Litter decomposition and C and N dynamics as affected by N additions in a semi-arid temperate steppe,Inner Mongolia of China

Litter decomposition is the fundamental process in nutrient cycling and soil carbon（C） sequestration in terrestrial ecosystems. The global-wide increase in nitrogen（N） inputs is expected to alter litter decomposition and,ultimately, affect ecosystem C storage and nutrient status. Temperate grassland ecosystems in China are usually N-deficient and particularly sensitive to the changes in exogenous N additions. In this paper, we conducted a 1,200-day in situ experiment in a typical semi-arid temperate steppe in Inner Mongolia to investigate the litter decomposition as well as the dynamics of litter C and N concentrations under three N addition levels（low N with 50 kg N/（hm2？a）（LN）, medium N with 100 kg N/（hm2？a）（MN）, and high N with 200 kg N/（hm2？a）（HN）） and three N addition forms（ammonium-N-based with 100 kg N/（hm2？a） as ammonium sulfate（AS）, nitrate-N-based with 100 kg N/（hm2？a） as sodium nitrate（SN）, and mixed-N-based with 100 kg N/（hm2？a） as calcium ammonium nitrate（CAN）） compared to control with no N addition（CK）. The results indicated that the litter mass remaining in all N treatments exhibited a similar decomposition pattern： fast decomposition within the initial 120 days, followed by a relatively slow decomposition in the remaining observation period（120–1,200 days）. The decomposition pattern in each treatment was fitted well in two split-phase models, namely, a single exponential decay model in phase I（〈398 days） and a linear decay function in phase II（≥398 days）. The three N addition levels exerted insignificant effects on litter decomposition in the early stages（〈398 days, phase I; P〉0.05）. However, MN and HN treatments inhibited litter mass loss after 398 and 746 days, respectively（P〈0.05）. AS and SN treatments exerted similar effects on litter mass remaining during the entire decomposition period（P〉0.05）. The effects of these two N addition forms differed greatly from those of CAN aft     

The return and loss of litter phosphorus in different types of sand dunes in Horqin Sandy Land, northeastern China

Litter phosphorus(P) return is important to maintain the P cycle and balance in the sandy land of arid areas.In this study,we determined the loss and return of litter P in sand dune areas and elucidated their relationship.We investigated litter production and litter P amount,and simulated leaf litter moving dynamics to understand the relationships between the loss of litter P and the total litter P,and between the return of litter P and the total litter P in active(AD),semi-stabilized(SSD) and stabilized(SD) dunes in Inner Mongolia,northeastern China.The vegetation litter P was 12.6,94.5,and 201.6 mg P/m2 in AD,SSD,and SD,respectively.A significant movement and loss of leaf litter P with time occurred on the three types of sand dunes.As a result,the loss of P was 7.4,46.9,and 69.8 mg P/m2 and the return of P was 5.5,47.6,and 131.8 mg P/m2 in AD,SSD,and SD,respectively.The relationship between both loss and return of P and total litter P in AD,SSD,and SD was revealed by linear regression.The slope of the regression line indicated the rate of loss or return of litter P.From AD to SD,the loss rate showed a declining slope(0.52,0.32,and 0.17 for AD,SSD,and SD,respectively),and the return rate showed a rising slope(0.48,0.67,and 0.83 for AD,SSD,and SD,respectively).The loss of litter P should be regarded in the local management of vegetation and land in sand dune areas.Improved vegetation restoration measures are necessary to decrease litter P loss to maintain the stability of ecosystems in sand dune areas.     

Community structure and carbon and nitrogen storage of sagebrush desert under grazing exclusion in Northwest China

Overgrazing is regarded as one of the key factors of vegetation and soil degradation in the arid and semi-arid regions of Northwest China.Grazing exclusion(GE)is one of the most common pathways used to restore degraded grasslands and to improve their ecosystem services.Nevertheless,there are still significant controversies concerning GE’s effects on grassland diversity as well as carbon(C)and nitrogen(N)storage.It remains poorly understood in the arid desert regions,whilst being essential for the sustainable use of grassland resources.To assess the effects of GE on community characteristics and C and N storage of desert plant community in the arid desert regions,we investigated the community structure and plant biomass,as well as C and N storage of plants and soil(0-100 cm depth)in short-term GE(three years)plots and adjacent long-term freely grazing(FG)plots in the areas of sagebrush desert in Northwest China,which are important both for spring-autumn seasonal pasture and for ecological conservation.Our findings indicated that GE was beneficial to the average height,coverage and aboveground biomass(including stems,leaves and inflorescences,and litter)of desert plant community,to the species richness and importance values of subshrubs and perennial herbs,and to the biomass C and N storage of aboveground parts(P<0.05).However,GE was not beneficial to the importance values of annual herbs,root/shoot ratio and total N concentration in the 0-5 and 5-10 cm soil layers(P<0.05).Additionally,the plant density,belowground biomass,and soil organic C concentration and C storage in the 0-100 cm soil layer could not be significantly changed by short-term GE(three years).The results suggest that,although GE was not beneficial for C sequestration in the sagebrush desert ecosystem,it is an effective strategy for improving productivity,diversity,and C and N storage of plants.As a result,GE can be used to rehabilitate degraded grasslands in the arid desert regions of Northwest China.     

Distribution pattern of Caragana species under the influence of climate gradient in the Inner Mongolia region,China

There is a strong climate gradient in the Inner Mongolia region, China, with solar radiation and air temperature increasing but precipitation decreasing gradually from the northeast to the southwest. Sixteen Cara- gana species exist in the Inner Mongolia region. These Caragana species exhibit a distribution pattern across moisture zones and form a geographical replacement series. In order to examine the mechanisms responsible for Caragana species distribution pattern, we selected 12 Caragana species that exhibit a distinct distribution pattern across multiple moisture zones in the Inner Mongolia region, and determined the relationships between the leaf ecological and physiological traits of these Caragana species and the aridity index and solar radiation. Along with the climatic drought gradient and the solar radiation intensification from the northeast to the southwest, leaf eco- logical characteristics of Caragana species changed drastically, i.e. the leaf shape gradually turned from flat into tegular or tubbish; the leaf hair became denser, longer and lighter in color; the leaf area, leaf biomass and specific leaf area(SLA) decreased significantly; the leaf thickness and the ratio of leaf thickness to leaf area increased sig- nificantly; and the leaf chlorophyll content decreased significantly. As the climatic drought stress increased, osmotic potentials of the main osmotic adjustment substances and the cytoplasmic ion concentration of Caragana species increased significantly. Meanwhile, the total and free water contents and water potential of leaves decreased sig- nificantly; the ratio of bound to free water increased significantly; the stomatal conductance and transpiration rate reduced significantly; and the water use efficiency(WUE) increased significantly. In addition, with the intensification of climatic drought stress, peroxidase(POD) and superoxide dismutase(SOD) activities in leaves increased sig- nificantly. As a result, the malondialdehyde(MDA) content increased while the oxygen free radical content decreased. Our results showed that most of the leaf ecological and physiological traits of the 12 Caragana species varied in ac- cordance with the climatic drought gradient in the Inner Mongolia region, which reflected the adaptation of the Cara- gana species to the local climate conditions. With relatively more active metabolism and faster growth, the Caragana species in the northeast had strong competitive abilities; on the other hand, with stronger resistance to climatic drought stress, the Caragana species in the southwest could survive in harsh environments. Based on our results, we con- cluded that both the environmental gradients and the adaptive responses of Caragana species to their environments played important roles in the formation of the Caragana species distribution pattern across the Inner Mongolia region.     

Changes in soil organic carbon and nitrogen after 26 years of farmland management on the Loess Plateau of China

Soil carbon(C) and nitrogen(N) play a crucial role in determining the soil and environmental quality. In this study, we investigated the effects of 26 years(from 1984 to 2010) of farmland management on soil organic carbon(SOC) and soil N in abandoned, wheat(Triticum aestivum L.) non-fertilized, wheat fertilized(mineral fertilizer and organic manure) and alfalfa(Medicago Sativa L.) non-fertilized treatments in a semi-arid region of the Loess Plateau, China. Our results showed that SOC and soil total N contents in the 0–20 cm soil layer increased by 4.29(24.4%) and 1.39 Mg/hm2(100%), respectively, after the conversion of farmland to alfalfa land. Compared to the wheat non-fertilized treatment, SOC and soil total N contents in the 0–20 cm soil layer increased by 4.64(26.4%) and 1.18 Mg/hm2(85.5%), respectively, in the wheat fertilized treatment. In addition, we found that the extents of changes in SOC, soil total N and mineral N depended on soil depth were greater in the upper soil layer(0–30 cm) than in the deeper soil layer(30–100 cm) in the alfalfa land or fertilizer-applied wheat land. Fertilizer applied to winter wheat could increase the accumulation rates of SOC and soil total N. SOC concentration had a significant positive correlation with soil total N concentration. Therefore, this study suggested that farmland management, e.g. the conversion of farmland to alfalfa forage land and fertilizer application, could promote the sequestrations of C and N in soils in semi-arid regions.     

Vertical root distribution and root cohesion of typical tree species on the Loess Plateau,China

Black locust(Robinia pseudoacacia L.) and Chinese pine(Pinus tabulaeformis Carr.) are two woody plants that are widely planted on the Loess Plateau for controlling soil erosion and land desertification. In this study, we conducted an excavation experiment in 2008 to investigate the overall vertical root distribution characteristics of black locust and Chinese pine. We also performed triaxial compression tests to evaluate the root cohesion(additional soil cohesion increased by roots) of black locust. Two types of root distribution, namely, vertical root(VR) and horizontal root(HR), were used as samples and tested under four soil water content(SWC) conditions(12.7%, 15.0%, 18.0% and 20.0%, respectively). Results showed that the root lengths of the two species were mainly concentrated in the root diameter of 5–20 mm. A comparison of root distribution between the two species indicated that the root length of black locust was significantly greater than that of Chinese pine in nearly all root diameters, although the black locust used in the comparison was 10 years younger than the Chinese pine. Root biomass was also significantly greater in black locust than in Chinese pine, particularly in the root diameters of 3–5 and 5–10 mm. These two species were both found to be deep-rooted. The triaxial compression tests showed that root cohesion was greater in the VR samples than in the HR samples. SWC was negatively related to both soil shear strength and root cohesion. These results could provide useful information on the architectural characteristics of woody root system and expand the knowledge on shallow slope stabilization and soil erosion control by plant roots on the Loess Plateau.     

Summer atmospheric boundary layer structure in the hinterland of Taklimakan Desert,China

Understanding the characteristics of the structure of desert atmospheric boundary layer and its land surface process is of great importance to the simulations of regional weather and climate.To investigate the atmospheric boundary layer structure and its forming mechanism of Taklimakan Desert,and to improve the accuracy and precision of regional weather and climate simulations,we carried out a GPS radiosonde observation experiment in the hinterland of Taklimakan Desert from 25 June to 3 July,2015.Utilizing the densely observed sounding data,we analyzed the vertical structures of daytime convective boundary layer and nighttime stable boundary layer in summer over this region,and also discussed the impacts of sand-dust and precipitation events on the desert atmospheric boundary layer structure.In summer,the convective boundary layer in the hinterland of Taklimakan Desert developed profoundly and its maximum height could achieve 4,000 m;the stable boundary layer at nighttime was about 400–800-m thick and the residual mixing layer above it could achieve a thickness over 3,000 m.Sand-dust weather would damage the structures of nighttime stable boundary layer and daytime convective boundary layer,and the dust particle swarm can weak the solar radiation absorbed by the ground surface and further restrain the strong development of convective boundary layer in the daytime.Severe convective precipitation process can change the heat from the ground surface to the atmosphere in a very short time,and similarly can damage the structure of desert atmospheric boundary layer remarkably.Moreover,the height of atmospheric boundary layer was very low when raining.Our study verified the phenomenon that the atmospheric boundary layer with supernormal thickness exists over Taklimakan Desert in summer,which could provide a reference and scientific bases for the regional numerical models to better represent the desert atmospheric boundary layer structure.     

Above- and below-ground biomass and carbon stocks of different tree plantations in central Iran

In arid and semi-arid lands using industrial wastewater for irrigating tree plantations offers a great opportunity to fulfill the purpose of Clean Development Mechanism by sequestering carbon in living tissues as well as in soil. Selection of tree for plantation has a great effect on the goal achievements, especially when the managers deal with afforestation projects rather than reforestation projects. The objective of this study was to quantify the above- and below-ground biomass accumulation and carbon storages of the 17-year-old monoculture plantations of mulberry(Morus alba L.), black locust(Robinia pseudoacacia L.), Eldar pine(Pinus eldarica Medw.) and Arizona cypress(Cupressus arizonica Greene) planted in central Iran. To assess the potential carbon storage, we destructively measured individual above- and below-ground tree biomass and developed and scaled models at stand level. Furthermore, carbon content at three soil depths(0–15, 15–30, 30–45 cm), the litter and the understory were assessed in sample plots. The results showed that the total amount of carbon stored by Eldar pine(36.8 Mg/hm2) was higher than those stored by the trees in the other three plantations, which were 23.7, 10.0, and 9.6 Mg/hm2 for Arizona cypress, mulberry and black locust plantations, respectively. For all the species, the above-ground biomass accumulations were higher than those of the below-ground. The root mass fractions of the deciduous were larger than those of the coniferous. Accordingly, the results indicate that the potential carbon storages of the coniferous were higher than those of the deciduous in arid regions.     

Interaction between Cd and Pb in the soil-plant system: a case study of an arid oasis soil-cole system

The Hexi Corridor,our study area,is located in Northwest China and is also the most developed area of oasis farming in arid regions of Northwestern China.However,the rapid development of metallurgy and chemical industries in this region poses a great threat to the accumulation of heavy metals in crops.The objectives of this study are(1)to determine the influence of heavy metals on plant growth;(2)to assess the translocation capability of heavy metals in soil-plant system;and(3)to investigate the interaction between heavy metals.Pot experiments were conducted on cole(Brassica campestris L.)grown in the arid oasis soils singly and jointly treated with cadmium(Cd)and lead(Pb).Nine treatments were applied into the pots.Under the same planting conditions,three scenarios of Cd,Pb and Cd–Pb were designed to compare the interaction between Cd and Pb.The results showed that the response of cole weights to Cd,Pb and Cd–Pb treatments was slight,while Cd and Pb uptakes in cole were more sensitive to the single effects of Cd and Pb concentration in soils from the lower treatment levels.Under the influence of the single Cd,Pb and joint Cd–Pb treatments,Cd concentrations were lower in the cole roots than in the shoots,while for Pb,the results were opposite.Comparison studies revealed that the interaction of Cd and Pb could weaken the cole’s ability to uptake,concentrate and translocate heavy metals in arid oasis soils.     

Shrub presence and shrub species effects on ground beetle assemblages (Carabidae,Curculionidae and Tenebrionidae) in a sandy desert,northwestern China

Shrub presence has an important effect on the structuring of ground beetles in desert ecosystems. In this study, in order to determine how shrubs and different species influence ground beetle assemblages in a sandy desert scrubland dominated by two different shrub species, namely Calligonum mongolicum and Nitraria sphaerocarpa, we sampled the ground beetles using pitfall traps during spring, summer and autumn in 2012. At the community level, the activity density of the ground beetles was shown to be significantly higher under shrubs than in intershrub bare habitats in spring; but an opposite pattern occurred in autumn, suggesting the presence of season-specific shrub effects on the activity density of the ground beetles. Meanwhile, at the trophic group level, the activity density and species richness of predators were significantly greater under shrubs than in intershrub bare habitats in spring, whereas an opposite trend occurred on the activity density in autumn. N. sphaerocarpa shrubs had a positive effect on the activity density of herbivores in the three seasons, and C. mongolicum shrubs had a positive effect on the activity density of detritivores in spring and autumn. At the species level, more Microdera sp. was captured under shrubs than in intershrub bare habitats in spring. During the same time, we also found that C. mongolicum shrubs had a positive effect on Blaps gobiensis in spring, Carabus sp. in autumn, and Tentyria sp. in spring and autumn, and N. sphaerocarpa shrubs had a positive effect on Cyphogenia chinensis, Sternoplax setosa in spring and summer, and Curculionidae sp. 1 in summer and autumn. The study results suggest that shrub presence, shrub species and season variation are important factors for ground beetle assemblages in this desert ecosystem, but the responses of beetles differed among trophic and taxonomic levels.     

Contrasting effects of nitrogen addition on litter decomposition in forests and grasslands in China

Nitrogen (N) addition has profound impacts on litter-mediated nutrient cycling. Numerous studies have reported different effects of N addition on litter decomposition, exhibiting positive, negative, or neutral effects. Previous meta-analysis of litter decomposition under N addition was mainly based on a small number of samples to allow comparisons among ecosystem types. This study presents the results of a meta-analysis incorporating data from 53 published studies (including 617 observations) across forests, grasslands, wetlands, and croplands in China, to investigate how environmental and experimental factors impact the effects of N addition on litter decomposition. Averaged across all of the studies, N addition significantly slows litter decomposition by 7.02%. Considering ecosystem types, N addition significantly accelerates litter decomposition by 3.70% and 11.22% in grasslands and wetlands, respectively, clearly inhibits litter decomposition by 14.53% in forests, and has no significant effects on litter decomposition in croplands. Regarding the accelerated litter decomposition rate in grasslands due to N addition, litter decomposition rate increases slightly with increasing rates of N addition. However, N addition slows litter decomposition in forests, but litter decomposition is at a significantly increasing rate with increasing amounts of N addition. The responses of litter decomposition to N addition are also influenced by the forms of N addition, experiential duration of N addition, humidity index, litter quality, and soil pH. In summary, N addition alters litter decomposition rate, but the direction and magnitude of the response are affected by the forms of N addition, the rate of N addition, ambient N deposition, experimental duration, and climate factors. Our study highlights the contrasting effects of N addition on litter decomposition in forests and grasslands. This finding could be used in biogeochemical models to better evaluate ecosystem carbon cycling under increasing N deposition due to the differential responses of litter decomposition to N addition rates and ecosystem types.     

Dependency of litter decomposition on litter quality,climate change,and grassland type in the alpine grassland of Tianshan Mountains,Northwest China

Litter decomposition is an important component of the nutrient recycling process and is highly sensitive to climate change. However, the impacts of warming and increased precipitation on litter decomposition have not been well studied, especially in the alpine grassland of Tianshan Mountains. We conducted a manipulative warming and increased precipitation experiment combined with different grassland types to examine the impact of litter quality and climate change on the litter decomposition rate based on three dominant species (Astragalus mongholicus, Potentilla anserina, and Festuca ovina) in Tianshan Mountains from 2019 to 2021. The results of this study indicated there were significant differences in litter quality, specific leaf area, and leaf dry matter content. In addition, litter quality exerted significant effects on litter decomposition, and the litter decomposition rate varied in different grassland types. Increased precipitation significantly accelerated the litter decomposition of P. anserina; however, it had no significant effect on the litter decomposition of A. mongholicus and F. ovina. However, warming consistently decreased the litter decomposition rate, with the strongest impact on the litter decomposition of F. ovina. There was a significant interaction between increased precipitation and litter type, but there was no significant interaction between warming and litter type. These results indicated that warming and increased precipitation significantly influenced litter decomposition; however, the strength was dependent on litter quality. In addition, soil water content played a crucial role in regulating litter decomposition in different grassland types. Moreover, we found that the litter decomposition rate exhibited a hump-shaped or linear response to the increase of soil water content. Our study emphasizes that ongoing climate change significantly altered litter decomposition in the alpine grassland, which is of great significance for understanding the nutrient supply and turnover of litter.     

Rhizosphere organic phosphorus fractions of Simon poplar and Mongolian pine plantations in a semiarid sandy land of northeastern China

The aim of this study was to investigate the role of rhizosphere organic phosphorus(P) in soil P supply in semiarid forests and the effects of tree species on rihizosphere organic P. We examined organic P fractions in rhizosphere and bulk soils of mono-specific Simon poplar(Populus simonii) and Mongolian pine(Pinus sylvestris var. mongolica) plantations in a semiarid sandy soil of Horqin Sandy Land in Northeast China. Total organic P(TPo) accounted for 76% of total P across the two stands. The concentration of organic P(Po) fractions decreased in the order of Na OH-Po>Res-Po>HCl-Po>Na HCO3-Po in both plantations. The concentration of Na HCO3-Po was 38% and 43% lower in rhizosphere soil than in bulk soil in Simon poplar and Mongolian pine plantations, respectively. In contrast, total P, TPo and Na OH-Po significantly accumulated in rhizosphere soil in Simon poplar plantations, but no change in Mongolian pine plantations. Soil recalcitrant organic P fractions were positively correlated with soil organic carbon. The results suggest that rhizosphere labile organic P was an important source of plant-available P in this semiarid region, but the dynamic of rhizosphere recalcitrant organic P fractions varied with tree species and was correlated to organic carbon dynamics.     

The impact of the herbicide glyphosate on leaf litter invertebrates within Bitou bush, Chrysanthemoides monilifera ssp rotundata, infestations

Chrysanthemoides monilifera ssp rotundata (L) T Norl (Bitou bush) is a serious environmental weed along the southeast coast of Australia. The herbicide glyphosate is commonly used to control C monilifera on the New South Wales coastline, but there have been few studies examining the effects of this herbicide on invertebrate communities in the field, especially on sand dunes. Control and impact sites were selected in coastal hind dunes heavily infested with C monilifera, and the impact sites were sprayed with a 1:100 v/v dilution of glyphosate-isopropyl 360 g AE litre(-1) SL (Roundup Biactive). Leaf litter invertebrates were sampled before spraying and after spraying by collecting fixed areas of leaf litter in both the control and impact sites. Samples were sorted for particular invertebrates involved in leaf litter decomposition and some of their predators. This study did not identify any significant direct or indirect effects on leaf litter invertebrate abundance or community composition in the four months following herbicide application. The litter invertebrate assemblages were highly variable on a small spatial scale, with abiotic factors more strongly regulating leaf litter invertebrate numbers than glyphosate application. These results conflict with previous studies, indicating that the detrimental indirect effects herbicide application has on non-target litter invertebrates may depend upon the application rate, the vegetation community and structure and post-spray weather.     

Effects of the fungicide triphenyltin hydroxide on soil fauna mediated litter decomposition

The effects of an organotin pesticide, fentin hydroxide (triphenyltin (IV) hydroxide; TPTH) , on the soil fauna mediated decomposition of poplar leaf litter were examined. The responses of micro-ecosystems (MES) containing soil animals were compared to MES without fauna. The isopod Porcellio scaber Latr. was chosen as a representative saprotrophic soil fauna species. TPTH was added in four concentrations, ranging from 0.1 to 100 μg (g dry litter)^?1. MES respiration was used as a measure of decomposition rate. To measure the nitrogen mineralisation by microflora and isopods, ammonium and nitrate concentrations in the litter were determined. Analyses of the litter showed that TPTH was not degraded during the experiment. TPTH had a short-term effect on microbial respiration, which diminished after two days. Ammonium production by isopods within the system was the most sensitive parameter for the effects of TPTH . The No Observed Effect Concentration (NOEC) was 10 μg g^?1. It was concluded that, while TPTH is a fungicide, it does not seem to be very toxic to microbial respiration and ammonification as measured within the micro-ecosystem; isopod activities are more sensitive.     

典型荒漠植物凋落物分解及养分动态研究

采用分解网袋法,对古尔班通古特沙漠南缘粗柄独尾草(Eremurus inderiensis)、尖喙牻牛儿苗(Erodium oxyrrhynchum)和沙漠绢蒿(Seriphidium santolinum)3种荒漠植物叶、茎和根的分解、养分释放特性进行了研究。结果表明：叶片、茎、根系的质量损失过程均符合指数衰减模型。经过364 d的分解,粗柄独尾草叶、粗柄独尾草根、尖喙牻牛儿苗叶、尖喙牻牛儿苗茎、尖喙牻牛儿苗根、沙漠绢蒿茎、沙漠绢蒿根的失重率分别为41.96%、81.94%、42.18%、29.32%、47.02%、20.66%和20.71%;3种植物根、茎、叶的分解速率存在显著差异,分解速率依次为：粗柄独尾草根>叶;尖喙牻牛儿苗根>叶>茎;沙漠绢蒿根>茎。在整个分解过程中,N和P含量总的趋势表现为释放,叶、根凋落物质量损失与初始N、P含量显著负相关,非生物因素对其分解有重要影响。     

Litter decomposition and nutrient dynamics of three woody halophytes in the Taklimakan Desert Highway Shelterbelt

Litter decomposition is a crucial biogeochemical process for C and nutrient cycling in nutrient-constrained environments, but the controlling factors on litter decomposition in an extremely arid desert region such as the Taklimakan Desert are relatively unknown. To evaluate the litter decomposition and nutrient dynamic characteristics, five primary litter types of three woody halophytes (Haloxylon ammodendron, Calligonum arborescens, and Tamarix ramosissima) along the Taklimakan Desert Highway Shelterbelt were monitored in litterbags during 420 days, when placed on the soil surface and buried by sand, respectively. The results indicated that the decomposition rate decreased in the order of assimilative branches of H. ammodendron (HA, 0.94), branches of T. ramosissima (TB, 0.55), assimilative branches of C. arborescens (CA, 0.53), seeds of C. arborescens (CS, 0.41), and old branches of H. ammodendron (HB, 0.21) in the surface placement. In contrast, the litters buried by sand displayed a significantly accelerated decomposition rate (F?=?12.28, P?H. ammodendron and branches of T. ramosissima presented P accumulation in both placements, whereas nutrients (N, P, K) and C showed a release pattern during the litter decomposition process, which was influenced by initial litter contents and decomposition rate.     

Litter-mediated allelopathic effects of kudzu (Pueraria montana) on Bidens pilosa and Lolium perenne and its persistence in soil

This study investigated the allelopathic effects of kudzu litter on the seed germination and early growth of Bidens pilosa and Lolium perenne . The bioassays, with various concentrations (10, 20, 30, 40, and 50 g L⁻¹) of aqueous kudzu litter leachate, significantly affected the germination percentages and radicle growth of both species. These parameters decreased progressively when the seedlings were exposed to increasing concentrations of leachate. The root and shoot length, dry weight, and chlorophyll concentration of the B. pilosa and L. perenne seedlings also were significantly affected when they were grown in leachate-amended soil. However, the chlorophyll fluorescence values of the seedlings subjected to different concentrations of aqueous kudzu litter leachate indicated that the mere presence of leachate in the soil was not stressful for the plants. The seedlings of both species were under stressful conditions only when they were grown in the soil that was treated with higher concentrations of leachate (30, 40, or 50 g L⁻¹). A 6 week decomposition study of the kudzu litter in soil was conducted to observe the retention of phenolic content in the soil. The results showed that, although the concentration of dissolved organic carbon decreased with increasing decomposition, the phenolic concentration was not significantly affected when the observation period ended. This suggests that the phytotoxic properties of kudzu litter remain stable in soil systems for a considerable amount of time after incorporation into the soil.