Interactive effects of soil temperature and moisture on soil N mineralization in a Stipa krylovii grassland in Inner Mongolia,China

Determining soil N mineralization response to soil temperature and moisture changes is challenging in the field due to complicated effects from other factors. In the laboratory, N mineralization is highly dependent on temperature, moisture and sample size. In this study, a laboratory incubation experiment was carefully designed and conducted under controlled conditions to examine the effects of soil temperature and moisture on soil N mineralization using soil samples obtained from the Stipa krylovii grassland in Inner Mongolia, China. Five temperature(i.e. 9°C, 14°C, 22°C, 30°C and 40°C) and five moisture levels(i.e. 20%, 40%, 60%, 80% and 100% WHC, where WHC is the soil water holding capacity) were included in a full-factorial design. During the 71-day incubation period, microbial biomass carbon(MBC), ammonium nitrogen(NH4 +-N) and nitrate nitrogen(NO3--N) were measured approximately every 18 days; soil basal respiration for qCO2 index was measured once every 2 days(once a week near the end of the incubation period). The results showed that the mineral N production and net N mineralization rates were positively correlated with temperature; the strongest correlation was observed for temperatures between 30°C and 40°C. The relationships between moisture levels and both the mineral N production and net N mineralization rates were quadratic. The interaction between soil temperature and moisture was significant on N mineralization, i.e. increasing temperatures(moisture) enhanced the sensitivity of N mineralization to moisture(temperature). Our results also showed a positive correlation between the net nitrification rate and temperature, while the correlation between the NH4 +-N content and temperature was insignificant. The net nitrification rate was negatively correlated with high NH4 +-N contents at 80%–100% WHC, suggesting an active denitrification in moist conditions. Moreover, qCO2 index was positively correlated with temperature, especially at 80% WHC. With a low net nitrification rate and high soil basal respiration rate, it was likely that the denitrification concealed the microbial gross mineralization activity; therefore, active soil N mineralization occurred in 60%–80% WHC conditions.     

放牧压力下大针茅群体遗传多样性的RAPD分析

大针茅(Stipa grandis)是我国北方典型草原上最重要的饲用植物之一,分布广,数量大,是优势种之一。本研究应用RAPD技术检测大针茅植物不同放牧压力下群体的遗传多样性,探索放牧强度与遗传分化的相互联系。在放牧和对照群体中,利用18个有效引物共获得了129个位点,其中多态性位点为105个,占81.40%,说明个体发生较高的遗传变异。两个群体都具有特异性位点,说明放牧压力导致某些位点发生了变化,但遗传变异主要存在于群体内(遗传一致度为90.43%)。     

典型草原退化群落恢复演替过程中大针茅组织细胞变化的研究

将显微照相和地理信息系统的理论与方法相结合,应用于组织解剖学中。通过对内蒙古锡林郭勒盟典型草原不同退化研究样地大针茅(Stipa grandis)营养器官茎和叶组织细胞变化的研究,揭示出草原植物小型化的内在机制。随着群落恢复演替的进程,三个群落样地中的大针茅植株的叶和茎的解剖结构呈现出相同的变化趋势,即恢复时间越长,其组成器官的细胞数目越多。从相反的过程来看,叶和茎都发生了小型化。然而,叶和茎的小型化机理又有不同。研究表明:(1)从叶片的解剖结构来看,叶脉数目的减少导致了小型化。(2)从茎的解剖结构来看,茎的各种组织细胞数目的减少导致了小型化。     

放牧对短花针茅草原土壤微生物和土壤养分的影响及其季节动态

研究了短花针茅草原不同季节、不同放牧梯度内土壤微生物数量、土壤养分的变化及土壤微生物与土壤养分之间的相关性,结果表明:轻度放牧区(LG)和重度放牧区(HG)内土壤微生物数量春季最高,土壤微生物数量(0-10 cm)在三个放牧区内随着季节的变化均呈下降趋势。而在10-20 cm,对照区内土壤微生物数量的高峰期出现在夏季然后开始下降,轻度放牧区和重度放牧区土壤微生物随着季节的变化而下降。土壤微生物数量到了秋季在三个放牧梯度内均呈现显著性的差异,土壤养分也是在秋季出现了显著性差异(P<0.05)。土壤微生物总数在不同放牧梯度内的变化规律是对照和轻度放牧区均大于重度放牧区。土壤微生物与土壤有机质和土壤全氮呈较强的正相关。     

放牧制度对短花针茅草原主要植物种群繁殖特征的影响

本文对短花针茅荒漠草原划区轮牧与自由放牧条件下主要植物种群的繁殖特性进了比较分析。结果表明 ,划区轮牧与自由放牧相比有利于短花针茅生殖枝的形成 ,且能够产生较多的种子 ;划区轮牧有利于主要植物种群实生苗的存活 ,但禁牧条件下对实生苗的生长更有利 ;短花针茅草原主要植物种群以无性繁殖为主 ,有性繁殖机会较少 ,且受降雨量的影响较大     

高寒草地西北针茅生长发育特征及与气象因子的关系

利用1999～2009年连续11年的定位观测数据,研究了高寒草地西北针茅的生长发育特征与气象因子的关系。结果表明,在3月中旬,如果气温升高,返青日会推迟,这主要因为高温促使土壤水分蒸发,而土壤干旱阻碍返青;返青后,如果≥0℃的积温不足或累计日照时数不足,针茅的抽穗期会推迟;开花期的当日平均气温在10～20℃,如果抽穗-...     

小针茅荒漠草原土壤水分动态及其对降雨的响应

揭示干旱、半干旱地区生态系统土壤水分动态对于进一步认识生态系统过程与功能机制,提出应对气候变化影响的途径均具有重要意义。以小针茅草原为对象,基于连续4 a逐时监测的土壤含水量(地表以下15 cm)与降雨数据,结合邻近气象站过去50 a的降雨资料,探讨了荒漠草原土壤水分动态规律及其对降雨的响应。结果表明:1受降雨分布格局的影响,荒漠草原土壤水分动态存在单峰型和双峰型两种模式;2地表以下15 cm处的土壤水分对5 mm以下降雨事件没有响应,18 mm以上的降雨对该土层土壤水分才具有较强的补充作用,土壤所需的降雨量比沙地和荒漠区更高;3降雨量越大、降雨强度越大或降雨前土壤含水量越高,土壤水分对降雨的响应就越迅速。未来气候变化可能对荒漠草原区浅根型植物生长不利,从而对畜牧业生产产生重要影响。     

Impacts of livestock grazing on a savanna grassland in Kenya

The dynamics of most rangelands in Kenya remain to be poorly understood.This paper provides baseline information on the response of a semiarid rangeland under different livestock grazing regimes on land inhabited by the Massai people in the east side of Amboseli National Park in Kenya.The data were collected from grasslands designated into four types:(1) grassland from previous Massai settlements that had been abandoned for over twenty years;(2) grassland excluded from livestock grazing for eight years;(3) a dry season grazing area;and (4) a continuous grazing area where grazing occurred throughout all seasons.Collected data included grass species composition,grass height,inter-tuft distance,standing grass biomass and soil characteristics.The results indicated that continuous grazing area in semiarid rangelands exhibited loss of vegetation with negative,long-term effects on grass functional qualities and forage production,whereas grassland that used traditional Maasai grazing methods showed efficiency and desirable effects on the rangelands.The results also showed that abandoned homestead sites,though degraded,were important nutrient reservoirs.     

Long-term effects of mowing on plasticity and allometry of Leymus chinensis in a temperate semi-arid grassland,China

Mowing is an important land management practice for natural semi-arid regions.A growing body of empirical evidence shows that different mowing regimes affect the functioning of grassland ecosystems.However,the responses of plant functional traits to long-term mowing and their allometric scaling under long-term mowing are poorly understood.For a better understanding of the effects of mowing on grassland ecosystems,we analyzed the allometric traits of leaves and stems of Leymus chinensis(Trin.) Tzvel.,a dominant grass species in eastern Eurasian temperate grassland,at different mowing intensities(no clipping,clipping once every two years,once a year and twice a year).Experiments were conducted on plots established over a decade ago in a typical steppe of Xilinhot,Inner Mongolia,China.Results showed that most of the functional traits of L.chinensis decreased with the increased mowing intensity.The responses of leaves and stems to long-term mowing were asymmetric,in which leaf traits were more stable than stem traits.Also significant allometric relationships were found among most of the plant functional traits under the four mowing treatments.Sensitive traits of L.chinensis(e.g.leaf length and stem length) were primary indicators associated with aboveground biomass decline under high mowing intensity.In conclusion,the allometric growth of different functional traits of L.chinensis varies with different long-term mowing practices,which is likely to be a strategy used by the plant to adapt to the mowing disturbances.     

小针茅草原植被地下与地上生物量季节动态及根冠比变化规律

利用内蒙古苏尼特右旗小针茅荒漠草原生长季地上、地下生物量数据,分析小针茅草原植被地上、地下生物量以及根冠比的季节动态,并建立根冠比季节动态模型。研究结果表明：① 小针茅草原植被地上生物量季节变化呈单峰型曲线,地上生物量的峰值出现在6月下旬,为46.14 g•m^-2,地下生物量季节动态表现为“N”型变化规律,最高值出现在7月下旬,最低值出现在8月下旬,分别为1 275.46 g•m^-2和365.1 g•m^-2。② 2011年小针茅草原植被根冠比季节波动较大,最小根冠比为16.8, 出现在8月下旬, 最大根冠比为51.05, 出现在7月下旬。③ 小针茅草原植被地上生物量与根冠比具有较明显的相关关系,8月的相关关系最好,相关系数达到0.626,可以用8月的地上生物量模拟根冠比的变化。     

不同强度放牧对贝加尔针茅草原土壤微生物和土壤呼吸的影响

在一个生长季内,对贝加尔针茅草甸草原不同强度放牧地段(非牧段,轻牧段,中牧段和重牧段,以放牛为主)土壤呼吸作用强度与土壤微生物数量和部分土壤理化性状进行了测定和相关性分析。结果表明,不同强度放牧对土壤呼吸作用和土壤微生物数量均产生不同程度影响,即在非牧段,土壤呼吸作用和土壤微生物数量最强(多);其余各放牧段,随着放牧强度增加,土壤呼吸作用减弱,微生物数量增加,但在各放牧段间均未达到差异显著水平(p(0.05)。土壤呼吸强度与土壤温度和相对含水量间具有显著的相关性(p(0.05),与土壤微生物数量和土壤pH值之间相关性不显著(p(0.05)。说明在该草地放牧较重时首先对土壤物理环境造成不利影响,进而影响土壤微生物的呼吸作用,对微生物数量未产生实质性改变。     

不同强度放牧对贝加尔针茅草原群落和土壤理化性质的影响

在一个生长季内,比较分析了贝加尔针茅草甸草原不同放牧强度地段(非牧段,轻牧段,中牧段和重牧段,以放牛为主)植物群落的总地上现存量、总投影盖度、平均高度和土壤理化性质的变异。结果表明,不同强度放牧条件下各项指标均呈规律性变化,表现为植被的生长状况和土壤状况随着放牧强度的增加而劣化,且群落总地上现存量、总投影盖度、群落高度之间具有显著的相关性。土壤的pH值和电导率与地面凋落物的量之间存在显著负相关。考虑各项指标对放牧反应的敏感性、变化的稳定性和测定的方便性,可以把群落盖度、土壤化学性质的变化作为草地健康评价的关键指标。     

Termite effects on soils and plants are generally consistent along a gradient in livestock grazing

Livestock grazing is a major driver of ecosystem functions in drylands and would be expected to influence soil biota such as termites. We examined changes in soil chemistry and plant community composition on mounds constructed by the subterranean termite Anacanthotermes ahngerianus along a gradient in grazing intensity in an arid steppe in north-eastern Iran. The grazing gradient was represented by increasing distance from an area used by resting livestock, and plant and soil attributes measured within three adjacent microsites (termite mounds, non-mound controls, intervening annular zone surrounding the mounds). Values of soil EC; pH; exchangeable Ca, Mg, and Na; and total nitrogen and organic carbon were greatest in mound soils and declined from mounds to control microsites. Mounds were completely devoid of plants. Annular zones had three-times less cover than the control sites, but there were no differences in diversity or evenness. Electrical conductivity values were ten-times greater on mounds than controls close to resting sites, but the difference diminished rapidly with distance from resting sites. For all other soil and plant variables, differences between microsites were consistent across the grazing gradient. Increased grazing intensity was associated with increasing soil pH, EC and sand content, and reduced plant cover. Overall our study shows that the effects of termites on soil chemistry and plant cover varied little across the grazing gradient. Our results suggest that termite mounds may sustain their role as sites of enhanced soil nutrients under even high levels of grazing.     

Seasonal dynamics of ground cover in Cirsium arvense – a basis for estimating grazing losses and economic impacts

Analysis of the economics of managing Cirsium arvense in grazed pastures worldwide has been hampered by a lack of data on the within‐year seasonal dynamics of the weed and its impact on the yield of palatable herbage. To redress this, the seasonal pattern in within‐patch percentage ground cover of the weed was determined from measurements on 39 dairy and 66 sheep and/or beef cattle farms in New Zealand during 2009–2010 and 2010–2011. This pattern was then scaled using farmer estimates of peak whole‐farm cover to derive mean monthly covers for dairy, beef, sheep/beef, sheep and deer farms. These monthly covers corresponded, respectively, to mean annual percentage covers of 2.7, 1.7, 3.0, 5.9 and 2.9% and to mean annual percentage losses in pasture growth (palatable herbage yield) of 3.6, 2.3, 4.0, 7.8 and 3.9%. The latter, in combination with 2011–2012 farm statistics, revealed that C. arvense caused a national loss in pastoral farm gross revenue in New Zealand in 2011–2012 of $685 million ($446 m dairy, $233 m sheep/beef, $6 m deer). Beyond the scope of this paper, the monthly covers and their corresponding monthly losses in pasture growth provide a basis for modelling the economic impacts of C. arvense and its management at a farm scale. More generally, the analytical method that we have developed is appropriate for evaluating the economic impact of any weed in a grazed pasture, particularly those exhibiting pronounced seasonal patterns in occupancy, such as annuals and deciduous perennials.     

Impacts of land disturbance and restoration on runoff production and sediment yield in the Chinese Loess Plateau

Land disturbance and land restoration are important factors influencing runoff production and sediment yield in the semi-arid loess regions of China. This study compared the runoff production and sediment yield during the early stage after land disturbance(ESLD) with those during restoring stage after land disturbance(RSLD). Grey relational analysis was used to analyse the importance of each one of the influencing factors(vegetation, rainfall, soil and topography) in affecting the runoff production and sediment yield. Our results showed that during ESLD, topography was the most critical factor controlling the runoff production, while soil was the most important factor controlling the sediment yield. During RSLD, vegetation was more important in affecting runoff production, while rainfall was more important in affecting sediment yield. In additional, this study demonstrated that both the runoff production and the sediment yield can be effectively reduced by restoring vegetation on severely-disturbed lands, thus providing an important theoretical basis for better implementations of the Grain for Green Program. Our results revealed that the vegetation types of Hippophae rhamnoides+Pinus tabulaeformis and H. rhamnoides are better plant selections for land restoration in this area, especially for relatively gentle slopes(i.e., less than 20 degrees).     

Effect of spatial scale and topography on spatial heterogeneity of soil seed banks under grazing disturbance in a sandy grassland of Horqin Sand Land, Northern China

Soil seed banks play an important role in the distribution and composition of plant communities in semiarid grassland ecosystems.However,information on how spatial scale influences the spatial heterogeneity of soil seed banks in a grassland under grazing disturbance is still lacking.Based on field sampling and greenhouse germination,we measured the species composition and seed density of soil seed banks at different spatial scales (30 m×30 m,30 m×60 m and 30 m×90 m)along a topographical gradient in a sandy grassland in Horqin Sand Land, Northern China.By applying geostatistical methods,we examined how spatial scale and topography affected the spatial distribution of soil seed banks in the study area.Our results showed that the total number of species in soil seed banks,as well as the number of dominant annuals,increased with the increase of spatial scales.Seed density in soil seed banks decreased with the increase of spatial scales due to an increase in the slopes and relative heights of the sampling points.Geostatistical analysis showed that the relative structural variance(C/(C0+C))of seed density and species richness were over 65%for all spatial scales,indicating that these variables had an obvious spatial autocorrelation and the spatial structured variance accounted for the largest proportion of the total sample variance.Spatial autocorrelation of seed density in soil seed banks increased with the increase of measured scales,while that of species richness showed a reverse trend.These results suggest that the total number of species in soil seed banks is spatial scale dependent and lower topography may accommodate more seeds.Spatial distribution of seed density in soil seed banks is also scale dependent due to topographic variation.Grassland management,therefore,needs to consider local grazing disturbance regime,spatial scale and topography.     

保护性耕作对黄土高原旱地表土容重和水分入渗的影响

通过在陇中黄土高原半干旱区进行保护性耕作的定位研究,探讨了保护性耕作对土壤容重以及渗透性能的影响。结果表明:与传统耕作(T)、免耕无覆盖(NT)、传统耕作结合秸秆还田(TS)相比,试验的前2～3a免耕覆盖(NTS)使得土壤容重增大,而后保持稳定状态不再持续增加。通过对渗吸率、宏观毛管长度、有效孔径以及饱和导水率等指标的比较发现,免耕覆盖(NTS)对土壤的渗透性能有显著的改善作用。     

Drought trend analysis in a semi-arid area of Iraq based on Normalized Difference Vegetation Index,Normalized Difference Water Index and Standardized Precipitation Index

Drought was a severe recurring phenomenon in Iraq over the past two decades due to climate change despite the fact that Iraq has been one of the most water-rich countries in the Middle East in the past.The Iraqi Kurdistan Region(IKR)is located in the north of Iraq,which has also suffered from extreme drought.In this study,the drought severity status in Sulaimaniyah Province,one of four provinces of the IKR,was investigated for the years from 1998 to 2017.Thus,Landsat time series dataset,including 40 images,were downloaded and used in this study.The Normalized Difference Vegetation Index(NDVI)and the Normalized Difference Water Index(NDWI)were utilized as spectral-based drought indices and the Standardized Precipitation Index(SPI)was employed as a meteorological-based drought index,to assess the drought severity and analyse the changes of vegetative cover and water bodies.The study area experienced precipitation deficiency and severe drought in 1999,2000,2008,2009,and 2012.Study findings also revealed a drop in the vegetative cover by 33.3%in the year 2000.Furthermore,the most significant shrinkage in water bodies was observed in the Lake Darbandikhan(LDK),which lost 40.5%of its total surface area in 2009.The statistical analyses revealed that precipitation was significantly positively correlated with the SPI and the surface area of the LDK(correlation coefficients of 0.92 and 0.72,respectively).The relationship between SPI and NDVI-based vegetation cover was positive but not significant.Low precipitation did not always correspond to vegetative drought;the delay of the effect of precipitation on NDVI was one year.     

Seasonal dynamics of soil water content in the typical vegetation and its response to precipitation in a semi-arid area of Chinese Loess Plateau

Soil water content is a key limiting factor for vegetation growth in the semi-arid area of Chinese Loess Plateau and precipitation is the main source of soil water content in this area. To further understand the impact of vegetation types and environmental factors such as precipitation on soil water content, we continuously monitored the seasonal dynamics in soil water content in four plots (natural grassland, Caragana korshinskii, Armeniaca sibirica and Pinus tabulaeformis) in Chinese Loess Plateau. The results show that the amplitude of soil water content fluctuation decreases with an increase in soil depth, showing obvious seasonal variations. Soil water content of artificial vegetation was found to be significantly lower than that of natural grassland, and most precipitation events have difficulty replenishing soil water content below a depth of 40 cm. Spring and autumn are the key seasons for replenishment of soil water by precipitation. Changes in soil water content are affected by precipitation, vegetation types, soil evaporation and other factors. The interception effect of vegetation on precipitation and the demand for water consumption by transpiration are the key factors affecting the efficiency of soil water replenishment by precipitation in this area. Due to artificial vegetation plantation in this area, soil will face a water deficit crisis in the future.