3种高寒草甸土壤CO2通量及碳密度差异变化

在祁连山东缘选择珠芽蓼草甸(P)、针茅草地(S)、杜鹃灌丛草甸(R)3种高寒草甸,利用LI-8100A土壤CO2通量自动测定系统与室内分析相结合的研究方法,分析了土壤有机碳密度、碳通量的动态及其与环境因子的关系。结果表明:不同植被类型的土壤有机碳密度差异显著,大小顺序为R>S>P,随土壤深度的增加,土壤碳密度降低;土壤CO2通量大小顺序为S>P>R,样地P、S呈单峰变化。峰值均出现于14∶00～15∶00;土壤CO2通量与近地面的空气湿度、碳含量显著负相关,与土壤温度、近地大气温度显著正相关,与土壤含水量无明显相关性。     

Implications of changes to the transhumance system for conservation of the mountain catchments in eastern Lesotho

Abstract

The mountain catchments above 2 750 m a.s.l. in eastern Lesotho are a proclaimed Managed Resource Area (MRA) as a result of official concern about degradation of the grasslands of the alpine belt, and of recent parastatal interventions in the local livestock economy. However, the demarcation of the MRA may be inappropriate because it ignores recent changes in the transhumance system which threatens to cause greater degradation of the grasslands in the subalpine belt, particularly in the lower subalpine zone. In response to a variety of ecological and social factors, Basotho have modified the transhumance system by establishing winter grazing posts in this zone which lies between the summer grazing post areas in the subalpine zone and the alpine belt and the villages. The former areas are now used more intensively than the latter areas, thereby increasing the potential for greater degradation in the lower subalpine than in the upper subalpine zone and in the alpine belt. It is argued that the conservationist perspective, by which the MRA was demarcated needs to be broadened to include these lower valleys in view of these ecological dynamics.     

RESENSIES—REVIEWS

Results at harvesting are described of two comprehensive NPK fertilizer experiments with E. grandis on sites previously under wattle in the Natal Midlands. The experimental sites differ considerably in respect of physiography, climate, and soil. The difference in climate and soil are clearly evident from the respective analyses of soil samples from the sites, one soil of a dystrophic series belonging to the Griffin form, and the other a mesotrophic series of the Hutton form.

Except in one instance, nitrogen application showed no significant response, which is expected on these nitrogen-enriched soils of old wattle plantations. There is a tendency, which in one instance was significant, that nitrogen has a depressive effect on E. grandis, but this is ascribed to burning the transplants when the fertilizer is too concentrated and applied too close to the trees.

Superphosphate application on these sites gives highly profitable results, the additional net profit per ha being nearly R400 on the better site and at least R35 on the poorer site. The optimum application rate on the better site is not more than 130 g superphosphate (8,3% P) per tree, while the optimum rate on the poorer site might be as high as 260 g.

Significant responses to potash application are limited to mesotrophic soils and are of a curvilinear nature. This last phenomenon especially is difficult to explain, but is known to have occurred elsewhere.     

Soil inorganic nitrogen composition and plant functional type determine forage crops nitrogen uptake preference in the temperate cultivated grassland,Inner Mongolia

ABSTRACT

Plant nitrogen (N)-acquisition strategy affects soil N availability, community structure, and vegetation productivity. Cultivated grasslands are widely established to improve degraded pastures, but little information is available to evaluate the link between N uptake preference and forage crop biomass. Here an in-situ ¹⁵N labeling experiment was conducted in the four cultivated grasslands of Inner Mongolia, including two dicots (Medicago sativa and Brassica campestris) and two monocots (Bromus inermis and Leymus chinensis). Plant N uptake rate, shoot- and root biomass, and concentrations of soil inorganic-N and microbial biomass-N were measured. The results showed that the root/shoot ratios of the dicots were 2.6 to 16.4 fold those of the monocots. The shoot N concentrations of the dicots or legumes were 40.6% to 165% higher than those of the monocots or non-legumes. The four forage crops in the cultivated grassland preferred to uptake more NO₃^?-N than NH₄⁺-N regardless of growth stages, and the NH₄⁺/NO₃^? uptake ratios were significantly lower in the non-legumes than in the legumes (p < 0.05). Significant differences in the NH₄⁺-N rather than NO₃^?-N uptake rate were observed among the four forages, related to plant functional types and growth stages. The NH₄⁺ uptake rate in the perennial forages exponentially decreased with the increases in shoot-, root biomass, and root/shoot ratio. Also, the plant NH₄⁺/NO₃^? uptake ratio was positively correlated with soil NH₄⁺/NO₃^? ratio. Our results suggest that the major forage crops prefer to absorb soil NO₃^?-N, depending on soil inorganic N composition and belowground C allocation. The preferential uptake of NO₃^?-N by forages indicates that nitrate-N fertilizer could have a higher promotion on productivity than ammonium-N fertilizer in the semi-arid cultivated grassland.     

Field-Scale Evaluation of Calcium Ammonium Nitrate,Urea, and Urea Treated with N-(N-Butyl) Thiophosphoric Triamide Applied to Grassland in Ireland

This study investigated the effects of nitrogen (N) source, rate, and timing of application on dry-matter yield (DMY), N responses, N uptake and N-use efficiency (NUE) in a grass crop. The experiment used three fertilizer treatments: calcium ammonium nitrate (CAN), urea, and urea treated with N-(n-butyl) thiophosphoric triamide (NBTPT), applied at 0 (control), 25, 50, and 75 kg ha^?1 of N over eighteen application timings. Results showed relatively lower agronomic performance of urea compared with CAN when applied in early spring. Urea reported lower N responses, lower relative DMY (90 percent), and relative N uptake (85 percent), which translated in lower NUE (0.45 kg kg^?1) compared with CAN (0.70 kg kg^?1). In spring fertilizer applications, urea and NBTPT showed DMY and NUE values comparable to those obtained with CAN. However, NBTPT enhanced overall performance of urea, which was shown with increasing temperatures toward summer or increasing N application rates. For summer applications, the efficiency of urea was less (P < 0.05) than that of CAN or NBTPT in all measured parameters, suggesting greater ammonia volatilization loss in urea-treated grass. Nitrogen saved in volatilization improved uptake and responses in NBTPT-treated grass, and hence DMY was not affected compared with CAN in summer fertilizer applications. The results of this study are supportive of increased usage of urea-based fertilizers treated with NBTPT.     

长期围栏封育对天山中部草地土壤有机碳及微生物量碳的影响

以天山中部中科院巴音布鲁克草原生态观测站三种类型草地长期（26 a）围栏封育样地为研究对象,通过野外调查取样结合室内分析的方法,研究了长期（26 a）围栏封育对草地土壤有机碳和微生物量碳含量的影响,结果表明：（1）围栏外（自然放牧条件下）,表层的土壤有机碳含量为高寒草甸（165.29 g·kg-1）〉高寒草甸草原（98.73 g·kg-1）〉高寒草原（83.54 g·kg-1）,微生物量碳含量依次为高寒草甸草原（181.70 mg·kg-1）〉高寒草甸（146.37 mg·kg-1）〉高寒草原（43.06 mg·kg-1）。围栏封育后,高寒草甸、高寒草甸草原、高寒草原表层土壤有机碳含量分别提高了11.37%、3.26%和2.21%;高寒草甸草原和高寒草甸微生物量碳含量分别增长2.89%和12.04%,而高寒草原降低40.36%。（2）从围栏内外土壤剖面来看,土壤有机碳、微生物量碳含量随着土壤深度的增加依次降低,微生物熵也随土壤深度的增加呈现降低的趋势。（3）微生物量碳含量与土壤速效钾、全磷含量达到极显著负相关（P〈0.01）,与速效磷含量达到极显著正相关（P〈0.01）,与土壤有机碳、全氮、全钾含量呈显著正相关（P〈0.05）与土壤速效氮含量正相关,但不显著。     

若尔盖湿地土壤酶活性和理化性质与微生物关系的研究

本文旨在研究若尔盖湿地土壤退化过程中四种典型土壤(泥炭土、沼泽土、草甸土、风沙土)中脲酶、过氧化氢酶、转化酶、多酚氧化酶活性及其与理化性质、微生物数量的相关性分析。结果表明:随着土壤深度增加,脲酶、转化酶活性逐渐降低,过氧化氢酶、多酚氧化酶活性逐渐升高;随着土壤退化程度的加剧,脲酶和转化酶活性总体呈下降趋势;泥炭土、沼泽土、草甸土中过氧化氢酶活性显著高于风沙土;多酚氧化酶活性随退化程度加剧呈上升趋势,但在沼泽土中活性最低。泥炭土、沼泽土、草甸土中转化酶及风沙土中过氧化氢酶与土壤理化性质、微生物数量的相关性较显著。因此土壤酶活性(脲酶、转化酶)、理化性质(含水量、有机质、全氮、全磷、全钾)、微生物数量能较好地指示当地土壤退化状况。     

基于气象要素空间分布模拟优化的中国草地综合顺序分类

依据草地综合顺序分类系统(CSCS)原理,利用中国区域1961—2004年的气象信息数据,以及1km分辨率的DEM(高程)数据,借助ArcGIS平台,采用优化的气象要素模拟方法——多元回归+残差分析(AMMRR),以及3种传统插值方法,模拟了中国多年平均的>0℃年积温(Σθ)和年均降水量(r)的空间分布,并利用AMMRR法对中国草地进行分类。研究结果表明:1)AMMRR模拟得到的Σθ和r与实测样本的相关系数分别为0.976和0.974,极显著相关(p<0.01);相对平均误差(RME)、平均绝对误差(MAE)和均方根误差(RMSE)都小于3种传统插值方法。2)AMMRR通过经纬度、海拔高度与气象要素间的多元回归以及残差分析修正,不仅弥补了原始站点不足且分布不均匀的缺点,而且也充分体现了海拔落差较大区域气象要素的垂直变化。气象站点分布密集的区域,4种方法模拟的效果较一致,其空间格局与真实地理环境相似;但站点稀疏而且分布不均匀的区域,只有AMMRR的模拟结果才能反映出小尺度空间分布中地形的空间分异作用,结果比较理想。3)依据CSCS,中国草地包括除炎热极干热带荒漠类(ⅦA7)的其他41个地带性草地类。从南到北,Σθ减小,依次分布着炎热潮湿雨林类(ⅦF42)-亚热潮湿常绿阔叶林类(ⅥF41)-暖热潮湿落叶、常绿阔叶林类(ⅤF40)-暖温潮湿落叶阔叶林类(ⅣF39);从东向西,r降低,依次分布着微温潮湿针叶阔叶混交林类(ⅢF38)-微温湿润森林草原、落叶阔叶林类(ⅢE31)-微温微润草甸草原类(ⅢD24)-微温微干温带典型草原类(ⅢC17),地带性规律明显。     

施氮和增雨对内蒙古半干旱地区草原土壤微生物群落碳源利用潜力的影响

已有许多研究证明,中国北方草地生态系统的植物群落结构和组成对气候变化和氮沉降较为敏感,但是关于草原土壤微生物群落响应多重环境因子变化方面的研究较薄弱。水和氮是陆地生态系统生产力的两大限制性因子。本研究在内蒙古多伦半干旱草原地区进行增雨和施氮的野外控制试验,以模拟未来该地区的降水变化和氮沉降,使用微生物群落水平生理图谱法,监测样地土壤理化指标和土壤微生物群落碳源利用潜力的变化。3年的跟踪监测结果显示:增雨显著提高了半干旱草原地区土壤含水量和有机质含量;施氮和增雨同时施氮则显著提高了土壤可溶性氮含量,降低了土壤pH;施氮和增雨都没有单独引起土壤微生物群落碳源利用潜力的显著变化,而在同时增雨和施氮试验处理下,微生物群落碳源利用潜力得到提高,说明在水和氮都充足的条件下,土壤微生物碳源利用潜力才会显著提高。以上研究结果预示着在未来降雨增加和氮沉降的全球变化背景下,中国北方半干旱草地生态系统的碳循环速率可能会加快。     

封育对退化草原植被恢复及土壤理化性质影响的研究进展

封育是退化草原生态系统恢复的有效措施之一。在梳理现有封育研究成果的基础上,归纳封育对植物多样性、生物量、植被演替、土壤物理与化学性状的影响效应,发现:受地理区域、气候条件及封育前退化程度等本底条件的影响,封育条件下植被多样性呈现出显著增加、基本稳定和明显下降3种结果,生物量则表现为围封初期增加,围封时间过长不利于维持较高生物量的变化趋势;封育使得种群拓殖能力与群落资源冗余,土壤种子库结构改善、密度增长,退化草原呈正向演替,并可能出现3种演替模式。封育消除了土壤紧实层,改善了土壤结构与性状,但对土壤养分的影响效应不一致。基于研究现状,提出今后应深入研究的6个内容与方向,对丰富封育条件下退化草原恢复效应具有指导意义。