Carbon accumulation, nitrogen and phosphorus use efficiency of Sophora davidii seedlings in response to nitrogen supply and water stress

A greenhouse experiment was conducted to explore whether additional nitrogen (N) supply could enhance carbon (C) accumulation, and phosphorus (P) use efficiency (NUE_P) of Sophora davidii seedlings under dry conditions. Two-month-old seedlings were subjected to a completely randomized design with three water (80, 40 and 20% water field capacity (FC)) and three N supply (N0: 0, Nl: 92 and Nh: 184 mg N kg⁻¹ soil) regimes. Water stress decreased C, N and P accumulation, NUE_P, N and P uptake efficiency (NUtE_N and NUtE_P) regardless of N supply. The S. davidii seedlings exhibited strong responses to N supply, but the responses were not consistent with the various N supply levels. Nl increased C, N and P accumulation, and improved NUE_P, NUtE_N and NUtE_P in the same water treatment. In contrast, Nh did few or even depress effects on C, N and P accumulation, and NUE_P, although NUtE_N and NUtE_P increased with Nh in the same water treatment. Even so, NUE_N decreased with increase of N supply in the same water treatment. The results suggested that appropriate or low N supply should be recommended for S. davidii seedling establishment in dry environment by improving C accumulation and NUE_P.     

不同温度和沙埋深度对砂生槐种子萌发及幼苗生长的影响

在沙地环境中,沙埋是影响植物种子萌发和幼苗存活的一个重要因素。砂生槐是西藏特有的沙生植物,主要分布在雅鲁藏布江中游地区及拉萨河、年楚河等主要支流宽谷区。对砂生槐幼苗进行了控制沙埋试验,研究了不同温度和沙埋深度对砂生槐种子萌发特性的影响。结果表明,温度和沙埋深度显著影响砂生槐种子的萌发率和出苗率。在15～30 ℃的温度范围内,随着温度的升高,种子萌发率显著下降,15 ℃时,其种子萌发率达到最高值;砂生槐种子能在深度≤10 cm的沙埋中萌发,≤8 cm的沙埋中出苗,在此范围内,随着沙埋深度的增加,砂生槐种子的萌发率和出苗率逐渐降低。沙埋深度在植株高度的33％时,砂生槐幼苗能够存活,且总生物量大于未沙埋幼苗;当沙埋深度增至植株高度的66％时,砂生槐幼苗存活率降至43％,生长受到抑制;而当沙埋深度增至植株高度的100％和133％时,没有砂生槐幼苗存活。可见砂生槐植株在适应沙埋环境方面主要采用调整生物量分配模式的生态对策。     

西藏日喀则流沙固定的几个问题

1995年首次在西藏日喀则进行固沙植物的引种试验,大多数中国内地固沙植物不适应该地的流动沙丘,沙面高温和生长季短是主要制约因素。沙木蓼和籽蒿表现最好;油蒿种子不能成熟,因此不能做后续植物;乡土植物砂生槐在播种当年出苗率低、生长缓慢,只能用做后期植物。在西藏日喀则,有效的植物固沙程序是:在保护措施(草方格沙障、砾石层)下,在流动沙丘上播种外来种沙木蓼、籽蒿和油蒿或移栽籽蒿,同时播种乡土植物砂生槐。在沙木蓼和籽蒿种群衰退、油蒿种群未衰退但不能靠天然下种自行更新时,砂生槐开始发挥固沙作用,并最终凭其适沙特性和长寿命接替先锋固沙植物有效地固定沙丘。选择乡土固沙植物应将重点放在蒿属和锦鸡儿属上。     

荒漠植物苦豆子和苦马豆种子硬实特性与活力关系研究

 以荒漠边缘采集的苦豆子和苦马豆种子为材料,研究其硬实特性及其与活力的关系。结果表明,每日内吸胀的种子数量随时间推移,以一定比列下降,苦豆子非硬实种子吸胀速率较缓慢,第10天后吸胀率降到1%,苦马豆非硬实种子第3天后下降到1%,第13—16天突然上升后又下降到1%。两种豆类种子都显示出硬实种子发芽率、发芽指数、活力指数、脱氢酶、呼吸速率、超氧化物歧化酶(SOD)均高于非硬实种子,而电导率、浸出液可溶性糖和丙二醛(MDA)低于非硬实种子,缓慢吸胀的硬实种子活力指标高于快速吸胀的硬实种子,这表明硬实种子吸胀过程中存在吸胀损伤。而在非硬实种子中,根据以上活力指标判断,晚吸胀的种子比早吸胀的种子活力高。     

Fog water interception by Sophora denudata trees in a Reunion upper-montane forest, Indian Ocean

The forest water balance has never been studied in Reunion Island (Indian Ocean). This study focuses on the interception of fog water by Sophora denudata, an endemic tree, which provides an important water input into the hydrologic budget of the upper-montane forest. Canopy throughfall, rainfall and fog have been compared. The first data were obtained in 2001 in Nez de Bœuf, 2040 m asl, from manual rain gauges. The measurements were made during the day only. The aim was to propose a typology of events, to understand the spatial pattern of canopy throughfall, especially fogdrip, and their relation to the trade-wind direction. A second series of experiments, carried out in 2004 in Piton de Tangues, 2150 m asl, investigated how throughfall and atmospheric water varied with time, using automatic instruments such as the shielded Grunow-type fog collector. Here measurements were made continuously and night data were not excluded. Over a period of 8 months, the throughfall gauges, which were placed under the trees, indicated 1180 mm whereas the total amount of rainfall had reached only 948 mm. The difference (232 mm) is attributed to fog. Of 278 events, 234 showed fog contribution; fog occurred alone in 167 cases. The observations confirm what was found in Nez de Bœuf, namely that fog or rain can occur separately or together. The role of fog contribution to the forest water budget is significant: the spatial variation of canopy throughfall does not only depend on the type of event, but also on wind direction.     

Growth and reproduction of <Emphasis Type="Italic">Sophora moorcroftiana</Emphasis> responding to altitude and sand burial in the middle Tibet

Sophora moorcroftiana, an endemic leguminous shrub in Tibet, is found in valleys, slopes, terraces from 3,000 to 3,900 m above sea level along the middle reaches of the Yarlung Zangbo River. S. moorcroftiana is more tolerant of sand burial than other species in the valleys and is regarded as an ideal species for studying acclimatization to climatic factors. Stem basal diameter showed decline as altitude increased from 3,039 to 3,928 m in the Yarlung Zangbo River valley. Population density increased with the rise of altitude. However, seed bank density, seed germination and seed weight of S. moorcroftiana did not change with changing elevation. Plants responded to altitude variances with remarkable sensitivities. Stem basal diameter size declined along the vertical gradient between plateau and mountainside. Both in alpine and plateau areas, plants similarly adapted growth to altitude, but displayed different responses with respect to reproductive parameters, such as seed bank density, dry weight of seed, seed germination, seedling density and sapling density. Sand accretion remarkably reduced seed bank density and seedling density of the total population of S. moorcroftiana, but could promote shoot sprouting and shoot growing on the individual scale that stimulated the overall development of the population. The results suggested that this particular foredune species did not merely tolerate sand burial, but actually responded positively to sand accumulation.     

西藏砂生槐种群结构与点格局分析

以雅鲁藏布江中游砂生槐种群为研究对象,采用相邻格子法分别在半固定沙地和固定沙地设立20 m×30 m的样方,通过对不同生境条件下种群年龄结构、空间分布格局以及不同径级空间关联等方面的研究,探讨了砂生槐种群结构与空间格局及其影响因素。结果表明,半固定沙地和固定沙地砂生槐种群年龄结构与种群（总和）特征基本一致,均呈基部宽、顶部狭,随径级增大个体数减少的趋势。砂生槐种群中幼龄体的空间分布呈明显的集群分布,随着年龄等级的增加,由中幼龄体不同尺度下的集群和随机分布交替出现过渡到大龄等级下的随机分布。半固定沙地砂生槐种群不同径级的空间关系有正相关和不相关两种方式,变化趋势是随着径级差距的加大,幼体与其他径级砂生槐的空间正相关性逐渐减弱;固定沙地砂生槐种群不同径级的空间关系均呈正相关。     

雅鲁藏布江中游干旱沙地砂生槐种群结构与点格局分析

砂生槐（Sophora moorcroftiana）是雅鲁藏布江中游干旱河谷区植被群落的重要建群种,具有极强的耐瘠薄、抗风沙等生态适应性和防风固沙、保持水土功能。为了揭示砂生槐种群的结构、生长特征和空间分布规律,运用大小级组成和Ripley’s K函数分别研究了砂生槐的种群结构和空间点格局,发现砂生槐个体主要集中在中等大小（冠幅40～80 cm,高度20～40 cm）范围,幼苗期成活率较低,中等个体抗逆和生存能力较强。砂生槐种群的发展演替过程可以概括为：少数个体集群性定居→在原有聚集尺度范围繁殖→种群改良局部环境,密度增大,种内竞争加剧→种群向更大尺度扩散和壮大,演替进入顶极阶段。砂生槐种群各大小级都呈现以9 m左右尺度斑块状聚集分布的特征,在实地生态恢复过程中应遵循其生长和自然分布规律,人工栽培中应重点注意冠幅＜20 cm、高度＜13 cm阶段幼苗的抚育,另外应首先选择土质等条件相对优越的小生境种成适当规模的集群分布形式,充分发挥其防风沙的能力、提高栽培成活率和固沙效率。