1. The quantitative relationship between size and reproductive output is a central aspect of a plant's strategy: the conversion of growth into fitness. As plant allocation is allometric in the broad ...sense, i.e. it changes with size, we take an allometric perspective and review existing data on the relationship between individual vegetative (V, x-axis) and reproductive (R, y-axis) biomass within plant populations, rather than analysing biomass ratios such as reproductive effort (R/(R+V)). 2. The allometric relationship between R and V among individuals within a population is most informative when cumulative at senescence (total R-V relationship), as this represents the potential reproductive output of individuals given their biomass. Earlier measurements may be misleading if plants are at different developmental stages and therefore have not achieved the full reproductive output their size permits. Much of the data that have been considered evidence for plasticity in reproductive allometry are actually evidence for plasticity in the rate of growth and development. 3. Although a positive x-intercept implies a minimum size for reproducing, a plant can have a threshold size for reproducing without having a positive x-intercept. 4. Most of the available data are for annual and monocarpic species whereas allometric data on long-lived iteroparous plants are scarce. We find three common total R-V patterns: short-lived, herbaceous plants and clonal plants usually show a simple, linear relationship, either (i) passing through the origin or (ii) with a positive x-intercept, whereas larger and longer-lived plants often exhibit (iii) classical log-log allometric relationships with slope <1. While the determinants of plant size are numerous and interact with one another, the potential reproductive output of an individual is primarily determined by its size and allometric programme, although this potential is not always achieved. 5. Synthesis. The total R-V relationship for a genotype appears to be a relatively fixed-boundary condition. Below this boundary, a plant can increase its reproductive output by: (i) moving towards the boundary: allocating more of its resources to reproduction, or (ii) growing more to increase its potential reproductive output. At the boundary, the plant cannot increase its reproductive output without growing more first. Analysing size-dependent reproduction is the first step in understanding plant reproductive allocation, but more integrative models must include time and environmental cues, i.e. development.
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BFBNIB, FZAB, GIS, IJS, INZLJ, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZRSKP
Climate change is associated with more intense phases of heat, drought or precipitation that can have a negative impact on soil properties. Our goal was to understand if elevated CO2 (eCO2) and ...temperature (eT), and a multicomponent (eCO2eT) climate effect will influence soil properties from cereal‐legume intercrops differently compared to sole crops. We hypothesized that cereal‐legume intercrops can regulate climate effects, causing soil properties and greenhouse gas fluxes to be similar to ambient climate conditions. eT and eCO2eT decreased soil organic carbon (C) (p = .001) and nitrogen (N) (p = .003) but increased (p = .011) soil nitrate in all crop systems, compared to ambient conditions. For crop systems, soil ammonium was lower (p = .001) with all climate effects, but nitrate was greater (p = .011) with eCO2 and eCO2eT compared to ambient conditions. The microbial community had a preferential (p = .024) consumption of C3 sources in the sole crops. Climate effects also influenced how C and N were accessed by microbes in all crop systems, shifting (p = .001) species richness and microbial community structure. CO2 fluxes were greater (p = .001) with eT and eCO2, whereas N2O fluxes were greater (p = .005) with eCO2 and eCO2eT. However, greenhouse gas fluxes from the intercrop were similar between eT or eCO2eT and ambient conditions. For soil properties, we rejected our hypothesis since cereal‐legume intercrops did not have an advantage over sole crops to cope with single‐ and multicomponent climate effects, but we partially accepted our hypothesis since greenhouse gas fluxes were similar between AMB and eT or eCO2eT.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Nitrogen use efficiency is higher in newer than in older maize (Zea mays L.) hybrids, but the physiological mechanisms underlying differences in N‐use efficiency are unknown. The objective of this ...study was to quantify differences between an older and a newer maize hybrid in their response to N availability throughout the life cycle at both the leaf and the whole‐plant level. An older and a newer maize hybrid were grown in a field hydroponic system located near Guelph, ON, in 2005 at a high and a low N level. Leaf carbon exchange rate (CER), chlorophyll index, and the thylakoid electron transport rate (ETR) were measured weekly from 2 wk presilking to 8 wk postsilking. Plant‐component dry matter and N content were determined from 1 wk presilking to maturity. At the leaf level, leaf CER declined during the grain‐filling period, and the decline was greater under low than high N availability. The decline in leaf CER during the grain‐filling period was less in the newer than in the older hybrid under both high and low N availability, and differences in leaf CER were associated most strongly with a reduction in leaf CER per unit absorbed photosynthetic photon flux density. At the whole‐plant level, reduction in grain yield in low vs. high N was greater in the older than in the newer hybrid. The hybrid × N interaction for grain yield was attributable predominantly to a greater decline in the proportion of dry matter allocated to the grain in the older hybrid.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Abstract
Adequate management of N supply, plant density, row spacing, and soil cover has proved useful for increasing grain yields and/or grain yield stability of rainfed crops over the years. We ...review the impact of these management practices on grain yield water-related determinants: seasonal crop evapotranspiration (ET) and water use efficiency for grain production per unit of evapotranspired water during the growing season (WUEG,ET,s). We highlight a large number of conflicting results for the impact of management on ET and expose the complexity of the ET response to environmental factors. We analyse the influence of management practices on WUEG,ET,s in terms of the three main processes controlling it: (i) the proportion of transpiration in ET (T/ET), (ii) transpiration efficiency for shoot biomass production (TEB), and (iii) the harvest index. We directly relate the impact of management practices on T/ET to their effect on crop light interception and provide evidence that management practices significantly influence TEB. To optimize WUEG,ET,s, management practices should favor soil water availability during critical periods for seed set, thereby improving the harvest index. The need to improve the performance of existing crop growth models for the prediction of water-related grain yield determinants under different management practices is also discussed.
This review highlights the significance of management practices in enhancing water-related grain yield determinants (evapotranspiration and water use efficiency) with a particular focus on the maize crop.
Soil nitrogen (N) is one of the most important nutrients for plant productivity and microbial activity in terrestrial ecosystems. However, soil N is also readily affected by land management ...practices, influencing N2O emissions. This study assessed N dynamics in soil from different crop systems including a 1:2 (one row of maize and two rows soybean) and 2:3 (two rows of maize and three rows of soybean) intercrop and a maize and soybean sole crop as a result of residue addition from maize or soybeans. This was achieved through a 140-day incubation study using δ15N natural abundance. The effect of residue addition on soil TN was greater than its influence on crop systems when compared to treatments with no residue addition (Cont). The influence of residue addition on intercrops was most readily observed in the fractionated soil. Light fraction N (LF-N) and soil microbial biomass N (SMB-N) were significantly greater (p<0.05) in the intercrops than in the sole crops. Residue amended treatments were significantly (p<0.05) depleted in δ15N-TN, δ15N-LF and δ15N-SMB compared to Cont treatments. The δ15N-SMB was significantly enriched (p<0.05) compared to that of the residue, TN and LF-N. Residue amended treatments had significantly lower (p<0.05) N2O emissions than Cont treatments. However, N2O emissions were not significantly different (p<0.05) between soybean and maize amended treatments, nor between intercrops and sole crops. Our results demonstrate that the addition of contrasting residue types influenced short-term N dynamics in intercrops differently than sole crops.
•Residue and agroecosystem management type affected short-term N dynamics.•The effect of residue addition on intercrops was most readily observed in soil fractions.•Intercropping is a sustainable land management practice.•Residue addition decreased soil N2O emissions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The Argentine Pampa is one of the major global regions for the production of maize (Zea mays L.) and soybean (Glycine max L. Merr.), but intense management practices have led to soil degradation and ...amplified greenhouse‐gas (GHG) emissions. This paper presents preliminary data on the effect of maize‐soybean intercrops compared with maize and soybean sole crops on the short‐term emission rates of CO2 and N2O and its relationship to soil moisture or temperature over two field seasons. Soil organic carbon (SOC) concentrations were significantly greater (p < 0.05) in the maize sole crop and intercrops, whereas soil bulk density was significantly lower in the intercrops. Soil CO2 emission rates were significantly greater in the maize sole crop but did not differ significantly for N2O emissions. Over two field seasons, both trace gases showed a general trend of greater emission rates in the maize sole crop followed by the soybean sole crop and were lowest in the intercrops. Linear regression between soil GHG (CO2 and N2O) emission rates and soil temperature or volumetric soil moisture were not significant except in the 1:2 intercrop where a significant relationship was observed between N2O emissions and soil temperature in the first field season and between N2O and volumetric soil moisture in the second field season. Our results demonstrated that intercropping in the Argentine Pampa may be a more sustainable agroecosystem land‐management practice with respect to GHG emissions.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Background and aims Reliance on nitrogen (N) fertilizers to maintain crop productivity requires a thorough understanding of the transformation of this nutrient within the soil-plant system. Organic ...matter input from a mixture of crop residues, such intercrop systems, influence N transformations differently compared to sole crops. We tested the hypothesis that N mineralization and immobilization differ between cereal-legume intercrops and sole crops. Methods A short-term experiment using 15N isotopic pool dilution was conducted in 2007 and 2012 in maize (Zea mays L.) and soybean (Glycine max L. Merr.) sole crops and 1:2 (1 row maize:2 rows soybean) and 2:3 (two rows maize:3 rows soybean) intercrops. Soil characteristics, gross mineralization and immobilization, and net immobilization to a 10 cm depth were quantified. Results Soil characteristics (pH, bulk density, soil organic carbon (C), total N, and C:N) were not significantly different (P<0.05) among treatments, but differed significantly (P<0.05) between years (2007 vs. 2012). Soil NH4+-N was significantly lower (P<0.05) in the maize sole crop. Gross N mineralization, immobilization and net immobilization, were significantly different (P<0.05) among treatments and between years. Relative NH4+-N immobilization was significantly different (P<0.05) among treatments and between years, showing the lowest values in the intercrops. The amount of NH4+-N mineralized per day was significantly greater (P<0.05) in the 2:3 intercrop and was significantly different (P<0.05) between years in the 2:3 intercrop. Residence time of NH4+-N was significantly longer (P<0.05) in the soybean sole crop and 1:2 intercrop followed by the 2:3 intercrop and the maize sole crop. Conclusions Intercropping contributed to the long-term immobilization of N and therefore was a more sustainable land-management practice than sole cropping. The adoption of cereal-legume intercrops will curb our currently growing reliance on N fertilizers.
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BFBNIB, DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NMLJ, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Leaf rolling is an adaptive mechanism associated with water deficiencies; however, the physiological processes and environmental factors contributing to leaf rolling are not fully understood. The ...objective of this study was to examine (i) a possible relationship between the degree of leaf rolling and soil water content and (ii) the possible influence of vapor pressure deficit (VPD) on the degree of leaf rolling. Leaf rolling was measured on maize (Zea mays L.) plants grown in pots and subjected to various soil drying and atmospheric VPD treatments. The experimental results indicated that (i) high VPD by itself does not readily induce leaf rolling, and (ii) leaf rolling was observed in proportion to the extent of soil drying. The values of the fraction of transpirable soil water thresholds for the decline in normalized transpiration rate and for the initiation of plant leaf rolling were sensitive to environmental conditions (VPD and temperature). With soil drying, leaf rolling was initiated slightly after the initiation of a decrease in the transpiration rate.
Core Ideas
Well‐watered plants under elevated vapor pressure deficit did not show leaf rolling.
Genotypic differences existed in water content of drying soil for initiation of leaf rolling.
Leaf rolling was initiated slightly after initiation of decrease in transpiration rate.
Linear relationship existed between decreasing transpiration rate and degree of leaf rolling.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Corn stover is a biogas feedstock capable of enhancing agriculture bioenergy potential. Although the influence of growing conditions on biogas yield of corn stover has been reported, the joint ...effects of water and nitrogen on biogas production potential have not been addressed. A two year experiment (Exp. 1 and Exp. 2) was conducted in Balcarce, Argentina to assess nitrogen supply effects on stover composition and potential methane yield of corn crops grown under contrasting water regimes. Treatments were a combination of two nitrogen fertilization doses (0 and 120 kg ha−1) and two water regimes (irrigated and rainfed). Biomass composition (mass closure procedure) was determined, a BMP test was carried out and first-order kinetic parameters were obtained. Interactive effects of nitrogen and water on stover composition were found. BMP tests showed that the biogas production rate (k) decreased upon irrigation while its response to nitrogen depended on water availability. Nitrogen supply decreased specific biogas potential (Bmax) independently of water availability. Methane yield increased with nitrogen fertilization under irrigation, while it decreased under rainfed conditions. The observed water and nitrogen supply interactive effects on stover yield, methane yield and biomass conversion efficiency highlights the importance of considering the joint effects of multiple factors when trying to assess the effects of the environment on biomass quality for bioenergy purposes.
•Nitrogen supply did not increase corn stover yield in water limited environments.•Nitrogen supply decreased specific biogas potential disregarding water availability.•Water and nitrogen interact in their effects on final methane yield.•Irrigation increased methane yield at any nitrogen status.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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