Subtropical Natural Forest Research Articles

Different responses of soil bacterial and fungal communities to nitrogen deposition in a subtropical forest

China has experienced a widespread increase in N deposition due to intensive anthropogenic activities, particularly in the subtropical regions. However, the effects of long-term N deposition on soil bacterial and fungal abundance, diversity, and community composition remain largely unclear. We assessed the effects of N deposition on soil microbial communities in summer and winter, using quantitative polymerase chain reaction and Illumina Miseq sequencing of bacterial 16S rRNA and fungal ITS genes from subtropical natural forest soils. The abundance of both soil bacteria and fungi exhibited a decreasing pattern with increasing N deposition rates. Nitrogen deposition increased bacterial diversity in both summer and winter, whereas fungal diversity was significantly decreased in summer, but greatly increased under the highest level of N deposition (150 kg N ha−1 yr−1) in winter. Nitrogen deposition significantly increased the relative abundance of bacterial phyla Actinobacteria, Chloroflexi, and WPS-2, but decreased that of Acidobacteria and Verrucomicrobia. In addition, N deposition significantly decreased the relative abundance of Ascomycetes, but did not exert any significant effect on Basidiomycetes. The bacterial and fungal community compositions were greatly influenced by N deposition, with soil N availability and soil pH identified as the two most influential soil properties. This study demonstrates that the fungal community was more sensitive than the bacterial community to N deposition, and further emphasizes the importance of simultaneously evaluating soil bacterial and fungal communities in response to global environmental changes.

Spatial pattern dynamics among co-dominant populations in early secondary forests in Southwest China

The canopy of subtropical natural forests usually consists of several co-dominant populations (CDPs), which play a crucial role in forest structure, formation of the forest environment, and ecological function. However, little attention has been given to changes in spatial patterns in CDPs during natural succession. Cyclobalanopsis glauca (Thunb.) Oerst., Quercus variabilis Blume, and Pinus yunnanensis var. tenuifolia W.C. Cheng & Y.W. Law are canopy species that form CDPs in zonal forests along the Nanpan River in southwest China. We used the g(r) function and its bivariate distribution model, g12(r), which is based on distances between pairs of points, to explore the dynamics of the three CDP species with respect to distribution patterns and spatial correlations in two secondary forests (one 30-year-old forest [30-YF] and one 57-year-old forest [57-YF]). The following key results were obtained: (1) there was a clumped pattern in the 30-YF, but the intensity of aggregation varied among populations and life stages. The distribution pattern gradually shifted to become random with longer succession time (i.e., 30-YF vs. 57-YF), expansion of the observation scale (r = 0–20 m), and at later life stages. (2) Aside from the mid-sized C. glauca trees and large P. yunnanensis trees, the trees repulsed each other at certain scales (r = 0–2, 5–6, 11–12, 14–16 m) in the 30-YF. Almost all of the life stages in the CDPs were independently correlated. This independent correlation was exacerbated by a longer succession time. (3) An increase in life stages and longer succession also promoted independent changes in intraspecific correlations. (4) Intraspecific correlations were stronger than interspecific correlations. Our results showed that reducing exclusive competition is essential to coexistence in CDPs. Inter- and intra-specific repulsion may occur at the same time, but intraspecific repulsion was the main driving force behind the random distributions and independent correlations.

Tree species classification using UAS-based digital aerial photogrammetry point clouds and multispectral imageries in subtropical natural forests

Tree species composition of forest stand is an important indicator of forest inventory attributes for assessing ecosystem health, understanding successional processes, and digitally displaying forest biodiversity. In this study, we acquired high spatial resolution multispectral and RGB imagery over a subtropical natural forest in southwest China using a fixed-wing UAV system. Digital aerial photogrammetric (DAP) technique was used to generate multi-spectral and RGB derived point clouds, upon which individual tree crown (ITC) delineation algorithms and a machine learning classifier were used to identify dominant tree species. To do so, the structure-from-motion method was used to generate RGB imagery-based DAP point clouds. Then, three ITC delineation algorithms (i.e., point cloud segmentation (PCS), image-based multiresolution segmentation (IMRS), and advanced multiresolution segmentation (AMRS)) were used and assessed for ITC detection. Finally, tree-level metrics (i.e., multispectral, texture and point cloud metrics) were used as metrics in the random forest classifier used to classify eight dominant tree species. Results indicated that the accuracy of the AMRS ITC segmentation was highest (F1-score = 82.5 %), followed by the segmentation using PCS (F1-score = 79.6 %), the IMRS exhibited the lowest accuracy (F1-score = 78.6 %); forest types classification (coniferous and deciduous) had a higher accuracy than the classification of all eight tree species, and the combination of spectral, texture and structural metrics had the highest classification accuracy (overall accuracy = 80.20 %). In the classification of both eight tree species and two forest types, the classification accuracies were lowest when only using spectral metrics, indicated that the texture metrics and point cloud structural metrics had a positive impact on the classification (the overall accuracy and kappa accuracy increased by 1.49–4.46 % and 2.86–6.84 %, respectively).

Wild edible plant used by ethnic peoples on the boundary of subtropical & temperate natural forest, Mamlay watershed, South Sikkim

Wild edible plants (WEPs) are a rich bio-resource of Sikkim, Himalaya having a high nutritional value. Local people of the Sikkim commonly use wild edible plants in their diet on regular basis. This present study aimed at documenting wild edible plants utilized by the local inhabitants of Mamlay watershed which was carried out during the year 2017-2019. The study explored a total of 49 wild edible plants belonging to 31 families, 44 genera, and 49 species. About 34 WEPs were recorded from temperate natural forest TNF and 31 wild edible plants were recorded from subtropical natural forest STNF. Two studies conducted with a gap of twenty years revealed that a large part of WEPs recorded is from tree source showing a marked forest dependency. The collection of WEPs in the form of entire plants, roots or tubers was at the lowest suggesting the people’s awareness to conservation and also revealed that market price value of wild edible plants has increased highly in the study area.

Species Association of the Dominant Tree Species in an Old-Growth Forest and Implications for Enrichment Planting for the Restoration of Natural Degraded Forest in Subtropical China

Subtropical natural forests are unique due to their ecological and economic functions. However, most of these forests are highly degraded, which impairs the ability to provide ecological and economic benefits. Enrichment planting is an important approach to restore natural degraded forests. Species arrangement is of great importance to inform enrichment planting. Species association refers to the interrelationship of different species occupying a habitat and is a static description of the organic connection formed by the interaction of species. Species association, therefore, provides a scientific basis for species arrangement in enrichment planting. Additionally, because an old-growth forest is a climax community that has attained great age without significant disturbance, the species association in an old-growth forest can provide valuable information on the reference conditions for forest management. In this study, the species association between dominant tree species (including saplings and adult trees) was investigated in an old-growth forest in the Gutianshan National Nature Reserve in Zhejiang province in subtropical China. The objective of the study was to inform species arrangement for enrichment planting. The result showed that the overall species association exhibited a significant net positive association, indicating a dynamic balance of stable structure and species composition in the old-growth forest. Additionally, the pairwise species association was examined using the χ2 test, the Dice index, and Spearman’s rank correlation coefficient; significant positive and negative pairwise species associations were detected. Based on the species association and the light requirements of the tree species, an optimal species arrangement was determined to support enrichment planting for restoring natural degraded forests. It is expected that the results of this study will contribute to the restoration of natural degraded forests in subtropical China.

Creating forest management units with Hot Spot Analysis (Getis-Ord Gi*) over a forest affected by mixed-severity fires

ABSTRACTThe rehabilitation of degraded subtropical natural forests is a global concern. A detailed assessment of their structure is a challenging and costly prerequisite because diverse structures exist depending on the cause and degree of degradation. Recent remote sensing concepts and technologies provide a detailed picture of actual forest structure, even in difficult terrain. When it comes to planning and implementing rehabilitation measures on the ground, however, meaningful forest management units (FMUs) must be created that are large enough to allow technical implementation, but which are also homogenous in structure. To date, the delineation of FMUs has, in most cases, been achieved qualitatively based on expert knowledge. The aim of this contribution is to develop and demonstrate a method for creating and delineating meaningful FMUs based on quantitative information acquired from remote sensing and spatial statistics. Therefore, a case study was conducted in a 3940-ha fire-degraded forest area in the Argentinean cloud forest of Yungas Pedemontana. A plot-based field inventory and an aerial survey with an unmanned aerial vehicle were conducted. The Adjusted Canopy Coverage Index (ACCI), as a metric for stand structure, was formulated to predict basal area from canopy height models. A SPOT6 image of the area was object-based segmented and classified into four fire-severity strata by training it with the ACCI values. The resulting classification presented a mosaic pattern in which the stands are homogenous but far too small (average 3129 m2) for planning adaptive management. Therefore, features in close proximity with similar structure (i.e. ACCI values) were aggregated using the Hot Spot Analysis (Getis-Ord Gi*) tool from the Arc geographic information system environment to create FMUs. Clusters were calculated at four scales: 10, 20, 30 and 40 ha (resulting in threshold radii of 178, 252, 309 and 357 m, respectively), using ACCI values as the variable of aggregation. As a result, average cluster areas were obtained of 33.9 ha for the shortest threshold distance of analysis and 138.5 ha for the greatest threshold distance. The tool significantly aggregated between 30.7% and 60.8% of the area into either coldspots or hotspots of ACCI, facilitating the delineation of FMUs for the planning of adaptive rehabilitation measures. There is a trade-off, however, between the gain in area of the FMUs and the loss of homogeneity: for a 357 m distance threshold, 12% more of the area was misclassified, compared with a 178 m threshold.

Root litter inputs exert greater influence over soil C than does aboveground litter in a subtropical natural forest

Changes in plant net primary production due to climate change can influence aboveground and belowground litter inputs to forest soils. We aim to examine the effects of such changes on soil carbon in subtropical forest ecosystems where these effects have not been thoroughly investigated. We manipulated aboveground litter inputs and excluded roots in a factorial design, and measured the effects of each treatment and their interactions on soil carbon (C) and soil microbial community structure. After only 3 years of treatment, aboveground litter addition and root exclusion respectively caused 9% and 21% reductions in soil C concentration in the 0–10 cm soil, likely through different mechanisms. The reduction of soil C with aboveground litter addition was attributed to a priming effect, while reduced root-derived C inputs were likely the cause of the C reduction associated with root exclusion. PLFA analysis showed that both aboveground and belowground litter manipulations reduced Gram-positive bacteria biomass (by 30%–58%) compare to the control, but only root exclusion significantly reduced the actinobacteria biomarkers (by 46%–58%). Fungi, arbuscular mycorrhizal fungi, and ratios of Gram-negative to Gram-positive bacteria and bacteria to fungi did not differ among treatments. Our results show that root-derived C inputs exert a stronger control on soil C concentrations and microbial community structures than aboveground litter does in subtropical natural forest soils. Our study also highlights that that both increases in aboveground litter and decreases in belowground C input to soil can lead to reduced soil C.

Phosphorus addition accelerates fine root decomposition by stimulating extracellular enzyme activity in a subtropical natural evergreen broad-leaved forest

Nitrogen (N) plays a vital role in litter decomposition by interacting with microbial activity in temperate and boreal ecosystems. However, in tropical and subtropical forests, where low soil phosphorus (P) availability is widespread, how P affects litter decomposition remains unclear. In the present study, litter-bag method was used to conduct fine root decomposition by P addition experiment in a subtropical natural evergreen broad-leaved forest. Fine roots were collected from two tree species: Cunninghamia lanceolata and Castanopsis carlesii, and their mixture in equal proportion as well. At the end of 2-year experiment, we found an enhancement of soil total P, available P, pH and microbial biomass carbon content, and increased abundance of all the examined microbial groups and total PLFA biomass after P addition. Annual decomposition constants of fine roots of both tree species and the mixture (0.615–1.049) were all elevated, but to different extents by P addition, with fine roots of lower initial P concentration corresponding to higher increase in decomposition rate. Average acid phosphatase activities during decomposition were significantly decreased, but there was a general increase for β-glucosidase (βG), cellobiohydrolase (CBH), phenol oxidase, peroxidase (PerOx) and N-acetyl glucosaminidase (NAG) activities. The response ratios of enzyme activities, which differed for the three experimental fine roots, corresponded to the individual increase in decomposition rates. Correlation analysis demonstrated that fine root decomposition rates were significantly related to initial P concentration, extractives and acid-insoluble fractions of fine roots, and activities of βG, CBH, NAG and PerOx as well. Taken together, our results demonstrate that fine root decomposition can be constrained by P availability through affecting microbial activity in this subtropical natural forest.

Nitrogen Addition Affects Soil Respiration Primarily through Changes in Microbial Community Structure and Biomass in a Subtropical Natural Forest

Forest soil respiration plays an important role in global carbon (C) cycling. Owing to the high degree of C and nitrogen (N) cycle coupling, N deposition rates may greatly influence forest soil respiration, and possibly even global C cycling. Soil microbes play a crucial role in regulating the biosphere–atmosphere C exchange; however, how microbes respond to N addition remains uncertain. To better understand this process, the experiment was performed in the Castanopsis kawakamii Hayata Nature Reserve, in the subtropical zone of China. Treatments involved applying different levels of N (0, 40, and 80 kg ha−2 year−1) over a three-year period (January 2013–December 2015) to explore how soil physicochemical properties, respiration rate, phospholipid fatty acid (PLFA) concentration, and solid state 13C nuclear magnetic resonance responded to various N addition rate. Results showed that high levels of N addition significantly decreased soil respiration; however, low levels of N addition significantly increased soil respiration. High levels of N reduced soil pH and enhanced P and C co-limitation of microorganisms, leading to significant reductions in total PLFA and changes in the structure of microbial communities. Significant linear relationships were observed between annual cumulative respiration and the concentration of microbial biomass (total PLFA, gram-positive bacteria (G+), gram-negative bacteria (G−), total bacteria, and fungi) and the microbial community structure (G+: G− ratio). Taken together, increasing N deposition changed microbial community structure and suppressed microbial biomass, ultimately leading to recalcitrant C accumulation and soil C emissions decrease in subtropical forest.

Effect of Microenvironment on Species Distribution Patterns in the Regeneration Layer of Forest Gaps and Non-Gaps in a Subtropical Natural Forest, China

The aim of this study was to explore the effect of gap environmental factors on the plant population regeneration pattern in the Castanopsis kawakamii natural forest. We used the detrended canonical correspondence analysis (DCCA) method to study coupling relationships between species distribution in the regeneration layer and environmental factors. The results showed that: (1) The main environmental factors that influenced species distribution in the forest gaps and non-gaps were different, and the highest explanation rate of environmental factors was the soil temperature below the surface 10 cm (ST10); (2) The relationships between species distribution in the regeneration layer of the forest gaps and non-gaps were mainly restricted by environmental factors, given the environmental factors complied with the ecological niche hypothesis; and (3) For the endangered C. kawakamii population, there were positive and negative relationships between the environmental factors and the various species in the forest gaps and non-gaps, whilst the effects of such relationships were varied. Some management operations, including the creation of artificial gaps and adequate fertilization in the non-gaps, could more effectively promote the growth and regeneration of the C. kawakamii population.

Survivorship of plant species from soil seedbank after translocation from subtropical natural forests to plantation forests

The enhancement of biodiversity is an important strategy to improve the structure and functioning of monoculture plantations. However, compared with seedling transplanting, there is limited information about the utilization of soil seedbanks in regenerating plantation forests. In the present study, to investigate the potential application of soil seedbanks in plantation forest regeneration, the topsoil (0–10 cm) of natural forests was translocated to different monoculture plantations, namely, Acacia crassicarpa, Castanopsis hystrix and Eucalyptus urophylla monocultures. Seed germination, seedling growth and related environmental conditions of the plantation forests were monitored in the experiment. Although, at the very start, large numbers of seedlings emerged from the soil seedbank, only nine species survived after 2.5 years, including seven tree species and two shrub species. Notably, Machilus chekiangensis, a tree species with high economic value, was established in the plantation forests. Except for the common species that emerged in the three plantations, there were some special species that were only associated with a specific plantation. Redundancy analysis revealed that nitrogen from both the natural forest and plantation forest soil had significant effects on seedlings growth. However, environmental conditions such as light (reflected by leaf area index), soil temperature, moisture and pH showed no obvious influence on seedling growth. Our study suggests that soil seedbank translocation from a natural forest to a plantation forest can be a useful approach for plantation forest regeneration because it could introduce valuable plant species and improve the plant biodiversity.

Reforestation with loblolly pine can restore the initial soil carbon stock relative to a subtropical natural forest after 30 years

We hypothesized that long-term loblolly pine (Pinus taeda L.) land-use restores SOC stock and lability of a subtropical Cambisol to the original levels of the natural forest (NF). Additionally, we hypothesized that roots are the major contributor to SOC and that soil stores most of the ecosystem total carbon (ETC). We investigated a chronosequence of loblolly pine land-use of 17 (first rotation) and 32 years (second rotation, unthinned or thinned) following clearing of the NF. The original SOC stock to 100 cm of NF (209 ± 9.4 Mg C ha−1) was depleted by 22% after 17 years of pine, possibly because of intense soil disturbance and low quantity and quality of the residue inputted during the pine stand implementation. However, the SOC stock was restored to the original stock of NF after 32 years of pine, with the input of above and belowground biomass at harvest of the first rotation possibly playing a role in this recovery. Thinning did not affect SOC stocks after 1 year. The POM-C reduced after 17 years and was not recovered after 32 years. We could not ascertain in 5-year evaluation whether root or litter was the major contributor to SOC. Soil held 72% of the ETC in NF and 48–59% in pine plantations, confirming that it stores most of the ETC. Overall, long-term loblolly pine land-use seems to restore the original soil carbon stock in this subtropical site, regardless of some lability losses.

Decreased soil organic P fraction associated with ectomycorrhizal fungal activity to meet increased P demand under N application in a subtropical forest ecosystem

Phosphorus (P) is an essential but limited nutrient in highly weathered subtropical or tropical forest soils; however, increased P demands owing to elevated nitrogen (N) deposition might further exacerbate the P limitation in these regions. How soil P fractions respond to N enrichment and the underlying mechanisms are not yet understood completely. To address this issue, we conducted an experiment with 3 years of N addition to a Castanopsis carlesii natural forest in Fujian, China; the soil P fractions, microbial biomass, enzyme activities, and phospholipid fatty acid (PLFA) levels were determined. We found that N addition did not significantly alter the microbial biomass C (MBC) and microbial biomass N (MBN), but significantly decreased microbial biomass P (MBP); further, the ratios of MBC:MBP and MBN:MBP increased significantly after N application, indicating that N enrichment enhanced the P demands of plants and soil microorganisms. Moreover, neither resin-P nor NaHCO3-P (extracted by resin and NaHCO3, respectively) was decreased, whereas organic P extracted by NaOH (NaOH-Po) was decreased after N addition, implying that NaOH-Po is a potentially significant source of available P. In particular, appositive correlation between abundance of ectomycorrhizal fungi and NaOH-Po and significant relationships between acid phosphomonoesterase activity (ACP) and labile P contents were noted, suggesting that ectomycorrhizal fungi can play a major role in the depletion of soil organic P, and these enzyme activities can mobilize the unavailable P to labile P in the investigated forest. Taken together, our results revealed a novel mechanism for the maintenance of soil labile P in a subtropical natural forest under chronic stress of N deposition.

Determining light requirements of groundcover plants from subtropical natural forest using hemispherical photography

In order to determine light requirements of indigenous groundcover plants for potential use in urban landscaping, we conducted a plant census in Yinpingshan Nature Reserve, Dongguan, China, and measured canopy structure and understory light regimes using hemispherical photography. We found that canopy openness, transmitted direct solar radiation, and transmitted diffuse solar radiation exhibited highly significant spatial heterogeneity. Species composition and diversity of groundcover plants were highly dependent on canopy structure and understory light condition. Greater diversity and more stems of groundcover plants were associated with greater canopy openness and understory radiation in most cases. Highly significant differences in species composition were detected along canopy openness, transmitted direct solar radiation, and transmitted diffuse solar radiation gradients, respectively. We also detected indicator species for specific understory light regimes, which will provide useful information when applying such species in urban greening under various light environments.

Efficacy of generic allometric equations for estimating biomass: a test in Japanese natural forests

Accurate estimation of tree and forest biomass is key to evaluating forest ecosystem functions and the global carbon cycle. Allometric equations that estimate tree biomass from a set of predictors, such as stem diameter and tree height, are commonly used. Most allometric equations are site specific, usually developed from a small number of trees harvested in a small area, and are either species specific or ignore interspecific differences in allometry. Due to lack of site-specific allometries, local equations are often applied to sites for which they were not originally developed (foreign sites), sometimes leading to large errors in biomass estimates. In this study, we developed generic allometric equations for aboveground biomass and component (stem, branch, leaf, and root) biomass using large, compiled data sets of 1203 harvested trees belonging to 102 species (60 deciduous angiosperm, 32 evergreen angiosperm, and 10 evergreen gymnosperm species) from 70 boreal, temperate, and subtropical natural forests in Japan. The best generic equations provided better biomass estimates than did local equations that were applied to foreign sites. The best generic equations included explanatory variables that represent interspecific differences in allometry in addition to stem diameter, reducing error by 4-12% compared to the generic equations that did not include the interspecific difference. Different explanatory variables were selected for different components. For aboveground and stem biomass, the best generic equations had species-specific wood specific gravity as an explanatory variable. For branch, leaf, and root biomass, the best equations had functional types (deciduous angiosperm, evergreen angiosperm, and evergreen gymnosperm) instead of functional traits (wood specific gravity or leaf mass per area), suggesting importance of other traits in addition to these traits, such as canopy and root architecture. Inclusion of tree height in addition to stem diameter improved the performance of the generic equation only for stem biomass and had no apparent effect on aboveground, branch, leaf, and root biomass at the site level. The development of a generic allometric equation taking account of interspecific differences is an effective approach for accurately estimating aboveground and component biomass in boreal, temperate, and subtropical natural forests.

A Comparison of Tree Species Diversity in Two Subtropical Forests, Guangxi, Southwest China

Natural karst forests can support very high level of biodiversity, but difference of species diversity between the natural karst forests and non-karst forests is still less concerned. To analyze the difference of species diversity of the natural karst forests and non-karst forests in subtropics, we made a census of all woody species with diameter at breast height (dbh)≥1 cm in a 1-ha plot in Mulun subtropical karst forests and a 1-ha plot in Maoershan subtropical non-karst forests, Guangxi of south-western China. Species richness in Mulun plot (120 species) was higher than that in Maoershan plot (116 species). Mulun plot contained more families and genera, more stems and a larger proportion of rare species (species of individuals less than or equal to 1 ha -1 ). At smaller scale ( 5000 m 2 ). Total basal area in Mulun plot (18.47 m 2 ) was smaller than that in Maoershan plot (30.74 m 2 ). Size structure distribution of all woody species in the two plots showed insignificant difference. The ten most dominant species, families and genera were quite different in the two plots. In Mulun plot, the most important species and family were Sinosideroxylon wightianum and Sapindaceae, while in Maoershan plot, Castanopsis carlesii and Fagaceae were the most important species and family. All these results suggest that middle subtropical natural karst forest in Mulun supports diverse species with high spatial variability, and their species composition are quite different with non-karst forests. This study implies that special attention is needed on selecting suitable species in karst forest restoration and vegetation management strategies.

Stand structure of the subtropical natural forest in the Yambaru area of Okinawa Island : a comparison of a 60-year-old secondary forest and a mature non-clear-cut forest

Stand structure of the subtropical natural forest in the Yambaru area of Okinawa Island : a comparison of a 60-year-old secondary forest and a mature non-clear-cut forest

Reconstruction of environmental changes based on growth rates and carbon and oxygen isotopic compositions of a stalagmite in Imamura Cave, Minami-Daito Island, southwest Japan

Speleothems are typical terrestrial carbonates and their formation is dependent on a variety of geological, hydrological, chemical and climatic factors. For the reason, isotopic compositions of speleothems are known as a good indicator of paleoclimate and paleoenvironment. Especially, the  13 C values are considered to be related to vegetation around the limestone cave, decay of organic matter within the soil zone and isotopic compositions of the adjacent carbonate host rocks. Therefore, we attempted reconstruction of environmental changes associated with cultivation by pioneers since 1900, based on carbon and oxygen isotopic composition of a speleothem in Imamura Cave, Minami-Daito Island, southwest Japan. To reconstruct the environmental changes since 1900, when first pioneers settled in the island, a stalagmite collected in 2012 was utilized. Dating of the stalagmite was carried out based on annual bands. Samples for the isotopic study were taken along the growth axis from the top 4-cm of the stalagmite at a sampling interval of 0.5 mm. As a result, an average growth rate is 44.9m/year before 1900, while the rate is 226. 7m/year after 1900. This drastic change of the growth rate is considered due to the change of vegetation around the cave from sub-tropical natural forests to sugarcane fields. The  13 C values before and after 1900 range from -10.94 to -3.98‰ 13 C PDB and from -2.52 to -0.86‰ 13 C PDB , respectively. The abrupt increase of the  13 C values at 1900 means that the contribution of the isotopically heavier carbon derived from sugarcane to ground water increased with cultivation. Further, some fluctuations of the  13 C values are observed since 1900, and those seem to be related to the yield of sugarcane per unit area. On the other hand, the  18 O values range from -8.57 to -6. 70‰ 18 O PDB , and the values before and after 1900 are not so different. However, some fluctuations of the  18 O values are recognized, and it seems that the fluctuations are correlated with the ratio of the precipitation in summer to total annual precipitation. This suggests that the  18 O values of the stalagmite reflect the seasonal

Fungal decomposition of woody debris of Castanopsis sieboldii in a subtropical old‐growth forest

AbstractFungi, especially basidiomycetes, are the primary agents of woody debris decomposition in terrestrial forest ecosystems. However, quantitative data regarding the abundance and decay activity of wood‐inhabiting fungi are lacking, especially for tropical and subtropical areas. This study demonstrates the dynamics of decay columns of wood‐inhabiting fungi within decaying woody debris of Castanopsis sieboldii and the wood decay activities of those fungi in a subtropical natural forest. Among six basidiomycetes and two ascomycetes observed as sporocarps on fallen boles of C. sieboldii, Microporus affinis was most abundantly observed in terms of frequency of sporocarps and as percentage area of decay columns within cross‐sections of boles, especially those in the early stages of decomposition. In decay columns of M. affinis, both acid‐unhydrolyzable residue (AUR) and holocellulose decayed simultaneously, and wood relative density decreased to 45.8% of that of fresh C. sieboldii wood. A pure culture decay test under laboratory conditions showed that M. affinis was a strong decomposer of AUR and holocellulose. These results suggest that M. affinis has a central role in lignocellulose decomposition of wood of C. sieboldii in the early stages of decomposition.

Litterfall, litter decomposition and nutrient dynamics in a subtropical natural oak forest and managed plantation in northeastern India

In northeastern India, subtropical forests are over-exploited for timber, fuel wood and common agricultural practice like shifting cultivation, which are responsible for the degradation of natural forest. In degraded areas, large-scale plantations of different species of Quercus have been raised since 1980 for the production of economic Tasar silk. Conversion of natural forest into plantation affects the process of nutrient cycling due to management practices. Thus, it would be of importance to study the litterfall, litter decomposition process and the factors regulating the rate of litter decay in these ecosystems to improve recommendations for their management and conservation. We recorded litterfall by using litter traps and decomposition of leaf litter by nylon net bag technique to understand the amount of organic matter and nutrient return and their release in soils of forest and plantation in Manipur, northeast India. Total litterfall was 419.9 g m −2 year −1 in plantation and 547.7 g m −2 year −1 in forest. Litter decomposition rate was faster at plantation site than the forest in the early stage of litter decomposition whereas the reverse was observed at later stages of decomposition. Stepwise regression analysis showed the significant role of relative humidity and mean temperature on mass loss rates in the forest. Relative humidity, maximum temperature, population of fungi and actinomycetes were the best predictor variables for mass loss rates in plantation. Nutrient retranslocation efficiency and the immobilization of N and P in forest litter were higher than plantation. This suggests that Q. serrata growing in natural ecosystem in oligotrophic condition adapted strong nutrient conservation mechanisms to compete with the other plant species for the meager soil nutrients. The same species in plantation loses these adaptive capabilities because of exogenous supply of nutrients and in the absence of intense competition with other plant species. Thus, the optimization of organic and chemical fertilizer input in plantation is recommended for maintaining the soil fertility level to produce quality leaf for silkworm by conserving essential nutrients in the system.