Quantifying water stress effect on daily light use efficiency in Mediterranean ecosystems using satellite data

The capacity of six water stress factors(ε′(i))to track daily light use efficiency(ε)of water-limited ecosystems was evaluated.These factors are computed with remote sensing operational products and a limited amount of ground data:ε′1 uses ground precipitation and air temperature,and satellite incoming global solar radiation;ε′(2) uses ground air temperature,and satellite actual evapotranspiration and incoming global solar radiation;ε′_(3) uses satellite actual and potential evapotranspiration;ε′_(4) uses satellite soil moisture;ε′_(5) uses satellite-derived photochemical reflectance index;and ε′_(6) uses ground vapor pressure deficit.These factors were implemented in a production efficiency model based on Monteith’s approach in order to assess their performance for modeling gross primary production(GPP).Estimated GPP was compared to reference GPP from eddy covariance(EC)measurements(GPP EC)in three sites placed in the Iberian Peninsula(two open shrublands and one savanna).ε′_(i) were correlated to ε,which was calculated by dividing GPP EC by ground measured photosynthetically active radiation(PAR)and satellite-derived fraction of absorbed PAR.Best results were achieved by ε′(1),ε′(2),ε′(3) and ε′(4) explaining around 40% and 50% of ε variance in open shurblands and savanna,respectively.In terms of GPP,R^(2)≈0.70 were obtained in these cases.

Effects of extreme soil water stress on photosynthetic efficiency and water consumption characteristics of Tamarix chinensis in China's Yellow River Delta

Soil moisture is a major limiting factor for plant growth on shell ridge islands in the Yellow River Delta. However, it is difficult to carry out situ experiment to study dominant plant photosynthesis physiological on the shell ridge islands under extreme soil water stress. To evaluate the adaptability of plants to light and moisture variations under extreme soil moisture conditions present on these islands, we measured photosynthetic gas exchange process, chlorophyll fluorescence, and stem sap flow variables for 3-year-old trees of Tamarix chinensis Lour, a restoration species on these islands, subjected to three types of soil water levels： waterlogging stress （WS）, alternating dry-wet （WD）, and severe drought stress （SS） to inform decisions on its planting and management on shell ridge islands. Gas exchange, chlorophyll fluorescence, and stem sap flow in T. chinensis were then measured. Net photosynthetic rate （PN）, transpiration rate （E）, and water use efficiency （WUE） were similar under WS and alternating dry-wet conditions, but their mean E and WUE differed significantly （P 〈 0.05）. Under SS, the PN, E and WErE of T. chinensis leaves varied slightly, and mean PN, E and WUE were all low. Apparent quantum efficiency （AQY）, light compensation point （LCP）, light saturation point （LSP）, and maximum net photosynthetic rate （PNmax） of leaves were not significantly different （P 〉 0.05） under WS and dry-wet conditions; however, under extreme drought stress, compared with the dry-wet conditions, LCP was higher, Lsp was lower, and AQy and PNmax were both at the lowest level. Therefore, drought stress weakened light adaptability of leaves, and the efficiency of light transformation was poorer. （3） Maximum photochemical efficiency （Fv/Fm） and the actual photochemical efficiency （ΦPSII） were similar under waterlogged stress and dry-wet conditions, indicating a similar healthy photosynthetic apparatus and photosynthetic reaction cen- ter activity, respectively. Under SS, Fv/Fm was 0.631, and the coefficient of non-photochemical quenching （NpQ） was 0.814, which indicated that while the photosynthetic mechanism was damaged, the absorbed light energy was mainly dissipated in the form of heat, and the potential photosynthetic productivity was significantly reduced. The daily cumulants of sap flow of T. chinensis under drywet alternation and severe drought stress were. 22.25 and 63.97% higher, respectively, than under waterlogging stress. Daily changes in sap flow velocity for T. chinensis differed under the three soil water levels. Stem sap flow was weak at night under severe drought stress. Under drywet alternation, daytime average stem sap flow velocity was the highest, and night stem flow accounted for 10.26% of the day cumulants, while under waterlogged stress, the average nightly stem flow velocity was the highest, accounting for 31.82% of the day cumulants. These results provide important information for regional vegetation restoration and ecological reconstruction.

LIGHT INTERCEPTION AND USE EFFICIENCY DIFFER WITH MAIZE PLANT DENSITY IN MAIZE-PEANUT INTERCROPPING

Intercropping increases crop yields by optimizing light interception and/or use efficiency.Although intercropping combinations and metrics have been reported,the effects of plant density on light use are not well documented.Here,we examined the light interception and use efficiency in maize-peanut intercropping with different maize plant densities in two row configurations in semiarid dryland agriculture over a two-year period.The field experiment comprised four cropping systems,i.e.,monocropped maize,monocropped peanut,maize-peanut intercropping with two rows of maize and four rows of peanut,intercropping with four rows of maize and four rows of peanut,and three maize plant densities(3.0,4.5 and 6.0 plants m^(-1) row)in both monocropped and intercropping maize.The mean total light interception in intercropping across years and densities was 779 MJ·m^(-2),5.5%higher than in monocropped peanut(737 MJ·m^(-2))and 7.6%lower than in monocropped maize(843 MJ·m^(-2)).Increasing maize density increased light interception in monocropped maize but did not affect the total light interception in the intercrops.Across years the LUE of maize was 2.9 g·MJ–1 and was not affected by cropping system but increased with maize plant density.The LUE of peanut was enhanced in intercropping,especially in a wetter year.The yield advantage of maize-peanut intercropping resulted mainly from the LUE of peanut.These results will help to optimize agronomic management and system design and provide evidence for system level light use efficiency in intercropping.

The contribution of distant hybridization with decaploid Agropyron elongatum to wheat improvement in China

Wheat is a staple food crop in the world as well as in China. Because of the progress of wheat breeding and other agricultural ＂sci-technologies, the wheat grain yield per unit area has increased more than five folds from 1952 to 2006 in China. The first part of this article briefly reviews the history of wheat breeding in China. Second, the establishment of ＂Triticum aestivum-Agropyron＂ distant hybridization system and its contribution to wheat production and breeding in China are summarized. Finally, the future challenges of wheat breeding are discussed, which include how to increase the utilization efficiencies of water, soil nutrient and light energy through breeding. As an example, our research progress on how to increase light use efficiency in wheat through breeding is introduced and discussed.

A recommended rate for application of Chaetomium globosum ND35 fungus fertilizer on poplar plantations in China

Previous studies showed that Chaetomium globosum ND35 fungus fertilizer can improve the microbial community structure and enzyme activities of replanted soil. However, it remains unclear whether can improve the physiological and ecological characteristics of plants under successive rotation. In this study, we investigated the photosynthetic, physiological, and biochemical indexes including photosynthetic parameters, chlorophyll fluorescence, and chlorophyll content of 1-yeax-old poplar seedlings under seven different doses （range from 0 to 1.67 g kg-1） of C. globosum ND35 fungus fertilizer to study the effects of fungus fertilizer on photosynthesis of Poplar. Our results showed that： （1） With increasing application of fungus fertilizer in replanted soil, chlorophyll content of poplar leaves （Chl） increased, while physiological indexes such as electron transport rate （ETR）, net photosynthetic rate （Pn）, quantum efficiency （φ）, nitrate reductase （NR） activity and root vigor initially increased and then declined. Meanwhile, heat dissipation that depended on the xanthophyll cycle declined and nonphotochemical quenching （NPQ） initially increased and then decreased. When the dose of C. globosum ND35 fungus fertilizer was 0.67 g kg-1 （T3） and 1.00 g kg-1 （T4）, excess light energy of photosynthetic apparatus was reduced, and photosynthetic apparatus distributed more light energy to the direction of photochemical reactions, which improved the efficiency of energy use. Plant height and biomass of leaves, stems, and roots were maximum at T3. We conclude that applying appropriate amounts of C. globosum ND35 fungus fertilizer can improve root physiological activity and capacity for use of light by poplar leaves. This can improve the operating states of the photosynthetic apparatus and lead to increased photosynthetic efficiency of poplar leaves and accumulation of dry matter.This suggests a strategy to alleviate the successive rotation obstacle of soil nutrient depletion.

Simulating Alpine Vegetation Net Primary Productivity by Remote Sensing in Qinghai Province,China

Primary productivity of ecosystem is important indicator about ecological assessment. Remote sensing technology has been used to monitor net primary productivity （NPP） of ecological system for several years. In this paper, the remotely sensed NPP simulation model of alpine vegetation in Qinghai Province of Tibet Plateau was set up based on the theory of light use efficiency. Firstly a new approach based on mixed pixels and Support Vector Machine （SVM） algorithm were used to correct simulated NPP values derived from Moderate Resolution Imaging Spectroradiometer （MODIS） data. Finally, spatial distribution and monthly variation characteristics of NPP in Qinghai Province detail. The result showed in 2006 were analyzed in that NPP of vegetation in Qinghai Province in 2006 ranged from o to 422 gC/m2/a and the average NPP was 151 gC/m2/a. NPP gradually increased from northwest to southeast. NPP of different vegetation types were obviously different. The average NPP of broad-leaved forest was the largest （314 gC/m2/a）, and sparse shrub was the smallest （101 gC/m2/a）. NPP in Qinghai Province significantly changed with seasonal variation. The accumulation of NPP was primarily in the period （from April to September） with better moist and heat conditions. In July, the average NPP of vegetation reached the maximum value （43 gC/m2）. In our model, the advantage of traditional LUE models was adopted, and our study fully considered typicalcharacteristics of alpine vegetation light use efficiency and environmental factors in the study area. Alpine vegetation is the most important ecological resource of Tibet Plateau, exactly monitoring its NPP value by remote sensing is an effective protection measure.

Hedgerow Intercropping Maize or CowpealSenna for Drymatter Production in Semi-Arid Eastern Kenya

In a long term study photosynthetically active radiation was monitored for three rainy seasons to measure the effects of hedgerow intercropping in rotation with maize and cowpea in a senna/siamea and panicum/grass strip on biomass yield and light use efficiency. Maize/cowpea intercropped with senna siamea or grass stripped were compared with sole maize and cowpea. A ceptometer was applied to measure PAR interception by sole maize or cowpea or crop/tree and grass/crop interfaces and separation of PAR used by each plant or tree/grass component. Hedgerow intercropping increased PAR interception and biomass formation. C4 plants had higher LUE than C3 plants while combining C4 and C3 in the agroforestry system lowered LUE. The tree/crop interfaces increased PAR interception than at 1 m and 2 m away from the hedgerow. The row of maize or cowpea at lm intercepted more PAR than the row at 2 m from hedgerow while the cowpea row next to the hedgerow was depressed compared to the rows in the middle rows which had higher yields. The maize or cowpea row next to the grass strip was more stressed than the rows in the middle of the alley.

Growth,nutritional quality,and energy use efficiency in two lettuce cultivars as influenced by white plus red versus red plus blue LEDs

Red plus blue light-emitting diodes(LEDs)are commonly applied in plant factories with artificial lighting due to photosynthetic pigments,which absorb strongly in red and blue light regions of the spectrum.However,plants grown under natural environment are used to utilizing broad-wide spectrum by long-term evolution.In order to examine the effects of addition light added in red plus blue LEDs or white LEDs,green and purple leaf lettuces(Lactuca sativa L.cv.Lvdie and Ziya)were hydroponically cultivated for 20 days under white LEDs,white plus red LEDs,red plus blue LEDs,and red plus blue LEDs supplemented with ultraviolet,green or far-red light,respectively.The results indicated that the addition of far-red light in red plus blue LEDs increased leaf fresh and dry weights of green leaf lettuce by 28%and 34%,respectively.Addition of ultraviolet light did not induce any differences in growth and energy use efficiency in both lettuce cultivars,while supplementing green light with red plus blue LEDs reduced the vitamin C content of green leaf lettuce by 44%and anthocyanin content of purple leaf lettuce by 30%compared with red plus blue LEDs,respectively.Spectral absorbencies of purple leaf lettuce grown under red plus blue LEDs supplemented with green light were lower in green light region compared with those grown under red plus blue LEDs,which was associated with anthocyanin contents.White plus red LEDs significantly increased leaf fresh and dry weights of purple leaf lettuce by 25%,and no significant differences were observed in vitamin C and nitrate contents compared with white LEDs.Fresh weight,light and electrical energy use efficiencies of hydroponic green and purple leaf lettuces grown under white plus red LEDs were higher or no significant differences compared with those grown under red plus blue LEDs.In conclusion,white plus red LEDs were suggested to substitute for red plus blue LEDs in hydroponic lettuce(cv.Lvdie and Ziya)production in plant factories with artificial lighting.

Asymmetric Ridge–Furrow and Film Cover Improves Plant Morphological Traits and Light Utilization in Rain-Fed Maize

Light is one of the most important natural resources for plant growth. Light interception （LI） and use efficiency （LUE） are often affected by the structure of canopy caused by growing pattern and agronomy managements. Agro-nomy practices, such as the ridge-furrow system and plastic film cover, might affect the leaf morphology and then light transmission within the canopy, thus change light extinction coefficient （k）, and LI and LUE. The objective of this study is to quantify LI and LUE in rain-fed maize （Zea Mays L.）, a major cropping system in Northeast China, under different combinations of ridge-furrow and film covering ratios. The tested ridge-furrow system （DRF： ＂double ridges and furrows＂） was asymmetric and alternated with wide ridge （0.70 m in width and 0.15 m in height）, narrow furrow （0.10 m）, narrow ridge （0.40 m in width and 0.20 m in height）, and narrow furrow （0.10 m）. Field ex-periments were conducted in 2013 and 2014 in Jilin Province, Northeast China. Four treatments were tested： no ridges and plastic film cover （control, NRF）, ridges without film cover （DRF0）, ridges with 58% film cover （DRF58）, and ridges with 100% film cover （DRFl00）. DRF0 significantly increased LI by 9% compared with NRF, while film cover showed a marginal improvement. Specific leaf area in DRF experiments with film cover was significantly lower than in NRF, and leaf angle was 16% higher than in NRF, resulting in a 4% reduction in k. LUE of maize was not increased by DRF0, but was significantly enhanced by covering film in other DRF experiments, especially by 22% in DRF100. The increase of LUE by film cover was due to a greater biomass production and a lower assimilation portioning to vegetative organs, which caused a higher harvest index. The results could help farmers to optimize maize managements, especially in the region with decreased solar radiation under climate change.

Effects of LED light quality on the growth of pepper seedling in plant factory

The extensive environment,especially low temperature and weak lighting in winter and spring,which limits the growth of pepper(Capicum annuum L.)seedlings,the use of plant factory with artificial lighting technology can effectively control the lighting environment to produce high-quality seedlings.In this study,white LED lamps with R:B ratio of 0.7(L0.7)and 1.5(L1.5)and red-blue LED lamps with R:B ratio of 3.5(L3.5)were used to cultivate seedlings of“CAU-24”pepper in the light intensity of 250μmol/m^(2)·s and photoperiod of 12 h/d,white fluorescent lamps with R:B ratio of 1.7(F1.7)was used as control.The results showed that plant height,stem diameter,hypocotyl length,biomass accumulation,light energy use efficiency(LUE)and electric energy use efficiency(EUE)of pepper seedling under L1.5 were the highest.After 36 days of sowing,the dry weight of shoot reached 302.8±45.2 mg/plant.Leaf area reached maximum value of 153.5±22.0 cm^(2) under L0.7.The contents of chlorophyll a,chlorophyll b and total chlorophyll of pepper seedling leaves under all kinds of LED light were greater than F1.7,but there was no significant difference in net photosynthetic rate.The total dry weight with lamp electric power consumption of L1.5 were 3.0 g/(kW·h)which was 1.5,2,and 3 times greater than that of L3.5,L0.7,and F1.7,respectively.Therefore,compared with fluorescent lamp and other LED lamps,the white LED light quality with R:B ratio of 1.5 is suitable for pepper seedling production in plant factory because of the high LED lighting efficiency,greater LUE and EUE.

Potential promoted productivity and spatial patterns of medium-and low-yield cropland land in China

With a continuously increasing population and better food consumption levels, im- proving the efficiency of arable land use and increasing its productivity have become funda- mental strategies to meet the growing food security needs in China. A spatial distribution map of medium- and low-yield cropland is necessary to implement plans for cropland improvement In this study, we developed a new method to identify high-, medium-, and low-yield cropland from Moderate Resolution Imaging Spectroradiometer （MODIS） data at a spatial resolution of 500 m. The method could be used to reflect the regional heterogeneity of cropland productiv- ity because the classification standard was based on the regionalization of cropping systems in China. The results showed that the proportion of high-, medium-, and low-yield cropland in China was 21%, 39%, and 40%, respectively. About 75% of the low-yield cropland was lo- cated in hilly and mountainous areas, and about 53% of the high-yield cropland was located in plain areas. The five provinces with the largest area of high-yield cropland were all located in the Huang-Huai-Hai region, and the area amounted to 42% of the national high-yield cropland area. Meanwhile, the proportion of high-yield cropland was lower than 15% in Hei- Iongjiang, Sichuan, and Inner Mongolia, which had the largest area allocated to cropland in China. If all the medium-yield cropland could be improved to the productive level of high-yield cropland and the low-yield cropland could be improved to the level of medium-yield cropland, the total productivity of the land would increase 19% and 24%, respectively.

Large-scale estimates of gross primary production on the Qinghai-Tibet plateau based on remote sensing data

Vegetation gross primary production(GPP)is an important variable for the carbon cycle on the Qinghai-Tibetan Plateau(QTP).Based on the measurements from 12 eddy covariance flux sites,we validated a light use efficiency model(i.e.EC-LUE)to evaluate the spatial-temporal patterns of GPP and the effect of environmental variables on QTP.In general,EC-LUE model performed well in predicting GPP at different time scale over QTP.Annual GPP over the entire QTP ranged from 575 to 703 Tg C,and showed a significantly increasing trend from 1982 to 2013.However,there were large spatial heterogeneities in long-term trends of GPP.Throughout the entire QTP,air temperature increase had a greater influence than solar radiation and precipitation(PREC)changes on productivity.Moreover,our results highlight the large uncertainties of previous GPP estimates due to insufficient parameterization and validations.When compared with GPP estimates of the EC-LUE model,most Coupled Model Intercomparison Project(CMIP5)GPP products overestimate the magnitude and increasing trends of regional GPP,which potentially impact the feedback of ecosystems to regional climate changes.

Estimation of Terrestrial Net Primary Productivity in China from Fengyun-3D Satellite Data

Currently,the satellite data used to estimate terrestrial net primary productivity(NPP)in China are predominantly from foreign satellites,and very few studies have based their estimates on data from China’s Fengyun satellites.Moreover,despite their importance,the influence of land cover types and the normalized difference vegetation index(NDVI)on NPP estimation has not been clarified.This study employs the Carnegie–Ames–Stanford approach(CASA)model to compute the fraction of absorbed photosynthetically active radiation and the maximum light use efficiency suitable for the main vegetation types in China in accordance with the finer resolution observation and monitoring-global land cover(FROM-GLC)classification product.Then,the NPP is estimated from the Fengyun-3D(FY-3D)data and compared with the Moderate Resolution Imaging Spectroradiometer(MODIS)NPP product.The FY-3D NPP is also validated with existing research results and historical field-measured NPP data.In addition,the effects of land cover types and the NDVI on NPP estimation are analyzed.The results show that the CASA model and the FY-3D satellite data estimate an average NPP of 441.2 g C m^(−2) yr^(−1) in 2019 for China’s terrestrial vegetation,while the total NPP is 3.19 Pg C yr^(−1).Compared with the MODIS NPP,the FY-3D NPP is overestimated in areas of low vegetation productivity and is underestimated in high-productivity areas.These discrepancies are largely due to the differences between the FY-3D NDVI and MODIS NDVI.Compared with historical field-measured data,the FY-3D NPP estimation results outperformed the MODIS NPP results,although the deviation between the FY-3D NPP estimate and the in-situ measurement was large and may exceed 20%at the pixel scale.The land cover types and the NDVI significantly affected the spatial distribution of NPP and accounted for NPP deviations of 17.0%and 18.1%,respectively.Additionally,the total deviation resulting from the two factors reached 29.5%.These results show that accurate NDVI products and land cover types are important prerequisites for NPP estimation.

Modeling of maize gross primary production using MODIS imagery and flux tower data

Maize is one of the most important crops cultivated on the global scale.Accurate estimation of maize Gross Primary Production(GPP)can provide valuable information for regional and global carbon budget studies.From site level to regional/global scales,GPP estimation depends on remote sensing or eddy covariance flux data.In this research,the 8-day composite GPP of maize was estimated by Moderate Resolution Imaging Spectroradiometer(MODIS)and flux tower data at eight study sites using a Regional Production Efficiency Model(REG-PEM).The performance of the model was assessed by analyzing the linearly regression of GPP estimated from the REG-PEM model(GPPEST)with the GPP predicted from the eddy covariance data(GPPEC).The coefficient of determination,root mean squared error and mean absolute error of the regression model were calculated.The uncertainties of the model are also discussed in this research.The seasonal dynamics(phases and magnitudes)of the GPPEST reasonably agreed with those of GPPEC,indicating the potential of the satellite-driven REG-PEM model for up-scaling the GPP in maize croplands.Furthermore,the maize GPP estimated by this model is more accurate than the MODIS GPP products(MOD17A2).In particular,MOD17A2 significantly underestimated the GPP of maize croplands.The uncertainties in the REG-PEM model are mostly contributed by the maximum light use efficiency and the fraction of photosynthetically active radiation.

Higher plant photosynthetic capability in autumn responding to low atmospheric vapor pressure deficit

It has been long established that the terrestrial vegetation in spring has stronger photosynthetic capability than in autumn.However,this study challenges this consensus by comparing photosynthetic capability of terrestrial vegetation between the spring and autumn seasons based on measurements of 100 in situ eddy covariance towers over global extratropical ecosystems.At the majority of these sites,photosynthetic capability,indicated by light use efficiency(LUE)and apparent quantum efficiency,is significantly higher in autumn than in spring,due to lower atmosphere vapor pressure deficit(VPD)at the same air temperature.Seasonal VPD differences also substantially explain the interannual variability of the differences in photosynthetic capability between spring and autumn.We further reveal that VPD in autumn is significantly lower than in spring over 74.14% of extratropical areas,based on a global climate dataset.In contrast,LUE derived from a data-driven vegetation production dataset is significantly higher in autumn in over 61.02% of extratropical vegetated areas.Six Earth system models consistently projected continuous larger VPD values in spring compared with autumn,which implies that the impacts on vegetation growth will long exist and should be adequately considered when assessing the seasonal responses of terrestrial ecosystems to future climate conditions.