Impacts of land use/land cover change and climate change on the runoff in Yuan River basin based on SWAT model
[Background] Yuan River is one of the most important international rivers in Southwest China. Whether the ecological environment of the Yuan River basin is healthy or not has an essential impact on the social and economic development along the coast and the ecological security of other countries in the downstream of the river basin. Therefore, it is of considerable significance to clarify the specific impact of land use/land cover change (LUCC) and climate change on the status of water resources in Yuan River. However, there are few reports on this aspect at present. [Methods] The SWAT model was used to quantitatively analyze the effects of LUCC and climate change on basin runoff, and combined with RCP4.5 and RCP8.5 emission scenarios to predict the runoff change of Yuan River basin. [Results] 1) SWAT model is suitable for runoff simulation of the Yuan River basin. The model parameter R2 and ENS (efficiency coefficient of Nash-Sutcliffe) of the calibration period are 0.63 and 0.62, respectively, and the R2 and ENS of the verification period are 0.62 and 0.60, respectively. 2) Extreme land-use scenario simulation shows that the contribution of various land-use types to runoff formation is the strongest in agricultural land, the second in grassland, and the weakest in woodland. 3) The increase of runoff caused by LUCC in Yuan River basin from 2006 to 2015 is due to the transformation of forest land into grassland. The decrease of flow caused by climate change results from both the reduction of precipitation and the increase of temperature, and the reduction of runoff caused by climate change is more significant than that caused by LUCC. [Conclusions] 1) Climate change dominates runoff change in the Yuan River basin between 2006 and 2015. 2) Under the two emission scenarios of RCP4.5 and RCP8.5, the runoff reduction rate in the Yuan River basin from 2021 to 2050 is 1.82 times and 2.36 times that of the measured runoff reduction rate from 1971 to 2015, respectively. And the decreasing trend of the RCP8.5 scenario with higher carbon emission is significantly higher than that of the RCP4.5 scene, which is 1.3 times higher than that of the RCP4.5 scenario.
Recovery mechanism of Cynodon dactylon and Morus alba after re-emergence in the water-level-fluctuating zone of the Three Gorges Reservoir
[Background] The restoration of the vegetation in the water-level-fluctuating zone is widely valued by the public. This work is aimed to explore the physiological and structural adaptation mechanism of Cynodon dactylon and Morus alba surviving on the water-level-fluctuating zone. [Methods] The natural surviving C. dactylon and the two-year native M. alba (plant height in 1.5-2.0 m) at 171 m and 0,10 and 70 d after re-emergence of the water-level-fluctuating zone were sampled as the study materials. The C. dactylon and M. alba of the same age at 177 m without submergence were sampled as controls (CK). Their growth and physiological indexes (number of fibrous roots, diameter of root, stem length or height of a tree, internode length, number of branches, area of a single leaf, chlorophyll content, soluble sugar content, soluble protein content, free proline content, SOD activity, CAT activity, and root vitality) as well as the anatomical structure changes were analyzed. [Results] 1) The root system of C. dactylon after flooding decreased, and the growth of the aerial parts was inhibited. Most of the growth indexes were recovered to the level of land growth after 70 d of re-emergence. The stem diameter and plant height of M. alba decreased after 70 d of re-emergence, and there was still difference compared to the control. 2) There was no difference in the ratio of chlorophyll a/b between C. dactylon and the CK after 70 d of re-emergence, and the ratio of M. alba was 2.07 at the same time, which was still different from the CK. 3) The recovery rate of osmoregulation substance from roots of C. dactylon to the CK was faster than that of leaves, and there was no difference after 70 d of re-emergence. Some indexes from roots of M. alba in the same period did not restore to the normal level. 4) SOD and CAT of new leaves of C. dactylon and M. alba decreased gradually after re-emergence, and there was no significant difference between them after re-emergence of 70 d. The recovery rate of antioxidant enzyme and TTC content in C. dactylon root was faster than that of M. alba. 5) Most of the cells in the roots and stems of C. dactylon had become larger after submergence, and irregular atmospheric cavity fusion occurred. The structure of the roots was restored to the CK after 70 d of re-emergence. Some of the cells in the cortex of M. alba roots were dissociated, and the number of vessel cells significantly increased. After 70 d of re-emergence, there was still significant difference between the roots of flooded gorup and the CK of M. alba. [Conculsions] The structure and physiological indexes of roots and stems of C. dactylon actively are started the compensation effect quickly after re-emergence, while the M. albais has a slow start compensation mechanism, which is also a reason that the adaptability range of M. alba is narrower than C. dactylon.
YOU Longhui, NIE Sen, CHENG Fensheng, YOU Huiming, BU Jianxia, LIN Wenquan, YE Gongfu
Soil loss control effects of four interplanting modes in the Pinus massoniana stands of red soil erosion area in Fujian province
[Background] The ecological public welfare forests in the south of China are mainly consisted of Pinus massoniana and Cunninghamia lanceolata pure forests. Because of lacking of diversity of vegetation species and simplicity of tree's structure, it is hard to harness the red soil erosion areas where the soil erosion is devastating. This research is aimed to analyze the influence on runoff and sediment and nutrient losses on slope gradient, after low-efficiency P. massoniana forest intercropping different native broad-leaved tree species, and to provide reference for red soil erosion harnessing and tree species selection of low-efficiency P. massoniana forest in similar areas. [Methods] Choosing the similar low-efficiency P. massoniana forests in Changting red soil erosion area of Fujian province and intercropping Myrica rubra, Sapindus mukorossi, Camellia oleifera and Gardenia jasminoides 4 typical reconstructed stands, the undisturbed low-efficiency pure P. massoniana in the same area was used as control. By setting up typical runoff plot we investigated the runoff,sediment yield and nutrient loss characteristics and screened out broad-leaved tree species which have better runoff and sediment reduction. [Results] 1) In 2018, the rainfalls in the sample plots mainly occurred in May to October, accounting for 63.7% of the total annual rainfall, and the precipitation and frequency causing runoff and sediment yield accounted for 72.8% and 95.6% in the annual year. 2) From May to October the yields of runoffs in 4 P. massoniana modes intercropping M. rubra, S. mukorossi, C. oleifera and G. jasminoides respectively decreased by 24.96%-42.19%, 13.93%-53.68%, 4.55%-26.45%, and 8.59% -32.98%, compared with the control group of pure P. massoniana forest, and sediment yield decreased by 60.19%-84.86%, 55.07%-87.14%, 20.91%-67.06%, and 27.22%-72.66% respectively. 3) In contrast to the control plots of pure P. massoniana forest, the total nitrogen, ammonium nitrogen, nitrate nitrogen loss and total carbon loss in the erosion sediment of P. massoniana forest interplanting with M. rubra and S. mukorossi were almost similar, respectively increased 48.33%-48.79%, 103.66%-139.05%, 39.75% -42.29%, and 63.14%-66.57%, however the modes of intercropping C. oleifera and G. jasminoides increased by 19.96% -22.52%, 74.89%-92.62%, 15.44%-16.42%, and 25.24%-28.14%. In general, the loss pattern of other nutrients was similar to that of runoff and sediment yield, showing that the mode of intercropping was lower than that of pure P. massoniana forest. 4) Principal component analysis showed that with the effect on rainfall and runoff, P. massoniana interplanting with M. rubra or S. mukorossi was more likely to cause the loss of soil carbon and nitrogen, while P. massoniana interplanting C. oleifera or G. jasminoides more easily caused the loss of soil phosphorus and potassium. [Conclusions] Low-efficiency P. massoniana forest intercropping indigenous broad-leaved tree species which are suitable for planting, constructing a multi-layer forest structure may result in the biomass increase of litter and root system, to a certain extent it even may improve the reduction of soil erosion on the slope of the low-efficiency P. massoniana forest land. Interplanting M. rubra or S. mukorossi will be more fruitful than that of C. oleifera or G. jasminoides, in the short term.
Quantitative evaluation and analysis of human impact on net primary productivity of vegetation in northern Shaanxi
[Background] Under the double influence of ecological construction and energy development, the ecological environment in northern Shaanxi is facing great pressure. Quantitative study on the human impact on net primary productivity (NPP) of vegetation, which is the basis of quantitative study on human impact on regional ecosystem, can lay a foundation for trade-off analysis between regional soil and water conservation services and socio-economic development. Therefore, it is necessary to quantitatively study the impact of human activities on NPP of vegetation in northern Shaanxi. [Methods] Based on the normalized differenced vegetation index (NDVI) data which was validated, the vegetation coverage data and the climate data which was resampled to 250 m resolution, the NPP of vegetation and its human impact value were calculated using CASA model and the human impact assessment model respectively. Then the spatio-temporal variation of human impact on NPP was analyzed using the Theil-Sen trend degree. Finally, the specific human factors were made an empirical analysis based on the statistics data and land use degree data. [Results] 1) The impact of human activities on vegetation NPP in northern Shaanxi showed an annual trend of increasing positive impact and decreasing negative impact from 2001 to 2014. The negative impact decreased by 3.40 g/(m2·a) and the positive impact increased by 0.91 g/(m2·a). Especially in 2013, the positive impact of human activities on vegetation NPP was the strongest. 2) The positive and negative effects of human activities on vegetation NPP were mainly increasing trend. The positive trend of human impact was obvious in the central and eastern regions, the highest positive trend value was 40.39 g/(m2·a), and the positive effects of significant and significant changes were mainly located in the hilly and gully region along the Kuye River in Fugu county and Shenmu county, as well as the Yuxi River Wetland at the junction of Yuyang district and Mizhi county. While the negative trend of human impact was obvious in the northwest and southern regions, the highest negative trend value was -37.17 g/(m2·a), and the negative effects of significant and significant changes were mainly distributed in the northern energy area and the farming and pastoral areas in the middle east. 3) The "Grain for Green Project" was the main reason for the positive influence of vegetation NPP. The increase of the proportion of energy industry and the urban expansion were the main reasons for the gradual increase of human negative influence. And there was not a simple linear relationship between the human impact of vegetation NPP and land use degree. [Conculsions] The human positive impact of vegetation NPP shows an increasing trend, while the negative impact decreasing. The effect of ecological governance has been obvious, but the human negative impact is still stronger in the northern energy area and the southern tableland agricultural area, thus the ecological governance should be further strengthened.
WANG Zhigang, WANG Jiale, HAN Pei, LIU Honghu, YANG Kun, ZHANG Chao, ZHANG Pingcang
Characteristics analysis and spatial distribution mapping of soil loss tolerances in Beijing
[Background] Soil loss tolerances is a fundamental basis for accessing soil loss and ecological conditions, thus analyzing its characteristics plays an important role in practice for providing a guidance to local prevention and control of soil erosion and ecological construction. Current soil loss tolerances are for large regions and they are too general to reflect the detailed variation in soil erosion within projects for soil erosion and water loss control. This study analyzes the characteristics of soil loss tolerance distribution in Beijing, providing data for setting proper soil tolerances and supporting soil and water conservation management in different districts. [Methods] Soil loss tolerances of soil genus in Beijing were calculated by the productivity index model and soil thickness. The values of soil subgroups and groups were then obtained by an area weighted method according to those of soil genus and these values were analyzed and compared by nested variance analysis and multiple comparisons. Finally, a distribution map of the soil loss tolerance in Beijing was made by the values for soil subgroups which acted as the mapping unit. [Results] In Beijing, the soil loss tolerance of main soil genus were between 50-313 t/(km2·a) with an area weighted mean of 194 t/(km2·a). In most parts of Beijing, these values were <150 t/(km2·a), 53.4% of the total area were in the range of 100-150 t/(km2·a) and 23.8% were in the range of 50-100 t/(km2·a). These obtained soil loss tolerances of soil subgroups were significantly different while those of soil groups were not significantly different. The soil loss tolerance of skeletal soils (<100 t/(km2·a)) were lower than others. It indicated that these soils had been severely eroded by washing off fine particles during the formation process, only remaining a thin layer of coarse fragments with low fertility. Mountain soils were suffering severe erosion, and the soil loss tolerance became lower with the increase of erosion intensity. The soil loss tolerance values were <150 t/(km2·a) in the mountain area in west, north, and northeast of Beijing, while they were >150 t/(km2·a) in the plain area in the southeast. [Conculsions] The difference among soil loss tolerance cannot be shown in the soil group level but it is clear in the soil subgroup level. Although the soil loss tolerances in soil genera level are more detailed, it is not easy to use and manage the scattered patches on the map because of their great number. Therefore, it is optimal to select the values in subgroup level as the mapping unit to make soil loss tolerance distribution map in Beijing.
GONG Xinglong, CHEN Kunting, CHEN Xiaoqing, YOU Yong, CHEN Jiangang, ZHAO Wanyu, LANG Jie
On the causes of “8·4” debris flow disaster at Zechawa Gully
[Background] On 4 August 2016, a debris flow event occurred in Zechawa Gully, Jiuzhai Valley, Sichuan province. During this debris flow event, the pedestrian walkways were buried, and the only scenic road from Nuorilang Waterfall to Long Lake was blocked, causing serious impact on the scenic area. The rainfall data from precipitation stations showed that the maximum 1 h rainfall and 24 h cumulative rainfall on 4 August 2016 were 10.0 mm and 17.5 mm respectively, which were far below the rainfall intensity of the study area at once in 10-year, and the scale of the debris flow disaster was inconsistent with rainfall. [Methods] To clarify the cause of the debris flow disaster, field investigations were conducted, and the debris flow peak discharge was obtained by the cross-section survey method, rain-flood method and dam breach analysis. [Results] The debris flow peak discharges at the two typical mud mark cross sections estimated by the cross-section survey method were 33.29 m3/s and 36.69 m3/s respectively, which were similar to the debris flow peak discharge (32.73 m3/s) at once in 20-year period. The debris flow peak discharges calculated by dam breach analysis varied in 36.5 m3/s to 43.6 m3/s, which were similar with the peak discharge obtained by the cross-section survey method. The total volume of the debris flow material calculated by the equation recommended by Specification of Geological Investigation for Debris Flow Stabilization was 1.48×104 m3, which was consistent with the field measured value 1.39×104 m3, and further supported the calculated debris flow peak discharge obtained from the cross-section survey method and dam breach analysis. [Conculsions] Based on our research results, the debris flow on 4 August 2016 was caused by dam breach, and the scale of the debris flow was equivalent to that at once in 20-year. The destruction of check dam in the channel has produced an amplification effect on the peak discharge, aggravating the debris flow disaster. Affected by the Ms 7.0 Jiuzhaigou earthquake recently, more than 20×104 m3 of loose material are active for debris flow events in the future, and the frequency and scale of debris flow disasters in Zechawa Gully will increase in the future. The original design standard of the debris flow mitigation countermeasures for once in 20-year was low, and the engineering countermeasures with the design standard of 50-year period should be taken after the Ms 7.0 Jiuzhaigou earthquake, and concrete materials should be used to construct control projects (such as check dams) to reduce the risk of breach.
SONG Yuanyuan, XING Xianshuang, QI Fei, LIU Xia, DONG Mingming, WU Zhenyu, LI Xiang, YAO Xiaoyou
Spatial and temporal distribution patterns of agroforestry activities and its related characteristics of soil and water loss
[Background] In recent years, due to the improvements of landuse transfer policies, the development of agroforestry activities had been enhanced significantly. However, the increasing of agroforestry activities aggravated soil and water loss, especially in hilly and mountain areas. Therefore, it became very important to understand the patterns and relationships between the agroforestry activities and its related soil and water loss. [Methods] Rongcheng, the Key Control Area of Soil Erosion in Shandong province, was selected as the study area. In this area, remote sensing, field investigation, and soil erosion simulation were used to analyze the spatial and temporal distribution patterns of agroforestry activities. In addition, the effects of agroforestry activities on soil and water loss and its related environmental factors were quantified in this study. [Results] 1) From 2014 to 2017, there were 36 plots (>2 hm2, max.=62.5 hm2, and min.=2.58 hm2) disturbed by agroforestry activities with a total area of 591.33 hm2 involving 11 administrative districts. 2) Within the disturbed 36 plots, agroforestry activities resulted in the changes in engineering practices, micro-topographies (slope and slope length), and understory vegetation cover. Among those changes, the low-standard terraced farmland was transferred to high-benefit economic forest such as orchard with higher slope (mainly 2°-5°, followed by 5°-8°, and >8° accounting for 12%, and max.=19°), and longer slope length (avg.=300-500 m and max.=750 m). The vegetation coverage changed from high coverage to low coverage, and then steadily increased. 3) The agroforestry activities aggravated the severity of soil and water loss in those disturbed plots, and the intensity of soil erosion jumped from slight level to light and medium levels. Moreover, the erosion modulus of post disturbed plots increased 6-11 times than prior disturbed plots, and the disturbed plots did not recover to the original conditions even after a 4-year recovery period. [Conclusions] Therefore, the increasing of agroforestry activities may accelerate the soil and water loss through destroying the understory vegetation cover and modifying local micro-topographies, especially in hilly and mountain areas. This research revealed the realistic situations and difficulties to restore the disturbed areas of agroforestry activities. Moreover, for the disturbed areas, more practical managements and policies need to be implemented to control agroforestry activities and soil erosion.
Response of biomass and antioxidant enzyme activities of Gymnocarpos przewalskii seedlings to drought stress
[Background] Drought stress affects the biomass accumulation and distribution between the aboveground and roots, results in excessive accumulation of active oxygen and lipid peroxidation, while plants evolve antioxidant enzyme system. Gymnocarpos przewalskii originates from Tethys, is the rare relic species of the Tertiary period in the desert area of central Asia and plays an important role in keeping stable of desert ecosystem. The research is to analyze the biomass accumulation and distribution pattern of the seedlings, the antioxidant characteristics of the leaves and roots under drought stress for revealing the drought resistance mechanism and to provide some theoretical basis for rare species conservation and vegetation restoration in desert area. [Methods] Taking one-year-old seedlings of Gymnocarpos przewalskii as the experiment material and using pot experiment, four water gradients were set, including the control, light water stress, moderate water stress and severe water stress, the soil water content was kept at 45%-50%, 30%-35%, 15%-20% and 5%-10% of the field capacity respectively by weighing method, with 10 repetitions per pot experiment, leaves and roots were collected after being treated 90 d and the biomass and physiological indexes were measured. The difference in biomass, root-shoot ratio, malondialdehyde (MDA) content and antioxidant enzyme activities in leaves and roots was analyzed. [Results] Under drought stress, biomass of the whole plant and the aboveground significantly reduced, the underground biomass decreased remarkably under the moderate and severe stress, and the aboveground biomass decreased more, thus the root-shoot ratio increased and was significantly higher under the severe stress compared to the control. MDA content in roots and leaves increased remarkably under drought stress compared with the control, the higher the drought stress degree was, the more serious the peroxidation damage was, and the increase amplitude of MDA content in roots was higher than that in leaves under the same treatment. With the increase of the drought stress, superoxide dismutase (SOD) activity in leaves and roots first significantly increased then decreased, it was obviously higher than the control in roots but significantly lower in leaves under severe stress, which indicated that the scavenging effect of SOD to reactive oxygen was limited especially in leaves. Peroxidase (POD) activity markedly decreased in roots but significantly increased in leaves under stress treatments compared to the control, showing that POD played obvious antioxidation in leaves, and POD was not the key enzyme scavenging H2O2 in the roots under drought stress. Catalase (CAT) activity increased significantly in leaves and roots under drought stress. Ascorbate peroxidase (APX) activity showed increasing trend under stress treatment, the difference was significant among the treatments in roots, and it changed markedly under moderate and severe stress in leaves. [Conculsions] Drought stress clearly affected the growth of Gymnocarpos przewalskii seedlings, but it could increase biomass distribution to roots to adapt the drought. Drought stress caused obvious peroxidation damage to the leaf and root membrane system, and the damage was more serious in roots. The leaves protected the membrane system by synergistic action of SOD, CAT, POD and APX enzymes, and the roots mainly reduced damage of reactive oxygen by SOD, CAT and APX.
YE Xin, YU Feiyan, ZHOU Runhui, WANG Kunyue, WANG Min, DONG Hongjun, HAO Jianfeng
Differences of species diversity of herbaceous vegetation and soil anti-scourability in different habitats of riparian zone along Wenjiang Section of Jinma River
[Background] Riparian plants have the effect of preventing riverbank erosion and collapse, while river development, quarrying and sand dug activities have destroyed the vegetation in the riparian zone, resulting in a decline in plant diversity and changes in soil properties, and the ability of riverbanks to prevent floods is weakened. Therefore, this study tried to explore the differences in species diversity of different plant communities and the differences of their soil anti-scourability, with the purpose of screening out dominant species for vegetation restoration. [Methods] Five typical plots of different habitat types (gravel land, flood land, Phragmites australis land, Saccharum arundinaceum land, and bunker land) were selected in the riparian zone of Jinma River and three plots of each type were selected, totaling 15 plots. The name, coverage and other indicators of the herb were recorded for calculating species diversity indices. The undisturbed soil scouring flume method was used to determine the soil erosion resistance. Finally, the correlation analysis of the species diversity indexes and soil erosion resistances were carried out. [Results] 1) The riparian zone was rich in herbaceous plants with a total of 39 families, 94 genera and 136 species, mainly Poaceae and Compositae. Shannon-Wiener diversity index H, Simpson dominance index H' and the Pielou uniformity index Jsw changed similarly, the maximum value appeared in gravel land closest to the river, the minimum appeared in P. australis land with the highest terrain. As for species richness index (D), the bunker land was the highest and the S. arundinaceum land was the lowest. 2) With the erosion processing, the sediment yield of runoff in each habitat type decreased continuously, and the soil anti-scourability enhanced continuously. The soil anti-scourability index (IAS) from the largest to the smallest was P. australis land (24.53 L/g) > flood land (4.10 L/g) > S. arundinaceum land (1.06 L/g) > gravel land (0.31 L/g) > bunker land (0.27 L/g), among which P. australis land, flood land and S. arundinaceum land presented fine soil anti-scour performance. 3) Correlation analysis showed that soil anti-scourability index (IAS) was negatively correlated with Shannon-Wiener diversity index H, Simpson index H' and Pielou uniformity index Jsw, suggesting that the soil anti-scourability of habitat types with high species diversity was poor. [Conculsions] To sum up, bunker land and gravel land have the highest level of species diversity. P. australis land, flood land and S. arundinaceum land have strong anti-scourability. Therefore, as the dominant species of P. australis land, flood land and S. arundinaceum land, plant P. australis, Imperata cylindrica and S. arundinaceum have good effects of water and soil conservation and bank protection. They can be used as a good species choice for vegetation restoration in the riparian zone.
XIAO Shihong, ZHANG Weiqiang, HUANG Fangfang, GAN Xianhua, CAI Jian, ZHU Ziwei
Effect of CO2 enrichment on photosynthetic characteristics in the leaves of Heritiera littoralis seedlings under salinity treatment
[Background]Heritiera littoralis is an endangered semi mangrove tree species. Recently, the community structure, biological characteristics, medicinal value, fruit characteristics and germination technology and genetic diversity of H. littoralis have mainly been analyzed by scholars, but the high CO2 concentration on photosynthetic characteristics in the leaves of H. littoralis seedlings under salinity treatment has been less investigated. It is important to explore the effects of elevated CO2 on photosynthesis characteristics in H. littoralis under salinity treatment, which is essential to provide references for the application of H. littoralis to the vegetation restoration in coastal areas. [Methods] 1-year-old H. littoralis seedlings were used for comparison test in the green house of Guangdong Academy of Forestry in Guangzhou. Salinity treatment was simulated using salt solution concentration gradients of 0 (CK) and 2.5% (salinity treatment) at different CO2 concentration (400, 600 and 800 μmol/mol). There were 16 repeats in each concentration, thus totally 96 pots. After 60 days, photosynthetic physiological parameters were measured by LI-6800 photosynthesis instrument (LI-COR, USA). Then modified rectangular hyperbolic model was adopted to fit the photosynthesis light-response curves at different CO2 concentration and CO2 response curves of H. littoralis leaves of salinity treatment. [Results] 1) After the experiment treatment, with the increase of CO2 concentration, net photosynthetic rate (Pn), maximum net photosynthetic rate (Pnmax), apparent quantum yield (AQY), light saturation point (LSP), dark respiration rate (Rd), water use efficiency (WUE) and intercellular CO2 concentration (Ci) in the leaves of H. littoralis seedlings increased, while light compensation point (LCP), transpiration rate (Tr) and stomatal conductance (Gs) decreased. 2) At the same CO2 concentration, Pn, Pnmax, AQY, LSP, LCP, Rd, Tr and Gs under salinity treatment were lower than those under control, while the difference of WUE and Ci between the two treatment groups were not significant. 3) With the increase of photosynthetic active radiation (PAR), Tr and Gs showed an increasing trend, WUE increased first and then decreased slowly, while Ci decreased linearly and then reached a steady state. 4) Maximum carboxylation rate (Vcmax), maximum rate of electron transport (Jmax), triose-phosphate utilization efficiency (TPU), Pnmax, initial carboxylation efficiency (CE) and photorespiration rate (RP) under salinity treatment were lower than those under control, while CO2 saturation point (Cisat) and CO2 compensation point (Γ) showed an opposite trend. 5) Tr and Gs decreased with the increase of CO2 concentration, while WUE and Ci presented linear increase. [Conclusions] The increase of CO2 concentration promotes the increase of Pn, Pnmax, AQY, LSP, Rd, WUE and Ci. Higher CO2 concentration in the environment can increase the photosynthetic efficiency of H. littoralis leaves, especially when the light intensity is high. The salt stress can reduce the photosynthetic rate of H. littoralis leaves significantly. The results of this research indicate that the increase of CO2 concentration promotes the growth of H. littoralis seedling, while salinity treatment inhibits its growth.
ZHANG Wanlu, YUAN Zaijian, LI Dingqiang, ZHENG Mingguo, LIAO Yishan, CAI Qiangguo, HUANG Yanhe, CAI Chongfa, NIU Dekui, WANG Zhiguo
Discussion of the “Benggang” concept and its English translation
[Background] Benggang is a typical geo-hazard in the tropical and subtropical areas of South China with the greatest scale of water and soil erosion and serious ecological damage. It is an erosional geomorphology that the soil in the red soil hilly of south China collapses continuously along the gully wall, under the action of hydraulic and gravity, and finally forms a huge wound. With the urgent attention of the country to the management of Benggang erosion in South China, this niche geomorphology vocabulary now gradually tends popular. In addition, with the exchange and cooperation of soil and water erosion globally, the research achievement for Benggang has attracted international attention. [Methods] In this paper, the concept and connotation of Benggang were discussed, based on the comprehensive summary of the development, morphology and destination of Benggang. On the other hand, the English translation for Benggang was analyzed by comparing the domestic and international erosional landforms, and by discussing the present translations for Benggang. [Results] 1) Benggang is usually developed in tropical and subtropical granite areas with 20-50 m weathering crust, and exists in a small amount in glutenite, argillaceous shale, phyllite and other rock areas. There are about 239,100 Benggangs in China and the average annual sediment yield by Benggang erosion is about 67,239,000 t in recent decades. 2) A Benggang system can be divided into five parts: upper catchment area, collapsing wall, colluvial deposit, scour channel, and alluvial fan. Typical Benggang landforms are characterized by arc-shaped, linear-shaped, ladle-shaped, composite-shaped, and claw-shaped. 3) According to the development conditions, mechanism, and region of Benggang, it is different from the erosion landforms in foreign countries. Therefore, there is no appropriate native English word that can be used as the translation of Benggang. In addition, Benggang is also significantly different from the soil erosion landforms in China, such as landslide and debris flow, which are dominated by gravity erosion. At present, the most common English translations of Benggang include Benggang (transliteration) and collapsing gully (translating meaning). In recent three years, 23 international journal articles were published using Benggang, with an average growth rate of 56.4%, and 33 articles were published using collapsing gully, with an average growth rate of 40.1%. This shows Benggang transliteration has been recognized to a large extent. [Conculsions] Benggang transliteration is applied to highlight its unique cultural characteristics and cultural connotation, which will also contribute to the understanding of domestic and foreign scholars for Benggang's uniqueness and further promote the internationalization of soil and water conservation research in China.
LI Yifan, GAN Xianhua, ZHANG Weiqiang, XIAO Shihong, HUANG Yuhui, HUANG Fangfang
Niche characteristics of dominant species in the forest community in Yantian district of Shenzhen city
[Background] There are both mountainous and coastal landforms in the Yantian district of Shenzhen city. Studying on the niche characteristics of dominant species in tree layer and shrub layer of the forest community in Yantian district has important research value for the study of soil erosion in the transition from mountain to coastal landforms, and provides a corresponding scientific reference for local vegetation allocation and soil and water conservation projects and theoretical support for forest resource management and operation. [Methods] To explore the niche characteristics of the dominant species in the forest community in Yantian district of Shenzhen city, 6 large quadrats representing regional population characteristics were selected for investigation in August 2018. Data on tree number, tree height, DBH, crown diameter and height under the branches of tree layer species, as well as data on tree number, base diameter, crown diameter and height of the shrub layer species were investigated. Niche breadth and niche overlap were used to discuss the niches of the dominant species in the tree and shrub layers of the community on the basis of field plot surveys. [Results] 1) The Levins (BL) and Shannon (BS) niche breadth indexes for Psychotria asiatica in the shrub layer were 2.77 and 0.10, ranking 5 and 14, respectively, but the importance value was 18.02. 2) In the tree layer, the niche width of Ficus variolosa Lindl. ex Benth. was the largest, and the BL and BS were 5.08 and 1.70, respectively and, the niche width of Rhododendron henryi Hance was the smallest. 3) In the shrub layer, the niche width of Diplospora dubia (Lindl.) was the largest, and the BL and BS were 4.67 and 1.26, respectively, and the niche widths of Enkianthus quinqueflorus Lour. and Symplocos stellaris Brand was the smallest. The average niche overlaps of the tree layer and shrub layer were 0.40 and 0.32, respectively, and the overlap values of most species pairs were below 0.5. In addition, the niche breadths of Schima superba Gardn. et Champ. and Acacia confusa Merr. in the tree layer were relatively small, but the niche overlap reached 0.9. [Conculsions] The Levins and Shannon niche breadth index values ranked in the same order but were different than the important values. The niche overlap of species pairs with larger niche breadths was larger, but they were not completely consistent. The competition of the dominant species in the community of the study area was not intense and the community was relatively stable.
Analysis of research progress on check-dam in China
[Background] As an important soil and water conservation engineering measure to prevent and control soil erosion in the Loess Plateau, check-dams have great social, economic and ecological benefits, which have attracted much attention of researchers. However, few researchers have elaborated on the research progress of check-dam in China from the perspective of scientific literature. In order to clarify the current research situation of check-dams in China, we analyzed and summarized its research topics and the evolution of its phased frontier. [Methods] Considering that there are some alternative names related to check-dam in Chinese, the retrieval formula was determined as (TI or KY = ‘check-dam’ or ‘juqiu’ or ‘dam land’ or ‘slurry-fall dam’ or ‘gully dam system’ or ‘small watershed dam system’ or ‘key dam’). We chose CNKI, the largest Chinese literature database, as the retrieval source. After retrieving and clearing data, we excluded repetitive and low-correlation papers. Meanwhile, we retrieved Web of Science and Scopus and other databases, and the retrieval results were less than 100 papers. And we found that most of the papers did not deviate from research topics in China, thus we did not count those retrieval results. At last, 2 158 papers related to check-dam from 1954 to 2019 were studied and analyzed by CiteSpace, VOSviewer and other tools. In addition, we cited 21 necessary references, and they explain the background and knowledge of check-dams in China. [Results] 1) Along with the changes of times, the degree of attention and characteristics of the research on the check-dam are changing.The amount of research papers on check-dam varies greatly in different periods, reaching its peak in 2003 and tending to be stable in recent years. 2) Research institutions in this field have distinct regional characteristics. The top 20 high-yield institutions are basically distributed in Shaanxi province, Shanxi province, and Gansu province. On the other hand, the degree of cooperation between research institutions is low. There is still much room for mutual cooperations between institutions. 3) The research on check-dam can be roughly divided into three aspects: construction of check-dam, comprehensive management of dam systems in small watersheds, and management of check-dam. The research frontier also has great changes in different periods. 4) In the future, the research may focus on the further optimization of dam layout, the relationship between various levels, the exploration of new construction technology and the risk control of dams. [Conculsions] Through summarizing and analyzing research progress and research hot topics on check-dam in China, it is conducive to researchs to comprehensively understand research history and present situation of check-dam in China.The layout of dam system and its impact still need continuous attention, and the application of new technology, dam system safety and risk control may be the focus of attention in the future. Strengthening the research in these aspects is conducive to the further development of check-dam.
