Effects of sand burial on survival, growth, gas exchange and biomass allocation of Ulmus pumila seedlings in the Hunshandak Sandland, China

BACKGROUND AND AIMS: In the last decade, the number of young plants of Ulmus pumila in the Hunshandak Sandland has decreased sharply because of severe sand burial, and their ecological protective function has been weakened. In order to develop an understanding of the tolerance of U. pumila to sand burial and to suggest reasonable measures to protect the sparse-elm-grassland ecosystem, the effects of burial on the survival, growth, photosynthesis and biomass allocation in U. pumila were studied. METHODS: Seedlings were buried at five different depths in pot experiments: no burial (control), partial burial (33 % and 67 % stem height), and complete burial (100 % and 133 % stem height). Growth analyses and measurements of photosynthesis were carried after the plants had been uncovered. KEY RESULTS: All the plants survived partial burial, but about 30 % and 80 % of the seedlings died as a result of the 100 % and 133 % sand burial treatments, respectively. The numbers of newly produced leaves and branches, and the height of the stems of the seedlings in the 33 % and 67 % burial treatments during the period of the experiment were significantly greater than those in the control. Furthermore, net photosynthetic rate, transpiration rate and water use efficiency were also elevated by the partial burial, but not affected by burial time. This might be attributed to the increased root length, which improved water acquisition. The biomass and biomass allocation of the seedlings were significantly changed by the burial treatments and burial times. The biomass was enhanced by partial burial but was reduced by complete burial at each burial time. However, the biomass allocation was not significantly changed by the 33 % and 67 % sand burial treatments 2 or 4 weeks following the burial. CONCLUSIONS: Ulmus pumila was shown to be tolerant to partial sand burial, but must be protected from complete burial.     

浑善达克沙地榆树疏林自然保护区核心区设计的初步研究

为了保护浑善达克沙地榆树(Ulmus pumila)疏林景观,拟建立自然保护区。基于榆树疏林植被图,运用ArcGIS分析榆树疏林斑块数量、面积、破碎化程度,发现该区榆树疏林斑块大小差异较大,小斑块较多,斑块边界割裂严重,破碎化程度高,需要及时加以保护。按照景观生态学原理、生物岛屿地理学设计自然保护区原则,选择疏林斑块集中分布区,作为潜在核心区,运用ArcGIS的缓冲区分析功能,设计不同的宽度,发现斑块边界向外延伸3 km能够连接较多的斑块,而占用较少的非疏林斑块土地面积。同时调查斑块外不同距离样方与疏林斑块的群落相似度,发现1 km以内能够包含大于10%相似度的群落。由此而初步确定的核心区分布在正蓝旗23个嘎查,面积1 531 km²,约占全旗总面积的13%。     

Species composition and colonization of dark septate endophytes are affected by host plant species and soil depth in the Mu Us sandland,northwest China

Investigations into the edaphic associations, host affiliations and soil depth of dark septate endophytes (DSE) in arid desert environments can help explain their spatial distribution and the response mechanisms in desert ecosystems. Soils were sampled to a depth of 50 cm in the rhizospheres of Psammochloa villosa, Hedysarum laeve and Artemisia ordosica in the Mu Us sandland of northwest China in July 2015. The plant species and soil depth significantly influenced the distribution and colonization of DSE. Hyphal and total root colonization were significantly higher under P. villosa than the others in the 0–20 cm layer. The maximum colonization of P. villosa and H. laeve occurred in the 10–20 cm and 20–30 cm soil layers, respectively, while 30–40 cm soil layer under A. ordosica. Of twelve DSE species isolated from the roots of these plants, Phoma radicina and Bipolaris zeae were reported in desert ecosystems for the first time. Hyphal colonization was significantly and positively correlated with soil total nitrogen (TN) and significantly and negatively correlated with the soil carbon/nitrogen (C/N) ratio. Microsclerotial colonization was significantly and positively correlated with soil organic carbon (SOC), and total colonization was significantly and positively correlated with soil TN and total phosphorus (TP) and significantly and negatively correlated with soil C/N. Variation of DSE colonization was mostly attributed to effects of plant species. We concluded that the species composition and colonization of the DSE fungi were influenced by the plant species, soil depth and soil nutrient availability in this desert ecosystem. This research provides a basis for further understanding the ecological adaptability of DSE and their roles in promoting vegetation restoration and reducing desertification in arid ecosystems.     

毛乌素沙地中间锦鸡儿根瘤菌遗传多样性及16S rDNA全序列分析

野生豆科植物中间锦鸡儿是毛乌素沙地的优势种。从蛋白质和DNA水平分析与其共生的根瘤茵的遗传多样性。在蛋白质水平上,24株中间锦鸡儿根瘤菌和9株参比菌株分为2组,A组包含95．8％供试中间锦鸡儿根瘤菌,参比菌株聚为B组,菌株GH72不与其余供试根瘤菌聚类。应用16S　rDNA　PCR—RFLP方法将供试菌株分为22种基因型,中间锦鸡儿根瘤菌组成12种,其余10种由参比菌株构成。表明中间锦鸡儿根瘤菌具高水平遗传多样性。选取代表菌株GH2001进行16S　rDNA全序列测定。与已知相关根瘤菌菌株16S　rDNA进行同源性比较,构建系统发育树状图。GH2001位于Rhizobium分支,与且Agrobacterium radiobacter,Ag.rubi,Rhizobium giardinii,R.mongolense,R.yanglingense,R.galegae和R.huautlense的序列同源性分别达到99％、98．3％、96．3％、95．5％、95．6％、95．27％和95．7％。     

沙埋对半灌木羊柴幼苗的存活、生长和生物量分配的影响

羊柴 (HedysarumlaeveMaxim .)是中国北方沙地飞播进行植被恢复与重建的主要植物种。在晚春与夏初的出苗期 ,羊柴幼苗经常遭受不同深度的沙埋。研究旨在探明沙埋对羊柴幼苗存活、生长和生物量分配格局的影响。6周的沙埋试验结果显示 :当沙埋深度达到其株高时 ,约有 70 %的幼苗死亡 ;沙埋深度达到其株高的 133%时 ,可使羊柴幼苗全部死亡 ;沙埋深度分别为株高的 33%和 6 7%时 ,羊柴幼苗的整株生物量、叶片生物量、根系生物量以及相对生长率都相应地高于非沙埋的对照 (即 :0 %沙埋 )。与非沙埋的对照相比 ,羊柴幼苗在 33%和 6 7%沙埋条件下并不显著地改变其生物量分配格局 ;并且羊柴幼苗的叶数和株高与对照无明显差异 ,但试验期内的新生叶数是沙埋处理 (即 :33%、6 7%和 10 0 %沙埋 )的幼苗明显地高于非沙埋的对照。     

The Role of Soil Seed Banks in Natural Restoration of the Degraded Hunshandak Sandlands, Northern China

The density of seeds in soil seed banks and the species composition of both seed banks and aboveground vegetation were examined in naturally restored sites (NRS) and aerially seeded sites (ASS) in the Hunshandak sandlands of northern China. Five sites were naturally restored 1, 2, 4, 8, and 15 years ago and four sites were aerially seeded 1, 2, 5, and 7 years ago. In total, 36 species were recorded in the seed bank and 41 species in the aboveground vegetation for all NRS, whereas the numbers were 17 and 19, respectively, for ASS, indicating that the NRS can support higher diversity of species than the ASS. During the initial 2 years of restoration, introduced alien shrubs by aerial seeding dominated the vegetation of ASS, although there were indigenous pioneer species in the seed bank which failed to establish in the community. In contrast, indigenous species were dominant components in both the seed bank and the vegetation at the NRS. These findings suggest that the establishment of introduced species might have restricted the germination of certain indigenous pioneer species. Seed bank density of NRS significantly increased with time from 459 ± 76 seeds m⁻² at NRS2 to 3,351 ± 694 seeds m⁻² at NRS15, showing that the seed bank in degraded grassland is large enough to allow natural restoration. It is not always necessary to actively introduce seeds to enhance vegetation diversity.     

浑善达克沙地典型灌木和草本植物对模拟降雨的不同反应

为了探讨不同生活型对瞬时降雨的适应策略,比较了浑善达克沙地常见灌木羊柴(Hedysarum fruticosum Pall.)和其共生草本植物猪毛菜(Salsola callina Y.L. Chang)在降雨解除干旱后的生理生态反应.光合速率(Pn)、蒸腾速率(E)、气孔导度(gs)、PSⅡ最大光化学效率(Fv/Fm)和叶片水势(ψleaf)均随着模拟降雨量的增加而增大;羊柴的水分利用效率(WUE)随降雨量的变化不大,而猪毛菜的WUE却随降雨量的增加一直处于下降趋势.两种植物的Pn和Fv/Fm都在雨后3 d完全恢复,而gs和ψleaf却提前1或2 d恢复,这说明气孔和非气孔因素综合限制了羊柴和猪毛菜的同化速率.两种植物对模拟降雨量的反应方式不同,15 mm的雨量就使羊柴的Pn、E和gs达到最大值,而猪毛菜却随着雨量的增加一直增大.我们认为,羊柴和猪毛菜对于模拟降雨的反应在时间上具有同步性,但对雨量的反应方式却不一致,猪毛菜对水分的利用不经济且瞬时反应,而羊柴可以被认为是节约型用水植物.     

毛乌素沙地景观生态类型与灌丛生物多样性初步研究

本文利用数量方法对毛乌素沙地景观生态类型进行了自上面而下的等式划分,共划分出１０种景观生态类型,并总结了各种景观生态类型的主要性质,对其景观管理措施进行了讨论,还对所划分出的景观生态类型的灌丛的生物多样性进行了分析,其物种丰富度低,而优势度较高,无效均匀度较低,提出毛乌素沙地草地管理的景观和生物多样性原则。     

毛乌素沙地农牧生态系统能值分析与耦合关系

针对毛乌素沙地脆弱农业生态系统生产力实际,根据复合生态系统耦合理论,借助能值理论及分析方法,选择毛乌素沙地偏农区的榆阳区和偏牧区的乌审旗为比较研究对象,对两地近27a的农牧耦合系统初级生产力、次级生产力及系统耦合状况进行了对比分析,探讨性提出了区域农牧系统耦合程度的演变规律。结果表明,榆阳区是偏农型的农牧耦合产业发展模式,乌审旗是偏牧型的牧农耦合产业发展模式;榆阳区有以耗粮型生猪、禽类生产为主的势头,乌审旗有以节粮型草食动物生产为主的势头;榆阳区和乌审旗的初级生产力、次级生产力及A(有效能值利用率)、B(单位低质能产品转化成高质能产品率)、SCD(系统耦合度)值均沿时间序列增大,且SCD值有呈三阶段型增长的规律性。依据研究结果,最后提出了毛乌素沙地农牧生态系统耦合发展的途径,以期能为沙地农牧生态系统稳健发展提供可靠的理论支撑与政策导向。     

根茎半灌木羊柴对光合同化物的克隆整合

羊柴为根茎半灌木,主要分布于我国北方半干旱区的沙地。该种的营养繁殖是由根茎的水平延伸使顶端分生组织与腋生分生组织序列化不断产生而进行的。本项研究采用^14C标记和去叶实验,探讨了母株、子株所组成的分株对内的光合同化物的整合。在24h的传输中,相当可观量的14C光合同化物自母株传输给子株、子株的根系和根茎,且它们的汇活度均超过了10%。在^14C-光合化物向基向传输（由子株向母株）中,传输率较小,且汇活度不足1%,但根茎在这一传输中的汇活度却超过2%。去叶影响着母株与子株之间的光合同化物整合。保持完整的母株增大向遭受去叶的子株传输光合产物;反之亦然。母相提并论和子株都向根茎传输一定量的同化物,表明根茎自分株获得光合同化物的支持。羊柴的相连分株间通过根茎而发生克隆整合,可能使其分株和基株在不利的沙地生境中都获得净收益。