浑善达克沙地几种优势植物的生态适应

浑善达克沙地是我国北方干旱半干旱区的主要沙地和严重荒漠化地区之一。同时也是我国内陆沙尘的主要源区之一。研究当地植物对沙地环境的适应方式有助于当地的荒漠化治理，加快生态环境恢复。本文应用（温室和野外）实验生态学方法研究了沙地植物对水分、沙埋和养分异质性环境的生态适应对策。 浑善达克沙地属于半干旱区域。在一次降雨过后，适合植物生长的湿沙层逐渐下降，或者说不适合植物生长的干沙层逐渐加厚。为了能够有效地从沙层中获得水分，植物的根系的伸长的速度必须大于湿沙层下降的速度。因此，当地分布的植物的根系则应该具有相应的形态、生长和生物量投资方面的可塑性。羊柴（Hedysarum laeve Maxim. (Leguminosae) ）是当地的主要半灌木和固沙植物。我们研究了羊柴幼苗对不同土壤含水量和不同模拟降雨量的反应格局，以及移动沙丘生长季节的土壤含水量变动规律。发现，大于3％土壤含水量适合羊柴幼苗生长。最适土壤含水量为12%－20% 。在生长季节早期，羊柴幼苗比较容易在沙丘上定居。如果没有充分的后续降雨的话，萌发后的幼苗在沙丘顶部、落沙坡中部和后部定居比较困难。降雨量越大，根系越深、总根长越大、根系直径越大、侧根越多、根冠比越低。 在干旱半干旱区域的沙地，种子萌发的时间和地点对于植物的定居和存活具有关键作用。通过温室实验，研究了小叶锦鸡儿和羊柴的种子萌发和出苗对不同深度的沙埋的反应，及其与种子大小的关联。结果表明，小叶锦鸡儿和羊柴的种子萌发和出苗对浑善达克沙地的自然生境表现出相似的生态适应。这两个种的种子萌发的适宜温度为10-15ºC, 这是当地春季的平均温度。由于这两个种的种子萌发是光敏感的，所以它们的种子萌发受土壤含水量和光照强度二者之间的平衡调节。2 cm 的较浅沙埋最有利于种子萌发和出苗。种子埋得越深，种子的萌发率和出苗率越低，更多的种子受胁迫休眠保存在土壤中作为种子库。不同大小的种子的不同萌发能力也是一种重要的生态适应，这可以调节种子在合适的时间和合适的沙埋深度萌发和出苗。 冰草（Agropyron cristatum (L.) Gaertn）是浑善达克沙地植物群落中占优势的多年生根茎草本植物之一。种子在合适的地点和时间萌发以及幼苗在合适的地点和时间生长，对于冰草在沙地环境条件下生存和分布具有重要意义。本文研究了浑善达克沙地4-10月份土壤含水量变动情况和冰草种子萌发、出苗和幼苗生长对土壤含水量的响应。结果表明，4月下旬至5月上中旬的土壤含水量对冰草种子萌发、出苗和定居极为关键。控制条件下，冰草种子萌发的最适土壤含水量是12%-20%，出苗以及幼苗生长的最适土壤含水量是12%-16%。当土壤含水量低于3%，冰草种子不能萌发，土壤含水量低于6%时，幼苗不能出土和定居。当土壤含水量达到16%时，冰草幼苗生物量有所下降。在6%-8%的土壤含水量条件下，植株将更多的生物量投资于根的生长。 本文对浑善达克沙地低湿滩地、滩地-风沙沉积过渡区到风沙沉积区的赖草（Leymus secalinus （Georgi） Tzvel.）分株数、地上生物量、土壤水分和养分异质性进行了研究。结果表明，从低湿滩地、滩地-风沙沉积过渡区到风沙沉积区，随着土壤养分的降低，赖草分株数和地上生物量反而增加。赖草的分株数在三种生境中都存在空间自相关。并且，从低湿滩地、过渡区到风沙沉积区空间自相关的变程逐渐增加。地上生物量同样存在空间自相关，但变程以过渡区最大，风沙沉积区最低。土壤水分仅仅在风沙沉积区存在空间自相关。在三种生境条件下，土壤全氮和有机质的空间分布格局相似，都在低湿滩地和过渡区存在空间自相关且变程相似。在风沙沉积区不存在空间自相关。赖草的空间分布格局在低湿滩地为偏离随机适度聚集的分布格局，在过渡区近似于聚居分布，而在风沙沉积区为均匀分布格局。 豆科锦鸡儿属（Caragana ）植物因其可以生物固氮而在草原生态系统当中具有特殊的地位。定量分析小叶锦鸡儿（Caragana microphylla ）灌丛在浑善达克沙地不同生境条件下的分布格局，有助于理解植被与土壤养分循环之间的关系和合理制定退化沙地的恢复对策。本文采用地统计学中的半方差分析和分形分析两种方法研究了浑善达克沙地小叶锦鸡儿灌丛的空间分布格局，分析了不同生境中小叶锦鸡儿灌丛的植被、土壤水分和养分间的相关性。结果表明（1）小叶锦鸡儿灌丛在三种生境条件下（滩地、固定沙丘和半固定沙丘）的盖度、土壤有机质和全氮的空间分布符合球状模型，空间自相关显著;（2）土壤pH值在滩地和固定沙丘的空间分布符合球状模型且空间自相关显著，但在半固定沙丘空间自相关不显著;（3）土壤水分在三种生境中的空间分布都符合线性模型，空间自相关显著。（4）植被的变异尺度（变程）小于各个土壤要素的变异尺度。植被（小叶锦鸡儿灌丛）的分布和形成过程决定了土壤养分的分布和形成过程。当地的豆科植物在养分“沃岛”现象的形成中起了重要作用，合理的利用和布局当地的豆科植物，可以更加有效地补充草地生态系统的养分，从而有利于加快当地生态系统的恢复进程。

Formulation of a tropical town energy budget (t-TEB) scheme

This work describes the tropical town energy budget (t-TEB) scheme addressed to simulate the diurnal occurrence of the urban heat island (UHI) as observed in the Metropolitan Area of Rio de Janeiro (MARJ; -22A degrees S; -44A degrees W) in Brazil. Reasoning about the tropical urban climate have guided the scheme implementation, starting from the original equations from Masson (Bound-Lay Meteorol 94:357-397, 2000). The modifications include (a) local scaling approaches for obtaining flux-gradient relationships in the roughness sub-layer, (b) the Monin-Obukhov similarity framework in the inertial sub-layer, (c) increasing aerodynamic conductance toward more unstable conditions, and (d) a modified urban subsurface drainage system to transfer the intercepted rainwater by roofs to the roads. Simulations along 2007 for the MARJ are obtained and compared with the climatology. The t-TEB simulation is consistent with the observations, suggesting that the timing and dynamics of the UHI in tropical cities could vary significantly from the familiar patterns observed in mid-latitude cities-with the peak heat island intensity occurring in the morning than at night. The simulations are suggesting that the thermal phase shift of this tropical diurnal UHI is a response of the surface energy budget to the large amount of solar radiation, intense evapotranspiration, and thermal response of the vegetated surfaces over a very humid soil layer.

Soil moisture monitoring at the field scale using neutron probe

Measurement of the moisture variation in soils is required for geotechnical design and research because soil properties and behavior can vary as moisture content changes. The neutron probe, which was developed more than 40 years ago, is commonly used to monitor soil moisture variation in the field. This study reports a full-scale field monitoring of soil moisture using a neutron moisture probe for a period of more than 2 years in the Melbourne (Australia) region. On the basis of soil types available in the Melbourne region, 23 sites were chosen for moisture monitoring down to a depth of 1500 mm. The field calibration method was used to develop correlations relating the volumetric moisture content and neutron counts. Observed results showed that the deepest “wetting front” during the wet season was limited to the top 800 to 1000 mm of soil whilst the top soil layer down to about 550mmresponded almost immediately to the rainfall events. At greater depths (550 to 800mmand below 800 mm), the moisture variations were relatively low and displayed predominantly periodic fluctuations. This periodic nature was captured with Fourier analysis to develop a cyclic moisture model on the basis of an analytical solution of a one-dimensional moisture flow equation for homogeneous soils. It is argued that the model developed can be used to predict the soil moisture variations as applicable to buried structures such as pipes.

High subsoil chloride concentrations reduce soil water extraction and crop yield on Vertosols in north-eastern Australia

Salinity, sodicity, acidity, and phytotoxic levels of chloride (Cl) in subsoils are major constraints to crop production in many soils of north-eastern Australia because they reduce the ability of crop roots to extract water and nutrients from the soil. The complex interactions and correlations among soil properties result in multi-colinearity between soil properties and crop yield that makes it difficult to determine which constraint is the major limitation. We used ridge-regression analysis to overcome colinearity to evaluate the contribution of soil factors and water supply to the variation in the yields of 5 winter crops on soils with various levels and combinations of subsoil constraints in the region. Subsoil constraints measured were soil Cl, electrical conductivity of the saturation extract (ECse), and exchangeable sodium percentage (ESP). The ridge regression procedure selected several of the variables used in a descriptive model, which included in-crop rainfall, plant-available soil water at sowing in the 0.90-1.10 m soil layer, and soil Cl in the 0.90-1.10 m soil layer, and accounted for 77-85% of the variation in the grain yields of the 5 winter crops. Inclusion of ESP of the top soil (0.0-0.10 m soil layer) marginally increased the descriptive capability of the models for bread wheat, barley and durum wheat. Subsoil Cl concentration was found to be an effective substitute for subsoil water extraction. The estimates of the critical levels of subsoil Cl for a 10% reduction in the grain yield were 492 mg cl/kg for chickpea, 662 mg Cl/kg for durum wheat, 854 mg Cl/kg for bread wheat, 980 mg Cl/kg for canola, and 1012 mg Cl/kg for barley, thus suggesting that chickpea and durum wheat were more sensitive to subsoil Cl than bread wheat, barley, and canola.

Parameter estimation of a two-horizon soil profile by combining crop canopy and surface soil moisture observations using GLUE

Estimation of soil parameters by inverse modeling using observations on either surface soil moisture or crop variables has been successfully attempted in many studies, but difficulties to estimate root zone properties arise when heterogeneous layered soils are considered. The objective of this study was to explore the potential of combining observations on surface soil moisture and crop variables - leaf area index (LAI) and above-ground biomass for estimating soil parameters (water holding capacity and soil depth) in a two-layered soil system using inversion of the crop model STICS. This was performed using GLUE method on a synthetic data set on varying soil types and on a data set from a field experiment carried out in two maize plots in South India. The main results were (i) combination of surface soil moisture and above-ground biomass provided consistently good estimates with small uncertainity of soil properties for the two soil layers, for a wide range of soil paramater values, both in the synthetic and the field experiment, (ii) above-ground biomass was found to give relatively better estimates and lower uncertainty than LAI when combined with surface soil moisture, especially for estimation of soil depth, (iii) surface soil moisture data, either alone or combined with crop variables, provided a very good estimate of the water holding capacity of the upper soil layer with very small uncertainty whereas using the surface soil moisture alone gave very poor estimates of the soil properties of the deeper layer, and (iv) using crop variables alone (else above-ground biomass or LAI) provided reasonable estimates of the deeper layer properties depending on the soil type but provided poor estimates of the first layer properties. The robustness of combining observations of the surface soil moisture and the above-ground biomass for estimating two layer soil properties, which was demonstrated using both synthetic and field experiments in this study, needs now to be tested for a broader range of climatic conditions and crop types, to assess its potential for spatial applications. (C) 2012 Elsevier B.V. All rights reserved.

Sensitivity of meteorological input and soil properties in simulating aerosols (dust, PM10, and BC) using CHIMERE chemistry transport model

The objective of this study is to evaluate the ability of a European chemistry transport model, `CHIMERE' driven by the US meteorological model MM5, in simulating aerosol concentrations dust, PM10 and black carbon (BC)] over the Indian region. An evaluation of a meteorological event (dust storm); impact of change in soil-related parameters and meteorological input grid resolution on these aerosol concentrations has been performed. Dust storm simulation over Indo-Gangetic basin indicates ability of the model to capture dust storm events. Measured (AERONET data) and simulated parameters such as aerosol optical depth (AOD) and Angstrom exponent are used to evaluate the performance of the model to capture the dust storm event. A sensitivity study is performed to investigate the impact of change in soil characteristics (thickness of the soil layer in contact with air, volumetric water, and air content of the soil) and meteorological input grid resolution on the aerosol (dust, PM10, BC) distribution. Results show that soil parameters and meteorological input grid resolution have an important impact on spatial distribution of aerosol (dust, PM10, BC) concentrations.

Effects of afforestation on soil carbon turnover in China's subtropical region

Afforestation in China's subtropics plays an important role in sequestering CO2 from the atmosphere and in storage of soil carbon (C). Compared with natural forests, plantation forests have lower soil organic carbon (SOC) content and great potential to store more C. To better evaluate the effects of afforestation on soil C turnover, we investigated SOC and its stable C isotope (delta C-13) composition in three planted forests at Qianyanzhou Ecological Experimental Station in southern China. Litter and soil samples were collected and analyzed for total organic C, delta C-13 and total nitrogen. Similarly to the vertical distribution of SOC in natural forests, SOC concentrations decrease exponentially with depth. The land cover type (grassland) before plantation had a significant influence on the vertical distribution of SOC. The SOC delta C-13 composition of the upper soil layer of two plantation forests has been mainly affected by the grass biomass C-13 composition. Soil profiles with a change in photosynthetic pathway had a more complex C-13 isotope composition distribution. During the 20 years after plantation establishment, the soil organic matter sources influenced both the delta C-13 distribution with depth, and C replacement. The upper soil layer SOC turnover in masson pine (a mean 34% of replacement in the 10 cm after 20 years) was more than twice as fast as that of slash pine (16% of replacement) under subtropical conditions. The results demonstrate that masson pine and slash pine plantations cannot rapidly sequester SOC into long-term storage pools in subtropical China.

Drivers of soil net nitrogen mineralization in the temperate grasslands in Inner Mongolia, China

Soil net nitrogen mineralization (NNM) of four grasslands across the elevation and precipitation gradients was studied in situ in the upper 0-10 cm soil layer using the resin-core technique in Xilin River basin, Inner Mongolia, China during the growing season of 2006. The primary objectives were to examine variations of NNM among grassland types and the main influencing factors. These grasslands included Stipa baicalensis (SB), Aneulolepidum Chinense (AC), Stipa grandis (SG), and Stipa krylovii (SK) grassland. The results showed that the seasonal variation patterns of NNM were similar among the four grasslands, the rates of NNM and nitrification were highest from June to August, and lowest in September and October during the growing season. The rates of NNM and nitrification were affected significantly by the incubation time, and they were positively correlated with soil organic carbon content, total soil nitrogen (TN) content, soil temperature, and soil water content, but the rates of NNM and nitrification were negatively correlated with available N, and weakly correlated with soil pH and C:N ratio. The sequences of the daily mean rates of NNM and nitrification in the four grasslands during the growing season were AC > SG > SB > SK, and TN content maybe the main affecting factors which can be attributed to the land use type.

Stable Carbon Isotopic Composition in Soil Organic Carbon and C3/C4 Source Variations at the Haibei Alpine Meadow

Stable carbon isotopes of organic matter originated from different soil layers (0～5 cm, 5～15 cm, 15～25 cm, 25～35 cm, 35～50 cm, 50～65 cm) were investigated in the Haibei Alpine Meadow Ecosystem Research Station of the Chinese Academy of Sciences. The preliminary results indicated that δ13C values of soil organic matter increased with increased soil depth. δ13C of soil organic carbon in 0～5 cm layer showed the lowest value, -25.09‰; while 50～65 cm soil layer possessed the lowerδ13C value, -13.87‰. Based on mass balance model of stable isotopes, it was proposed that the percentage of C4 carbon source tend to increase with increased soil depth. The preliminary study indicated that alpine meadow might have undergone a successive process from C4-dominated community to C3-dominated one. However, changing δ13C values in atmospheric CO2 overtime and different processes of soil organic carbon formation (or eluviation) might somewhat contribute to increasing δ13C values. In this case, mass balance model would underestimate C3 community and overestimate C4 community.

Effects of grassland conversion and tillage intensities on soil microbial biomass, residues and community structure

Agricultural intensification has a strong impact on level of soil organic matter (SOM), microbial biomass stocks and microbial community structure in agro-ecosystems. The size of the microbial necromass C pool could be about 40 times that of the living microbial biomass C pool in soils. Due to the specificity, amino sugar analysis gives more important information on the relative contribution of fungal and bacterial residues to C sequestration potential of soils. Meanwhile, the relationship between microbial biomass and microbial necromass in soil and its ecological significance on SOM are not fully understood and likely to be very complex in grassland soils. This thesis focuses on the effects of tillage, grassland conversion intensities and fertilisation on microbial biomass, residues and community structure. The combined analyses of microbial biomass and residue formation of both fungi and bacteria provided a unique opportunity to study the effect of tillage, grassland conversion and fertilisation on soil microbial dynamics. In top soil at 0-30 cm layer, a reduction in tillage intensity by the GRT and NT treatments increased the accumulation of saprotrophic fungi in comparison with the MBT treatment. In contrast, the GRT and NT treatments promoted AMF at the expense of saprotrophic fungi in the bottom soil layer at 30-40 cm depth. The negative relationship between the ergosterol to microbial biomass C ratio and the fungal C to bacterial C ratio points to the importance of the relationship between saprotrophic fungi and biotrophic AMF for tillage-induced changes in microbial turnover of SOC. One-season cultivation of winter wheat with two tillage events led to a significant loss in SOC and microbial biomass C stocks at 0-40 cm depth in comparison with the permanent grassland, even 5 years after the tillage event. However, the tillage induced loss in microbial biomass C was roughly 40% less in the long-term than in the short-term of the current experiment, indicating a recovery process during grassland restoration. In general, mould board tillage and grassland conversion to maize monoculture promoted saprotrophic fungi at the expense of biotrophic AMF and bacteria compared to undisturbed grassland soils. Slurry application promoted bacterial residues as indicated by the decreases in both, the ergosterol to microbial biomass C ratio and the fungal C to bacterial C ratio. In addition, the lost microbial functional diversity due to tillage and maize monoculture was restored by slurry application both in arable and grassland soils. I conclude that the microbial biomass C/S ratio can be used as an additional indicator for a shift in microbial community. The strong relationships between microbial biomass and necromass indices points to the importance of saprotrophic fungi and biotrophic AMF for agricultural management induced effects on microbial turnover and ecosystem C storage. Quantitative information on exact biomass estimates of these two important fungal groups in soil is inevitably necessary to understand their different roles in SOM dynamics.

The role of rainfall intensity and soil in determining rates of flow through cryoturbated chalk

The effects of different water application rates (3, 10, 15 and 30 mm/h) and of topsoil removal on the rate of downward water movement through the cryoturbated chalk zone in southern England were investigated in situ. During and after each application of water, changes in water content and matric potential of the profile were monitored and percolate was collected in troughs. The measured water breakthrough time showed that water moved to 1.2 m depth quickly (in 8.2 h) even with application rate as low as 3 mm/h and that the time was only 3 h when water was applied at a rate of 15 mm/ h. These breakthrough times were about 150 and 422 fold shorter, respectively, than those expected if the water had been conducted by the matrix alone. Percolate was collected in troughs within 3.5 h at 1.2 m depth when water was applied at 30 mm/h and the quantity collected indicated that a significant amount of the surface applied water moved downward through inter-aggregate pores. The small increase in volumetric water content (about 3%) in excess of matrix water content resulted in a large increase in pore water velocities, from 0.20 to 5.3 m/d. The presence of soil layer had effect on the time taken for water to travel through the cryoturbated chalk layer and in the soil layer, water took about 1-2 h to pass thorough, depending on the intensity.

Microbial populations and the activity of the soil under agricultural and agricultural-pastoral systems

The effects of agricultural-pastoral and tillage practices on soil microbial populations and activities have not been systematically investigated. The effect of no-tillage (NT), no-tillage agricultural-pastoral integrated systems (NT-I) and conventional tillage (CT) at soil depths of 0-10, 10-20 and 20-30 cm on the microbial populations (bacteria and fungi), biomass-C, potential nitrification, urease and protease activities, total organic matter and total N contents were investigated. The crops used were soybean (in NT, NT-I and CT systems), corn (in NT and NT-I systems) and Tanner grass (Brachiaria sp.) (in NT-I system); a forest system was used as a control. Urease and protease activities, biomass-C and the content of organic matter and total N were higher (p < 0.05) in the forest soil than the other soils. Potential nitrification was significantly higher in the NT-I system in comparison with the other systems. Bacteria numbers were similar in all systems. Fungi counts were similar in the CT and forest, but both were higher than in NT. All of these variables were dependent on the organic matter content and decreased (p < 0.05) from the upper soil layer to the deeper soil layers. These results indicate that the no-tillage agricultural-pasture-integrated systems may be useful for soil conservation.

Effect of liming on the mineral nutrition and yield of growing guava trees in a typic hapludox soil

High soil acidity influences the availability of mineral nutrients and increases that of toxic aluminium (Al), which has a jeopardizing effect on plant growth. The objective of this research was to evaluate the effects of soil liming on the development of guava (Psidium guajava L.) plants, on soil chemical characteristics, and on fruit yield. The experiment was carried out at the Bebedouro Citrus Experimental Station, state of São Paulo, Brazil, in a Typic Hapludox soil, from August 1999 to March 2003. The treatments consisted of limestone dose: D0 = zero; D1 = half dose; D2 = total dose; D3 = 1.5 times the dose, and D4 = 2 times the dose to raise the V value to 70%. The doses corresponded to zero, 1.85, 3.71, 5.56, and 7.41tha(-1) applied to the upper soil layer (0-30cm deep) before planting. The results showed that liming caused an improvement in the evaluated soil chemical characteristics up to a depth of 60cm in soil samples both in the line and between lines. The highest fruit yields were obtained when the base saturation reached a value of 55% in the line and 62% between the lines. Foliar levels of calcium (Ca) and magnesium (Mg) were 8.8 and 2.5gkg-1, respectively. The highest limestone dose maintained the soil base saturation (at the layer of 0-20cm) in the line close to 55% during at least 40 months after the incorporation of limestone.