黄土区封育和放牧草地物种多样性和地上生物量对氮素添加的响应

氮素添加对草地生态系统地上生物量具有普遍促进作用,但对解释引起物种多样性丧失的机制仍存在较大争议。本研究以黄土高原半干旱区长期封育和连续放牧草地为对象,通过设置不同氮素添加水平来探索两种典型的草地管理方式下群落地上生物量、物种多样性、群落组分结构对氮素添加的响应及其异同以及物种多样性与地上生物量的关系,并研究这些响应的潜在生态学机制。结果显示,1)氮素添加显著提高长期封育草地地上生物量的同时降低了物种多样性;放牧草地群落地上生物量、物种多样性对氮素添加的响应与封育草地相同,但其响应程度均小于封育施肥草地;2)草地群落物种多样性随地表凋落物生物量增加而降低,随植被透光率增加而升高; 3)封育施肥草地Shannon-Wiener多样性指数与地上生物量存在显著线性负相关关系,而放牧施肥草地的物种多样性与地上生物量不存在显著的相关关系。以上结果表明放牧能够减缓施肥对物种多样性的负效应,在轻微降低物种多样性的前提下显著提高群落地上生物量,是一种合理的草地管理方式。     

干旱区土地利用和土壤改良及植被恢复方式对沙地养分的恢复效应

为研究干旱区土地利用、土壤改良和植被恢复方式对沙地养分的恢复效果,在乌兰布和沙漠东北缘开展试验研究。研究表明,土地利用方式和人为合理的经营活动对沙漠化土地肥力的恢复和提高有较大影响,在农业耕作制度中,其改土培肥效应以草田轮作最高,农作物套种次之,农作物单种最低;在荒漠沙地上种植农作物较果树更有利于保护土壤生态环境;在荒漠沙地上造林,应以防护林为主,不宜营造大规模杨树速生丰产林;在沙地上营造灌木薪炭林,可起到改良贫瘠沙地的功效;在沙地上种植沙打旺、草木樨和苜蓿均可有效的提高沙化土地肥力,以沙打旺效果最好,草木樨次之,苜蓿最差;在围栏封沙育草中,不同植物群落类型对沙地土壤改良效果有所不同,多植物群落优于单一植物群落。土壤氮磷比由高到低依次排序为白刺＋沙蒿＞沙蒿＋沙竹＞沙蒿＞沙竹＞小花棘豆＋沙蒿＞白刺＞小花棘豆,土壤氮磷比的高低主要取决于氮素水平。     

封育草地与弃耕地土壤碳氮固持及固持速率动态

研究植被恢复对土壤碳氮动态的影响,对了解陆地生态系统碳氮循环,应对全球温室效应具有重要意义。本研究以黄土高原丘陵区封育草地和弃耕地为对象,分别以放牧草地和农田为参照,对比分析了封育14年草地和弃耕地0~300 cm土层土壤有机碳(SOC)和土壤全氮(STN)储量、固持量及固持速率。结果表明,封育草地和弃耕地显著增加SOC储量,并且二者封育14年后SOC储量相同;在0~200 cm土壤中,封育14年草地与弃耕地STN储量相对于对照并无增加,0~300 cm土壤中,封育14年草地STN储量显著高于弃耕地(P<0.05);弃耕地SOC固持及固持速率显著高于封育草地,封育14年弃耕地SOC固持主要发生在0~140 cm表层土壤;0~100 cm土壤弃耕地STN固持及固持速率显著高于封育草地,0~300 cm土壤弃耕地STN固持及固持速率显著低于封育草地。以上结果表明,封育和弃耕均可显著提高土壤碳储量,并未明显提升土壤氮储量,弃耕地有较高的SOC固持量及固持速率。     

围栏封育对草地土壤养分改良效果的研究进展

围栏封育是目前较为普遍的一种退化草地恢复措施,不仅有利于植被的恢复,也有利于土壤养分的改善。本文综述了了国内近年有关围栏封育对草地土壤有机质、氮、磷和钾含量影响的相关研究成果,归纳概括了影响封育改良土壤养分含量的因素,指出了今后的研究方向,为我国退化草地封育效益合理性研究和指导草地利用提供一定的基础资料和科学依据。     

刈割和封育对松嫩草原碱化羊草草地土壤跳虫群落的影响

应用类群数、个体密度和多样性指数等多个群落参数,研究刈割活动和围栏封育对松嫩草原碱化羊草草地土壤跳虫群落特征的影响.本研究共捕获土壤跳虫1 086只,分别隶属于8科18属.研究结果表明,围栏封育能够提高草地土壤跳虫的类群数、个体密度和多样性,其中个体密度提高最为迅速和显著;但长期刈割活动造成恶化的土壤理化环境对跳虫类群数量增长和群落食物网的复杂性与稳定性的提高制约是长期的;凋落物的存在与否对草地土壤跳虫群落有较大的影响,其中凋落物的累积有助于退化草地土壤跳虫群落的恢复,而凋落物的流失可能会使草地土壤跳虫群落进一步退化.     

Community structure and carbon and nitrogen storage of sagebrush desert under grazing exclusion in Northwest China

Overgrazing is regarded as one of the key factors of vegetation and soil degradation in the arid and semi-arid regions of Northwest China.Grazing exclusion(GE)is one of the most common pathways used to restore degraded grasslands and to improve their ecosystem services.Nevertheless,there are still significant controversies concerning GE’s effects on grassland diversity as well as carbon(C)and nitrogen(N)storage.It remains poorly understood in the arid desert regions,whilst being essential for the sustainable use of grassland resources.To assess the effects of GE on community characteristics and C and N storage of desert plant community in the arid desert regions,we investigated the community structure and plant biomass,as well as C and N storage of plants and soil(0-100 cm depth)in short-term GE(three years)plots and adjacent long-term freely grazing(FG)plots in the areas of sagebrush desert in Northwest China,which are important both for spring-autumn seasonal pasture and for ecological conservation.Our findings indicated that GE was beneficial to the average height,coverage and aboveground biomass(including stems,leaves and inflorescences,and litter)of desert plant community,to the species richness and importance values of subshrubs and perennial herbs,and to the biomass C and N storage of aboveground parts(P<0.05).However,GE was not beneficial to the importance values of annual herbs,root/shoot ratio and total N concentration in the 0-5 and 5-10 cm soil layers(P<0.05).Additionally,the plant density,belowground biomass,and soil organic C concentration and C storage in the 0-100 cm soil layer could not be significantly changed by short-term GE(three years).The results suggest that,although GE was not beneficial for C sequestration in the sagebrush desert ecosystem,it is an effective strategy for improving productivity,diversity,and C and N storage of plants.As a result,GE can be used to rehabilitate degraded grasslands in the arid desert regions of Northwest China.     

围栏封育对退化灌丛草地群落土壤特性和植被的影响

以雅鲁藏布江中游半干旱河谷山地灌丛草地群落为研究对象,采用野外调查和室内试验结合的方法,研究了围栏封育对灌丛草地植被及土壤养分含量的影响,以期为有效修复雅鲁藏布江中游河谷山地植被退化提供科学参考。结果表明:围栏封育3年土壤有机质、全磷、速效磷、速效钾含量均高于围栏外,土壤表层(0～10cm)养分含量增加显著(P<0.05),随着土壤深度的增加,土壤养分含量与围栏外逐渐趋于一致,至30～40cm到达相同水平;围栏封育后灌丛草地群落高度和产量显著增加(P<0.05),分别比围栏外增加了74%和101%,高度、产量增加主要是由禾本科和莎草科引起;围栏封育对群落组成和物种重要值产生不同程度的影响,主要表现为生物多样性增加,禾本科、莎草科等适口性好的物种重要值增加,杂草类不可食物种重要值相对下降;Rarefaction曲线法结果显示,围栏内物种多样性大于围栏外,与传统多样性指数方法结果一致。     

生长季封育和氮添加对退化高寒沼泽湿地土壤水分状况的影响

为探讨封育和氮添加对退化高寒湿地恢复的影响，本研究在青藏高原东部轻中度退化高寒湿地设置生长季禁牧和氮添加处理试验，并测定了群落结构和生产力、物种丰富度、土壤水分和氮、磷元素含量等指标。结果表明生长季禁牧能够显著提高退化湿地土壤水分含量、土壤速效氮含量和群落净初级生产力，提高禾草类物种在群落中的占比，而降低杂类草物种的占比；氮添加及二者的交互作用对退化湿地植物群落上述指标的影响不显著，但是氮添加处理有增加地上生物量和提高土壤含水量的趋势。本研究还提出了一个围栏封育和氮添加对退化高寒湿地恢复（以土壤水分含量为指标）影响的概念模型。生长季禁牧和氮添加有助于高寒退化湿地的恢复，因此在未来高寒湿地的保护和修复中应该考虑适度禁牧和养分添加。     

封育对黄土高原天然草地深层土壤碳、氮储量的影响

封育是当前恢复和改良退化草地的重要措施,准确评估植被变化过程中土壤碳、氮储量动态,具有重要的生态意义。本研究以宁夏云雾山封育30年天然草地和未封育草地土壤为研究对象,对深层(0-500cm)土壤有机碳(SOC)、全氮(STN)固持动态进行分析。结果表明,封育30年草地土壤碳含量(0-440cm)显著高于未封育草地(P0.05),但是草地SOC变化临界层不明显,未封育草地SOC含量变化临界层大约位于130cm处;封育与未封育草地STN含量在130cm以下显著降低,STN的累积均发生在60-320cm土壤中,而表层(0-60cm)和较深层(320cm)中STN积累较少;封育30年草地340-500cm土壤SOC储量趋于稳定,每20cm土层约为11.5 mg·hm~(-2),未封育草地140-500cm土壤SOC储量趋于稳定,每20cm土层维持在8mg·hm~(-2);封育30年草地0-100cm土壤SOC、STN储量分别占0-500cm土层的44.8%和27.2%,0-200cm分别占72.2%和38.5%,0-300cm分别占83.5%和64%,0-400cm分别占92.2%和80.1%。因此,深层土壤有着大量的碳、氮储量信息,对于100-500cm土壤碳、氮动态研究非常必要。     

Effectiveness of electro-fencing for restricting the ranging behaviour of wildlife: a case study in the degazetted parts of Akagera National Park

Several national parks on the African continent have been fenced to mitigate human–wildlife conflict, but the effectiveness of different fencing strategies seems to vary between regions. Here, we assessed the effectiveness of electro-fencing for restricting movement patterns of several wild ungulates in Akagera National Park (NP), Rwanda. Following the turmoil of the Rwandan genocide and civil war (1991–1995), large numbers of returning war refugees brought about an increasing pressure on land use, after which considerable parts of the western Akagera NP and adjacent Mutara Game Reserve were degazetted, followed by the construction of an electric fence in 2013 and a helicopter-based game-drive of ungulates into the modern park. We conducted distance sampling of wildlife and domestic livestock in the Uruhita plain – now no longer part of Akagera NP but bordering the modern Akagera NP to the west – for extended periods of time (2010–2015) before and after fencing. For abundant species population densities could be calculated, whereas for other species encounter frequencies are reported. We report on continuously high cattle densities, and increasing encounter frequencies of sheep/goats in the Uruhita plain. We found decreasing densities of zebra (Equus quagga) and decreasing encounter frequencies of waterbuck (Kobus ellipsiprymnus), stagnant encounter frequencies in the case of topi (Damaliscus lunatus jimela) and stagnant densities of impala (Aepyceros melampus). The latter species can jump fences, and we argue that competitive release and reduced predation may be the prime factors leading impala to (temporarily) exploit grasslands outside the modern national park.