•Straw mulch was effective in increasing soil organic carbon (SOC) content.•Straw mulch improves the soil N, P and soil water content in 0–10 cm soil layer.•Straw mulch treatments significantly ...increased the soil enzyme activity.•Enzyme activities are related to nutrient dynamics, particularly SOC and available N.•The crop yield and water use efficiency were significantly higher with straw mulch.
Addition of organic material, such as crop straw mulch in most soils is considered a strategy for sustainable agricultural production. We conducted a two-year experiment in 2015 and 2016 to determine changes in soil biochemical properties and maize yield in response to treatment with wheat-straw mulch. The treatments consisted of the addition of different levels of wheat-straw mulch (S1: 0, S2: 2500, S3: 5000 kg ha−1). Soil samples from four depths (0.1, 0.2, 0.3, and 0.4 m) were collected and analyzed. Soil enzymes, such as invertase, phosphatase, urease, and catalase, were significantly higher in the S3 treatment than in the S1 treatment. Values were greater for the samples collected at 0.1 m soil depth than those collected from deeper soil layers. Regarding soil properties, soil organic carbon (SOC), available nitrogen (AN), available phosphorus (AP), total nitrogen (TN), total phosphorus (TP), and soil water content (SWC) were significantly higher in S3 at 0–0.1 m soil depth than in other treatments. Compared with the (S1), an average increase in SOC, AN, AP, TN, TP, and SWC in 0–0.4 m soil depth with full straw mulch (S3), were 32.4, 31.9, 32.0, 11.8, 16.7, and 18.5%, higher, respectively. On average, urease, phosphatase, invertase, and catalase increased by 15.1, 11.0, 88.4, and 24.0%, respectively in the S3 treatment compared with that in the S1 treatment at 0–0.1 m depth, and decreased with increasing soil depth. The S3 treatment had increased grain yield (7%), biomass yield (28%), and water use efficiency (8%), compared with the S1 treatment. Overall, our results suggested that the S3 straw mulch treatment (5000 kg ha−1) could be used to sustain maize productivity and promote a better relationship between soil enzymes and soil properties in the semi-arid conditions of the Guanzhong area.
Hydraulic impairment due to xylem embolism and carbon starvation are the two proposed mechanisms explaining drought‐induced forest dieback and tree death. Here, we evaluate the relative role played ...by these two mechanisms in the long‐term by quantifying wood‐anatomical traits (tracheid size and area of parenchyma rays) and estimating the intrinsic water‐use efficiency (iWUE) from carbon isotopic discrimination. We selected silver fir and Scots pine stands in NE Spain with ongoing dieback processes and compared trees showing contrasting vigour (declining vs nondeclining trees). In both species earlywood tracheids in declining trees showed smaller lumen area with thicker cell wall, inducing a lower theoretical hydraulic conductivity. Parenchyma ray area was similar between the two vigour classes. Wet spring and summer conditions promoted the formation of larger lumen areas, particularly in the case of nondeclining trees. Declining silver firs presented a lower iWUE than conspecific nondeclining trees, but the reverse pattern was observed in Scots pine. The described patterns in wood anatomical traits and iWUE are coherent with a long‐lasting deterioration of the hydraulic system in declining trees prior to their dieback. Retrospective quantifications of lumen area permit to forecast dieback in declining trees 2–5 decades before growth decline started. Wood anatomical traits provide a robust tool to reconstruct the long‐term capacity of trees to withstand drought‐induced dieback.
•A 2-years field experiment was conducted to study the optimal irrigation and nitrogen rates for drip-irrigated winter wheat.•Combination of nitrogen rate of 240 kg ha−1 and irrigation quota of 40 mm ...maximized wheat growth and grain yield.•High water use efficiency and acceptable nitrogen partial factor productivity also appeared in the combination.
Drip irrigation has been gradually adopted for winter wheat production in the North China Plain (NCP) due to significant saving from using irrigation water and improving water and nitrogen use efficiencies. However, the optimal water and nitrogen application rates for drip-irrigated wheat are still unclear. A field experiment with five nitrogen application rates (0, 120, 180, 240, and 300 kg ha−1, referred as N0, N1, N2, N3, and N4) and three irrigation levels (40, 30, and 20 mm per irrigation, referred as I1, I2, and I3) was conducted during the 2015–2016 and 2016–2017 winter wheat seasons to study the effects of irrigation and nitrogen rates on crop growth, yield, and the water and nitrogen use efficiencies. Results showed that increasing irrigation and nitrogen application rates notably improved actual evapotranspiration, leaf area index, aboveground biomass, grain yield, and water use efficiency (WUE) of winter wheat. However, nitrogen application rates exceeding 240 kg ha−1 were not beneficial for wheat growth, grain yield, WUE, and irrigation water use efficiency (IWUE). The maximum grain yields of 8034 and 8760 kg ha−1 were achieved in N3I1, which had WUE of 2.08 and 2.23 kg m−3, and IWUE of 4.46 and 4.87 kg m−3 in 2015–2016 and 2016–2017, respectively. At the same time, N3I1 did not result in much reduction of nitrogen partial factor productivity (NPFP) (average of 34.99 kg kg−1 in N3I1 for two seasons). Considering comprehensively growth, yield, WUE, IWUE, and NPFP, combination of N rate of 240 kg ha−1 and irrigation quota of 40 mm per irrigation was optimal pattern for drip-irrigated winter wheat. These results may provide a scientific basis for water and nitrogen management of drip-irrigated winter wheat in the NCP.
The demand for freshwater resources has increased in recent times and has been exacerbated by escalating global population and increasing drought indices in the world’s agricultural zones. Irrigated ...agriculture is inevitably a wasteful water user that has deprived other sectors of the scarce resource. Improving water use efficiency in irrigated agriculture is therefore crucial for sustainable agricultural production to thrive. There is potential to improve water use efficiency through smart irrigation systems, especially with the advent of wireless communication technologies, monitoring systems, and advanced control strategies for optimal irrigation scheduling. This paper reviews state-of-the-art smart monitoring and irrigation control strategies that have been used in recent years for irrigation scheduling. From the literature review, closed-loop irrigation control strategies are efficient than open-loop systems which do not cater for uncertainties. It is argued that combining soil-based, plant, and weather-based monitoring methods in a modelling environment with model predictive control can significantly improve water use efficiency. This review shall help researchers and farmers to choose the best irrigation monitoring and control strategy to improve irrigation scheduling in open field agricultural systems.
•A review of smart irrigation monitoring and control strategies in precision agriculture.•A detailed discussion on monitoring for real-time irrigation scheduling.•A summary of irrigation control strategies and potential water savings.•Potential opportunities for improving water use efficiency in open-field agriculture presented.
Most studies assume midday gas exchange measurements capture the leaf's daytime performance. However, stomatal conductance (g
) and photosynthesis (A
) fluctuate diurnally due to endogenous and ...environmental rhythms, which can affect intrinsic water use efficiency (iWUE). Six Sorghum lines with contrasting stomatal anatomical traits were grown in environmentally controlled conditions and leaf gas exchange was measured three times a day. Stomatal anatomy and kinetic responses to light transients were also measured. Highest A
and g
, and lowest iWUE, were observed at midday for most lines. Diurnally averaged iWUE correlated positively with morning and midday iWUE, and negatively with the time taken for stomata to close after transition to low light intensity (k
). There was significant variation among sorghum lines for k
, and smaller k
correlated with lower g
and higher stomatal density (SD) across the lines. In turn, g
was negatively correlated with SD and regulated by the operational stomatal aperture regardless of stomatal size. Altogether, our data suggest a common physiology to improve iWUE in sorghum related to the control of water loss without impacting photosynthesis relying on higher SD, lower stomatal aperture and faster stomatal closing in response to low light intensity.
Water-use efficiency (WUE) is an important indicator of carbon–water interactions and is defined as the ratio of vegetation productivity to water loss. However, how WUE varies along climate and ...vegetation gradients at the regional scale remains elusive. In this study, we investigated the spatial patterns of plant-canopy WUE (PWUE, i.e., ratio of gross primary productivity to plant transpiration) and ecosystem WUE (EWUE, i.e., ratio of gross primary productivity to evapotranspiration) in the Chinese Loess Plateau (CLP), which has seen large changes in the biosphere-atmosphere carbon and water cycles due to large-scale revegetation with the CLP. Spatial responses of PWUE and EWUE variations to the mean annual precipitation (MAP), mean annual air temperature (MAT), and normalized difference vegetation index (NDVI) gradients were examined based on remote-sensing and geostatistical model-based datasets. Results showed that mean EWUE estimated from two approaches was 1.26 ± 0.28 and 1.37 ± 0.68 g C kg−1 H2O, respectively, lower than the mean PWUE (3.16 ± 0.71 g C kg−1 H2O) across the CLP. EWUE and PWUE estimates showed similar spatial distributions, generally with higher values in the areas with more water available. Precipitation sensitivities of EWUE and PWUE appeared to be positive except the very cold regions, and gradually decreased with increasing MAT in the forest-steppe and forest zones. Spatial variation in EWUE is intrinsically affected by both of PWUE and ecosystem water allocation (i.e., ratio of transpiration to evapotranspiration), and NDVI sensitivity of EWUE is dominant by ecosystem water allocation, leading to postive sensitivity of EWUE to NDVI for most MAP range in the CLP. PWUE variation depends on the geographic patterns of vegetation communities determined by precipitation pattern, leading to relatively lower and stable NDVI sensitivity than EWUE along the MAP gradient in the CLP. Our study revealed the divergent spatial responses of WUE to climate and vegetation gradients at the plant-canopy and ecosystem levels, which could enhance our understanding on the regional-scale carbon-water relationships across multiple organismic levels, and provide essential information for the WUE upscaling and modeling efforts.
•PWUE and EWUE were both higher for more humid forest and forest-steppe areas.•PWUE variation was dominantly controlled by geographic pattern of precipitation.•EWUE variation was jointly regulated by PWUE and ecosystem water allocation.•NDVI sensitivity of PWUE was lower than EWUE along precipitation gradient.
Crassulacean acid metabolism (CAM) is a specialized mode of photosynthesis that features nocturnal CO2 uptake, facilitates increased water-use efficiency (WUE), and enables CAM plants to inhabit ...water-limited environments such as semi-arid deserts or seasonally dry forests. Human population growth and global climate change now present challenges for agricultural production systems to increase food, feed, forage, fiber, and fuel production. One approach to meet these challenges is to increase reliance on CAM crops, such as Agave and Opuntia, for biomass production on semi-arid, abandoned, marginal, or degraded agricultural lands. Major research efforts are now underway to assess the productivity of CAM crop species and to harness the WUE of CAM by engineering this pathway into existing food, feed, and bioenergy crops. An improved understanding of CAM has potential for high returns on research investment. To exploit the potential of CAM crops and CAM bioengineering, it will be necessary to elucidate the evolution, genomic features, and regulatory mechanisms of CAM. Field trials and predictive models will be required to assess the productivity of CAM crops, while new synthetic biology approaches need to be developed for CAM engineering. Infrastructure will be needed for CAM model systems, field trials, mutant collections, and data management.
Summary
Chloride (Cl−) has been recently described as a beneficial macronutrient, playing specific roles in promoting plant growth and water‐use efficiency (WUE). However, it is still unclear how Cl− ...could be beneficial, especially in comparison with nitrate (NO3−), an essential source of nitrogen that shares with Cl− similar physical and osmotic properties, as well as common transport mechanisms. In tobacco plants, macronutrient levels of Cl− specifically reduce stomatal conductance (gs) without a concomitant reduction in the net photosynthesis rate (AN). As stomata‐mediated water loss through transpiration is inherent in the need of C3 plants to capture CO2, simultaneous increase in photosynthesis and WUE is of great relevance to achieve a sustainable increase in C3 crop productivity. Our results showed that Cl−‐mediated stimulation of larger leaf cells leads to a reduction in stomatal density, which in turn reduces gs and water consumption. Conversely, Cl− improves mesophyll diffusion conductance to CO2 (gm) and photosynthetic performance due to a higher surface area of chloroplasts exposed to the intercellular airspace of mesophyll cells, possibly as a consequence of the stimulation of chloroplast biogenesis. A key finding of this study is the simultaneous improvement of AN and WUE due to macronutrient Cl− nutrition. This work identifies relevant and specific functions in which Cl− participates as a beneficial macronutrient for higher plants, uncovering a sustainable approach to improve crop yield.
Significance Statement
We have identified anatomical and cellular mechanisms altered by macronutrient Cl− levels that result in lower stomatal conductance and increased mesophyll diffusion conductance to CO2. Simultaneous improvement of AN and WUE due to macronutrient Cl− nutrition can be of great relevance for increasing C3 crop productivity.
Changes in tree physiology driven by environmental change can alter the balance of forest ecosystem carbon and water fluxes. We performed a meta-analysis of published tree ring literature, comprising ...36 different species across 84 sites globally, to show stimulated leaf photosynthesis, not reduced stomatal conductance, is primarily responsible for recently increasing tree intrinsic water use efficiency (iWUE), which integrates the balance between carbon and water fluxes. Furthermore, we show trends in tree iWUE are similar in magnitude to the increase in atmospheric CO
2
over the 20th century and that climate interacts with CO
2
to modulate tree iWUE. These findings will help to guide efforts of refining the role of forests in process-based models under future environmental change.
We conducted a meta-analysis of carbon and oxygen isotopes from tree ring chronologies representing 34 species across 10 biomes to better understand the environmental drivers and physiological mechanisms leading to historical changes in tree intrinsic water use efficiency (iWUE), or the ratio of net photosynthesis (
A
net
) to stomatal conductance (
g
s
), over the last century. We show a ∼40% increase in tree iWUE globally since 1901, coinciding with a ∼34% increase in atmospheric CO
2
(C
a
), although mean iWUE, and the rates of increase, varied across biomes and leaf and wood functional types. While C
a
was a dominant environmental driver of iWUE, the effects of increasing C
a
were modulated either positively or negatively by climate, including vapor pressure deficit (VPD), temperature, and precipitation, and by leaf and wood functional types. A dual carbon–oxygen isotope approach revealed that increases in
A
net
dominated the observed increased iWUE in ∼83% of examined cases, supporting recent reports of global increases in
A
net
, whereas reductions in
g
s
occurred in the remaining ∼17%. This meta-analysis provides a strong process-based framework for predicting changes in tree carbon gain and water loss across biomes and across wood and leaf functional types, and the interactions between C
a
and other environmental factors have important implications for the coupled carbon–hydrologic cycles under future climate. Our results furthermore challenge the idea of widespread reductions in
g
s
as the major driver of increasing tree iWUE and will better inform Earth system models regarding the role of trees in the global carbon and water cycles.
Increasing water‐use efficiency (WUE), the ratio of carbon gain to water loss, is a key mechanism that enhances carbon uptake by terrestrial vegetation under rising atmospheric CO2 (ca). Existing ...theory and empirical evidence suggest a proportional WUE increase in response to rising ca as plants maintain a relatively constant ratio between the leaf intercellular (ci) and ambient (ca) partial CO2 pressure (ci/ca). This has been hypothesized as the main driver of the strengthening of the terrestrial carbon sink over the recent decades. However, proportionality may not characterize CO2 effects on WUE on longer time‐scales and the role of climate in modulating these effects is uncertain. Here, we evaluate long‐term WUE responses to ca and climate from 1901 to 2012 CE by reconstructing intrinsic WUE (iWUE, the ratio of photosynthesis to stomatal conductance) using carbon isotopes in tree rings across temperate forests in the northeastern USA. We show that iWUE increased steadily from 1901 to 1975 CE but remained constant thereafter despite continuously rising ca. This finding is consistent with a passive physiological response to ca and coincides with a shift to significantly wetter conditions across the region. Tree physiology was driven by summer moisture at multi‐decadal time‐scales and did not maintain a constant ci/ca in response to rising ca indicating that a point was reached where rising CO2 had a diminishing effect on tree iWUE. Our results challenge the mechanism, magnitude, and persistence of CO2's effect on iWUE with significant implications for projections of terrestrial productivity under a changing climate.
We measured carbon isotopes from tree rings in the northeastern USA forests to reconstruct century‐long intrinsic water use efficiency (iWUE). We found that iWUE increased since the turn of the 20th century, but leveled off after 1975 CE coincident with a regional shift to unprecedented pluvial conditions. Summer moisture regulated tree physiology and altered the CO2 effect on iWUE away from proportionality in the recent decades.
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