Karst Forest Research Articles

Comparative study of the stoichiometric characteristics of karst and non-karst forests in Guizhou, China

Carbon (C), nitrogen (N), and phosphorous (P) levels and their stoichiometry in plant components (leaves, branch trunks, roots) of trees in a karst forest and non-karst forest are compared. The results show that the C contents, C:N and C:P ratios of dominant species in the karst forest were lower than those in the non-karst forest, but the N and P and the N:P ratio were higher; C:N:P ratios in plant organs of trees in the karst forest were in the order of trunks > roots > branches > leaves. However, C:N:P ratio in the non-karst forest trees were trunks > branches > roots > leaves. Moreover, ratio of C:N:P in trunks was highest and lowest in leaves in both forests. In non-karst forest trees, N:P was in the order of leaves > roots > branches > trunks. There were no significant differences in the ratio of N:P in different plant components of trees in the karst forest. However, in karst and non-karst forest trees, the ratio of N:P in leaves was highest; positive correlations between N and P contents, and N and N:P ratios were observed in both karst and non-karst forests (p < 0.001). Negative correlations between P and N:P ratios (p < 0.05) were observed in karst forest trees, while positive correlations were observed in non-karst forest trees.

Comparing the Water-holding Characteristics of Broadleaved, Coniferous, and Mixed Forest Litter Layers in a Karst Region

Karst forests are often located in mountainous regions, and because of various geological factors both soil and water loss are major conservation concerns. We investigated the water-holding characteristics of 3 typical karst forest types through field sampling and laboratory experiments. The results showed that (1) the total litter mass of the coniferous forest was significantly higher than that of either the mixed forest or the broadleaved forest; (2) the mass of semidecomposed litter was significantly higher than that of undecomposed litter; (3) the litter layers of the mixed and coniferous forests had similar maximum water-holding capacity, whereas the maximum water-holding capacity of the broadleaved forest was significantly lower; (4) the maximum water-retention capacity of both the mixed and coniferous forests was significantly higher than that of the broadleaved forest; and (5) water-absorption rate and maximum water-holding capacity varied significantly across forest and litter types, with the mixed forest and undecomposed litter layers tending both to hold more water and to absorb water more quickly than the other forest types or the semidecomposed litter layer. Because of the elevated water-holding capacity and absorption rate of the mixed forest in karst regions, special emphasis on the conservation of this complex forest ecosystem is critical from both hydrological and ecological perspectives.

Spatial Patterns and Drivers of Microbial Taxa in a Karst Broadleaf Forest.

Spatial patterns and drivers of soil microbial communities have not yet been well documented. Here, we used geostatistical modeling and Illumina sequencing of 16S rRNA genes to explore how the main microbial taxa at the phyla level are spatially distributed in a 25-ha karst broadleaf forest in southwest China. Proteobacteria, dominated by Alpha- and Deltaproteobacteria, was the most abundant phylum (34.51%) in the karst forest soils. Other dominating phyla were Actinobacteria (30.73%), and Acidobacteria (12.24%). Soil microbial taxa showed spatial dependence with an autocorrelation range of 44.4–883.0 m, most of them within the scope of the study plots (500 m). An increasing trend was observed for Alphaproteobacteria, Deltaproteobacteria, and Chloroflexi from north to south in the study area, but an opposite trend for Actinobacteria, Acidobacteira, and Firmicutes was observed. Thaumarchaeota, Bacteroidetes, Gemmatimonadetes, and Verrucomicrobia had patchy patterns, Nitrospirae had a unimodal pattern, and Latescibacteria had an intermittent pattern with low and high value strips. Location, soil total phosphorus, elevation, and plant density were significantly correlated with main soil bacterial taxa in the karst forest. Moreover, the total variation in soil microbial communities better explained by spatial factors than environmental variables. Furthermore, a large part of variation (76.8%) was unexplained in the study. Therefore, our results suggested that dispersal limitation was the primary driver of spatial pattern of soil microbial taxa in broadleaved forest in karst areas, and other environmental variables (i.e., soil porosity and temperature) should be taken into consideration.

Nitrogen functional gene activity in soil profiles under progressive vegetative recovery after abandonment of agriculture at the Puding Karst Critical Zone Observatory, SW China

At the end of the 20th century, China launched the ‘Grain-for-Green’ Project (GGP) that recommended the abandonment of low-yielding sloping farmland (>15°) prone to soil degradation by erosion, to allow recovery through natural vegetative regeneration. The effect of this policy on soil nitrogen (N) cycling, as fertilization applications are also withdrawn after abandonment, is poorly understood. A space-for-time approach was applied to investigate the responses of nitrogen functional genes (NFGs) in soil profiles (surface to bedrock) associated with progressive vegetative recovery (sloping farmland > recently abandoned sloping farmland > secondary forest > primary forest) at the Puding Karst Critical Zone Observatory in Guizhou province, southwest China. Coincident soil chemical properties (dissolved organic carbon (DOC), nitrate (NO3--N), ammonium (NH4+-N), available inorganic phosphorus (AP), soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP)) were also quantified. We found that the absolute abundance of NFGs significantly varied according to the phase of vegetation recovery, and that concentrations of AP and NO3--N were the best explanatory variables. The external N from fertilizer application promoted the absolute abundances of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in sloping farmland. The relative abundances of chiA (associated with decomposition) increased with soil depth across all vegetation recovery phases. The relative abundances of chiA and nifH (associated with N fixation) accounted for the largest proportion (58–72%) of the measured NFGs, indicating that active N-acquisition increased along the vegetation recovery gradient. The ratios of (chiA + nifH)/(AOA + AOB) and the sums of (nirK + nirS) were larger in the forest soil than those of sloping farmland and abandoned sloping farmland, implying a greater capacity for N storage potential, though accompanied by increased gas N emission potential, in the karst forest ecosystems. Our results provide a new and comprehensive understanding of soil N cycling potentials at the microscale in degraded and recovering karst ecosystems.

High Mortality and Low Net Change in Live Woody Biomass of Karst Evergreen and Deciduous Broad-Leaved Mixed Forest in Southwestern China

Repeated observation based on large permanent monitoring plots is a key method for directly understanding forest regeneration dynamics. Karst forests grow slowly in adverse habitats and possess a special regeneration mode. However, no data can support these properties because no repeated observations have been performed. The mortality, recruitment, and net change in live woody biomass (NPPlw) of a karst evergreen and deciduous broad-leaved mixed forest in Central Guizhou Province, Southwestern China, were studied on the basis of a short-term continuous monitoring (3 years) of a 2 ha plot. The species richness of individuals with a diameter at breast height (DBH) ≥ 1 cm decreased from 66 to 58 during the study period. Eight species disappeared, and no new species appeared. The individual number declined from 16,821 to 15,003 because most species indicated more deaths than recruitments. Trees presented the lowest mortality rate, and shrubs presented the highest recruitment rate among the species. Individual death number decreased with the increase in DBH classes. The estimated aboveground NPPlw was 8.41 t ha−1 year−1. The survivors, recruitments, and deaths contributed 10.88, 0.11, and −2.58 t ha−1 year−1, respectively. Trees (8.37 t ha−1 year−1), rather than shrubs (0.04 t ha−1 year−1) and lianas (−0.004 t ha−1 year−1), were the major contributors. The karst forest presented higher mortality and lower NPPlw than nonkarst forests in subtropical China and in the world.

Fog Water Is Important in Maintaining the Water Budgets of Vascular Epiphytes in an Asian Tropical Karst Forests during the Dry Season

Fog may be an important source of water for forest vascular epiphytes on trees, because they lack direct access to sources of soil water, but little is known about the water use proportions from various sources and potential water uptake pathways in epiphytes. Here, we analyzed leaf carbon isotope ratios as a measure of water use efficiency (WUE), proportions of fog, rain, and soil water use, and foliar water uptake (FWU) in species of epiphyte and their host trees in a tropical karst dwarf forest in China during the dry season. We found that the WUE, as represented by leaf δ13C, was generally enriched in the epiphyte species compared to their host trees. Epiphytes used substantial proportions of fog water, whereas water use in the host trees was dominated by soil water. The leaves of epiphytes and host trees absorbed water following immersion in water for 3 h and FWU possibly related to foliar epicuticular structures, such as fungal endophytes. Our results show a divergence of water use strategies between epiphytes and their hosts and highlight the importance of fog water for epiphytes during the dry season and under a climate change scenario with a reduced occurrence of fog events.

Co-regulation of photosynthetic capacity by nitrogen, phosphorus and magnesium in a subtropical Karst forest in China

Leaf photosynthetic capacity is mainly constrained by nitrogen (N) and phosphorus (P). Little attention has been given to the photosynthetic capacity of mature forests with high calcium (Ca) and magnesium (Mg) in the Karst critical zone. We measured light-saturated net photosynthesis (Asat), photosynthetic capacity (maximum carboxylation rate [Vcmax], and maximum electron transport rate [Jmax]) as well as leaf nutrient contents (N, P, Ca, Mg, potassium [K], and sodium [Na]), leaf mass per area (LMA), and leaf thickness (LT) in 63 dominant plants in a mature subtropical forest in the Karst critical zone in southwestern China. Compared with global data, plants showed higher Asat for a given level of P. Vcmax and Jmax were mainly co-regulated by N, P, Mg, and LT. The ratios of Vcmax to N or P, and Jmax to N or P were significantly positively related to Mg. We speculate that the photosynthetic capacity of Karst plants can be modified by Mg because Mg can enhance photosynthetic N and P use efficiency.

Estimating aboveground biomass using Pléiades satellite image in a karst watershed of Guizhou Province, Southwestern China

Biomass in karst terrain has rarely been measured because the steep mountainous limestone terrain has limited the ability to sample woody plants. Satellite observation, especially at high spatial resolution, is an important surrogate for the quantification of the biomass of karst forests and shrublands. In this study, an artificial neural network (ANN) model was built using Pleiades satellite imagery and field biomass measurements to estimate the aboveground biomass (AGB) in the Houzhai River Watershed, which is a typical plateau karst basin in Central Guizhou Province, Southwestern China. A back-propagation ANN model was also developed. Seven vegetation indices, two spectral bands of Pleiades imagery, one geomorphological parameter, and land use/land cover were selected as model inputs. AGB was chosen as an output. The AGB estimated by the allometric functions in 78 quadrats was utilized as training data (54 quadrats, 70%), validation data (12 quadrats, 15%), and testing data (12 quadrats, 15%). Data-model comparison showed that the ANN model performed well with an absolute root mean square error of 11.85 t/ha, which was 9.88% of the average AGB. Based on the newly developed ANN model, an AGB map of the Houzhai River Watershed was produced. The average predicted AGB of the secondary evergreen and deciduous broadleaved mixed forest, which is the dominant forest type in the watershed, was 120.57 t/ha. The average AGBs of the large distributed shrubland, tussock, and farmland were 38.27, 9.76, and 11.69 t/ha, respectively. The spatial distribution pattern of the AGB estimated by the new ANN model in the karst basin was consistent with that of the field investigation. The model can be used to estimate the regional AGB of karst landscapes that are distributed widely over the Yun-Gui Plateau.

Contrasting ecological roles of non-native ungulates in a novel ecosystem.

Conservation has long focused on preserving or restoring pristine ecosystems. However, understanding and managing novel ecosystems has grown in importance as they outnumber pristine ecosystems worldwide. While non-native species may be neutral or detrimental in pristine ecosystems, it is possible that even notorious invaders could play beneficial or mixed roles in novel ecosystems. We examined the effects of two long-established non-native species—Philippine deer (Rusa marianna) and feral pigs (Sus scrofa)—in Guam, Micronesia, where native vertebrate frugivores are functionally absent leaving forests devoid of seed dispersers. We compared the roles of deer and pigs on seedling survival, seed dispersal and plant community structure in limestone karst forests. Deer, even at low abundances, had pronounced negative impacts on forest communities by decreasing seedling and vine abundance. By contrast, pigs showed no such relationship. Also, many viable seeds were found in pig scats, whereas few were found in deer scats, suggesting that pigs, but not deer, provide an ecosystem function—seed dispersal—that has been lost from Guam. Our study presents a discrepancy between the roles of two non-native species that are traditionally managed as a single entity, suggesting that ecological function, rather than identity as a non-native, may be more important to consider in managing novel systems.

Soil microbial processes and resource limitation in karst and non‐karst forests

Abstract Soil micro‐organisms play a key role in soil biogeochemical cycles, but their growth and activities are often limited by resource availability. Understanding soil processes that are driven by micro‐organisms and resource limitation of microbes will help to elucidate controls on soil fertility and improve the ability to predict the responses of an ecosystem to global changes. As a widespread ecosystem type, karst ecosystem develops from limestone or dolomite with unique soil; however, karst ecosystems remain poorly understood regarding their soil microbial processes and microbial resource limitation. Here, ecoenzymatic stoichiometry was used as an indicator of microbial resource limitation, and to model major microbial processes (i.e. decomposition of soil organic carbon and microbial respiration) in a karst and a non‐karst forest. Results showed that the modelled decomposition and respiration rates were significantly higher in the karst forest than in the non‐karst forest. In addition, results of ecoenzymatic stoichiometry showed that the karst forest was more carbon‐limited than the non‐karst forest. In contrast, the karst forest was likely saturated with nitrogen, but the non‐karst forest was limited by nitrogen. Both the karst and non‐karst forests were limited by phosphorus, but phosphorus deficiency was more evident in the non‐karst forest than in the karst forest. These findings highlight the specific profiles of karst ecosystems, and they suggest that the responses of karst ecosystems to global changes should be very different compared to other ecosystems. A plain language summary is available for this article.

Discovery of a diverse cave flora in China.

Few studies document plants in caves. Our field observations of a widespread and seemingly angiosperm-rich cave flora in SW China lead us to test the following hypotheses, 1) SW China caves contain a diverse vascular plant flora, 2) that this is a relic of a largely absent forest type lacking endemic species, and 3) that the light environment plants occupy in caves is not distinct from non-cave habitats. To do so we surveyed 61 caves and used species accumulation curves (SAC) to estimate the total diversity of this flora and used a subsample of 14 caves to characterise the light environment. We used regional floras and existing conservation assessments to evaluate the conservation value of this flora. We used observations on human disturbance within caves to evaluate anthropogenic activities. Four-hundred-and-eighteen vascular plant species were documented with SACs predicting a total diversity of 529–846. Ninety-three percent of the species documented are known karst forest species, 7% are endemic to caves and 81% of the species are angiosperms. We demonstrate that the light environment in caves is distinct to that of terrestrial habitats and that a subset of the flora likely grow in the lowest light levels documented for vascularised plants. Our results suggest that the proportion of species threatened with extinction is like that for the terrestrial habitat and that almost half of the entrance caverns sampled showed signs of human disturbance. We believe that this is the first time that such an extensive sample of cave flora has been undertaken and that such a diverse vascular plant flora has been observed in caves which we predict occurs elsewhere in SE Asia. We argue that the cave flora is an extension of the karst forest understory present prior to catastrophic deforestation in the 20thC. We suggest that within SW China caves serve as both refuges and a valuable source of germplasm for the restoration of karst forest. We also propose that caves represent a distinct habitat for plants that is most similar to that of the forest understory, but distinct with respect to the absence of trees, leaf litter, root mats, higher levels of atmospheric CO2, and lower diurnal and annual variation in temperature and humidity. We highlight tourism, agriculture and the absence of legislated protection of caves as the main current threats to this flora.

广西地区喀斯特与非喀斯特山地森林树木物种多样性及系统发育结构比较

PDF HTML阅读 XML下载 导出引用 引用提醒 广西地区喀斯特与非喀斯特山地森林树木物种多样性及系统发育结构比较 DOI: 10.5846/stxb201808021643 作者: 作者单位: 广西大学林学院,广西大学林学院,广西大学林学院,广西大学林学院,广西大学林学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划子课题（2016YFC0502101-04）；广西重点研发计划项目（桂科AB16380254）；广西"八桂学者"人才项目（2016A32） Comparison of the species diversity and phylogenetic structure of tree communities in karst and non-karst mountains in Guangxi Author: Affiliation: College of Forestry, Guangxi University,,,,College of Forestry, Guangxi University 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:以广西地区植被调查集资料总共365个群落样方（样方面积在300-1000 m2，50%左右为400 m2）为基础，将样方分为海拔≤1000 m喀斯特和非喀斯特森林以及海拔 > 1000 m的非喀斯特森林三类生境，探讨这3种生境森林物种丰富度和群落系统发育结构差异及其与年均温的关系。结果表明，海拔≤1000 m非喀斯特森林含有4种以上的科比海拔 > 1000 m非喀斯特森林多24科，比喀斯特森林多18科，其中樟科、壳斗科、山茶科、杜鹃花科等都是两种非喀斯特森林生境的重要组成科；大戟科为喀斯特森林含有种数最多的科，其中出现在非喀斯特森林的山茶科和杜鹃花科等没有在喀斯特森林出现。森林物种多样性及系统发育指数与年均温不相关或相关不强；海拔≤1000 m的喀斯特与非喀斯特森林的Gleason物种多样性指数没有显著差异，而海拔 > 1000 m的非喀斯特森林的Gleason指数比另外两种生境显著高。海拔≤1000 m非喀斯特森林系统发育多样性PD指数比中山地带的非喀斯特生境的森林高。喀斯特森林和海拔 > 1000 m非喀斯特的绝大部分样地以及海拔≤1000 m的非喀斯特大部分样地都表现出系统发育结构聚集，推测生境过滤在广西地区喀斯特和非喀斯特森林群落构建中发挥着主要作用。但是喀斯特和海拔 > 1000 m的非喀斯特两种生境森林群落发生系统发育发散的比例都比海拔≤1000 m的非喀斯特森林低，揭示生境过滤在这两个生境更为明显。 Abstract:We compiled data of 365 tree community plots from the literature, which were sampled across Guangxi and varied in plot area from 400 to 1000 m2(with 50% of plots 400 m2), and characterized the species diversity and community phylogenetic diversity (PD) and structure, and their relationship with the mean annual temperature (MAT) of the sampling location in three types of forest habitats:non-karst with an elevation of ≤ 1000 m, non-karst with an elevation of > 1000 m, and karst with an elevation of ≤ 1000 m. We found that in comparison of the number of the families with more than 4 species in the forests, the non-karst forests with an elevation of ≤ 1000 m contained 24 more families than non-karst forests with an elevation of < 1000 m, and 18 more families than karst forests. Lauraceae, Fagaceae, Theaceae, and Ericaceae are important and common families of non-karst forests at both low and high elevations. Euphorbiaceae was the family that contains the largest number of species in karst forests. Theaceae and Ericaceae that appeared in the non-karst forests were absent in karst forests. The species diversity and phylogenetic structure index of the tree communities in the three habitats were not significantly associated with the MAT. Gleason's diversity indices of karst and non-karst forests with an elevation of ≤ 1000 m were not significantly different, but significantly lower that of non-karst forests with an elevation of > 1000 m. The PD of the non-karst forests with elevations ≤ 1000 m was higher than that of the non-karst forests with elevations of either > 1000 m, indicating the former is favourable for hosting the more distant-related species. The phylogenetic net relatedness index (NRI) and the nearest taxon index (NTI) revealed that most of the forest plots in the three habitats showed phylogenetic clustering, and a small proportion of plots displayed phylogenetic overdispersion or randomness. These suggest that habitat filtration plays a major role in the community assembly of karst and non-karst forests in Guangxi. The proportions of plots with phylogenetic overdispersion in the karst forests and non-karst forests with an elevation of > 1000 m were lower that in the non-karst forests with an elevation of ≤ 1000 m, revealing that environmental filtration was stronger in these two habitats. 参考文献 相似文献 引证文献

桂西北喀斯特常绿落叶阔叶混交林物种多样性分布格局的尺度效应

PDF HTML阅读 XML下载 导出引用 引用提醒 桂西北喀斯特常绿落叶阔叶混交林物种多样性分布格局的尺度效应 DOI: 10.5846/stxb201709231713 作者: 作者单位: 中国科学院亚热带农业生态研究所,中国科学院亚热带农业生态研究所,中国科学院亚热带农业生态研究所,中国科学院亚热带农业生态研究所,中国科学院亚热带农业生态研究所,广西壮族自治区木论国家级自然保护区管理局,中国科学院亚热带农业生态研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划项目（2016YFC0502405）；广西重点研发计划项目（桂科AB16380255，桂科AB17129009）；国家自然科学基金项目（31770495）；广西特聘专家项目 Scale-dependent spatial patterns for species diversity in a karst evergreen and deciduous broad-leaved mixed forest of northwest Guangxi Author: Affiliation: Institute of Subtropical Agriculture Chinese Academy of Sciences,Institute of Subtropical Agriculture Chinese Academy of Sciences,Institute of Subtropical Agriculture Chinese Academy of Sciences,Institute of Subtropical Agriculture Chinese Academy of Sciences,Institute of Subtropical Agriculture Chinese Academy of Sciences,,Institute of Subtropical Agriculture Chinese Academy of Sciences Fund Project: Dthe National Key Research and Development Program ( 2016YFC0502405), the Guangxi Key Research and Development Program (AB17129009, AB16380255), the National Natural Science Foundation of China (31370485, 31370623, 31400412), and the Guangxi Program of Distinguished Expert 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:物种多样性的空间分布格局及其与尺度的关系研究对于了解群落物种多样性形成机制具有重要意义。为了探讨喀斯特地区物种多样性空间分布格局的尺度效应，以喀斯特常绿落叶阔叶混交林25 hm2样地的（胸径DBH≥1）木本植物为研究对象，分析了6个空间尺度（5 m×5 m，10 m×10 m，20 m×20 m，50 m×50 m，100 m×100 m，250 m×250 m）上的多度、物种丰富度、Shannon-Wiener指数、Simpson指数以及Pielou均匀度指数的变化规律。结果表明：物种多样性指数的空间分布均表现出较高的空间异质性；物种多样性指数的方差随取样尺度增加呈现单峰分布特征，并且在100 m×100 m尺度上达到最大值；物种多样性指数的变异系数随尺度的增加呈线性下降趋势，其中，Shannon-Wiener指数、Simpson指数以及Pielou均匀度指数均在5 m×5 m至20 m×20 m尺度上明显减小；在大于50 m×50 m的尺度上，物种丰富度与多度的正相关性不显著（P > 0.05）。喀斯特常绿落叶阔叶混交林物种多样性的空间分布格局与不同空间尺度密切相关，深入解析物种多样性随空间尺度的变化模式，需要在类似的森林生态系统做更多的研究。 Abstract:Spatial distribution patterns of species diversity and their relationships with scale are of great significance to understand the mechanism of community species diversity formation. Here, a field survey was conducted to assess the variation in species diversity along spatial scales in a karst evergreen and deciduous broad-leaved mixed forest, Southwest China. Based on the dataset of woody plants (DBH ≥ 1) from a 25 hm2 plot, the spatial distribution patterns of species abundance, species richness, and Shannon-Wiener, Simpson, and Pielou's evenness indices were analyzed at six spatial scales-5 m×5 m, 10 m×10 m, 20 m×20 m, 50 m×50 m, 100 m×100 m, and 250 m×250 m. The results showed that spatial distributions of species diversity indices were highly heterogeneous. The variance of species diversity indices changed with spatial scale following a unimodal pattern, i.e., with a maximum value at the 100 m×100 m scale. Variation coefficients of species diversity decreased linearly with increasing scale. The Shannon-Wiener, Simpson, and Pielou's evenness indices decreased sharply at the 5 m×5 m and 20 m×20 m scales. No significant positive relationship was found between species richness and abundance at scales over 50 m×50 m (P > 0.05). Our results suggest that the spatial pattern of species diversity in this evergreen and deciduous broad-leaved mixed karst forest is closely related to spatial scale. To better understand spatial variation of species diversity across spatial scales, more such studies in other similar forest ecosystems are needed. 参考文献 相似文献 引证文献

Variations of plant functional traits and adaptive strategy of woody species in a karst forest of central Guizhou Province, southwestern China

Variations of plant functional traits and adaptive strategy of woody species in a karst forest of central Guizhou Province, southwestern China

Tree species effects on asymbiotic N2 fixation in subtropical karst and non-karst forests

Asymbiotic dinitrogen (N2) fixation (ANF) plays an important role in determining forest nitrogen (N) availability. Yet, the controls on ANF variation within or between forests remain poorly understood. In the present study, ANF in bulk leaf litter (or litter ANF hereafter) and soil (or soil ANF hereafter) within the crown radius of the dominant tree species was investigated in a karst forest over limestone and a nearby non-karst forest over clasolite, southwest China. Lithology exerted significant (P < 0.05) influences on ANF in litter but not in soil. ANF in litter was 4.9 times higher in the karst forest than in the non-karst forest. Tree species had significant effects on litter ANF in the karst and non-karst forests with the rates varying 23-fold and 71-fold, respectively. Significant effect of tree species on soil ANF was only encountered in the non-karst forest. The strongest explanatory variables were substrate and forest specific, but generally included litter moisture, total nitrogen, total phosphorus, calcium and soil organic carbon. The findings suggest that tree species and lithology may provide new mechanisms explaining the great variation of ANF within and between forests, respectively.

Divergent responses of biological nitrogen fixation in soil, litter and moss to temperature and moisture in a karst forest, southwest China

Free-living biological N2 fixation (BNF) in soil, litter and moss is an important pathway for external nitrogen (N) inputs to unmanaged terrestrial ecosystems. However, how free-living BNF responses to temperature, moisture and their interaction have not been well understood, especially in the subtropical regions. Here we investigated the responses of BNF in soil, litter and moss to temperature (15, 25 and 35 °C) and moisture (low, intermediate and high levels) over a one-week period under laboratory conditions. The samples were collected in a subtropical karst forest, southwest China. We found that the responses of BNF in moss, litter and soil to temperature and moisture were divergent. Litter and soil BNF rates increased with temperature under the three moisture levels. However, moss BNF rates were decreased, not changed or increased by warming under low, intermediate and high moisture levels, respectively. At each temperature, the BNF rates increased with moisture for moss and litter. However, the patterns of moisture responses were different at the three temperatures for soil BNF, which was not changed and increased by moisture at 15 °C and 25 °C, respectively; and was greatest under intermediate moisture, but lowest under low moisture at 35 °C. The temperature sensitivity of BNF was generally highest for litter, intermediate for soil and lowest for moss. In contrast, the moisture sensitivity of BNF was generally highest for moss, intermediate for soil, and lowest for litter. Our findings suggest that different temperature or moisture sensitivities of BNF for the three substrates should be integrated into terrestrial ecosystem models in order to better predict N inputs via BNF under climate change.

Leaf trait variations associated with habitat affinity of tropical karst tree species.

Karst hills, that is, jagged topography created by dissolution of limestone and other soluble rocks, are distributed extensively in tropical forest regions, including southern parts of China. They are characterized by a sharp mosaic of water and nutrient availability, from exposed hilltops with poor soil development to valleys with occasional flooding, to which trees show species‐specific distributions. Here we report the relationship of leaf functional traits to habitat preference of tropical karst trees. We described leaf traits of 19 tropical tree species in a seasonal karst rainforest in Guangxi Province, China, 12 species in situ and 13 ex situ in a non‐karst arboretum, which served as a common garden, with six species sampled in both. We examined how the measured leaf traits differed in relation to species’ habitat affinity and evaluated trait consistency between natural habitats vs. the arboretum. Leaf mass per area (LMA) and optical traits (light absorption and reflectance characteristics between 400 and 1,050 nm) showed significant associations with each other and habitats, with hilltop species showing high values of LMA and low values of photochemical reflectance index (PRI). For the six species sampled in both the karst forest and the arboretum, LMA, leaf dry matter content, stomatal density, and vein length per area showed inconsistent within‐species variations, whereas some traits (stomatal pore index and lamina thickness) were similar between the two sites. In conclusion, trees specialized in exposed karst hilltops with little soils are characterized by thick leaves with high tissue density indicative of conservative resources use, and this trait syndrome could potentially be sensed remotely with PRI.

Spatial distribution of tree species in evergreen-deciduous broadleaf karst forests in southwest China

Understanding the spatial distribution of tree species in subtropical evergreen-deciduous broadleaf karst forest is fundamental to studying species coexistence and karst species diversity. Here, complete spatial randomness and heterogeneous Poisson process models were used to analyze the spatial distribution patterns of 146 species with at least one individual per ha in a 25-ha plot in southwest China. We used canonical correspondence analysis (CCA) and the torus-translation test (TTT) to explain the distributions of observed species. Our results show that an aggregated distribution was the dominant pattern in Mulun karst forests; the percentage and intensity of aggregated decreased with increasing spatial scale, abundance, mean diameter at breast height (DBH), and maximum DBH. Rare species were more aggregated than intermediately abundant and abundant species. However, functional traits (e.g., growth form and phenological guild) had no significant effects on the distributions of species. The CCA revealed that the four analyzed topographic variables (elevation, slope, aspect, and convexity) had significant influences on species distributions. The TTT showed that not all species have habitat preferences and that 68.5% (100 out of 146 species) show a strongly positive or negative association with at least one habitat. Most species were inclined to grow on slopes and hilltops.

Soil Gross Nitrogen Transformations in Typical Karst and Nonkarst Forests, Southwest China

AbstractSoil gross nitrogen (N) transformations are crucial for assessing forest N status. Although there is evidence suggesting that the N cycle is open in the karst forest, southwest China, process‐based investigation of gross soil N transformations is limited. In the current study, gross soil N transformations were investigated using 15N isotope dilution and 15N tracer techniques in a typical karst forest with calcareous soil (Calcareous lithosols) in comparison with an adjacent nonkarst forest with red soil (Haplic acrisol).The gross rates of N mineralization, nitrification, dissimilatory nitrate reduction to ammonium (DNRA), and nitrate immobilization were significantly greater in the karst forest. Ammonium immobilization was comparable to gross N mineralization, so that ammonium could be efficiently conserved in the nonkarst forest. Meanwhile, the produced nitrate was mostly retained via DNRA and nitrate immobilization. This resulted in a negligible net nitrate production in the nonkarst forest. In contrast, ammonium immobilization rate only accounted for half of gross N mineralization rate in the karst forest. The nitrate retention capacity is relatively low, with 41.6 ± 4.2% of the produced nitrate being retained via DNRA and nitrate immobilization. Due to relatively low nitrate retention capacity, nitrate was accumulated in the karst forest soil. Our results indicate that the nonkarst forest with red soil holds a very conservative N cycle, but the N cycle in the karst forest is leaky.

A new species of Cyrtodactylus (Squamata: Gekkonidae) and the first record of C. otai from Son La Province, Vietnam.

We describe a new species of Cyrtodactylus on the basis of four specimens collected from the limestone karst forest of Phu Yen District, Son La Province, Vietnam. Cyrtodactylus sonlaensis sp. nov. is distinguished from the remaining Indochinese bent-toed geckos by a combination of the following characters: maximum SVL of 83.2 mm; dorsal tubercles in 13-15 irregular rows; ventral scales in 34-42 rows; ventrolateral folds prominent without interspersed tubercles; enlarged femoral scales 15-17 on each thigh; femoral pores 14-15 on each thigh in males, absent in females; precloacal pores 8, in a continuous row in males, absent in females; postcloacal tubercles 2 or 3; lamellae under toe IV 18-21; dorsal head with dark brown markings, in oval and arched shapes; nuchal loop discontinuous; dorsum with five brown bands between limb insertions, third and fourth bands discontinuous; subcaudal scales distinctly enlarged. In phylogenetic analyses, the new species is nested in a clade consisting of C. huongsonensis and C. soni from northern Vietnam and C. cf. pulchellus from Malaysia based on maximum likelihood and Bayesian analyses. In addition, we record Cyrtodactylus otai Nguyen, Le, Pham, Ngo, Hoang, Pham & Ziegler for the first time from Son La Province based on specimens collected from Van Ho District.