Dinghushan Biosphere Reserve Research Articles

Using the kingfisher (Alcedo atthis) as a bioindicator of PCBs and PBDEs in the dinghushan biosphere reserve, China

The Dinghushan Biosphere Reserve is a nature reserve and a site for the study of tropical and subtropical forest ecosystems. Rapid industrialization and intensive electronic waste-recycling activities around the biosphere reserve have resulted in elevated levels of industrial organic contaminants in the local environment that may cause adverse effects on wildlife that inhabits this area. In the present study, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and 2 alternative brominated flame retardants (BFRs)-decabromodiphenyl ethane (DBDPE) and 1,2-bis(2,4,6-tribromophenoxy) ethane (BTBPE)-were investigated in the biosphere reserve and a reference site by using the kingfisher (Alcedo atthis) as a bioindicator. Residue concentrations in kingfishers from the Dinghushan Biosphere Reserve ranged from 490 ng/g to 3000 ng/g, 51 ng/g to 420 ng/g, 0.44 ng/g to 90 ng/g, and 0.04 ng/g to 0.87 ng/g lipid weight for ∑PCBs, ∑PBDEs, DBDPE, and BTBPE, respectively. With the exception of the BTBPE, these levels were 2 to 5 times higher than those detected in kingfishers from the reference site. The contaminant patterns from the biosphere reserve were also different, with larger PCB contributions in comparison with the reference site. The estimated predator-prey biomagnification factors (BMFs) showed that most of the PCB and PBDE congeners and BTBPE were biomagnified in kingfishers from the biosphere reserve. The calculated toxic equivalent quantity (TEQ) concentrations of major coplanar PCB congeners in kingfishers from the biosphere reserve ranged from 18 pg/g to 66 pg/g wet weight, with some of these TEQ concentrations reaching or exceeding the levels known to impair bird reproduction and survival.

Substantial amounts of carbon are sequestered during dry periods in an old-growth subtropical forest in South China

A number of continuous eddy covariance measurements and long-term biomass inventories had proved that old-growth forests are carbon sinks worldwide. The present study estimated the net ecosystem productivity (NEP) for an old-growth subtropical forest at the Dinghushan Biosphere Reserve in South China to investigate the temporal pattern of carbon sequestration, both seasonally and annually. The measured NEP over 7 years (from 2003 to 2009) showed that this forest was a net carbon sink, ranging from 230 (in 2008) to 489…−2 year−1 (in 2004). The greatest value of NEP was found in the driest year and the lowest value in the wettest year during the study period. Within a year, NEP during the dry season was about 81.4 % higher than for the wet season. Accordingly, the dry season at seasonal scale and dry years at interannual scale are key periods for carbon sequestration in this forest. The strong seasonality of ecosystem or soil respiration (ER or SR) compared with gross primary productivity (GPP) resulted in substantial amounts of carbon being sequestered during dry seasons. A decrease of GPP and an increase of ER or SR demonstrated the lower carbon uptake in rainy years. From this study, we conclude that GPP and living biomass carbon increment are not overriding parameters controlling NEP. The variations in ER or SR driven by the rainfall scheme were the dominant factor determining the magnitude of NEP in this forest in South China.

Nutrient limitation on ecosystem productivity and processes of mature and old-growth subtropical forests in China.

Nitrogen (N) is considered the dominant limiting nutrient in temperate regions, while phosphorus (P) limitation frequently occurs in tropical regions, but in subtropical regions nutrient limitation is poorly understood. In this study, we investigated N and P contents and N:P ratios of foliage, forest floors, fine roots and mineral soils, and their relationships with community biomass, litterfall C, N and P productions, forest floor turnover rate, and microbial processes in eight mature and old-growth subtropical forests (stand age >80 yr) at Dinghushan Biosphere Reserve, China. Average N:P ratios (mass based) in foliage, litter (L) layer and mixture of fermentation and humus (F/H) layer, and fine roots were 28.3, 42.3, 32.0 and 32.7, respectively. These values are higher than the critical N:P ratios for P limitation proposed (16–20 for foliage, ca. 25 for forest floors). The markedly high N:P ratios were mainly attributed to the high N concentrations of these plant materials. Community biomass, litterfall C, N and P productions, forest floor turnover rate and microbial properties were more strongly related to measures of P than N and frequently negatively related to the N:P ratios, suggesting a significant role of P availability in determining ecosystem production and productivity and nutrient cycling at all the study sites except for one prescribed disturbed site where N availability may also be important. We propose that N enrichment is probably a significant driver of the potential P limitation in the study area. Low P parent material may also contribute to the potential P limitation. In general, our results provided strong evidence supporting a significant role for P availability, rather than N availability, in determining ecosystem primary productivity and ecosystem processes in subtropical forests of China.

Effect of Acid Deposition on Soil Ca<sup>2+</sup> Contents of Two Forest Ecosystems in Dinghushan Biosphere Reserve

Acid rain is one of the global environmental problems that have become a very serious issue especially in southern China. Calcium ions are the nutrients needed by plants, the Ca2+ contents in forest soils would change greatly when influenced by acid deposition, and even limiting the growth of plants seriously. In this paper, two major forests’ soil of Dinghushan Biosphere Reserve, Monsoon evergreen broadleaf forest (MEBF) and Pine and broad-leaf mixed forest (PBMF), which located at the low subtropics of China, were selected to discuss the dynamics of exchangeable calcium ions under different acidity. It showed that in 2009, the calcium ions’ background values, (0.2918mg/L), in the MEBF are higher than that of the PBMF, (0.1345mg/L). For the two forests’ soils, the contents of exchangeable Ca2+ varied greatly with soil depth, but the MEBF ecosystem would be more stable than the PBMF.

Quantifying the hydrological responses to climate change in an intact forested small watershed in Southern China

AbstractResponses of hydrological processes to climate change are key components in the Intergovernmental Panel for Climate Change (IPCC) assessment. Understanding these responses is critical for developing appropriate mitigation and adaptation strategies for sustainable water resources management and protection of public safety. However, these responses are not well understood and little long‐term evidence exists. Herein, we show how climate change, specifically increased air temperature and storm intensity, can affect soil moisture dynamics and hydrological variables based on both long‐term observation and model simulations using the Soil and Water Assessment Tool (SWAT) in an intact forested watershed (the Dinghushan Biosphere Reserve) in Southern China. Our results show that, although total annual precipitation changed little from 1950 to 2009, soil moisture decreased significantly. A significant decline was also found in the monthly 7‐day low flow from 2000 to 2009. However, the maximum daily streamflow in the wet season and unconfined groundwater tables have significantly increased during the same 10‐year period. The significant decreasing trends on soil moisture and low flow variables suggest that the study watershed is moving towards drought‐like condition. Our analysis indicates that the intensification of rainfall storms and the increasing number of annual no‐rain days were responsible for the increasing chance of both droughts and floods. We conclude that climate change has indeed induced more extreme hydrological events (e.g. droughts and floods) in this watershed and perhaps other areas of Southern China. This study also demonstrated usefulness of our research methodology and its possible applications on quantifying the impacts of climate change on hydrology in any other watersheds where long‐term data are available and human disturbance is negligible.

Soil Acidification in Response to Acid Deposition in Three Subtropical Forests of Subtropical China

Long-term changes in soil pH, the current status of soil acidification, and the response of bulk soil and soil water pH to experimental nitrogen addition under three subtropical forests were investigated in Dinghushan Biosphere Reserve of subtropical China. The results showed that the mineral soil pH at 0–20 cm depth declined significantly from 4.60–4.75 in 1980s to 3.84–4.02 in 2005. Nitrogen addition resulted in the decrease of pH in both bulk soil and soil water collected at 20-cm depth. The rapid decline of soil pH was attributed to long-term high atmospheric acid deposition (nitrogen and sulphur) therein. The forest at earlier succession stage with originally higher soil pH appeared to be more vulnerable to acid deposition than that at later succession stage with originally low soil pH.

Turnover Rate of Soil Organic Matter and Origin of Soil 14Co2 in Deep Soil from a Subtropical Forest in Dinghushan Biosphere Reserve, South China

This paper examines the carbon isotopes (13C, 14C) of soil organic carbon (SOC) and soil CO2 from an evergreen broadleaf forest in southern China during the rainy season. The distribution of SOC δ13C, and SOC content with depth, exhibits a regular decomposition of SOC compartments with different turnover rates. Labile carbon is the main component in the topsoil (0–12 cm) and has a turnover rate between 0.1 and 0.01 yr–1. In the middle section (12–35 cm), SOC was mainly comprised of mediate carbon with turnover rates ranging between 0.01 and 0.025. Below 35 cm depth (underlayer section), the SOC turnover rate is slower than 0.001 yr–1, indicating that passive carbon is the main component of SOC in this section. The total production of humus-derived CO2 is 123.84 g C m–2 yr–1, from which 88% originated in the topsoil. The middle and underlayer sections contribute only 10% and 2% to the total humus-derived CO2 production, respectively. Soil CO2 δ13C varies from –24.7‰ to –24.0‰, showing a slight isotopic depth gradient. Similar to soil CO2 δ13C, Δ14C values, which range from 100.0‰ to 107.2‰, are obviously higher than that of atmospheric CO2 (60–70‰) and SOC in the middle and underlayer section, suggesting that soil CO2 in the profile most likely originates mainly from SOC decomposition in the topsoil. A model of soil CO2 Δ14C indicates that the humus-derived CO2 from the topsoil contributes about 65–78% to soil CO2 in each soil gas sampling layer. In addition, the humus-derived CO2 contributes ∼81% on average to total soil CO2 in the profile, in good agreement with the field observation. The distribution and origin of soil 14CO2 imply that soil CO2 will be an important source of atmospheric 14CO2 well into the future.

Simulating dynamics of managed monsoon evergreen broad-leaved forest in south China

The forest succession model FORDYN is developed based on TREEDEV model. TREEDEV is a process-based tree growth model, that calculates tree growth based on carbon and nitrogen balance, and is calculated using on the photo-production of leaves, respiration, nitrogen content of all organisms and that in soil, and other losses due to respiration, litter and renewal of stems, branches, leaves and roots. In the FORDYN model succession is divided into three phases called early, middle and late succession, and the transition between these three succession phases is distinguished by a difference in leaf area index. As a verification of the model we used the characteristics and available data of a monsoon evergreen broad-leaved forest in Dinghushan Biosphere Reserve (DHS-BR). The model was validated with natural forest data. In addition, a sensitivity analysis was performed in which 30 independent variables were varied and analyzed in connection with their influence on 16 dependent variables describing forest conditions. The simulation results describe the changes in total biomass, carbon and nitrogen change in plant–litter–soil system of an undisturbed monsoon evergreen broad-leaved forest during succession. We compared these findings with simulation in which different logging management strategies were used. The results show that having a longer logging cycle, delaying the first logging time and a smaller logging fraction the scenario can contribute to a sustainable forest development, while still having a positive economic yield.

Carbon isotope analysis for source identification of atmospheric formaldehyde and acetaldehyde in Dinghushan Biosphere Reserve in South China

Formaldehyde and acetaldehyde are two most abundant carbonyls in ambient air. Biogenic emission has been proposed as a significant source other than anthropogenic emissions and atmospheric secondary formation. Here at a forest site in South China, the carbon isotopic compositions of formaldehyde and acetaldehyde emitted from leaves of three tree species ( Litsea rotundifolia, Canarium album and Castanea henryi) were measured in comparison with the bulk carbon isotopic compositions of tree leaves. δ 13C data of the emitted aldehydes (from −31‰ to −46‰) were quite different for tree species, which were all more depleted in 13C than the tree-leaf bulk δ 13C values (from −27‰ to −32‰). Formaldehyde in ambient air at the forest site had δ 13C values different from those of leaf-emitted formaldehyde, indicating other sources for ambient formaldehyde apart from direct emission from leaves, most probably the photooxidation of biogenic hydrocarbon like isoprene and monoterpene. The δ 13C differences of acetaldehyde between ambient data and those of tree leaves emission were less than 1‰, implying direct biogenic emission as the dominant source.

Soil respiration associated with forest succession in subtropical forests in Dinghushan Biosphere Reserve

This paper reports the results of soil respiration (SR, including heterotrophic and autotrophic respiration), in a presumably successional series (early, middle and advanced) of subtropical forests in Dinghushan Biosphere Reserve in Guangdong Province, China. A static chamber method was used to characterize SR in dynamics of diurnal and seasonal patterns. The relationships of SR with soil temperature (ST) at 5 cm depth and with soil moisture (SM) at 0–10 cm depth were studied in order to estimate the annual SR of each of the forests. The annual SR in a climax forest community, monsoon evergreen broad-leaved forest (MEBF) was estimated as 1163.0 g C m −2 year −1 and in its successional communities, coniferous and broad-leaved mixed forest (MF) and the Masson pine forest (MPF) were 592.1 g C m −2 year −1, 1023.7 g C m −2 year −1, respectively. In addition, removal of surface litter led to the reduction of annual SR by 27–45% in those three forests. Analysis of the results indicated that the annual SR was highly correlated with both ST and SM. Furthermore, ST and SM themselves were highly correlated with each other across season in this study area. Thus for seasonal predictive SR model, either ST or SM could be integrated. However, for SR daily change prediction, both ST and SM were required because of confounding effects of ST and SM on a diurnal time scale. The Q 10 values of SR derived from ST dependence function were 2.37, 2.31 and 2.25 in the three forests: MPF, MF and MEBF, respectively, suggesting a decreasing trend of the Q 10 with the degree of forest succession.

Soil nitric oxide emissions after nitrogen and phosphorus additions in two subtropical humid forests

Soil nitric oxide (NO) emissions after the addition of nitrogen (N) and phosphorus (P) were studied at a broadleaf forest and a pine forest in Dinghushan Biosphere Reserve, south China. N was applied at 5 g N m−2 (or 50 kg N ha−1) and P was applied at 4 g P m−2 as NH4Cl (AN), NaNO3 (NN), NH4Cl + Na2HPO4 (AP), NaNO3 + Na2HPO4 (NP), and Na2HPO4 (P) in water solutions, respectively, in comparison with water and blank controls. Enhancement of NO emission by N addition alone was greater than that by combined addition of N and P in both forests due to the P‐limiting soil nutrient status. In both forests, temporal pattern of NO emission after adding NO3−‐N was different with that after adding NH4+‐N. NO3−‐N addition resulted in immediate NO fluxes for the broadleaf and to a lesser extent the pine forest site. In both forests, nitrification contributed more than denitrification to NO production although denitrification also played an important role in the broadleaf forest. N addition induced greater NO emission in the mature broadleaf forest than in the primary pine forest. Over the 50‐day experimental period, averaged NO fluxes in plots adding AN, NN, AP, and NP were 3.3, 2.3, 1.9, and 1.8 times that in the water control plots, respectively, for the broadleaf forest and 2.7, 1.6, 1.5, and 1.3 times that in the water control plots, respectively, for the pine forest. Applied N loss as NO‐N in AN, NN, AP, and NP plots were 2.8%, 1.6%, 1.1%, and 1.0%, respectively, in the broadleaf forest; and 2.6%, 1.0%, 0.8% and 0.4%, respectively, in the pine forest. On the average, N loss as NO from the forest floors was approximately 2% of the applied N as NH4+ or NO3− alone, quite similar to that measured by Hall and Matson (1999) from forest floors in the Hawaiian Islands.

Effect of N and P addition on soil organic C potential mineralization in forest soils in South China

Atmospheric nitrogen deposition is at a high level in some forests of South China. The effects of addition of exogenous N and P on soil organic carbon mineralization were studied to address: (1) if the atmospheric N deposition promotes soil C storage through decreasing mineralization; (2) if the soil available P is a limitation to organic carbon mineralization. Soils (0-10 cm) was sampled from monsoon evergreen broad-leaved forest (MEBF), coniferous and broad-leaved mixed forest (CBMF), and Pinus massoniana forest (PMF) in Dinghushan Biosphere Reserve (located in Guangdong Province, China). The soils were incubated at 25 degrees C for 45 weeks, with addition of N (NH4NO3 solution) or P (KH2PO4 solution). CO2-C emission and the inorganic N (NH4(+)-N and NO3(-)-N) of the soils were determined during the incubation. The results showed that CO2-C emission decreased with the N addition. The addition of P led to a short-term sharp increase in CO2 emission after P application, and the responses of CO2-C evolution to P addition in the later period of incubation related to forest types. Strong P inhibition to CO2 emission occurred in both PMF and CBMF soils in the later incubation. The two-pool kinetic model was fitted well to the data for C turnover in this experiment. The model analysis demonstrated that the addition of N and P changed the distribution of soil organic C between the labile and recalcitrant pool, as well as their mineralization rates. In our experiment, soil pH can not completely explain the negative effect of N addition on CO2-C emission. The changes of soil inorganic N during incubation seemed to support the hypothesis that the polymerization of added nitrogen with soil organic compound by abiotic reactions during incubation made the added nitrogen retard the soil organic carbon mineralization. We conclude that atmospheric N deposition contributes to soil C accretion in the three subtropical forest ecosystems, however, the shortage of soil available P in CBMF and PMF may also retard soil organic C mineralization.

Soil nitric oxide emissions from two subtropical humid forests in south China

Due to the dense population, rapid industrialization, and intensified agricultural activities, some regions in Asia are hot spots of airborne nitrogen oxides and also areas with increasing nitrogen deposition. Therefore the cycling of nitrogen gases in Asia might be of increasing importance on both a regional and a global scale for atmospheric chemistry and budgets of nitrogen. Yet, to date, knowledge of soil NO emission is quite limited in Asia, particularly in forest ecosystems. In this study, soil NO emissions in two subtropical humid forests, a broadleaf forest in climax successional stage and a pine forest in primary successional stage, were measured throughout the year 2005 in Dinghushan Biosphere Reserve, south China. In the broadleaf forest, mean NO emission in wet season (14.9 ng N m−2 s−1) was lower than in dry season (23.8 ng N m−2 s−1). In the pine forest, however, mean NO emission in wet season (17.1 ng N m−2 s−1) was higher than in dry season (7.9 ng N m−2 s−1). In both forests, soil water content was the dominant factor controlling the seasonal patterns of NO emissions, and soil NO emission was significantly correlated to percent water filled pore space (%WFPS) in a quadratic manner (p < 0.001). Annual NO emissions in the broadleaf forest and the pine forest were preliminarily estimated to be 6.1–6.9 and 4.0–4.3 kg N ha−1 yr−1, respectively, by using three upscaling methods.

Changes of Soil Water, Organic Matter, and Exchangeable Cations Along a Forest Successional Gradient in Southern China

Information on the distribution patterns of soil water content (SWC), soil organic matter (SOM), and soil exchangeable cations (SEC) is important for managing forest ecosystems in a sustainable manner. This study investigated how SWC, SOM, and SEC were influenced in forests along a successional gradient, including a regional climax (monsoon evergreen broad-leaved forest, or MEBF), a transitional forest (coniferous and broad-leaved mixed forest, or MF), and a pioneer forest (coniferous Masson pine ( Pinus massoniana) forest, or MPF) of the Dinghushan Biosphere Reserve in the subtropical region of southern China. SWC, SOM, and SEC excluding Ca 2+ were found to increase in the soil during forest succession, being highest in the top soil layer (0 to 15 cm depth) except for Na +. The differences between soil layers were largest in MF. This finding also suggested that the nutrients were enriched in the topsoil when they became increasingly scarce in the soil. There were no significant differences ( P = 0.05) among SWC, SOM, and SEC. A linear, positive correlation was found between SWC and SOM. The correlation between SOM and cation exchange capacity (CEC) was statistically significant, which agreed with the theory that the most important factor determining SEC is SOM. The ratio of K + to Na + in the topsoil was about a half of that in the plants of each forest. MF had the lowest exchangeable Ca 2+ concentration among the three forests and Ca 2+:K + in MPF was two times higher than that in MF. Understanding the changes of SWC, SOM, and CEC during forest succession would be of great help in protecting all three forests in southern China.

Partitioning soil respiration of subtropical forests with different successional stages in south China

The methods of root-excision and trenching were employed concurrently in the present study in order to partition total soil respiration ( R total) into root respiration ( R root), rhizomicrobial respiration ( R rhizo) and root free soil microbial respiration ( R rfs). This study was conducted under the monsoon evergreen broad-leaf forest (BF), the pine forest (PF) and the pine and broad-leaf mixed forest (MF) in Dinghushan Biosphere Reserve, subtropical China from April 2001 to March 2002. The three forests represent different successional stages in this region. Our results showed that mean R total were 477.9 ± 96.3, 429.5 ± 61.0 and 435.4 ± 95.1 mg CO 2 m −2 h −1 in BF, PF and MF, respectively. R total were significantly higher in rain season than those in dry season. However, no significant variations were found among three forests. Soil respiration rates were highly dependent on the combined effects of soil temperature and soil water content. R root was significantly higher in rain season than that in dry season, with the values of 113.8–166.0 mg CO 2 m −2 h −1 in rain season and 48.6–97.1 mg CO 2 m −2 h −1 in dry season. There were no significant differences for R rfs and R rhizo between rain and dry season. However, the contributions of each component to R total in rain season differed from those in dry season. In rain season, R root-to- R total, R rfs-to- R total and R rhizo-to- R total ratios were in the range of 26.1–35.4, 40.6–43.7, and 20.9–36.6%. In dry season, they were 18.1–22.1, 44.8–47.6 and 30.3–37.1%, respectively.

Soil uptake of carbonyl sulfide in subtropical forests with different successional stages in south China

The uptake rates of carbonyl sulfide (COS) by soils in subtropical forests with different successional stages were measured using static chambers in Dinghushan Biosphere Reserve (DBR) in south China from July 2004 to March 2005. The three typical tropical forests studied included monsoon evergreen broad‐leaf forest (BF), pine and broad‐leaf mixed forest (MF) and pine forest (PF), representing forests with different succession stages in the region. COS exchange rates were also compared between the plots with litter‐fall remaining (plots L) and those with litter‐fall removed (plots S) in each forest. Results showed that these forest soils all acted as sinks for COS with exchange rates of −1.22 to −11.82 pmol m−2 s−1. The MF in the midsuccessional stage had significantly higher uptake rates, and the mean exchange rates in the BF, MF, and PF were −3.90, −4.77, and −3.65 pmol m−2 s−1, respectively. COS uptake rates at plots L were higher than those at plots S. Mean COS fluxes were significantly higher in March (−6.06 pmol m−2 s−1) than those in July (−3.60 pmol m−2 s−1), August (−3.82 pmol m−2 s−1), September (−3.45 pmol m−2 s−1), and October (−3.54 pmol m−2 s−1). Significant correlation was observed between the COS uptake rates and soil respiration rates or microbial biomass, indicating that microbial activity was an important factor controlling the soil uptake of COS. Significant correlations between COS fluxes and initial COS mixing ratios were only observed in the BF and MF. COS fluxes showed no correlation with soil temperature or water content alone in any of the three forests, but do correlate well with soil temperature and water content together in polynomial forms with an order of 2.

Responses of chlorophyll fluorescence and xanthophyll cycle in leaves of Schima superba Gardn. & Champ. and Pinus massoniana Lamb. to simulated acid rain at Dinghushan Biosphere Reserve, China

Schima superba and Pinus massoniana distributed over large areas in southern China both are dominant species at Dinghushan Biosphere Reserve. In the present study, the changes of chlorophyll fluorescence and xanthophyll cycle in the leaves of S. superba and P. massoniana exposed to simulated acid rain (SAR) were measured. When exposed to high light, the PSII photochemistry efficiency (Fv/Fm), efficiency of energy conversion in PSII (ΦPSII) and photochemical quenching (qP) of both S. superba and P. massoniana all decreased when acidity of SAR increased. Regarding non-photochemical quenching (qN), S. superba exposed to SAR had higher value than control plants, but there was no significant difference between the respective seedlings of P. massoniana. As for xanthophyll cycle of the two plant species, the leaves of S. superba exposed to SAR showed a higher content of carotenoids and a higher ability to convert violaxanthin to zeaxanthin than leaves of P. massoniana, which was consistent with S. superba exhibiting a stronger resistance to high light than P. massoniana. Although both species were susceptible to acid rain as shown by our results, P. massoniana was more susceptible compared to S. superba. These results provide an insight into how to protect the forest ecosystem at Dinghushan Biosphere Reserve.

Preliminary Response of Soil Fauna to Simulated N Deposition in Three Typical Subtropical Forests

ABSTRACT A field-scale experiment arranged in a complete randomized block design with three N addition treatments including a control (no addition of N), a low N (5 g m−2 year−1), and a medium N (10 g m−2 year−1) was performed in each of the three typical forests, a pine (Pinus massoniana Lamb.) forest (PF), a pine-broadleaf mixed forest (MF) and a mature monsoon evergreen broadleaf forest (MEBF), of the Dinghushan Biosphere Reserve in subtropical China to study the response of soil fauna community to additions of N. Higher NH+4 and NO−3 concentrations and a lower soil pH occurred in the medium N treatment of MEBF, whereas the NO−3 concentration was the lowest in PF after the additions of N. The response of the density, group abundance and diversity index of soil fauna to addition of N varied with the forest type, and all these variables decreased with increasing N under MEBF but the trend was opposite under PF. The N treatments had no significant effects on these variables under MF. Compared with the control plots, the medium N treatment had significant negative effect on soil fauna under MEBF. The group abundance of soil fauna increased significantly with additions of higher N rates under PF. These results suggested that the response of soil fauna to N deposition varied with the forest type and N deposition rate, and soil N status is one of the important factors affecting the response of soil fauna to N deposition.

Different Patterns of Changes in the Dry Season Diameter at Breast Height of Dominant and Evergreen Tree Species in a Mature Subtropical Forest in South China

AbstractInformation on changes in diameter at breast height (DBH) is important for net primary production (NPP) estimates, timing of forest inventory, and forest management. In the present study, patterns of DBH change were measured under field conditions during the dry season for three dominant and native tree species in a monsoon evergreen broad‐leaved forest in the Dinghushan Biosphere Reserve. For each tree species, different patterns of DBH change were observed. In the case of the fast‐growing tree species Castanopsis chinensis Hance, large diurnal fluctuations occur, with a peak DBH in the early morning (around 05:00 h) that decreases to a minimum by about 14:00 h. Both Schima superba Gardn. et Chemp and Cryptocarya chinensis (Hance) Hemsl. exhibited less diurnal swelling and shrinkage. Diurnal fluctuations for these species were observed on a few occasions over the period of observation. Graphical comparisons and statistical analysis of changes in DBH with meteorological variables indicate that for different trees, the different changes in DBH observed responded to different meteorological variables. Large stem changes were found to occur for Ca. chinensis trees that were associated with variations in solar radiation. However, both S. superba and Cr. chinensis were found to be less sensitive to solar radiation. Changes in the DBH of these two species were found to be controlled mainly by soil temperature and soil moisture. During the later dry season, with a lower soil temperature and soil moisture, all three tree species stopped growing and only negligible shrinkage, expansion, or fluctuation occurred, suggesting that the optimum time to measure tree growth in the Dinghushan Biosphere Reserve is the later dry season.(Managing editor: Ya‐Qin Han)

Estimates of soil respiration and net primary production of three forests at different succession stages in South China

AbstractSoil respiration (heterotropic and autotropic respiration, Rg) and aboveground litter fall carbon were measured at three forests at different succession (early, middle and advanced) stages in Dinghushan Biosphere Reserve, Southern China. It was found that the soil respiration increases exponentially with soil temperature at 5 cm depth (Ts) according to the relation Rg=a exp(bTs), and the more advanced forest community during succession has a higher value of a because of higher litter carbon input than the forests at early or middle succession stages. It was also found that the monthly soil respiration is linearly correlated with the aboveground litter carbon input of the previous month. Using measurements of aboveground litter and soil respiration, the net primary productions (NPPs) of three forests were estimated using nonlinear inversion. They are 475, 678 and 1148 g C m−2 yr−1 for the Masson pine forest (MPF), coniferous and broad‐leaf mixed forest (MF) and subtropical monsoon evergreen broad‐leaf forest (MEBF), respectively, in year 2003/2004, of which 54%, 37% and 62% are belowground NPP for those three respective forests if no change in live plant biomass is assumed. After taking account of the decrease in live plant biomass, we estimated the NPP of the subtropical MEBF is 970 g C m−2 yr−1 in year 2003/2004. Total amount of carbon allocated below ground for plant roots is 388 g C m−2 yr−1 for the MPF, 504 g C m−2 yr−1 for the coniferous and broad‐leaf MF and 1254 g C m−2 yr−1 for the subtropical MEBF in 2003/2004. Our results support the hypothesis that the amount of carbon allocation belowground increases during forest succession.