Six subterranean clover cultivars (representing early and late flowering genotypes from three subspecies) were used to describe and quantify their phenological development. The vegetative (V) and ...reproductive (R) development phases, in response to different environments created by eight sowing dates were quantified. The period from sowing to emergence was constant in thermal time at 110°Cd and the first trifoliate appeared at ~300°Cd. Crops sown in autumn had the longest period from runner initiation until floral bud initiation (R1), which would allow an extended period of grazing, particularly for later flowering cultivars like ‘Denmark’. To maximise seed set (particularly in year 1) a maximum period between R3 and R11 is required (seed set window). This ranged from 319 ± 42.3°Cd for ‘Leura’ to 661 ± 73.1°Cd for ‘Narrikup’. The complete crop life cycle from sowing (V0) to maturity (R11) ranged from 1269 ± 31°Cd (equivalent of 123 ± 6.3 days) for ‘Antas’ sown in July to 2799 ± 47°Cd (300 ± 3.9 days) for ‘Woogenellup’. When sowing occurred in an increasing photoperiod (June–November) the life cycle of all cultivars was 59% shorter than when sown in a decreasing photoperiod. The numeric scale was able to describe all the variation in the phenological phases and could be used to quantify thermal time requirements for specific phenophases. This would allow subterranean clover management to be optimised (husbandry, grazing and seed harvest) at a local level, and provides the basic parameters for inclusion in annual pasture simulation models.
Phenological stages for subterranean clover “Denmark” from field experiments, Lincoln University, New Zealand. Phenological phases are vegetative (V) and reproductive (R).
Climate predictions for New Zealand for the coming decades suggest rising temperatures (+0.7–3 °C), increased diurnal temperature and variable precipitation patterns that differ around the country ...and with seasons. The most common pattern of annual precipitation indicates the largest increases in the west of the South Island and the largest decreases in the east of the North Island and coastal Marlborough. The phenophases of subterranean clover were estimated and quantified using a thermal time-based model under different climate scenarios based on greenhouse gases and aerosol pathways over the 21st century, known as the Representative Concentration Pathways (RCPs), at two periods (mid and end of the century). The estimated flowering (R3) and post- flowering (R6-R11) date change showed a consistent trend across all districts. The largest date advances (≥ 5 days) were predicted for the three current latest flowering districts (Mackenzie, Queenstown and Central Otago). A reduction of the plant’s life cycle, for both ‘Early’ and ‘Late’ maturity cultivars may have undesired consequences for forage yield so genetic material with later flowering dates may be useful. Adaptation strategies to mitigate the future warming effects include using ‘Late’ flowering cultivars and greater use of supplementary feed through summer dry conditions.
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•Under the studied climate scenarios, temperature driven phenological stages advanced.•The most early projected flowering time occurred in RCP8.5 and the least early was in RCP2.6.•Phenological changes were smaller in warm Northern districts than southern districts.•Climate change shortened the plant life cycle regardless of cultivar maturity group.
Flowering time of subterranean clover as a function of genotype (cultivars) and environment (temperature and photoperiod) from Australia and New Zealand datasets. The photoperiod response to the ...descending (April-July, Decreasing Pp, solid line) and ascending (July- November, Increasing Pp, dashed line) mean photoperiod for subterranean clover with early (red symbols) and late flowering time (blue symbols).
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•The flowering time is a key physiological aspect in subterranean clover management.•The thermal time requirement for flowering ranged from 628 to 2600 °Cd.•The response to photoperiod was mathematically estimated for different genotypes.
Quantification of thermal time requirements for flowering in subterranean clover is vital to inform cultivar choice on farm, management strategies and for predictive purposes in biophysical models. As an annual crop, the viability of subterranean clover relies on its ability to regenerate by reaching flowering and setting seeds to establish the crop in the following growth season. This study reanalysed published datasets on flowering time of subterranean clover to estimate thermal-time requirements, considering interactions between genotypes and environmental aspects (temperature and photoperiod). Fifteen peer-reviewed publications from New Zealand and Australia were used that included 369 independent data points from 1955 to 2000.
The estimated time from sowing to flowering ranged from 44 to 271 days or 628–2600 °C d. Temperature was the main driver of flowering, but photoperiodism influenced subterranean clover reproductive development. There was a strong hysteresis in the relationship between time to flower and photoperiod (Pp), depending on the Pp direction (increasing or decreasing Pp). Explanatory functions in response to photoperiod value and direction were estimated for different genotypes (“early” and “late”-cycle cultivar groups). There was a strong seasonality explained by a total requirement of 1090 ± 94.8 °Cd or 740 ± 79.8 °Cd for late and early cultivars in an increasing photoperiod. In a decreasing photoperiod the thermal time target increased at a rate of 977 ± 90.9 °Cd/h and 834 ± 68.7 °Cd/h for late and early cultivars, respectively.
The low organic matter and nitrogen levels in the soils, as well as the high weed pressure, typical of Mediterranean agroecosystems, necessitate a valid and sustainable alternative management. The ...utilization of cover crops such as
Trifolium subterraneum
L. may represent an innovative and efficient option for low-input and organic agricultural systems. In a 3-year experiment, we evaluated the effect of
T. subterraneum
and spontaneous flora cover cropping, with or without burying dead mulch into the soil, on the quali-quantitative composition of the weed seed bank in an apricot orchard. Moreover, the bacteria
Nitrosomonas europaea
and
Azotobacter vinelandii
, involved in the soil N cycle, and the content of ammoniacal and nitric soil nitrogen were quantified. For the first time, we demonstrated that
T. subterraneum
cover cropping with the incorporation of dead mulches into the soil on the one hand reduced weed biodiversity and the seed bank size (− 70% compared to conventional management following the standard commercial practices), while, on the other hand, increased the amount of
N. europaea
(+ 109%),
A. vinelandii
(+ 145%), NH
4
+
(+ 137%) and NO
3
−
(+ 478%) in the soil. This approach was therefore found to be a major improvement in low-input agriculture and organic farming, and it can be applied in Mediterranean orchards as an eco-friendly strategy with the aim of reducing synthetic herbicides for weed control and mineral nitrogen fertilizers as the sole source of nitrogen supply.
Coefficients that describe phenological development of subterranean (sub) clover (Trifolium subterraneaum L.) were derived from field and controlled environment experiments. These were combined with ...national scale historical climate data to estimate when key stages in the life cycle occur at different locations in New Zealand. Based on a 20 mm accumulated rainfall threshold in autumn, sub clover germination and emergence in eastern regions of the South and North Islands occurred between 10th and 24th March and later (~ 31st March) in the cooler southern areas of the South Island, after 36 ± 6.0°Cd and 115 ± 9.0°Cd, respectively. During this time the absolute photoperiod decreases from 13.7 h to 11.6 h (at latitude −34.3950) and from 14.4 h to 11.1 h (at latitude-47.2590). In spring, flowering was estimated to commence in August in North Island locations but from September onwards in South Island locations. The group of cultivars classified as ‘Late’ flowering by plant breeders were estimated to flower in the North Island starting by mid-August compared with mid-September to mid-October in southern (cooler) regions. The safe grazing period was estimated as 25% longer for ‘Late’ cultivars than the ‘Early’ cultivars. The quantification of these key phenophases can be extrapolated to different regions to enhance strategic management of weed control, grazing times and closing dates for seed set. This should enable increased species persistence of sub clover in pasture swards.
Estimations dates for key plant development stages of ‘Early’ subterranean clover cultivars. V3 = first trifoliate; V6 = fourth trifoliate; VR_R= transition to reproductive phase; R3 = 50% of plants with open flower; R6 = pollinated flower start pegging; R11 = burr change from green to brown colour and starts to dry off. Display omitted
•A subterranean clover management map was created for New Zealand using climate data and published equations to estimate phenology.•Subterranean clover germination and seedling emergence was estimated to occur later in the cooler southern areas of the South Island.•Flowering of ‘Early’ cultivars ranged from August 5th in the Far North district to October 27th in Central Otago.•For ‘Late’ cultivars, flowering dates ranged from September 4th in the Far North and December 1st in Central Otago.•The safe grazing period prior to flowering ranged from 110 to 260 days, depending on cultivar, maturity, and location.
All higher plants show developmental plasticity in response to the availability of nitrogen (N) in the soil. In legumes, N starvation causes the formation of root nodules, where symbiotic ...rhizobacteria fix atmospheric N2 for the host in exchange for fixed carbon (C) from the shoot. Here, we tested whether plastic responses to internal N of legumes are altered by their symbionts. Glasshouse experiments compared root phenotypes of three legumes, Medicago truncatula, Medicago sativa and Trifolium subterraneum, inoculated with their compatible symbiont partners and grown under four nitrate levels. In addition, six strains of rhizobia, differing in their ability to fix N2 in M. truncatula, were compared to test if plastic responses to internal N were dependent on the rhizobia or N2‐fixing capability of the nodules. We found that the presence of rhizobia affected phenotypic plasticity of the legumes to internal N, particularly in root length and root mass ratio (RMR), in a plant species‐dependent way. While root length responses of M. truncatula to internal N were dependent on the ability of rhizobial symbionts to fix N2, RMR response to internal N was dependent only on initiation of nodules, irrespective of N2‐fixing ability of the rhizobia strains.
Most plants respond to changes in nitrogen availability with plastic responses in root and shoot architecture and allocation. Legumes can additionally form nitrogen‐fixing nodules, but it is not known how nodulation impacts on other phenotypic responses to nitrogen in legumes. This study shows that the presence of nodules can alter root length and root mass ratio responses to nitrogen and that these responses were dependent or independent of nitrogen fixation from the nodules, respectively. This finding was specific for the model legume Medicago truncatula, with different responses in clover and alfalfa.
Under changing climate, plants need combined ability to cope with co‐occurring biotic/abiotic stresses. Understanding simultaneous plant responses to multiple stresses offers unique insights towards ...developing effective strategies to mitigate effects of such stresses in plants. Quantitative reverse transcription PCR was used to determine and compare relative gene expression ratios (RGERs) of three disease resistance‐related genes, chalcone synthase, GA protein, and phenylalanine ammonia lyase (PAL), and three abiotic stress‐related genes, a LRR receptor‐like protein kinase (RPK), heat shock protein 81, and Trifolium repens cold responsive protein, across seven durations of infection by the root pathogen Pythium irregulare under three temperature regimes in three Trifolium subterraneum varieties of varying resistance. Temperature and genotype drove biotic and abiotic stress‐related gene expression in Pythium‐infected plants. RGERs of tested genes and their relationships differed across varieties, temperatures, and infection duration (ID). These are the first studies to report expression of defence‐related genes in relation to either biotic or abiotic stress in subterranean clover. The current study not only demonstrates how RGERs of tested genes and their relationships differ across varieties, temperatures, and ID, but also highlights as yet unexploited opportunities to use these biotic/abiotic‐related genes together to develop new varieties with combined biotic/abiotic stress resistances in forage legumes that are suitable for changing climate scenarios. Examples could include RGERs of PAL to identify “temperature‐stable” disease‐resistant varieties, and RGERs of RPK to eliminate susceptible and temperature‐sensitive genotypes.
Studies define how temperature and plant genotype drive biotic/abiotic stress‐related gene expression in Pythium‐infected plants and highlight opportunities to develop biotic/abiotic stress‐resilient varieties.
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