Subtropical Forest In South China Research Articles

Soil aggregate size distribution mediates microbial responses to prolonged acid deposition in a subtropical forest in south China

Extended exposure to acid rain has vastly limited soil microbial activity with the consequences for soil carbon (C) storage, but less is known about the microbial responses within soil aggregates that to some extent determine soil C stabilization. Here, we investigated the main microbial group compositions and the relevant potential enzyme activities within different soil aggregates sizes (microaggregates (<250 μm), small macroaggregates (250–2000 μm), and microaggregates (>2000 μm)) in a subtropical forest with decade-long simulated acid rain (SAR) treatments. Four SAR treatments were set by irrigating plots with water of different pH values (i.e., 3.0, 3.5, 4.0, and 4.5 as a control). Results showed that the SAR treatment significantly inhibited microbial activities, specifically decreasing both bacterial and fungal abundances, leading to declines in C-degrading potential enzyme activities. Conversely, potential enzyme activities related to phosphorus (P) and nitrogen (N) mineralization as well as the enzyme stoichiometry for P/N ratio significantly increased under the SAR treatment. The SAR treatment showed no significant differences in microbial abundance across the three soil aggregate sizes. However, it had a more pronounced effect on potential enzyme activities in their optimal aggregate sizes, such as hydrolytic enzymes like β-glucosidase in macroaggregates and oxidases like phenol oxidase and peroxidase in microaggregates. Overall, C-degrading potential enzyme activities were more strongly decreased in the microaggregates than in macroaggregates, and the distribution in aggregates was significantly altered, transforming from large to small sizes under the SAR treatment, which together may boost SOC stabilization and accumulation. Additionally, our findings indicate that prolonged acid rain also caused soil nutrient limitation and imbalance, particularly for P, in subtropical forests. This study highlights the importance of soil aggregate size in regulating microbial responses to acid rain, which should be integrated into ecosystem models to predict soil biogeochemical cycles under future climate conditions.

Climatic drivers of litterfall production and its components in two subtropical forests in South China: A 14-year observation

Understanding the climatic triggers of litterfall production is essential for simulating nutrient cycling in forest ecosystems. However, the mechanisms underlying litterfall dynamics in subtropical forests remain unclear because of the complex canopy phenological strategies. Herein, we explored this by investigating a unique litterfall dataset (including components such as leaves, branches, flowers and fruits, and miscellaneous, etc.) spanning a 14-year observation period (2005–2018) in two typical subtropical evergreen forest ecosystems in South China: a mixed conifer-broadleaf forest (MF) and a monsoon evergreen broadleaved forest (MEBF). We found that the annual total litterfall production, often dominated by leaf litterfall, was significantly higher in MF (10.21 ± 2.09 t∙hm−2) than in MEBF (7.74 ± 2.21 t∙hm−2) (P < 0.01). Generally, forest litterfall production occurred mostly during the wet season and was profoundly correlated with the monthly maximum wind speed (rMF = 0.70, rMEBF = 0.71, P < 0.01), it contributed exceeded 80% to the total litterfall and the leaf and branch components. Whereas during the dry season, the forest litterfall process was dramatically weakened, showing a significant correlation with the mean temperature (rMF = 0.48, rMEBF = 0.68, P < 0.01). Further analysis showed that during the dry season, the cumulative contribution rates of temperature factors to the total litterfall and the leaf and branch components exceeded 60%, indicating a leading role of temperature in triggering forest litterfall processes. Notably, when excluding the typhoon disturbances, it is observed that temperature, alongside wind speed, emerges as a significant determinant of forest litterfall production during the wet season. Those two factors collectively account for almost 60% of the total litterfall and the leaf and branch components. Our findings have potential significance in improving our understanding of carbon and nutrient cycling in subtropical forest ecosystems under climate change conditions.

Tree-ring data reveal trees are suffering from severe drought stress in the humid subtropical forest

The young secondary forests in subtropical regions of China play an important role in the global carbon cycle and China’s ecological and economic security. These values are closely related to tree radial growth (RW), primarily affected by climate changes, especially climate warming. Here, we measured the RW of six common tree species in subtropical China (Cunninghamia lanceolata, Pinus massoniana, Metasequoia glyptostroboides, Liquidambar formosana, Choerospondias axillaris, and Lithocarpus glaber) and quantified how each responded to climate warming. Temperature and moisture were the main climate factors limiting the growth of tree species in the study area. The growth of tree species other than L. formosana and P. massoniana was negatively correlated with temperature and positively correlated with relative humidity. Precipitation in the growing season was negatively correlated with the growth of L. formosana and M. glyptostroboides and positively affected the growth of the other tree species. The radial growth trends of trees growing in similar terrain and climate conditions were similar, but their degree of variation was different. Compared to broad-leaved tree species (L. formosana, C. axillaris, and L. glaber), coniferous tree species (C. lanceolata, P. massoniana, and M. glyptostroboides) were more climate-sensitive, particularly C. lanceolata. Climate warming can potentially extend the growing period and promote the radial growth of the study tree species, but more often leads to drought stress that inhibits radial growth. The long-term drought during 2004–2015 significantly reduced the radial growth of most species, especially conifers which are more vulnerable to drought than broad-leaved trees. Our results highlight that most tree species in the humid subtropical forest in South China are suffering from severe drought stress, which significantly affects forest carbon sequestration. It is probably a good warning for current plantation policy and species selection to better achieving the “Carbon Peaking & Carbon Neutrality” goals of the Chinese government.

Topographical Influence on Snag Distribution in a Subtropical Forest in South China

Snags are highly important for many wildlife species and ecological processes. In this study, we analyzed the relationship between snags and topographic factors in a secondary forest plot in South China. Data on 544 snags were collected and recorded from 236 subplots in a permanent plot (400 subplots). The frequency of Castanopsis carlesii and Schima superba was higher than that of other species. The snags derived mostly from saplings and small trees, and the presence of snags decreased as the DBH and height increased after 25 years of logging. The snags displayed an aggregated spatial pattern distribution, which was strongly correlated with elevation, slope steepness, and slope aspect (p &lt; 0.05), as revealed by canonical correspondence analysis (CCA); however, the response of snags varied with topographic factors. Our results demonstrate that topography is an important factor that affects the snag spatial distribution in the subtropical secondary forest. These results will further improve our understanding of forest dynamics and provide guidance for forest management and biodiversity conservation.

Effects of Simulated Nitrogen Deposition and Micro-Environment on the Functional Traits of Two Rare and Endangered Fern Species in a Subtropical Forest

Although the effects of N deposition on forest plants have been widely reported, few studies have focused on rare and endangered fern species (REFs). Information is also lacking on the effects of micro-environments on REFs. We investigated the effects of N addition (canopy and understory N addition, CAN, and UAN) and micro-environments (soil and canopy conditions) on the functional traits (growth, defense, and reproduction; 19 traits in total) of two REFs-Alsophila podophylla and Cibotium baromet-in a subtropical forest in South China. We found that, compared to controls, CAN or UAN decreased the growth traits (e.g., plant height, H) of C. baromet, increased its defense traits (e.g., leaf organic acid concentrations, OA), delayed its reproductive event (all-spore release date), and prolonged its reproductive duration. In contrast, A. podophylla showed increased growth traits (e.g., H), decreased defense traits (e.g., OA), and advanced reproductive events (e.g., the all-spore emergence date) under CAN or UAN. Meanwhile, the negative effects on the C. baromet growth traits and A. podophylla defense traits were stronger for CAN than for UAN. In addition, the soil chemical properties always explained more of the variations in the growth and reproductive traits of the two REFs than the N addition. Our study indicates that, under simulated N deposition, C. baromet increases its investment in defense, whereas A. podophylla increases its investment in growth and reproduction; this may cause an increasing A. podophylla population and decreasing C. baromet population in subtropical forests. Our study also highlights the importance of considering micro-environments and the N-addition approach when predicting N deposition impact on subtropical forest REFs.

Fungal Communities Are More Sensitive to the Simulated Environmental Changes than Bacterial Communities in a Subtropical Forest: the Single and Interactive Effects of Nitrogen Addition and Precipitation Seasonality Change.

Increased nitrogen deposition (N factor) and changes in precipitation patterns (W factor) can greatly impact soil microbial communities in tropical/subtropical forests. Although knowledge about the effects of a single factor on soil microbial communities is growing rapidly, little is understood about the interactive effects of these two environmental change factors. In this study, we investigated the responses of soil bacterial and fungal communities to the short-term simulated environmental changes (nitrogen addition, precipitation seasonality change, and their combination) in a subtropical forest in South China. The interaction between N and W factors was detected significant for affecting some soil physicochemical properties (such as pH, soil water, and NO3- contents). Fungi were more susceptible to treatment than bacteria in a variety of community traits (alpha, beta diversity, and network topological features). The N and W factors act antagonistically to affect fungal alpha diversity, and the interaction effect was detected significant for the dry season. The topological features of the meta-community (containing both bacteria and fungi) network overrode the alpha and beta diversity of bacterial or fungal communities in explaining the variation of soil enzyme activities. The associations between Ascomycota fungi and Gammaproteobacteria or Alphaproteobacteria might be important in mediating the inter-kingdom interactions. In summary, our results suggested that fungal communities were more sensitive to N and W factors (and their interaction) than bacterial communities, and the treatments' effects were more prominent in the dry season, which may have great consequences in soil processes and ecosystem functions in subtropical forests.

Abiotic Drivers of Seedling Bank Diversity in Subtropical Forests of Southern China

Abiotic factors are important to shape plant community composition and diversity through processes described as environmental filtering. Most studies on plant diversity in forests focus on adult trees, while the abiotic drivers of forest seedling community characteristics are less understood. Here, we studied seedling banks’ composition, richness, diversity, and abundance, and investigated their relationships with microsite abiotic conditions along a wide elevational gradient. We sampled seedling communities in 312 1-m2 quadrats, distributed in 13 one-ha plots in four subtropical forests in south China, covering an elevation gradient of 1500 m, for 2 years. We measured light availability, slope, and 11 soil nutrients for each seedling quadrat. We used analysis of similarities and multivariate analysis of variance to compare the composition and abiotic drivers of the four forests’ seedling communities. We then used mixed models and structural equation modeling to test the direct and indirect effects of abiotic factors on seedling species richness, diversity, and abundance. The differences in seedling community composition among these forests were mostly explained by differences in elevations and soil nutrients. Seedling diversity as Shannon and Simpson diversity index decreased with increasing elevation and increased with increasing slope, but seedling abundance and species richness did not. Elevation had an indirect effect on Simpson’s diversity index through modulating the direct effects of soil properties. Our findings show that soil properties play a prominent role in favoring differentiation in species composition among the four forests we studied and provide additional evidence to decreasing species diversity with elevation. However, this was reflected in decreasing Shannon and Simpson indices rather than species richness, which is more commonly studied. Whether and to what extent future environmental changes in climate and soil acidification will alter future forest composition and diversity needs to be investigated.

Auxin concentration and xylem production of Pinus massoniana in a subtropical forest in south China.

Auxin is involved in various developmental processes of plants, including cell division in cambium and xylem differentiation. However, most studies linking auxin and xylem cell production are performed in environments with a strong seasonality (i.e., temperate and boreal climates). The temporal dynamics of auxin and cambial activity of subtropical trees remain basically unknown. In this study, we sampled four microcores weekly in three individuals of Chinese red pine (Pinus massoniana Lamb.) from February to December 2015-16 to compare xylem formation with auxin concentration in subtropical China. During the entire period of sampling, the number of cambial cells varied from 2 to 7, while the number of cells in the enlarging zone ranged from 1 to 4 and from 1 to 5 in the wall-thickening zone. In 2015, the average auxin concentration was 3.46ngg-1, with 33 xylem cells being produced at the end of the year. In 2016, a lower auxin concentration (2.59ngg-1) corresponded to a reduced annual xylem production (13.7 cells). No significant relationship between auxin concentration and number of xylem cells in differentiation was found at the weekly scale. Unlike in boreal and temperate forests, the lack of wood formation seasonality in subtropical forests makes it more difficult to reveal the relationship between auxin concentration and number of xylem cells in differentiation at the intra-annual scale. The frequent and repeated samplings might have reduced auxin concentration in the developing cambium and xylem, resulting in a lower xylem cell production.

Diagnosing the impacts of climate extremes on the interannual variations of carbon fluxes of a subtropical evergreen mixed forest

Climate extremes are expected to have severe impacts on carbon cycle balance and ecosystem services, because of the highly nonlinear dependence of many carbon processes on climate variability. These impacts, such as the European heatwave in 2003, have been well documented for some temperate forests. However, few studies have been conducted on subtropical forests, which play a significant role in the global carbon cycle. Here, we analyzed continuous carbon flux measurements of a subtropical forest in South China from 2003 to 2016, during which the forest experienced extreme cold and hot spells and a prolonged drought. We found that the forest was a strong carbon sink, taking up about 400 to 740 g C m−2 yr−1 in most years, and that the forest became a much weaker sink or even a carbon source during two extreme periods. This large interannual variation of net carbon uptake by this forest resulted from the different responses of gross primary production (GPP) and terrestrial ecosystem respiration (TER) to climate extremes. The observed reduction in GPP during extreme years was well simulated by lowering maximum leaf carboxylation rate (vcmax) in a process-based model. Parameter optimization suggests that the reduced vcmax in the model recovered quickly after hot and cold spells but remained low after the prolonged drought. During the prolonged drought, the observed tree mortality and litter fall significantly increased, which increased TER in the following year. This lagged response in TER significantly contributed to the weakened carbon sinks of the forest during the two extremes. Our study highlights the importance of community dynamics and lagged response of the terrestrial carbon cycle to climate extremes.

Topographic differences in nitrogen cycling mediate nitrogen retention in a subtropical, N-saturated forest catchment

N leaching and gaseous N emissions from forested catchments are controlled by soils differing in nitrogen (N) status and turnover depending on landscape position. To understand the impact of topography on N retention and dissipation in forested catchments suffering from high atmospheric N deposition, we carried out an ex-situ15N-tracing study with soils from a hillslope (HS) and a hydrologically connected groundwater discharge zone (GDZ) of an N-saturated subtropical forest in South China. Despite being severely N-saturated, soil from HS incorporated a substantial amount of added 15N–NH4+ instantly into recalcitrant organic N. The remaining NH4+ was cycled via a microbial loop of fast N immobilization and re-mineralization, slowly releasing NH4+ for autotrophic nitrification. Heterotrophic nitrification was only observed right after tracer application. Added 15N–NO3- cycled between soil microbial biomass and dissolved organic N without being stored in the recalcitrant organic N pool, explaining the strong propensity of HS soils for NO3− leaching. By contrast, the soil from GDZ acted as a sink for added N by incorporating 15N–NH4+ into recalcitrant organic N and denitrifying 15N–NO3- to gaseous N. Here, N immobilization exceeded N mineralization, suggesting N limitation. Heterotrophic nitrification was the main pathway of NH3 oxidation in the GDZ soil, and N2O–N contributed substantially to N removal. Abiotic processes played a role in NO3− incorporation into organic N but not in N2O production, while DNRA was negligible in either soil. Overall, our findings suggest strong topographic control on N cycling, which might explain the unexpectedly high N retention and removal from N-saturated forests in subtropical China.

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The humid tropical and subtropical forests in South China harbour a rich diversity of crustose lichens. As a result of taxonomic studies of Anisomeridium, two species new to science are described. Comparisons and discussions with similar species are given. In addition, a key to the species of Anisomeridium in China is also provided.

Seedling growth and survival responses to multiple soil properties in subtropical forests of south China

Soil properties and light availability have been long recognized as fundamental drivers of species distribution and are especially important during the regeneration phase. The role of nutrients such as exchangeable base cations is poorly understood, despite forests facing considerable changes in soil composition due to climatic change and atmospheric acid deposition, including in south China.With the aim of understanding the response of naturally regenerating seedling communities to a wide range of abiotic conditions, we quantified seedling growth and survival of over 2000 seedlings representing 166 morpho-species within four subtropical forests in south China, for two years. We assessed their responses to canopy openness, and a natural gradient of soil characteristics: moisture, pH, total nitrogen (N), total carbon (C), C:N ratio, available phosphorus (P), available potassium (K), calcium (Ca), iron (Fe), magnesium (Mg), manganese (Mn), and sulfur (S). We conducted our analyses at three levels: landscape (1), forest site (4), and species (7).We found statistically clear effects of several soil properties on seedling growth and survival, at all levels of analysis, while canopy openness showed a minimal negative effect on survival and none on growth. Seedling growth was positively affected by increasing soil Ca and Mn and negatively by increasing soil Mg at the landscape level (all four forest sites combined). Seedling survival responded positively to soil Fe and C:N ratio, but negatively to soil Ca, Mg, Mn, N, and S. The observed patterns were forest site- and species-specific. These results are especially relevant in a region experiencing severe changes in soil conditions as well as intense deforestation and land use change. Reforestation programs should consider the site specificity of soil properties with respect to a wide range of soil nutrients when planning restoration activities.

Intrinsic biotic factors and microsite conditions drive seedling survival in a species with masting reproduction.

Seedling recruitment following a masting event, where more fruits are produced in synchrony and intermittently compared with other species, plays a crucial role in determining species diversity and community structure. Such seedling recruitment can be superabundant, but followed by high mortality shortly thereafter. Differences in biotic factors such as seedling characteristics, competition, and herbivory, and microsite‐specific abiotic factors could determine seedling fate in space and time.In a subtropical forest in south China, for 2 years using censuses conducted every 1–2 months, we monitored 40 seed traps and 120, 1 m2 quadrats in five 1‐ha plots located from 1,400 to 1,850 m asl for the masting maple species, Acer campbellii subsp. sinense (Pax) P.C.DeJong. We measured biotic—conspecific and heterospecific seedling density, species richness, herbivory, seedling height, and leaf number—and abiotic—canopy openness, slope, and aspect—factors to assess drivers of seedling survival and evaluated A. campbellii subsp. sinense presence in the soil seed bank (SSB).The masting seed dispersal peak and seedling emergence peak occurred between October 2017 and January 2018, and May 2018, respectively. Of 688 selected seedlings, mortality was 92.7% within one year. No seeds were observed in the SSB. Seedling height and leaf number positively affected seedling survival, while seed placement as measured by aspect also showed effects on survival. Conspecific and heterospecific density and herbivory did not show any clear effect. Higher probabilities of seedling survival were found in areas with larger canopy openness (≥12% canopy gap size) and in steeper microsites (≥35°). Synthesis. Masting is mainly studied as a population‐level phenomenon from the fruiting tree perspective. Our study of individual seedling fate revealed that intrinsic biotic factors and seed placement were key drivers of survival. Although biotic determinants such as competition from conspecifics or heterospecifics or herbivory did not determine survival, their ubiquitous presence may be an underlying equalizer in community dynamics where seedlings that overcome biotic pressures, if placed at the right microsite, are at better odds at being recruited to the next life history stages.

An optimal ensemble of the Noah-MP land surface model for simulating surface heat fluxes over a typical subtropical forest in South China

Accurate estimation of land surface heat fluxes is critical to climate and air quality forecasting, which needs an appropriate parameterization in land surface models. The benchmarking method was applied to search for the optimal combination of the physical parameterization based on Noah land surface model with multi-physics options (Noah-MP). The effect of integrated physical mechanisms on the simulation of land surface energy fluxes in a typical subtropical forest (Dinghushan Forest Ecosystem Research Station) over South China is further investigated. The most sensitive process is the soil moisture threshold for evaporation while there are six processes have little or no effect on heat simulation. The optimal combination options are referred as follow: prescribed table leaf area index (LAI) and vegetation fraction, Jarvis scheme for canopy stomatal resistance, Noah soil moisture scheme, SIMGM model for runoff and groundwater, original Noah consistent scheme for surface layer drag coefficient and two-stream applied to grid-cell scheme for radiation transfer.

Monitoring canopy recovery in a subtropical forest following a huge ice storm using hemispherical photography.

We estimated canopy structure and transmitted radiation using hemispherical photography in four monitoring years (2008-2010, 2016) following the 2008 huge ice storm in a subtropical forest in south China, so as to assess changes in canopy biophysical parameters during forest recovery from natural disturbance. Significant decrease in canopy openness (CO), transmitted direct radiation (TransDir), and transmitted diffuse radiation (TransDif), as well as significant increase in leaf area index (LAI), were found in the disturbed forest stand in the subsequent years following the ice storm, indicating rapid canopy recovery. In contrast, these biophysical parameters of the undisturbed forest stand were quite stable during the monitoring years. The strength of relationships between CO and other canopy biophysical parameters decreased in the disturbed stand along the monitoring years. The disturbed stand had common slopes for the CO-TransDir and CO-TransDif models in the first two monitoring years, but different slopes for the CO-LAI model between the first and the subsequent monitoring years, while the undisturbed stand had common slopes for all the regression models in the first three monitoring years following the huge ice storm. These results showed that stronger correlations of LAI or TransDir with CO were characteristic of less complex canopies, such as those damaged by disturbance; the sensitivity of transmitted radiation in response to CO decreased with canopy recovery. Our findings demonstrated that forests with different canopy structure varied in biophysical parameters, which can be quantified by hemispherical photography.

Denitrification as a major regional nitrogen sink in subtropical forest catchments: Evidence from multi-site dual nitrate isotopes.

Increasing nitrogen (N) deposition in subtropical forests in south China causes N saturation, associated with significant nitrate (NO3- ) leaching. Strong N attenuation may occur in groundwater discharge zones hydrologically connected to well-drained hillslopes, as has been shown for the subtropical headwater catchment "TieShanPing", where dual NO3- isotopes indicated that groundwater discharge zones act as an important N sink and hotspot for denitrification. Here, we present a regional study reporting inorganic N fluxes over two years together with dual NO3- isotope signatures obtained in two summer campaigns from seven forested catchments in China, representing a gradient in climate and atmospheric N input. In all catchments, fluxes of dissolved inorganic N indicated efficient conversion of NH4+ to NO3- on well-drained hillslopes, and subsequent interflow of NO3- over the argic B-horizons to groundwater discharge zones. Depletion of 15 N- and 18 O-NO3- on hillslopes suggested nitrification as the main source of NO3- . In all catchments, except one of the northern sites, which had low N deposition rates, NO3- attenuation by denitrification occurred in groundwater discharge zones, as indicated by simultaneous 15 N and 18 O enrichment in residual NO3- . By contrast to the southern sites, the northern catchments lack continuous and well-developed groundwater discharge zones, explaining less efficient N removal. Using a model based on 15 NO3- signatures, we estimated denitrification fluxes from 2.4 to 21.7kgNha-1 year-1 for the southern sites, accounting for more than half of the observed N removal. Across the southern catchments, estimated denitrification scaled proportionally with N deposition. Together, this indicates that N removal by denitrification is an important component of the N budget of southern Chinese forests and that natural NO3- attenuation may increase with increasing N input, thus partly counteracting further aggravation of N contamination of surface waters in the region.

Gaseous elemental mercury (GEM) fluxes over canopy of two typical subtropical forests in south China

Abstract. Mercury (Hg) exchange between forests and the atmosphere plays an important role in global Hg cycling. The present estimate of global emission of Hg from natural source has large uncertainty, partly due to the lack of chronical and valid field data, particularly for terrestrial surfaces in China, the most important contributor to global atmospheric Hg. In this study, the micrometeorological method (MM) was used to continuously observe gaseous elemental mercury (GEM) fluxes over forest canopy at a mildly polluted site (Qianyanzhou, QYZ) and a moderately polluted site (Huitong, HT, near a large Hg mine) in subtropical south China for a full year from January to December in 2014. The GEM flux measurements over forest canopy in QYZ and HT showed net emission with annual average values of 6.67 and 0.30 ngm-2h-1, respectively. Daily variations of GEM fluxes showed an increasing emission with the increasing air temperature and solar radiation in the daytime to a peak at 13:00, and decreasing emission thereafter, even as a GEM sink or balance at night. High temperature and low air Hg concentration resulted in the high Hg emission in summer. Low temperature in winter and Hg absorption by plant in spring resulted in low Hg emission, or even adsorption in the two seasons. GEM fluxes were positively correlated with air temperature, soil temperature, wind speed, and solar radiation, while it is negatively correlated with air humidity and atmospheric GEM concentration. The lower emission fluxes of GEM at the moderately polluted site (HT) when compared with that in the mildly polluted site (QYZ) may result from a much higher adsorption fluxes at night in spite of a similar or higher emission fluxes during daytime. This shows that the higher atmospheric GEM concentration at HT restricted the forest GEM emission. Great attention should be paid to forests as a crucial increasing Hg emission source with the decreasing atmospheric GEM concentration in polluted areas because of Hg emission abatement in the future.

Changes in vegetation and soil properties during recovery of a subtropical forest in South China

Secondary forests account for a large amount of subtropical forest due to persistent anthropogenic disturbance in China. The interaction between vegetation and soil during recovery process is rather complex and dependent on forest conditions. Understanding how vegetation and soil properties changes and how their relationship develops in secondary forests is key to effective forest restoration and management. Here we explored the patterns of vegetation and soil properties as well as their correlations during forest recovery process in a subtropical forest in south China. Plots of three forest types, i.e., broadleaf-conifer mixed forest, broadleaved forest and old growth stand, were established to represent the recovery stages. The results showed that diversity patterns in the tree, shrub and herb layers were different: in the tree layer the species diversity peaked at the intermediate stage, while in the understory layers it decreased chronologically. Most of the soil factors showed an increasing trend, and different effects of soil factors were found for the three layers as well as for the two spatial scales. Together, our results suggested that vegetation and soil might be interdependent during the recovery course. Further studies are needed on exploring how vegetation interplays with soil at different scales and how nutrient limitations affects the vegetation development in a chronosequence.

杉木人工林凋落物生态化学计量与土壤有效养分对长期模拟氮沉降的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 杉木人工林凋落物生态化学计量与土壤有效养分对长期模拟氮沉降的响应 DOI: 10.5846/stxb201711242095 作者: 作者单位: 南昌工程学院,南昌工程学院,南昌工程学院,江西农业大学,南昌工程学院,南昌工程学院 作者简介: 通讯作者: 中图分类号: 基金项目: 江西省教育厅科技项目（GJJ161118）；国家自然科学基金项目（31360175，31570444）；江西省主要学科学术和技术带头人项目（20162BCB22021）；2016年南昌工程学院大学生科研训练计划项目（2016053） Litterfall ecological stoichiometry and soil available nutrients under long-term nitrogen deposition in a Chinese fir plantation Author: Affiliation: Nanchang Institute of Technology,,Nanchang Institute of Technology,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:凋落物分解的快慢和养分释放的速度决定了生态系统中土壤有效养分的供应。探讨全球变化条件下森林生态系统凋落物与土壤养分的变化规律，有利于深入认识凋落物-土壤相互作用的养分调控因素，从而揭示生态系统C、N、P循环。通过模拟氮沉降增加试验，分4个水平处理，分别为0、60、120、240 kg N hm-2 a-1。模拟氮沉降13年后，分析了杉木人工林凋落物中不同组分（落叶、落枝、落果）生态化学计量与土壤有效养分（有效氮、碱解氮、速效磷、速效钾）的关系。结果表明：氮沉降（N1、N2和N3）显著提高了落叶和落枝的N含量，平均增幅分别为35.27%和32.21%；高水平氮沉降（N3）处理显著降低了落叶和落枝的C/N，平均降幅分别为25.95%和22.32%，但N3增加了落枝和落果N/P，平均增幅分别为38.4%和31.7%；氮沉降对凋落物各组分的C、P和C/P均影响不显著。氮沉降处理显著增加了土壤NO3--N和NH4+-N含量，均表现为N3 > N2 > N1 > N0，其中NO3--N含量更容易受氮沉降处理的影响，表现为更大的增幅。N2显著增加0-20 cm土层的碱解氮含量，N1显著降低0-20 cm土层的速效钾，但氮沉降对速效磷含量没有影响。凋落物生态化学计量与土壤有效养分之间的Pearson相关和冗余分析（RDA）表明，凋落物生态化学计量与土壤有效养分之间关系紧密，凋落物P含量（蒙特卡罗检验，P=0.018）和C/P比值（P=0.037）对土壤有效养分影响显著。凋落物中C/N比值、C/P比值与土壤有效养分呈显著负相关，其比值越高越不利于土壤有效养分的累积。 Abstract:Nitrogen (N) deposition because of continuous anthropogenic emission of air pollutants, is one of three major drivers of global change. Elevated N deposition may lead to N saturation, soil acidification, plant nutrient imbalances, and even forest productivity decline. Nutrients released from litterfall decomposition represent a large part of the input to the soil, which has been studied extensively in forest ecosystems around the globe. However, the relationship between soil nutrient availability and litterfall remains largely unknown regarding nitrogen deposition, especially in subtropical forests in South China. In the present study, the litterfall and soil nutrients were determined in a nitrogen-loaded Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantation forest. A field experiment with simulated N additions at three doses, N1 (60 kg N hm-2 a-1), N2 (120 kg N hm-2 a-1), and N3 (240 kg N hm-2 a-1), with N0 as the control (0 kg N hm-2 a-1), was conducted by adding the required amount of urea dissolved in 20 L water. This field experiment was initiated in January 2004 with continuous operation and was monitored for almost 13 years. Ten 1 m×1 m litter collecting frames were randomly set up in each plot in January 2004. Litterfall samples were collected monthly and mixed together into one sample per plot. We selected litterfall samples in June 2016 and separated them into fallen leaf, branch, and fruit. In total, there were 12 plots×3 components=36 samples. Soil samples were collected randomly at the depths of 0-20 cm, 20-40 cm, and 40-60 cm in each plot in June 2016, which together (4 treatment levels×3 doses×3 soil layers) constituted 36 samples. The ecological stoichiometry of fallen leaves, branches, and fruits, and soil available nutrients, such as ammonium N (NH4+-N), nitrate N (NO3--N), alkali-hydrolyzed N, available P, available K were measured. Our results showed that N deposition increased N content by 35.27% in fallen leaves and 32.21% in fallen branches averagely. The high level of N addition (N3) decreased the carbon to N (C/N) ratio by 25.95% and 32.21% in fallen leaves and branches, respectively, but increased the N to phosphorus (N/P) ratio in fallen branches by 38.4% and in fallen fruits by 31.7%. Nitrogen loads produced no significant effects on litterfall C content, P content, or the C/P ratio. The concentrations of soil NH4+-N and NO3--N increased significantly with increasing N deposition levels at all three soil depths, with stronger response from NO3--N. The N1 treatment significantly suppressed soil available K, whereas the N2 treatment significantly promoted soil alkali-hydrolyzed N at 0-20 cm, but N deposition showed no significant effect on soil available P. Pearson's correlation and redundancy analysis (RDA) between litterfall ecological stoichiometry and soil available nutrients indicated that litterfall P concentration (Monte Carlo (999), P=0.018) and C/P ratio (P=0.037) were the major determinants of soil available nutrients. Negative relationships exited between the litterfall C/N ratio, C/P ratio, and soil available nutrients, which suggested that higher ratios were unfavorable to the accumulation of soil available nutrients. 参考文献 相似文献 引证文献

Resolving phylogenetic relationships and species delimitations in closely related gymnosperms using high-throughput NGS, Sanger sequencing and morphology

Plastid genomes have been widely applied to elucidate plant evolution at higher taxonomic levels, but have rarely been considered useful for addressing close relationships. Here, we resolve the phylogeny and taxonomy of the Chinese lianoid Gnetum clade (Gnetales), using high throughput and Sanger sequencing techniques and studies of plant morphology. Despite previous efforts, relationships among taxa and the taxonomy within the clade have remained unclear. We generated 11 plastid genomes representing one arborescent and four lianoid species. Phylogenetic analyses were conducted using (a) the entire plastid genomes and (b) the protein-coding genes only. Sequence divergence among the lianoid species was substantial, with 9345 variable sites. Four variable regions were identified, targeted and sequenced for an additional 54 specimens and analyzed together with one nuclear ribosomal marker. Results from the phylogenetic analyses corroborate G. parvifolium as sister to the remaining lianoid species and support the presence of at least five additional species in the Chinese lianoid clade: G. catasphaericum, G. formosum, G. luofuense, G. montanum and G. pendulum. Following morphological investigations, G. giganteum and G. gracilipes are included in and synonymized with G. pendulum. Gnetum hainanense is included in and synonymized with G. luofuense. Two names, G. indicum and G. cleistostachyum, remain questionable. A taxonomic revision and a key to Chinese lianoid Gnetum are presented. Internal nodes in the Chinese lianoid Gnetum clade are from the Miocene and onwards and coincide with the expansion of tropical to subtropical forests in South China, which may have facilitated speciation in the clade.