近20年黄土高原生态系统服务研究进展

生态系统服务是自然生态系统及其物种提供的供给和维持人类生存的条件和过程,是人类通过生态系统的功能直接或间接得到的产品或服务,具有典型的区域性特征。黄土高原是黄河流域重要生态安全屏障,生态建设规模大、历时长,是我国生态系统服务研究的重要案例区。已有研究针对黄土高原生态系统服务进行物质量与价值量估算、权衡与协同关系识别和供需关系评估,但不同结论之间缺少归纳和对比。研究对近20年来黄土高原地区生态系统服务研究的文献总体特征和主要研究发现分析表明:相关中英文论文数量和被引频次整体呈上升趋势,研究内容上主要关注黄土高原生态系统服务的定量估算,近年来逐渐向生态系统服务权衡分析和供需关系评估拓展;黄土高原地区自退耕还林以来,各项生态系统服务总量呈上升趋势,呈现出东南增量较多、西北增量较少的空间格局;黄土高原地区供给服务和调节服务存在较明显的权衡关系,但在不同尺度上强度分异明显;区域内生态系统服务供给量和需求量均呈增加趋势,供需匹配状况具有明显时空差异。面向当前研究中物质量评估种类不足、价值量估算高度不确定、权衡与协同现象缺乏归因、空间流动性体现不足等问题,未来黄土高原生态系统服务研究有待加强面向生态产品价值实现的生态系统服务价值估算,空间流动视角下的生态系统服务供需关系评估,以及基于生态系统服务权衡情景模拟的国土空间优化。

交错和矩形布置对树状植被地表剪应力和输沙率的影响

植被布置方式是影响风对地表剪切作用的重要因素,进而影响植被的防沙效应。在风洞内测量了刚性树状植株模型在交错布置和矩形布置条件下的地表剪应力分布、总剪应力和输沙率,并分析了它们在两种布置方式下的差异。结果表明,在3种植株密度(18、32、50株·m^(-2))下,交错布置时植株周围平均地表剪应力比矩形布置时分别减小8.5%~11.9%、13.8%~16.5%、15.3%~17.2%。交错布置时剪应力分解模型参数β值(平均值220)大于矩形布置(平均值180),而两种布置的m值非常接近。在相同来流风速和植株密度下,交错布置时植被地表输沙率均小于矩形布置情况,平均减小值为24%,而输沙率随平均地表摩阻风速的变化规律不受植被排列方式的影响。本文结果有助于从地表剪应力角度理解布置方式在植被防风蚀研究中的作用。

土壤粉尘释放能力与土壤性质关系的初步研究

土壤粉尘释放能力是决定区域粉尘释放强度的关键因素,但一直缺少适合的土壤性质指标进行表征。采用野外取样分析与风洞实验手段,就土壤粉尘释放能力与土壤性质的关系进行初步研究。结果表明:各种与风蚀相关的土壤基本理化性质中,只有粉沙和沙粒含量对土壤粉尘释放能力的影响较显著,土壤粉尘释放能力随土壤中粉沙和沙粒含量增加具有先增大后降低的趋势,支持了有关学者提出的中等质地土壤具有最强粉尘释放能力的观点。土壤粉尘释放能力与土壤干团聚体粒度组成关系紧密,具有随土壤可蚀性颗粒中粒径<0.05 mm细颗粒含量(C<_(0.05/<0.85))增加呈线性规律显著增加,随土壤可蚀性颗粒中粒径0.1~0.5 mm跃移颗粒含量(C_(0.1-0.5/<0.85))增加呈幂函数规律显著降低的趋势。各项土壤理化性质指标中,土壤干团聚体中粒径<0.05 mm细颗粒含量(C<0.05)不仅能够反映各种土壤基本理化性质对土壤粉尘释放能力的综合影响,而且与决定土壤粉尘释放能力的两个正向指标——土壤可蚀性颗粒含量(C_(<0.85))和C_(<0.05/<0.85)均呈显著的线性正相关关系,应是表征团聚体发育土壤表面粉尘释放能力较合适的土壤性质指标,这得到土壤样品分析结果的初步证实,但还需要进一步的实验验证。

Nitrogen Addition Decreases Soil Respiration without Changing the Temperature Sensitivity in a Semiarid Grassland

The mechanisms underlying the response of soil respiration(Rs) to nitrogen(N) addition remain to be explored in semiarid ecosystems. This study was conducted to determine the effect of N addition on soil microbial composition, Rs and the temperature sensitivity of Rs(Q10). The N addition experiment was carried out in a semiarid grassland in China, with N fertilizer application rates of 0, 2, 4, 8, 16, or 32 gN m-2yr-1. Microbial phospholipid fatty acids(PLFAs), Rs and Q10 were measured, and their relationships with soil properties were determined for three growing seasons. The results showed that N addition significantly increased the content of soil dissolved organic carbon(DOC) and inorganic nitrogen(IN), and decreased soil p H. With respect to soil microbes, N addition reduced soil PLFAs, reduced the fungi to bacteria ratio(F:B) and increased the gram-positive bacteria to gram-negative bacteria ratio(G+:G–). Rs under the N2, N4, N8, N16 and N32 treatments decreased by 2.58%, 14.86%, 22.62%, 23.97% and 19.87%, respectively, compared to the N0(control) treatment. The results of structural equation models showed that N addition reduced Rs by lowering soil PLFAs and altering the microbial composition. However, N addition had no significant effect on either Q10, soil total organic carbon(TOC) or total nitrogen(TN), indicating that N addition alleviated soil carbon loss and was unlikely to change the potential for a bigger loss under global warming.

Soil Priming Effect Mediated by Nitrogen Fertilization Gradients in a Semi-arid Grassland, China

The priming effect is well acknowledged in soil systems but the effect of nitrogen(N)fertilization remains elusive.To explore how N modifies the priming effect in soil organic matter(SOM),one in situ experiment with 13C labeled glucose addition(0.4 mg C g^–1 soil,3.4 atom %^13C)was conducted on soil plots fertilized with three gradients of urea(0,4 and 16 g N m^–2 yr^–1).After glucose addition,the soil CO2 concentration and phospholipid fatty acid(PLFA)were measured on day 3,7,21 and 35.The study found that N fertilization decreased soil CO2,PLFA and the fungi to bacteria ratio.Glucose triggered the strongest positive priming in soil at 0 g N m^–2 yr^–2,meanwhile N fertilization decreased SOM-derived CO2.Soil at 4 g N m^–2 yr^–2 released the largest amount of glucose-derived carbon(C),likely due to favorable nutrient stoichiometry between C and N.Stable microbial community biomass and composition during early sampling suggests"apparent priming"in this grassland.This study concludes that N fertilization inhibited soil priming in semi-arid grassland,and shifted microbial utilization of C substrate from SOM to added labile C.Diverse microbial functions might be playing a crucial role in soil priming and requires attention in future N fertilization studies.

Soil Respiration Dynamics and Influencing Factors in Typical Steppe of Inner Mongolia under Long-term Nitrogen Addition

We investigated soil respiration(Rs)dynamics and influencing factors under different nitrogen(N)addition levels(0,2,4,8,16,32 g m^–2 yr^–1)on typical grassland plots in Inner Mongolia.We measured soil respiration,temperature,moisture and nutrients.We found that N addition did not change dynamic characteristics of Rs;daily and seasonal dynamics followed a single peak curve.N addition reduced Rs during the growing season.Rs under N2,N4,N8,N16 and N32 treatments decreased by 24.00%,21.93%,23.49%,30.78%and 28.20%in the growing season,respectively,compared to the N0 treatment.However,Rs in the non-growing season was not different across treatments.Rs was significantly positively correlated with soil temperature and moisture and these two factors accounted for 72%–97% and 74%–82% of variation in Rs,respectively.The soil respiration temperature sensitivity (Q10) was between 2.27 and 4.16 and N addition reduced Q10 except in the N8 treatment.

Spatial Distribution of Surface Soil Organic Carbon Density and Related Factors along an Urbanization Gradient in Beijing

Urban surface soil has a unique set of structures and processes that affect surface soil organic carbon density(SOCdensity) and its spatial variations. Using Beijing as a case study, and assisted by field investigations and experiments, we analyzed the spatial distribution of SOCdensity in different land use types and functional regions, and assessed associated factors such as urbanization level, the physiochemical properties of soil and plant configurations. The present study aims to provide useful information about the mechanisms driving soil organic carbon and climate change in developing and developed areas in urbanized regions like Beijing. Results indicate that P is the main factor positively influencing SOCdensity in most regions. Because of the specific interference directly related to human beings in urban areas, with decreases in the urbanization level, more physiochemical factors of soil can influence SOCdensity. SOCdensity under grasses is not significantly different from that under other plant compositions. Urbanization processes decrease the heterogeneity of the spatial pattern of SOCdensity in most land use types, but increased its contents when the area reached a developed level in Beijing. More factors related to human interference and spatial variation of surface soil carbon storage, especially under impervious land in urban areas, should be considered in future studies.