative when precipitation intensity reached 50 and 100mm in the wet season. These findings indicated that soil CO(2) efflux could be changed via pulse-like fluxes in subtropical forests in southern China as fewer but extreme precipitation events occur in the future.

Different patterns of ecosystem carbon accumulation between a young and an old-growth subtropical forest in Southern China

Using long-term (22 years) measurements from a young and an old-growth subtropical forest in southern China, we found that both forests accumulated carbon from 1982 to 2004, with the mean carbon accumulation rate at 227 ± 59 g C m−2 year−1 for young forest and 115 ± 89 g C m−2 year−1 for the old-growth forest. Allocation of the accumulated carbon was quite different between these two forests: the young forest accumulated a significant amount of carbon in plant live biomass, whereas the old-growth forest accumulated a significant amount of carbon in the soil. From 1982 to 2004, net primary productivity (NPP) increased for the young forest, and did not change significantly for the old-growth forest. The increase in NPP of the young forest resulted from recruitment of some dominant tree species characteristic of the subtropical mature forest in the region and an increase in tree density; decline of NPP of the old-growth forest was caused by increased mortality of the dominant trees.

Effects of elevated nitrogen deposition on soil microbial biomass carbon in major subtropical forests of southern China

The effects of elevated nitrogen deposition on soil microbial biomass carbon (C) and extractable dissolved organic carbon (DOC) in three types of forest of southern China were studied in November, 2004 and June, 2006. Plots were established in a pine forest (PF), a mixed pine and broad-leaved forest (MF) and monsoon evergreen broad-leaved forest (MEBF) in the Dinghushan Nature Reserve. Nitrogen treatments included a control (no N addition), low N (50 kg N/(hm2·a)), medium N (100 kg N/(hm2·a)) and high N (150 kg N/(hm2·a)). Microbial biomass C and extractable DOC were determined using a chloroform fumigation-extraction method. Results indicate that microbial biomass C and extractable DOC were higher in June, 2006 than in November, 2004 and higher in the MEBF than in the PF or the MF. The response of soil microbial biomass C and extractable DOC to nitrogen deposition varied depending on the forest type and the level of nitrogen treatment. In the PF or MF forests, no significantly different effects of nitrogen addition were found on soil microbial biomass C and extractable DOC. In the MEBF, however, the soil microbial biomass C generally decreased with increased nitrogen levels and high nitrogen addition significantly reduced soil microbial biomass C. The response of soil extractable DOC to added nitrogen in the MEBF shows the opposite trend to soil microbial biomass C. These results suggest that nitrogen deposition may increase the accumulation of soil organic carbon in the MEBF in the study region.

Large Loss of Dissolved Organic Nitrogen from Nitrogen-Saturated Forests in Subtropical China

Dissolved organic nitrogen (DON) has recently been recognized as an important component of terrestrial N cycling, especially under N-limited conditions; however, the effect of increased atmospheric N deposition on DON production and loss from forest soils remains controversial. Here we report DON and dissolved organic carbon (DOC) losses from forest soils receiving very high longterm ambient atmospheric N deposition with or without additional experimental N inputs, to investigate DON biogeochemistry under N-saturated conditions. We studied an old-growth forest, a young pine forest, and a young mixed pine/ broadleaf forest in subtropical southern China. All three forests have previously been shown to have high nitrate (NO3 ) leaching losses, with the highest loss found in the old-growth forest. We hypothesized that DON leaching loss would be forest specific and that the strongest response to experimental N input would be in the N-saturated old-growth forest. Our results showed that under ambient deposition (35‐50 kg N ha -1 y -1 as throughfall input), DON leaching below the major rooting zone in all three forests was high (6.5‐16.9 kg N ha -1 y -1 ). DON leaching increased 35‐162% following 2.5 years of experimental input of 50‐150 kg N ha -1 y -1 . The fertilizer-driven increase of DON leaching comprised 4‐17% of the added N. A concurrent increase in DOC loss was observed only in the pine forest, even though DOC:DON ratios declined in all three forests. Our data showed that DON accounted for 23‐38% of total dissolved N in leaching, highlighting that DON could be a significant pathway of N loss from forests moving toward N saturation. The most pronounced N treatment effect on DON fluxes was not found in the old-growth forest that had the highest DON loss under ambient conditions. DON leaching was highly correlated with NO3 leaching in all three forests. We hypothesize that abiotic incorporation of excess NO3 (through chemically reactive NO2 ) into soil organic matter and the consequent production of N-enriched dissolved organic matter is a major mechanism for the consistent and large DON loss in the N-saturated subtropical forests of southern China.

Preliminary observations of wild black-crested gibbons (Hylobates concolor concolor) in Yunnan province, people's republic of China

Black-crested gibbons (Hylobates concolor concolor), which inhabit the subtropical forests of southern China and northern Vietnam, have until now never been the subject of any systematic behavioral or ecological field study. This report presents the findings of a three-month field study of wild black-crested gibbons in the Wuliang and Ailao Mountain Game Reserves in Yunnan Province, People's Republic of China. The sites visited consisted of temperate, subtropical, broadleaf evergreen forests, with trees belonging to the families Elaeocarpaceae, Fagaceae, Lauraceae, Magnoliaceae, and Theaceae. Black-crested gibbons were documented from four sites visited and were found to be polygynous, with an average group size of seven to eight animals. The family groups were observed to comprise one adult male, from one to four adult females, and numerous offspring of various ages. Both sexes of this species emit interactive songs, and various features of this loud vocal behavior were analyzed and are discussed here. Since all other gibbon species were found to inhabit only tropical rain forests and live in strictly monogamous family groups, some of the ecological and evolutionary implications of these findings are also presented.

Census and survey of wild black-crested gibbons (Hylobates concolor concolor) in Yunnan Province, People's Republic of China.

Black-crested gibbons (Hylobates concolor concolor) inhabit the subtropical forests of Southern China and Northern Vietnam, and have never previously been the subject of any systematic behavioral or ecological study. This report presents the findings of a three-month census and survey of black-crested gibbons in the Wuliang and Ailao Mountain Game Reserves in Yunnan province, China. The censusing methods used here were similar to those techniques used during other census studies of gibbons. The sites visited were subtropical broadleaf evergreen forests, with trees belonging to the families Fagaceae, Theaceae, Magnoliaceae, Lauraceae and Elaeocarpaceae. A total of 23-25 groups of black-crested gibbons were documented from 4 sites visited, and a group density estimate from all sites averaged 0.82 groups/km2. These gibbons were found to be polygynous with an average family group size of 7-8 animals, comprising 1 adult male, 1-4 adult females and numerous offspring of various ages. Some of the ecological and evolutionary implications of these findings are also presented.