Fine-scale spatial distribution of soil organic carbon and its fractions after afforestation with Pinus sylvestris and Salix psammophila in a semiarid desert of China

半干旱沙漠中樟子松和沙柳造林后土壤有机碳及其组分的小尺度空间分布 半干旱沙漠造林有助于改善土壤功能以及增加土壤有机碳(SOC)固定,但人们对造林后SOC及其不稳定(LOC)组分的小尺度空间分布了解甚少。本研究以毛乌素沙地东南缘樟子松(Pinus sylvestris)和沙柳 (Salix psammophila)为研究对象,量化了距离树体20、80、150和240 cm处SOC、LOC组分及其相关变量的小尺度空间分布。研究结果表明,沙柳和樟子松造林显著提高了SOC、总氮(TN)、可溶性有机碳 (DOC)、微生物碳(MBC)和易氧化有机碳(ROOC)含量;在距离树体20 cm处,0–100 cm土层樟子松SOC 储量比沙柳高27.21%;在距离树体80和150 cm处,沙柳SOC储量分别比樟子松高5.50%和5.66%;与流 沙地相比,在距离树体20、80、150 和240 cm处,沙柳和樟子松SOC储量显著增加了94.90%、39.50%、 27.10%和18.50%;沙柳和樟子松ROOC分别占SOC的14.09%和18.93%。总之,造林促进了半干旱流沙地SOC的积累,樟子松比沙柳分配更多的有机质到距离树体<80 cm范围内的土体中。     

古尔班通古特沙漠固定沙丘上白梭梭和梭梭的空间分布及种间关联性

为了探讨沙漠中固沙灌木种群共存和演替机制, 本文基于古尔班通古特沙漠东南缘固定沙丘上白梭梭(Haloxylon persicum)和梭梭(H. ammodendron)种群的地理位置和生长发育阶段信息(幼株、营养株、生殖株和死株), 采用点格局分析方法(g(r)函数)及Monte-Carlo随机模拟检验和零模型选取的方法, 分析了固沙灌木白梭梭和梭梭种群不同生长发育阶段在0-20 m尺度内的空间分布格局及种间关联性。结果表明: (1)两个种群在研究尺度范围内呈聚集分布, 随着尺度的增大, 其聚集强度逐渐减弱; (2)两个种群整体上呈负关联关系, 尺度越大负关联关系越显著; (3)白梭梭种群生长发育阶段相差越大, 个体间正关联关系越显著; 梭梭种群生长发育阶段越接近, 个体间正关联关系越显著; (4)两个种群中龄级较大的个体(如营养株、生殖株和死株)会对对方种群中龄级较小的幼株产生一定的抑制作用; 同时, 随着两个种群中个体的成长, 双方受到的抑制作用逐渐减弱, 主要表现为正关联和无关联。总体而言, 古尔班通古特沙漠固定沙丘白梭梭和梭梭种群的分布格局整体上为聚集分布, 随龄级增加聚集性减弱, 受生境异质性和扩散限制的影响明显。种间关系多为负相关, 种内不同生长发育阶段之间均为正关联关系。     

准噶尔荒漠土壤多功能性的空间变异特征及其驱动因素

荒漠是重要的陆地生态系统之一, 其生态系统极其脆弱, 极易发生荒漠化。荒漠土壤的稳定和功能对于荒漠生态系统结构和功能的维持至关重要。但在荒漠地区, 大多数土壤功能的研究还主要集中在单一的土壤功能性。本研究基于准噶尔荒漠79个样点的土壤有机碳(SOC)、氮(N)、磷(P)、有效氮(AN)和有效磷(AP)等指标, 通过平均值法和因子分析法计算土壤多功能(soil multifunctionality, SMF)指数, 研究SMF空间变异特征及驱动因素。空间分析所示从整体来看, 荒漠SMF在空间分布上具有较大的异质性, 自西向东, SMF总体呈现逐渐增加的趋势, 而从南向北, SMF呈现先增加后降低的趋势。最优拟合显示, SMF与年均降雨量(MAP)和年均温(MAT)呈显著二次函数关系, 随着MAP和MAT的增加表现出先降低后升高的趋势; SMF与pH和植被增强指数(EVI)呈显著线性关系, SMF随着pH的增加表现出显著降低趋势, 而随着EVI的增加表现为显著上升的趋势; SMF与Aridity (干旱度)之间既符合二次函数关系也呈现线性关系(二者R²相同), 随Aridity增加而减少。结构方程模型结果表明, 土壤含水率(SWC)是SMF变化的最重要的驱动因素, 其次为EVI。土壤pH、SWC、MAT、Aridity和EVI对荒漠SMF具有显著的直接效应, 其中SWC和EVI为显著正效应, 其他为负效应。MAP、经度(Lon)、纬度(Lat)和海拔(Alt)可通过影响MAT等指标对SMF产生间接效应。研究结果对深入理解准噶尔荒漠SMF的空间变异特征及驱动因素具有重要意义, 将有助于预测环境变化对荒漠生态系统多功能性的影响, 为生态系统科学管理服务。     

Water availability shapes edaphic and lithic cyanobacterial communities in the Atacama Desert

In the Atacama Desert, cyanobacteria grow on various substrates such as soils (edaphic) and quartz or granitoid stones (lithic). Both edaphic and lithic cyanobacterial communities have been described but no comparison between both communities of the same locality has yet been undertaken. In the present study, we compared both cyanobacterial communities along a precipitation gradient ranging from the arid National Park Pan de Azúcar (PA), which resembles a large fog oasis in the Atacama Desert extending to the semiarid Santa Gracia Natural Reserve (SG) further south, as well as along a precipitation gradient within PA. Various microscopic techniques, as well as culturing and partial 16S rRNA sequencing, were applied to identify 21 cyanobacterial species; the diversity was found to decline as precipitation levels decreased. Additionally, under increasing xeric stress, lithic community species composition showed higher divergence from the surrounding edaphic community, resulting in indigenous hypolithic and chasmoendolithic cyanobacterial communities. We conclude that rain and fog water, respectively, cause contrasting trends regarding cyanobacterial species richness in the edaphic and lithic microhabitats.     

Germination response of Arabian desert species to gibberellic acid and potassium nitrate seed treatment

Abstract

Desert plant species commonly use seed dormancy to prevent germination during unfavorable environmental conditions and thus increase the probability of seedling survival. Seed dormancy presents a challenge for restoration ecology, particularly in desert species for which our knowledge of dormancy regulation is limited. In the present study the effect of gibberellic acid (GA₃) and potassium nitrate (KNO₃) on seed dormancy release was investigated on eight Arabian desert species. Both treatments significantly enhanced the germination of most species tested. GA₃ was more effective than KNO₃ in enhancing germination percentage, reducing mean germination time and synchronizing the germination in most of the studied species. Light requirement during germination was species-specific, but in general the presence of light promoted germination more effectively when combined with KNO₃ and GA₃. The wide variation in dormancy and germination requirements among the tested species is indicative of distinct germination niches, which might assist their co-existence in similar habitat/environmental conditions. Seed pre-treatments that optimize germination in this habitat must therefore be assessed for individual species to improve the outcomes of ecological restoration.     

Short-term patterns in water and nitrogen acquisition by two desert shrubs following a simulated summer rain

A field experiment was conducted at the Jornada Long-Term Ecological Research (LTER) site in the Chihuahuan Desert of New Mexico to compare the rapidity with which the shrubs Larrea tridentata and Prosopis glandulosa utilized water, CO² and nitrogen (N) following a simulated summer rainfall event. Selected plants growing in a roughly 50-m² area were assigned to treatment and control groups. Treatment plants received the equivalent of 3 cm of rain, while no supplemental water was added to the control plants. Xylem water potential (_x) and net assimilation rate (A_net) were evaluated one day before and one and three days after watering. To monitor short-term N uptake, soils around each plant were labeled with eight equally distant patches of enriched ¹⁵N before watering. Each tracer patch contained 20 ml of 20 mM ¹⁵ NH₄ ¹⁵NO³ (99 atom%) solution applied to the soil at 20 cm from the center of the plant at soil depths of 10 and 20 cm. Nitrogen uptake, measured as leaf ¹⁵N, was evaluated at smaller time intervals and for a longer period than those used for _x and A^net. Both A^net and ^x exhibited a significant recovery in watered vs. control Larrea plants within 3 days after the imposition of treatment, but no such recovery was observed in Prosopis in that period. Larrea also exhibited a greater capacity for N uptake following the rain. Leaf ¹⁵N was five-fold greater in watered compared to unwatered Larrea plants within 2 days after watering, while foliar ¹⁵N was not significantly different between the watered and unwatered Prosopis plants during the same period. Lack of a significant change in root ¹⁵ NO^{– 3} uptake kinetics of Larrea, even three days after watering, indicated that the response of Larrea to a wetting pulse may have been due to a greater capacity to produce new roots. The differential ability of these potential competitors in rapidly acquiring pulses of improved soil resources following individual summer rainfall events may have significant implications for the dynamic nature of resource use in desert ecosystems.     

Nutrient mobilization and processing in Sonoran desert riparian soils following artificial re-wetting

Research in river-floodplain systems has emphasized the importance of nutrient delivery by floodwaters, but the mechanisms by which floods make nutrients available are rarely evaluated. Using a laboratory re-wetting experiment, we evaluated the alternative hypotheses that increased nutrient concentrations in riparian groundwater during flash floods are due to (H1) elevated nutrient concentrations in surface floodwaters entering the riparian zone or (H2) re-mobilization of nutrients from riparian soils. We sampled soils from the riparian zone of a 400m reach of Sycamore Creek, AZ. Two sub-samples from each soil were re-wetted with a solution that mimicked the chemistry of floodwaters, with one sub-sample simultaneously treated with a biocide. We also measured structural characteristics of soils (texture, organic matter, moisture, and extractable nutrients) to investigate relationships between these characteristics and response to re-wetting. Riparian soils exhibited considerable variation in physical and chemical structure. Soil organic matter, moisture, and texture co-varied among samples. Re-wetting increased concentrations of nitrate and ammonium, and decreased SRP, relative to initial concentrations. Live soils were significantly lower in NO3-and SRP than biocide-treated samples. Extractable DIN pools were the best predictors of mobilization, and soil organic matter was strongly correlated with nitrate losses, probably via its relationship with microbial uptake. Nutrient mobilization and processing also varied considerably with depth, lateral position, and among plots. We estimate that 70–80% of N in riparian groundwater during flash floods is re-mobilized from riparian soils, but are unable to reject the hypothesis that flood inputs may be important sources of nutrients to riparian soils over longer time scales.     

塔南绿洲生态系统持续发展近期优化模式

基于对塔克拉玛干沙漠南缘各绿洲水资源的时空分布特征和目前各绿洲灌溉渠系利用系数的分析,通过野外对典型防护林防风效益的监测和风洞模拟实验,以及在塔克拉玛干沙漠南缘策勒绿洲进行了１５年的沙漠化土地综合治理试验示范研究经验,提出了近期内塔克拉玛干沙漠南缘绿洲生态系统持续发展系列优化模式：塔克拉玛干沙漠南缘适度绿洲优化模式、塔克拉玛干沙漠南缘绿防护林结构优化模式、塔克拉玛干沙漠南缘荒漠化土地综合整治优化模