Growing Season Mean Research Articles

Comprehensive climate factor characteristics and quantitative analysis of their impacts on grain yields in China's grain-producing areas

Climate change elements are important indicators for assessing the impact of climate change on the agricultural economy. A Comprehensive Climate Factor (CCF) that is composed of three indicators, growing season mean temperature, precipitation and sunshine hours indicators was developed. These indicators are aggregated into a single index that is a measure of the sensitivity of regionally integrated climate change. This paper uses this factor to explore the integrated climate variations over China's grain-producing areas in 1981–2015, divide the areas into climate change-sensitive zones, and quantitatively assess the impact intensity of CCF variation on grain yield. The results indicate that the growing season mean CCF basically increased in most grain-producing areas. The climatic tendency of the North plate is greater than that of the South plate, reaching 0.52 decade−1, and the South plate has a quasi-4a periodic variation. The patterns of the impact of climate change on grain yield show that the impact intensity of climate change gradually decreased in each decade (from 0.25 to 0.2) and was stronger in the southwest than in the northeast. This research can be applied to improve the accuracy of economic-climate model simulations and predictions and to provide a theoretical reference and scientific support for assessing the impact and risk of climate change.

Viticulture and Winemaking under Climate Change

The importance of viticulture and the winemaking socio-economic sector is acknowledged worldwide. The most renowned winemaking regions show very specific environmental characteristics, where climate usually plays a central role. Considering the strong influence of weather and climatic factors on grapevine yields and berry quality attributes, climate change may indeed significantly impact this crop. Recent-past trends already point to a pronounced increase in the growing season mean temperatures, as well as changes in the precipitation regimes, which has been influencing wine typicity across some of the most renowned winemaking regions worldwide. Moreover, several climate scenarios give evidence of enhanced stress conditions for grapevine growth until the end of the century. Although grapevines have a high resilience, the clear evidence for significant climate change in the upcoming decades urges adaptation and mitigation measures to be taken by the sector stakeholders. To provide hints on the abovementioned issues, we have edited a special issue entitled: “Viticulture and Winemaking under Climate Change”. Contributions from different fields were considered, including crop and climate modeling, and potential adaptation measures against these threats. The current special issue allows the expansion of the scientific knowledge of these particular fields of research, also providing a path for future research.

Potential climate change adaptation strategies for winter wheat production in the Texas High Plains

Winter wheat is one of the major crops in the Texas High Plains (THP) region, which is facing challenges from climate change (CC) and exhausting irrigation water supplies from the Ogallala Aquifer. The goal of this study was to assess the impacts of CC on winter wheat production in the THP and evaluate potential adaptation strategies using the Decision Support System for Agrotechnology Transfer (DSSAT) CERES-Wheat model. A thorough calibration of the model against field data resulted in a satisfactory simulation of phenology, leaf area index, grain yield (percent error, |PE| <4.7%), biomass (|PE| <7.1%), and evapotranspiration (|PE| <11.9%). The evaluated model was then used for: (i) predicting winter wheat yield and irrigation water use, and (ii) evaluating six potential winter wheat cultivars under CC at three sites in the THP. Mixed trends were found for irrigated yield in the future across the study sites due to differences in climate and soils. Irrigation water use of winter wheat is expected to decrease in the future due to improved water use efficiency at elevated atmospheric CO2 concentration and reduced growing season length due to temperature rise. Dryland yield is expected to increase due to improved crop water use efficiency. Among the virtual cultivars tested for CC adaptation, increasing potential number of grains and vigorous root system were found to be the most desirable traits, since these cultivars had higher yield and lower or comparable irrigation water use than the reference cultivar. Long-maturity and stay-green cultivars were found to be not advisable due to significantly higher irrigation water use than the reference cultivar. Overall, the results showed that winter wheat production in the THP could benefit from CC under milder climatic conditions (mean growing season temperature <13 °C). Enhancing yield potential traits and root architecture should be considered for screening cultivars for CC adaptation.

Spatial variation in oak (Quercus spp.) radial growth responses to drought stress in eastern North America

Dendroecology provides a means to evaluate how mature trees have responded to climate stresses in the recent past and provides one approach for projecting how existing forests will respond to future climate change. This study documented spatial variation in the strength of growth–climate associations for six oak (Quercus) species at 284 sites in eastern North America that span substantial gradients of temperature and site water balance. Radial growth of oaks was more strongly related to growing-season precipitation and the ratio of precipitation to potential evapotranspiration at sites in the western part of the study region where drought conditions occur more frequently. Growth was more strongly related to growing-season mean maximum temperature in the warmer, southern part of the study region. Growth of oaks was not strongly related to site water balance or temperature in the northeastern part of the study region. These results indicate that if climate change results in increased growing-season drought stress, this will adversely affect mature oak trees growing in the southern and western parts of eastern North America, but oaks growing in northeastern North America have more safe space for change before they will suffer reduced growth and vigor.

Diurnal and Seasonal Variations in Soil Respiration of Four Plantation Forests in an Urban Park

Understanding the carbon dynamics of urban trees and forests is one of the key components for developing mitigation strategies for climate change in a fast-paced urbanized world. This study selected four plantation forests composed of poplar, black locust, Chinese pine and mixture of poplar and black locust, located in an urban forest park on a well-drained fluvial plain with same land-use history. The diurnal and seasonal changes in soil respiration (Rs) and biophysical factors were measured from April 2015 to March 2016. At the diurnal scale, Rs varied out of phase with soil temperature (Ts) and the time-lag occurred in May and July when Ts was relatively high and soil moisture (Ms) was low. Strong seasonal variations in Rs were mainly determined by Ts, while the growing-season mean Rs positively correlated with the fine root biomass (FRB), soil organic carbon content (SOC), and total nitrogen content (TN) for all the forests. FRB alone could explain 75% of the among-stand variability. This study concluded that urban forest plantations have similar soil respiration dynamics to forest ecosystems in non-urban settings.

Increased spatial heterogeneity in vegetation greenness due to vegetation greening in mainland China

Spatial heterogeneity in vegetation greenness (VG) can influence earth surface process and resource ecology. However, its long-term change and driving forces remain poorly understood. In this study, MODIS enhanced vegetation index (EVI) data was used to examine the change in spatial heterogeneity in VG and its relationships with vegetation greening in mainland China during 2000–2017. Moving window standard deviation and range of growing season mean EVI (GSEVI) were used as proxies for spatial heterogeneity in VG. It was found that moving window standard deviation of GSEVI increased significantly over 33.8% to 53.7% of mainland China during 2000–2017, while it decreased significantly over less than 5% of mainland China. The results of moving window range of GSEVI were similar to moving window standard deviation of GSEVI. These may be explained by: (1) increased standard deviation and range of GSEVI accompanied by increased GSEVI value; and (2) faster greening speed in dense than in sparse vegetated areas. Additionally, the increased spatial heterogeneity in VG means the increased difference in VG between arid and humid regions, and between urban cores (UCs) and rural areas. These may primarily be attributed to slower greening speed in arid than in humid regions, and in UCs than in rural areas. Thus some benefits from vegetation greening may be much less in arid than in humid regions, and in UCs than in rural areas. Overall, this study analyzed an interesting phenomenon that vegetation greening may increase spatial heterogeneity in VG, which has a series of implications for environment and human activities.

Impacts of Chinese Grain for Green program and climate change on vegetation in the Loess Plateau during 1982–2015

Remote sensing based vegetation index provides a practical method for the monitoring of vegetation dynamics at regional and global scales. Here, using a long-term remotely sensed normalized difference vegetation index (NDVI) dataset, we quantified the vegetation changes in the Loess Plateau (LP) over the last three decades (1982–2015), which includes the period before the Chinese“Grain for Green Program”(GGP) was launched (1982–1999), and the period after the GGP (1999–2015). The correlations between the NDVI and four climate related variables, i.e., precipitation, temperature, root-soil moisture (RSM), and a drought proxy-standardized evapotranspiration deficit index (SEDI), were also examined. The results indicated that, (i) the GGP strongly changed the vegetation in the LP. The growing-season mean NDVI (GSM-NDVI) and the annual mean NDVI (AM-NDVI) decreased slightly before the GGP launched in 1999, with slopes of −3.38×10−3 and−8.00×10−4year−1, respectively. However, they showed slight and significant (p<0.05) increases after the GGP, with slopes of 4.75×10−3 and 2.32×10−3year−1, respectively. (ii) Climate change (i.e., warming and drying) resulted in adverse effects on vegetation in the LP during the period before the GGP. However, the observed changes (i.e., wetting and reduced drought) exerted positive effects on the vegetation during the period after the GGP. (iii) Inter-annual variations of spatially averaged NDVI over the LP were primarily determined by RSM rather than any other climate related variables. In the southeastern LP, the inter-annual variation of GSM-NDVI was mainly determined by precipitation and SEDI, while the inter-annual variation of AM-NDVI was mainly caused by SEDI and RSM. Inter-annual variations of both GSM-NDVI and AM-NDVI were mainly determined by SEDI and RSM in the northwestern LP, and by temperature in the southwestern LP.

Relationship between Climatic Variables and Finger Millet Yield in Syangja, Central Nepal

Temperature and rainfall are important climatic variables on which the yield of crops depends. The increase in temperature and changing pattern of rainfall in an area reliably influence the yield of crops. This paper is based on a study conducted in Syangja district of central Nepal and analyses the climatic variables and yields of finger millet (Eleusine coracana). Changes in the total harvestable area, yearly yield and relationship of climatic variables on yield were analyzed based on correlation and regression analysis of detrended yield and climatic variables for 1980-2016 periods. The total growing season precipitation at different stations of district showed mixed trends of increasing and decreasing. The growing season mean temperature of Chapakot station was not changed but that of Syangja station has increased by 0.009°C/year from 1980-2016. Both maximum and minimum temperature of Syangja station showed increasing rate of 0.026°C but that of Chapakot station showed maximum temperature increased at the rate of 0.017°C and minimum temperature decreased by 0.012°C annually. The result showed that there was a positive and normal relationship between maximum temperature and yield (r=0.298) whereas there were negative relationship with minimum temperature and rainfall. The multi-linear regression model described that 42.8% of finger millet yield is controlled by climatic variables. If the temperature and rainfall continue to rise, the impact is likely to be negative on finger millet production in future. However, overall crop production can be positive with increase in the temperature at relatively higher altitudes provided basic conditions like fertilizers are met.

Benefits and limitations to straw- and plastic-film mulch on maize yield and water use efficiency: A meta-analysis across hydrothermal gradients

Abstract Ridge-furrow mulching can reduce soil evaporation and conserve rainfall, thereby increasing crop yield and water use efficiency (WUE) in dryland cropping systems. In this study, we collected 837 observations from 50 published papers and used meta-analysis to investigate whether ridge-furrow and mulching practices are equally effective on maize yield, WUE and evapotranspiration (ET) across a range of precipitation and temperature gradients and soil types in China. Five practices were included: (i) straw mulch on flat plots (SMF), (ii) straw mulch on ridge-furrow plots (SMR), (iii) plastic mulch on flat plots (PMF), (iv) plastic mulch on ridge-furrow plots (PMR), and (v) flat plots without mulch, which was used as a control (CK). The meta-analysis showed that both straw mulch and plastic mulch significantly increased maize yields and WUE (except for SMR), and that plastic mulch was more effective than straw mulch in increasing yields, particularly in cold and dry environments. PMR has the highest yields and is more effective in clay loam than in silt loam soils. Straw mulch, but particularly plastic mulch, increased the soil moisture compared to the CK, while plastic mulch increased soil temperature, mainly in spring. However, the positive effect of plastic mulch on maize yield diminished with increasing mean growing-season temperature and precipitation, reaching zero (similar to the CK of no mulch and flat plots) when the growing-season precipitation was greater than 770 mm and the mean growing-season air temperature exceeded 24 °C. The small benefit of straw mulch (on average about 12%) was similar across the precipitation and temperature gradients, including when the benefits of plastic mulch reached zero. While our analysis has shown the benefits of ridge-furrow plastic mulch on yield and water-use efficiency, it has also highlighted the limitations of the benefits. The results provide a guide to the regions where plastic-film mulch and ridge-furrow planting are likely to improve maize yields and regions where the benefits are likely to be limited.

Declining Potential Yield and Rain-fed Yield of Corn in the Corn Belt of Northeastern China during the Past Three Decades

In the past three decades, corn yield in the Corn Belt of North-eastern China (CBNC) have increased under changing in climate and crop management. Quantifying the changes in crop potential production and rain-fed production is essential to determine the yield-contributing and yield-limiting factors and enhance crop productivity. In this paper we conducted correlation and regression analyses of climate and simulated corn yield over the period 1980 to 2011 in CBNC. It was found that the daily minimum temperature and solar radiation were the dominant factor to corn potential production, especially the climate in the post-silking period; the rain-fed production was susceptible to maximum temperature, precipitation, and relative humidity, and the result was showed that relative humidity had a stronger effect than precipitation. According to a regression analysis of the corn potential yield and the climate factors, the results indicate that corn potential yield decreased 1010 and 1314 kg ha-1 for each 1°C increase growing season mean and minimum temperature, respectively; rain-fed yield declined 2819 and 2437 kg ha-1 for each increase 1°C growing season mean and maximum temperature, respectively.

Climatic Effects on Site Productivity of Red Pine Plantations

Climatic effects on site productivity of red pine (Pinus resinosa Aiton) plantations were examined. A stand height/site index equation with climate variables incorporated in the height growth model was developed from stem analysis data. These data were collected from 90 dominant or co-dominant red pine trees sampled from even-aged monospecific plantations located on 30 sites (3 trees per site) broadly distributed across Ontario, Canada. The stand height equation was fit using a nonlinear mixed-effects approach. Climatic effects on site productivity were examined by regressing site index against commonly reported climate variables. Three site-specific climate attributes explained 63% of the variability in observed site index. These climate variables were examined to be incorporated into the stand height growth models. However, only two climate variables—growing season total precipitation (GSTP) and growing season mean temperature (GSMT)—were significant in the model without random effects and autocorrelation. In the presence of random effects and autocorrelation, however, only GSMT remained significant in the model. Stand heights were predicted for three randomly selected locations (eastern, western, and southern Ontario) for the growth periods 2011 to 2040 and 2041 to 2070 under two (2.6 and 8.5 Watts/m2) emissions trajectories known as Representative Concentration Pathways (RCPs). At the end of both growth periods, projected heights were reduced under both climate change scenarios (compared to those under a no-climate-change scenario) at all locations. Under both scenarios, the decrease in height growth was more pronounced in the south than in the east or west. The developed height growth models can be used to estimate stand heights for red pine plantations in a changing climate. Using the same models, site index of a plot/stand can also be estimated by calculating height at a given base (index) age. In the absence of climate data, the model fitted without climate variables can be applied to estimate stand heights and site indices.

Seasonal divergence in the responses of vegetation growth to PDO in Tibetan Plateau, China

Regional-scale normalized difference vegetation index (NDVI) derived from satellite remote sensing observations and gridded climate data were used to study the seasonal responses and underlying mechanisms of vegetation growth over Tibetan Plateau to Pacific Decadal Oscillation (PDO) at period of 1982-2015, by performing Spearman correlation analysis and enhanced multivariate regression model: structural equation model (SEM). The results showed that there was significant negative correlation between PDO index and mean growing-season (April-October) NDVI over Tibetan Plateau; however, marked seasonal divergence in the relationship between PDO and vegetation growth existed among different seasons. It characterized with stronger negative correlation between PDO and NDVI in autumn than in summer, and winter PDO had significant effect on consequent summer vegetation growth. Additionally, it showed great divergence in control processes of PDO on vegetation growth among different seasons, with significant control of PDO on both temperature and precipitation in summer, and significant control of PDO on temperature only in autumn.

Antagonistic effects of growing season and autumn temperatures on the timing of leaf coloration in winter deciduous trees.

Autumn phenology remains a relatively neglected aspect in climate change research, which hinders an accurate assessment of the global carbon cycle and its sensitivity to climate change. Leaf coloration, a key indicator of the growing season end, is thought to be triggered mainly by high or low temperature and drought. However, how the control of leaf coloration is split between temperature and drought is not known for many species. Moreover, whether growing season and autumn temperatures interact in influencing the timing of leaf coloration is not clear. Here, we revealed major climate drivers of leaf coloration dates and their interactions using 154 phenological datasets for four winter deciduous tree species at 89 stations, and the corresponding daily mean/minimum air temperature and precipitation data across China's temperate zone from 1981 to 2012. Results show that temperature is more decisive than drought in causing leaf coloration, and the growing season mean temperature plays a more important role than the autumn mean minimum temperature. Higher growing season temperature and lower autumn minimum temperature would induce earlier leaf coloration date. Moreover, the mean temperature over the growing season correlates positively with the autumn minimum temperature. This implies that growing season mean temperature may offset the requirement of autumn minimum temperature in triggering leaf coloration. Our findings deepen the understanding of leaf coloration mechanisms in winter deciduous trees and suggest that leaf life-span control depended on growing season mean temperature and autumn low temperature control and their interaction are major environmental cues. In the context of climate change, whether leaf coloration date advances or is delayed may depend on intensity of the offset effect of growing season temperature on autumn low temperature.

Climate effects on vegetation vitality at the treeline of boreal forests of Mongolia

Abstract. In northern Mongolia, at the southern boundary of the Siberian boreal forest belt, the distribution of steppe and forest is generally linked to climate and topography, making this region highly sensitive to climate change and human impact. Detailed investigations on the limiting parameters of forest and steppe in different biomes provide necessary information for paleoenvironmental reconstruction and prognosis of potential landscape change. In this study, remote sensing data and gridded climate data were analyzed in order to identify main distribution patterns of forest and steppe in Mongolia and to detect environmental factors driving forest development. Forest distribution and vegetation vitality derived from the normalized differentiated vegetation index (NDVI) were investigated for the three types of boreal forest present in Mongolia (taiga, subtaiga and forest–steppe), which cover a total area of 73 818 km2. In addition to the forest type areas, the analysis focused on subunits of forest and nonforested areas at the upper and lower treeline, which represent ecological borders between vegetation types. Climate and NDVI data were analyzed for a reference period of 15 years from 1999 to 2013. The presented approach for treeline delineation by identifying representative sites mostly bridges local forest disturbances like fire or tree cutting. Moreover, this procedure provides a valuable tool to distinguish the potential forested area. The upper treeline generally rises from 1800 m above sea level (a.s.l.) in the northeast to 2700 m a.s.l. in the south. The lower treeline locally emerges at 1000 m a.s.l. in the northern taiga and rises southward to 2500 m a.s.l. The latitudinal gradient of both treelines turns into a longitudinal one on the eastern flank of mountain ranges due to higher aridity caused by rain-shadow effects. Less productive trees in terms of NDVI were identified at both the upper and lower treeline in relation to the respective total boreal forest type area. The mean growing season temperature (MGST) of 7.9–8.9 ∘C and a minimum MGST of 6 ∘C are limiting parameters at the upper treeline but are negligible for the lower treeline. The minimum of the mean annual precipitation (MAP) of 230–290 mm yr−1 is a limiting parameter at the lower treeline but also at the upper treeline in the forest–steppe ecotone. In general, NDVI and MAP are lower in grassland, and MGST is higher compared to the corresponding boreal forest. One exception occurs at the upper treeline of the subtaiga and taiga, where the alpine vegetation consists of mountain meadow mixed with shrubs. The relation between NDVI and climate data corroborates that more precipitation and higher temperatures generally lead to higher greenness in all ecological subunits. MGST is positively correlated with MAP of the total area of forest–steppe, but this correlation turns negative in the taiga. The limiting factor in the forest–steppe is the relative humidity and in the taiga it is the snow cover distribution. The subtaiga represents an ecological transition zone of approximately 300 mm yr−1 precipitation, which occurs independently from the MGST. Since the treelines are mainly determined by climatic parameters, the rapid climate change in inner Asia will lead to a spatial relocation of tree communities, treelines and boreal forest types. However, a direct deduction of future tree vitality, forest composition and biomass trends from the recent relationships between NDVI and climate parameters is challenging. Besides human impact, it must consider bio- and geoecological issues like, for example, tree rejuvenation, temporal lag of climate adaptation and disappearing permafrost.

Velocity of change in vegetation productivity over northern high latitudes

Warming is projected to increase the productivity of northern ecosystems. However, knowledge on whether the northward displacement of vegetation productivity isolines matches that of temperature isolines is still limited. Here we compared changes in the spatial patterns of vegetation productivity and temperature using the velocity of change concept, which expresses these two variables in the same unit of displacement per time. We show that across northern regions (>50°N), the average velocity of change in growing-season normalized difference vegetation index (NDVIGS, an indicator of vegetation productivity; 2.8 ± 1.1 km yr-1) is lower than that of growing-season mean temperature (T GS; 5.4 ± 1.0 km yr-1). In fact, the NDVIGS velocity was less than half of the T GS velocity in more than half of the study area, indicating that the northward movement of productivity isolines is much slower than that of temperature isolines across the majority of northern regions (about 80% of the area showed faster changes in temperature than productivity isolines). We tentatively attribute this mismatch between the velocities of productivity and temperature to the effects of limited resource availability and vegetation acclimation mechanisms. Analyses of ecosystem model simulations further suggested that limited nitrogen availability is a crucial obstacle for vegetation to track the warming trend.

LCE: leaf carbon exchange data set for tropical, temperate, and boreal species of North and Central America.

Leaf canopy carbon exchange processes, such as photosynthesis and respiration, are substantial components of the global carbon cycle. Climate models base their simulations of photosynthesis and respiration on an empirical understanding of the underlying biochemical processes, and the responses of those processes to environmental drivers. As such, data spanning large spatial scales are needed to evaluate and parameterize these models. Here, we present data on four important biochemical parameters defining leaf carbon exchange processes from 626 individuals of 98 species at 12 North and Central American sites spanning ~53° of latitude. The four parameters are the maximum rate of Rubisco carboxylation (Vcmax ), the maximum rate of electron transport for the regeneration of Ribulose-1,5,-bisphosphate (Jmax ), the maximum rate of phosphoenolpyruvate carboxylase carboxylation (Vpmax ), and leaf dark respiration (Rd ). The raw net photosynthesis by intercellular CO2 (A/Ci ) data used to calculate Vcmax , Jmax , and Vpmax rates are also presented. Data were gathered on the same leaf of each individual (one leaf per individual), allowing for the examination of each parameter relative to others. Additionally, the data set contains a number of covariates for the plants measured. Covariate data include (1) leaf-level traits (leaf mass, leaf area, leaf nitrogen and carbon content, predawn leaf water potential), (2) plant-level traits (plant height for herbaceous individuals and diameter at breast height for trees), (3) soil moisture at the time of measurement, (4) air temperature from nearby weather stations for the day of measurement and each of the 90d prior to measurement, and (5) climate data (growing season mean temperature, precipitation, photosynthetically active radiation, vapor pressure deficit, and aridity index). We hope that the data will be useful for obtaining greater understanding of the abiotic and biotic determinants of these important biochemical parameters and for evaluating and improving large-scale models of leaf carbon exchange.

Potential Consequences of Repeated Severe Drought for Shortgrass Steppe Species

Future climate projections indicate temperatures in the shortgrass steppe region are likely to increase up to 3°C by midcentury, with a corresponding reduction in soil moisture even without precipitation deficit. Although periodic drought is a natural disturbance in shortgrass rangeland, negative effects on characteristic shortgrass species are possible as the frequency and severity of drought events increase in comparison with recent historic norms. As part of a study intended to detect vegetation changes at a shortgrass steppe site on Colorado’s eastern plains, frequency and canopy cover percentage were measured in 37 permanently marked plots over a period of 17 yr. The study period included the two lowest total annual precipitation yr (2002 and 2012) in the period of record for regional weather stations, exceeding even the driest years of the extended 1930s drought. Growing season mean temperatures during those drought years were 1°C and 1.6°C above the 1971−2000 average, respectively. Three of the six perennial grass species monitored showed a decline over the period of the study. Blue grama (Bouteloua gracilis), a dominant and important forage species in the shortgrass steppe, declined in both cover and frequency, while alkali sacaton (Sporobolus airoides), not an important forage species, slightly increased. In addition to changes in graminoid dominance, we observed an increase in cholla (Cylindropuntia imbricata) and a decrease in sandsage (Artemisia filifolia) densities between 1999 and 2015. Even if total productivity of the shortgrass steppe is maintained under warming and drying conditions, changes in species composition have implications for rangeland quality with regard to its use for livestock grazing and use by wildlife such as small mammals and songbirds.

Evidence for a weakening strength of temperature-corn yield relation in the United States during 1980–2010

Temperature is known to be correlated with crop yields, causing reduction of crop yield with climate warming without adaptations or CO2 fertilization effects. The historical temperature-crop yield relation has often been used for informing future changes. This relationship, however, may change over time following alternations in other environmental factors. Results show that the strength of the relationship between the interannual variability of growing season temperature and corn yield (RGST_CY) has declined in the United States between 1980 and 2010 with a loss in the statistical significance. The regression slope which represents the anomalies in corn yield that occur in association with 1 degree temperature anomaly has decreased significantly from −6.9%/K of the first half period to −2.4%/K–−3.5%/K of the second half period. This implies that projected corn yield reduction will be overestimated by a fact of 2 in a given warming scenario, if the corn-temperature relation is derived from the earlier historical period. Changes in RGST_CY are mainly observed in Midwest Corn Belt and central High Plains, but are partly reproduced by 11 process-based crop models. In Midwest rain-fed systems, the decrease of negative temperature effects coincides with an increase in water availability by precipitation. In irrigated areas where water stress is minimized, the decline of beneficial temperature effects is significantly related to the increase in extreme hot days. The results indicate that an extrapolation of historical yield response to temperature may bias the assessment of agriculture vulnerability to climate change. Efforts to reduce climate impacts on agriculture should pay attention not only to climate change, but also to changes in climate-crop yield relations. There are some caveats that should be acknowledged as the analysis is restricted to the changes in the linear relation between growing season mean temperature and corn yield for the specific study period.

Variations in Growing-Season NDVI and Its Response to Permafrost Degradation in Northeast China

Permafrost is extremely sensitive to climate change. The degradation of permafrost has strong and profound effects on vegetation. The permafrost zone of northeastern China is the second largest region of permafrost in China and lies on the south edge of the Eurasian cryolithozone. This study analyzed the spatiotemporal variations of the growing-season Normalization Difference Vegetation Index (NDVI) in the permafrost zone of northeastern China and analyzed the correlation between NDVI and ground surface temperatures (GST) during the years 1981–2014. Mean growing-season NDVI (MGS-NDVI) experienced a marked increase of 0.003 year−1 across the entire permafrost zone. The spatial dynamics of vegetation cover had a high degree of heterogeneity on a per pixel scale. The MGS-NDVI value increased significantly (5% significance level) in 80.57%, and this increase was mostly distributed in permafrost zone except for the western steppe region. Only 7.72% experienced a significant decrease in NDVI, mainly in the cultivated and steppe portions. In addition, MGS-NDVI increased significantly with increasing growing-season mean ground surface temperature (GS-MGST). Our results suggest that a warming of GS-MGST (permafrost degradation) in the permafrost region of northeastern China played a positive role in increasing plant growth and activities. Although increasing ground surface temperature resulted in increased vegetation cover and growth in the short time of permafrost degradation, from the long term point of view, permafrost degradation or disappearance may weaken or even hinder vegetation activities.

Genetic differentiation and plasticity interact along temperature and precipitation gradients to determine plant performance under climate change

Summary Understanding species' abilities to cope with changing climate is a key prerequisite for predicting the future fates of species and ecosystems. Despite considerable research on species responses to changing climate, we still lack understanding of the role of specific climatic factors, and their interactions, for species responses. We also lack understanding of the relative importance of plasticity vs. adaptation in determining the observed responses. As a model, we use a dominant clonal grass, Festuca rubra, originating from a natural climatic grid of 12 localities in western Norway that allows factorial combinations of temperature (mean growing season temperatures ranging from 6·5 to 10·5 °C) and precipitation (annual precipitation ranging from 600 to 2700 mm). We grew clones from all populations in four growth chambers representing the four climatic extremes in the climate grid (warm/cold × wet/dry). Genetic differentiation and direction and magnitude of plastic responses vary systematically among populations throughout the climatic grid. Growth‐related plant traits are highly plastic and their degree of plasticity depends on their origin. In contrast, the traits reflecting species' foraging strategy are not plastic but vary with the climate of origin. Levels of plasticity of growth‐related traits and genetically differentiated foraging traits thus might constrain local populations' ability to cope with novel climates. Synthesis. Shifts in temperature and precipitation, at the scale and direction expected for the region in the next century, are likely to dramatically affect plant performance. This study illustrates how the interplay between genetic differentiation and plasticity in response to both temperature and precipitation will affect the specific responses of species to climate change. Such complex responses will affect how climate‐change impacts scale up to the community and ecosystem levels. Future studies thus need to specifically consider regionally relevant climate‐change projections, and also explore the role of genetic differentiation and plasticity and how this varies within local floras. Our study also demonstrates that even widespread species with seemingly broad climatic niches may strongly differ in their population performance and plasticity. Climate‐change studies should therefore not be limited to rare and restricted species.