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     

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。     

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.     

Effects of ultraviolet(UV) radiation and litter layer thickness on litter decomposition of two tree species in a semi-arid site of Northeast China

Forests and grasslands in arid and semi-arid regions receive high-intensity ultraviolet(UV) radiation year-round. However, how the UV radiation affects the litter decomposition on the forest floor remains unclear. Here, we conducted a field-based experiment in 2011 in the southeastern Horqin Sandy Land, Northeast China, to investigate the effects of UV radiation, litter layer thickness, and their interaction on the mass loss and chemical properties of decomposing litter from Xiaozhuan poplar(Populus × xiaozhuanica) and Mongolian pine(Pinus sylvestris var. mongolica) plantation trees. We found that UV radiation accelerated the decomposition rates of both the Xiaozhuan poplar litter and Mongolian pine litter. For both species, the thick-layered litter had a lower mass loss than the thin-layered litter. The interaction between UV radiation and litter layer thickness significantly affected the litter mass loss of both tree species. However, the effects of UV radiation on the chemical properties of decomposing litter differed between the two species, which may be attributed to the contrasting initial leaf litter chemical properties and morphology. UV radiation mostly had positive effects on the lignin concentration and lignin/N ratio of Xiaozhuan poplar litter, while it had negative effects on the N concentration of Mongolian pine litter. Moreover, litter layer thickness and its interaction with UV radiation showed mostly positive effects on the N concentration and lignin/N ratio of Xiaozhuan poplar litter and the ratios of C/N and lignin/N of Mongolian pine litter, and mostly negative effects on the C/N ratio of Xiaozhuan poplar litter and the N concentration of Mongolian pine litter. Together, these results reveal the important roles played by UV radiation and litter layer thickness in the process of litter decomposition in this semi-arid region, and highlight how changes in the litter layer thickness can exert strong influences on the photodegradation of litter in tree plantations.     

Effect of nitrogen and phosphorus addition on leaf nutrient concentrations and nutrient resorption efficiency of two dominant alpine grass species

Nitrogen (N) and phosphorus (P) are two essential nutrients that determine plant growth and many nutrient cycling processes. Increasing N and P deposition is an important driver of ecosystem changes. However, in contrast to numerous studies about the impacts of nutrient addition on forests and temperate grasslands, how plant foliar stoichiometry and nutrient resorption respond to N and P addition in alpine grasslands is poorly understood. Therefore, we conducted an N and P addition experiment (involving control, N addition, P addition, and N+P addition) in an alpine grassland on Kunlun Mountains (Xinjiang Uygur Autonomous Region, China) in 2016 and 2017 to investigate the changes in leaf nutrient concentrations (i.e., leaf N, Leaf P, and leaf N:P ratio) and nutrient resorption efficiency of Seriphidium rhodanthum and Stipa capillata, which are dominant species in this grassland. Results showed that N addition has significant effects on soil inorganic N (NO₃^--N and NH₄⁺-N) and leaf N of both species in the study periods. Compared with green leaves, leaf nutrient concentrations and nutrient resorption efficiency in senesced leaves of S. rhodanthum was more sensitive to N addition, whereas N addition influenced leaf N and leaf N:P ratio in green and senesced leaves of S. capillata. N addition did not influence N resorption efficiency of the two species. P addition and N+P addition significantly improved leaf P and had a negative effect on P resorption efficiency of the two species in the study period. These influences on plants can be explained by increasing P availability. The present results illustrated that the two species are more sensitive to P addition than N addition, which implies that P is the major limiting factor in the studied alpine grassland ecosystem. In addition, an interactive effect of N+P addition was only discernable with respect to soil availability, but did not affect plants. Therefore, exploring how nutrient characteristics and resorption response to N and P addition in the alpine grassland is important to understand nutrient use strategy of plants in terrestrial ecosystems.     

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.     

Changes in soil carbon stocks and related soil properties along a 50-year grassland-to-cropland conversion chronosequence in an agro-pastoral ecotone of Inner Mongolia, China

Land use change significantly influences soil properties.There is little information available on the long-term effects of post-reclamation from grassland to cropland on soil properties.We compared soil carbon(C) and nitrogen(N) storage and related soil properties in a 50-year cultivation chronosequence of grassland in the agro-pastoral ecotone of Inner Mongolia.Field surveys on land use changes during the period of 1955-2002 were conducted to build a chronosequence of cropland of different ages since the conversion from grassland.The results showed that soil C and N storage,soil texture,and soil nutrient contents varied with land use types and cropland ages(P<0.01).In the 0-30 cm soil layer,the soil organic carbon(SOC) density was significantly lower in the croplands(3.28 kg C/m2 for C50 soil) than in the grasslands(6.32 kg C/m2).After 5,10,15,20,35,and 50 years of crop planting(years since the onset of cultivation),the SOC losses were 17%,12%,19%,47%,46%,and 48%,respectively,compared with the grasslands.The soil total nitrogen(TN) density of the grasslands was 65 g N/m2,and TN density of the cropland soil was 35 g N/m2 after 50 years of crop planting.Both the SOC and TN densities could be quantitatively determined by a negative exponential function of cropland age(P<0.0001,R2=0.8528;P<0.0001,R2=0.9637).The dissolved organic carbon(DOC) content,soil available potassium(AK) content,clay content,and pH value were decreased;and the soil bulk density and sand content were increased since the conversion of grassland into cropland during the 50-year period.Our results show soil nutrients were higher in grassland than in cropland.The conversion of grasslands to croplands induced a loss of soil C storage and changes of related soil properties.The reclamation time of cultivated soil(cropland age) had significant effects on soil properties in the study area.     

Carbon inputs regulate the temperature sensitivity of soil respiration in temperate forests

Litter and root activities may alter the temperature sensitivity (Q₁₀) of soil respiration. However, existing studies have not provided a comprehensive understanding of the effects of litter and root carbon inputs on the Q₁₀ of soil respiration in different seasons. In this study, we used the trench method under in situ conditions to measure the total soil respiration (R_total), litter-removed soil respiration (R_no-litter), root-removed soil respiration (R_no-root), and the decomposition of soil organic matter (i.e., both litter and root removal; R_SOM) in different seasons of pioneer (Populus davidiana Dode) and climax (Quercus liaotungensis Mary) forests on the Loess Plateau, China. Soil temperature, soil moisture, litter biomass, fine root biomass, litter carbon, and root carbon were analyzed to obtain the drive mechanism of the Q₁₀ of soil respiration in the two forests. The results showed that the Q₁₀ of soil respiration exhibited seasonality, and the Q₁₀ of soil respiration was higher in summer. The litter enhanced the Q₁₀ of soil respiration considerably more than the root did. Soil temperature, soil moisture, fine root biomass, and litter carbon were the main factors used to predict the Q₁₀ of different soil respiration components. These findings indicated that factors affecting the Q₁₀ of soil respiration highly depended on soil temperature and soil moisture as well as related litter and root traits in the two forests, which can improve our understanding of soil carbon-climate feedback in global warming. The results of this study can provide reference for exploring soil respiration under temperate forest restoration.     

Effects of vegetation near-soil-surface factors on runoff and sediment reduction in typical grasslands on the Loess Plateau,China

Vegetation near-soil-surface factors can protect topsoil from erosion,however,their contributions to the reduction of soil erosion,especially under natural rainfall events,have not been systematically recognized.This study was performed to quantify the effects of near-soil-surface factors on runoff and sediment under natural rainfall events on grasslands dominated by Bothriochloa ischaemum(Linn.)Keng(BI grassland)and Artemisia gmelinii Thunb.(AG grassland)in two typical watersheds on the Loess Plateau,China in 2018.By successive removal of the plant canopy,litter,biological soil crusts(BSCs)and plant roots,we established five treatments including plant roots,plant roots+BSCs,plant roots+BSCs+litter,intact grassland and bare land in each grassland type.In total,twenty runoff plots(5 m×3 m)with similar slopes and aspects were constructed in the two types of grasslands.Results showed that plant canopy,litter and roots reduced runoff,while BSCs,which swelled in the presence of water,increased runoff.In contrast,all of these factors reduced sediment yield.In addition,the reductions in runoff and sediment yield increased with I30(maximum 30-min rainfall intensity)for each vegetation near-soil-surface factor except for BSCs.Among these factors,plant canopy had the largest contribution to runoff reduction,accounting for 48.8% and 39.9% in the BI and AG grasslands,respectively.The contributions of these vegetation near-soil-surface factors to sediment yield reduction were similar(21.3%-29.9%)in the two types of grasslands except for BSCs in the AG grassland(10.3%).The total reduction in runoff in the BI grassland(70.8%)was greater than that in the AG grassland(53.1%),while the reduction in sediment yield was almost the same in both grasslands(97.4%and 96.7%).In conclusion,according to the effects of different vegetation near-soil-surface factors on runoff and sediment production,our results may provide more complete insight and scientific basis into the effects of various vegetation related factors in controlling soil erosion.     

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.     

Effects of spring fire and slope on the aboveground biomass,and organic C and N dynamics in a semi-arid grassland of northern China

The aboveground primary production is a major source of carbon(C) and nitrogen(N) pool and plays an important role in regulating the response of ecosystem and nutrient cycling to natural and anthropogenic disturbances. To explore the mechanisms underlying the effect of spring fire and topography on the aboveground biomass(AGB) and the soil C and N pool, we conducted a field experiment between April 2014 and August 2016 in a semi-arid grassland of northern China to examine the effects of slope and spring fire, and their potential interactions on the AGB and organic C and total N contents in different plant functional groups(C_3 grasses, C_4 grasses, forbs, Artemisia frigida plants, total grasses and total plants).The dynamics of AGB and the contents of organic C and N in the plants were examined in the burned and unburned plots on different slope positions(upper and lower). There were differences in the total AGB of all plants between the two slope positions. The AGB of grasses was higher on the lower slope than on the upper slope in July. On the lower slope, spring fire marginally or significantly increased the AGB of C_3 grasses, forbs, total grasses and total plants in June and August, but decreased the AGB of C_4 grasses and A.frigida plants from June to August. On the upper slope, however, spring fire significantly increased the AGB of forbs in June, the AGB of C_3 grasses and total grasses in July, and the AGB of forbs and C_4 grasses in August. Spring fire exhibited no significant effect on the total AGB of all plants on the lower and upper slopes in 2014 and 2015. In 2016, the total AGB in the burned plots showed a decreasing trend after fire burning compared with the unburned plots. The different plant functional groups had different responses to slope positions in terms of organic C and N contents in the plants. The lower and upper slopes differed with respect to the organic C and N contents of C_3 grasses, C_4 grasses, total grasses, forbs, A. frigida plants and total plants in different growing months. Slope position and spring fire significantly interacted to affect the AGB and organic C and N contents of C_4 grasses and A. frigida plants. We observed the AGB and organic C and N contents in the plants in a temporal synchronized pattern. Spring fire affected the functional AGB on different slope positions, likely by altering the organic C and N contents and, therefore,it is an important process for C and N cycling in the semi-arid natural grasslands. The findings of this study would facilitate the simulation of ecosystem C and N cycling in the semi-arid grasslands in northern China.     

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.     

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.     

干热河谷罗望子人工林凋落物分解及养分释放

通过长期野外监测和分析,研究了金沙江干热河谷罗望子人工林凋落物分解和养分释放动态,结果表明:经过420d分解期,林地A和林地B的凋落物残留率为42.57%和29.22%,半衰期为0.87a和0.75a,周转期为4.81a和3.61a;养分迁移方式,K元素是淋溶-富集-释放;N、Ca、Mg、Cu元素是富集-释放,Fe元素是富集,P元素在林地A和林地B中迁移方式略有差异;养分释放特征,P、Ca、Mg元素表现为净释放,七种元素释放率大小,林地A和林地B均为:Ca﹥K﹥P﹥Mg﹥N﹥Cu﹥Fe;P、K、Ca、Mg元素易分解和循环,返回林地时间较短,易被林木吸收。罗望子林凋落物的分解总体特征符合亚热带气候的地带性特点,受气温和降雨量影响较小。     

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.     

近20年来乌鲁木齐河下游地区生态系统服务价值的动态变化

利用TM卫星遥感数据,通过CIS方法,根据Costanza等提出的生态系统服务价值计算方法,对比分析乌鲁木齐河下游地区1989-2007年的土地利用/覆盖与生态系统服务价值的变化.结果表明:1989-2007年,研究区生态系统服务价值从1.95×109元/a增长至2.40×109元/a,而年增长率有所下降,从1989-...     

吉林西部土地利用/覆被变化与湿地生态安全响应

以ARCGIS数据集成分析平台,利用吉林西部1930-2000年的土地利用数据,研究了该区景观组分变化、景观结构变化、景观组分转移过程及湿地生态安全响应.结果表明:草地、湿地、林地、水域等景观组分的面积比重呈递减趋势,湿地几乎在每个阶段都是净损失,除了被大量开垦为耕地外,湿地还大量转化为草地.LUCC的湿地生态安全响应主要表现为湿地大面积丧失、湿地植被变化、湿地需水量不足、湿地景观异质性变化和湿地景观的破碎化等,这为理解LUCC与湿地生态安全响应机制和区域生态建设提供了科学依据.     

天山高寒草原植物叶片氮磷化学计量特征对氮沉降的响应

人类活动和气候变化导致的大气氮沉降急剧升高，将会影响高寒草原植物养分循环。为了研究氮沉降对高寒草原植物养分含量及生态化学计量学特征的影响。依托2009年在新疆天山巴音布鲁克高寒草原设置的长期氮沉降研究平台，于2017年7月和10月采集溚草（Koeleria cristata）、二裂委陵菜（Potentilla bifurca）和天山赖草（Leymus tianschanicus）3种植物的成熟叶和老叶，分析3种植物叶片N、P元素生态化学计量对不同施氮水平的响应规律。结果表明：① 3种植物养分浓度及其化学计量比在成熟叶和老叶之间存在较大差异，成熟叶和老叶的N、P含量分别为12.78 mg·g^-1、0.88 mg·g^-1和6.88 mg·g^-1、0.46 mg·g-1mg·g^-1。3种植物成熟叶和老叶的N元素含量均为：二裂委陵菜>天山赖草>溚草,P元素含量同N元素含量趋势一致；② 氮添加增加了成熟叶和老叶N浓度，分别达12%和48%；成熟叶与老叶P浓度对氮添加的响应规律不一致，成熟叶P浓度对氮添加的响应与物种有关，而老叶P浓度呈一致的下降趋势；氮添加对成熟叶和老叶N∶P的比值影响亦不同，其中相对于成熟叶，老叶的N∶P呈显著增加趋势。③ 植物叶片的N元素、P元素和N∶P比三者之间的相关分析表明:N元素和N∶P之间呈显著正相关关系(P<0.05),在生长旺盛期和枯黄期，溚草和天山赖草的N与P元素之间没有发现显著相关性(P>0.05)，而二裂委陵菜呈现一定的差异性，在生长旺盛期二裂委陵菜叶片N与P元素呈显著的正相关、枯黄期呈显著的负相关(P<0.05)。表明长期氮的添加显著影响了3种植物叶片的养分含量和生态化学计量，不同物种间存在一定差异，未来氮沉降升高将会影响天山山地草原的植物养分循环。     

Assessing ecological vulnerability in western China based on Time-Integrated NDVI data

Arid and semi-arid areas are the most vulnerable regions to climate change.Clear understanding of the effects of climate change on ecosystems in arid and semi-arid regions and the ecosystem vulnerability is important for ecosystem management under the background of climate change.In this study,we conducted a vulnerability assessment on various ecosystems from 1982 to 2013 in western China with large areas of arid and semi-arid lands based on the Time-Integrated Normalized Difference Vegetation Index(TINDVI)data and climate data.The results indicated that grasslands were the most vulnerable ecosystem to climate change in western China,especially for those in Tibetan Plateau.Croplands in oases were not vulnerable to climate change compared to rain-fed croplands in semi-arid regions(e.g.Gansu and Inner Mongolia),which was attributed to the well-developed drip irrigation technology in oases.Desert and Gobi ecosystems were slightly vulnerable to climate change during the past several decades.The assessment results,as revealed in this study,can provide a reference for taking appropriate actions to protect the ecosystems in western China.     

20世纪90年代内蒙古自治区土地利用动态与风力侵蚀动态对比研究

内蒙古是我国风力侵蚀较为严重的地区之一,同时也是我国土地利用方式剧烈变化的地区之一。依据两期土地利用数据以及相应年代的土壤风力侵蚀数据,研究了20世纪90年代内蒙古自治区土地利用和风力侵蚀的静、动态格局。根据土地利用和风力侵蚀的空间分布及动态变化特点,设计了内蒙古土地利用—风力侵蚀动态区划,基于该区划详细讨论了内蒙古不同地区占主导地位的土地利用动态与风力侵蚀动态,由此揭示了两者之间存在的驱动——被驱动关系。研究发现,在过去10年里,内蒙古土地利用和风力侵蚀的基本格局没有太大变化,但风力侵蚀在总体上是增强了,而土地利用的变化主要反映为草地的退化和耕地的扩张。土地利用动态与风力侵蚀动态有着良好的时空对应关系草地的退化与耕地的扩张导致了显著的风力侵蚀增强,而草地的改善以及耕地的收缩对风力侵蚀的影响不是很大,这同时也表明了土地利用动态对风力侵蚀动态正、反向驱动力的不平衡性。