黄刺玫叶片光合生理参数的土壤水分阈值响应及其生产力分级

在半干旱黄土丘陵区,以3年生天然次生灌木黄刺玫为材料,研究了叶片光合生理参数对土壤水分(RWC)的响应特征及光合生产力分级。结果表明:当RWC在33.8%—81.3%时,叶片净光合速率(Pn)和蒸腾速率(Tr)的变化曲线为明显的双峰曲线;上午阶段(11:00时之前)Pn的下降主要是气孔限制引起的,下午以非气孔限制为主;随着RWC的增加,Pn、Tr第1峰值出现的时间延后;在此水分范围内,Pn日均值一直维持在较高水平,Pn最高值((8.5±1.8)mmol·m-2·s-1)出现在RWC为71.7%时。水分利用效率(WUE)对RWC的响应有所差异,当RWC大于47.1%时,WUE呈不明显的双峰曲线,第1峰值出现在13:00时,并且前后时段WUE变化不大。RWC为47.1%时,WUE维持在最高水平,日均值为(2.72±0.59)μmol/mmol。根据Pn、Tr、WUE和RWC的定量分析,以及从黄土丘陵区生态、经济效益同时考虑,适合黄刺玫生长的RWC在33.8%—71.7%之间。以光合生理参数为指标对黄刺玫土壤水分有效性及生产力进行分级与评价,确定RWC>90.4%或RWC<33.8%时为"中产中效水";RWC在71.7%—81.3%和47.1%—71.7%时分别为"高产中效水"和"高产高效水",!其中RWC在57.4%左右时为"最优产效水";RWC在18.8%—26.5%时为"低产低效水"。

春夏两季连翘光合作用的土壤水分阈值效应及生产力分级

【目的】研究春、夏两季连翘叶片光合作用多级土壤水分梯度的响应过程,阐明连翘光合作用的土壤水分阈值效应和生产力分级范围,并进行季节间比较,为春、夏季土壤水分胁迫下连翘的风险诊断和田间植物的土壤水分管理提供科学依据。【方法】以2年生连翘苗木为材料开展温室盆栽试验,通过测定人工给水后植物自然耗水的方法分别获取春季14组和夏季10组土壤水分梯度,利用Li-6400光合作用系统测定2个季节连翘叶片的光合作用光响应过程,并以净光合速率（P_n）和水分利用效率（WUE）分别作为评价土壤水分对连翘的＂产＂、＂效＂指标,研究2个季节连翘的土壤水分阈值效应及其生产力分级。【结果】1）当春、夏季土壤相对含水量（RSWC）分别降低至37.5%和46.2%时,随着RSWC继续降低,P_n和WUE显著降低,连翘光合作用的气孔限制转为非气孔限制,P_n和Gs之间由线性正比关系转为非线性正比关系;2）春、夏季P_n,WUE对RSWC的响应过程均可用多项式较好地拟合,由此可确定2个季节连翘的P_n水分补偿点、P_n均值水分点、WUE均值水分点、P_n水分饱和点和WUE水分高效点,借助坐标轴图示,可将土壤水分对连翘的有效性分为无产无效水（春季RSWC≤26.1%,夏季RSWC≤26.4%）、低产低效水（春季RSWC为26.1%～37.5%,夏季RSWC为26.4%～46.2%）、中产中效水（春季RSWC为37.5%～39.5%或80%～100%,夏季RSWC为46.2%～47.8%或95.7%～100%）、高产中效水（夏季RSWC为47.8%～49.2%,83.7%～95.7%）和高产高效水（春季RSWC为39.5%～80.0%,夏季RSWC为49.2%～83.7%）;3）夏季土壤水分阈值（水分补偿点除外）均高于春季,有效水分范围（低产低效水、中产中效水、高产中效水、高产高效水）内夏季各级＂产-效＂水的上限、下限均高于春季,表明连翘对土壤水分含量的要求因生长发育时期不同而异。【结论】植物水分管理中要兼顾生长发育时期的影响,同时为了获得较高的连翘＂产＂、＂效＂水平,需维持春季39.5%≤RSWC≤80.0%、夏季49.2%≤RSWC≤83.7%的高产高效水。

春玉米叶片光合生理参数对土壤水分的阈值响应及其生产力分级

试验设正常灌水处理和干旱胁迫处理,讨论春玉米叶片的光合生理参数对土壤水分的阈值响应并进行生产力分级。结果表明:正常灌水处理的叶片光合速率(Pn)、蒸腾速率(Tr)和气孔导度(Gs)呈单峰曲线变化,胞间CO2浓度(Ci)和气孔限制值(Ls)对水分变化具有相反的响应变化。干旱胁迫处理下叶片的Pn、Tr在进行控水后明显下降,灌浆以前Pn下降主要是由气孔限制引起的。随着水分胁迫的加剧,光合结构受损,Pn下降,主要受非气孔因素限制。短期干旱胁迫会适当降低玉米的水分利用效率(WUE),但是下降程度不显著,WUE能达到中等水平。长期严重的水分胁迫后,WUE下降明显,与正常灌水处理相比差异极显著。以光合生理参数为指标对玉米土壤水分有效性及生产力进行分级与评价,确定当36.8%<土壤相对湿度(RWC)<42.7%时为低产低效水;42.7%<RWC<60.4%时,为中产中效水;60.4%<RWC<77.5%时,为中产高效水;77.5%<RWC<80.6%时,为高产高效水。RWC在77.5%左右时,为最优产效水。

森林生产力区划和量化分级方法研究——以辽宁省为例

采用宏观区划和微观量化分级相结合的方法,利用气候、植被和立地区划数据,首次在全国大区域尺度上实现森林生产力三级区划,同时,结合多期森林资源清查地面样地数据实现森林生产力量化分级。以辽宁森林生产力区划和量化分级成果为案例,详细介绍本研究的技术路线和方法。该研究可为林业区划、森林生态系统功能评价等研究和实践提供理论和方法依据。

Examination of Silicate Limitation of Primary Production in Jiaozhou Bay,North ChinaⅢ.Judgment Method,Rules and Uniqueness of Nutrient Limitation Among N,P,and Si

Analysis and comparison of Jiaozhou Bay data collected from May 1991 to February 1994(12 seasonal investigations) provided by the Ecological Station of Jiaozhou Bay revealed the characteristic spatiotemporal variation of the ambient concentration Si:DIN and Si:16P ratios and the seasonal variation of Jiaozhou Bay Si:DIN and Si:16P ratios showing that the Si:DIN ratios were < 1 throughout the year in Jiaozhou Bay; and that the Si:16P ratios were < 1 throughout Jiaozhou Bay in spring, autumn and winter. The results proved that silicate limited phytoplankton growth in spring, autumn and winter in Jiaozhou Bay. Analysis of the Si:DIN and Si:P ratios showed that the nutrient Si has been limiting the growth of phytoplankton throughout the year in some Jiaozhou Bay waters; and that the silicate deficiency changed the phytoplankton assemblage structure. Analysis of discontinuous 1962 to 1998 nutrient data showed that there was no N or P limitation of phytoplankton growth in that period. The authors consider that the annual cyclic change of silicate limits phytoplankton growth in spring, autumn and winter every year in Jiaozhou Bay; and that in many Jiaozhou Bay waters where the phytoplankton as the predominant species need a great amount of silicate, analysis of the nutrients N or P limitation of phytoplankton growth relying only on the N and P nutrients and DIN:P ratio could yield inaccurate conclusions. The results obtained by applying the rules of absolute and relative limitation fully support this view. The authors consider that the main function of nutrient silicon is to regulate and control the mechanism of the phytoplankton growth process in the ecological system in estuaries, bays and the sea. The authors consider that according to the evolution theory of Darwin, continuous environmental pressure gradually changes the phytoplankton assemblage's structure and the physiology of diatoms. Diatoms requiring a great deal of silicon either constantly decrease or reduce their requirement for silicon. This will cause a series of huge changes in the ecosystem so that the whole ecosystem requires continuous renewal, change and balancing. Human beings have to reduce marine pollution and enhance the capacity of continental sources to transport silicon to sustain the continuity and stability in the marine ecosystem.nt

Inorganic Carbon Parameters Responding to Summer Hypoxia Outside the Changjiang Estuary and the Related Implications

The eutrophication, hypoxia and coastal acidification are attracting more and more attention. In this study, inorganic carbon parameters, including dissolved inorganic carbon （DIC）, total alkalinity （TA） and calculated partial pressure of CO2 （pCO2）, obtained from a summer cruise in August, 2009, were used to investigate their integrated response to biological processes accompanying the oxygen depletion in the areas off the Changjiang Estuary. According to the observations, the typical hypoxia occurred in the bottom water just outside the Changjiang Estuary with Dissolved Oxygen （DO） lower than 2.00 mg L^-1. The biological uptake in the surface water and the decomposition of organic matter in the bottom water were fully coupled with each other. The high concentration of Chl_a （Chl_a = 10.9μgL^-1） and DO （9.25 mgL^-1）, profoundly decreased DIC concentration 0828 μmolkg^-1） and elevated pH （8.42） was observed in the surface water. The correspondingly increased DIC and depletion of oxygen were observed in the bottom water. The semi-quantitative analysis proved that the locally-produced phytoplankton, determined by primary productivity, was deposited to the bottom and contributed about 76% of total amount of the organic carbon decomposition in the bottom. However, in the bottom hypoxia （DO = 2.05 mgL^-1） area observed in the Southern Zhejiang coastal water, the responding patterns of inorganic carbon parameters deviated from the previous one. The expanding of Changjiang Diluted Water （CDW）, the adding of Hangzhou Bay water （with high DIC concentration） and Coastal Current together modify the DIC background value in this area, and the local degeneration and upwelling process may also help to offset the local DIC removed by net biological uptake in surface water. In addition when the mixing occurring in autumn, which may break the summer stratification, the excess release of high DIC in the bottom water to the subsurface water could have an important influence on coastal acidification and the CO2 uptake capacity in this area.

Impacts of Climate Change on Net Primary Productivity in Arid and Semiarid Regions of China

In recent years, with the constant change in the global climate, the effect of climate factors on net primary productivity(NPP) has become a hot research topic. However, two opposing views have been presented in this research area: global NPP increases with global warming, and global NPP decreases with global warming. The main reasons for these two opposite results are the tremendous differences among seasonal and annual climate variables, and the growth of plants in accordance with these climate variables. Therefore, it will fail to fully clarify the relation between vegetation growth and climate changes by research that relies solely on annual data. With seasonal climate variables, we may clarify the relation between vegetation growth and climate changes more accurately. Our research examined the arid and semiarid areas in China(ASAC), which account for one quarter of the total area of China. The ecological environment of these areas is fragile and easily affected by human activities. We analyzed the influence of climate changes, especially the changes in seasonal climate variables, on NPP, with Climatic Research Unit(CRU) climatic data and Moderate Resolution Imaging Spectroradiometer(MODIS) satellite remote data, for the years 2000–2010. The results indicate that: for annual climatic data, the percentage of the ASAC in which NPP is positively correlated with temperature is 66.11%, and 91.47% of the ASAC demonstrates a positive correlation between NPP and precipitation. Precipitation is more positively correlated with NPP than temperature in the ASAC. For seasonal climatic data, the correlation between NPP and spring temperature shows significant regional differences. Positive correlation areas are concentrated in the eastern portion of the ASAC, while the western section of the ASAC generally shows a negative correlation. However, in summer, most areas in the ASAC show a negative correlation between NPP and temperature. In autumn, precipitation is less important in the west, as opposed to the east, in which it is critically important. Temperatures in winter are a limiting factor for NPP throughout the region. The findings of this research not only underline the importance of seasonal climate variables for vegetation growth, but also suggest that the effects of seasonal climate variables on NPP should be explored further in related research in the future.

Recent leveling off of vegetation greenness and primary production reveals the increasing soil water limitations on the greening Earth

Global vegetation photosynthesis and productivity have increased substantially since the 1980s,but this trend is heterogeneous in both time and space.Here,we categorize the secular trend in global vegetation greenness into sustained greening,sustained browning and greening-to-browning.We found that by 2016,increased global vegetation greenness had begun to level off,with the area of browning increasing in the last decade,reaching 39.0 million km^(2)(35.9%of the world’s vegetated area).This area is larger than the area with sustained increasing growth(27.8 million km^(2),26.4%);thus,12.0%±3.1%(0.019±0.004 NDVI a^(-1))of the previous earlier increase has been offset since 2010(2010–2016,P<0.05).Global gross primary production also leveled off,following the trend in vegetation greenness in time and space.This leveling off was caused by increasing soil water limitations due to the spatial expansion of drought,whose impact dominated over the impacts of temperature and solar radiation.This response of global gross primary production to soil water limitation was not identified by land submodels within Earth system models.Our results provide empirical evidence that global vegetation greenness and primary production are offset by water stress and suggest that as global warming continues,land submodels may overestimate the world’s capacity to take up carbon with global vegetation greening.

Distribution of living radiolarians in spring in the South China Sea and its responses to environmental factors

Using a planktonic net(62-?m mesh) and a Rose-Bengal staining method, we studied the spatial distribution of living radiolarians in spring along two sections of the South China Sea(SCS) in spring and discussed the responses of living radiolarian distribution to tropical environmental factors. Generally, the highest abundance of living radiolarians occurred at the depth range of 25–75 m, where the chlorophyll-a maximum and the highest primary productivity were. In contrast, the maximum living abundance occurred in the top 25 m in cold eddies in the open seas and the abundance decreased with depth. We found that the inhibition effect of changing salinity(due to runoffs) on living radiolarians was much stronger than the promotion effect of mesoscale cold eddies. We observed that large variation of temperature was unfavorable for living radiolarians. The dominant species composition consisted of tropical-subtropical warm species. We identified some indicator species for tropical environments. Living Didymocyrtis tetrathalamus tetrathalamus could be an indicator for tropical surface water or mixed-layer water, and even for tropical oligotrophic water. Living Tetrapyle octacantha could be used to indicate tropical thermocline and eutrophic environment. Living Acanthodesmia vinculata could indicate tropical surface and subsurface waters. T. octacantha and A. vinculata should only be used as indicators for upwelling in the open seas, i.e., far away from river mouths. Living Siphonosphaera polysiphonia preferred to form colonies, which might be related to the effect of warm eddies. Living Cyrtopera laguncula and living Cornutella profunda occurred in the tropical upper layer, even in the surface layer, which suggests that they should not be used as indicators for intermediate and deep waters.

Carbon-water coupling and its relationship with environmental and biological factors in a planted Caragana liouana shrub community in desert steppe,northwest China

The carbon and water cycle,an important biophysical process of terrestrial ecosystems,is changed by anthropogenic revegetation in arid and semiarid areas.However,there is still a lack of understanding of the mechanisms of carbon and water coupling in intrinsic ecosystems in the context of human activities.Based on the CO,and H,O flux measurements of the desert steppe with the planted shrub Caragana liouana,this study explored the carbon and water flux coupling of the ecosystem by analyzing the variations in gross primary productivity(GPP),evapotranspiration(ET)and water use efficiency(WUE)and discussing the driving mechanisms of biological factors.The seasonal variation in climate factors induced a periodic variation pattern of biophysical traits and carbon and water fluxes.The GPP and ET fluctuated in seasons,but the WUE was relatively stable in the growing season.The GP,ET and WUE were significantly driven by global radiation(R,),temperature(T,and T),water vapor pressure deficit,leaf area index and plant water stress index(PWSI).However,R,temperature and PWSI were the most important factors regulating WUE.R,and temperature directly affected WUE with a positive effect but indirectly inhibited WUE by rising PWSl.Plant water stress inhibited photosynthesis and transpiration of the planted shrub community in the desert steppe.When the plant water stress exceeded a threshold(PWSI>0.54),the WUE would decrease since the GPP responded more quickly to the plant water stress than ET.Our findings suggest that policies related to large-scale carbon sequestration initiatives under afforestation must first fully consider the status of water consumption and WUE.

A CLASSIFICATION INDICES-BASED MODEL FOR NET PRIMARY PRODUCTIVITY （NPP） AND POTENTIAL PRODUCTIVITY OF VEGETATION IN CHINA

Net Primary Productivity （NPP） is an important parameter, which is closely connected with global climate change, the global carbon balance and cycle. The study of climate- vegetation interaction is the basis for research on the responses of terrestrial ecosystemto global change and mainly comprises two important components： climate vegetation classification and the NPP of the natural vegetation. Comparing NPP estimated from the classification indices-based model with NPP derived from measurements at 3767 sites in China indicated that the classification indices-based model was capable of estimating large scale NPP. Annual cumulative temperature above 0~C and a moisture index, two main factors affecting NPP, were spatially plotted with the ArcGIS grid tool based on measured data in 2348 meteorological stations from 1961 to 2006. The distribution of NPP for potential vegetation classes under present climate conditions was simulated by the classification indices-based model. The model estimated the total NPP of potential terrestrial vegetation of China to fluctuate between 1.93 and 4.54 Pg C year-1. It pro- vides a reliable means for scaling-up from site to regional scales, and the findings could potentially favor China＇s position in reducing global warming gases as outlined in the Kyoto Protocol in order to fulfill China＇s commitment of reducing greenhouse gases.