Heliotropium europaeum only germinates following sufficient rainfall to allow reproduction

Regions with Mediterranean climates are seasonally arid and provide a niche for ephemeral species which germinate following discrete and variable rainfall during summer. These species must be able to detect when conditions are suitable for completion of their life cycle. Common heliotrope (Heliotropium europaeum) is one such species. It is considered a weed in its naturalised habitat in southern Australia as it uses resources that could be used by ensuing crops, and is toxic to livestock.We examined common heliotrope's germination responses to temperature and water potential, the effect of simulated rainfall on seedling emergence and plant growth in lysimeters.Fresh seeds of common heliotrope have relatively high optimum temperatures and water potentials for germination (around 35 °C and 0 MPa). Germination percentage of seeds extracted from the soil seed bank varies seasonally. In the soil types and climate of the study area, 24.2 mm is the minimum amount of rainfall resulting in emergence. Evapotranspiration required to reach minimal reproductive output was 19.4 mm.Common heliotrope's germination requirements have been selected to ensure that it will only germinate after sufficient rainfall to allow reproductive output. This is the mechanism through which common heliotrope detects its temporal niche.     

Groundwater use by native plants in response to changes in precipitation in an intermountain basin

Many arid basins in western North America are likely to experience future changes in precipitation timing and amount. Where shallow water tables occur, plant acquisition of groundwater and soil water may be influenced by growing season precipitation. We conducted a rainfall manipulation experiment to investigate responses of four common native plant species to ambient, increased, and decreased summer monsoon rainfall. We measured plant xylem pressure potentials (Ψ) and stable oxygen isotope signatures (δ¹⁸O) to assess effects of altered precipitation on plant water relations and water acquisition patterns. Reduced rainfall decreased Ψ more in the grasses Sporobolus airoides and Distichlis spicata than the more deeply rooted shrubs Sarcobatus vermiculatus and Ericameria nauseosa. E. nauseosa had little response to natural or experimental differences in available soil water. Plant xylem water δ¹⁸O indicated that S. airoides and D. spicata are almost entirely dependent on rain-recharged soil water, while E. nauseosa is almost entirely groundwater-dependent. Sarcobatus vermiculatus used groundwater during dry periods, but utilized precipitation from soil layers after large rainfall events. Persistent changes in precipitation patterns could cause shifts in plant community composition that may alter basin-scale groundwater consumption by native plants, affecting water availability for human and ecosystem uses.     

Influence of canopy and topographic position on soil moisture response to rainfall in a hilly catchment of Three Gorges Reservoir Area,China

Rainfall provides essential water resource for vegetation growth and acts as driving force for hydrologic process, bedrock weathering and nutrient cycle in the steep hilly catchment. But the effects of rainfall features, vegetation types, topography, and also their interactions on soil water movement and soil moisture dynamics are inadequately quantified. During the coupled wet and dry periods of the year 2018 to 2019, time-series soil moisture was monitored with 5-min interval resolution in a hilly catchment of the Three Gorges Reservoir Area in China. Three hillslopes covered with evergreen forest(EG), secondary deciduous forest mixed with shrubs(SDFS) and deforested pasture(DP) were selected, and two monitoring sites with five detected depths were established at upslope and downslope position, respectively. Several parameters expressing soil moisture response to rainfall event were evaluated, including wetting depth, cumulative rainfall amount and lag time before initial response, maximum increase of soil water storage, and transform ratio of rainwater to soil water. The results indicated that rainfall amount is the dominant rainfall variable controlling soil moisture response to rainfall event. No soil moisture response occurred when rainfall amounts was 8 mm, and all the deepest monitoring sensors detected soil moisture increase when total rainfall amounts was 30 mm. In the wet period, the cumulative rainfall amount to trigger surface soil moisture response in EG-up site was significantly higher than in other five sites. However, no significant difference in cumulative rainfall amount to trigger soil moisture response was observed among all study sites in dry period. Vegetation canopy interception reduced the transform ratio of rainwater to soil water, with a higher reduction in vegetation growth period than in other period. Also, interception of vegetation canopy resulted in a largeraccumulated rainfall amount and a longer lag time for initiating soil moisture response to rainfall. Generally, average cumulative rainfall amount for initiating soil moisture response during dry period of all sites(3.5–5.6 mm) were less than during wet period(5.7–19.7 mm). Forests captured more infiltration water compared with deforested pasture, showing the larger increments of both soil water storage for the whole soil profile and volumetric soil water content at 10 cm depth on two forest slopes. Topography dominated soil subsurface flow, proven by the evidences that less rainfall amount and less time was needed to trigger soil moisture response and also larger accumulated soil water storage increment in downslope site than in corresponding upslope site during heavy rainfall events.     

沙地降雨入渗水分动态

应用土壤水动力学基本原理，结合先进仪器的使用，从动力学角度，以能态观点定量研究沙地水分入渗动态。通过野外现场观测，分析不同深度含水率和吸力随时间变化过程，研究沙地降雨入渗水分传递过程，探讨入渗条件下沙地水分运动的动力学机制和特征。     

Comparative hydrological behaviour of two small catchments in semi-arid Zimbabwe

This paper describes and compares the hydrological responses of runoff, soil moisture and groundwater levels to rainfall events for two small semi-arid catchments over a 2-year period. Romwe received 1430 and 756 mm of rainfall in the 19999/00 and 2000/01 season, respectively. Mutangi received 756 and 615 mm of rainfall in the same years. Romwe generated 520 and 102 mm of runoff in the 19999/00 and 2000/01 seasons, respectively, while Mutangi generated 82 and 69 mm of runoff in the same years. The runoff response of the catchments was dominated by a relatively quick response to rainfall and with little or no significant contribution from regional groundwater or ‘old water’ sources. Total soil moisture storage to a depth of 120 cm was higher at Romwe than Mutangi for the entire study period reflecting the differences in the soil types. The groundwater level was closer to the surface and responded more quickly to rainfall at Romwe compared to Mutangi where water levels were between 12 and 16 m below the surface. There was a significant relationship between profile soil moisture and water table level at Romwe and none was observed at all in Mutangi. Significant (p<0.05) monthly rainfall runoff relationships were observed at both Romwe and Mutangi. At Romwe and Mutangi 91% and 76% of the runoff variation was accounted for by rainfall in the 1999/00 season, respectively. The rainfall–runoff relationship were different at Romwe for the two seasons, it was higher in the 1999/00 season than the 2000/01 season when 91% and 49% of the runoff variation was due to rainfall, respectively. The relationships were almost similar at Mutangi during the two seasons.     

Hydraulic redistribution by two semi-arid shrub species: Implications for Sahelian agro-ecosystems

Hydraulic redistribution is the process of passive water movement from deeper moist soil to shallower dry soil layers using plant roots as conduits. Results from this study indicate that this phenomenon exists among two shrub species (Guiera senegalensis and Piliostigma reticulatum) that co-exist with annual food crops in Sahelian agro-ecosystems. Real-time measurements were conducted for soil water content, soil water potential and microclimate variables notably; air temperature, relative humidity, wind speed, precipitation and solar irradiance. Additionally, sap flow measurements were conducted in shrub roots using the thermal dissipation technique on intact and coppiced shrubs. Monthly predawn leaf water potential was measured using a portable pressure chamber. Soil water potential (Ψ_s) at the 20 cm depth declined significantly during the dry season with diel changes in Ψ_s of −0.6 to −1.1 MPa. These variations were attributed to passive water release from shrub roots resulting in overnight rewetting of drier upper soil layers. Sap flow measurements on tap and lateral shrub roots indicated daily reversals in the direction of flow. During the peak of the dry season, both positive (toward shrub) and negative (toward soil) flows were observed in lateral shrub roots with sap flow in the lateral roots frequently negative at night and rapidly becoming positive soon after sunrise. The negative sap flow at night in superficial lateral roots and the periodic positive flow in the descending tap roots were indicative of hydraulic redistribution. Hydraulic redistribution may be an important mechanism for drought stress avoidance while maintaining plant physiological functions in both shrubs and neighboring annuals in water-limited environments.     

Water content and land use history controlling soil CO2 respiration and carbon stock in savanna soil and groundnut fields in semi-arid Senegal

Decomposition of soil organic carbon (SOC) regulates the partitioning between soil C-stock and release of CO₂ to the atmosphere and is vital for soil fertility. Agricultural expansion followed by decreasing amounts of SOC and soil fertility is a problem mainly seen in tropical agro-ecosystems where fertilizers are in short supply. This paper focuses on factors influencing temporal trends in soil respiration measured as CO₂ effluxes in grass savanna compared with groundnut (Arachis hypogaea L.) fields in the semi-arid part of Senegal in West Africa. Based on laboratory experiments, soil CO₂ production has been expressed as a function of temperature and soil water content by fit equations. Field measurements included soil CO₂ effluxes, soil temperatures and water contents. Effluxes in grass savanna and groundnut fields during the dry season were negligible, while effluxes during the rainy season were about 3–8 μmol CO₂ m^?2 s^?1, decreasing to less than 1 μmol by the end of the growing season. Annual soil CO₂ production was simulated to be in the range of 31–38 mol C m^?2. Furthermore, a controlled water addition experiment revealed the importance of rain during the dry season for the overall turnover of soil organic matter.     

Effects of seasonal breeding on productive performance of pastoral goat herds in northern Kenya: a longitudinal analysis of growth in kids and body weight development of does

This paper investigates whether liveweight development of kids and dams can be improved by introducing a seasonal breeding regime in goat herds maintained under pastoral management in northern Kenya. The experimental treatment consisted of six consecutive mating seasons. Traits studied comprise relative growth rates of kids (g kg^−0·75 day⁻¹) from birth until 2 years of age, liveweight development of kids (kg) from birth until 2 years of age, and body weight development (kg) of does over a reproductive cycle of 1 year duration. No systematic effect of mating season on birth weights of kids could be detected, whereas the experiment succeeded in demonstrating that mating season has an impact upon body weight development of kids. The highest average preweaning weight gains were achieved by kids born in the period from October to May, while growth performance was seriously compromised when birth took place at the middle of the long dry season. However, the differences between mating season groups had almost completely disappeared by 1 year of age. The mating season treatment produced marked differences in weight development curves in does. During gestation, does were advantaged when they were mated just prior to the long rainy season, while the largest relative liveweight gains over the entire reproductive cycle were achieved by does mated during the short rains. It is concluded that seasonal breeding does not confer any major advantage in terms of liveweight production of young livestock, except that mating during the short dry season from December to January should be avoided. Similarly, a clear effect on body weights of does at the end of the reproductive cycle could only be observed when mating occurred during this period.     

Spatiotemporal variability of cultivable microfungal communities inhabiting a playa area in the western Negev Desert,Israel

The soil dilution plate method was used to examine spatiotemporal changes in microfungal communities inhabiting the playa and interdune areas in the western Negev Desert, Israel. Soil samples were collected from the 0–50 cm depth at 10 cm intervals at both habitats during the wet and dry seasons of 2010. Forty-six species belonging to 31 genera were identified, 14 and 12 species were common to both habitats during the wet and dry seasons. The colony-forming units (CFUs) ranged from 75 to 4875 and from 500 to 6925 CFU g⁻¹ dry soil at the playa and interdune, respectively. More diverse species and higher microfungal density were recorded during the wet season compared to the dry season at both habitats, and the microfungal communities inhabiting the playa were characterized by lower species diversity and CFU compared with the interdune regardless of soil depth and sampling season. With the increase in soil depth, decreasing trends were found in both species diversity and CFU throughout the study period, especially in the playa soils. Generally, Cladosporium cladosporioides, Alternaria alternata, Ulocladium atrum, and Fusarium spp. were widespread at the playa with high relative abundance, as were Penicillium and Aspergillus spp. at both habitats.     

Winter establishment of the alien annual Schismus barbatus is not affected by insect herbivory in Northern-Central Monte Desert

We studied the effect of ant herbivory on the establishment and survival of the annual plant Schismus barbatus. We hypothesized that ants may control this species when biomass of native plants is generally low during their vegetative period. We predicted that ant herbivory will decrease plant survival and reproduction. We tested our prediction with an insect exclosure experiment in a sandy desert of Northern-Central Monte.We found more than 12 000 established seedlings per square meter on early May, after two consecutive rain pulses of ca. 20 mm each. Overall, we found that almost 75% of recruited plants survived by the end of the cool season (September), and that 22–24% of the initially established plants survived as mature reproductive plants by the end of the growing season (December). Contrary to our expectation, insect herbivory did not affect plant establishment, plant survival or the proportion of flowering and fruiting individuals of S. barbatus.The large number of seedlings reported, the ability to exploit a temporal window free of plant competitors and enemies, and the availability of microsites where this species can succeed, all suggest that S. barbatus may have the potential to become an important plant invader in the Monte Desert.     

Nest dynamics of Constrictotermes cyphergaster (Termitidae,Nasutitermitinae) and its association with the supporting vegetation in a semiarid area,northeast, Brazil

We evaluated growth, abandonment, decay and emergence of new nests of the Neotropical termite Constrictotermes cyphergaster (Termitidae) and its association with the supporting vegetation in an area of caatinga (arid thorn scrub in the state of Paraíba, northeastern Brazil). In an area of 1 ha, a total of 272 nests were observed monthly, from March 2005 to March 2007. Of these, 245 nests were small, 9 were of medium size, and 18 were large nests. During the rainy season (from June to February), nests grew 94.2 L, whereas during the dry season (March–May), their total growth was 23 L. The number of abandoned nests was positively correlated with rainfall. Decomposition of nests was greater during the rainy season. The pattern of nest distribution was associated with the distribution of the primary supporting plants. Rainfall appears to be one of the most important factors in the dynamics of growth of nests of C. cyphergaster in the caatinga.     

青海高原近40 a降水变化特征及其对生态环境的影响

 利用青海省1961-2002年26个代表站逐日雨量资料和高原东部地区10个站的降水自记资料,分析了近40 a来降水量、雨日、雨强的气候变化特征。结果表明:青海高原近40 a来年降水量无明显的变化,但夏半年降水量呈减少趋势,冬半年降水量呈明显的增多趋势；夏半年降水量和雨日虽在减少,但降水强度在增大；夏半年降水量的减少主要是降水日数的减少造成的,而冬半年降水量的增加是由于雨日增多和每个降水日平均雨量的增大所造成；随着气候变暖,夏、秋季降水明显偏少,出现暖干化的气候趋势。     

苏打盐碱土地区不同土地利用类型的地表水分蒸渗特征

选择东北松嫩平原西部典型地区,采用FAO56方法和实际田间定期观测相结合,分析了当地旱田和碱斑地两种主要土地利用类型地表水分蒸散和入渗特征及其对土地盐碱化的影响。结果表明:对于玉米地这样相对蒸散量比较大的旱作农田来讲,水分亏缺和盐碱化主要发生在根层,而对表层土壤,即使在偏干旱年份,仍然有足够的水分入渗量来维持盐分平衡。碱斑地随着植被的破坏,总体上表层土壤蒸发和入渗量基本平衡,但是由于土壤水分蒸发过程中盐分浓度要比入渗过程中的盐分浓度大,表层土壤依然向盐碱化方向发展。采取适当的土地利用方式,建立耗水量与该地区降雨水平相适应的植被系统是控制区域土地盐碱化发展的关键。     

Growth and water relation parameters in drought-stressed Coriaria nepalensis seedlings

In the present study, growth and water relation parameters were analysed in drought-stressed Coriaria nepalensis Wall. seedlings. C. nepalensis seedlings were subjected to four drought cycles of 7, 14, 21, and 28-days, and to one control level (watered on alternate days) in a glasshouse. The seedlings failed to survive a 28-days drought during summer. Osmotic adjustment (defined as the decrease in osmotic potential at zero or full turgor in response to water deficit) was measured as the difference between the osmotic potential of seedlings watered on alternate days (control) and those subjected to 21-days drought cycle. Seedlings subjected to 21-days drought had a predawn water potential of −2.60 MPa, and showed an osmotic adjustment of −1.95 MPa at full turgor and −2.17 MPa at zero turgor. The growth of seedlings was positively related to moisture and with water potential. With decline in soil moisture the root:shoot ratio increased while leaf weight ratio decreased. Leaf characteristics, such as leaf number, leaf area, leaf area ratio, specific leaf area and leaf drop, were also affected by moisture stress. This study has indicated that osmotic adjustment is a major adaptive mechanism of C. nepalensis that aids successful regeneration of seedlings in degraded sites with inhospitable soil conditions.     

Rainfall regulates decomposition of buried cellulose in the Namib Desert

Because of the aridity of the Namib Sand Sea, it has long been assumed that decomposition of buried plant material was largely independent of rainfall. Losses were attributed to consumption by detritivores that forage year-round. Moisture-limited micro-organisms were reported to occur in low densities in Namib sands, supporting the assumption that rainfall was insignificant in regulating decomposition. Observations of abundant macrofungal fruiting from buried plant material and herbivore dung, following a 12 mm rain, suggested the importance of rain-induced decomposition had been underestimated. We used cellulose substrates to compare material loss during dry periods and following differing amounts of rain. Strips of cotton cloth and filter paper, buried at 10 cm depths at five disjunct locations, were sequentially removed over 10 months. A period of at least 170 days elapsed before rains, ranging from 4–46 mm, fell at all locations. Material loss during the dry period averaged 8·2% (range 0–16·7%), and was attributed to macrodetritivore consumption. In marked contrast, an average of 84·1% of the material (range 64·7–97·2%) was lost following rains greater than 9 mm. Wet substrates were heavily colonized by fungi, and termites and tenebrionid beetle larvae were observed feeding on fungus-colonized substrates. Stepwise regression analysis revealed that rainfall, rather than duration of burial, was the primary factor determining substrate loss in the Namib Sand Sea. Although rain events are infrequent and ensuing periods of moist soil are brief, substrate loss following rains is highly significant relative to that occurring in the absence of rain. In contrast to more mesic deserts, rainfall is an important trigger of decomposition in the Namib Sand Sea where soils are too dry to support significant decomposition, except when episodically moistened by rain.     

Rehabilitation of arid rangelands: Intensifying water pulses from low-intensity winter rainfall

The improvement of water availability for plant growth is of major concern for successful rehabilitation in degraded (semi)arid rangelands. This study investigates how rehabilitation techniques affected soil-wetting and soil water storage after a typical low-intensity winter rainfall event in the Succulent Karoo, South Africa.We compared the impact of six rehabilitation treatments (brushpacks, fertilizer, dung, hessian, microcatchments and planting, each applied with and without livestock exclusion) on soil water status after a typical winter rainfall event of 5.2 mm, one year after treatment implementation. We also recorded the impacts of the treatments on soil infiltrability and surface compaction.Treatment induced differences in soil infiltrability and compaction did not affect soil-wetting during the rainfall event since the rainfall rate was too low for the production of runoff. Brushpacks and planting resulted in accumulation of water in the soils below these treatments, probably by capturing wind-driven water droplets. Soil water retention was prolonged by all treatments that shaded the soil (brushpacks, dung, hessian, planting). One year of livestock exclusion did not affect any of the measured parameters significantly.This study highlights mechanisms through which rehabilitation measures may achieve an intensification of water pulses for plant growth under conditions of low-intensity winter rainfall.     

RAINFALL CHANGE AND ITS IMPLICATIONS FOR BELG HARVEST IN SOUTH WOLLO, ETHIOPIA

Most farmers in the Ethiopian highlands depend on rain‐fed agriculture. Some areas have the favourable situation of having two rainy seasons, Belg (February‐May) and the long rainy season Kiremt (June‐October), which is the case in some parts of South Wollo. Tef (Eragrostis tef) is the staple crop that farmers prefer to grow and the 90‐day variety is suitable for growing during the short rainy season. One out of eight Ethiopians lives in tef potential areas which have Belg rainfall. The aim in this study is to analyse rainfall variation in South Wollo, in particular the area east of the small town of Hayk, and to study its effect on the ability to grow tef during the Belg season. Results from interviews showed that a more difficult farming situation had emerged during the past 40 years, largely due to deterioration of physical resources such as rainfall. Rainfall is analysed by comparing daily rainfall data from four stations in two periods, 1963 to 1982 and 1984 to 2003, for changes in totals, seasonal distribution and variability. Coefficient of variance, rainy days, rainfall intensity and dry spells were analysed. Results from this study show that there have been minor rainfall changes but greater rainfall variability. During fieldwork key informants were asked if they were able to harvest tef during the past nine years, a period that has been used in a model of rainfall influence on tef cultivation during the Belg season. In both 20–year periods, farmers were able to grow tef every second year. In spite of a greater variability in rainfall the farmers proved their knowledge and flexibility and were able to harvest tef in the same number of years during both periods.     

金沙江干热河谷不同植被坡面土壤水分时空分布特征

于2016年7~12月和2017年4月的旱、雨季期间,以金沙江干热河谷苴那小流域内的银合欢（Leucaena Benth）林地、车桑子（Dodonaea angustifolia）灌丛地和扭黄茅（Heteropogon cantortus）草地为研究对象,通过网格法和土钻法采集并测定了（0~100 cm）土层的土壤含水量,应用经典统计法和地统计学方法分析该区域不同林草植被下坡面土壤水分的动态变化特征。结果表明：（1）研究区土壤含水量总体较低,雨季显著大于旱季,旱、雨季均表现为灌丛地>草地>林地,呈中度至强度变异（0.07~0.28之间）。（2）不同林草植被下旱、雨季土壤水分具有相似的空间自相关性,自相关系数均由正向负转变,但由正向负转变的滞后距离有所不同,且雨季大于旱季,呈中等或强等空间自相关性。（3）不同林草植被下的土壤水分空间结构不同,林地、灌丛地和草地旱雨季最佳拟合模型均为球状模型;相同林草植被下各土层旱、雨季土壤水分的空间分布特征相似,但旱季的分布格局差异更显著,不同林草植被下深层土壤水分分布比表层土壤水分的分布更为复杂,土壤水分呈明显的斑块或条带状分布,含水量高值区和低值区位置不固定。总之不同林草植被类型会改变局部地段土壤水分空间分布,降雨会加强这种差异的趋势,但土壤水分仍具一定空间连续性。     

兰州市南北两山人工灌木林地土壤水分动态

通过定位监测与对比分析,对兰州市南北两山不同生境下柠条和柽柳林地的土壤水分变化情况及土壤水分亏缺状况进行了研究。结果表明:水分亏缺程度、耗水量、耗水强度、吸水能力、根系周围土壤深层水分下降速度,都表现为：柠条>柽柳\.据此认为,在兰州市南北两山这种较干旱地区,如果立地条件允许,更适宜种植柽柳。土壤水分的季节性变化是降水和植物生长综合作用的结果,降水和植物生长对土壤表层的含水量影响较为显著,而对深层土壤水分的作用不明显。土壤水分的季节变化与降水和植物生长的季节性变化相似,可分为三个时期：春季水分消耗期、夏季水分补给期、秋末冬季土壤水分平稳期。