Using shading field experiments,four treatments were conducted as follows:without shading(CK),60 percent shading(T1),40 percent shading(T2),20 percent shading(T3).Each organ dry matter weight of winter wheat(Triticum aestivum L.,Yangmai13)was observed at regular time,meanwhile dry matter accumulation and distribution responses were determined under different shading condition.With the effects of air temperature and combine solar irradiation factors,the models of dry matter accumulation and distribution responses of winter wheat were established.The results showed that temperature reducing and solar radiation hindered dry matter accumulation of winter wheat,especially for the root,stem and spike.Shading was serious negative effect on them.It was negative effect in the early period and be positive influence in late period for leaf.At the same time,it also influenced seriously distribution proportion of dry matter.Along with the change of effective accumulative temperature,dry matter accumulation and distribution of winter wheat under different shading condition all presented quadratic parabolic curve changes.With three factors(effective accumulative temperature,accumulative daily difference in temperature and solar radiation accumulation),the model simulated well dry matter accumulation and distribution of winter wheat under different shading condition,and could provide practical value for the growth analysis and production management to winter wheat growing.
To in-depth understand the injury of increased ozone concentration at surface to grain quality of winter wheat,the Open-Top Chambe(rOTC)was used to make field experiment in Nanjing area,which were designed to CF100 and CF150,controlled by 100 nL·L-1 and 150nL·L-1 in daytime during whole fumigating periods,and control (CK)by unfiltered air,respectively.The results of indoor experiments for the grain quality in winter wheat showed that there were significant differences among the treatments in contents of grain protein components and amino acid components:(1)The size order of total amino acids of grain was CF100 CF150 CK,but the essential amino acids was CF150 CF100 CK.It was significant difference between the three treatments (P0.05)(.2)The crude protein contents in winter wheat was increasing with the increase of ozone concentrations,but there were different variation trends for their compositions,among which the size order of albumin and globulin contents were CF150 CF100 CK,prolamin and glutenin content were CF100 CF150 CK(.3)Starch contents was decreased with the increasing of the ozone concentration,with significant negative correlation.The starch contents of winter wheat in CF100 and CF150 declined by 4.06% and 16.61%,compared with CK,respectively.On the whole,ozone stress on winter wheat was conducive to the nutritional quality of grain,improved processing quality.
In order to grasp the spatial and temporal distribution of extreme heat in China,a threshold is determined with Detrended Fluctuation Analysis(DFA) for 83 stations across the country,and the period and mutation in 10 regions across China are tested with Permutation Entrop(PE).It has been found that the frequency change of extreme heat in China demonstated characteristics of oscillations of 7 years,10～13 years and 16～20 years,and the mutation mainly happened in the 1960s and 1977—1983.Maximum frequency occurred in the early 1950s,and then sharply decreased until the late 1980s when an obvious growth trend appeared.The maximum frequency in the southern is higher than that in the northen part of China,with high and low frequencies concentrated in spatial distribution.
Movement path and offset distance of the planting area,production,yield per unit gravity centre was studied by using paddy planting area,production and yield per unit of 31 provinces(cities,autonomous regions) data from 1949 to 2009.The results displayed that:(1) the gravity centre of paddy planting area and production has been moving to northeast from 1949 to 2009.(2) The track of paddy yield per unit gravity centre moved to east before 1970's and move back after that in the north-south direction;In the east-west direction,the range movement of paddy yield per unit gravity centre fluctuated rise-decline between about 33-34°N.(3) By comparing the offset distance of gravity centre,the variation of paddy yield per unit gravity centre was the largest,followed by the yield every year,while the excursion distance of paddy plant area was the least;by comparing the offset direction,the years of moving to the northeast and southwest more than move to the southeast and northwest,it indicated that the imbalance of paddy production in the northeast and southwest was more serious.(4) Plant area and production of paddy change faster in the south-north direction than the east-west direction,while the paddy yield per unit change faster in the east-west direction than the south-north direction.
Since the middle of 1960s,the main characteristics of the climatic change in Ningxia are that,the temperature has risen and on the other side the precipitation has decreased.Around 1986,there had a abrupt temperature change,and then the average temperature has increased by 1.0℃.The simulation forecast showed that the average temperatures of winter,summer and the whole year would significantly increase,and the precipitation will increase over baseline period in Ningxia in 2080s.For the main crops,after the climate warming in Ningxia,the production of wheat has declined significantly in the range of 30% to 60%.However,the climate change has created the condition to introduce the high yielding varieties of rice which could decrease the yield change rate and ensuring high yield.The increase of temperature within 2.8℃ would benefit the maize production,but more than 2.8℃ may cut down the production.The increase of average temperature in growth period has had a negative impact on potato production,the growth period would begin earlier and end later,which could extend the growing season about 15 days.For the local agricultural production in Ningxia,just as the wolfberry,watermelon and wine grapes have been affected by the adverse effects of climate warming and rainfall decrease and supplemental irrigation must be taken in reason.The climate warming also has provided more adequate and more favorable energy resources to the growth of thermophilic crops like wine grapes,corn etc.which would improve the quality of these crops.In addition,climate warming has enlarged the suitable plant areas,and also has changed the varieties of crops from the early maturation to the late,developed the multi-cropping system to the north and increased the multiple cropping indexes.But the warming trend would increase the adverse impact of pest and disease on the crops.In irrigated areas,it is favorable to develop the characteristic agriculture of thermophilic crops,just like but not limited to wine grapes and watermelon,through expanding the plant area.
Evapotranspiration(ET)is the major process of Earth's surface water and heat exchange,and has obvious spatial variation.The development and application of remote sensing technology make the regional estimation of ET realistic.This paper reviewed the research progress in the remote sensing regional ET estimation models,including single and two-layer models based on land surface energy balance,with the focus on the algorithm and characteristics of the Atmosphere-Land Exchange Inverse model(ALEXI)developed in recent years.To overcome the limitation of meteorological data,the ALEXI was coupled with Two-Source Energy Balance model(TSEB)and simplified atmospheric boundary layer model,and thereby,improved the estimation accuracy.Substantial studies showed that the ALEXI evaporative stress index(ESI)had strong capacity in regional drought monitoring.In order to give a better operational drought monitoring service,the combination of multi-source remote sensing data fusion technology,land surface data assimilation system,and remote sensing ET estimation models could be an important research field in the future.
A ground‐based sky radiometer was used to measure direct and diffuse solar irradiances at Dunhuang, China from January 1999 to March 2001. The aerosol optical thickness (AOT), Angstrom exponent ( α ), volume size distributions, single scattering albedo and refractive index of aerosols were simultaneously retrieved using the “SKYRAD” inversion code and their seasonal variations and statistical characteristics were studied. The results reveal that during the study period, the AOT at Dunhuang varied seasonally, with the maximum AOT occurring in the spring and the minimum AOT occurring in the fall. The variation in α showed an opposite pattern, with a minimum in the spring and a maximum in the fall. A simple exponential function can express the relationship between AOT and α . The frequency distributions of AOT and α approximately follow a lognormal probability distribution and a normal probability distribution, respectively. The aerosol volume size distributions can be characterized by the sum of two lognormals distributions, and represent an accumulation mode with a radius of about 0.25 um, and a coarse mode with a radius of about 7.7 um. A pseudomode with a radius of about 1.69 um located between the accumulation mode and coarse mode is present in the springtime. The single scattering albedo showed a slight increasing trend with wavelength in spring, summer and autumn and a decreasing trend with wavelength in winter. The maximum value of the real part of the refractive index occurs at 400 nm, and the minimum value occurs at 875 nm for all seasons. Two Gaussian models were developed to describe the frequency distribution of the real part of the aerosol refractive index; the results indicate that the differences between the fits are greatest in the spring. The statistical characteristics of the frequency distributions of aerosol properties might provide a way to identify and estimate aerosol optical properties in areas located near dust regions.
Stress effects of surface increased ozone concentration on winter wheat photosynthesis, lipid peroxidation and antioxidant systems in varied growth stages (jointing stage, booting stage, blooming stage and grain filling stage) were studied, the winter wheat was exposed to open top chambers (OTCs) in an open field conditions to three levels ozone concentrations (CK, 100 nmol x mol(-1), 150 nmol x mol(-1)). The results revealed that within 150 nmol x mol(-1) ozone concentration, as the ozone concentration and time increased,total chlorophyll content,chlorophyll a and b contents of winter wheat leaves were general declined,but compared to CK, the total chlorophyll and chlorophyll a content of T1 treatment groups were a little higher at booting and blooming stage; the conductance of stomatal was affected, the activation of unit leaf area decreased, intercellular CO2 concentration and stomatal limitation value showed a fluctuation change tendency. At the same time, a self-protective mechanism of winter wheat were launched. Concrete expression of SOD activity first increased rapidly and then gradually decreased, the activity of POD showed a decrease firstly and then rapidly increased. From the jointing stage to the blooming stage and from the grain filling stage one to grain filling stage two, the activity of CAT rapidly increased first and then comparatively decreased, but the content of MDA kept steadily rising. The carotenoid content increased first and then decreased, heat dissipation of unit leaf area increased. These results indicate that antioxidant enzymes can not completely eliminate excessive reactive oxygen species in vivo of winter wheat, then lead to accumulation of reactive oxygen species, further exacerbate the lipid peroxidation, that result in the increase of membrane permeability, degradation of chlorophyll, reduction of net photosynthetic rate, imposing on the winter wheat leaves senescence process.
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