Eucalyptus carbon stock estimation in subtropical regions with the modeling strategy of sample plots–airborne LiDAR–Landsat time series data

Updating eucalyptus carbon stock data in a timely manner is essential for better understanding and quantifying its effects on ecological and hydrological processes.At present,there are no suitable methods to accurately estimate the eucalyptus carbon stock in a large area.This research aimed to explore the transferability of the eucalyptus carbon stock estimation model at temporal and spatial scales and assess modeling performance through the strategy of combining sample plots,airborne LiDAR and Landsat time series data in subtropical regions of China.Specifically,eucalyptus carbon stock estimates in typical sites were obtained by applying the developed models with the combination of airborne LiDAR and field measurement data;the eucalyptus plantation ages were estimated using the random localization segmentation approach from Landsat time series data;and regional models were developed by linking LiDAR-derived eucalyptus carbon stock and vegetation age(e.g.,months or years).To examine the models’robustness,the developed models at the regional scale were transferred to estimate carbon stocks at the spatial and temporal scales,and the modeling results were evaluated using validation samples accordingly.The results showed that carbon stock can be successfully estimated using the age-based models(both age variables in months and years as predictor variables),but the month-based models produced better estimates with a root mean square error(RMSE)of 6.51 t⋅ha1 for Yunxiao County,Fujian Province,and 6.33 t⋅ha1 for Gaofeng Forest Farm,Guangxi Zhuang Autonomous Region.Particularly,the month-based models were superior for estimating the carbon stocks of young eucalyptus plantations of less than two years.The model transferability analyses showed that the month-based models had higher transferability than the year-based models at the temporal scale,indicating their possibility for analysis of carbon stock change.However,both the month-based and year-based models expressed relatively poor transferability at a spatial scale.This study provides new insights for cost-effective monitoring of carbon stock change in intensively managed plantation forests.

Leaf phenology rather than mycorrhizal type regulates soil nematode abundance,but collectively affects nematode diversity in seven common subtropical tree species

The underlying mechanisms of the relationships between tree species and the soil micro-food web in forest ecosystems remain uncertain,primarily ascribed to an insufficient understanding on how tree functional traits drive soil nematode communities,including in subtropical forests.We investigated the impacts of seven subtropical tree species(evergreen:Pinus massoniana,Mytilaria laosensis,Ilex chinensis,Michelia macclurei;and deciduous:Liquidambar formosana,Quercus acutissima,and Betula luminifera)on the soil nematode communities.We found that the abundance of soil nematodes was not affected by mycorrhizal types,but it was around 83%higher under the deciduous trees than the evergreen trees,indicating the importance of leaf phenology to the abundance of soil nematodes.Nonetheless,both the evergreen and the arbuscular mycorrhizal trees increased soil nematode diversity,resulting from changes in root traits and soil properties.Furthermore,root traits(root C,root N,and root C:N ratio),and soil properties(total C,total N,moisture content,and bulk density)were the best predictors of the community composition of soil nematodes,indicating a key role of resource quality and soil microhabitat in regulating soil nematodes.In contrast,the ectomycorrhizal trees had lower plant parasite and Wasilewska indices,and evenness,whereas the evergreen trees slightly improved the evenness of soil nematodes.This study suggests that tree species affect the soil food web through changes in soil conditions and plant functional traits in subtropical forests.

Resorption Efficiency of Four Cations in Different Tree Species in a Subtropical Common Garden

High rainfall in subtropical regions can leach cation elements from ecosystems,which may limit plant growth.Plants often develop efficient resorption patterns to recycle elements,but there is relatively little available information on this topic.In February 2012,a common garden was established in a subtropical forest by planting dominant trees from the area.Green and senescent leaves were sampled from 11 tree species.The concentrations of potassium(K),calcium(Ca),sodium(Na)and magnesium(Mg)were determined,and the resorption efficiencies were calculated.The results showed significant K,Na and Mg resorption in most of the investigated tree species,while Ca mainly displayed accumulation.Evergreen coniferous and evergreen broad-leaved trees(such as Cunninghamia lanceolata,Pinus massoniana,Cinnamomum camphora,and Michelia macclurei)exhibited relatively higher resorption efficiencies of K(39.0%-87.5%)and Na(18.3%-50.2%)than deciduous broad-leaved trees.Higher Mg resorption efficiencies(>50%)were detected in Liriodendron chinense,C.lanceolata and P.massoniana than in other trees.Overall,evergreen coniferous and evergreen broad-leaved trees could show higher cation resorption than deciduous broad-leaved trees.K and Mg resorption efficiencies and Ca accumulation decrease with increasing nutrient concentrations in green leaves.Our results emphasize that nutrient resorption patterns largely depend on elements and plant functions,which provides new insights into the nutrient use strategies of subtropical plants and a reference for the selection of suitable tree species in this region.

Grain size and surface micro-texture characteristics and their paleoenvironmental significance of Holocene sediment in southern margin of the Gurbantunggut Desert,China

The southern margin of the Gurbantunggut Desert,China,is characterized by alternating layers of aeolian and alluvial deposits.Investigating the characteristics of arenaceous sediment in this area is of significant importance for understanding the interactive processes of wind and water forces,as well as the provenance of sediment.However,there are relatively few investigations on the characteristics of such sediment at present.In this study,we researched three aeolian-alluvial interactive stratigraphic profiles and different types of surface sediment on the desert-oasis transitional zone of southern margin of the Gurbantunggut Desert.Based on the optically stimulated luminescence(OSL)dating of aeolian sand and analyses of quartz sand grain size and surface micro-texture,we explored the aeolian-alluvial environmental change at southern margin of the desert in Holocene,as well as the provenance of sediment.The results indicated that the grain size characteristics of different types of sediment in the stratigraphic profiles were similar to those of modern dune sand,interdune sand,muddy desert surface soil,and riverbed sand.Their frequency curves were unimodal or bimodal,and cumulative probability curves were two-segment or three-segment,mainly composed of suspension load and saltation load.The quartz sand in the sediment at southern margin of the desert had undergone alternating transformation of various exogenic forces,with short transportation distance and time,and sedimentary environment was relatively humid.In Holocene,southern margin of the desert primarily featured braided river deposits,and during intermittent period of river activity,there were also aeolian deposits such as sand sheet deposits,stabilized dune deposits,and mobile dune deposits.The provenance for Holocene alluvial deposits at southern margin of the desert remains relatively constant,with the debris of the Tianshan Mountains being the primary provenance.Aeolian sand is mainly near-source recharge,which is formed by in situ deposition of fluvial or lacustrine materials in southern margin of the desert transported by wind erosion,and its provenance was still the weathered debris of the Tianshan Mountains.In addition,the sand in interior of the desert may be transported by northwest wind in desert-scale,thus affecting the development of dunes in southern margin of the desert.The results of this study provide a reference for understanding the composition and provenance changes of desert sand in the context of global climate change.

Spatiotemporal pattern of climate change in the China-Myanmar Economic Corridor from 1901 to 2018

The China-Myanmar Economic Corridor(CMEC) is an important part of China's Belt and Road Initiative and an important area for global ecology and biodiversity. In this study, the annual and seasonal spatiotemporal patterns of temperature and precipitation in the CMEC over the past century were investigated using linear tendency estimation, the Mann-Kendall mutation test, the T-test, and wavelet analysis based on the monthly mean climatic data from 1901 to 2018 released by the Climatic Research Unit(CRU) of the University of East Anglia, UK. The results show that the CMEC demonstrated a trend of warming and drying over the past 100 years, and the rate of change in Myanmar was stronger than that in Yunnan Province of China. The warming rate was 0.039 ℃/10a. Precipitation decreased at a rate of -6.1 mm/10a. From the perspective of spatial distribution, temperature was high in the central and southern, low in the north of the CMEC, and the high-temperature centers were mainly distributed in the southern plain and river valley. Precipitation decreased from west to east and from south to north of the CMEC. From the perspective of the rate of change, warming was stronger in central and northern CMEC than in southern and northeastern CMEC. The rate of precipitation decline was stronger in the central and western regions than in the eastern region. This study provides a scientific reference for the CMEC to address climate change and ensure sustainable social and economic development and ecological security.

Late Pleistocene aeolian activity in Haitan Island, Southeast China: Insights from optically stimulated luminescence dating of coastal dunes on marine terraces

The 'Old Red Sand' is a type of semicemented medium-fine sandy sediment that is red(10R_4/8) or brown red(2.5YR_4/8) in colour and is found in late Quaternary deposits. The sediments have distinctive characteristics and are a critical archive for understanding climatic changes in the coastal areas of East Asia. The ages of the late Quaternary aeolian sand dunes from Haitan Island in the coastal area of South China are still in debate. In this study, three sets of marine terraces were identified in the northern region of Haitan Island. Aeolian dune sands are well preserved on the top of these terraces. Quartz Optically Stimulated Luminescence dating and the distribution of the formation ages demonstrated that the palaeo-dunes are deposits from the middle-late period of the Late Pleistocene(Q_3^(2-3)). The period may be divided into three stages, 100-90 ka, 70-60 ka, and 40-20 ka, in which the palaeo-dunes of the first two stages are more widespread and were formed separately during a low-sea level period of the Marine Isotope Stages 5 b and 4. Several depositional palaeo-flood event records were preserved during the last stage due to the increasing gradient of mountain gullies formed during the Last Glacial Maximum.

Chronology of coastal aeolian deposition and its paleo-environmental implications on the Liuao Peninsula of South China

Coastal dunes are a common geomorphic type in sandy coastal zones.They are a record of the coupled evolutionary processes of the wind and ocean waves.Many coastal dune fields have developed on the east coast of Fujian China and now occur as widespread typical coastal aeolian sand landforms on the Liuao Peninsula,Gulei Peninsula and Dongshan Island,but it is difficult to evaluate the dynamic geomorphologic process of sandy coast due to the lack of systematic and accurate chronological data.In this study,we selected the Hutoushan(HTS)aeolian dune on the Liuao Peninsula as the research object.Optical dating and grain-size analysis were applied to sand samples from the aeolian sequence of a profile of the HTS dune.The results show that the ages of seven samples of this profile were in the range of 37.8–0.19 ka from 4.0 to 0.2 m deep.These correspond to the Marine Isotope Stage 3(MIS3),abrupt climatic change events of 4.2 and 1.1 ka and the Little Ice Age(LIA),respectively.These samples displayed evidence of a longer-term climate trend in this area.The period of formation of this coastal aeolian dune corresponds to a cold and arid climate associated with the East Asia Winter Monsoon(EAWM).Periods of dune fixation and rubification are evidence of a hot and humid climate.Mobilization and stabilization of the aeolian dune is an important characteristic of the coastal evolution in South China since the late Pleistocene.

In situ nitrogen removal processes in intertidal wetlands of the Yangtze Estuary

Estuarine and intertidal wetlands are important sites for nitrogen transformation and elimination.However,the factors controlling nitrogen removal processes remain largely uncertain in the highly dynamic environments.In this study,continuous-flow experiment combined with 15 N isotope pairing technique was used to investigate in situ rates of denitrification and anaerobic ammonium oxidation(anammox)and their coupling with nitrification in intertidal wetlands of the Yangtze Estuary.The measured rates varied from below the detection limit to 152.39μmol N/(m^2·hr)for denitrification and from below the detection limit to 43.06μmol N/(m^2·hr)for anammox.The coupling links of nitrogen removal processes with nitrification were mainly dependent on nitrate,organic carbon,sulfide,dissolved oxygen and ferric iron in the estuarine and intertidal wetlands.Additionally,it was estimated that the actual nitrogen removal processes annually removed approximately 5%of the terrigenous inorganic nitrogen discharged into the Yangtze Estuary.This study gives new insights into nitrogen transformation and fate in the estuarine and intertidal wetlands.

Effects of organic matter on the distribution of rare earth elements in red soil aggregates during ecological restoration

Rare earth elements(REEs)are widely applied in high-tech fields.However,their increasing presence in the food chain poses significant risks to human health.At present,little is known about the effects of organic matter on the distribution of ion-adsorbed REEs in soil aggregates during ecological restoration.Red soil derived from coarse-grained granite in Southern China is both prone to ecosystem degradation from soil erosion and rich in REEs.Understanding the distribution of REEs in soil aggregates undergoing ecological restoration is helpful to formulate effective measures for controlling the environmental migration of REEs.Four sites that had undergone different durations/degrees of ecological restoration were selected in the areas to analyze.REEs concentration of six different aggregates sizes(<0.25,0.25-0.5,0.5-1,1-2,2-5,and>5 mm)were analyzed and the enrichment coefficients were calculated in 4 sample sites of severe-degraded ecosystem in Changting County,Fujian Province,Southern China.The results showed that the total rare earth elements(TREEs)concentration in the aggregates increased from 213 mg kg^(-1) to 528 mg kg^(-1) with the extension of the ecological restoration time.At the initial stages of ecological restoration,there was no significant difference in the TREEs concentration among the six aggregates sizes.However,in the middle and late stages of restoration,the concentration of TREEs increased significantly with the decrease of aggregate size.The concentration of individual REEs showed three changing trends with sizes of aggregates during ecological restoration,respectively:1)no obvious regular change(S1),2)a V-shaped change trend(S2),and 3)increasing concentration with the decrease of aggregate size(S3 and S4).Ce and Eu showed a positive and negative anomaly in the soil aggregates,respectively.Moreover,the light rare earth elements(LREEs)were enriched,while the heavy rare earth elements(HREEs)were depleted during the initial stages,and the HREEs were enriched during the middle and late stages of restoration.The correlation coefficient between organic matter and REEs in aggregates was generally low;however,LREEs showed a stronger correlation with organic matter than that of HREEs during the initial stages of ecological restoration.The correlation between organic matter and HREEs gradually increased and even exceeded that of LREEs with on-going ecological restoration.The distribution of REEs concentration in degraded soil aggregates in Southern China showed obvious variability with the ecological restoration time.

Gap edge canopy buffering of throughfall deposition in a subalpine natural forest

Base cation loads are rarely considered in forest gap edge canopies,but they can play critical roles in capturing or buffering atmospheric deposition in forests with frequent gap disturbances,such as subalpine forests.We selected an expanded gap edge canopy and a closed canopy in a subalpine natural forest on the eastern Tibetan Plateau.The throughfall deposition and canopy exchange processes of common base cations(K^(+),Ca^(2+),Na^(+),and Mg^(2+))were continuously studied over two years.The results showed that the enrichment ratio and fluxes had lower levels of base cations in the gap-edge canopy than in the closed canopy,which indicated that base cations were concentrated more in the closed canopy than in the gap-edge canopy.Although Ca^(2+)in the gap-edge canopy showed a higher net throughfall flux,the annual net throughfall fluxes of K^(+),Na^(+) and Mg^(2+) within the gap-edge canopy were 1.83,6.75 and 2.95 times lower than those in the closed canopy,respectively.Moreover,dry deposition fluxes of base cations significantly decreased in the gap edge canopy compared to those in the closed canopy,and the decreasing tendency was more significant during the snowy season than during the rainy season.Overall,these results suggest that the amount of base cations in subalpine natural forest ecosystems may be overestimated when the throughfall deposition of ions in gap edge canopies is ignored.

全球尺度上氮添加影响植物生物量分配但不影响不同器官间的异速生长关系

生物量在不同器官间的分配是植物对环境变化响应的一个关键生态生理学过程。然而,在全球尺度上有关不同陆地生态系统植物生物量分配对氮沉降响应的认识还比较欠缺。本文通过整合分析333篇己发表文章的5474个观测值,基于“最优分配假说”和“异速分配假说”,评估了全球尺度上氮添加对植物生物量及其在不同器官间分配的影响。结果表明:(1)氮添加显著增加了整株植物或不同器官的生物量,降低了根冠比和根质量分数,但对叶质量分数和茎质量分数无显著影响;(2)氮添加对不同器官质量分数的影响受实验条件、植物功能性状、纬度、氮添加率等因子单独或交互作用的调控;(3)氮添加对生物量在不同器官间的异速分配率无显著影响,表明氮添加导致的根冠比和根质量分数减少是在异速分配模式下由整株植物生物量增加而致。虽然氮添加改变了地上和地下部分的质量分数,但不同器官生物量间异速分配模式的稳定性表明“异速分配假说”能更好地描述植物生物量分配对氮添加的响应规律。该研究结果将有助于深入认识氮沉降环境下植物生物量的分配规律,同时表明将生物量分配纳入有关氮沉降对陆地生态系统影响的预测模型中的重要性。

Microfossil evidence of rice cultivation on the Southeast China Coast 7500 years ago

Located on the southeast coast of China,Fujian is an important junction for the spread and migration of agriculture and populations from mainland Asia to Taiwan and the Island Southeast Asia.Research on the emergence of agriculture and its relationship with the regional environmental context is key to understanding the evolution of ancient human-land interactions in the coastal zone of China.This paper presents a detailed microfossil analysis of the Dapingding site,which is located in the lower reaches of the Min River on the southeast coast of China.We found a large number of phytoliths produced in rice stems and leaves from the cultural layers of this site,dated to 7,500 cal.a BP.In addition,we found rice husk impressions and rice phytoliths in the pottery sherds of these cultural layers.Among these phytoliths,rice bulliform phytoliths with≥9 fish-scale patterns indicating the degree of rice domestication,accounted for 44%.This percentage is much higher than the established standard for wild rice bulliform phytoliths with fish-scale patterns,suggesting that rice cultivation had already occurred on the southeast coast of China approximately 7,500 years ago.Subsequently,the starting time of agricultural activity on the southeast coast of China was pushed from 5,000 to 7,500 years ago.Comparing the regional history of sea level and coastline changes in the early to mid-Holocene,we suggest that the emergence of early rice cultivation in Southeast China was associated with high sea levels in the midHolocene and the last transgression in the Fuzhou Basin.The’Fuzhou Bay’,formed by the retreating coastline and transgression driven by high sea levels,may have provided a sea channel for the southward movement of northern rice farmers.

Increased microbial sequestration of soil organic carbon under nitrogen deposition over China’s terrestrial ecosystems

Background:China’s terrestrial ecosystems have been receiving increasing amounts of reactive nitrogen(N)over recent decades.External N inputs profoundly change microbially mediated soil carbon(C)dynamics,but how elevated N affects the soil organic C that is derived from microbial residues is not fully understood.Here,we evaluated the changes in soil microbial necromass C under N addition at 11 forest,grassland,and cropland sites over China’s terrestrial ecosystems through a meta-analysis based on available data from published articles.Results:Microbial necromass C accounted for an average of 49.5%of the total soil organic C across the studied sites,with higher values observed in croplands(53.0%)and lower values in forests(38.6%).Microbial necromass C was significantly increased by 9.5%after N addition,regardless of N forms,with greater stimulation observed for fungal(+11.2%)than bacterial(+4.5%)necromass C.This increase in microbial necromass C under elevated N was greater under longer experimental periods but showed little variation among different N application rates.The stimulation of soil microbial necromass C under elevated N was proportional to the change in soil organic C.Conclusions:The stimulation of microbial residues after biomass turnover is an important pathway for the observed increase in soil organic C under N deposition across China’s terrestrial ecosystems.

Changes in soil faunal density and microbial community under altered litter input in forests and grasslands

Root and foliar litter inputs are the primary sources of carbon and nutrients for soil fauna and microorganisms,yet we still lack a quantitative assessment to evaluate the effects of root and foliar litter on various groups of soil organisms across terrestrial ecosystems.Here,we compiled 978 paired observations from 68 experimental sites to assess the directions and magnitudes of adding and removing foliar and root litter on the soil faunal density and microbial biomass that was evaluated by phospholipid fatty acids(PLFAs)across forests and grasslands worldwide.We found that litter addition had only a marginal effect on soil faunal density but significantly increased the soil total microbial-,fungal-and bacterial-PLFAs by 13%,14%,and 10%,respectively,across ecosystems,suggesting that the soil microbial community is more sensitive to carbon source addition than soil fauna,particularly in soils with low carbon to nitrogen ratios.In contrast,removing litter significantly decreased the soil faunal density by 17%but had few effects on soil microorganisms.Compared with foliar litter,root litter input had a more positive effect on the development of soil fungal taxa.The effect of both litter addition and removal on soil faunal density and microbial biomass did not differ between humid and arid regions,but a greater influence was observed in grasslands than in forests for soil microbial community.Our results highlight that the increasing litter production under a global greening scenario would stimulate microbial activity in grasslands more than in forests,and this stimulation would be greater for soil microbes than soil fauna.