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961.
Maintaining crop residue on the soil surface is an important part of conservation tillage. Although broad effects of residues on soil temperature (Ts ) are well documented, the methods to predict soil temperatures under various surface residues and tillage conditions are limited. Using the Ts at 0-, 0.05-, 0.10-, and 0.30-m depths, we developed a simplified model to predict Ts for a uniform soil from air temperature (Ta ) data. Data were collected under various tillage and surface residue conditions after wheat ( Triticum aestivum L.) harvest. Residue management treatments were disk, sweep, and no-tillage (with standing or shredded residues). The model predicts maximum and minimum Ts at 0-, 0.05-, 0.10-, and 0.30-m depths using maximum and minimum Ts measured at 2-m above the soil surface, residue mass, apparent thermal diffusivity, and initial Ts profiles. Mean absolute deviation between simulated and measured maximum and minimum surface Ts were 0.53 and 0.44 °C or less, respectively. Root zone maximum and minimum T, were simulated within 0.14 to 0.91 and 0.27 to 0.95 °C, respectively, of the measured Ts . Greater precision of maximum and minimum soil temperature predictions with depth was obtained by using apparent thermal diffusivity calculated from initial Ts profiles. The proposed model can be useful in predicting Ts profiles required for crop growth modeling. 相似文献
962.
Biological characteristics of newly cultivated fodder plants for pastures of the arid zone in Uzbekistan 总被引:1,自引:0,他引:1
O. Kh. Khassanov T. Rachimova S. F. Tadzhiev 《Genetic Resources and Crop Evolution》1994,41(3):125-131
Summary
Haloxylon aphyllum, Kochia prostrata, Salsola orientalis, Ceratoides eversmanniana, and Artemisia ferganensis have been shown to be the most suitable species for establishing artificial pastures or for improving degenerated pastures in the deserts and semi-deserts of the Republic of Uzbekistan. These species are here characterized both ecologically and agronomically, and their adaptations to extremely arid conditions are described. 相似文献
963.
964.
We investigated factors influencing fish abundance and emigration across the boundaries of a no-take zone (NTZ), and its adjacent fished zones, within the Nabq Managed Resource Protected Area, South Sinai, Egyptian Red Sea. Underwater visual census of eight families of reef fish was undertaken at three depths across the whole NTZ (1.2 km), and for a similar distance into the adjacent fished zones. Because most fishing occurs in shallow water, the effect of the NTZ changed with depth. On reef flat transects (1 m depth), seven families showed significantly higher abundance in the NTZ, whereas at 10 m depth only two herbivorous families, Acanthuridae (surgeonfishes) and Siganidae (rabbitfishes) showed a significant difference, both being more abundant in the fished zones, an effect most likely due to reduced competition or predation. To look for evidence of emigration (spillover) of fish from the NTZ, data were also tested for evidence of gradients in abundance extending from within the NTZ to within the fished zones. In shallow water six families showed significant declines in abundance moving away from the centre of the NTZ, whereas at 10 m, the only significant gradients were for acanthurids and siganids, both becoming more abundant moving further into the fished zones. Comparisons of estimated fish length between areas also showed significant differences. The results indicate that at Nabq, while fishing reduces the abundance of most families, especially predators, abundance of some families and species, especially herbivores, may increase under light fishing pressure. Thus, spillover may occur to an extent and in a direction depending on trophic group and fishing intensity. 相似文献
965.
影响亚热带东部森林结构的因子分析 总被引:6,自引:0,他引:6
肖兴威 《东北林业大学学报》2004,32(5):19-20,34
利用第五次全国资源清查的部分数据,在我国亚热带东部地区构造了一条以温度为主要驱动的,长约750km、宽约100km,地跨安徽、江西、浙江、福建、广东五省的平行四边形样带,通过对样带内863块样地的胸径变异系数和有关林分因子、环境因子之间的相关分析,确定了不同因子对林分结构的影响程度,其中,林分的平均胸径对林分结构的影响最显著,林分密度、海拔高度、坡度、经纬度、土壤厚度等对林分结构也有影响。这些因子最多能够解释整个样带林分结构变化的35%。 相似文献
966.
长湖是湖北省第三大淡水湖泊,对维持长江中游地区生态平衡发挥着重要作用。为研究长湖草型湖区和藻型湖区浮游植物群落结构特征及其与环境因子的关系,于2020年4、7、10月和2021年1月对长湖进行了调查与分析。结果表明,草型湖区和藻型湖区分别鉴定出浮游植物80种和91种,以绿藻门种类数最多,分别为38种和50种。两类湖区均以小球藻属(Chlorella sp.)和小环藻属(Cyclotella sp.)为主要优势种。草型湖区和藻型湖区浮游植物丰度变化范围分别为0.59×107~2.34×107 cells/L和0.73×107~3.06×107 cells/L,生物量变化范围分别为8.98~18.48 mg/L和 0.08~21.40 mg/L。藻型湖区多样性指数略高于草型湖区,两湖区水质整体介于轻污染到中污染之间。冗余分析(RDA)结果显示,草型湖区浮游植物优势种主要受水温(WT)、溶解氧(DO)、总氮(TN)、总磷(TP)和水位(WL)影响,藻型湖区主要受DO、TN、氮磷比(N/P)和WL影响。研究可为长湖水生态系统的监测和管理提供科学依据。 相似文献
967.
968.
Raquel H. FLINKER M. Bayani CARDENAS Todd G. CALDWELL Gerald N. FLERCHINGER Roy RICH Peter B. REICH 《土壤圈》2021,31(5):783-795
Free-air carbon dioxide (CO2) enrichment (FACE) experiments provide an opportunity to test models of heat and water flow under novel, controlled situations and eventually allow use of these models for hypothesis evaluation. This study assesses whether the United States Department of Agriculture SHAW (Simultaneous Heat and Water) numerical model of vertical one-dimensional soil water flow across the soil-plant-atmosphere continuum is able to adequately represent and explain the effects of increasing atmospheric CO2 on soil moisture dynamics in temperate grasslands. Observations in a FACE experiment, the BioCON (Biodiversity, CO2, and Nitrogen) experiment, in Minnesota, USA, were compared with results of vertical soil moisture distribution. Three scenarios represented by different plots were assessed: bare, vegetated with ambient CO2, and similarly vegetated with high CO2. From the simulations, the bare plot soil was generally the wettest, followed by a drier high-CO2 vegetated plot, and the ambient CO2 plot was the driest. The SHAW simulations adequately reproduced the expected behavior and showed that vegetation and atmospheric CO2 concentration significantly affected soil moisture dynamics. The differences in modeled soil moisture amongst the plots were largely due to transpiration, which was low with high CO2. However, the modeled soil moisture only modestly reproduced the observations. Thus, while SHAW is able to replicate and help broadly explain soil moisture dynamics in a FACE experiment, its application for point- and time-specific simulations of soil moisture needs further scrutiny. The typical design of a FACE experiment makes the experimental observations challenging to model with a one-dimensional distributed model. In addition, FACE instrumentation and monitoring will need improvement in order to be a useful platform for robust model testing. Only after this can we recommend that models such as SHAW are adequate for process interpretation of datasets from FACE experiments or for hypothesis testing. 相似文献
969.
我国通过立法确立了专属经济区法律制度和地位,在专属经济区立法、执法、资源勘探养护、渔业管理、航运管理、海洋科技、海洋环境生态保护等方面进行了大量实践。主要介绍了我国专属经济区立法、执法、管理机构、渔业资源管理、海洋环境保护、海洋科学研究等方面的实践,并探讨了这些方面存在的问题。为提高我国专属经济区管理水平,更好地保障海洋权益,我国应加强争议岛礁和区域的管理和实际控制;尽快完善相关的法律法规;完善专属经济区管理体制;加强执法队伍建设,推进海上执法力量统一;着力推进海洋科技事业发展和海洋资源利用与养护。 相似文献
970.
选取新疆富蕴地震断裂带8种次生植物根际土壤,以同土层裸地为对照,测量土壤化学性质,利用末端限制性片段长度多态性技术研究塌陷区次生植物对土壤古菌群落的影响.结果表明,多数植物根际土壤养分显著(P<0.05)高于对照,其主要古菌类群为泉古菌门(Crenarchaeota)和广古菌门(Euryarchaeota),群落间多样性差异大,相似性低.不同植物根际土壤古菌的优势类群数量差异较大,鼠掌老鹳草高达18种,西北绢蒿少为2种.典范对应分析表明,土壤有机质含量对古菌优势类群分布影响最大(Hha Ⅰ酶切:r=0.94;Rsa l酶切:r=0.74),速效磷含量与古菌群落各多样性指数呈显著正相关(P<0.05),总氮含量与均匀度指数E呈显著正相关(P<0.05).新疆地震断裂带植被的恢复可影响根际土壤古菌群落的分布、组成和结构,其原因与植物根际土壤化学性质有关,同时在改善土壤肥力方面也有显著效果. 相似文献