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51.
Junxia Yan Zhong Hao Junjian Li 《Communications in Soil Science and Plant Analysis》2017,48(9):977-988
Shrub is one of the major vegetation types distributed mostly in the mountainous area in China, and its vegetation carbon storage is approximately one-third of both forests and grasslands. It is essential to investigate how soil temperature (Ts) and soil water content (Ws) affect soil respiration (Rs) in this ecosystem. The purpose of this study was to understand the correlations of Rs with Ts, Ws, and other factors in the shrubs. In the current study, Rs was characterized in three shrublands (hereafter, shrub 1, shrub 2, and shrub 3, respectively) located in different elevations over a 4-year period at a biweekly interval in the eastern Loess Plateau (Shanxi province) of China. Our results showed that the trend of seasonal change of Rs was controlled mainly by Ts and Ws. The measured mean Rs over 4 years was 3.64 ± 2.83 (mean ± S.D.), 2.69 ± 2.05, and 4.41 ± 3.28 μmol carbon dioxide (CO2) m?2 s?1 for shrubs 1, 2, and 3, respectively, exhibiting an increase trend with elevation increment. Over the season, Rs illustrated a significant change depending on the variation of Ts and Ws, with larger values appearing in summer when both Ts and Ws were high, and smaller values in winter or in summer whenever Ws was low. An exponential model (Rs = a e bTs) fitted well the relation between Rs and Ts for shrub 3, whereas linear (Rs = a Ws + b) and power (Rs = a Ws b) models of Rs to Ws fitted well for shrub 1. This indicated that at a lower elevation, Ws had a greater effect on Rs than that at a higher elevation. The reverse trend was true between Rs and Ts, i.e., at a higher elevation Ts had a greater effect on Rs than that at a lower elevation. The calculated Q10 values of 1.61, 3.03, and 3.73 for shrubs 1, 2, and 3 increased to 2.25, 3.63, and 4.07, respectively (when the data in low Ws conditions were excluded from the analysis), showing that Q10 increased with elevation increment. Furthermore, three two-variable models, one linear (Rs = a (Ts Ws) + b), and two nonlinear (Rs = a Ts b Ws c and Rs = a ebTs Ws c), were also well developed to predict the dependency of Rs on both Ts and Ws. Our research results might have important implications for the estimation of soil carbon emissions of the shrublands in this region. 相似文献
52.
The effects of fertilization on the distributions of organic carbon (OC) and nitrogen (N) in soil aggregates and whether these effects vary with cropping system have not been well addressed.Such information is important for understanding the sequestration of OC and N in agricultural soils.In this study,the distributions of OC and N associated with soil aggregates were analyzed in different fertilization treatments in a continuous winter wheat cropping system and a legume-grain rotation system in a 27-year field experiment,to understand the effects of long-term fertilization on the distributions of OC and N in aggregates and to examine the recovery of soil OC and N in a highland agroecosystem.Manure fertilizer significantly decreased soil bulk density but increased the amount of coarse fractions and their associated OC and N stocks in the soils of both systems.Fertilizers N + phosphorus (P) and manure had similar effects on total soil OC and N stocks in both systems,but had larger effects on the OC and N stocks in > 2 mm aggregates in the legume-grain rotation system than in the continuous winter wheat system.The application of P increased the OC and N stocks in > 2 mm aggregates and decreased the loss of N from chemical fertilizers in the legume-grain rotation system.The results from this study suggested that P fertilizer should be applied for legume-included cropping systems and that manure with or without chemical fertilizers should be applied for semiarid cropping systems in order to enhance OC and N accumulation in soils. 相似文献
53.
黄土高原地区玉米双垄全膜覆盖沟播栽培技术土壤水温条件及其产量效应 总被引:18,自引:0,他引:18
田间比较玉米双垄全膜覆盖沟播栽培技术新型覆膜方式(SL)与其他覆膜方式———条膜起垄覆盖(TL),条膜平铺覆盖(TP),全膜平铺覆盖(QP)以及不覆膜(CK)在土壤含水量,土壤温度及玉米产量三个方面差别。分析结果显示:新型覆膜方式SL在作物苗期和成株期的表层土壤含水量最高,地表蒸发量较小,集水效果最好;在苗期的表层地温高于其他处理,超出对照6.1℃。各处理玉米产量从高到低次序为SLQPTLTPCK。其中SL比QP增加21.9%,比TL增加64.8%,比TP增加32.1%,较CK提高了1045%。SL的经济收益是QP的1.2倍,TL的1.7倍,TP的1.3倍,CK的10.2倍。双垄全膜覆盖沟播栽培技术是黄土高原半干旱区一项有效的增产和提高农民经济收入的措施。 相似文献
54.
55.
《Strength and Conditioning Journal》2020,73(2):252-258
Understanding fall precipitation effects on rangelands could improve forage production forecasting and inform predictions of potential climate change effects. We used a rainout shelter and water addition to test effects of seasonal precipitation on soil water and annual net primary production of C3 perennial grass, C4 perennial grass, annual grasses, forbs, and all plants combined. Treatments were 1) drought during September−October and April−May (DD); 2) drought plus irrigation during September−October and drought during April−May (WD); 3) year-long ambient conditions (WW); and 4) ambient plus irrigation during September−October (W + W). Treatments created conditions ranking among the driest and wettest September−October periods since 1937. Fall water effects on soil water were not detectable by May at 15 cm and 30 cm. Effects persisted into July at 60 cm and 90 cm, depths below the primary root zone. With spring drought, annual net primary production was 344 kg ha−1 greater when the previous fall was wet rather than dry. No differences were detected between fall water treatments when spring was wet and fall was about 184% (1 938 ± 117 kg ha−1) or 391% of the median (1 903 ± 117 kg ha−1). Fall water increased C3 perennial grass when spring was also wet and had no effect under spring drought, when forage production concerns are greatest. Fall water did not affect C4 perennial grass, and extremely wet fall conditions reduced forb production about 50%. The greatest effect of fall water was increased annual grass production. Even record high levels of fall water had minor effects on biomass, functional group composition, and soil water that were short-lived and overwhelmed by the influence of spring precipitation. Movement of fall water to deep soil by the growing season suggests plants that would most benefit from fall precipitation are those that could use it during fall (winter annuals), or deep-rooted species (shrubs). 相似文献
56.
通过大坝沟乡农业生态系统的能量与物质的投入产出分析,评价系统的功能、结构特征,探讨该地区增强系统功能、提高系统生产力的有效措施。 相似文献
57.
Warm-season annual grasses may be suitable as forage crops in integrated weed management systems with reduced herbicide use. A 2-year field study was conducted to determine whether tillage system and nitrogen (N) fertilizer application method influenced crop and weed biomass, water use, water use efficiency (WUE), and forage quality of three warm-season grasses, and seed production by associated weeds. Tillage systems were zero tillage and conventional tillage with a field cultivator. The N fertilization methods were urea broadcast or banded near seed rows at planting. Warm-season grasses seeded were foxtail (Setaria italica L.) and proso (Panicum mileaceum L.) millets, and sorghum–sudangrass (Sorghum bicolor (L.) Moench × Sorghum sudenense Stapf.). Density of early emerging weeds was similar among treatments, averaging 51 m?2. Millets exhibited higher weed density and weed biomass than sorghum–sudangrass. At harvest, sorghum–sudangrass produced significantly greater biomass and N accumulation than either millet. Water use (157 mm) and WUE (25.1 kg mm-1 ha?1) of total biomass did not vary among treatments or grass entries. Weed seed production by redroot pigweed and green foxtail was respectively 93 and 73% less in sorghum–sudangrass than proso millet. Warm-season grasses offer an excellent fit in semiarid cropping systems. 相似文献
58.
Soybean plants (Glycine max L. cv. Akisengoku) were grown in water culture in a greenhouse. At the pod-setting and pod-filling stages, plants were subjected to stem-ringing or treated with high concentration of nitrate. Respiration and N2 fixation (acetylene reducing activity) were studied in individual nodules along with the concentrations of ATP and magnesium. There was a high positive correlation between respiration activity and acetylene reduction in soybean nodules. The maintenance respiration in mature nodules corresponded to a CO2 evolution of 5.5 µmol/g F.W., and the respiratory cost for nitrogen fixation was estimated at 2 mg C liberated/mg N fixed, though this value was probably underestimated due to CO2 fixation by the nodules. For the nitrogenase activity there was a threshold value of ATP concentration at around 0.15 µmol/g F.W., and the activity increased up to around 0.35 µmol/g F.W., beyond which the ATP concentration did not increase unlike the nitrogenase activity. The values for the magnesium concentration in the nodules detected in the present experiments were above the optimum level. 相似文献
59.
There are variations in soil respiration across vegetation types; however, it is unclear which factors are mainly responsible for the variations. A field experiment was conducted in 2008 and 2009 in a semiarid region of China to investigate the daytime and monthly variation of soil respiration across vegetation types and to determine the factors controlling the variation. An automated portable soil carbon dioxide (CO2) flux measurement system was used to measure the soil respiration in shrubland, grassland, fallow land, and cropland during the growing periods. The results showed that the relative daytime variation amplitude of soil respiration in the fallow land and cropland was as small as that of shrubland and grassland during July, but greater than that of shrubland and grassland during August and October. A hysteresis effect for the relationship between the daytime soil respiration and daytime soil temperature was observed for all four vegetation types. There was also a hysteresis effect for the relationship between the daytime soil respiration and daytime air temperature for the grassland. Over the study period, the monthly soil respiration rates of the fallow land and cropland were statistically comparable and significantly lower than those of the shrubland and grassland, with the exception of August, during which the monthly soil respiration of the cropland was as great as that of shrubland and grassland. The factors responsible for the monthly soil respiration variation across the vegetation types differed from month to month. In general, the soil temperature and soil water content were mainly responsible in August and September; however, the root biomass predominated in July and October. The results are valuable for accurately estimating regional carbon fluxes by considering the temporal variability of the soil respiration variation across vegetation types in the Loess Plateau of China. 相似文献
60.
Kyoichi Kumada 《Soil Science and Plant Nutrition》2013,59(1):106-111
I. Absorption Spectra of Some Artificial Humic Acids It is a well known fact that numerous dark brown or black and amorphous substances cap be produced from organic compounds by purely chemical processes. Some of them are called artificial humic acids, and have been used as a model of soil humic acids by many workers. But it is doubtful whether such artificial humic acids are considered to be a model of soil humic acids, even if there can be found any similarities in their properties. However it may be an useful method for the study of humus formation to compare artificial humic acids with soil humic acids, and to make efforts to find a good model or to prepare artificial humic acids comparable to soil humic acids under laboratory conditions. For this purpose, first of all, the author prepared artificial humic acids from glucose, hydroquinone and lignin, and their absorption spectra were determined. 相似文献